BackgroundPrompt gamma-ray activation image (PGAI) is a non-destructive element imaging method for large volume samples. Most of PGAI platforms are located in research reactors, which limit their applications. From the perspective of in-field applications, attractive alternative neutron sources are isotope neutron source and neutron generator. However, the neutron fluxes of these sources are much lower than that of reactor neutron source, which leads a poor spatial resolution.PurposeThis study aims to solve this problem by implementing an approach based on multi coded-aperture collimators.MethodsFirst of all, the Monte Carlo code MCNP5 was employed to calculate spatial distribution of Cl in a known sample, and the characteristic gamma rays were produced by the thermal neutrons absorbed by the sample. Then, 36 coded-aperture collimators with random holes were used to collimate gamma rays, and 36 gamma signals were collected by high-purity germanium detectors (HPGe). Finally, the imaging of Cl was reconstructed through these data and maximum likelihood expectation maximization (MLEM) algorithm, and the relative deviation (df) and structural similarity (SSIM) were chosen to evaluate the image quality.ResultsThe spatial resolution of the imaging is 1 cm×1 cm, and the relative deviation and SSIM between the reconstructed image and the original image are 0.065 8 and 0.952 1, respectively. After neutron self-shielding correction, the relative deviation and SSIM between the reconstructed image and the original image are 0.002 3 and 0.998 4, respectively, which shows a good agreement.ConclusionsThe proposed approach is efficient to measure the distribution of Cl element, hence for element imaging of plate samples, and the reconstructed image is consistent with the set sample image.
BackgroundThe Fukushima nuclear accident in 2011 exposed the shortcoming of high temperature oxidation resistance of zirconium alloy cladding. For this reason, the concept of accident tolerant fuel was proposed in the international nuclear fuel field. Cr-coated zirconium alloy cladding, as an accident tolerant fuel cladding near-term commercial technology approach, has received extensive attention.PurposeThis study aims to study the high-temperature oxidation behavior of Cr-coated Zr-4 alloys at different temperatures.MethodsCr-coated Zr-4 alloy was prepared by multi-arc ion plating, and oxidized in air atmosphere at 800?1 200 ℃ for 4 h. Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS) were used to analyze the surface and cross-sectional micro-morphologies of Cr coated Zr-4 alloy samples before and after high-temperature oxidation and the distribution of elements on the cross section. The orientation image microscopy (OIM), inverse pole figure (IPF) and pole figure (PF) of Cr coated Zr-4 alloy samples were obtained by electron backscatter diffraction (EBSD). The phase of the samples was obtained by glancing angle X-ray diffractometer (XRD).The effect of oxidation temperature on the microstructure, phase, Cr-Zr diffusion layer thickness and oxidation weight gain of Cr-coated Zr-4 alloy were investigated.ResultsThe results show that there are a large number of droplets of different sizes on the surface of the Cr-coated Zr-4 alloy samples prepared by multi-arc ion plating, and the Cr coating has a columnar crystal morphology and preferentially grows along the (110) crystal plane. After high temperature oxidation at 800~1 100 ℃ for 4 h, the surface of the sample is oxidized to different degrees, but the un-oxidized Cr coating still remains inside the coating, and no micro-cracks appear on the surface and cross-section of the sample. The thickness of the Cr-Zr diffusion layer increases linearly with the increase of the oxidation temperature, and the oxidation weight gain increases slowly. However, after high temperature oxidation at 1 200 ℃ for 4 h, the Cr coating on the surface of the sample was completely oxidized, a large number of cracks appeared on the surface and cross-section, and the thickness of the Cr-Zr diffusion layer and oxidation weight gain increased sharply.ConclusionsTherefore, the Cr-coated Zr-4 alloy prepared by multi-arc ion plating exhibited good high temperature resistance at 800~1 100 ℃, while accelerated oxidation occurred at 1 200 ℃.
BackgroundIn recent years, with increased awareness of environmental protection and safety, the development of nuclear logging tools using non-chemical sources such as X-ray instead of chemical sources like 137Cs has become a new trend. However, X-ray source usually has a lower energy level compared to chemical source, therefore the measurement accuracy is hardly satisfying the demand of density logging tool.PurposeThis study aims to investigates the detector spacing design of a X-ray source tool based on an existing multi-detector gamma density tool.MethodsBased on a 215.9 mm diameter borehole filled with water where the logging tool was eccentrically placed in, Monte Carlo software Geant 4 was employed for the simulation of the X-ray density logging in the formation density range of 1.7~3.0 g?cm-3. According to density sensitivity, detection efficiency and depth, a series of models of this logging tool with detector-to-source distance between 135 mm and 430 mm were simulated to analyze the detector responses. Finally, based on above data, the design of source spacing for detectors was determined for the X-ray density tool.ResultsThe finalized tool includes three NaI detectors with detector-to-source distances of 160 mm, 270 mm, and 344 mm, respectively. Simulation results show that the maximum wall detection depth reaches 120 mm with the vertical resolution of 344 mm, and the density measurement accuracy is 0.014 g?cm-3.ConclusionsThe feasibility of developing a potential X-ray density logging tool is validated by this study, providing reference for future design of nonchemical source density logging tool.
BackgroundDigital measurement system based on ADCs (analog-to-digital converter) has higher requirement on the signal to noise ratio (SNR) of sampled data. Among all the factors, the jitter of sampling clock has the most prominent effect on SNR.PurposeThis study aims to design a clock circuit based on dual-loop phase-locked loop to reduce the jitter of digital measurement system input clock.MethodsFirst of all, the influence of clock jitter on digital measurement system was analyzed. Then, the LMK04610 chip with dual loop PLL architecture of Texas Instruments was employed to design and implement a dual-loop phase-locked loop jitter cleaner circuit. The cores of this design were power supply design and the loop filter design. At last, the performance of the circuit was tested by using Rodschwarz phase noise analyzer.ResultsAfter testing, the dual-loop phase-locked loop jitter cleaner circuit can reduce the jitter of the 62.475 MHz source clock from more than 7 ps to less than 2 ps with output frequency of 499.8 MHz. The SNR of the sampled data is close to the theoretical value.ConclusionsDual-loop phase-locked loop jitter cleaner circuit has a good result and can provide reference for designers of digital measurement system.
BackgroundThe solid fuel thorium element molten salt reactors (MSR) have attracted more attention recent years. A3-3 graphite is chosen as the fuel matrix for MSR, thus its irradiation behavior and mechanical property is very important before the application.PurposeThe study aims to observe the irradiation defects and hardness of A3-3 matrix graphite after ion irradiation by slow positron beam and nano-indentation, respectively.MethodsThe matrix graphite of fuel elements was irradiated with 1 MeVXe ions to fluence of 5.8×1014 ions·cm-2 and 2.9×1015 ions·cm-2 respectively at room temperature. The slow positron beam and nano-indentation were employed to investigate the effect of Xe ions irradiation on vacancy defects and hardness of matrix graphite. The changes in irradiation induced defects distribution with depth and fluence were analyzed according to the obtained positron annihilation S parameters versus positron incidence energy or depth curves, compared to SRIM (Stopping and Range of Ions in Matter) calculation.ResultsResults from slow positron beam measurement show that 1 MeV Xe ions irradiation in matrix graphite introduces a damage layer with depth of about 600 nm, and the damage peak locates at about 250~350 nm in depth, consisted with SRIM simulation. The S parameters in irradiation samples increase significantly compared to virgin sample, which suggests that a high concentration of vacancy-type defects appeared within irradiation damage layer. In addition, the S parameters increase with the irradiation fluence, which shows that the concentration or size of vacancy-type defects increases. The nano-indentation results show that the hardness of irradiated graphite matrix is enhanced.ConclusionsThe enhanced hardness of A3-3 matrix graphite after ion irradiation is ascribed to the pinning of basal plane dislocation by the high concentration of vacancy type defects introduced by irradiation, consisted with the slow positron beam analysis. Slow positron beam is a very sensitive tool to study the irradiation defects.
BackgroundHigh-performance accelerators have higher requirements for operational reliability and stability. By analyzing the historical data that is routinely saved during accelerator operation, most failures can be judged. However, when some rapid failure processes occur, due to the insufficient granularity of the historical data stored conventionally, it is impossible to effectively analyze such rapid failure processes. When a failure occurs in a particle accelerator, fast acquisition techniques are needed to collect large amounts of data from various devices with precise timestamps. The failure occurrent process can be rapidly reconstructed by using these data to locate and judge the root cause of the failure. In order to obtain data accurately when a failure occurs, hardware devices with data cache function can be used at the front-end devices, and data can be locked and obtained in the synchronous trigger mode. That is, after receiving the synchronous trigger signal, data in the cache area of the front-end hardware device can be locked, and then read and stored.PurposeThis study aims to design a failure analysis system prototype based on the event-timing technique.MethodsTwo core parts of the prototype were implemented: global high-precision timestamp implementation and data assembly and acquisition analysis. As one of the key factors, the global high-precision time stamping of failure data was applied to analyzing failure causes. Based on a high-performance rubidium atomic clock and the event-timing system, high-precision time stamps were implemented in this prototype with synchronization accuracy better than 16 ns to provide global high-precision time stamps for time data. Structured data based on the normative type of EPICS 7 was adopted for assembling and publishing the data. Essential information, including the system name, the subsystem name, the device name, the device card number, the data sampling frequency, the event timestamp, and the latched data, was obtained from the structured data.ResultsThe prototype experiment results show that the failure sequence of different equipment can be distinguished by the obtained high-precision time data, confirming the high feasibility of our proposed failure analysis system.ConclusionsThe prototype designed in this study meets the requirements for rapid failure analysis of particle accelerators. And this prototype will be applied to the CSNS accelerator in the near future. In addition, it can also be applied to EPICS-based and event-timing based accelerator control systems.
BackgroundSolid oxide cell (SOC) is the core converter for hydrogen production by high temperature electrolysis of water vapor and hydrogen fuel utilization.PurposeThis study aims to develope two kinds of aqueous casting pastes of NiO-YSZ with different components for the batch preparation of SOC without the usage of a large number of organic solvents.MethodsA 10 cm×10 cm large-scale full-scale cell was prepared by screen printing the hydrogen electrode functional layer, electrolyte layer, barrier layer and oxygen electrode layer with NiO-YSZ support film at one time casting of about 450 μm. The effect of dispersant on the microstructure of hydrogen electrode support and the stability of the pastes were analyzed by scanning electron microscope (SEM). The performance of the SOCs were tested by I-V curve and electrochemical impedance.ResultsBased on the optimized NiO-YSZ supports, the prepared planar SOCs delivers a peak power density of 0.36 W·cm-2 at 750 ℃. The electrolysis current density of SOC can reach -0.68 A·cm-2 at 1.30 V in solid oxide electrolysis cell (SOEC) model.ConclusionsThe performances of the aqueous-based SOCs can be considered highly remarkable, thus supporting the success in scaling the fabrication of SOCs using more environ-mentally friendly processes than conventional ones.
BackgroundIn accelerator driven sub-critical system (ADS), the high-energy proton beam produced by accelerator is used to strike the target nucleus, and generate spallation neutrons as external neutrons to drive and maintain its operation. The power level and the safety of ADS are susceptible to the instability of proton beam, such as beam overpower (BOP) which is treated as the typical transient accident for ADS system. In ADS core, the sudden increases of power and temperature will be caused by BOP accident, which may exceed the safety limits of materials, threatening ADS safety.PurposeThis study aims to investigate the transient safety characteristics of the eXperimental accelerator driven system (XADS) under BOP accident.MethodsThe multi-physics coupling code MPC-LBE, in which the fuel pin heat conduction (HC) model and the point reactor kinetics (PK) model were coupled with self-developed computational fluid dynamics (CFD) code, was employed to simulate BOP accident of XADS. Firstly, the MPC-LBE simulation model of XADS was constructed and then the steady state condition was established. On this basis, the double and triple BOP accident cases were simulated, and the safety boundary of BOP accident conditions was also evaluated.ResultsFor the simulation results, in the double and triple BOP cases, the reactor powers increase to only 1.88 and 2.7 times of the original ones, respectively. The maximum temperature of the cladding is about 843 K in the triple BOP case, exceeding its safety limit.ConclusionsConclusions can be drawn that the negative temperature feedback effect plays an important role in protecting the reactor from power sharp rise, and the double BOP case can be treated as the BOP safety boundary of BOP accident in XADS.
BackgroundAt present, most of the contamination detection equipments for small items in domestic nuclear power plants are manually putting in and taking out the testing items, and the operation time is long and the steps are relatively tedious. According to the on-site demand of nuclear power and feedback on the use of similar imported equipment, contamination detection equipment based on the conveyor belt can effectively solve these drawbacks.PurposeThis study aims to design a small item γ pollution measuring instrument that can be used to transmit items with a conveyor belt, hence effectively improve the detection efficiency and save the cost of manual operation.MethodsSemi-automatic two-channel control design scheme was adopted, one through the motor driver to control the conveyor belt motor running mode, the other control the digital circuit of the radiation detector and the corresponding electrical parts through the main control board. Linkage of contamination monitoring status and item convey was achieved by the status control board associated with the motor drive. The background counting rate of the equipment in the background environment, the counting rate of the radioactive source at rest in the center of the measuring chamber and the dynamic counting rate of the radioactive source moving through the measuring chamber with the conveyor belt were tested and analyzed.ResultsThe results show that the minimum net count value of the detector is 81.6% of the average count in the static state. The net value of the minimum peak value of the detector at motion state is 89.3% of the average peak count, and the minimum detectable limit is 111 Bq.ConclusionsThe test performance of prototype is better than the reference standard and meets the design requirements.
BackgroundThe debris motion is an important phenomenon of a high-altitude nuclear detonation, which is also a foundation for the study of the geophysical phenomena such as the ionosphere effect and artificial radiation belt.PurposeThe study aims to clarify the debris motion characteristics and laws from a near-space nuclear detonation.MethodsFirstly, a fluid dynamics model of debris motion from a near-space nuclear detonation was established. Many influence factors were considered, such as the variation of energy dissipation, air density varies with height, gravity, air temperature rise caused by X-ray depositions and radiation cooling. Then the parameters of debris motion within the explosion equivalent of 1 kt~10 Mt and the explosion height of 30~80 km were systematically studied. The evolutions of parameters such as center height, horizontal radius, expanding velocity, ascending velocity, and shape of debris were given. Finally, the variation laws of typical characteristic parameters such as maximum ascending height and expanding radius changing with explosion height and explosion equivalent were summarized.ResultsWhen the explosion height is 30 km, the maximum rising height and the maximum horizontal radius at 5 min for a kiloton-level nuclear explosion debris are about 13~16 km and 4~5 km, the maximum rising height and the maximum horizontal radius at 5 min for a megaton-level nuclear explosion debris are about 20~40 km and 15~30 km. When the explosion height is 80 km, the maximum rising height and the maximum horizontal radius at 5 min for a kiloton-level nuclear explosion debris are about 30~50 km and 20~40 km, the maximum rising height and the maximum horizontal radius at 5 min for a megaton-level nuclear explosion debris are about 200~400 km and 110~220 km. When the explosion equivalent is small and the explosive height is low, the debris evolves into a flat ellipsoid. When the explosion equivalent is large and the explosion height is high, the debris evolves into an inverted pear shape.ConclusionsThe results show that the maximum height, horizontal radius, and speed of the debris cloud increase with the increase in the explosion height and explosion equivalent. The changes of the height, the horizontal radius, the rising time, and the shape of the debris obtained from the study are in good agreement with the literature estimation method. Those obtained motion parameters of debris can provide delayed radiation source information for the study of the geophysical phenomena such as the ionosphere effect and artificial radiation belt of nuclear explosion in near-space.
BackgroundDecommissioning of nuclear facilities generates large quantities of different types of radioactive material. According to the requirement of the waste packaging, most incompressible waste must be put into steel boxes directly, which makes it difficult to measure and obtain the activity of the radioactive material in the steel boxes.PurposeThis study aims to establish an approach for measuring radioactive waste in steel box based on the in situ objects counting system (ISOCS).MethodsIn this work, ISOCS was used to characterize the radioactive material in steel boxes. The corrections for the absorption coefficients and the geometry factors of the big bulky sources were calculated using the ISOXSW (ISOCS Calibration SoftWare) in situ efficiency calibration without a radioactive source software. The verification experiments were carried out using standard sources with similar size and geometry.ResultsThe results show that the measurement error of six symmetrical positions of steel box with standard 137Cs and 60Co radioactive source by ISOCS is less than 30%.ConclusionsThe study verifies that ISOCS software is able to accurately estimate the composition and activity of radioactive material in a steel box.
BackgroundThe energy produced by nuclear fusion on a Tokamak device is mainly exhausted through the divertor, its service life is directly affected by the interaction between huge heat flux from core and the divertor target. The large amount of impurity produced by the heat flux hitting the target leads to the reduction of the plasma confinement performance whilst pumping is an important means to control plasma density and impurity density.PurposeThis study aims to investigate the influence of pumping on the heat load of the target plate which is of reference significance for the future experiment.MethodsBased on the experimental parameters of the HL-2A Tokamak, SOLPS-ITER code was used to study the effect of pumping on the heat load of the divertor target under different upstream electron densities. Analysis was performed through density scanning to find the sensitive threshold whilst and atom-molecular collision process was applied to the effect of pumping on the distribution of plasma and neutral particle parameters in divertor region at different upstream electron density.ResultsDensity scanning results show that pumping near the detachment threshold (TetOSP~5 eV) has a greater effect on the thermal load of the target plate. When the pumping rate is 12 m3·s-1, 36 m3·s-1 and 96 m3·s-1 respectively, the miss threshold and thermal load peak of outer target plate are 1.11, 1.24, 1.39 and 1.37, 1.96, 2.54 times of those without pumping respectively.ConclusionIt is found that the decreases of deuterium molecular density results in the energy of the collision reaction power decreases when the upstream electron density exceeds the detachment threshold, leads to the increase of the temperature and energy flow of the plasma in the target plate.
BackgroundAt present, in the key stage of the construction of China Initiative Accelerator Driven System, various research institutes have also put forward corresponding core schemes for different purposes, including the accelerators drive advanced nuclear energy system (ADANES) proposed by Institute of Modern Physics, Chinese Academy of Sciences. Detailed calculation and analysis of its scheme can provide strong technical support for the sustainable development of nuclear energy and the national energy security strategy.PurposeThis study aims to analyze the steady-state neutronics characteristics of ADANES reactor with emphasis on the preliminary typical transient analysis under the typical accident conditions of fast reactor.MethodsThe NECP-SARAX (Nuclear Engineering Computational Physics Laboratory, System for Advanced Reactor Analysis at Xi'an Jiaotong University) code system, which was based on deterministic neutron transport theory, was applied to perform the detailed analysis. The main design parameters, including core length, neutron spectrum and reactivity feedback coefficients, were calculated under various fuel types, coolant types, and reactor geometry parameters. In addition, the primary transient characteristics were simulated, including unprotected transient over power and unprotected loss of flow transient. The changes of reactor power and the maximum fuel/coolant temperature were obtained and analyzed.Results & ConclusionsThe steady-state calculation results show that ADANES could achieve 10 effective full power year for each selected case. The reactivity feedback coefficients reach -5.4×10-5 K-1 in total so that the core has inherent safety under typical accident condition conditions during the simulated transient.
BackgroundNarrow rectangular channels are widely used in major thermal flow fields because of the compact structure and large heat transfer area.PurposeThis study aims to improve the prediction method of critical heat flux in the narrow rectangular channel and establishing the critical heat flux (CHF) mechanism model for the enhancement of reactor safety and economy.MethodsCHF experiments was carried out in the present study to identify the dominant mechanism in a narrow rectangular channel at different gap sizes. The visualization experiments were performed at pressures ranging from 1 MPa to 4 MPa, inlet subcooling from 60 K to 120 K, and mass flux from 350 kg·(m2·s)-1 to 2 000 kg·(m2·s)-1.ResultsAccording to the visual experiment results, two typical bubble behaviors are investigated in the narrow rectangular channel. Based on the bubble dynamics characteristics of narrow rectangular channels, a new CHF mechanism model was proposed, and a set of constitutive relations will be provided to close the developed model.ConclusionA comprehensive assessment of new model has been conducted and analyzed by using the experimental data for the upward flow in a vertical narrow rectangular channel and it has good accuracies of less than ±30% as relative to the experimental values.
Background Vertical cavity surface emitting lasers (VCSEL) have very high application value in space radiation environment. Purpose This study aims to explore the degradation rule and mechanism of 850 nm VCSEL in harsh radiation environment. Methods First of all, the MULASSIS tool was employed to calculate displacement damage dose (DDD) and design experimental scheme for 850 nm multimode VCSEL samples. Then, 3 MeV and 10 MeV proton irradiation experiments were conducted to obtain the degradation rule of parameters such as light output power and threshold current with the proton fluence, and to find that the degradation degree of light output power and threshold current were equal under the same DDD. Finally, the Silvaco software was used for modeling and simulation on an experimental basis to extract microscopic parameters such as trap density, donor and acceptor ionization density, mirror loss, radiation recombination rate and photon number. Results The simulation results are in good agreement with the experimental results, these results show that each parameter changes to different degrees with the increase of proton fluence. Conclusions The parameter degradation law and radiation damage mechanism of VCSEL can be deeply explored by simulation on the basis of the experimental law, and simulation results are of great significance for understanding the degradation mechanism of VCSEL.
Background The measurement of time-of-flight is one of the indispensable experimental contents in contemporary high-energy physics experiments and plays a vital role in exploring the essence of particle physics. Purpose This study aims to design a time to digital convertor (TDC) chip that meets the high-resolution time measurement requirements of time-of-flight detectors for high-speed flying particles in high-energy physics experiments. Methods First of all, a differential structure TDC was proposed and the main measurement part was realized by differential delay loop composed of time measurement core module, time measurement data transmission module, delay loop calibration module and clock generation module. Based on this structure, three parts of delay loop module, thermometer code generation module, and coarse count and fine count generation module were integrated into the core module of time measurement, and the 0.18 μm SMIC (Semiconductor Manufacturing International Corporation) process was adopted to achieve the TDC chip design. Results & Conclusions The designed TDC chip has a layout area of 1.35 mm×1.35 mm, a resolution of 17 ps, an accuracy of 8.5 ps (Root Mean Square, RMS), and a dynamic range of 0~210 μs. It can meet the current requirements for high-precision time measurement in high-energy physics.
Background In order to fast and conveniently measure X, γ and neutron radiation field simultaneously, portable multi-function radiation detector is highly demanded. Purpose This study aims to design a portable multi-function radiation detection system based on LaBr3(Ce) crystal, lithium aluminum silicate oxygen (LASO) neutron detector and high range Geiger-Muller (GM) counter. Methods After the optical signal output from the LaBr3 crystal was photoelectrically converted into electronic signal by the photomultiplier tube (PMT), the integrated digital multi-channel was used for data acquisition of electronic signal, and the subsequent data processing and calculation. The front signal processing circuits, such as amplification, discrimination and shaping, were designed for both the LASO neutron detector and the GM tube counter. Finally, the digital signal processed of the LaBr3 detector was transmitted to the ARM (Advanced RISC Machine) processor in the form of TTL (Transistor-Transistor Logic) serial port, and the pulse signal formed of the neutron detector and GM counter tube was connected to the external counting port of ARM processor. Energy spectrum was processed for nuclide identification and displayed by ARM processor whilst the low dose rate measurement base on the Gamma data collected by the LaBr3 detector, the neutron detector and the high range GM tube counter were counted at fixed time and converted from the count rate into the dose rate. Results & Conclusions The designed portable multi-function radiation detector realize simultaneous measurement of wide range (48 keV~3.0 MeV) γ, low-energy (48 keV~1.25 MeV) X-ray, (0.1~100 mSv∙h-1) neutron dose rates, and nuclide identification capability of LaBr3 spectrometer, and upload the data to PC through USB interface.
BackgroundIn recent years, electron cyclotron wave (ECW) heating and current drive (ECCD) have been widely used in tokamak discharge experiments. The inevitable presence of impurity particles in the tokamak plasma affects the ECCD through radiation energy, inhibition of turbulent transport, and change the collision rate. Changes in plasma density, temperature and other transport quantities caused by the change of impurity concentration, induce the changes of Shafranov displacement at the center of magnetic surface of the plasma.PurposeThis study aims to investigate the influence of impurity concentration changes on the ECW deposition position and current drive efficiency theoretically with consideration of all above related variations.MethodsThe One Modeling Framework for Integrated Tasks (OMFIT) platform was used to conduct integrated simulation study of the effect of impurity effect on ECW heating and current drive. The HL-2M Tokamak device parameters were combined with self-consistent coupled plasma equilibrium, external auxiliary heating and current drive, transport and other physical processes for simulation computation with the carbon ions as the unique impurity ions.ResultsThe simulation results show that when the influence of impurities on the plasma is considered, with the increase of the impurity concentration, the radial position of the ECW deposition first moves to the plasma core and then moves to the edge, and the current drive efficiency first increases and then decreases. Due to the competition between the radiation effect and the dilution effect of the impurity-plasma interaction, the radiation loss power basically increases linearly with the increase of Zeff, while the dilution effect suppresses the turbulence and improve the confinement, but the stabilization effect slows down with the increase of Zeff.ConclusionsWhen the influence of impurities on the plasma is not considered, the deposition position of ECW is basically unchanged, and the current drive efficiency decreases. Results of this study have guiding significance for electron cyclotron current drive (ECCD) to control the plasma current profile and control the instability of magnetic fluid.
Background Radiation shielding design is an important part of reactor design, and the development of new nuclear power technology for various kinds of reactors has put forward new demands on radiation shielding optimization design methods. Purpose This study aims to overcome the shortcomings of the traditional multi-objective optimization methods for shielding structures in dealing with the optimization problem of 3D shielding structures, such as slow optimization speed, difficulty in convergence, and poor globalization. Methods Based on the non-dominated sorting genetic algorithm Ⅲ (NSGA-Ⅲ), the many-objective optimization method for 3D shielding structure design for nuclear reactor was proposed. The Monte Carlo N-Particle Transport Code (MCNP) was employed to analyze comparative performance of the NSGA-III optimization method on the basis of the 3D shielding structure model of nuclear reactors, and shield weight, volume and radiation dose rate in specific regions were taken as the optimization targets. Results & Conclusions The numerical simulation results show that the NSGA-III based optimization method for 3D shielding structure design can search for the Pareto-optimal front more efficiently and stably, providing a new idea for the optimization of radiation shielding design.
Background Compared with transistors and small-scale integrated circuits, the total ionizing dose (TID) effect and testing of multifunctional large scale integrated microprocessors are more complex. The difficulty of testing is to analyze the failure mode of microprocessor online from limited information under irradiation. Purpose This study aims to develop an extendable on-line test system for TID effect of microprocessor and carry out preliminary application. Methods The testing system was composed of control circuit, extendable signal acquisition circuit, tested sample interface, upper computer and software. Multiple parametric measurement or functional verification methods such as power consumption current, on-chip memory, communication, clock, analog-to-digital/digital-to-analog converter (ADC/DAC) and direct memory access of microprocessor were provided. Sixteen microprocessors with feature size 40 nm were irradiated with 60Co source and tested on-line. Results After the irradiation dose is accumulated to (377.44±20.34) Gy(Si), all samples are malfunctional with digital communication interruption, sudden drop in current consumption, abnormal ADC/DAC output and so on. Conclusion Based on all 12 kinds of parametric measurement or functional verification results, the TID effect of this type of microprocessor is probable to be a functional failure caused by some kernel instructions. The on-line test system of this study can provide more direct data information for the total dose failure mode analysis.
Background The flow distribution in core for the liquid fuel molten salt reactor (MSR) is an important part of the thermal hydraulic design, and the hydraulic structure of reactor core plays a decisive role on flow distribution. Purpose This study aims to find out a suitable hydraulic structure design to make the core flow distribution match with the power distribution, and flatten the core temperature distribution for a 10 MW MSR. Methods First of all, a one-twelfth core model of liquid fuel MSR was established. Then, ANSYS FLUENT16.0 software was employed to conduct three-dimensional numerical simulation of the flow field. The influence of hydraulic structure of reactor core was analysed by changing the structure of upper plenum, downcomer and lower plenum, and the corresponding flow distribution characteristics of the core are obtained. Finally, a suitable structure was proposed after step-by-step improvement. Results The simulation results show that increasing of the height of upper plenum can balance the flow distribution between central and peripheral channels, increasing of the width of the downcomer can reduce the vortex flow at the downcomer outlet and flattens the flow distribution at the same time. The cylindrical lower structure with shroud in lower plenum can restrain the vortex to a certain extent and make the flow distribution more gentle. Based on the analysis above, a reasonable hydraulic structure is proposed for the molten salt reactor. Conclusions The results of this study provide important reference for the further optimization design of liquid fuel molten salt reactor.
BackgroundThe superconducting third harmonic cavity has been developed independently in Shanghai Synchrotron Radiation Facility (SSRF) and passed beam tests. The cavity electric field needs to be precisely controlled during operation to achieve the goal of stretching beam cluster and improving beam life.PurposeThis study aims to design a digital low level radio frequency (DLLRF) controller for superconducting third harmonic cavity at SSRF.MethodsThe hardware of controller was based on a field-programmable gate array (FPGA) board and a front-end board whilst in-phase/quadrature (I/Q) demodulation techniques were implemented in the software of controller. A synergistic strategy was adopted for driving the stepper motor with slow tuning speed and piezoelectric ceramic with fast tuning speed, and an algorithm for the quench detection for passive cavity. Finally, experimental tests were performed to verify the effectiveness of this designed DLLRF.ResultsWhen the state is in top-up mode over 120 mA, the amplitude stability has improved form ±5% with open loop to less than ±1% with close loop, the voltage of piezo has varies smoothly and stably within 120 V, and the beam life has improved more than doubled.ConclusionA digital low level radio frequency controller for the superconducting third harmonic cavity has been designed and satisfies the requirements for SSRF.
BackgroundHefei Advanced Light Facility (HALF) is a fourth-generation synchrotron radiation light source based on diffraction-limited storage ring. The timing system provides trigger signals for the HALF injector, storage ring and beamline, coordinates injection and beam measurement, and achieves filling of the storage ring bucket with any designated bunch pattern.PurposeThis study aims to design a timing system for HALF to reduce the trigger signal jitter of the HALF device to less than 30 ps, and stabilize the signal drift caused by the optical fiber length change.MethodsBased on the MTCA.4 event-driven products from Micro-Research Finland Oy (MRF), the event timing technology scheme was adopted to implement the timing system. Appropriate system frequencies for electron gun, microwave system and storage ring were selected to achieve different modes of storage ring bucket filling scheme. The timing system software was developed under Experimental Physics and Industrial Control System (EPICS) to coordinate with the control system of HALF, including an EPICS driver, database records, and operation interfaces. Delay compensation was applied to signal drift caused by the variation of optical fiber length. Finally, a prototype of the timing system was developed for performance tests.Results & ConclusionsThe results show that the jitter of the trigger signal is less than 24 ps, and the signal drift is controlled at about 3 ps after delay compensation, both meet the design requirements of HALF timing system.
As a strong candidate for the new type of non-volatile memories and artificial synaptic devices, memristor has a huge development prospect in aerospace, Mars exploration and other space science and application fields. Once large-scale application of memristor requires extremely stringent radiation resistance performance for the memristors. In order to improve the radiation resistance of memristors, it is necessary to explore the radiation effect mechanism and develop an effective radiation resistance technology. This paper summarizes the research status and trends of irradiation effects on memristors, describes the mechanism and analysis method of irradiation damage of memristor, and focuses on the irradiation effects of the memristors with transition metal oxide material system. Additionally, the possibility of scientific problems and key technologies are discussed, so as to provide some ideas for the radiation hardening and space application of memristor.
Background The expected signal rate of rare decay experiments, such as instance dark matter and neutrino less double beta decay experiments, is extremely low, which requires that the detector building materials have extremely low radioactivity. Low radioactive background control is one of the essential works in the rare decay experiments. 226Ra and 228Ra produced in the early decay chain of 238U and 232Th have low boiling point and high vapor pressure, removing the element Ra can break the 238U decay chain and keep a low radioactivity of 232Th-late for a long time. Purpose This study aims to investigate vacuum melting technique for low background titanium to reduce the impurity of isotopes that have negative impact on rare decay experiments and creating a low background environment for the detector running. Methods Firstly, the low background material samples were acquired by manual separation of radionuclides using physical and chemical methods. Then, radioactive impurity elements, such as K, Cs, Ra, Pb, Po and Rn with low boiling point and high vapor pressure, were volatilized in environment with high temperature and high vacuum level. Finally, radioactivity of these testing samples were measured by two sets of high-purity germanium γ spectrometer with measurement time extended to 7 days. Results Measurement results show signs of removal of radioactive isotopes by smelting-vacuum method, and the impurity in pure titanium smelted in vacuum electron beam furnace can reach the levels of (0.13±0.69) mBq∙kg-1 for 232Th-228Ac, and (0.07±0.29) mBq∙kg-1 for 238U-222Rn, respectively. Conclusions The smelting-vacuum method could provide reliable low background material for the container of the next generation PandaX detector.
Background Betatrons are widely used in non-destructive testing, cargo and vehicle security inspection systems, whilst the filament power supply is an important core component of small size betatron. Existing filament power supplies are not suitable for small size betatron. Purpose This study aims to develop a novel electron gun filament power supply for small size betatron to produce optimal radiation intensity. Methods An electron gun filament power supply composed of a filament duty cycle adjustment circuit and an injection current feedback circuit were designed on the basis of operating characteristics of a small size betatron. Two pulse-width modulation (PWM) signals were output from the digital signal processor (DSP) to drive the half-bridge circuit. Positive and negative alternating voltage pulses were output by the half-bridge circuit to the primary of the isolation transformer, and the secondary voltage of the transformer was loaded to the filament for heating of the filament. By collecting the betatron tube wall current and target current as the injection current feedback signal, the duty cycle of the filament voltage pulse was adjusted by DSP according to the feedback signal, and realizes the adjustment of the filament emission current, so that the current injected by the filament into the acceleration tube was kept at the optimal value. Results The experimental test results show that the filament power supply can keep the betatron output dose rate in the best state, and the output dose rate stability is better than 11.3%/10 min. Conclusions The filament power supply meets the requirements of small size betatron with advantages of good stability, wide adjustment range and small size. It can be applied to the small size betatron developed by the Engineering Research Center for Nuclear Technology Application of the Ministry of Education of East China University of Technology.
Background The radiation accident emergency drill is an important way to maintain and improve the response ability of emergency organizations, but at present, the evaluation of the drill is mainly based on the qualitative evaluation of the surface performance of the key links, there is not yet a systematic, full-flow, accurate and targeted evaluation method of exercises. Purpose This study aims to improve the quality and real-time evaluation of radiation accident emergency drill. Methods Firstly, the alternative evaluation indicators were summarized on the basis of literature survey. The method of expert investigation was used to check the alternative indexes and establish the evaluation index system. Then, the analytic hierarchy process (AHP) method was applied to the calculation of weight distribution, and the fuzzy comprehensive evaluation (FCE) was employed to build comprehensive evaluation model for radiation accident emergency exercises. Finally, based on the AHP-PCE, comprehensive scores of the evaluation indexes at all levels of three typical examples were calculated. Results The FCE-based model synthesizes the stage of the drill preparation, the drill implementation and the drill summary, and forms the general goal of the radiation accident emergency drill effect. The evaluation system of radiation accident emergency maneuver is set up with 5 first-level indexes and 15 s-level indexes to realize the comprehensive evaluation of the radiation accident emergency drill. Conclusions The example verification shows that the AHP-FCE model has a good adaptability and rationality, and has a good application value in the evaluation of radiation accident emergency drill.
Background Heat pipe cooled reactors (HPR) have good inherent safety. In the early stage of core design, heat pipe failure accident is usually one of the design basis accidents that need to be considered. Purpose This study aims to analyze the neutronic-thermalhydraulic coupling performance of a new type of megawatt heat pipe reactor. Methods Firstly the heat pipe cooled reactor system physical models, including the point kinetics model, the core and heat pipe model and radiation heat transfer model for the inner core cavity, were established according to the designed HPR prototype composed of heat pipe stack and supercritical CO2 Brayton cycle system with thermal power of 3.5 MW. Then, the finite element software FLUENT was employed to conduct neutronic-thermalhydraulic coupling calculation for the three-dimensional reactor core under the steady-state and heat pipe failure accidents. Finally, the core safety performance was evaluated by comparing the peak temperature of each component with the melting point of material. Results & Conclusions The results show the designed HPR has good safety performance under the steady state and single heat pipe failure. Radiation heat transfer in the core cavity cannot be ignored in the serious cascade three heat pipe failure accident in high power region. Meanwhile, the design cannot withstand cascading four heat pipe failure. By comparing the peak temperature of the multiple heat pipe failure with the peak temperature of the single heat pipe failure, it shows that the design has good inherent safety.
Background Superconducting undulator (SCU) prototype with small magnet gap of 5 mm, long magnet length of 4 m and high magnet field of 1.58 T was being developed at Shanghai High Repetition rate XFEL and Extreme light facility (SHINE). Compared to any other superconducting undulator, there is no cryocooler being installed on the cryostat in this SCU prototype. Purpose This study aims at the cooling design for the binary current leads for SCU's normal operating. Methods Binary current leads composed of normal conductive copper leads and high temperature superconducting current leads (HTS) were adopted for SCU to connect superconducting coils inside the cryostat and outer cables. Low-temperature helium gas was used to transport independent refrigerator system to the cooling tubes inside the prototype, hence the binary current leads were cooled. Thermal conduction components installed on the middle of the thermal shield were employed to transfer heat load of normal conductive copper leads, and heat load of copper leads was optimized by simulation. Auxiliary superconducting rods were designed for connecting cold ends of HTS in the cryostat test. Results The temperature difference between hot ends of HTS and low-temperature helium gas is less than 20 K from the result of cryostat test, all binary current leads is operating normally with full current. Conclusions It is practicable to use cooling tubes with low-temperature helium gas to cool binary current leads of the SCU prototype by thermal conduction, which is different from cooling solution for current leads in any other SCU being developed presently.
Background The corrosion of the secondary circuit has remained a challenging problem influencing the security and efficiency of a nuclear power plant. In an actual operation, an amount of alkalizer is usually added into the secondary circuit water to adjust its pH value to alleviate the corrosion of the pipelines. However, the very complex real working condition results in a significantly inhomogeneous distribution of the pH values, and the enclosed nature of the secondary circuit have frustrated various efforts to control the precise pH values at some key sites inside the circuit. So far, pH values around such key locations have been roughly estimated by either external simulating experiments or by using patented commercial software of foreign companies. However, it is difficult for such external simulations to take into account the various important working conditions. Purpose This study aims to develop a method without specific assumptions or uncontrolled approximations to calculate the distribution of pH values in the secondary circuit under its working conditions. Methods Firstly, the complex and repeated structure inside the steam generator was simplified and simulated by using one direct tube model. Except for the length, the other geometrical dimensions, support plates as well as the tube material etc. were chosen to be as similar as possible to the actual ones. Then, all temperature-dependent equilibriums involving H+ in water solution of the secondary circuit were considered with additional consideration of the equilibriums of the alkalizers in the gas and liquid phases. As an essentially field quantity defined on the space of the secondary circuit, these pH values together with other relevant parameters, such as temperature, fluid velocity etc. were depended on the position coordinates, and were calculated by using the finite element method coded in the COMSOL package. Finally, the boundary conditions of flowing rate and temperature of the water at the inlet were set as 1.0 m·s-1 and 543.2 K, respectively, and the pressure at the outlet was set as ~6.8 MPa, a stepwise linear heat flux model was used to simulate the thermal energy transfer from the primary side to the secondary one. The bubbly-flow model was used to simulate the actual steam-water fluid in the secondary side, which was assumed to be in a steady state working condition. Results The calculated pH field under the working conditions shows clearly an inhomogeneous distribution, e.g. ΔpH = ~ -0.6 from z = 0 to 3.8 m, due to the influences of the tube support plates, the temperature and the heat transfer, etc. The investigations on the ammonia/ethanolamine (ETA) binary alkalizer with different total concentrations of various NH3/ETA molar ratios show a better enhancing effect of ETA over ammonia for the pH value (ΔpH>~0.14), and reveal a saturation effect (molar ratio NH3:ETA≤ ~1:4). Conclusions The distribution of the pH values in the realistic working conditions can be calculated without resorting to empirical formulae and uncontrolled approximations. The developed method and the calculated results provide valuable information for solving the corrosion problem in the secondary circuit. The method and the model can be extended to simulate the more realistic conditions of a nuclear power plant.
BackgroundCosine function shaping (or cos shaping) is used to digitally shape nuclear pulse signals, as the shaping method is simple and has high operability and flexibility.PurposeThis study aims to explore different cosine shaping methods of nuclear pulse signals, and evaluate their effect.MethodsFirstly, based on the single exponential decay signal and cosine pulse signal, transfer functions and cascade formulas of three different cosine shaping methods in the Z-domain were derived. The influence of the parameter selection on the shaping effect in the cosine shaping algorithm was analyzed. Then, the cosine shaping methods were developed for the simulated nuclear signals and the actual sampled nuclear signals, and the cosine shaping, amplitude extraction, and energy spectrum construction of the digital nuclear signals were implemented in the field programmable gate array (FPGA) system. Finally, the gamma (γ) energy spectrum of 137Cs (NaI(Tl) detector) was evaluated using the different cosine shaping methods.ResultsThe results of γ energy spectrum from 137Cs (NaI(Tl) detector) demonstrate the satisfactory performance of all three digital cosine shaping algorithms in terms of energy resolution and counting. The symmetric zero-area cosine shaping performance index is improved relative to conventional methods.ConclusionsThe three kinds of digital cosine shaping methods all achieve accurate cosine shaping for simulated and real nuclear signals. The three cosine shaping methods proposed in this study may be applied to shape functions in other research areas.
BackgroundIn the process of in-situ leaching of uranium, pore blockage greatly limits the leaching efficiency of uranium, and the pore blockage is mainly due to the complex physical and chemical action of minerals and leaching agents in in-situ leaching of uranium.PurposeThis study aims at the influence mechanism of each mineral composition on pore blockage under the action of leaching agent in the process of in-situ leaching of uranium to realize the efficient exploitation of uranium resources.MethodsFirst of all, sandstones of uranium mine in Xinjiang were taken as the experimental samples, the relationship between the mineral composition and porosity in the process of acid in-situ leaching of uranium was studied through acid in-situ leaching experiment, and nuclear magnetic resonance experiment was employed every other period of time to obtain the porosity change curve in the process of uranium sandstone leaching. Then, the mineral characteristics of uranium sandstone were analyzed by X-ray diffractometer to find the changes of the mineral composition during uranium sandstone leaching. Finally, the influence of different minerals on porosity change was analyzed with the help of gray relational theory.ResultsThe results show that the pore blockage in the leaching process is mainly due to the complex physical and chemical action of many kinds of minerals, which will affect the solute transport process of other minerals in uranium sandstone and not only lead to the change of mineral composition but also affect the leaching of uranium. Through grey correlation analysis, it is found that calcium sulfate and magnesium silicate as plugging materials have a correlation degree of over 0.781 for porosity and uranium leaching rate. The physical adsorption of clay minerals can block the micropores of uranium sandstone, so its correlation with porosity and uranium leaching is 0.831 and 0.842 respectively, indicating that pore plugging has an impact on uranium leaching.ConclusionsAccording to the relationship between the change of mineral composition and pore blockage in the process of leaching, making appropriate adjustment can solve the problem of pore blockage, so as to realize the efficient exploitation of uranium resources.
BackgroundThe use of controlled X-ray sources instead of 137Cs radioactive sources in density logging has become a new trend. The high voltage on the target substrate significantly affects the intensity of the X-ray source, and the density measurement uncertainty can be maintained at 0.01 g?cm-3 when the high voltage is 350 kV.PurposeThis study aims to examine the depth-of-investigation characteristics and influence of a 350-kV high-voltage X-ray density logging instrument.MethodsThe depth of investigation of various source distance detectors in 20% water-bearing limestone formation was studied using the Monte Carlo method. By comparing the investigation characteristics of 350-kV high-voltage X-ray source and 137Cs source density logging, the reasons for the differences in the depth of investigation among them were analyzed. Moreover, the contribution of mudcake and formation to the detector and the density deviations of various detectors were analyzed via simulation. Finally, the influence of mudcake on the density logging response of the well wall was explored.ResultsThe results indicate that the depth of investigation of X-ray density logging instrument increases with the augment of source distance. Compared to the 137Cs source density logging, the scattered particles of the X-ray density logging are mainly concentrated at 1~3 cm from the bore wall, resulting in the depth-of-investigation differences between the two techniques. Furthermore, the contributions of mudcake and formation to different source distance detectors are different, and the detector density deviation decreases with the increase in source distance.ConclusionsThis study affords a theoretical basis for the depth-of-investigation characteristics and influence of 350-kV high-voltage X-ray density logging.
BackgroundIn the realm of cosmological ray studies employing plastic scintillation fibers, it is essential to conduct quantitative analyses of the photon number from the fiber's output pulse for the successful design of readout electronics.PurposeGiven the absence of a weak cursor setting device such as a single photon source. This study aims to quantitatively analyze the number of photons generated by photon incidents within the fiber calibrating without a weak photon source such as a single photon source.MethodsFirstly, photon numbers within weak optical pulses induced by muons in optical fibers with diameters of 1 mm and 2 mm were determinated by the calibration method that making use of inherent non-photogenerated carrier characteristics of the silicon photomultiplier tube (SiPM). Then, the Geant4 software was employed to simulate the theoretical photon yield of muons in these optical fibers, and the simulation results were compared with experimental data for validation.ResultsThe verification results indicate that the anticipated photon count in the optical pulses within fibers with diameters of the 1 mm and 2 mm fibers are 44 and 85, respectively. The deviation from the simulation results is 4.55% and 10.59%, respectively.ConclusionsThe results validate the efficiency of the low photon number measurement method, demonstrating its ability to accurately measure the photon count generated by the incident fiber without the need for additional calibration equipment. This method may extend to other scenarios that require the measurement of photon numbers in weak light pulse situations.
BackgroundThe high-temperature liquid lead-bismuth metal has a scouring and wear effect on the head of the axial flow lead-bismuth pump impeller blades in a lead-cooled fast reactor system, causing the protective layer on the blade surface to break down and material corrosion rate to accelerate.PurposeThis study aims to reduce the scouring wear effect of the high temperature liquid metals on blade surfaces.MethodsFirst of all, three types of leaf top clearance structures, i.e., plane, chamfered right angle, and chamfered rounded angle, were designed. Then, the reliability of the simulation results was verified by the scaling conversion method, and the commercial CFD software ANSYS CFX with SST k-ω turbulence model was employed to analyze the variation of flow velocity, shear force, and flow pattern with scouring and wear characteristics under different leaf top clearance structures. Finally, the energy loss of the high temperature liquid lead-bismuth metal on the material surface was analyzed using the wall entropy yield.ResultsAnalysis results show that the head and efficiency of the chamfered right angle model are reduced by 1.02% and 0.64%, respectively, compared with those of the flat surface under standard operating conditions, and the chamfered angle model shows a 0.51% reduction in the head and 0.51% efficiency increase. The impeller scouring wear effect occurs predominantly near the inlet edge of the blade rim, and the effect of the high temperature liquid metal on the blade head scouring wear is improved by the chamfered and rounded designs.ConclusionsThe chamfered and rounded designs reduces the mechanical energy loss on the blade surface by reducing the flow velocity at the top clearance and reducing the scouring wear effect at this location. Therefore, the rounded design and the right angle design could improve the influence of high-temperature liquid lead-bismuth metal on the erosion wear of the blade head.
BackgroundDirect-current radiofrequency (DC-RF) hybrid plasma has broad application prospects in the field of nuclear ultrafine powder material preparation owing to its characteristics of high temperature and high chemical activity.PurposeThis study aims to explore the flow and heat-transfer characteristics of DC-RF hybrid plasma, so as to provide references for the design and stable operation of the plasma generator device.MethodsFirst of all, the hybrid plasma generator was assumed to be a two-dimensional axisymmetric model, and the device was filled with pure argon plasma in a local thermodynamic equilibrium (LTE), steady, and turbulent flow state. Then, the ANSYS FLUENT software was employed to establish a two-dimensional model for the DC-RF hybrid plasma torch structure, and the spatial distributions of the temperature and flow field in DC-RF hybrid plasma torch were simulated using the k-ε turbulence model with SIMPLE algorithm based on velocity and pressure coupling solver. Finally, the effects of changes in the operating parameters were analyzed based on these results.Results & ConclusionsThe simulation results indicate that increases in the DC arc current, reaction gas flow rate, and cooling gas flow rate can reduce backflow effects at the entrance of hybrid plasma torch. The temperature and area of the plasma arc near the RF coil increase with the RF coil current. However, an excessive current and gas flow rate may adversely affect the operation of the device. Various requirements of material handling processes on the premise of stable operation of the device can be satisfied by adjusting working parameters for the control of the hybrid plasma flow field profiles.
BackgroundIn recent years, lead halide perovskite scintillators have received extensive attention in the field of X-ray imaging. Hard X-ray medical imaging in energy range of 20~120 keV using scintillator detectors, sensitivity and imaging spatial resolution are important performance indicators.PurposeThis study aims to explore X-ray imaging property of halide lead perovskite scintillators by simulation.MethodsFirst of all, 3D MAPbBr 3 quantum dots/polystyrene and 2D PEA 2PbBr 4 quantum dots/polystyrene scintillators were taken as research objects. Then, simulation code Geant4 was employed to establish detector model and simulate the X-ray relative detection efficiency and imaging spatial resolution of lead halide perovskite quantum dots/polymer composite scintillators. Finally, the effect of energy and the ratio of perovskite quantum dot occupation on the resolution were explained by secondary electron motion.ResultsThe results show that increasing the thickness of the composite scintillator and the proportion of perovskite quantum dots can improve the relative detection efficiency whilst reducing the thickness and increasing the proportion of perovskite quantum dots can improve the spatial resolution. When the absorption efficiency reaches 99.5%, 80% of 3D MAPbBr 3 quantum dots/polystyrene excited by 20 keV X ray obtain the same spatial resolution of 10 lp·mm-1 as CsI. When the incident energy increases to 50 keV, the spatial resolution of CsI is 8 lp·mm-1, while that of lead halide perovskite scintillators is less than 4 lp·mm-1.ConclusionsIt is shown by this study that lead halide perovskites have certain application potential in 20 keV low-energy X-ray medical imaging.
BackgroundCu-W composites are widely used in electric power, electronics, and plastic forming owing to the excellent electrical and thermal conductivities of copper combined with the outstanding strength and thermal properties of tungsten.PurposeThis study aims to investigate the extension of the solid solubility of the Cu-W immiscible system under high current pulsed electron beam (HCPEB) irradiation.MethodsFirst of all, the Cu-15W powder mixture was sintered by vacuum at 850 ℃ after ball milling for 5 h to prepare the Cu-W composites. After polishing, the Cu-W composites was exposed by a HOPE-1 type HCPEB device with 1, 5, 10 and 15 pulses, respectively. Then, Rigaku D/Max-2500/pc X-ray diffractometer (XRD) was used to analyze the phase constitutes of the milling powder, sintered samples and irradiated samples. The surface morphology was observed by JEOL JSM-7001F field emission scanning electron microscope (SEM). The energy dispersive spectrometer (EDS) in SEM was used for the examination of micro-region composition. Finally, the microstructures in the modified layer were characterized by JEOL-2100F transmission electron microscopy (TEM). The surface hardness of the sintered and irradiated samples with different pulses was measured using the HVS-1000 Vickers hardness tester.ResultsThe results reveal that Cu(W) solid solutions were formed during the process of ball milling, and the mass fraction of the solute element W in the Cu(W) solid solution reaches 0.88% after 5 h of ball milling. It was discovered that the solid solution undergoes exsolution reaction during heating using differential scanning calorimeter (DSC). The sintered sample surface was irradiated by a pulsed electron beam. The results demonstrate the formation of solid solution phase after HCPEB irradiation, whose solubility increases with the increase of the number of pulses. After 10 pulse irradiations, the mass percentage of solute element (W) in Cu(W) solid solutions reaches 1.63%. The surface hardness of irradiated samples increases significantly after HCPEB irradiation, and reaches 237.1 HV after 10-pulsed irradiation. Surface hardening is primarily caused by of solid solution strengthening and dispersion strengthening.ConclusionsThe present paper provides a meaningful instruction for preparing the immiscible alloy with high solid solubility and the excellent performance.
BackgroundThe experimental advanced superconducting tokamak (EAST) feeder system is an essential part of the device that connects the superconducting magnet and high-temperature superconducting current lead. It provides the magnet with feeding and energy release channels in the event of quenching. In recent years, owing to the increase in the inlet temperature of the toroidal field (TF) feeder system, the outlet temperature has occasionally exceeded the threshold of 6.1 K, resulting in the termination of the experiment.PurposeThis study aims to ensure the continuation of the EAST experiment by thermal stability analysis under new TF feeder outlet temperature threshold of 6.5 K.MethodsBased on the system structure and low-temperature operation data of the TF feeder and superconducting conductor, a mathematical model for temperature margin and current shunt temperature of superconducting conductor was established. Then, the mathematical model and GANDALF software were employed to calculate the temperature and stability margins of superconducting conductors during operation under different background magnetic fields and operating currents.ResultsThe calculations results indicate that under the new threshold of 6.5 K, the temperature margin of the conductor is greater than 1.5 K and that the stability energy margin is greater than 200mJ·cm-3.ConclusionsThe superconducting conductor remains safe for use after increasing the threshold.
BackgroundThe current radiation dose calculation technology can only give 3D static dose results of upright human body, which cannot meet the needs of future accurate protection.PurposeThis study aims to achieve 4D dose calculation by establishing a complete method.MethodsFirstly, three algorithms, namely, the rotation matrix method, the volume graph Laplace operator method and the As-Rigid-As-Possible (ARAP) method, were employed to realize the deformation of mesh phantom. Then the phantom deformation guided by motion capture was investigated, and the tetrahedral cutting technology based on Delaunay algorithm was applied to the high speed Monte Carlo calculation. Finally, the 4D dose calculation application system was implemented and used for field test of nuclear power plant (NPP).ResultsThe comparison between the calculated and measured individual 4D dose values shows that the deviation of Hp(10) is less than 10%, and the deviations of Hp(3) and Hp(0.07) are less than 15% are verified.ConclusionsThe reliability and practicability of 4D radiation dose calculation of human body proposed in this study are verified by application results in specific radiation operation process in NPP, which is expected to achieve precise protection of personnel in the future scenarios such as NPP operation and maintenance, nuclear facility decommissioning and medical interventional treatment.
Background55Fe is a low-energy radionuclide that is difficult to measure and decays to a ground state of 55Mn through pure electron capture (EC), accompanied by the emission of Auger electrons and low-energy X-ray. As iron is the main component of nuclear reactor building materials, significant amounts of 55Fe have been produced in nuclear reactors and other neutron-producing nuclear facilities.PurposeThis study aims to develop an 55Fe nuclide standard through the absolute measurement of 55Fe activity and provides activity traceability services for 55Fe measuring instruments to ensure the accuracy and consistency of the measurement results of calibration instruments.MethodsThe liquid scintillation triple-to-double coincidence ratio (TDCR) method was applied to determining the activity of 55Fe. First, based on nuclear and atomic data of 55Fe, the electron deposition spectrum of 55Fe in a scintillator was calculated using a random atomic rearrangement model. Second, the counting efficiency of single-energy electron was computed based on the free parameter model. The total efficiency curve of 55Fe was then obtained by summing the efficiency of all deposited electrons. Finally, the experimental counting efficiency was derived by measuring the TDCR value and combining it with the total efficiency curve to realize an absolute measurement of 55Fe activity.ResultsThe experimental results show that correction factors for the asymmetric effect of photomultiplier tube (PMT) quantum efficiency obtained on test samples are between 1.001 and 1.005. The measured specific activity of 55Fe is 94.15 kBq?g-1 with a relative standard uncertainty of 0.45%. Experimental efficiency is better than 63% for double coincidence logic sum of liquid scintillation counter.ConclusionsThis study demonstrates that low relative standard uncertainty of 55Fe activity could be achieved using the liquid scintillation TDCR method with high detection efficiency, and more consistent measurement results can be obtained after applying the asymmetry correction of PMT quantum efficiency.
As a wide variety of radioactive materials with different characteristics and potential environmental risks existed, the domestic classification of radioactive items management was made, and The Classification and List of radioactive materials (Trial) was formulated. In order to optimize the classification of radioactive materials in China, the current situation of the classification of radioactive materials and classification basis at home and abroad were investigated. The main differences of classification basis were summarized and followed by analysis of problems existing in the classification of radioactive materials in China. New ideas and suggestions to solving the problems was put forward. First, the enumeration items such as radioactive sources and radioactive wastes in the classification of radioactive materials needs to be deleted. Second, the Classification and List is suggested to be revised by adopting the United Nation (UN) Number corresponding to different classifications of radioactive material which is unique and consistent with the international. Finally, a reference for the revision of The Regulations on the Safety Management of The Transportation of Radioactive Materials and The Classification and List of radioactive materials (Trial) is provided.
BackgroundRadioactive oil is one of the organic "difficult wastes" produced by the operation of nuclear power plants.PurposeThis study aims to develop a nuclide separation and treatment technology for radioactive waste oil and explore engineering application.MethodsFirst of all, a set of radioactive oil nuclide separation and purification treatment engineering equipments was developed and applied to obtain test samples collected from one NPP. Then a nuclide separation and purification process based on the oxidative aging method were developed. Finally, the high-purity germanium for nuclide γ spectrometer was employed to measure 58Co, 60Co, 54Mn, 110mAg, 137Cs, 134Cs, 124Sb, 125Sb, 59Fe, 95Zr, 95N, etc., γ nuclides, low background liquid scintillation counter was applied to the measurement of 3H and 14C, and high sensitive automatic liquid scintillation counter was used to measure 55Fe and 63Ni. Total α and total β were obtained by using low background α/β measuring instrument. [Results and Conclusions] The results show that the decontamination coefficient of the oxidative aging process reaches more than 2 orders of magnitude; the radioactive oil treated by the engineering device amounts to the clearance level, hence can be managed as ordinary hazardous waste. The additional dose that may be caused in the process of incineration (including transportation) for the treated radioactive oil is far below the dose limits, which meets the dosage guidelines for reuse, and is in line with waste minimization principles.
BackgroundSawtooth oscillations are macroscopic instabilities in plasma. To better control the sawtooth oscillation in an advanced experimental superconducting tokamak (EAST) device, it is necessary to develop sawtooth controlling methods that help improve the confined performance of plasma in the EAST device.PurposeThis study aims to analyze sawtooth behavior under the on-axis heating by ion cyclotron resonance frequency (ICRF) wave in the EAST device.MethodsFirst of all, the soft X-ray integrated signal intensity data was used to analyze the sawtooth period and amplitude. The radius of q=1 surface and the plasma pressure gradient at q=1 surface were calculated using a soft X-ray intensity profile. Then the neutron yield flux was obtained from the neutron yield flux diagnostic data. Finally, the equilibrium reconstruction results of the equilibrium fitting algorithm (EFIT) were combined with polarimeter-interferometer (POINT) diagnostic data to investigate the relationship between the variation of ICRF and plasma current density.ResultsExperimental results show that the sawtooth period is positively correlated with the ICRF power, and the variation in sawtooth period is roughly same as that in sawtooth amplitude and plasma pressure gradient at q=1 surface. The ICRF power needs to exceed 0.8 MW to change the radius of q=1 surface. The sawtooth period and q=1 surface with ICRF power change are more sensitive under solely ICRF heating than under ICRF+lower hybrid wave (LHW)+electron cyclotron resonance heating (ECRH).ConclusionsSawtooth behavior of EAST plasma is affected by the fast ions produced by ICRF and the radius change of q=1 surface.
BackgroundRemote, large-scale, rapid and real-time detection of radioactive sources is of great significance for industrial investigation and environmental remediation. Gama camera can extract information such as the location, intensity and category of radioactive substances from a long distance, and is an effective detection tool. Due to the small detector area and the limited field of view (FOV) of the coded aperture, the detection efficiency of the current coded aperture γ cameras is low.PurposeThis study aims to propose a prototype of large area and highly sensitive coded aperture gamma imaging system based on a SPECT probe.MethodsFirst of all, the Hamamatsu BHP6601 single photon emission computed tomography (SPECT) probe with large area of 510 mm×390 mm and high intrinsic spatial resolution of 3.55 mm was selected as the detector of the system. Based on the detector by tectonic analysis, modified uniform redundant arrays (MURA) coding nesting mode was adopted with a rank of 23 and each unit aperture size of 22.1 mm×17 mm. Then, the system transmission matrix is obtained by using the gamma rays emitted from the radioactive sources at different angles of the FOV to reach the detector geometry through the coded aperture. Then, the geometric relationship between the radioactive source and the system is used to analyze and construct different radioactive source events. Next, the cumulative probability based on the system transmission matrix simulates the photon distribution on the detector. Finally, using Maximum Likelihood Expectation Maximization (MLEM) algorithm is built source image.ResultsThe results indicate that the non artifact field of view (NAFOV) is 57.32° in the X direction and 47.3° in the Y direction; and the spatial angle resolution is 2.94° in the X direction and 2.28° in the Y direction. The γ camera can accurately locate 3.7×107 Bq 137Cs single point source in 1 s at the distance of 18 m and 2 s to accurately reconstruct the position of 1.11×106 Bq 137Cs at the distance of 4 m away from the camera.ConclusionsThe γ camera of this study has a high detection capability for distant or low-activity radiation sources in large range.
BackgroundThere are no commercially available channel electron multipliers (CEMs) made of glass in domestic market of China; more complex CEMs with helix channels are scarcer.PurposeThis study aims to develop a CEM with a single helix channel, and test its performace for satisfying the requirements of high-end users of such products.MethodsFirst of all, a series of manufacturing process designs and improvements were made on the basis of the formula of microchannel sheet glass, resulting in the production of a single spiral channel electron multiplier with suitable performance. Then, a CEM analog mode test device with a disc-incense type tantalum filament as the input current and a CEM pulse-counting mode test device with an ultraviolet light-emitting diode combined with a gold cathode as the input signal were set up to conduct comprehensive testing of the device's performance parameters.ResultsThe newly developed CEM with single helix channel achieves gains of 1×104~1×106 in the analog mode and 1×107~1×108 in the pulse-counting mode. The gain value increases with the increase of the working voltage, and the rise time of the output pulse is 2~3 ns.ConclusionsThe overall performance of the developed CEM is close to that of foreign counterparts, and the CEM can be used in related instruments.
BackgroundWhen steam generator tube rupture (SGTR) occurs in the lead-bismuth cooled fast reactor, high pressure water/steam flows into the primary side filled with high temperature liquid metal. According to the location and size of the rupture, the leakage behaviors of the rupture may involve leak-before-break (LBB), single-phase critical flow or two-phase critical flow. Under the action of high temperature liquid metal, different forms of heat and mass transfer behaviors occur in the two-component multiphase system of water-metal, which has an important influence on the safe operation of the lead-bismuth cooled fast reactor.PurposeThis study aims at the bubble dynamic behavior in the descending flow field of liquid lead-bismuth alloy (LBE) in the tube bundle in different stages of SGTR caused by microcrack on the surface of the heat transfer tube during the drying stage and low flow single phase steam permeates the primary side.MethodsBased on the VOF method, a numerical simulation model of steam-LBE two-phase flow and phase interface capture was established to study the bubble growth and transport behaviors from single tube or 3×3 tube bundle in the downward flow field of high temperature LBE. The SST k- ω model was employed to solve the turbulence equation. The physical law of steam bubble movement was analyzed and its influence on the heat transfer and operation stability of steam generator was evaluated.ResultsThe results show that the dynamics behaviors of steam bubbles in the descending flow field are quite different from these in static liquid or upward flow. The steam bubbles may slide along the heat transfer tube surface after departure from the crack under the actions of LBE descending flow field and buoyancy. The steam bubbles may form a steam film covering the heat transfer tube surface or accumulate by quantity in the bundle.ConclusionsThese phenomena adversely affects the flow stability of the LBE and the heat transfer of the steam generator.
BackgroundThe electrostatic lens plays an important role in obtaining high quality focused electron/ion/slow positron beams with high spatial resolution and brightness. A novel electric lens, composed of simplified electrode structures with tube diameter gradually decreasing, is proposed for focusing charged particle beams with low energy and large spot size.PurposeThis study aims to investigate the beam dynamics of this designed electrostatic lens for validation.MethodsBased on overall structure of electric lens focusing system, the charged particle optical simulation software SIMION was employed to optimize the parameters of this focusing system. Then combined with electron beam experiments, the key technologies involved in the electronic lens were studied in detail, including influencing factors, their distributions, and the focusing performance of the lens.ResultsThe results show that the large transverse space of the initial electron beam can be compressed effectively by arranging the electrode structure and electric potential of the lens, with focusing efficiencies exceeding 80%.ConclusionsThe focusing method proposed in this study has significant lateral compression advantages with wide application prospects in many focusing scenarios of different charged particle beams, such as reactor positron sources.
BackgroundWith the development of negative ion based neutral beam injection system (NNBI) for China fusion engineering test reactor (CFETR), the output power control system of its supporting the radio frequency (RF) power source is one of the key technologies to realize the improvement of its performance.PurposeThe study aims to design an improved output power control system of RF power source to solve the problems of output power stability and insufficient control accuracy in the use of existing RF power sources.MethodsThe software and hardware separation control structure designed by ARM+CPLD dual-core were employed to ensure the operation efficiency of the output power control algorithm of the RF power source and the communication stability of the peripheral equipment. Multi-stage progressive power control method and 12-bit digital signal were adopted to control the opening and closing of RF power amplifier, so as to realize high-precision control of output power. The capacitive voltage divider method and current transformer method were combined to accurately sample the actual output power of the RF power source for implementing high-stability control of output power with a closed-loop power control method. Meanwhile, the upper computer software design of man-machine interaction based on serial communication of self-defined protocol was adopted to complete the man-machine interaction function of output power control.ResultsThe control system has perfect human-computer interaction software function, and test results of the prototype RF power output power control system with simulation load show that the control accuracy of the output power is higher than 0.1% when the rated output power is 50 kW, and the stability fluctuation is less than 0.5%.ConclusionsThis scheme with impedance matching networks is expected to meet the performance requirements of CFETR NNBI RF power supply for output power control.
The associated radioactive waste residue has characteristics of long half-life of nuclides, wide range of radioactive levels, and so on. There are many industries involved in associated radioactive waste in China with wide sources, large types and quantities, hence restrict the healthy development of the industry. This study aims to propose effective safety disposal measures suitable for the complex physical and chemical properties of such waste residues, large differences in regional distribution and disposal status. Through comparison and analysis with hazardous waste, medium and low level radioactive waste, uranium mining and smelting waste, the technical support for the regulatory concept of associated radioactive waste residue was provided. The current disposal methods, design requirements, applicable scenarios, advantages-disadvantages and application examples of this kind of waste residue were systematically introduced, and the disposal strategies of associated radioactive waste residue were suggested. Meanwhile, a typical case of a regional disposal site project was taken as example, the characteristics of the project and waste residue were deeply analyzed, and the countermeasures were given to provide reference for relevant disposal work. Finally, based on above work, some suggestions are put forward to promote the final disposal of associated radioactive waste residue in China.
BackgroundNuclear critical safety analysis is the key technology to ensure the safety of spent fuel reprocessing plant. However, the present critical safety analysis codes for solution system are either limited in the geometric scope of application, or have poor engineering practicability due to low computational efficiency.PurposeThis study aims to develop a method suitable for wide application range and high accuracy for nuclear critical safety analysis, so as to provide technical support for spent fuel reprocessing plant.MethodsAccording to the characteristics of spent fuel solution system, a set of methods, such as the zero-dimension cross-section calculation and whole system group condensation model, the three-dimensional space-time neutron dynamics model based on PCQS, and the R-Z two dimensional thermal and radiolysis gas simulation model, were combined to establish a paralleled 3D critical safety analysis code hydra-TD. In addition, some experiments of SILENE facility at France were modeled and calculated by using hydra-TD code to verify its effectiveness.ResultsThe verification results indicate that there are very small errors of key parameters such as the first fission power peak, multiplication time and total fission times.ConclusionThe code hydra-TD developed in this study can be applied to simulation of the multi-physics processes in the critical transients of the fuel solution, hence has the ability of critical safety analysis.
BackgroundTime series usually have the characteristics of linear and nonlinear. Single model has certain limitations, which proposes mixed models for time series prediction.PurposeThis study aims to explore the application of the combination of Mann-Kendall test, differential autoregressive mobile average model (ARIMA) and long and short-term memory (LSTM) used in the prediction of the number of operational events of nuclear power plants (NPP) collected in Nuclear Safety of China and Annual Report of Nuclear Safety.MethodsFirstly, the R software was used to build ARIMA (2,1,2) model to obtain the linear part of operation events with the number of nuclear power plant operation events from 1991 to 2018, and LSTM model was developed to predict the deviation sequences, hence the nonlinear part of the number of operation events was derived from those deviation sequences. Then, combined model of ARIMA and LSTM was established to predict the number of operational events. Finally, the predicted values based on measured data were verified by actual measured data.ResultsThe verification results show that the ARIMA and LSTM combination model can be employed to improve the prediction accuracy effectively by 3%, and the predicted values of operation events in nuclear power plants from 2019 to 2020 are similar to the data collected in Annual Report of Nuclear Safety.ConclusionsThe combined model can better fit the time series of the number of operating events of NPP and correct the error of the single model.
BackgroundIn the long-term uninterrupted work of the real-time on-line monitoring system of water radioactivity, the spectrum drift, line broadening and shift of peak position are caused by the temperature change of the detector and various electronic components and the aging of components, which leads to the difficulty of spectral line analysis and the error of analytical results.PurposeThis study aims to develop a calibration device for real-time on-line monitoring system of water radioactivity based on cerium bromide detector.MethodsThe device was designed to consists of 137Cs standard source (exemption source), lead block, lead chamber with calibration hole and linear motor. The optimum opening radius of the calibration hole and the optimum thickness of the lead block were obtained by Monte Carlo simulation. The standard 137Cs source was used as the standard reference peak, and the calibration of peak position and peak area, the peak position drift and peak area of 137Cs full-energy peak was analyzed by software with real-time gain calculation and parameters adjustment. Finally, the device was applied to the field application verification.Results & ConclusionsResults of Monte Carlo simulation indicate that the optimum radius of the calibration hole is 2.2 cm and the optimum thickness of the lead block is 5 cm. The verification results shows that the device can limit the change of peak position and peak area to ±1% and ±5%, respectively.
BackgroundThe startup time and startup-failure are widespread in most cold redundancy equipment of nuclear power plants (NPPs). The traditional static and dynamic fault tree cannot accurately model the startup time and startup-failure.PurposeThis study aims to model the startup time and startup-failure behaviors in cold redundancy systems, and provide suggestions for the improvement of reliability assessment methods.MethodsFirst, a DFT Monte Carlo simulation method was proposed for modeling and analyzing equipment's startup time and startup-failure behaviors in a cold redundancy system. Then, the emergency diesel generator set of the nuclear power plant was taken as an example, the distribution curve of system failure probability and the sensitivity of each component were obtained. Finally, the results were compared with the static fault tree method and traditional DFT method.Results1) The proposed method can model and analyze the start-up time and start-up failure behaviors of cold redundant equipment, reflecting the real failure scenarios and actual operation status of cold redundant systems. 2) The proposed method can accurately evaluate the system failure probability, identify highly sensitive equipment parameters in different time periods, and analyze the influence of start-up time on the system failure probability.ConclusionsThe proposed method has certain theoretical significance for the optimal design of NPP's cold redundancy systems.
BackgroundWith advantages of low system pressure, stable operation and good economic performance, molten salt heat exchanger has recently been widely applied to the field of energy as concentrating solar power, nuclear power engineering, high temperature hydrogen production, and so on.PurposeThis study aims to analyze the thermal stress generated in the main components of the U-tube heat exchanger due to the high operating temperature of the molten salt and the large temperature difference between the hot and cold fluids.MethodsFluid-thermal-solid coupling method was adopted in this study. First of all, the main thermal performance parameters of the heat exchanger were obtained by using computational fluid dynamics (CFD) computation, and compared with experimental results to verify the accuracy of the CFD fluid simulation results. On this basis, the heat transfer process was analyzed in details for the molten salt tube-shell heat exchange under the operating condition, and the flow field and temperature field of the heat exchanger were obtained. Finally, the stress field generated by the coupling of flow field, pressure field and temperature field was calculated by Ansys workbench finite element software, and the stress distribution of the tube sheet connected with the heat exchange tube and shell was emphatically analyzed to find the maximum stress value of the tube sheet and the stress change rule of some paths.ResultsThe result shows that the CFD fluid simulation method is feasible with a maximum deviation of 3.07%. The larger stress is found at the connection area between the tube plate and the non-tube, which is located near the inner tube wall on the shell-side with about 2 mm away from the lower surface of tube plate.ConclusionsResults of this study provides important reference for the actual operation and structural deign of molten salt heat exchanger.
BackgroundAmong the mitigating strategies for severe accidents, the in-vessel retention (IVR) is one of the useful remission measurements. The key point to evaluating IVR is to analyze that the final steady-state thermal load of the melt does not exceed the critical heat flux (CHF), which occurs during boiling heat transfer on the outer wall of the lower head, and the remaining wall thickness of the lower head can carry the melt to prevent the structural failure.PurposeThis study aims to analyze heat transfer of the reactor pressure vessel (RPV) lower head under severe accidents by using ASTEC code.MethodsFirst of all, the composition and mass of the molten substance were assumed to be UO2, 92 353.29 kg; Fe, 43 000 kg; Zr, 23 133.9 kg; Zr oxidation, 41.8%, for a large advanced pressurized water reactor (LAPWR). With the heavy metal oxide layer and metal layer of stable molten pool in the lower RPV of this LAPWR, the average value of core decay power and the physical properties of molten materials in RPV were input as the condition boundaries for ASTEC, the middle break accident sequence was selected for the calculation of the thermal parameters of the coolant, the outer wall CHF and the final thickness of the lower head. Then, the CHAWLA-CHAN heat transfer relationship was used to calculate the heat transfer coefficient between the melt and the inner wall of the lower head. The key safety related issues such as the heat transfer parameters of the outer wall of the lower head, the heat transfer through the lower head, and the wall thickness of the lower head were analyzed. Finally, the IVR effectiveness was estimated by the thermal properties and the structure of the lower head.ResultsWhen the decay power is 21 MW and the core molten pool is divided into two layers, the average thickness of the oxide layer is 1.6 m, and the metal layer is 0.8 m. The results show that the heat exchange is more intense in the upper part of the lower head, and the maximum value of the heat flux occurs at the junction of the two melt layers, which the corresponding surface angle is 77.5°~80°. The inner wall of the lower head will be melted by the molten metal layer in the location of the minimum thickness of the lower head, and the final remaining thickness is less than 2.0 cm.
BackgroundCompared with conventional rod-type nuclear fuel, annular fuel has higher power density and better heat transfer efficiency, which can significantly improve the safety and economy of the reactor.PurposeThis study aims to investigate the effect of ring fuel element geometry on the thermal performance and to correct the initial parameters.MethodsThe initial parameters of the ring fuel element were set and the thermal conductivity calculation program of the ring fuel element was prepared. The effects of the ring fuel flow distribution ratio, inner and outer cladding thickness, inner and outer air gap thickness and core block thickness on the thermal performance of the ring fuel element were investigated by three evaluation criteria developed and geometric corrections are made.ResultsAppropriately increasing the flow distribution ratio, decreasing the inner casing thickness, increasing the outer casing thickness, decreasing the inner and outer air gap spacing and decreasing the core block thickness can improve the thermal performance of the components; setting the flow distribution ratio to 1, the inner casing thickness 0.06 cm is amended to 0.04 cm, the outer casing thickness 0.06 cm is amended to 0.07 cm, the inner and outer air gap spacing 0.035 cm. The thickness of core block is amended to 0.5 cm.ConclusionsThermal performance of annular fuel elements is significantly improved after appropriate geometry correction is made.
Associated radioactive mines are widely distributed in China, with many industries, complex processes and technologies, close relationship with the public, and great impact on the radiation environment. They are relatively weak links in nuclear and radiation safety supervision. In the process of implementing the upper level document, some specific problems have to be faced, such as the definition of associated radioactive ore, the scope of associated radioactive ore development and utilization, etc. In the field of radiation environment supervision, there are issues such as effluent and radiation environment monitoring specifications that need to be solved. In particular, the treatment and disposal of associated radioactive solid waste is the key problem that currently restricts the sustainable development of associated radioactive ore development and utilization. The second national census of pollution sources reported the cumulative storage of associated radioactive solid waste in the country, and the radiation environment supervision situation is grim. In the scope of associated radioactive mines and some problems encountered in the supervision of radiation environment, this study aims to formulate a reasonable and feasible supervision system for associated radioactive mines, standardize supervision and management activities, and ensure the safety of the radiation environment according to scientific management methods, combined with the practice of supervision of associated radioactive mines. Suggestions on the definition of the scope and development and utilization of associated radioactive mines and the management of the inventory are put forward for solving the radiation environment supervision system with consideration on the storage period of associated radioactive solid waste, the management of nearby centralized disposal and disposal facilities. As the radiation environmental supervision of associated radioactive mines is still a relatively weak area in nuclear and radiation safety supervision system in China, radiation environmental impact assessment and environmental radiation self-monitoring need to be strengthened.
BackgroundThe annular fuel can increase the power density of the reactor due to its double-sided cooling, which is of great significance to the miniaturization and long-life operation of the pressurized water reactor.PurposeThis study aims at the calculation method of effective temperature of annular fuel cell by developing the thermal-hydraulic analysis code named THCAFS (Thermal-Hydraulic Code of Annular Fuel with Single channel) for annular fuel, and establishing a calculation model for the effective temperature of the annular fuel cell.MethodsBased on THCAFS, the thermal-hydraulic performance of the annular fuel cell designed by Westinghouse 4-loop PWR was analyzed, and the Code-to-Code comparison was carried out with the calculation results of VIPRE-01, TAFIX and NACAF. At the same time, the Monte Carlo code SERPENT was employed to simulate the radial power distribution and burnup process in the fuel rod, and the self-developed code THCAFS was used to simulate the thermodynamic behavior in the fuel rod, and the radial power distribution, nuclide density change and cell temperature field.Results & ConclusionsThe results show that THCAFS can be preliminarily applied to annular fuel design and thermal-hydraulic analysis. The maximum deviation of the ratio between the fitting function power and the simulated power under different fuel consumption does not exceed 2%. This effective temperature calculation method can also provide important reference value for the mechanism study of the relevant annular fuel resonance effective temperature.
BackgroundIn the aspect of long-distance transport and deposition of airborne nuclear pollutants, Eulerian-Lagrangian method can combine the theoretical advantages of the Lagrange method and Euler method, but and there are few studies in China.PurposeThis study aims to verify the effectiveness of this method for long distance transport and deposition of airborne nuclear pollutants by simulating a nuclear leakage accident of one nuclear power plant in China.MethodsAssuming that a nuclear power plant in the eastern coastal area of China has a leakage similar to the Fukushima nuclear accident, the numerical simulation of the long-distance transport process of nuclear pollutants in the atmosphere was carried out by using the Euler-Lagrangian method of MATCH (Multi-scale Atmospheric Transport and Chemistry) module in JRODOS (Java Real-time On-line Decision Support) system. The results of surface deposition and the distribution of dose rate field were combined with the actual weather map to verify the trend.ResultsThe simulation and verification results show that the wet deposition plays an important role in the removal of nuclear pollutants, and the Eulerian-Lagrangian method can give the main characteristics of long-distance transport and deposition of nuclear pollutants in the atmosphere.ConclusionsThe simulation results are in good agreement with the actual weather trend, and this method can provide auxiliary reference for China's nuclear accident consequence assessment and emergency decision-making.
BackgroundUN-U 3Si 2 composite fuels have a promising prospect in advanced future accident tolerant fuel elements. Its irradiation creep and thermal creep caused by in-reactor operation have an important influence on the irradiation-induced thermo-mechanical coupling behavior and safety of the fuel elements.PurposeThis study aims to develop a stochastic modeling method according to the metallographic structure of composite fuel and numerical simulation of the uniaxial tensile creep test of the UN-U 3Si 2 composite fuel (20% U 3Si 2).MethodsBased on the data of creep experiments from literatures, the dominated creep mechanisms of UN and U 3Si 2 polycrystalline fuels were analyzed, and their creep rate models considering vacancy diffusion and dislocation motion mechanisms were obtained by curve fitting. Then, the correlation model between the macroscopic creep of composite fuel and the contribution of each component was established on the basis of the homogenization theory and the removal of irradiation swelling effect. Finally, based on the metallographic structure diagram of composite fuels in the literatures, stochastic modeling method was developed and applied to the numerical simulation of the uniaxial tensile creep test of the UN-U 3Si 2 composite fuel (20% U 3Si 2).ResultsThe model predictions of UN and U 3Si 2 creep rates are in good agreement with the experimental results, validating the effectiveness of the model. The contribution of the component fuels to the macroscopic equivalent creep of the composite fuel is obtained by analysis of the underlying creep mechanism. When the fission density reaches 4.32×1027 fissions·m-3, the maximum von Mises stress at the interface between particles and matrix is about 6 times of the homogeneous tensile stress applied externally.ConclusionsThe research results indicate that the difference in the irradiation swelling of UN and U 3Si 2 will result in the strong internal mechanical interaction in the composite fuel whilst the existence of weakened stress regions leads to the negligible effect of irradiation swelling on the macroscopic equivalent creep strain of the composite fuel.
BackgroundTitanium and its alloys are widely utilized within the military, aerospace, shipping, nuclear energy, and biomedical fields because of the advantages of low density, high strength, good corrosion resistance, and high biocompatibility. Moreover, titanium films are important materials for surface protection due to their high hardness and good compactness. During the preparation of titanium films, the surface morphology and phase structure will be influenced by substrate properties (e.g., surface morphology and temperature), working gas pressure, and other factors. Substrate temperature mainly influences the growth process of thin films, which directly affects the grain structure of the films, and thus changes the corresponding mechanical properties.PurposeThis study aims to establish the relationship between substrate temperature and mechanical properties of titanium films.MethodsFirstly, titanium film samples were prepared at a substrate temperature range of 600~750 ℃ by using resistance evaporation coating on the surface of molybdenum substrate. Then, the structural characterization of the film was examined using X-ray diffraction (XRD) so as to obtain the preferred orientation of titanium film. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to identify the surface morphologies of the titanium films, including grain size distribution and surface roughness. Finally, an AFM nano-indentation method was performed to examine the mechanical properties of the titanium films and obtain the elastic modulus of titanium film.ResultsThe results demonstrate that the substrate temperature significantly influences the microstructure and mechanical properties of titanium films. When the substrate temperature increases from 600 ℃ to 750 ℃, the preferred orientation of titanium films changes from (101) to (002) due to the competition between the minimization of strain energy and surface energy. With the increase of substrate temperature, the mobility of titanium atoms on the substrate increases, resulting in increased average grain size, surface roughness, and elastic modulus of the titanium films. The average grain size increases by 26% as the substrate temperature increased from 600 ℃ to 750 ℃.ConclusionsThe microstructure, surface morphology, and mechanical properties of titanium films are sensitive to substrate temperature. A high substrate temperature in the process of resistance evaporation is more desirable to obtain titanium films with high mechanical properties.
BackgroundDouble-layered heat exchanger tubes can effectively reduce the probability of heat exchanger tube rupture accidents from design; however, the thermal contact resistance between tubes may decrease the heat transfer efficiency of the heat exchanger tubes. This is not conducive to the smooth heat export of the first circuit system of lead-bismuth reactor; therefore, there is an urgent need to optimize the design of heat exchanger tubes.PurposeThis study aims to optimize the structure of the double-layered tubular main heat exchanger, so as to improve its heat transfer efficiency.MethodsFirstly, the double layer heat exchange tube type main heat exchanger of lead bismuth reactor was taken as the research object, the interstices of double-layered heat exchanger tubes was filled with gallium-based graphene nanofluid as the thermal interface material. Then, the influence of heat exchanger tube length, wall thickness, outer diameter, and spacing on the heat transfer performance were analyzed and results were compared with that of a double-layered tubular main heat exchanger without the thermal interface material. Finally, taking the JF factor and cost efficiency ratio (CER) as optimization objectives and using the aforementioned four parameters as optimization variables, the heat transfer performance of the main heat exchanger was optimized and evaluated on the basis of a genetic algorithm, hence to obtain a new double-layered heat exchanger design for a lead-bismuth reactor.ResultsThe results of comparative calculations indicate that the total heat transfer coefficient, first-loop pressure drop, JF factor, and CER factor of optimized main heat exchanger increase by 5.79%, 2.32%, 5%, and 24.62%, respectively.ConclusionsFilling the gap of double-layered heat exchanger tubes with a gallium-based graphene nanofluid can effectively improve the heat transfer performance of the double-layered tube exchanger while reducing the accident probability of steam generator tube rupture.
The exploration of the critical point on the QCD (Quantum Chromodynamics) phase diagram is one of the most important goals of the beam energy scan program in relativistic heavy-ion collisions (RHIC-BES). Preliminary experimental measurement observed the non-monotonic behavior of net-proton fluctuations as a function of collision energy, which qualitatively agrees with the prediction of the static theoretical models and this hints the existence of the QCD critical point. The system created in heavy-ion collision is highly expanding system with which the dynamical effects dramatically modify the critical fluctuations near the QCD critical point. To confirm the existence of QCD critical point and study the phase structure of QCD system at finite temperature and finite density region, a series of dynamical models near the QCD critical point has been developed. This paper reviews the recent developments related to the exploration of the QCD critical point from experimental and theoretical viewpoints. In particular, we emphasize on the developments and challenges of the dynamical model near the QCD critical point and the first-order phase transition.
BackgroundThe annihilation radiation exhibits conspicuous features in the low-energy segment of the orbital gamma spectrum, which contains a substantial amount of geological information about the lunar surface. The fluence rate can reflect the element composition, density, maturity, and other characteristics directly.PurposeIn order to further clarify the primary source and influencing mechanism of annihilation radiation on the lunar surface.MethodsA quantitative model for the annihilation radiation characteristic peak of orbital gamma spectrometers was established. The gamma rays induced by protons of varying energies were simulated using GEANT4 to further understand the primary source and mechanism of annihilation radiation on the lunar surface. The data from the "Chang'e-1" high-energy particle detector (CE1-HPD) was used as the input term, and the annihilation radiation characteristic information induced by 4~400 MeV protons galactic cosmic rays interacting with five typical rocks was calculated. After subtracting the 0.511 MeV characteristic peak collected by the "Chang'e-1" gamma spectrometer (CE1-GRS) from natural radioactivity, the results were compared with the annihilation radiation fluence rate induced by 4~400 MeV protons galactic cosmic rays.ResultsThe results indicate that the rock's composition have a negligible effect on the annihilation radiation. The probability of cascading shower generating annihilation radiation is directly proportional to the incident proton energy. Additionally, the contribution of 4~400 MeV protons to the annihilation radiation present in the orbital gamma spectrum is relatively low, only (1.97±0.66)×10-4 .ConclusionsThe established model has proven to be accurate in reflecting the related characteristics of the gamma radiation field on the lunar surface and can be used for quantitative analysis of annihilation radiation. The results indicate that the contribution of 4~400 MeV protons galactic cosmic rays to the annihilation radiation present in the orbital gamma spectrum is minimal.
BackgroundThe pre-equilibrium cluster manifests the nuclear structure and reaction dynamics of collision system. The systematical investigation of cluster emission in transfer reactions is of significance in deep understanding of the synthesis of superheavy nuclei, shell evolution, new isotope production, etc.PurposeThe dynamics of pre-equilibrium cluster in a few of nucleon transfer reaction has been described by theoretical model, such as exciton model, cluster model. However, the cluster emission in massive transfer is very complicated because of the emission mechanism associated with the structure properties and also the dynamical process.MethodsIn this work, the pre-equilibrium cluster emission in massive transfer reaction has been systematically investigated within the dinuclear system model. The model has been successfully used for describing the massive fusion reaction and multi-nucleon transfer dynamics. The nucleon exchange and energy dissipation take place once the dinuclear system is formed. The nucleon transfer between the binary fragments is governed by the single-particle Hamiltonian and proceeds around the Fermi surface formed by the dinuclear system. The master equation is used for the nucleon transfer dynamics and the relative motion energy dissipation is taken into account. The dynamics of neutron, proton, deuteron, triton, 3He, 4He, 6,7Li and 8,9Be in collisions of 12C+209Bi, 40Ca+208Pb and 48Ca+238U near Coulomb barrier energies is analyzed, i.e., temporal evolution of production rate, kinetic energy spectra and angular distribution.ResultsIt is found that the emission probability of 4He is the same magnitude of proton emission and several orders larger than the one of 3He. Both the nuclear structure and dynamical effects influence the pre-equilibrium cluster production.ConclusionsThe pre-equilibrium clusters are emitted from the 'projectile-like' and 'target-like' fragments and the angular distributions manifest the similar trends. The kinetic energy spectra of clusters are shown as the Boltzmann distribution. The method is also extended to the cluster emission in weakly bound nuclei induced reactions by considering the preformation factor for the cluster construction.
Background131I-BEV-PTX-SPIONs is a type of nanoparticle used in cancer therapy. It is composed of four components: a radioactive isotope of iodine (131I), a chemotherapy drug called paclitaxel (PTX), a type of nanoparticle called superparamagnetic iron oxide nanoparticles (SPIONs), and a molecule called bevacizumab (BEV) which is an antibody that targets and blocks the growth of blood vessels that supply tumors.PurposeThis study aims to investigate the preparation and biological distribution of 131I-BEV-PTX-SPIONs.MethodsFirst of all, 131I-BEV-PTX-SPIONs were prepared, synthetized and identified. The transmission electron microscope (TEM) were employed to observe the particle characteristics. Then, 30 tumor-burdened nude mice were divided into the single targeting group and the dual targeting group for evaluation of 131I-BEV-PTX-SPIONs distribution in these nude mice, each group was divided into five sub-groups based on time points of 2 h, 6 h, 12 h, 24 h and 48 h, 3 in each sub-group. Finally, 131I-BEV-PTX-SPIONs were injected into the caudal vein of these mice, and experiments of biological distribution in vivo and SPECT imaging were carried out, and results were analyzed using GraphPad Prism 8.3 software.ResultsThe nanospheres in prepared 131I-BEV-PTX-SPIONs are obtained in good mono dispersion with a diameter of approximately 220 nm by TEM observation. 131I-BEV-PTX-SPIONs obtained in a high radiolabeling yield is about 81.4% with the radiochemical purity of over 99% and good stability shown in the 0.2 mol·L-1 PB buffer. And it could attain sustained PTX release in vitro. Comparing with the cellular uptake of 131I, a higher uptake and sustained PTX release in vitro are shown for 131I-BEV-PTX-SPIONs. Biodistribution experimental results show: After the injection of 131I-BEV-PTX-SPIONs, with the extension of time, the radiation count of the tumor is relatively higher, at 12 h reaching the peak. And the T/NT ratio increased gradually, and it reaches 7.8±0.50 at 48 h. The counts and the ratios at 6 h, 12 h, 24 h and 48 h are notably higher in the dual targeting group than the single targeting group (P131I-BEV-PTX-SPIONs, the tumor site has a radioactive build-up. With the extension of time, the accumulation of radioactivity increased and remained stable, and the T/NT ratio rises steadily.ConclusionsThese results demonstrated the potential of 131I-BEV-PTX-SPIONs in the diagnosis and treatment of lung cancer, and it was worthy of further study.
BackgroundMolten salt systems have been extensively applied in the generation of nuclear and solar energy owing to their excellent heat transfer and storage performance. Therefore, it is essential to explore their physical and chemical properties, which are largely determined by their composition and ionic structure. In this regard, high-temperature (HT) nuclear magnetic resonance (NMR) has been demonstrated as an effective solution for qualitative analysis. Due to the existence of vent holes on the top of the commercialized standard NMR sample cell, it is not suitable for the study of some volatile, toxic or radioactive molten salt systems.PurposeThis study aims to implement ceramic NMR sample cells that are suitable for different molten salt systems.MethodsFirstly, a novel sealed sample cell that meets the requirements of molten salt systems was designed and produced by using an inner tube comprising AlN, BN, and Al2O3 ceramic materials, and an outer tube composed of ZrO2 ceramic materials. Then, with KBr as the standard sample, temperature calibration for this sample cell was conducted on the basis of 79Br NMR method. Finally, LiCl-KCl two-component molten salt (59.2 mol% LiCl-40.8 mol% KCl, eutectic melting point 353 ℃) was selected for HT-NMR experiment to verify the accuracy of temperature calibration, and check the performance of the HT-NMR method.ResultsExperimental results show that the sample cells are applicable in molten salt systems at a maximum temperature of 700 ℃, which meets the detection requirements of most molten salt systems. Additionally, the measurement results of the 79Br chemical shift of the KBr samples and captured HT 35Cl NMR spectra of the LiCl-KCl molten salt verify the reliability of the sample cell.ConclusionsBased on the results, the HT-NMR (High Temperature NMR) sample cells proposed in this study can be widely applied in various fields when the molten salt system requirements are met.
BackgroundElliptical orbiting satellites passing through the inner radiation belt are exposed to high-energy and high-flux protons and electrons. Therefore, electronic devices of satellites need to resist ultra-high cumulative radiation doses.PurposeThis study aims to propose a composite material structure for shielding space protons and electrons, instead of the traditional aluminum structure.MethodsThe interaction of elliptical orbital protons and electrons with four shielding materials (polyethylene/polypropylene, tantalum and aluminum) was simulated by the MULASSIS (Multi-Layered Shielding Simulation Software). The radiation particle energy spectrum calculated by SPENVIS software was used as the input of MULASSIS particle energy spectrum. The changes of total dose and displacement dose after shielding with areal density of the four shielding materials were compared and analyzed. Finally, the most suitable composite shielding structure was selected by considering the proton and electron shielding effects and mechanical properties of the four materials.ResultsThe results show that under same areal density, the order of the shield effectiveness from large to small, of four different materials on orbital proton and electron is polypropylene, polyethylene, aluminum and tantalum, among which polypropylene and polyethylene have almost the same shielding effect. The polyethylene-aluminum composite shielding structure is selected for construction design. The shielding targets of total dose and displacement dose to ensure the reliable operation of elliptical satellites are 50 krad(Si) and 2×1010 p?cm-2 (equivalent to 10 MeV protons) respectively.ConclusionsCompared with the single aluminum shield, at least 27.8% shielding mass is saved by using the polyethylene-aluminum composite protective structure in the above ratio.
The searching for potential quantum chromodynamics (QCD) phase transition signals is a fundamental goal of on-going experiments on heavy-ion collisions, which is critical to understanding the properties of strongly interacting matter under extreme conditions, the inner structure of compact stars, gravitational waves emitted from neutron star mergers, etc. In particular, the beam energy scan program carried out at the Relativistic Heavy-Ion Collider (RHIC) provides a unique tool that enables studies into the QCD phase diagram and the conjectured QCD critical point. Besides the event-by-event fluctuation of conserved charges, which has been widely accepted as a useful study of the QCD critical point, the production of light nuclei can serve as a sensitive observable to the QCD phase transitions in high-energy heavy-ion collisions. The density fluctuation and correlation among nucleons are automatically encoded in the production of light nuclei in heavy-ion collisions. This study aims to demonstrate how to probe QCD phase transition with light nuclei production in heavy-ion collisions. The progress of studies in this area over the last few years is reviewed. The nucleon coalescence model provides a suitable tool for the study of the effects of density fluctuation/correlation on light nuclei production. A transport model based on the Nambu-Jona-Lasinio (NJL) model is developed to simulate the occurrence of the first-order chiral phase transition in heavy-ion collisions. Within the coalescence model for light nuclei production, the yield ratio NtNp/Nd2 of protons (p), deuterons(d), and tritons (t) is shown to be sensitive to the nucleon density fluctuation and correlation and can function as a good probe to the non-smooth QCD phase transition. The production of light nuclei in heavy-ion collisions encodes the information about baryon density fluctuations and correlations, and enhancements of the yield ratioNtNp/Nd2 could serve as an indicator for the occurrence of a first-order or second-order QCD phase transition.
BackgroundInert matrix fuel (IMF) can efficiently convert plutonium and long-lived minor actinides used for preventing the proliferation of nuclear weapons and improving spent fuel disposal, hence has been becoming a hot research topic in recent years. The sol-gel method has the advantage of uniform elemental distribution of the products and the wet operation process is less likely to produce radioactive dust, therefore, it has been used to prepare zirconium-based IMF in the research.PurposeThis study aims to prepare a colloidal solution with good dispersive properties and to obtain IMF microspheres with good sphericity, uniform size, and homogeneous elemental distribution.MethodsFirst of all, ThxZr1-xO2 inert matrix fuel was prepared by an external gelation process, and the sol-gel viscosity was used as the main gelation index. Then, the variation tendency of sol viscosity with c(NH4+)/c(NO3-) was investigated for different metal ions concentrations and different temperatures. Finally, the statistical distributions of colloidal particle sizes were obtained for different metal ions and reaction temperatures by laser particle sizing tests, and the X-ray diffraction (XRD) was used to study the structure of IMF after heat treatment at different temperatures.ResultsThe results showed that the complex gelation parameters and properties can be categorized and quantified using gelation field diagrams. In addition, ThxZr1-xO2 IMF kernels with uniform element distribution, good sphericity, and integral appearance were obtained by optimizing the process parameters. Zirconia showed low solubility behavior in the thorium-oxide system, leading to the generation of a biphasic structure.ConclusionsThe results of this study indicate that zirconium-based spherical IMF microspheres with good performance can be prepared by external gelation method.
BackgroundThe miniature fission ionization chamber is a widely used neutron detector for the in-core neutron flux monitoring of a nuclear reactor. Typically, the in-core neutron flux rate measurement system of a domestic CPR1000 nuclear power unit adopts a mobile miniature fission ionization chamber as the neutron probe to measure the neutron flux of the reactor and provide an in-core neutron flux distribution map during the operation. Therefore, it is an important piece of safety and control equipment for nuclear power plants.PurposeThis study aims to develope a mobile miniature fission ionization chamber neutron detector according to the service conditions and technical requirements of current foreign products.MethodsThe nuclear properties of self-made fission ionization chamber neutron detector was developed strictly following the national standard GB/T 7164-2022 and the industry standard NB/T 20215-2013. The gamma sensitivity was tested and compared with a reference commercial fission detector using a 60Co gamma source. The thermal neutron detection characteristic, including the length and slope of plateau, the thermal neutron sensitivity and linearity were tested in one test channel of the China Mianyang Research Reactor (CMRR) with neutron flux from 1×109 n?cm-2?s-1 to 4×1013 n?cm-2?s-1.Results & ConclusionsThe test results indicate that "domestic substitution" of this in-core safety product can be achieved, and the nuclear characteristics of self-developed prototypes are comparable to those of foreign products.
PurposeThis study aims to improve the low accuracy of the aerosol model in the ISAA code by developing high-precision natural deposition model of aerosol in the containment.MethodsFirstly, the aerosol dynamic shape factor was introduced to correct the natural deposition rate of non-spherical aerosols. Then, the gravity, Brownian diffusion, thermophoresis and diffusiophoresis deposition models were improved respectively. Finally, AHMED (Aerosol and Heat Transfer Measurement Device), ABCOVE (Aerosol Behavior Code Validation and Evaluation) and LACE (Light Water Reactor Aerosoal Containment Experiments) experiments were employed to validate and evaluate the improved ISAA code.ResultsCalculation results show that the improved model is applicable to more accurate simulation of the peak aerosol mass and responding to the influence of the containment pressure and temperature on the natural deposition rate of aerosols, and the calculation accuracy of the residual mass of aerosols in the containment is significantly improved simultaneously.ConclusionsThe performance of improved ISAA with high-precision aerosol models of this study meets the requirements for analyzing the natural deposition behavior of aerosol in containment of advanced PWRs in severe accident. In the future, further optimization will be made to address the problems found in the current aerosol model.BackgroudNuclear safety is the lifeline for the development and application of nuclear energy. In severe accidents of pressurized water reactor (PWR), aerosols, as the main carrier of fission products, are suspended in the containment vessel, posing a potential threat of radioactive contamination caused by leakage into the environment. The gas-phase aerosols suspended in the containment will settle to the wall or sump water through the natural deposition mechanism, thereby reducing atmospheric radioactivity.
BackgroundSerial X-ray crystallography has developed rapidly due to its advantages of data collection at room temperature, low radiation damage and time resolution. To solve protein structures by using the serial X-ray crystallography, a large amount of produced diffraction data needs to be screened for finding the effective diffraction patterns. The use of convolutional neural networks (CNN) can not only automate the data screening process, but also improve the accuracy of data classification comparing with the traditional "point finding method".PurposeThis study aims to explore five types of popular convolutional neural networks, i.e., AlexNet, GoogleNet, MobileNets, Vgg16, ResNet, for screening crystallographic diffraction patterns, and compare the accuracy and efficiency of them to build up a fast and accurate convolutional neural network tool for screening the diffraction patterns of different protein crystal samples.MethodsFirstly, the primitive data for model training extracted from the coherent X-ray image database, collected by Linac Coherent Light Source (LCLS) and Spring-8 Angstrom Compact free electron laser (SACLA), were pre-processed by gray level equalization and data enhancement. The deep learning models were trained by iteration of the preprocessed data. Then, the selected convolutional neural network through the comparison of accuracy and efficiency was used to process further the experimental data of protein crystals diffractions.ResultsThe results show that MobileNets not only has the accuracy similar to large networks such as ResNet, GoogleNet-Inception, but also runs faster.ConclusionsMobileNets provides an effective and convenient screening tool for serial X-ray crystallography experimental data.
BackgroundLiquid molten salt reactor has many features such as high economy, safety and on-line fuel processing. The emergency draining salt passive residual heat removal system (EDS-PRHRS) is a unique residual heat removal system design for liquid fuel molten salt reactor, in which safely export residual heat of the molten salt in the salt draining tank is the first requirement for EDS-PRHRS design.PurposeThis study aims to analyze the transient characteristics of EDS-PRHRS salt discharge tank during operation by simulation.MethodsFirstly, the accident analysis of the passive residual heat removal system was carried out. The peak temperature of the molten salt was mainly found in the full heat discharge phase of the salt discharge tank. Then, a computational model of the molten salt coupled to the heat exchanger element was established for this stage of the discharge tank and numerical simulations were carried out by using computational fluid dynamics (CFD) analysis software Fluent. The Mixture model was used to simulate the boiling heat exchange of water in the heat exchanger element. Finally, different parameter sensitivity analysis scenarios were designed to investigate the effect on the transient.ResultsThe analysis results show that the heat exchange power of the heat exchange element gradually decreases with time, and the temperatures of the outer wall and the hot spot of molten salt have a peak with time.ConclusionsBy increasing the axial height of the thimble and enhancing the emissivity of the air gap layer, the temperature peak can be significantly reduced, and the peak value can be slightly reduced by delaying the salt discharge time. In addition, the triangular arrangement of can delay the local solidification time. The study results can provide some reference for EDS-PRHRS design.
BackgroundLoss of Coolant Accidents (LOCAs) is a crucial research topic for nuclear reactor safety analysis, and understanding the thermal–hydraulic behavior of the rod bundle channels during the reflooding stage of a LOCA is essential.PurposeThis study aims to develop theoretical models of the reflooding stage in addition to providing benchmark data for evaluating the safety analysis code for LOCAs in a reactor and for the design of the residual heat removal system.MethodsA series of bottom reflooding tests were conducted on a 5×5 rod bundle in the film boiling test facility at the nuclear safety and operation laboratory (NUSOL) of Xi'an Jiaotong University using uniformly heated rods. The experimental results were analyzed in detail, and the surface parameters of the heated rod bundle were obtained by solving a one-dimensional transient inverse heat conduction problem. The effects of different experimental conditions on the velocity of the quench front propagation were investigated. Furthermore, the experimental results were compared and calculated using the thermal safety analysis code, and the problems with the thermal safety analysis code RELAP5 reflooding simulation are summarized.ResultsOur results indicate that a high inlet flow rate, high inlet subcooling degree, and low power density are favorable for the propagation of the cold front during the reflooding process. Additionally, the root mean square (RMS) error of the simulated quench time and peak cladding temperature (PCT) are 40.994 s and 61.465 K, respectively. However, the simulation results have a relatively large error compared with the experimental results in the post-critical heat flux (CHF) heat transfer stage, primarily owing to the issues with the boiling mode judgment and membrane boiling heat transfer model.ConclusionsThe experimental data of this study can serve as new verification data for flow and heat transfer prediction models during the reflooding process; it can also be used to evaluate and optimize the thermal-hydraulic safety analysis code. Loss of Coolant Accidents (LOCAs) is a crucial research topic for nuclear reactor safety analysis, and understanding the thermal-hydraulic behavior of the rod bundle channels during the reflooding stage of a LOCA is essential.
BackgroundThe recoil release caused by the collision of a neutron with a target nucleus has a significant impact on the analysis of activated corrosion product sources in a reactor. In water cooled reactors, a recoil release in the irradiated area can cause the activation corrosion products to leave the wall surface and enter the coolant, which then migrates to the non-irradiated area with the flow of coolant, thereby making the non-irradiated equipment also radioactive.PurposeThis study aims to analyze the influence of recoil release on the source term of activated corrosion product in reactor.MethodsBased on the investigation of the mode of action of recoil release in a reactor, a calculation model and a program module for recoil release was established and integrated into the CATE program. Then, the effects of recoil release on the concentrations of activation corrosion products in the nuclear reactor were analyzed by using two approaches, one involved specifying a recoil release probability, while the other involved dynamically calculating the recoil release probability. Finally, values of the main activated corrosion products nuclides 58Co and 60Co in the core and steam generator before and after considering recoil release were calculated, and the impact of recoil release on the activation corrosion products and its implications for the actual operation of the reactor were explored.ResultsThe calculation results indicate that the recoil release probability decreases from 45% at the beginning of the simulation to 0.3% at the end of the simulation. However, the variation pattern of the activity ratio of 58Co and 60Co in the core and steam generator remains the same as that without recoil release. The activity ratio is 91% and 203% respectively, compared to the case without recoil release.ConclusionsThe total probability of recoil release is related to the thickness of the corrosion product layer and gradually decreases with the operating time of the reactor.
BackgroundTo measure the beam positions of High Energy Photon Source (HEPS), different types of beam position monitors (BPMs) have been developed. The position sensitivity coefficient is an important parameter of BPMs by which the position of the beam can be calculated.PurposeThis study aims to establish a method for calculating the position sensitivity coefficient of BPMs.MethodsThe position sensitivity coefficients of various types of BPMs, such as round, elliptical, and octagonal pipes, were determined by using the boundary element method (BEM). The azimuth button angles in the elliptical BPM of the HEPS booster and the button distances in an octagonal BPM on the Beijing Electron Positron Collider II (BEPCII) storage ring were derivated by the application of BEM. Furthermore, the position sensitivity mappings of the BPMs was calculated.ResultsThe difference in sensitivity results of the round BPM calculated by the BEM and the analytical value is approximately 1%. The error between the calculated and experimental measurement results of the position sensitivity coefficients of the elliptical and octagonal sections is approximately 2%.ConclusionsThe BEM is a reliable method for calculating the position sensitivity coefficient of BPMs, which can be used in BPM design.
BackgroundEthylene is an important raw material in petrochemical industry. Semi-hydrogenation of acetylene in an ethylene is an industrially important process. Conventional supported monometallic Pd catalysts offer high acetylene conversion, but they suffer from very low selectivity to ethylene due to over-hydrogenation.PurposeThis study aims to prepare a catalyst with high acetylene conversion and simultaneous selectivity to ethylene, surpassing conventional Pd catalysts, and explore the structure activity relationship of palladium-bismuth catalyst in acetylene hydrogenation.MethodsFirstly, PdBi/SiO2 catalyst was synthesized via a deposition-precipitation method for industrial hydrogenation of acetylene to ethylene. Then, comparison of catalytic activity and selectivity with traditional catalysts in the semi hydrogenation reaction of acetylene was conducted. Finally, the X-ray Absorption Fine Structure (XAFS), High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM), and X-ray Energy Dispersive Spectroscopy (EDS) were employed to explore the reaction mechanism.ResultsCompared with the Pd catalyst, PdBi/SiO2 catalyst exhibits increased reactivity at a lower temperature, with 100% acetylene conversion and 90% selectivity.ConclusionsThe Pd-Bi alloys structure is confirmed to effectively inhibit the formation of PdHx, weaken the cracking rate of hydrogen and the adsorption of ethylene on palladium surface, and inhibit the excessive hydrogenation of ethylene to produce by-product ethane. The simple synthesis PdBi structure provides new ideas and insights for industrial catalysts.
Exploring the quantum chromodynamics (QCD) phase diagram at finite bayron density regime through the beam energy scan (BES) program at the relativistic heavy-ion collider (RHIC) is one of the key frontiers in high energy nuclear physics. The high precision data anticipated from the second phase of the BES program would potentially enable the discovery of the conjectured QCD critical point, a landmark point on the phase diagram. In this paper, the progress made by the beam energy scan theory (BEST) collaboration, which was formed with the goal of providing a theoretical framework for analyzing data from BESII, is reviewed. In addition, the challenge of investigating the QCD phase diagram with future facilities is discussed.
BackgroundThe numerical results from a neutron source, as the important input parameter for the transport calculation, directly affect the accuracy of shielding calculations for reactor. The apparent differences between core sources are related to their geometric model, burnup, and power distribution.PurposeThis study aims to improve the calculation accuracy of the core neutron source for nuclear reactor shielding.MethodsFirstly, the geometric weight of each component in the core was generated by analyzing the characteristics of the radial source distribution on the basis of neutron importance, and the fine source mesh calculation was conducted for the peripheral components with high geometric weight and the region with a large power gradient. Then, a layered approach for different axial height positions was employed to reduce the influence of the axial power peak factor to achieve stable transport calculation results, and the source and geometry meshes were mapped according to the volume weight method to ensure the conservation of total source. Finally, the NUREG/CR-6115 core as a benchmark model was used for numerical verification.ResultsNumerical verification results indicate that, compared with the average source calculation, the multi-weight source mesh mapping algorithm reduces the root mean square of the relative error in the fast neutron fluence by 18.46% between the transport calculation results and the reference value.ConclusionsThe multi-weight source mesh mapping algorithm can be employed to obtain an accurate source distribution, improve the accuracy of the shielding calculation, and satisfy the requirements of engineering applications.
BackgroundThe gas-cooled fast reactor (GFR) has great advantages of finance and sustainability which combines the features of high temperature gas-cooled reactor and fast reactor. However, safety issue has become the main challenge in the development of GFR due to the high temperature and high neutron flux in the GFR core. Coated particle fuel (CPF) has been widely used in high temperature reactor (HTR) due to the excellent high temperature tolerance.PurposeIn order to strengthen the safety property in GFR, this paper puts forward a block-type fuel assembly (FA) model based on CPF. Based on the FA model, neutronics analysis and thermal hydraulics validation is carried out to verify the rationality of the design.MethodsMonte Carlo method is used in the calculation. Physical parameters including plutonium fraction in the U-Pu mixture fuel, diameter of fuel pins/coolant channels, the number of coolant channels, pitch-to-diameter ratio, thickness of cladding and thickness of assembly wrapper were selected and sensitivity analysis were conducted on the FA property to these parameters.ResultsAnalysis results show that among the above six parameters, plutonium fraction and pitch-to-diameter ration have the most obvious effect on the neutronic property and the number of the coolant channels mainly influences the power distribution of the GFR FA. Finally, temperature distribution of the FA is calculated using single channel model under a low coolant fraction and requirements in terms of thermal-hydraulic property are put forward for the FA parameters.ConclusionsThe block-type FA model put forward in this paper meets the design requirements well. The research conclusion of this paper provides reference for the future study on GFR nuclear design.
BackgroundThe magnitude of the thermal stress in the first wall system is one of the key factors affecting the safe operation of the fusion reactor.PurposeThis study aims to investigate the effect of a rough substrate on the thermal stress in the W/316L stainless steel first wall system.MethodThe finite-element analysis software Ansys Workbench was employ to analyze the distribution of thermal stree in a W/316L stainless steel first wall system with a rough substrate. Depth analysis was conducted on factors such as the temperature, coating thickness, and substrate thickness that affect the magnitude of thermal stress. Meanwhile, starting from the interface shear stress in the system, the influence of rough substrate on the bonding strength of coatings was simultaneously investigated.ResultsThe simulation results indicate that the thermal stress in the rough substrate system increases with the the increase of temperature and substrate thickness, but decreases with the increase of coating thickness. The maximum thermal stress and the adhesive strength between the coating and the substrate are raised by the introduction of the rough substrate.ConclusionsResults of this study can provide reference for the development of high-adhesive strength first wall coating systems.
BackgroundTritium can be released into the environment in a loss of vacuum (LOVA) scenario in a fusion reactor. The simulation of the atmospheric dispersion behaviour of tritium is one of the core components of the assessment of the radioactive consequences.PurposeThis study aims to analyse the behaviour of tritium dispersion in the atmosphere after a fusion reactor accident.MethodsBased on the Gauss model and the Pasquill stability classification method, an analytical model of tritium dispersion was developed for transient cases considering the effects of gravitational settling, smoke lifting, and wind speed, etc. The calculation of the model for dry settling at the ground boundary was improved by adding ground reflection coefficients to the Gauss model. Finally, the Canadian tritium release experiment and the tritium release accident at the Savannah River plant in the United States were used to verify the applicability of the model.ResultsVerification results show that the accuracy of the developed model is the same as that of UFOTRI and the HotSpot 3.0 code. For the LOVA scenario of International Thermonuclear Experimental Reactor (ITER), the atmospheric dispersion behaviour of tritium is obtained for multiple release heights, different wind velocities and tritium phased releases.ConclusionsThe phased release of tritium results in two highly radioactive regions along the downwind direction, and the increase in release height and wind speed will enhance the atmospheric diffusion behaviour of tritium and thus reduce the accumulation of radioactivity in the near field.
Recent progress in studies on quantum chromodynamics (QCD) phase transition and related critical phenomena within the functional renormalization group (fRG) approach were reviewed, including the nonperturbative critical exponents and baryon number fluctuations, which are pertinent to the critical end point (CEP) in the QCD phase diagram. The fRG is a nonperturbative continuum field approach, in which quantum thermal fluctuations are successively integrated with the evolution of the renormalization group (RG) scale. Different methods of finding solutions to the flow or fixed-point equations of a nonperturbative effective potential have been discussed, for example, the Taylor expansion, expansion of the spatial dimension ε=4-d, and the recently proposed direct solution of the global potential. Furthermore, the baryon number of fluctuations is relevant to the critical phenomena of the CEP. Both have been discussed, and one explores the underlying reasons for the observed non-monotonic dependence of the kurtosis of the net proton number of distributions on collision energy in experiments.
BackgroundThe electron beams produced by laser plasma acceleration have excellent quality for pulse lengths of the order of fs. Due to the existence of a strong laser field, there are difficulties in direct applications, and more applications need to transmit the electron beams to the application terminal. The energy spread leads to the generation of energy chirp of the electron beam in the transmission.PurposeThis study aims to explore the design of the beam optics to compress the pulse length and keep it on the fs scale.MethodsAn achromatic beamline consisting of bending magnets and quadrupole magnets was designed to compress the pulse length of electron beams. Critical parameters of an achromatic beamline were given by a derived formula. Transformation matrix was employed to investigate the differences of the pulse lengths in achromatic transmission and non-achromatic transmission. The pulse lengths of electron beams with different energies were scanned with different deflection angles (0.3 rad, 0.6 rad, 0.9 rad) and deflection radii (0.15 m, 0.25 m, 0.35 m) to study the influence of beamline parameters. Finally, the magnetic field gradients of the quadrupole lens were adjusted to realize the compression of electron beams with different energies in a beamline.ResultsComparing to non-achromatic transmission, the pulse lengths of electrons with the same energy and different initial divergence angles can be compressed effectively in the achromatic beamline. The larger the deflection angle or the deflection radius, the longer the pulse duration of the electron beam with higher energy (>25 MeV). By adjusting the magnetic field gradients of the quadrupole lens, the pulse lengths can be reduced from more than 100 fs to around 20 fs at higher energies.ConclusionsUsing a fixed-size achromatic beamline, combined with magnetic field strength adjustment, the pulse lengths of electron beams with different energies can be kept on the order of fs after transmission.
The RHIC-STAR (Relativistic Heavy Ion Collider-Solenoid Tracker at RHIC) experiments have measured the cumulants of net-proton (a proxy for net-baryon), net-charge, and net-kaon (proxy of net-strangeness) multiplicity distributions in Au+Au collisions at different centers of mass with energies ranging from 7.7 GeV to 200 GeV. Recent results have shown that the ratio of the fourth-order net-proton cumulant over the second-order one (κσ2) exhibits a nonmonotonic energy dependence. In relativistic heavy-ion collision experiments, only information about the final state particles can be measured. Therefore, we investigated the fluctuations of the conserved charges (baryon, electric charge, and strangeness) in Au+Au collisions using a multiphase transport (AMPT) model. This model can basically describe the results measured by the RHIC-STAR experiment. More importantly, the AMPT model is used to understand the key impacts of the dynamical evolution of relativistic heavy-ion collisions on fluctuations and correlation functions, including the creation and diffusion of conserved charges, hadronization, hadronic rescatterings, and weak decays. It was discovered that the correlation between positive and negative charges may originate from the string melting mechanism. Baryon (proton) correlation functions are consistent with the expectation of baryon number conservation. Net-strangeness (net-kaon) originates from pair production. We studied the correspondence between representative quantities and their conserved charges and found that their behaviors are qualitatively consistent yet quantitatively different. Although the physics of quantum chromodynamics (QCD) critical fluctuations is not included in the AMPT model, our results are expected to provide a baseline for the search of possible critical behavior at the QCD critical end point in relativistic heavy-ion collisions. We incorporated critical density fluctuations into the model and found that they play a role.
BackgroundCompared with the traditional pressurized water reactor (PWR), the core design of large advanced PWR CAP1400 has significant changes, such as the increase in the number of fuel assemblies, the increase in reactor power, the increase in the average temperature of core coolant, etc. These changes have an important impact on the results of rod ejection accident, and then affect the safety of reactor.PurposeThis study aims to verify the safety of large advanced PWR under rod ejection accident condition and the influence of key input parameters on accident analysis results.MethodsBased on the neutron dynamics software TWINKLE and fuel performance analysis program FACTRAN, the typical four types of operating conditions, including the beginning of life the hot full power and the hot zero power, the end of life the hot full power and the hot zero power, were selected to carry out the simulation calculation of the control rod ejection accident analysis for large advanced PWR, and the sensitivity analysis of key input parameters of rod ejection accident conditions was performed by using the direct numerical perturbation method.Results & ConclusionsSimulation results show that the power peak is the most sensitive to the worth of rod ejection, but less sensitive to shutdown reactivity. The consequences of the control rod ejection accident designed for CAP1400 can meet the requirements of acceptance criteria and the reactor is in the safe and controllable state.
BackgroundA CdZnTe (CZT) detector is a compound semiconductor detector with a high atomic number and high detection efficiency, it can be used at room temperatures to detect short wavelength radiation such as X-ray and γ ray.PurposeThis study aims to investigate the factors affecting the energy spectrum characteristics of the CZT detector.MethodsThe geometric model of the detector was established by using Geant4 software, and the intrinsic detection efficiency and absorption rate of CZT crystal in the planar size of 10 cm×10 cm were simulated. The charge collection efficiency of the crystal was calculated using the Hecht formula and the γ-ray energy spectrum was obtained by collecting the deposition energy and position information in the crystal. By analyzing the physical properties of crystals, the impact of physical properties on detector performance was explored.ResultsSimulation results show that incomplete charge collection significantly influences the spectral performance of the detector. When the γ ray energy is less than 50 keV, the spectrum is not affected by hole wake whilst the influence of hole wake is more obvious when the energy is between 50 keV and 100 keV. The energy spectrum is gradually aggravated by the influence of hole wake when the γ ray energy is above 100 keV.ConclusionsThis effect of hole wake for CZT detector can be reduced by increasing the bias voltage, but the increased bias voltage shifts the spectrum's peak, and the shift amount is determined by the maximum charge collection efficiency of the crystal.
BackgroundLaser-induced breakdown spectroscopy (LIBS) is a new technology for testing and analyzing the composition and content of elements in materials.PurposeThis study aim to determine the content and distribution of hydrogen isotopes in hydrogen storage materials by using LIBS quantitative analysis technology.MethodsThrough independent design, construction and integration, a LIBS system was established for in-situ measurement of hydrogen isotopes in a vacuum chamber. Titanium sheets were used to prepare titanium-hydrogen samples with different concentrations of hydrogen and deuterium atoms to investigate the content and distribution of hydrogen isotopes in titanium using LIBS technology. The plasma parameters were calculated from the emission spectrum of titanium, and quantitative analysis on the content of hydrogen and deuterium atoms in the titanium sheet was carried out. Finally, the internal calibration method was employed to draw the calibration curves of hydrogen and deuterium, respectively, so as to determine the accuracy of this technology.ResultsThe plasma temperature calculated from the Boltzmann diagram is (16 000±1 000) K. Test results show that the linearity of calibration curves is increased by 4% by integrated intensity calibration, and the error of hydrogen isotope quantitative analysis is reduced by 2.8%. Based on the fitted curve, the concentration is consistent with the concentration determined by the pressure drop method during the sample preparation process. The average measurement error of hydrogen and deuterium is 3.19% and 1.94% respectively.ConclusionsProvided that the plasma state conforms to the local thermal equilibrium and the plasma temperature of different elements is consistent, LIBS quantitative analysis can accurately measure the contents of hydrogen isotopes by using the internal standard method. Signal enhancement effect and data accuracy of LIBS meet the requirements of quantitative analysis.
BackgroundThe nuclear transmutation is the only way to reduce the radioactive hazard of the high level long-lived radioactive minor actinides (MA). The majority of commercial reactors in operation in the world are pressurized water reactor (PWRs), hence the transmutation efficiency of minor actinide nuclide (MA) in PWR are crucial problem in the area of the nuclear waste disposal.PurposeThis study aims to improve the transmutation efficiency of MA and flatten the core power distribution by using MA nuclide for PWR.MethodsFirst of all, the HPR1000 (Hualong #1) model 177 core structure was taken as reference PWR, thermal-fast neutron convertible material 6LiD was introduced to design coated axially non-uniform MA/6LiD transmutation rods which structurally applicable to the PWR. The internal component of the transmutation rods was UO2, and the external component was the transmutation coating material composed of MA and 6LiD nuclides. The layout of the coating material on the transmutation rods was axially three, five and seven segments structure, and the coating thickness gradually decreased from the middle to both ends. Then, the Monte Carlo program RMC2.0 developed by the Reactor Engineering Calculation and Analysis Laboratory of Tsinghua University was employed to establish the core and calculate the effect of transmutation coating material composition on core keff.ResultsThe results show the best transmutation effect up to 23.25% is realized when the mass ratio of 6LiD to MA in the transmutation coating material is 2∶8. Among the coated axially nonuniform transmutation rods, the seven-segment transmutation rod has the best transmutation effect, and the transmutation rate is 25.43%. The best fission effect of three-segment transmutation rod has the fission rate of 4.48% for MA nuclide. At the same time, the transmutation rod with axial non-uniform structure can reduce the axial power peak factor of the core from 1.778 to 1.375.ConclusionsCompared with axially uniform rods, these axially non-uniform MA/6LiD transmutation rods have good transmutation efficiency, especially the fission rate, and good performance on flatten axial power distribution is achieved, simutanously.
BackgroundThe SXFEL (Soft X-ray Free-Electron Laser facility) is the first X-ray coherent light source in China. To monitor the beam loss in its undulator beamline, a quartz fiber beam loss monitoring system based on the Cherenkov radiation principle was designed and installed. The quartz fiber is insensitive to high-energy gamma rays, making it suitable for a strong SXFEL radiation field environment.PurposeThis study aims to apply quartz fiber beam loss monitoring (BLM) system to the undulator beamline of SXFEL, and carry out position calibration experiment to measure the fiber attenuation coefficient, and performance of the system in the beam tuning period.MethodsFirst, two pure quartz composition fibers with 400 μm inner diameter of core and high concentration of hydroxide ions were employed. The beam loss signal was generated by falling YAG (Ce:Y3Al5O12, target film) of the beam profile monitor at a fixed position and adjusting the trigger time delay to make the position of the beam loss signal the same as that of the beam profile monitor for position calibration experiment. Second, to measure the fiber attenuation coefficient, the coefficient was fitted by bringing the peak value of the beam loss signal generated by the falling YAG at different positions of the SBP (Shanghai-XFEL Beamline Project) beamline and the corresponding fiber position into the signal attenuation formula.ResultsThe fiber BLM can accurately reflect the position of the beam loss with upstream position resolution of approximate 0.2 m in the experiment test, as well as in the period of beam tuning. The refractive index of quazrtz firber core is approximately 1.5, hence the relationship between the beam loss position and signal arrival to upstream PMT time interval is 0.12 m·ns-1. The measured fiber attenuation coefficient is around 74 dB·km-1, which is consistent with the calculation result and similar to the measurement result of SPring-8 Angstrom Compact Free Electron Laser (SACLA) using the same type of optical fiber.ConclusionsThe fiber beam loss monitoring system has a good position resolution and has the potential to meet the requirements of SXFEL beam tuning.
Understanding the phase structures of strong interaction matter is an active frontier in nuclear physics research currently, and it will provide crucial insights into heavy-ion collision experiments as well as neutron star observations. Most studies in this area focus on the influence of extremely high temperatures and baryon densities on matter properties, especially pertaining to phase transitions such as the chiral symmetry breaking and color superconductivity. Recent experimental and theoretical studies reported that in non-central heavy-ion collisions, systems carry a large initial angular momentum that becomes very strong vorticity fields in the bulk fluid. This has thus introduced several new questions regarding the properties of strong interaction matter under vorticity fields, and have led to many novel results. Thermal field theory calculations based on rotating frame and mean-field approximation have been developed to study various phase transitions under rotation, such as chiral symmetry breaking, color superconductivity and superfluidity at high isospin asymmetry. The results have demonstrated important impacts of vorticity fields on the phase boundaries of these transitions, and have also revealed nontrivial new phase structures of strong interaction matter under rotation. A new dimension of the usual QCD phase diagram has been unveiled. The study of rotation-induced phase transition extends phase transition research to a broader space. There remain more unexplored issues that merit further study.
In high-energy heavy ion collisions, quarks and gluons are released from the colliding nucleus to form a new state of nuclear matter called deconfined quark gluon plasma (QGP). To study the transition from normal nuclear matter or hadron resonance gas to QGP, non-perturbative quantum chromodynamics (QCD) must be solved on supercomputers using the lattice numerical method (lattice Quantum Chromodynamics, lattice QCD). However, lattice QCD only works for zero and small baryon chemical potential regions that can be described by the Taylor expansion and provides the nuclear equation of state (EoS) and QCD transition in these regions. For large baryon chemical potential regions that cannot be described by the Taylor expansion, lattice QCD fails to provide the nuclear EoS and QCD transition owing to the famous sign problem. Machine learning helps to study the nuclear EoS and QCD phase transition. First, machine learning can determine the nuclear EoS and QCD transition using the momentum distribution of final state hadrons in heavy-ion collisions, with data from both heavy-ion collision experiments and relativistic hydrodynamic simulations. Second, it can contribute to the direct solution of the sign problem in lattice QCD. The present paper reviews the applications of machine learning to the study of the QCD phase transition in heavy-ion collisions. This study (1) introduces nuclear EoS and QCD transition as well as the difficulty of the lattice QCD method, (2) analyzes the nuclear EoS using Bayesian analysis, (3) identifies the nuclear EoS and QCD phase transition using different types of deep neural networks (e.g., convolutional neural network, point cloud network, and many-event averaging), (4) searches for critical self-similarity using a dynamical edge convolution-based graph neural network, (5) learns the quasi-particle mass using a physically informed network and auto-differentiation, (6) discards unphysical regions in the nuclear EoS with a critical endpoint using active learning, (7) discusses unsupervised learning for the nuclear liquid-gas phase transition, (8) determines the nuclear symmetry energy in heavy-ion collisions, (9) investigates Mach cones using deep learning assisted jet tomography, and (10) accelerates the sampling of lattice QCD configurations using a physically constrained neural network while solving the sign problem in lattice QCD using deep learning.
BackgroundNeutron radiography (NR) is an important nondestructive testing method. NR is particularly useful for detection of light materials in medium and large heavy samples. Especially, the fast neutrons can penetrate the heavy materials and reveal the structure of the light materials. Compared to accelerator neutron sources, the fission neutrons elicited from a reactor are stable and of high quality. The fission neutron imaging is a useful complementary testing technology, especially for industrial applications that require high throughput and large-scale testing.PurposeThis study aims to investigate the super field of view neutron imaging by fission neutrons elicited from research reactor.MethodsBased on theoretical analysis and Monte-Carlo simulation, one filter combination was employed to improve the proportion of fission neutrons in the thermal neutron beamline at China Mianyang Research Reactor (CMRR). A fission neutron imaging system was constructed by employing a large field fast neutron fluorescent screen, short focus distance lens, and scientific charge coupled device (CCD) camera. Finally, some samples were tested using fission neutron tomography.ResultsThe fission neutron flux reaches up to 3×105 cm-2·s-1 when the L/D ratio is about 260. The field of view of NR is up to 400 mm×400 mm with resolution was better than 0.5 mm. Using super field of view method, samples less than 600 mm can be tested with this new system.ConclusionsCombination of theoretical calculation and experimental methods, fission neutron imaging can be improved to overcome some of the limitations of traditional neutron radiography techniques, and meet the needs of large sample detection in the future.
The goal of relativistic heavy-ion collisions is to determine the phase boundary of quantum chromodynamics (QCD) phase transitions. Critically sensitive observables are suggested to be higher-order cumulants of conserved charges. The non-monotonous behavior of higher cumulants was observed at the relativistic heavy-ion collider (RHIC). However, it remains unclear whether these non-monotonous behaviors are critically related. We studied the influences of non-critical fluctuations, finite system size, and limited evolution time to determine if they cause non-monotonous behavior. First, we examined the minimum statistics required for measuring the fourth cumulant. The minimum statistic obtained using the centrality bin width correction (CBWC) method was 25 M. We suggest using a 0.1% centrality bin in the CBWC method instead of each Nch. With a 0.1 centrality bin width, 1 M statistics are sufficient. We then pointed out the statistical fluctuations from the limited number of final particles. By assuming the independent emission of each positive (or negative) charged particle, the statistical fluctuations of positive (or negative) charged particles were presented by a Poisson distribution, and the statistical fluctuations of net-charged particles were their evolution. The obtained statistical fluctuations for net protons, net electronic charges, and net baryons were consistent with those from the Hadron Resonance Gas model. In addition, the measured cumulants at RHIC/STAR are dominated by these Poisson-like statistical fluctuations. At the end of this section, we suggest the pooling method of mixed events and demonstrate that the sample of mixed events accurately presents the contributions of the background. Dynamic cumulants were defined as the cumulant of the original sample minus that of the mixed sample. Dynamical cumulants were shown to simultaneously reduce the influence of the statistical fluctuations, centrality bin width effects, and detector efficiency. Second, because the system is finite, the correlation length at the critical point is not developed to infinity in contrast to the system at thermal limits. Using a Monte Carlo simulation of the three-dimensional three-state Potts model, we demonstrated the fluctuations of the second- and fourth-order generalized susceptibilities near the temperatures of the external fields of the first-, second-, and crossover regions. Both the second- and fourth-order susceptibilities showed similar peak-like and oscillation-like fluctuations in the three regions. Therefore, non-monotonic fluctuations are associated with the second-order phase transition and the first-order phase and crossover in a finite-size system. The exponent of finite-size scaling (FSS) characterizes the order of transitions or crossover. To determine the parameters of the phase transition using the FSS, we studied the behavior of a fixed point in the FSS. To quantify the behavior of the fixed point, we define the width of the scaled observables of different sizes at a given temperature and scaling exponent ratio. The minimum width reveals the position of the fixed point in the plane of the temperature and scaling exponent ratio. The value of this ratio indicates the nature of the fixed point, which can be a critical, first-order phase transition line point, or crossover region point. To demonstrate the effectiveness of this method, we applied it to three typical samples produced by a three-dimensional three-state Potts model. The results show that the method is more precise and effective than conventional methods. Possible applications of the proposed method are also discussed. Finally, because of the limited evolution time, some processes in relativistic heavy-ion collisions may not reach thermal equilibrium. To estimate the influence of the nonequilibrium evolution, we used the three-dimensional Ising model with the Metropolis algorithm to study the evolution from nonequilibrium to equilibrium on the phase boundary. The order parameter exponentially approaches its equilibrium value, as suggested by the Langevin equation. The average relaxation time is defined. The relaxation time is well represented by the average relaxation time, which diverges as the zth power of the system size at a critical temperature, similar to the relaxation time in dynamical equations. During nonequilibrium evolution, the third and fourth cumulants of the order parameter could be positive or negative depending on the observation time, which is consistent with the calculations of dynamical models at the crossover side. The nonequilibrium evolution at the crossover side lasts briefly, and its influence is weaker than that at the first-order phase transition line. These qualitative features are instructive for experimentally determining the critical point and phase boundary in quantum chromodynamics.
One of the main goals of relativistic heavy-ion collision (HIC) is to search for the critical end point (CEP) of quantum chromodynamics (QCD), and distribution of the net-proton number from experimental measurements shows non-monotonic behavior, which indicates the existence of a CEP. The purpose of this work is to investigate the relationship between the net-proton number fluctuation and collision energy, and to explain the experimentally measured behavior. This study investigates the three-flavor Polyakov-loop Nambu-Jona-Lasinio (PNJL) model, which contains quark degrees from the NJL (Nambu-Jona-Lasinio) model and effective gluon contributions from Polyakov-loop, based on the equilibrium assumption and mean-field approximation. In addition, we study the phase diagram and C4/C2 of baryon number fluctuation as a function of collision energy along the freeze-out lines fitted from experimental data. With an appropriate form of freeze-out line, the collision energy decreases in the region of 7.7~200 GeV, and C4/C2 decreases slightly then increases, which is in agreement with the experimental data. Additionally, these results indicate that the equilibrium assumption is appropriate for the exploration of the system evolution after HIC, and the relationship between the freeze-out and phase transition lines is highly sensitive for observables.
BackgroundAccording to the requirements of unmanned underwater vehicles for high reliability, high power, and long-life power, the design scheme of the megawatt heat pipe nuclear reactor silent unmanned portable reactor (UPR-s) is proposed by Xi'an Jiaotong University.PurposeThis study aims to design the shielding scheme for UPR-s to ensure the radiation safety of the cabin.MethodsFirst of all, according to the UPS-s scheme applied to the underwater unmanned vehicle (UVV), the layout of the nuclear system and shielding was designed, and the source terms of the reactor core under both full power and shutdown status were calculated by using NECP-SARAX code. Then, initial shielding model was established with consideration of several alternative shielding materials. The deterministic neutron-photon shielding calculation code NECP-hydra was employed to analyze several shielding schemes: the initial model layout, composite shielding layout, and shadow shielding layout. Finally, the accumulated fast neutron fluence, photon dose and source intensity at the safety plane were analyzed, and a shielding optimization scheme meeting the requirements was proposed on the basis of the numerical analysis results.ResultsCalculation results of shielding optimization scheme show that the maximum accumulated fast neutron fluence and photon dose of the safety plane at full power are 9.48×1011 n·cm-2 and 7.29×105 rad, respectively. Under shutdown conditions, the maximum safe plane dose rate is 0.004 49 mSv·h-1, and the total weight of core plus shielding is 296.35 kg.ConclusionsThe key parameters of optimized shielding scheme, including the cumulative fast neutron fluence, photon dose, and total shielding weight, satisfy the given design requirements.
We review the current status of quantum chromodynamics (QCD) properties in strong magnetic fields from lattice QCD. After a general introduction, we briefly present the implementation of a background magnetic field onto a lattice and discuss the recent progress on QCD properties at zero temperature, QCD transition temperature and inverse magnetic catalysis, and QCD phase structure in strong magnetic fields. Finally, we summarize this study.
BackgroundHEPS (High Energy Photon Source) needs to control the beam orbit change within 10% of the cluster size within a certain frequency. In order to meet the beam orbit stability requirements in HEPS, it is necessary to establish a fast orbit feedback (FOFB) system.PurposeThis study aims to design and implement an effective feedback bandwidth of FOFB system that is greater than 500 Hz, and the delay of the whole system is less than 160 μs.MethodsBased on this requirement, a two-layer communication of loop centralized computing system network topology was designed and implemented for FOFB system of HEPS. And on this basis, the FPGA (field-programmable gate array) firmware algorithm of the signaling pathway of FOFB system was realized, including beam position acquisition, loop data transmission, FOFB algorithm, power control interface and the testing logic.ResultsThe measurement and analysis results show that each module in the data transmission link of the FOFB system can be used normally, and the total delay time of the system is about 140.46 μs, which has reached the intended design target.ConclusionsThe FOFB design of this study lays a foundation for the future construction, optimization and debugging of FOFB system on HEPS storage ring with good flexibility and scalability, providing a feasible solution for the future establishment of fast orbit feedback system in other storage rings.
BackgroundThe comprehensive research facility for fusion technology magnet performance research platform (MPRP) is a large-scale experimental platform established for advanced superconducting magnet experiments. The retrieval speed of MPRP historical data is slow due to massive storage.PurposeThe study aims to develop a MPRP data archiving system (MPDAS) and increase its retrieval speed.MethodsFirst of all, the experimental physics and industrial control system (EPICS) data archiving plug-in was designed for MPDAS. Both MongoDB Sharding and Replica Set mechanism were employed to build a highly scalable data storage architecture. Then, the core ideas of three traditional cache replacement algorithms, LRU (least recently used), LFU (least frequently used) and FIFO (first in first out) were drawn by MPDAS to establish a data temperature model based on Newton's law of cooling. A multi-dimensional feature data partitioning algorithm was implemented to integrate access time, access frequency and storage order, hence the hot and cold historical data were identified to realize data tiered storage. Finally, the retrieval speed of MPDAS was improved by preferentially accessing Redis when querying historical data, and selecting different retrieval strategies based on hit results and data integrity.ResultsThe system test results show that the functional characteristics of MPDAS meet the design requirements. Compared with FIFO, LRU, and LFU, the Redis hit rate of the MPDAS when the hot database stores 1% of the historical data is increased by 38.05%, 26.91%, and 11.06% respectively.ConclusionsBy increasing the hit rate of hot data, the average response time of data retrieval can be directly reduced. The retrieval response speed of MPDAS is effectively improved by quantifying the heat of historical data and dividing the heat and cold.
BackgroundIn the neutron activation calculation, the inherent uncertainty of the input nuclear data will cause a certain impact on the calculation results. The uncertainty of the calculation results plays an important role in the source term analysis and radiation shielding design of nuclear facilities.PurposeThis study aims to analyze the uncertainty of neutron activation calculation based on direct derivative method.MethodsFirstly, the direct derivation method and Gear algorithm for uncertainty analysis were investigated, and the activation coefficient matrix and sensitivity coefficient matrix were constructed. Then, the Gear algorithm was employed to solve the activation equation and sensitivity equation simultaneously, and the sensitivity coefficient of nuclide inventory to nuclear data was obtained. The relative uncertainty of nuclide inventory was obtained by combining the relative uncertainty of nuclear data. Finally, This method was integrated into the neutron activation program ABURN, and typical examples was selected to test and verify its performance.ResultsThe calculation results of the nuclide inventory and its sensitivity coefficient and relative uncertainty by the ABURN program have little deviation from the analytical solution and the numerical solution of the European activation program FISPACT, most of the deviations do not exceed 0.2%, and the maximum deviation does not exceed 1%.ConclusionsVerification results show that the method and procedure developed in this paper have the ability to analyze the sensitivity and uncertainty of nuclide inventory with high precision, and can provide tools and data support for the radiation protection of nuclear facilities and the source term analysis.
BackgroundSynchrotron radiation experimental methods have unique advantages in studying the structure and physical properties of materials, but it is a challenge for many experimental methods to achieve synchrotron radiation in situ high temperature conditions, especially above 2 000 K. Laser heating methods can achieve rapid, micro-region extreme high temperature conditions, and have become an important tool for the study of high temperature physical properties.PurposeThis study aims to develop a portable laser heating device for Shanghai Synchrotron Radiation Facility (SSRF) in situ experiments in the field of extreme high temperature research, such as high entropy alloys, turbine blades, aviation materials, etc.MethodsA 100 W continuously tunable near-infrared fiber laser was used as the heating souce, the sample was heated up by laser through the focusing lens and generated thermal radiation. The radiation spectrum was collected through the spectral collection focusing lens and measured by spectrometers. The temperature gradient and temperature stability of the sample were fitted by the blackbody radiation method. Finally, the melting experiment of pure tungsten sheets in vacuum was conducted to verify its maximum heating temperature, and the temperature gradient and stability measurement of the device were calibrated with platinum samples.ResultsWe Experimental results show that melting point of about 3 695 K for tungsten sheets in vacuum is achieved using this device, and X-ray diffraction patterns of MoS2 and CTAB-MoS2 materials under 1 608 K in situ are obtained at the surface diffraction beamline station of SSRF.ConclusionsThe laser heating method developed expands the extreme experimental conditions in SSRF, and provides an important means to study high temperature physics for materials.
BackgroundUnder the condition of sub-cooled nucleate boiling (SNB), corrosion products in primary coolant of nuclear reactor will deposit on the outer surface of fuel cladding, which is commonly called fuel crud. Previous literature shown, zinc injection in primary coolant is an important method to inhibit the fuel crud deposition on the fuel cladding surface.PurposeThis study aims to investigate the influence of zinc concentration on the behavior of fuel crud deposition, and eventually provide guidance for zinc injection in primary coolant of nuclear power plant.MethodsThe fuel crud deposition tests of domestic zirconium alloy fuel cladding in different zinc concentrations were carried out by using a self-made fuel crud deposition device. Tubular crud deposition test specimen with built-in heating unit was designed and prepared for simulation study. After the tests, stereo microscope (SM) and scanning electron microscope (SEM) were employed to observe the macro and micro morphology of fuel crud whilst the composition of of fuel crud was observed and analyzed by the energy dispersive spectroscopy (EDS) with SEM, and X-ray photoelectron spectroscopy (XPS) was used to analyze the contents of Zn and B elements in the crud phase and inside the crud.ResultsObservation results show that the chimney-like crud formed on the fuel cladding surface becomes less obvious with increasing the zinc concentration in the coolant and the crud surface becomes flatter. Simutabeously, the crud thickness, the ratio of Ni/Fe and the boron precipitation mass within the crud are decreasing with increase of the zinc concentration. When the zinc concentration increases to 100 μg?L-1, new Zn-containing phases precipitate within the crud.ConclusionsWithin the zinc concentration of 0~100 μg?L-1, zinc injection in primary coolant of reactor can significantly inhibit the crud deposition on the fuel cladding surface.
The use of the relativistic heavy ion collision experiment has extended our insights into the diverse possibilities available to a truly strongly-interacting system. The main goal of this experiment is to describe the properties of the different phases of quantum chromodynamics (QCD) and to chart the QCD phase diagram on the T-mu plane. For the phase diagram, apart from the general phase boundary lines, some specific characteristics such as the possible critical endpoint (CEP), associated coexistence region, and strongly-coupling quark-gluon plasma (sQGP) have to be identified. Here, the CEP separates the first-order phase transition from the second-order transition (or crossover) when the case beyond the chiral limit is considered. However, convincing signals have not yet been obtained using the relativistic heavy ion collider (RHIC) experiment. Theoretically, strong interaction systems hold significant features: asymptotic freedom in the ultraviolet region, dynamical chiral symmetry breaking, and confinement in the infrared region. Such features can be uniformly displayed in the phase structure of the matter in the temperature T and chemical potential planes. Consequently, several investigations have been experimentally and theoretically performed. However, the strong coupling feature in the low-energy region prevents the use of perturbative calculation methods, which creates the need for the development of nonperturbative approaches. Additionally, lattice QCD simulations have been widely implemented; however, the "sign problem" delays the progress in the large chemical potential region. Therefore, the Dyson-Schwinger equation (DSE) equation method and functional renormalization group approach, which inherently include both dynamical chiral symmetry breaking (DCSB) and confinement, play an important role. The QCD DSE approach is a method based on the continuum quantum field theory. The new criteria were proposed based on the DSE and studied using the deconfinement and Chiral symmetry restoration phase transition of QCD. Currently, functional methods can be used to provide a reliable estimation of the CEP location. First, reliability is achieved using a thorough investigation of the truncation of the DSE, state of the art truncation is then performed causing a converging result between the different methods, and the predication of the lattice simulation at low chemical potential is confirmed. The results show a fast convergence of the truncation owing to the infrared fixed point of the QCD coupling, which allows the capturing of the QCD running behavior using a finite set of two- and three-point Green functions. The estimated location of the CEP based on the current computation is μB at 600~650 MeV and T at 100~110 MeV. The existing functional QCD methods are non-perturbative continuum methods that are capable of simultaneously describing both the DCSB and confinement. Although they are limited by the truncations, the use of functional QCD approaches has resulted in progress in the study of the QCD phase structure and thermal properties, where a complete phase diagram and related thermal properties have been obtained in a large chemical potential range, which can provide a reference for the exploration of the QCD features. Most of the theoretical studies using effective models or certain truncations have observed the existence of the CEP; however, the determination of its location is still a work in progress because it varies based on the computation. Moreover, searching for QCD phase transition signals, particularly the CEP, is the main goals of current and future experimental programs on the relativistic heavy ion collider.
BackgroundCore fuel salt emergency drain system designed for fuel salt drain and afterheat removal, provides a safe shutdown mode for a molten salt reactor (MSR). It has important significance to evaluate reliability of the system for the safety of MSRs.PurposeThis study aims to quantitatively analyze the failure probabilty of the system and identify the pivotal factors that affecting the system failures, and provide suggestions for optimization of the system in engineering application.MethodsFirst of all, the fault tree analysis was employed to model the reliability of the core fuel salt drain system of MSRE through RiskSpectrum software. Then, the minimum cut sets and importance analysis was adopted to identify the most important basic event in fault tree of the system. Finally, two optimization methods, i.e., reduce the use of welds in bayonet cooling thimbles, and use different types of valves to isolate cooling gas flow of freeze valve, were proposed.ResultsThe results show that failure probability of the system is 5.62×10-4, and the identified pivotal factors affecting the system failures are welds leakage failures of thimbles and common cause failure of two groups valves of freeze valve. The optimization methods based on results of fault tree analysis can significantly reduce the system failure probability.ConclusionsThis study provides reference value for design and engineering application of the core fuel salt emergency drain system for MSRs.
BackgroundCompton imaging technology is a new radiation hotspot location technology that does not require collimation and has a wide field of view, high efficiency, and broad application prospects. With the development of nuclear technology, Compton cameras with the above-mentioned advantages have a wide range of applications not only in the nuclear industry but also in the field of nuclear medicine, hence recently become a popular research field worldwide.PurposeThis study aims to develop a double-layer separated Compton camera for far-field imaging of specific radiation scenes in nuclear facilities.MethodsFirst of all, two pixel-type cadmium zinc telluride (CZT) detectors and an application-specific integrated circuit (ASIC)-based readout electronics system were adopted for the development of a double-layer separated Compton camera. A list-mode maximum likelihood expectation maximization (LM-MLEM) image reconstruction algorithm was implemented in the host computer software. Then, 137Cs point source was used for experimental test of imaging performance of the system, and the parameters affecting the imaging performance, such as the detector layer spacing and area of the absorption layer, were optimized. Finally, far-field three-dimensional imaging of the radiation source was performed by moving the measuring position of the detector.ResultsThe test results show that the energy resolution of the CZT detectors is approximately 3% (FWHM@662 keV), which can determine the location of the point source at a distance of 5 m, and the angular resolution for θ and φ directions of the optimized system is approximately 10°.ConclusionsDouble-layer separated Compton camera of this study has advantages of adjustable structure, low detector cost, relatively simple readout electronics, and wide imaging field of view. The angular resolution of this double-layer separated Compton camera can be improved by proper adjustment of the imaging influence parameters (such as layer spacing and the area of the absorption layer).
BackgroundThe Gaussian pulse shaping algorithm has the advantages of high signal-to-noise ratio and low ballistic deficit. Therefore, the radiation detector output signal is often shaped to a Gaussian waveform in the actual nuclear radiation measurement system even if the signal is more likely to be a dual exponential signal.PurposeThis study aims at gaussian pulse shaping algorithm for dual exponential nuclear signals based on wavelet transform.MethodsBased on the simulated nuclear pulse signal, the influence of the shaping parameters on the pulse shape and the filtering performance of the shaped pulse was investigated. A FAST-SDD detector was used to acquire the X-ray fluorescence signals emitted by a standard manganese sample. The measured nuclear signals were processed by Gaussian pulse shaping and trapezoidal pulse shaping algorithms respectively before generating energy spectrum. The performance of the two shaping algorithms on filtering and pile-up pulse separation were compared by using the full width at half maximum and the area of the 5.89 keV peak.Results & ConclusionThe comparison results show that the best energy resolutions corresponding to Gaussian and trapezoidal pulse shaping algorithms are achieved when the peaking time ranges from 3.2 μs to 6.4 μs, and the difference between two algorithms is less than 5 eV. Besides, the Gaussian pulse shaping algorithm performs better than trapezoidal pulse shaping algorithm on pile-up pulse separation with the same peaking times.
BackgroundThe high-fidelity neutron transport calculation requires refined geometric modeling whilst the unstructured meshes have strong adaptability to copy with the changes bring by complex geometry structure, and overcome the deficiencies of structured meshes in modeling capability.PurposeThis study aims to develop and validate a two-dimensional shielding calculation code ThorSNIPE which can be used to improve the modeling ability for analysis complex problems.MethodsFirst of all, problem solving model was established with discrete ordinates method and finite element method on the basis of the first order Boltzmann transport equation. The computational performance of continuous finite element method and discontinuous finite element method were compared and analyzed. Mass-matrix lumping technique was further applied to improve the reliability of solving model. Then, a two-dimensional discrete ordinate-finite element shielding calculation program ThorSNIPE was developed on the basis of above model. Finally, the code was validated by BWR cell critical benchmark, Argonne-5-A1 fixed source benchmark and Dog leg duct benchmark.Results & ConclusionsThe numerical results show that calculation value provided by ThorSNIPE is in good agreement with reference value, indicating that ThorSNIPE is suitable for complex shielding calculation, and Mass-matrix lumping technique can effectively suppress the non-physical spatial oscillations without reducing the calculation accuracy.
BackgroundPlastic scintillators have potential for application in neutron detection. Two sizes (?2.54 cm×2.54 cm, ?5.08 cm×5.08 cm) of plastic scintillators are self-developed by scientific research team in the school of physics, Sichuan University.PurposeThis study aims to experimental test the neutron/gamma (n-) discrimination performance for two self-developed plastic scintillators.MethodsA photomultiplier tube (PMT) was used to build detection systems, and high speed oscilloscope (LECROY HDO6104A) was employed to sample signal of detector for the energy calibration of the self-developed plastic scintillator. The pulse amplitude spectrum of 137Cs γ radiation source was measured and compared with the MCNP5 simulation spectrum to obtain the position information of the Compton edge and accurately calibrate the energies of γ rays. The data obtained from a 241Am-Be neutron source were analyzed using the charge integration method, and parameters such as the figure of merit (FOM), peak-to-valley ratio for neutrons, and the proportion of leaked neutrons over all neutron events were used to quantify the n-γ discrimination in different energy zones. The detection efficiencies of two self-developed plastic scintillators relative to the Commercial off-the-Shelf (COTS) EJ-299-33A were determined.ResultsThe results show that the FOM of ?2.54 cm×2.54 cm self-developed plastic scintillator is higher that of ?5.08 cm×5.08 cm self-developed plastic scintillator, and the detection efficiency of two self developed plastic scintillators relative to EJ-299-33A is about 0.49 and 1.0, respectively.ConclusionsThe performance of the ?5.08 cm×5.08 cm self-developed plastic scintillator is comparable to that of the COTS plastic scintillator EJ-299-33A with near the same discrimination ability.
BackgroundAs an innovative nuclear fuel assembly, the helical cruciform fuel (HCF) assembly has the characteristics of large specific heat transfer area, short heat conduction path, strong inter-channel mixing and free from the grid spacers. Compared with the traditional cylindrical fuel assembly, the HCF assembly can raise the core power density with compromise on the safety margin. However, the concentrated stress might take place at the location of self-support points, resulting in the plastic deformation and even rupture.PurposeThis study aims to analyze the thermal-mechanical behaviors of HCF bundle under steady conditions and accident transitions, so as to obtain the stress and strain of HCF rods, based on which, the integrity of fuel cladding was assessed.MethodsFirstly, a 3×3 typical HCF geometrical assembly model without four rods in corners was constructed and discretized by hexahedral mesh. Then, the steady and transient convective conditions were applied to the outer surfaces of rods to simulate the various working conditions, including single phase, boiling, reactivity insertion accident and loss of coolant accident. Finally, the governing equations for mechanics and heat transfer were established and solved in ANSYS using the thermal and mechanical modules.ResultsThe results show that, the maximum von Mises stress and plastic deformation take place at the location where adjacent rods contact, where the stress and strain are determined by both the contact constrain condition and the temperature difference between cladding inner and outer surfaces. However, at the elbow of the blades, the stress and strain are mainly affected by the radial temperature gradient in the cladding material. For the cladding, the plastic deformation is larger while the von Mises stress is smaller under the flow boiling condition compared with these under the single-phase cooling condition. Furthermore, the integrity of fuel cladding can be maintained under the conditions of reactivity insertion and loss of coolant accidents, where the stress and the temperature are lower than the break limit and the zirconium-water reaction temperature, respectively.ConclusionsFrom the thermal-mechanical analysis on the HCF assembly, this kind of innovative fuel assembly shows good mechanical performance under normal and accidental conditions.
BackgroundThe primary coolant flow rate is essential in preventing departure from nucleate boiling. The implementation of a low-leakage core loading pattern in advanced passive (AP) technology-based nuclear power units has increased the temperature difference gradient at the core outlet, resulting in elevated uncertainty in the flow rate calculations when using the heat balance method.PurposeThis study aims to validate a measurement and calculation method based on the Bernoulli equation model for accurately determining the primary coolant flow rate in AP nuclear power units, hence meeting the design and regulatory requirements.MethodsFirst of all, measurements were conducted for the primary loop main equipment and bend pipe flowmeter pressure differentials during the commissioning phases. Calorimertic balance tests were performed at power levels of 50%, 75%, 90%, and 100%. Then, the bend pipe flowmeter coefficients were calibrated using the flow rate values obtained from the hot function test and 100% rated thermal power (RTP). Finally, based on weighted factors, the total flow rate values for the reactor coolant system (RCS) were calculated with emphasis on the minimization of uncertainties.ResultsThe proposed measurement and calculation method yields primary coolant flow rate values with a relative error of less than 4%. The total flow rate after loading is within the range of 95.8% to 104% of the expected optimum flow rate. The uncertainty of the volumetric flow rate calculated from NAPs is lower than 1.9%, demonstrating a novel approach for precise measurements in other units.ConclusionsThe method of this study offers an advanced perspective for reactor coolant precise measurements in other units, with primary coolant flow rate values exhibiting minimal relative error and volumetric flow rate values from NAPs demonstrating low uncertainty.
BackgroundSilver nanoclusters, being a novel variety of nanomaterial, have garnered significant attention owing to their exceedingly minute dimensions, and distinct physical and chemical characteristics.PurposeThis study aims to present a straightforward and efficient method for fabricating silver nanoclusters composites using radiation technology.MethodsFirstly, silver nanoclusters in aqueous solution were directly synthesized through radiation reduction. By means of radiation grafting technique, polyacrylic acid templates was grafted onto an array of matrix materials, thereby producing solid templates. Subsequently, these solid templates were employed to achieve in situ synthesis of silver nanoclusters composites, obviating the need for water-soluble template materials. Finally, the fluorescence detection performance and catalytic performance of silver nanoclusters were tested by fluorescence spectrometer and the UV visible spectrum.ResultsThe silver nanoclusters and composites prepared in this study have retained the photoluminescence and catalytic activity characteristic of silver nanoclusters, thereby presenting potential applications in metal ion detection and catalytic degradation of 4-nitrophenol. Furthermore, it is noteworthy that the combination of the base material and silver nanoclusters is capable of manifesting a synergistic effect, thereby enhancing the overall performance of silver nanoclusters.ConclusionsThe utilization of radiation technique has enabled a simplified route of silver nanocluster composites. In addition, the versatility of this synthesis route extends across a variety of matrix materials, thereby broadening the scope of potential applications for silver nanocluster composites.
We aim to study the effects of chemical potential and angular velocity on the critical endpoint of quantum chromodynamics (QCD). We used several probes (drag force, jet quenching parameter, heavy vector meson spectral function) to characterize the phase transition and studied gravitational waves from the holographic QCD phase transition in the early universe. We used different holographic QCD models to discuss the QCD phase transition, energy loss, spectral function, and gravitational waves. We found that the chemical potential and angular velocity changed the location of the critical endpoint, and the drag force and jet quenching parameter were temperature dependent and enhanced near the phase transition temperature. The magnetic field had a nontrivial effect on the spectral function. We conclude that the chemical potential decreases ωc, and the angular velocity decreases μc and the phase transition temperature. The jet quenching parameter and drag force can characterize the phase transition, and the magnetic field promotes the dissociation of heavy vector mesons. Moreover, the energy density of gravitational waves decreases as the gluon condensate increases, and the peak frequency shifts downward with increasing gluon condensate.Exploring the phase structure of QCD is an important task in high-energy heavy ion collision physics, and recently, there has been considerable interest in the QCD phase transition for rotating backgrounds.
BackgroundThere is usually a strong coupling of neutronics-thermal hydraulics (N-TH) fields inside nuclear reactors.PurposeThis study aims to accurately simulate the multi-physics fields in nuclear reactors by developing a three-dimensional N-TH coupling code MORPHY tailored to advanced complex reactors.MethodsFirst of all, a three-dimensional triangular-z nodal variational nodal method (VNM) was employed for neutronics calculation. and the stiffness confinement method (SCM) was used to solve the neutron temporal-spatial equation; thermal hydraulic calculations were based on the one-dimensional multi-channel model and the one-dimensional cylindrical thermal conductivity model. Then, the accuracy of neutron dynamics was verified by TWIGL benchmark, Dodds benchmark, and the typical pressurized water reactor (PWR) benchmark NEACRP. Finally, the effects of different coupling methods and angle discrete orders on the results were analyzed and compared against reference solutions by PARCS.ResultsVerification results of TWIGL benchmark show that the deviation of relative power from the reference results is less than 0.5%. Compared with the results of Dodds benchmark, it verifies the MORPHY code's ability to describe unstructured meshes. The transient coupling calculation capability of MORPHY is verified by NEACRP benchmark.ConclusionsNumerical solutions by MORPHY are in good agreement with reference results of the TWIGL, Dodds and NEACRP benchmark problems. It is concluded that MORPHY can adapt to the transient N-TH coupling analysis of nuclear reactor cores.
BackgroundAerosol particle size of radon progeny is the key parameter of the radiation dose conversion coefficient in radon progeny. It is necessary to develop a measuring device for the aerosol particle size of radioactive aerosol to measure the aerosol particle size distribution of environmental radon progeny. Inertial impactor is a kind of widely used particulate classification sampler.PurposeThis paper aims to design and implement an impactor applicable to radon progeny aerosol with a cutting size of 1 μm.MethodsFirst of all, several kinds of inertial impactors were analyzed on the basis of aerodynamic theory, the design parameters of the impaction sampler structure, such as the diameter of the collecting plate, the distance between the collecting plate and the inner wall, the distance between the nozzle and the collecting plate, the height of the nozzle, were simulated by using computational fluid dynamics (CFD) analysis software Fluent and discrete phase model. Then, based on simulation results, a set of optimized design parameters were obtained and a porous impingent sampler was implemented for radon progeny aerosol. Finally, this impactor was calibrated by a GRIMM11-D aerodynamics particle size analyzer in a laboratory.ResultsThe optimized design parameters show that the nozzle distance D, the nozzle height T, the distance S from the nozzle to the collecting plate, and the nozzle diameter W have relationship of D/W=1.5~3.5, T/W=1~5, S/W=1. The experimental calibration results of designed porous impingent sampler are basically consistent with that of CFD numerical simulation with dp50=(1±0.07) μm, σg1=1.33, σg2=1.35, and the cutting particle size of the impactors meets the practical application requirements.ConclusionsThis paper focuses on the design of an impactor sampler. Through simulation and comparison tests with ELPI+ instrument, the effective cutting of 1 μm particle size is realized, which provides convenience and ideas for the further optimization design and online particle size fractional measurement of radioactive aerosol.
The nuclear fusion reaction using deuterium and tritium fuel produces a large number of neutrons, γ rays and activation products, which have an impact on the radiation safety of people and the environment. In order to reduce the impact of ionizing radiation, it is necessary to know accurately well the time and space distribution information of nuclear radiation field intensity in fusion device. The magnetic confinement fusion devices built in the world have established a complete nuclear radiation monitoring system according to their own operating conditions to deal with the potential impact of ionizing radiation. By monitoring the radiation dose during the operation and maintenance of the magnetic confinement fusion device, the ionizing radiation and radionuclide data of the experimental site and the surrounding environment are obtained, which provides data support for radiation safety protection management. Based on the investigation of radiation monitoring systems of magnetic confinement fusion device at home and abroad, the main ionizing radiation source terms and monitoring system architecture are reviewed in this paper, and the measuring methods and common detectors of neutron and γ radiation dose in magnetic confinement fusion are introduced. Finally, the research status of radiation monitoring system for nuclear fusion devices at home and abroad is summarized, and the development trend and goal of nuclear radiation monitoring system in the future are prospected.
Several experiments are being conducted at heavy-ion colliders around the world to determine the location of the proposed critical end point of quantum chromodynamics (QCD) in the T-μB phase diagram. As the presence of a very strong magnetic field is relevant to peripheral heavy-ion collisions, magnetars, and the early Universe, it is important to investigate the effect of a high magnetic field strength on QCD phase diagrams. We summarize the recent status and new developments in studies investigating QCD phase transitions under an extremely strong magnetic field. By doing so, we believe that this work will promote both theoretical and experimental research in this field. TheT-B phase diagrams are produced by Lattice QCD simulations. Other phase diagrams (E-B, μB-B,μI-B, andΩ-B) are mainly studied by using the chiral effective Nambu Jona-Lasinio model. A rotating magnetic field is adopted for the study of color superconductivity. The Ginzburg-Landau approximation is used to studyπ-superfluidity andρ-superconductivity in a very strong magnetic field. Physical effects, besides a magnetic fieldB, can also be measured when sketching a QCD phase diagram, such as temperatureT, strong electric fieldE, chemical potentialsμ, and rotational angular velocityΩ. We present five QCD phase diagrams: T-B,E-B, μB-B,μI-B, andΩ-B. The following phases are present in many (if not all) of the five QCD phase diagrams: chiral symmetry breaking, chiral symmetry restoration, inhomogeneous chiral phase, π0-condensation,π-superfluidity,ρ-superconductivity, and color superconductivity. The running of the coupling constant with magnetic field is consistent with the decrease of the pseudo-critical deconfinement temperature, providing a natural explanation for the inverse magnetic catalysis effect. We also found that a chiral anomaly induces pseudoscalar condensation in a parallel electromagnetic field, and that there appears to be a chiral-symmetry restoration phase in theE-B phase diagram. Without consideration of confinement, color superconductivity is typically favored for large baryon chemical potential; however, chiral density wave is also possible in the largeB and relatively smallμB region of the phase diagram. In an external magnetic field, theπ-superfluid with finite isospin chemical potential acts similarly to a Type-II superconductor with finite electric chemical potential. Bothπ-superfluidity andρ-superconductivity are possible in a parallel magnetic field and rotation, but the latter is more favored for largerΩ particles.
BackgroundPack cementation aluminizing technology is a common method for preparing tritium barrier coatings, and its relative parameters during the preparation process have an important influence on the microstructure of the aluminide layer and the tritium barrier properties of the in-situ oxidized Al2O3 coating.PurposeThis study aims to investigate the effects of pack aluminizing conditions on the microstructure of the Fe-Al layer and analyze the related kinetic analysis of the aluminizing process.MethodsFirst of all, a pack aluminizing process activated by 1 wt% AlCl3 was used to fabricate aluminide coatings on the substrate of 316L stainless steel in the 923 K to 1 173 K range. Then, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) were employed to characterize the cross-sectional microstructure and composition of the aluminized layer. Finally, the effects of aluminizing temperature and time on the microstructure and composition of the aluminized layer were analyzed, and the kinetic parameters of the formation of the Fe-Al layer and the relationship between aluminizing time and the thickness of the aluminized layer were further obtained.Results & ConclusionsThe experimental results show that the main phases of the aluminized layer are Fe2Al5 and FeAl with a certain amount of FeAl(Cr,Ni) precipitates. The high aluminizing temperature would accelerate the growth of aluminized layer and lead to the formation of a thick intermediate layer between the substrate and outer aluminized layer above 1 023 K. Simultaneously, extending the aluminizing time could increase the thickness of the Fe-Al layer, but has no effect on the phase composition. The relation between aluminizing temperature and the growth velocity of the Fe-Al layer is in accord with Arrhenius' equation, and the relative activation energy of the aluminizing process is about 79.23 kJ·mol-1. During the process of pack aluminizing, the relationship between the aluminizing time and the Fe-Al coating thickness is h=14.585t1/2+19.514.
BackgroundHard X-ray Imager (HXI) is one of the three scientific payloads onboard of the advanced space-based solar observatory (ASO-S). The calorimeter of HXI consists of 99 LaBr3 crystal and photomultiplier tube (PMT) detection units. A highly integrated charge-measurement application-specific integrated circuit (ASIC) with model IDE3381 is adopted in the front-end electronics of the calorimeter to process the signals from the 99 detection units on the space-limited and power-limited satellite platform.PurposeThis study aims to evaluate the radiation tolerance of model IDE3381 ASIC in a space radiation environment.MethodsA test bench with a flexible structure was designed by separating the device undergoing testing from the data acquisition (DAQ) system, hence shielding DAQ from the radiation environment. The performance of ASIC was automatically tested and monitored in the test bench during radiation tests. Both single-event effect (SEE), including single-event upset and single-event latch-up, and total ionizing dose (TID) tests were carried out by using a heavy ion beam and 60Co gamma-ray, respectively.ResultsThe test results show that the SEE threshold of model IDE3381 ASIC is greater than 75 MeV?cm2?mg-1, and the TID capacity is greater than 30 krad(Si).ConclusionsThe radiation tolerance of the charge measurement ASIC (model IDE 3381) meets the requirements of ASO-S HXI flight model.
BackgroundStable isotopes play a crucial role in a variety of fields such as energy, military, semiconductor, agriculture, medicine, pharmacology, biology, food industry, and chemistry. With the rapid growth of nuclear science and technology applications in China, there has been an increasing demand for isotopes that cannot be met by current production capacities. Thus, the development of electromagnetic isotope separators capable of producing high yields and high isotopic purity has become necessary.PurposeThis study aims to develop an electromagnetic isotope separator based on a 2.45 GHz microwave ion source and isotopic magnet for studying a number of important heavy isotopes, such as xenon and molybdenum isotopes.MethodsFirstly, adjustable axial magnetic field in the source was designed by a double-solenoids to obtain high density plasma, and a high coupling efficiency matching waveguide was optimized by CST microwave computing module. Then. a crucible built in the discharge chamber was used to melt metal oxide for generating heavy metal ion beams. Finally, the discharge chamber, microwave coupling waveguides and heating oven of the ion source were simulated and designed for the generation of heavy ions.ResultsSimulation result shows that the temperature around the crucible is 917 ℃ when the current of heating wire is set to 70 A, and 100 mA hydrogen beam is generated during commissioning. The designed crucible in the discharge chamber can generate metal vapor efficiently for ionization, and achieve producing 20 emA Xe+ and 5 emA Mo+ respectively at the energy of 40 keV.ConclusionsThe feasible scheme of the magnetic field and microwave coupling design of this study are verified. The design of the 2.45 GHz electron cyclotron resonance (ECR) ion source provides a feasible and effective solution for the high yields isotope ions.
BackgroundSilicon carbide junction barrier Schottky (SiC JBS) diode is a kind of power device based on wide bandgap semiconductor. SiC JBS diode is expected to become an important part of electric propulsion systems in the radiation application field in the future space exploration due to its excellent high-voltage, high-frequency and high-power characteristics. However, there are a large number of protons in the typical orbit of spacecraft, which always threaten the stable operation of spacecraft, including its key components.PurposeThis study aims to explore the resist ability of SiC JBSs to the degradation of medium energy proton irradiation, and clarify the mechanism of radiation effect of SiC JBSs from medium energy proton.MethodsBased the proton equivalent displacement damage dose in low Earth orbit for ten years, the SiC JBSs were firstly irradiated using 10 MeV protons at fluences ranging from 3×109 cm-2 to 3×1010 cm-2 at room temperature and without bias voltage. And the macro electrical characteristics of the SiC JBSs both before and after irradiation, including the forward current-voltage (I-V), reverse I-V and capacitance-voltage (C-V) characteristics, were tested. Then the irradiation-induced defects characteristics were tested by deep level transient spectrum (DLTS). Further, the related degradation mechanism that was associated with this phenomenon was also investigated using based on the test data and mathematical calculation. Finally, irradiation experiments of accelerator protons were carried out for commercial SiC JBSs.ResultsThe results show that the forward electrical characteristic of the SiC JBSs is stable, and the leakage current decreases at low reverse safety voltage. But the rated breakdown voltage is seriously degraded with the increase of irradiation fluence. The main contribution to the change of SiC JBSs characteristics originates from the increase of interface charge, deep level defects and Schottky barrier height, and the decrease of carrier density and carrier diffusion length in the drift region.ConclusionsAnalysis of the radiation damage process and mechanism of SiC JBSs in this study provides a research basis for its evaluation and verification before applied to medium energy proton environment.
BackgroundUnder high-temperature operating conditions, the tritium would be generated inside the core of thorium-based molten salt reactor (TMSR) and probably diffuse through the structural material into the environment. Establishing an Al2O3/Ni-Al composite tritium permeation barrier coating may help address this issue.PurposeThis study aims to explore the optimal preparation process, especially the in-situ oxidation process.MethodsThe Al2O3/Ni-Al composite coating was prepared on the surface of GH3535 alloy by pack cementation aluminizing (PCA) followed by vacuum in-situ oxidation, and the effects of oxidation temperature and vacuum on the microstructure of Al2O3 films were analyzed by experiments. Grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM), X-ray energy dispersive spectroscopy (EDS) were used to characterize the phase composition and crystal structure of the alumina film, as well as morphologies of the surface and cross-section.ResultsThe experimental results show that the low oxygen partial pressure can increase the forming temperature of alumina film, but can form a more compact film with flat surface. Higher oxidation temperature is conducive to the formation of thicker alumina films, but also greatly increases the surface defects.ConclusionsBy in-situ oxidation process at 1.2 Pa-850 ℃-72 h, alumina thin films with good properties can be obtained on the surface of GH3535 alloy: The phase of film contains γ and α, the thickness is about 0.8 μm, and the surface is compact without defects.
The quantum chromodynamics (QCD) phase diagram is of great interest to researchers in the field of high energy nuclear physics. We review the present research status of several aspects of this topic. This review includes the search for the phase transition mechanism resulting in high-order baryon number fluctuations, how chiral imbalance, finite volume, and under rotations affect the QCD diagram, and the applications of the equation of states of dense QCD matter in the study of compact stars. The Nambu-Jona-Lasinio model and Dyson-Schwinger equations approach are the most commonly used methods described in this review. It is found that the theoretical results of high-order baryon number fluctuations are in good agreement with the experimental data. The chiral imbalance, finite volume, and rotation of quark-gluon plasma (QGP) have a quantitative impact on the chiral condensate and the QCD phase structure. In the study of compact stars, the theoretical results from equation of states of dense QCD matter agree well with pulsar observations. Further research will be required to form a complete understanding of the QCD phase diagram, particularly given the abundance of QGP.
BackgroundThe activation method is taken to measure the in-core distribution of neutron spectrum for the designed 10 MW solid-fuel thorium molten-salt reactor (TMSR-SF1). The neutron activation foil sample is loaded outside the reactor and quickly transported to the measurement position in the reactor through the transmission device for irradiation, and then is transferred outside of reactor to the energy spectrum samples for de-spectrographic analysis.PurposeIn order to realize the rapid entry and exit of the neutron activation foil sample into and out of the reactor, a pneumatic conveying system with double-layer casing is designed in this research.MethodsThe principle of the conveying system and the structure of the double-casing tube were adopted in this study. ANSYS Fluent software and 6DOF dynamic grid technology were used to analyze the movement and stress of the sample under different pipe gaps, so as to determine the sample pipe gap value. Then the flow parameters and gas-solid two-phase flow resistance of the conveying system were calculated in detail using the pneumatic conveying theory. Finally, a prototype was developed for experiments to verify the principle of the conveying system.ResultsThe analysis results showed that the sample speed is decreased with the increase of the pipe gap. The experiments results show that the velocity of the sample and the pressure loss of the gas-solid two-phase flow increase with the increase of the gas flow rate. Under the same flow rate, the experimental speed of the sample movement and the pressure loss of the gas-solid two-phase flow are in good agreement with the theoretical calculations.ConclusionsThe pneumatic convey system with double-casing tube can be applied to transport the sample into and out of the reactor, and the theoretical calculations values of pneumatic conveying parameters in this study are reliable.
Experimental evidences at the relativistic heavy ion collisions (RHIC) and large hadron collider (LHC) have demonstrated the formation of quark gluon plasma (QGP) in ultra-relativistic heavy-ion collisions at a small baryon chemical potential, where the phase transition from hadronic matter to QGP is suggested to be a crossover from state-of-the-art lattice quantum chromodynamics (QCD) calculations. It has been conjectured that there is a first-order phase transition and a critical point at a finite μB region in the QCD phase diagram. This study reviewed recent progress in searching for the QCD critical point from RHIC-STAR experiments.
The atomic nucleus, governed by short-range nuclear force, is a quantum many-body system that plays a vital role in the visible energy-mass dynamics of the universe and significantly influences the sustenance, development of society, and the security of nations. There have been numerous discoveries in the past decades concerning exotic structures and properties of short-lived nuclei. These findings have sparked breakthroughs in our understanding of nuclear structures and have given rise to a new field called radioactive ion beam physics, which focuses on the study of unstable nuclei. For more than 30 years, the Beijing Tandem-Accelerator Nuclear-Physics National Laboratory has provided a basic research platform for low-energy nuclear physics experiments. The experimental nuclear physics team at Peking University has continuously developed a dedicated experimental apparatus, conducted a series of physics experiments at the Beijing HI-13 tandem accelerator, and achieved important results related to exotic nuclear structures. In this article, we present several notable experimental achievements of our team at the HI-13 accelerator. These include the investigation of the shape evolution of germanium isotopes (around A=70) using in-beam γ-spectroscopy, the exploration of cluster structures in light neutron-rich nuclei through direct nuclear reactions, and the development and commissioning of collinear laser spectroscopy experiments at the Beijing Radioactive Ion-beam Facility.
BackgroundNarrow rectangular channels are widely used in various fields because of their compact structure and other advantages.PurposeThis study aims to improve the prediction method of critical heat flux (CHF) in narrow rectangular channels for reactor safety and economy by conducting CHF visualization tests in narrow rectangular channels with different gap size to explore the CHF triggering mechanism.MethodsFirstly, a high-temperature and high-pressure experimental loop with narrow rectangular channels was built, and the visualisation video and thermal-hydraulic data were collected simultaneously. It was found that the flow patterns correspond to bubble flow, slug flow, churn flow and annular flow when CHF occurs with the gap size of 5 mm, 3 mm, 2 mm and 1 mm, respectively.ResultsBefore the occurrence of CHF, bubble flow, slug flow and churn flow experience temperature fluctuations. In the annular flow, the CHF involves a gradual expansion of the area from the initial dry spot; in the churn flow, the CHF covers a smaller area; while the slug flow affected the widest area; in the bubble flow, the temperature fluctuations at the heating wall are the most frequent. Furthermore, when the system pressure is in the range of 1?4 MPa and the gap size is 1 mm, there is a non-linear relationship between the system pressure and the CHF, while in the other channels the CHF increases as the system pressure increases.ConclusionsThe narrow gap size has a very important effect on CHF in narrow rectangular channels, and the findings of this paper can lay the foundation for the establishment of a CHF mechanism model in narrow rectangular channel.
BackgroundShanghai High Repetition rate XFEL and Extreme light facility (SHINE) employs a White Rabbit (WR)-based timing system. This timing system operates via the utilization of beamline–endstation division, which receives external reference timing signals and distributes them to each beamline and endstation via WR timing network devices, including master nodes, WR switches and slave nodes.PurposeThis study aims to develop a timing equipment control system (TECS) to address the requirements of remote monitoring and control of distributed timing equipment.MethodsBased on Experiment Physics and Industrial Control System (EPICS) and Simple Network Management Protocol (SNMP), an approach for acquiring timing equipment parameters was employed. These parameters was stored in the resident memory database though EPICS Input/Output Controller (IOC) and accessed via a user interface developed with PyDM (Python Display Manager). Archive and retrieval of timing equipment parameters were implemented in the Archiver Appliance historical archiving system. Finally, test environment was set up in laboratory to verify the validity and reliability of this TECS.Results & ConclusionsThis control system underwent testing exhibits its effective functionalities, including real-time monitoring equipment parameters, as well as remote control of equipment signal delay and pulse width. These capabilities are essential in meeting the requirements of SHINE beamlines and endstations.
BackgroundIsoscalar pairing plays an important role in the spin-isospin excitation of nuclei. The discovery of super Gamow-Teller (GT) states in N≈Z nuclei has motivated researchers to explore the effects of isoscalar pairing on spin-isospin excitations.PurposeThis study aims to investigate the effects of the isoscalar pairing interaction on GT and spin-dipole (SD) transitions in 42Ca.MethodsBy solving the relativistic Hartree-Bogoliubov equation, we obtained the canonical single-nucleon basis and occupation amplitudes, which were used as inputs for the quasiparticle phase-random approximation (QRPA) calculation. Using the QRPA model, the GT and SD transitions in 42Ca were calculated, where the Gaussian isoscalar pairing force was adopted, with its strength being a free parameter.ResultsFor GT states, the isoscalar pairing mixed the spin-flip transition configuration into the low-lying GT state, enhancing the collectivity of the low-energy GT state and significantly increasing its transition strength. Meanwhile, the isoscalar pairing force induced a shift of the low-energy GT state toward lower energies owing to the attractive properties of the isoscalar pairing force. For SD states, the isoscalar pairing force hardly affected the strengths and energies of SD states in 42Ca.ConclusionsIsoscalar pairing force was essential for restoring the SU(4) symmetry and hence reproducing the low-energy super GT state of 42Ca in the experiment, whereas it hardly affected the SD states.
BackgroundThe trend towards increasingly narrow apertures in multipole magnets poses a challenge to many conventional measurement methods. Consequently, these methods' applicability in small aperture multipole magnets is limited. However, the single stretched wire measurement technique has emerged as a promising alternative due to its minimal space requirements within the measurement domain. Therefore, this technique is well-suited for accurately measuring magnetic fields in small aperture magnets.PurposeThis study aims to introduce a novel approach for analyzing the gradient integral and multipole errors of the quadrupole magnet, to address the limitations associated with the current single stretched wire method (SSWM).MethodsFirstly, a magnetic measurement system based on the single stretched wire method was constructed with two boasted key advantages: minimal space occupation within the measurement domain, and flexible motion modes. Then, leveraging these features, measurements of the four poles of a quadrupole magnet by employing a hyperbolic trajectory was acquired, and a new technique for analyzing both the gradient integral and multipole errors associated with the quadrupole magnet was developed. Finally, the feasibility of this SSWM was verified by comparing the results obtained from our system to those derived from the rotating coil method.ResultsMeasurement results of a quadrupole magnet with the inscribed radius of 11 mm and gradient of 100 T?m-1 by SSWM show that the repeatability of three measurements is better than ±1.5×10-4 which is less than one-third of the maximum value of multipole error of 5×10-4, so it can meet the measurement requirements.ConclusionsThe methodology outlined in this study for constructing the measurement system and analyzing the resultant data offers a practical and effective solution for the future magnetic field measurements of small aperture magnets.
BackgroundThe propagation of pressure waves in nuclear energy systems will cause hydraulic load effects, and it is particularly important for the analysis of structural loads to accurately simulate the propagation process of pressure waves. System analysis codes such as RELAP5, TRACE, etc. are widely used in the simulation and analysis of reactor pressure wave propagation. But system analysis codes can only simulate one-dimensional pressure wave propagation behavior.PurposeTo cope with the multi-directional and multi-dimensional pressure wave propagation issue, corresponding model and algorithm study is carried out in this paper to investigate the two-dimensional pressure wave propagation behavior in two-phase steam-water flow condition.MethodsBy employing a four-step algorithm of time-step separation, and a non-equilibrium phase transition heat transfer model, a two- dimensional two-phase flow pressure wave propagation code (TPFPWPC-2D) is developed based on 2D axisymmetric cylindrical coordinate system. The code verification is carried out by using a typical benchmark of steam-water two-phase shock tube. Finally, in order to verify the ability of TPFPWPC-2D code to simulate the two-dimensional propagation of pressure waves, numerical simulations of the pressure wave propagation behavior in a cylindrical space region were conducted.ResultsThe results of code verification show that the new code proposed here agrees well with the two system analysis codes RELAP5 and WAHA. The 2D simulation application shows that the new code can capture the 2D propagation processes of pressure wave reasonably, especially the reflection and superposition characteristics.ConclusionsFrom the results mentioned above, conclusions can be drawn that the new code developed in this paper can simulate the two-dimensional axisymmetric propagation characteristics reasonably in both quantitative and qualitative levels.
BackgroundDue to the complex structure of the ventilation ducts in nuclear facilities, the concentration distribution of radionuclides such as aerosols in the ducts is uneven. The inhomogeneity of aerosol distribution brings great challenges to the sampling representativeness of radiation monitoring. In chemical processes, static stirring devices are commonly used to enhance the homogeneity of the product mix. However, this device has not been applied in the nuclear power field.PurposeAccordingly, this study aims to improve the mixing uniformity of aerosols in air supply pipelines by using static stirring devices, so as to provide a reference for the representativeness of radiation monitoring sampling.MethodsThe stirring effects of three different stirring devices were investigated through numerical simulations. The RNG k-ε model was used to simulate the gas phase flow field, and the discrete phase model (DPM) was employed in ANSYS CFX software to simulate the behavior of aerosol particles. Selection of the particle size of aerosols followed the recommendations in the sampling representative standards, with the specific size of 10 μm. The other boundary conditions in the simulation were based on the actual operating conditions of a nuclear power plant. As a result, the effects of different stirring devices on the flow field and aerosol concentration distribution were obtained.ResultsThe static stirring device can form strong swirls, thereby improving the uniformity of aerosol distribution. Increasing the twist angle of the blades and the proportion area of the inner blades strengthened the generated vortex field, further affecting the diffusion of aerosols. The static stirring device with an increased inner blade area exhibited a moderate swirl intensity, and better stirring effect than those of the other two structures. The coefficient of variation of the aerosol concentration decreased by 30.60%.ConclusionsInstalling a static stirring device in an air supply duct is a feasible method to improve the mixing uniformity of aerosols. Owing to the complex structure of ventilation ducts in nuclear facilities, the concentration distribution of radionuclides, such as aerosols, in the ducts is uneven. This inhomogeneous aerosol distribution poses significant challenges to the sampling representativeness of radiation monitoring. In chemical processes, static stirring devices are commonly used to enhance the homogeneity of the product mix. However, these devices have not yet been applied in the field of nuclear power.
BackgroundThe accurate acquisition and correlation coincidence of positron annihilation signal form the basis of the lifetime spectrum sensitive characterization of microscopic defects in materials. The complex radiation background interferes with the acquisition of positron annihilation signals, particularly in the study of neutron radiation damage of nuclear structural materials. The γ ray background generated by radionuclides induced by neutron activation affects the measurement results of positron lifetime spectrometer.PurposeThis study aims to investigate the effect of γ background on positron annihilation lifetime measurement.MethodsFirst of all, the positron lifetime measurement system is built in a "fast-fast coincidence" manner, and radiation background simulation experiments are designed by selecting two typical nuclides, 60Co and 137Cs sources, with nearby feature γ photon energy for measuring positron annihilation lifetime. Then, the spectra under two typical activity ratios are compared with the activated neutron-irradiated samples.ResultsThe simulation results indicate that the double high energy γ rays generated by 60Co sources are the primary factors affecting the spectrum shape and lifetime components. When the 60Co/22Na activity ratio is relatively low, 1.9, the peak-to-valley ratio of the spectrum significantly degrades, with the increase of random coincidence probability caused by radiation background. Further, at high activity ratio of 3.3, besides random coincidence, the false coincidence probability increases sharply, and the spectral shape is evidently distorted. For neutron-irradiated RPV steel, the lifetime value is reduced by 17% and 46% at low and high activity, respectively, compared with the non-irradiated samples.ConclusionsUsing the simulation method of radiation background sources and the influence rules of interference γ in this study, new techniques for eliminating γ background could be further explored in positron annihilation lifetime measurement.
BackgroundAs an innovative technology of nuclear power, magnetically suspended high-temperature molten salt canned motor pump (referred to as molten salt canned motor pump) can be used in the fourth generation molten salt reactor (MSR). Improving pump performance via hydraulic optimization design is significant to fourth-generation nuclear power technology.PurposeThis study aims to investigate the influence of different working fluids on the hydraulic optimization design of magnetically suspended high-temperature molten salt-canned motor pumps and provide suggestions for the optimal design of magnetically suspended high-temperature molten salt-canned motor pumps.MethodsFirstly, ANSYS CFX software was employed to perform a numerical simulation of a magnetically suspended high-temperature molten salt canned motor pump. Based on response surface methodology (RSM), approximate models between significant parameters and optimization objectives were established. Then, taking the efficiency and head as optimization objectives, a non-dominated sorting genetic algorithm II (NSGA-II) was used to design the magnetically suspended high-temperature molten salt canned motor pump under molten salt and water.ResultsCompared with water working fluid, the optimization space of the pump under molten salt working fluid is larger. When the efficiency of the optimization model under the two working fluids is the same, the impeller inlet diameter and the blade outlet placement angle of the molten salt optimization model are reduced, whereas the impeller outlet width and the diffuser throat plane width are increased. The efficiency of the finally determined molten salt optimization model is increased by 0.75% and the head is raised by 0.078 2 m whilst the efficiency of the water optimization model is increased by 0.55%, and the head is reduced by 0.035 9 m.ConclusionsThe research results of this study can be used to guide the hydraulic structure design of a magnetically suspended high-temperature molten salt-canned motor pump.
We reviewed the recent progress on strange particle production and hypernuclear physics both in experiments and in theories. The temporal evolutions of nucleons and resonances are described by the Skyrme energy density functional and relativistic covariant density functional theory, in which the meson-nucleon and hyperon-nucleon interactions are considered. Calculations are performed for the reactions of 12C+12C, 40Ca+40Ca, 112Sn+112Sn, and 197Au+197Au. The in-medium effects and high-density symmetry energy from the production of kaon, antikaon, and hyperon (Λ, Σ, Ξ) are investigated systematically. A quantum coalescence method is used to construct the hypernucleus, and the phase-space distribution is investigated in terms of the mass, charge, kinetic energy, rapidity distribution, collective flows, etc. Pre-equilibrium cluster emission in heavy-ion collisions is analyzed by implementing 2-, 3-, and 4-body nucleon collisions. The relativistic quantum molecular dynamics model is introduced by including ρ and δ coupling for nucleon transportation, and the collective flows are calculated for protons and neutrons.
Aerospace integrated circuits represent core components of space electronic systems, and anti-radiation hardening is a key technology to ensure the reliable operation of aerospace integrated circuits in the space domain. As the feature sizes of integrated circuits shrink to the nanometer scale, the single-event effect gradually becomes the most critical factor limiting the radiation-hardened performance level of aerospace integrated circuits. In this study, radiation hardened by design is utilized as a method to develop radiation-hardened performance. Based on single-event radiation tests on a heavy ion accelerator, new methods are proposed for the single-event test evaluation of new processes and devices. Consequently, new technique development and radiation effect law research are also undertaken. The effectiveness of the design hardening technology is evaluated, and a single-event radiation damage mechanism is discovered. The proposed technology provides key support for the production of high-reliability and long-lifetime aerospace integrated circuit products.
BackgroundIn the Shanghai High Repetition rate XFEL (X-ray free electron laser) and Extreme Light (SHINE) facility, the vertical linear polarization laser is generated by using 40 planar superconducting undulators (SCUs) with a period length of 16 mm, length of 4 m, and a gap of 4 mm. At present, the Hall probes are the most reliable method for measuring the undulator magnetic field whilst the positioning accuracy of the sensitive center of the Hall probe is one of the main factors affecting the accuracy of magnetic field measurement.PurposeThis study aims to calibrate the position of the Hall probes' sensitive region for magnetic field measurements of SCU with high-precision.MethodsThe experimental platform for magnetic field point measurement of SCUs was introduced in details, a sledge with three mounted Hall probes and a retro-reflector were applied for magnetic field measurement. By flipping the sledge, the lateral distance between the sensitive centers of the Hall probe and each other were obtained, so did the lateral distance between the sensitive centers of the Hall probe and the apex of the pyramid prism. Therefore, the position of the Hall probes' sensitive region and center of the retro-reflector were calibrated.Results & ConclusionsThe positional calibration of the Hall probes has an accuracy higher than ±10 μm, which meets the requirements for magnetic field measurement.
BackgroundDuring reactor operation, zirconium (Zr) alloy cladding is continuously oxidized as it gets in contact with fuel, and combines with the fuel to form a firm chemical interaction layer. This affects the thermal conductivity of the fuel gap, the mechanical properties of the cladding, and the mechanical interaction of the fuel cladding.PurposeThis work aims to obtain relevant analytical data on the chemical interaction layer between the irradiation Zr-alloy cladding and uranium oxide (UO2) pellets in a pressurized water reactor (PWR).MethodsFirst of all, the D13 intact fuel rod with a burnup of 45 GWd·tU-1 for PWRs in a nuclear power plant was chosen as UO2 pellets with a pellet enrichment of 4.45 wt%, and M5 Zr-alloy was used as the cladding materials. Then, a series of operations (cutting, pellet separation, inlaying, secondary cutting, inlaying, and polishing of cladding tubes) was conducted in the hot cell. The polished sample was transferred to the lead chamber and the UO2 fuel pellet was removed using 4 mol?L-1 of nitric acid solution. The cladding tube was separated from the chemical interaction layer, and a low-speed cutter was used to cut the cladding tube to a width of 2~3 mm in the glove box. Finally, the morphology and structure of the chemical interaction layer were analyzed using metallographic microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and hot cell Raman spectroscopy.ResultsThe analysis results show that the gap between the fuel pellet and cladding is approximately 14~19 μm after the fuel running to a burnup of 45 GWd·tU-1. In the chemical interaction layer, the time sequence of mechanical contact at different locations is different, resulting in discontinuity of the interaction layer. The SEM-EDS results show that the chemical interaction layer is in the shape of "worms" composed of U, Zr, and O to form a mixed phase (U,Zr)Ox compound.ConclusionsThe results of this study indicate that the chemical interaction layer is mainly composed of tetragonal zirconia (t-ZrO2) and monoclinic zirconia (m-ZrO2).
Supernovae are the most gorgeous fireworks that people can observe in the universe. Their explosion can produce a maximum luminosity 10 billion times that of the Sun, helping scientists see farther. Type Ia supernovae can be used as a standard candle to facilitate measurement of the distance between galaxies in the universe. A supernova explosion will also propel a large number of heavy elements into interstellar space, which is a major driving force for the chemical evolution of galaxies. In addition, supernovae are crucial to the origin of elements in the Milky Way, the formation of the structure of the solar system, and the evolution of life on the Earth. The study of supernovae will further enrich our understanding of the universe and help us solve the mysteries of the expansion of the universe, the generation of heavy elements, and the origin of life. At present, scientists predict that the next supernova will explode at any time, and preparations are in progress for observing the coming supernova.
The year 2023 marks the 35th anniversary of the establishment of the Beijing Tandem Accelerator Nuclear Physics National Laboratory. Accelerators and nuclear reactors are the two main tools for studying nuclear science. In 1988, the Tandem Laboratory was officially founded, serving as a significant research hub for nuclear physics in our country. It has consistently played a leading role in nuclear science innovation, achieving 140 000 h of stable operation. The laboratory has undertaken research in nuclear physics research, nuclear data measurement, nuclear physics applications, and interdisciplinary studies. This has resulted in a series of internationally recognized basic and technological achievements that meet national major demands, fostering a group of outstanding talents. It has provided solid support for the continuous development of nuclear physics research and nuclear technology strategy in our country. This article provides a comprehensive overview of the 35 years of development of the Tandem Laboratory.
BackgroundTo date, various nuclides up to Z = 118 have been discovered and synthesized, raising the challenge of synthesizing nuclides with Z ≥ 119. Recently, the fusion-evaporation reactions 243Am54Cr, xn119297-x and 243Am55Mn, xn120298-x have been suggested as methods for synthesizing new elements with Z = 119 and 120. As α-decay is a powerful tool for the identification of new elements or nuclides, accurate predictions of the α-decay properties of the reaction products could be a useful reference for future experiments.PurposeThis study aims to provide quantitative predictions of the α-decay, spontaneous fission, and β-decay half-lives for the α-decay chains of 293, 294119 and 294, 295120 and to demonstrate the competition between the decay modes for these nuclei.MethodsAn improved density-dependent cluster model (DDCM+) is used to calculate the α-decay half-lives, taking the anisotropy of the surface diffuseness into account. The spontaneous fission half-lives are calculated using the Karpov formula, which is related to the fissility parameter and fission barrier height of the potential energy surface. The β-decay half-lives are determined using a finite-range droplet model (FRDM).ResultsThe predictive α-decay half-lives for the α-decay chains of 293, 294119 and 294, 295120 are obtained using the DDCM+ model, and the theoretical half-lives of the spontaneous fission and β-decay for these nuclides are also presented.ConclusionsFor the α-decay chains of 293, 294119 and 294, 295120, α-decay is predicted to be the dominant decay mode for most of the nuclei, while the half-lives of spontaneous fission and β-decay are predicted to be comparable to those of the α-decay near the region of A = 261. We expect that these results will serve as a useful reference for the synthesis of new isotopes in the future.
The fundamental properties of unstable nuclei are highly related to the nuclear structure and effective nucleon-nucleon interaction, and they can be used to study various exotic structures of unstable nuclei. Laser spectroscopy is a powerful tool used to study nuclear properties and structure by probing the hyperfine structure and isotope shift of the corresponding atoms or ions, from which the nuclear properties can be extracted in a nuclear model-independent manner. Multi-step laser resonance ionization spectroscopy (RIS) can be used to measure the atomic or ionic hyperfine structure. Based on this approach, various experimental techniques have been developed at radioactive ion beam (RIB) facilities worldwide to study the nuclear properties and structure of atomic nuclei. In this paper, the RIS approaches and relevant RIS experimental techniques are first introduced. Subsequently, the recently-developed collinear resonance ionization spectroscopy experimental technique, which can be used to measure the atomic or ionic hyperfine structure spectrum with a high-resolution and high sensitivity and plays an important role in the study of the nuclear properties and structure of unstable nuclei in the large mass regions of nuclear charts, is discussed in detail. Finally, the development status of RIS and its application in domestic RIB facilities are discussed.
BackgroundShanghai High repetition rate XFEL (X-ray free electron laser) and Extreme light facility (SHINE) is a high-repetition-rate X-ray-free electron laser. The timing system of the beamlines and endstations must provide high-precision bunch IDs and a timing trigger for the equipment that works in single-pulse mode.PurposeThis study aims to design a data acquisition (DAQ) testing system to simultaneously acquire X-ray bunch IDs with their corresponding detector data package for subsequent data processing.MethodsThis DAQ testing system was developed on the Zynq UltraScale+ system-on-chip (SOC), and the White Rabbit protocol was employed for the timing system environment. A Bunch ID obtained from the FPGA mezzanine card (FMC) of the embedded White Rabbit node (WRN) was transferred to the server using a TCP protocol stack built on LwIP (light weight internet protocol). Finally, a Basler camera was employed to test this DAQ system, in which the pypylon library was applied to raw data acquisition software for camera snapshot whilst two channels of data were collected by an upper computer and saved to a database for comparison.Results & ConclusionsThe number of bunch IDs obtained by this acquisition test system is the same as that of image frames taken by Basler camera, which demonstrates that the testing system can satisfy the requirements of bunch ID acquisition in SHINE beamlines and endstations.
Backgroundβ-decay half-life is one of the fundamental physical properties of unstable nuclei and plays an important role in nuclear physics and astrophysics.PurposeThis study aimed to provide accurate nuclear β-decay half-life predictions and reasonable uncertainties associated with the predictions.MethodsNuclear β-decay half-lives were studied based on the Bayesian neural network (BNN) approach. Three types of neural networks with x = (Z, N), x = (Z, N, Qβ), and x = (Z, N, δ, Qβ) were constructed as inputs to explore the influence of the input on the prediction. The posterior distributions were sampled using the Markov chain Monte Carlo algorithm. The mathematical expectations and standard deviations of the neural network predictions on the posterior distributions were used as the predicted values and errors of the BNN approach.ResultsThe learning accuracy can be significantly improved by incorporating the β-decay energy and physical quantity related to the nuclear pair effect into the neural network input layer and then using the logarithm of β-decay half-life as the network output. For nuclei with half-lives of less than 1 s, the prediction accuracy is approximately 0.2 orders of magnitude, which is similar to that afforded by the BNN method by learning the differences between the logarithms of the experimental half-lives and theoretical results.ConclusionsThe Bayesian neural network can accurately predict β-decay half-lives. When extrapolated to the unknown nuclear region, the predicted β-decay half-lives agree with the results of other theoretical models within errors, especially for nuclei with Z ? 50.
BackgroundWith the increase of complexity of reactor core design, the core modeling and calculation have brought challenges.PurposeThis study aims to implement the accurate modeling and calculation of unstructured geometry core.MethodsBased on discrete ordinate nodal method for arbitrary triangular-z geometry, the precise modeling and mesh generation of unstructured core were established by constructive solid geometry (CSG), and Block-Jacobi parallel algorithm was employed to reduce calculation time of reactor core. Finally, based on the developed SARAX program, core physics calculations for new complex geometries of a space reactor and a heat pipe reactor were performed for accuracy verification by using Block-Jacobi parallel algorithm combining with established precise model and mesh.ResultsThe verification results show that the effective multiplication factor and radial power distribution agree with that of multi-group Monte-Carlo calculation. The calculation deviation of eigenvalues is less than 3.00×10-3, and the relative deviation of radial power distribution is less than 1.5%.ConclusionsResults of this study show that SARAX code has the ability of modeling and higher accuracy in the calculation of unstructured geometry core.
BackgroundThe neutronics and thermal-hydraulic characteristics of lead-bismuth cooled reactors are significantly affected by the geometric configuration of fuel assembly and lattice parameters. Reactor cores loaded with different geometry type fuel assemblies have different critical dimensions and fuel loadings under the same refueling cycle and thermal-hydraulic constraints.PurposeThis study aims to analyze these key factors and select a geometric structure of fuel assembly that is conducive to miniaturization and lightweight of lead-bismuth reactor.MethodsFirst of all, the core model of a 4 MWt small lead-bismuth reactor was established, and simulation analysis of reactor physical characteristics was conducted using the RMC Monte Carlo program developed independently by the Reactor Engineering Calculation and Analysis Laboratory of Tsinghua University and the nuclear database ADS-2.0 released by the International Atomic Energy Agency (IAEA) in 2008. Then, three fuel assembly schemes of rod bundle type, annular type and honeycomb coal type were selected for comparison and analysis in term of fuel consumption characteristics, reactivity coefficient and steady-state thermal parameters under the same core size, fuel loading, coolant flow area, cladding and air gap volume, 10-year refueling cycle and basically consistent steady-state thermal safety margin.Results & ConclusionsThe results show that compared with the rod bundle fuel assembly and the annular fuel assembly, the honeycomb coal fuel assembly has good steady-state thermal characteristics and hard neutron spectrum. The core of the honeycomb coal fuel assembly can realize smaller core size and fuel loading, and has obvious expansion negative feedback, and can effectively flatten the power distribution and reduce the core pressure drop. It is a fuel assembly solution that is conducive to the miniaturization and light weight of lead-bismuth reactors.
BackgroundMachine learning, which has been widely applied to scientific research in recent years, can be used to investigate the inherent correlations within a large number of complex data.PurposeWe evaluate the performances of two types of machine-learning algorithms for correcting nuclear mass models, reconstructing the impact parameter in heavy-ion collisions, and extracting the symmetry energy slope parameter. We also discuss the extrapolation and generalization ability of the machine-learning models.MethodFor correcting the nuclear mass models, 10 characteristic quantities are fed into the LightGBM to mimic the residual between the experimental and the theoretical binding energies. For impact parameter or symmetry energy, two types of observables constructed based on the particle information simulated by using the UrQMD transport model for setting up the different impact parameters or symmetry energy slope parameters are used as inputs to a conventional neural network and the LightGBM to extract the original information.ResultAnalysis of these nuclear physics problems reveals the potential applicability of machine-learning methods.ConclusionsMachine-learning methods can be used to investigate new physical problems, thereby promoting the development of both theory and experiment.
BackgroundThe core corium may melt through the reactor pressure vessel wall then lead to the failure of the second barrier during a serious accident. Core catcher can collect and cool the corium and prevent the development of severe accident.PurposeThis study aims to establish a computational model to explore the cooling process of crucible core catcher adopted by VVER (Vodo-Vodyanoi Energetichesky Reactor) designed by Russia.MethodsAccording to the derived parameters based on VVER core catcher design data, non-isothermal flow calculation module of COMSOL was established to simulate the flow field, temperature field, and crust distribution of corium pool. The solidus temperature and liquidus temperature and the exponential form change of corium viscosity were referred to the research results of VULCANO item.ResultsFor the double layered structure of the corium pool in core catcher, the metal layer solidifies quickly after a core meltdown accident. Constantly changing natural convection flows are formed in the upper and middle part of the oxide layer and the temperature distribution is relatively uniform. No strong convection exists in the lower part of the oxide layer lead to obvious thermal stratification. Most of the corium cooled in the upper part of the oxide layer will transfer to the lower part by gravity and natural convection before full solidification, resulting in a slow increase in the thickness of the upper crust and a rapid increase in the bottom crust of the oxide layer.ConclusionsThe safety margin of crucible core catcher of VVER is sufficient, however the relevant equipment, support and auxiliary system are required to remain operational for a long time to realize the design function.
BackgroundIn a pressurized water reactor (PWR) loss-of-coolant accident (LOCA), high temperature and high internal pressure of the fuel rod can lead to ballooning of fuel rod cladding, which causes a partial blockage of flow area in a subchannel. Such flow blockage would influence the core coolant flow and thus affect the core heat transfer during reflood phase and subsequent severe accidents. However, the commonly used integrated severe accident analysis codes use simple parametric models to simulate these aspects and therefore cannot consider the influence of multiple coupled factors. This results in a lack of accuracy of the simulation results.PurposeThis study aims to analyze the key phenomena in core degradation, and develop a thermal-mechanical (TM) behavior module for assessing the failure of cladding and analyzing the flow blockage.MethodsFirst of all, the fuel rod thermal–mechanical behavior (FRTMB) module developed for analyzing the TM behavior of fuel rods was integrated into the integrated severe accident analysis code (ISAA). Then, on the basis of the FRTMB module, the flow blockage model of the ISAA-FRTMB code was improved to suit for simulating changes in coolant flow rate caused by fuel rod deformation. Finally, the QUENCH-LOCA-0 experiment was simulated by using improved ISAA-FRTMB code to verify the correctness and effectiveness of the model, and the peak cladding temperatures were compared in order to verify the validity of the flow blockage model.ResultsThe results including cladding failure time, circumferential strain, flow blockage rate and cladding temperature predicted by the code are in good agreement with the experimental data. The maximum circumferential strain of the simulated cladding, as indicated by the experimental results, is in the range of 25%?50%, and the errors of the predicted cladding rupture time and temperature are within 4%.ConclusionUnder the stress caused by internal pressure, the cladding deforms outward owing to thermal creep with the increase of temperature. Rapid thermal creep and swelling lead to cladding failure. The maximum circumferential strain of the simulated cladding, as indicated by the experimental results, is in the range of 25%?50%, and the errors of the predicted cladding rupture time and temperature are within 4%. The correctness and effectiveness of FRTMB module are thus verified.
The physics of radioactive nuclear beams is one of the frontiers of nuclear physics. New phenomena and physics appear in exotic nuclei far from the β-stability line. The neutron skin is an exotic phenomena in unstable nuclei and is closely correlated with the properties of the equation of state (EOS) of asymmetric nuclear matter and neutron stars. This study sought to examine previous studies on the effect of the neutron skin on nuclei-nuclei collisions to identify good observables for determining the neutron skin thickness, which could in turn be used to investigate the EOS of asymmetric nuclear matter. Various theoretical models are used to study the effect of neutron skin in nuclei-nuclei collisions. The statistical abrasion-ablation (SAA) and isospin-dependent quantum molecular dynamics (IQMD) models are used to study the neutron abrasion cross-section, neutron/proton ratio, and t/3He ratios. A nuclear structure model is used to investigate the relation between the neutron skin and α-cluster formation, α decay, nuclear surface, and nuclear temperature. Strong correlations have been found between the neutron skin thickness and neutron abrasion cross-section, neutron/proton ratio, and t/3He ratios, photo production, and other quantities. By measuring quantities that have a strong correlation with the neutron skin, the skin thickness can be obtained. The EOS of asymmetric nuclear matter and properties of neutron stars can be studied or constrained by using the obtained neutron skin data. Further investigations are necessary for determining observables that are useful for determining the neutron skin thickness from experimental measurements.
BackgroundThe China Spallation Neutron Source (CSNS) is a multidisciplinary research platform. Its high-energy 1.6 GeV proton beam serves various applications in aerospace devices and particle detector testing. However, certain irradiation applications and high-performance detectors require different beam energies. A degrader was designed to adjust the proton energy to a desired range.PurposeThis study presents a reasonable degrader scheme for the 1.6 GeV proton test beam at the CSNS.MethodsThe physical process of the 1.6 GeV high-energy proton beam passing through a degrader made of either of three different materials (iron, copper, and tungsten) was simulated using FLUKA, a Monte Carlo particle transport code. Parameters such as the degrader thickness, the energy deposition, the outgoing proton beam intensity, and the irradiation dose were determined through simulations. The optimal degrader material was identified. In addition, a continuously adjustable structure of the degrader was given.ResultsIron displays slight advantages in terms of energy deposition and radiation dose distribution, compared to copper and tungsten. Furthermore, the phase-space distribution of the outgoing proton beam and the secondary pion beam were also given, providing important references for future beam-line design.ConclusionAn optimal degrader structure made of iron for the CSNS high-energy proton beam is proposed. The secondary pion test beam is also feasible at the proton test end station. This is a significant development for future engineering design.
Nuclear data, especially neutron nuclear data, forms the foundation of national defense, nuclear energy development, and the applications of nuclear technology. It also plays a critical role in fundamental nuclear physics research. The quality of nuclear data directly impacts the effectiveness, safety, reliability, and economy of related devices and products. Experimental data serves as the foundation for developing theoretical models and nuclear data libraries. Therefore, experimental research holds a paramount position in nuclear data research. The experimental research on nuclear data in China commenced in the mid-1950s and has achieved fruitful results after decades of development. In this article, we provide a brief overview of the progress made in experimental research on nuclear data in China and outline potential future advancements.
BackgroundLow-level radioactive wastewater (LLW) is generated during the operation of nuclear facilities. Usually, LLW is discharged directly into the ocean in the form of liquid effluent after purification under the discharge management limits. However, discharging LLW into inland water bodies is difficult for inland nuclear facilities because of the poor dispersion and the lack of public acceptance. Thus, LLW disposal has become one of the challenges limiting the development of inland nuclear facilities. Liquid-to-gas discharge, which is based on high-pressure spray evaporation technology, is an alternative solution for LLW disposal for inland nuclear facilities.PurposeThis study aims to develop and validate a model for simulating spray flow and evaporation to assess the design feasibility.MethodsA numerical method coupling a two-phase flow model, mass transfer model, and heat transfer model were established to describe droplet evaporation during the flow process. To validate this numerical method, a sample high-pressure spray evaporation system was developed which included three key subsystems: carrier gas generation, source term generation, and measurement systems. Finally, considering evaporation and deposition factors, three experimental cases were designed for experimental comparison of the droplet diameter, number, and deposition rate among these cases.ResultsThe comparison results show that the numerical method is highly consistent with the experimental results, with a maximum uncertainty of 15%.ConclusionsThe numerical model developed in this study can be used for the technological design of liquid-to-gas LLW discharge based on high-pressure spray evaporation technology.
BackgroundFLiBe is commonly used as the coolant and carrier salt in liquid molten salt reactors (MSRs). Its certain moderating properties and thermal neutron scattering attributes affect the neutronic performance of the MSR, and this in turn influences the physical design and safe operation of the reactor. Consequently, studying FLiBe's thermal neutron scattering data is essential for MSRs.PurposeThis study aims to analyze the influence of of FLiBe thermal neutron scattering on neutronic performances of a 65-MW MSR.MethodsFirst, according to the requirements, a core model of a 65-MW MSR was established by using the general Monte Carlo procedure. Then, the neutronics performance of the MSR was calculated by considering the scattering cross-section of the free gas model and FLiBe thermal neutron scattering data (e.g., the neutron spectrum, effective multiplication factor, and nuclide reactivity rate). Finally, the changes in the influence of FLiBe thermal neutron scattering effect on neutronic properties under different energy spectra were compared.ResultsThe computation results show that, by considering the thermal scattering effect of FLiBe molten salt, the neutron energy spectrum in the core of the MSR becomes harder, 235U fission rate decreases, the keff value of the reactor decreases, but the density coefficient in the temperature reaction coefficient of the fuel keeps almost unchanged, and the Doppler coefficient decreases by 0.28×10-5 K-1. With the hardening of the energy spectrum, the variation in the 235U fission rate reduction decreases, and the decrease in keff caused by thermal neutron scattering changs from 9.2×10-4 to 2×10-4.ConclusionsTherefore, it is necessary to incorporate FliBe's thermal neutron scattering data into the physical calculations for the MSR core.
BackgroundBecause of the excellent properties of lead-based materials as reactor coolants, lead-based fast reactors have become a key type of fourth-generation advanced nuclear energy systems. A small passive long-life Lead–bismuth -cooled fast Reactor (SPALLER) is designed by the University of South China for profound research.PurposeThis study aims to improve the inherent safety and cost-effectiveness of lead–bismuth-cooled fast reactors, and determine the maximum core power of this kind of reactor.MethodsFirstly, the SPALLER was taken as research object, and five steady-state limitations and two accident limitations were proposed to meet the transportation size, material durability, and long-term operational stability of the reactor core and ensure safety under accident conditions. Then, a neutronics maximum power calculation platform was built through Latin hypercube sampling and a Kriging proxy model whilst the steady-state limitations were considered as multi-objective optimization problems with complex multidimensional nonlinear constraints. Meanwhile, the neutronics maximum power and natural circulation power of SPALLER-100 at different core heights were calculated by taking the natural circulation ability of SPALLER-100 into account. Finally, a design scheme was obtained to meet the requirements of neutronic and thermal-hydraulic assessments of this reactor while producing maximum power. Consequently, during the full life-cycle of SPALLER-100, a safety analysis of three typical accident scenarios (loss of heat sink, transient over power, and coolant inlet temperature undercooling) was performed using a quasi-static reactivity balance approach.ResultsThe results show that the maximum core power can be increased from 100 MW to 120 MW, and the neutronics maximum power calculation platform has high accuracy with safe and economical maximum power scheme.ConclusionsThis study can provide reference for other types of natural circulation reactors to maximize power output.
BackgroundThe space environment contains numerous high-energy particles, and a single high-energy particle passing through a spacecraft shell bombards the electronic devices within, triggering single-particle effects such as device logic state upset and function failures, which, in turn, affect spacecraft operation reliability and mission accomplishment.PurposeNotably, ground accelerator irradiation tests provide an important and effective means for simulating space single event effects and for predicting the risks of single event effect rates for electronic devices in space applications. Generally, electronic devices can be used in spacecraft only if their resistance radiation indicators meet astronautical application requirements.MethodsSpacecraft are typically exposed to space radiation particles, primarily heavy ions and protons; therefore, single event effect simulation testing for electronic devices relies predominantly on heavy ion and proton accelerators. To address the requirements of single event effect testing, technologies such as large-area beam expansion and homogenization, high-precision beam current diagnosis, and efficient test terminals have been developed to fulfill the requirements of various test tasks.ResultsParticular focus is placed on the CIAE's (China Institute of Atomic Energy) heavy ion single event and proton single event effect simulation test techniques and the heavy ion microbeam technique for radiation sensitive area identification for electronic devices. Subsequently, the aforementioned techniques are applied to a single event effect risk evaluation for astronautical electronic devices.ConclusionsIn the future, the demand for radiation-resistant devices is expected to continue to increase in the aerospace, nuclear industry, and other radiation application fields. It is, therefore, necessary to further exploit the irradiation potential of existing domestic single event effect simulation equipment and establish new accelerator platforms with improved capacity for single event effect simulation testing.
Large volumes of water containing tritium are generated during the operation, decommissioning, and incident-management of nuclear installations and related facilities, and are expected to increase with the ongoing expansion of nuclear power generation. If released into the environment, this water could pose a substantial environmental threat to living organisms. However, conventional isotope separation techniques, such as cryogenic distillation and catalytic exchange, are inadequate for efficiently isolating significant quantities of low-level tritiated water because of the complex machinery and excessive energy required, and the potential for hydrogen-gas detonation. In contrast, water distillation (WD), as a traditional technology, has the unique advantages of simple operation, no corrosive and toxic substances, and no hydrogen explosion risk, but problems of small separation coefficient and low efficiency always exist in this technique. However, the separation effect of WD can be effectively improved by improving the process variables in the process of WD, such as temperature, distillation column diameter, and packing dimensions, so as to adapt WD to the separation of industrial tritiated water. This study provides a thorough exposition of the basic principles and distinctive features of water distillation and examines the effect of various operational parameters on separation efficiency to adapt the process for the industrial separation of tritiated water. The impact of various process variables on the separation efficiency of tritiated water via distillation was investigated, and results show that optimizing these variables can markedly improve the separation efficiency of water distillation. In particular, decreasing the dimensions of the packing material or altering its properties can lead to higher separation factors and lower residual tritiated water concentration. These findings suggest that water distillation can be used for the separation of tritiated water. By optimizing its operational parameters, water distillation can become a viable method for the industrial separation of tritiated water and is expected to play a significant role in this field in the future.
BackgroundElliptic flow (v2) is one of the most important observations for exploring the properties of nuclear matter using heavy-ion collisions. v2 is not only affected by dynamic processes but is also related to the Fermi momentum of the initial nucleus.PurposeThis study aims to quantitatively determine the effect of the initial Fermi momentum on the time evolution of v2.MethodsFirst, based on the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model, gold-gold (Au+Au) collisions at beam energies of 0.4A GeV and 0.8A GeV with impact parameter b = 6 fm were simulated. In the initial stage, three cases were considered: without Fermi momentum, with Fermi momentum, and with half-Fermi momentum. Then, by reverse tracing the nucleons that were emitted at mid-rapidity (|y0|<0.1) throughout the reaction process, the time evolution of v2 for these traced nucleons was investigated in detail. Finally, the influence of the initial Fermi momentum on v2 of the nucleons in the mid-rapidity region in heavy-ion collisions at intermediate energies was examined.ResultsThe yield of free nucleons calculated by considering the Fermi momentum was much larger than that obtained without the Fermi momentum, owing to the reduction in nucleon-nucleon collisions. However, v2 shows the opposite effect; it is obtained by considering that the Fermi momentum is much smaller than that in the latter case because of the stronger blocking effect of the spectator nucleons.ConclusionsOur results indicate that the initialization of the nucleon momentum must be carefully considered in the transport model.
With the rapid development of radioactive-ion-beam facilities worldwide, many exotic nuclear phenomena have been observed or predicted in nuclei far from the β-stability line or close to the neutron (proton) drip lines, such as halos in atomic nuclei and shape decoupling in deformed halo nuclei. The study of exotic nuclear phenomena, including halos, is at the frontier of current nuclear physics research. The covariant density functional theory (CDFT) is one of the most successful models in nuclear physics. The CDFT has been widely used to study structures and properties of exotic nuclei. The deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) has been developed and achieved a self-consistent description of deformed halo nuclei by including deformation and continuum effects, with the deformed relativistic Hartree-Bogoliubov equations solved in the Dirac Woods-Saxon basis. The DRHBc theory has been used to predict the deformed halo structure in 44Mg and the shape decoupling between the core and halo. The theory has also been used to address unresolved problems concerning the radius and configuration of valence neutrons in 22C, deformed halos in carbon and boron isotopes, particles in the classically forbidden regions in magnesium isotopes, and other similar phenomena. The rotational excitation of deformed halos has been investigated by implementing an angular momentum projection based on the DRHBc theory. This investigation has shown that the effects of deformed halos and shape decoupling are also present in the low-lying rotational excitation states of deformed halo nuclei.
BackgroundThe metallic materials utilized for nuclear reactors undergo corosion due to the inherient high-temperature and high-pressure environment. Consequently, the corrosion products may be deposited in the core, called crud, and impact the fuel operation, core reactivity, and primary radioactivity, such as crud-induced localized corrosion or crud-induced power shift.PurposeThus, this study aimed to establish a model that can quantitatively analyze these corrosion products, the results of which can then be used to evaluate the impact of these products.MethodsBased on the corrosion and release dynamic theory, combined with the assumption of metallic oxide volume ratio (Pilling-Bedworth Ratio), a corrosion and release model of metallic materials was developed. The model was validated based on experimental data from Inconel 690.ResultsThe verification result indicates that the proposed model is reasonable and scientific, and hence can be used to quantify the amount of main corrosion and release products of metallic materials for nuclear reactors.ConclusionsThis study provides a model of the main elements of corrosion products including Ni and Fe ferrite for PWR plants, which can be used for evaluating the impact of corrosion products. However, some of the microelements of corrosion cannot be quantified by using this model as the corresponding equations were over-determined. Hence this aspect requires further research in the future.
BackgroundNuclear high-temperature resistant ceramic materials have been widely used in nuclear energy, military, and aerospace fields in recent years owing to their excellent thermal insulation and high-temperature oxidation resistance.PurposeThis study aims to investigate the mass and heat transfer process between plasma fluid and flying particles in supersonic plasma spraying during the preparation of yttrium-stabilized zirconia thermal barrier coatings, so as to reveal the process parameters of flying particles.MethodsFirstly, the computational fluid dynamics (CFD) approach was employed to simulate the interaction between flying particles in the plasma spraying process. Then, a three-dimensional mathematical model of the plasma spraying flow field was established, and the jet characteristics of different spraying parameters in the de Laval nozzle and the melting and stress state of flying particles were analyzed by using this model. Furthermore, the online monitoring device Spray Watch 2i (Osier, Finland) was used to compare the online measurement of the velocity and temperature of flying particles obtained with the simulation results.ResultsThe comparison results show that relative errors are within 15%, verifying the simulation results effectively by experimental results. When the spraying power is reduced from 71 kW to 36 kW (i.e., reduced by 49.2%), the maximum velocity of the plasma jet is reduced by 8.5%, and the maximum temperature is reduced by 22.2%.ConclusionsA correlation between plasma spraying parameters, jet characteristics, and melting of flying particles is revealed in this study, providing theoretical guidance for the precise control of high-performance thermal insulation coating structures required for accident resistant fuel cladding in nuclear reactions.
BackgroundRecently, global concerns regarding the illicit transportation and trafficking of nuclear materials and other radioactive sources have increased, leading to increased demands for efficient and rapid security and non-proliferation technologies. The International Atomic Energy Agency's Incident and Trafficking Database has reported 3 235 confirmed incidents involving nuclear and other radioactive materials out of regulatory control from 1993 to 2017. Of these incidents, 278 are associated with trafficking or malicious use of materials such as highly enriched uranium, plutonium, and plutonium-beryllium neutron sources. Therefore, developing depth-of-interaction detector for neutrons and gamma rays is important for effective control of nuclear and radiation materials at national and international cross points such as borders, ports, and airports.PurposeThis study aims to design a depth-of-interaction detector for neutrons and gamma rays and characterize its performance.MethodsHereby, an EJ276 plastic scintillator (Φ3 cm× 15 cm) coupled with two silicon photomultipliers (SiPMs) in both sides was designed as a depth-of-interaction detector for neutrons and gamma rays. The short gate time was optimized to achieve better neutron/gamma-ray discrimination, and the reaction position was determined based on the amplitude ratio and time of flight (TOF) difference between signals from two sides. Finally, Am-Be neutron source and 137Cs γ source were applied to detector parameter optimization and resolution calibration for performance characterization.ResultsExperimental results demonstrate that good consistency in the detection efficiency of the detector at different incident positions, where the resolution of the one-dimensional reaction position is approximately 4.4 cm.ConclusionsThe designed depth-of-interaction detector can be used toreplace detector arrays in neutron scatter cameras and coded-aperture imagers to reduce costs and system complexity.
We developed a Gamow shell model based on first principles and successfully applied it to the nuclei around driplines. Herein, we review the theoretical and technical developments of this method. Starting from the realistic nuclear forces, the model uses the Berggren basis, which contains bound, resonant, and scattering continuum states. Therefore, the Gamow shell model can handle the coupling to the continuum. In the complex-momentum plane, we used many-body perturbation theory (i.e., so-called Q^-box folded diagrams) to derive the Hamiltonian for the valence space. Subsequently, the shell-model calculations, which included the resonance and continuum effects, were performed. Therefore, such ab initio calculations can describe the weakly bound properties of nuclei near driplines and unbound resonance properties of nuclei beyond driplines. In this study, the symmetry breaking between oxygen isotopes and their mirror nuclei is discussed, and the important continuum effects on the excitation spectra of neutron-rich carbon isotopes are analyzed.
BackgroundThe medical isotope production aqueous reactor (MIPR) has advantages of small size, low power, and high inherent safety, hence is one of better candidate reactor types for the production of 99Mo and other medical isotopes.PurposeThis study aims at the effects of extraction methods and reprocessing capacity on the production efficiency of 99Mo based on low-enriched uranium MIPR designed with neutronic optimization.MethodsFirst, the calculation method was verified according to existing experimental data, and the neutronic optimization of the MIPR was performed for core design by using SCALE6.1 code and ENDF/B-VII database with 238 groups. Then, the 99Mo production efficiency under different extraction methods as well as processing capacities was investigated based on the optimized core structure. The range of achievable critical uranium concentration and enrichment was determined.ResultsThere is a minimum critical mass under different enrichment, and with the increase of 235U enrichment, the uranium concentration at the minimum critical uranium mass decreases. The effective multiplication factor decreases linearly with an increase in nitric acid concentration, and the corresponding nitric acid reactivity coefficient is approximately -1.400×10-2 L·mol-1. With an increase in uranium concentration, the void and temperature reactivity coefficients decrease, and the corresponding reactivity coefficients are approximately (-100~-250)×10-3 ℃-1 and (-18~-30)×10-5 ℃-1.ConclusionThe production efficiency of the MIPR production of the 99Mo online extraction method is slightly greater than that of the offline batch processing method with an increment of about 16% under a five-day production cycle. The reprocessing capability has a greater impact on the production efficiency of the online extraction method. If the reprocessing rate is increased five times, the increment of production efficiency is about 113% under a five-day production cycle.
Academician ZHANG Huanqiao is an outstanding scientist cultivated by the new China in the 1950s. The impoverished and weak war environment of the old China and the hardship era of the new China have nurtured his patriotic determination to serve his motherland. He adhered to the frontline of scientific research and devoted himself wholeheartedly to it. His research fields spanned neutron physics, fission physics and heavy-ion nuclear physics, and he has achieved excellent results under difficult conditions. He committed himself to the country and measured the urgently needed nuclear data to cooperate with nuclear weapon development. He is rigorous and realistic, and repeatedly verifies the experimental results to ensure accuracy. He dares to take the lead and constantly delves into new research fields. All his actions reflect a silent loyalty and love for his motherland and science. He is an inheritor and speaker of the older generation scientists' spirit, and a microcosm of the scientist's spirit and the development of science and technology in the new China. We write this article for sharing on the occasion of academician ZHANG Huanqiao's 90th birthday.
BackgroundThe calculation error of the stacked pulse amplitude generated by traditional pulse shaping methods leads to distortion in the X-ray fluorescence spectrum; thus, it is difficult to accurately analyze the spectrum measured in a high-stacking rate background.PurposeThis study aims to propose a transformer model based on deep learning for the pulse amplitude estimation of radiation measurements using high-performance silicon drift detectors.MethodsFirstly, multi-head attention was applied to the transformer model, and an encoder-decoder structure with embedded positional encoding was employed to estimate the amplitude of stacked pulses. Then, a predefined mathematical model was used to simulate the pulse signal output by the detector for model training, and Gaussian noise corresponding to thermal noise and shot noise was added to the signal to simulate real nuclear pulses. Finally, experimental verifications were carried out on powdered iron ore samples and powdered rock samples, and relative error, corresponding to the accuracy of pulse amplitude estimation, was used as a model performance evaluation indicator.Results & ConclusionsExperimental verification results show that the average relative error obtained for eight offline pulse sequences of powdered iron ore samples and powdered rock samples is 0.89%, which means that the model can accurately estimate the amplitude of stacked pulses.
The HI-13 tandem accelerator, located at the Beijing Tandem Accelerator National Laboratory, has been in operation for 35 years. To ensure the continued performance of the accelerator, the operation and maintenance team has prioritized focus on various aspects. The operation team conducted research that involved developing key components, cultivating a high-quality operational team, improving the machine time efficiency, and increasing the participation of users outside the China Institute of Atomic Energy (CIAE). The primary emphasis has been on developing key components and upgrading subsystems. These efforts have successfully maintained and improved the accelerator's performance, ensuring its safe and stable operation. Finally, the paper alse discusses the challenges faced by tandem accelerators and presents future development plans.
Cluster structures can be stable in the interior of atomic nuclei. The study of α-cluster structure of atomic nuclei and its effects are important topics in nuclear physics as well as astrophysics. In the past few decades, cluster structure effects in atomic nuclei have been much studied for heavy-ion nuclear reactions. This paper summarizes the authors' studies on the α-cluster structure effects on nuclei in nuclear reactions and relativistic heavy-ion collisions. For example, the cluster structure of atomic nuclei has been studied through giant resonances of atomic nuclei. The cluster structure of the nucleus is studied through the emission and correlation of particles (including neutrons, protons, and photons) in nuclear reactions and through collective flows. We extend the cluster effect of atomic nuclei to relativistic heavy-ion collisions, e.g., to the study of collective flows and their rise and fall, the HBT (Hanbury Brown and Twiss) correlation, multiplicity correlations, the dihadron azimuthal correlation, and electromagnetic fields.
BackgroundThe performance of solid oxide fuel cells (SOFCs) can be promoted by optimizing cathode materials.PurposeThis study aims to boost the electrochemical performances of cathodes for SOFCs by doping transition metal at the B-site of double perovskite.MethodsFirstly, a series of B-site doped PrBa0.8Ca0.2Co2O5+δ(PBCC) oxides as cathodes for SOFCs were prepared by sol-gel. The effects of B-site doped content and doped elements on the crystalline structure of the cathodes were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Then, the trends of conductivity and thermal expansion coefficient with B-site doped PBCC oxides were investigated. Finally, the electrochemical performances of cathodes with different B-site doped PBCC oxides were tested to find optimal doping element type and content.ResultsTest results show that polarization is reduced and the electrochemical catalytic activity is improved when 5 mol% of Fe is doped on the B-site of the PBCC cathode. Compared to the PBCC cathode, the max power density of the full cell with a 5-mol% Fe-doped cathode increases from 988 mW?cm-2 to 1 259 mW?cm-2 at 700 ℃.ConclusionsThe electrochemical performances of SOFCs can be boosted by modifying the B-site of double perovskite using transition metal.
BackgroundDynamic micro-computed tomography (micro-CT) using monochromatic X-ray offers higher density resolution and lower radiation damage compared to that using white X-ray, however balancing its imaging spatial and temporal resolution is challenging. Currently, the reported highest temporal resolution of monochromatic X-ray dynamic micro-CT is 13.3 Hz with a detector effective pixel size of 5 μm.PurposeThis study aims to develop a monochromatic X-ray dynamic micro-CT system with a higher spatial and temporal resolution to meet the experimental needs of the fast X-ray imaging beamline (BL16U2) users at Shanghai Synchrotron Radiation Facility (SSRF).MethodsFirstly, an experimental system of dynamic micro-CT with the high flux density monochromatic X-ray from an undulator source was established by combination of a high-speed rotary stage and a large numerical aperture triple-lens fast X-ray imaging detection system on the BL16U2 beamline at SSRF. Then, a demonstration experiment with a fast-foaming polyurethane material as a sample was performed to examine the spatial-temporal resolution of this experimental system, moreover a quantitative analysis of the bubble motion during foaming process was performed.ResultsExperimental results of foaming process of the fast-foaming polyurethane material based on the monochromatic X-ray dynamic micro-CT system show that a temporal resolution of 20 Hz of the dynamic micro-CT was achieved with 15 keV monochromatic X-ray and an effective detector pixel size of 2.2 μm.ConclusionsThe developed monochromatic X-ray dynamic micro-CT system has a high spatial-temporal resolution and can perform four-dimensional quantitative analysis of complex motion systems, providing a powerful experimental research platform for users of BL16U2 beamline at SSRF.
BackgroundMolten salt reactors, one of the important types of fourth-generation advanced reactors, use high-boiling-point molten salt as a nuclear fuel carrier after melting, hence have the characteristics of high-temperature output and normal-pressure operation. A heat-pipe molten salt reactor based on thermoelectric power generation has the advantages of its components, that is, high output temperature, high thermoelectric conversion efficiency, simple structure, safety, and reliability. Therefore, the reactor of heat-pipe molten salt has significant advantages in the field of energy systems as it is an ideal energy source for outer space and deep-sea exploration missions. However, because of the low thermal conductivity of the molten salt in the core, the dense arrangement of heat pipes complicates the heat transfer design of the thermal power generator in the condensing section of the heat pipes.PurposeThis study aims to design a heat-pipe–thermal power generation coupling system structure suitable for molten salt reactors, and analyze its heat transfer characteristics on the basis of design requirements of the reactor.MethodsFirstly, the condensing section of the core heat pipe was designed using a tower thermoelectric power generation system. A thermoelectric generator was placed between the outer wall of the hot-side tower and the inner wall of the cold-side tower, and the gap between the generators was made of an insulating material to reduce heat leakage. Then, a heat transfer simulation of a four-layer tower thermoelectric power generation system suitable for a heat-pipe molten salt reactor was performed using the ANSYS Workbench. Finally, temperature distribution and variation under different power values at each layer of the thermoelectric generator and every thermoelectric generator, etc., were analyzed.ResultsThe analysis results reveal that, when the system is running with maximum heat-pipe temperature of 696 ℃, the temperature distribution in the overall tower is uniform, the effective heat utilization rate is >96%, the system leakage heat is <4%, and the temperature difference between the two sides of the generator is >490 ℃, which is conducive for improving the thermoelectric conversion efficiency.ConclusionsThe structural design of this study is feasible and conducive for promoting the application of thermoelectric power generation in a heat-pipe molten salt reactor.
BackgroundAccelerator-driven subcritical systems (ADS) are among the most promising options for next-generation nuclear power systems. Various radionuclides are produced during the process of protons bombarding the target in the ADS, and the cross-sections of various long-lived radionuclides have not been accurately measured. These long-lived nuclides are related to ADS radioactive waste treatment, therefore, accurate evaluation of long-lived radionuclides generated in ADS spallation targets is a key topic in applied research.PurposeThis study aims to determinate production cross-sections of natPb(p,x)207Bi and natPb(p,x)194Hg reactions according to measurement data, and compare them with existing experimental and theoretical results.MethodsThe proton activation method was employed to effectively estimate the cross section of long-lived nuclides produced by the interaction between protons and spallation target materials. Four proton-irradiated natural lead samples were irradiated with protons at energies of 40 MeV, 70 MeV, 100 MeV, and 400 MeV for 90 min, 75 min, 40 min, and 25 min, respectively. After cooling for approximately 20 a, the samples were measured using an ultralow background gamma spectrometer GeTHU in the China Jinping Underground Laboratory (CJPL), and the GeTHU detection efficiency was calculated using the Simulation and Analysis for Germanium Experiments (SAGE) simulation framework. Combined with the irradiation parameters of the samples, the total production cross-sections of the two nuclides were calculated using a cross-section calculation formula. Experimental results are evaluated and compared with those of existing studies.ResultsThe production cross-sections of natPb(p,x)207Bi reaction in the natural lead samples irradiated by protons with four different energies (40 MeV, 70 MeV, 100 MeV and 400 MeV) are calculated as (40.70±3.59) mb, (19.31±1.43) mb, (13.15±0.96) mb, and (2.90±0.22) mb, respectively. The calculated production cross-section of natPb(p,x)194Hg reaction in the natural lead sample irradiated by protons with an energy of 400 MeV is (57.07±7.83) mb. Based on the same samples, the measurement results of cross-section remain consistent within the error range. The cross-sections of natPb(p, x)207Bi are closer to TENDL's evaluated cross-sections. The cross-section of natPb(p, x)194Hg is consistent with the theoretical expectation of INCL++/ABLA. In addition, different sources that contribute to the total uncertainty of both reactions are explained in detail.ConclusionsThe production cross-sections of natPb(p,x)207Bi and natPb(p,x)194Hg reactions measured herein were calculated independently and showed good agreement with existing results. These results demonstrate that GeTHU is capable of measuring low-activity and long-lived radionuclides in the CJPL. Finally, the results of this study also provide the latest experimental evidence for the evaluation of radioactive waste in ADS.
BackgroundComplete kinematic measurements in the medium or high-energy region is a common experimental method to study the structure and properties of exotic nuclides on the neutron-rich side. The experiment setup in the Cooling Storage Ring - Radioactive Ion Beam Line in Lanzhou (CSR-RIBLLII), a typical nuclear external target facility, comprises many detectors with different requirements. The anticoincidence (Veto) detector is an essential part of the external target facility for eliminating the interference of charged particles and measuring medium or high-energy neutrons with high reliability and performance by combining them with a neutron wall detector. The original Veto detector with photomultiplier (PMT) readouts has many disadvantages, such as low detection efficiency and poor uniformity, resulting in significant differences or contradictions between experimental and calculation results.PurposeThis study aims to upgrade the original Veto detector using wave length shifter fiber (WLS) and silicon photomultiplier (SiPM) to improve the detection efficiency of charged particles.MethodsFirstly, a new configuration for the anticoincidence Veto detector unit was designed and the detector thickness was increased by 5 mm compared to the previous Veto detector, resulting in a final thickness of 1 cm. The Veto detector was embedded with 15, 7, and 3 WLS fibers from both ends, and read using SiPM. Furthermore, to systematically explore the performance of the detector unit, a linear relationship was calibrated between the number of photons of the SiPMs and the number of Analog-to-Digital Converter (ADC) channels. This relationship was used to accurately calculate the threshold value, laying a foundation for calculating detection efficiency. Then, based on Multi-Wire Proportional Chamber (MWPC), a detection efficiency test platform was established, and time position conversion and track selection data analysis methods were developed as test methods. Finally, a detailed test on the whole and each part of the anticoincidence Veto detector unit was carried out on the MWPC test platform.ResultsTest results show the highest anticoincidence efficiencies of SiPMs at both ends for the Veto detector embedded with 15, 7, and 3 WLS fibers are 99.99%, 99.94%, and 99.82%, respectively; increased by over 22.74% compared with the original Veto detector.ConclusionsThe new Veto detector based on WLS fiber and SiPM readout meets the needs of the CSR-RIBLLII external target facility.
BackgroundThe triple-to-double coincidence ratio-?erenkov (TDCR-?erenkov) method can be applied to the activity measurement of radionuclides by detecting the ?erenkov photons produced in a non-scintillation solution. The computation of the detection efficiency of this method is based on the premise that the energy of emitted β is completely deposited in the solution. However, this precondition is ideal and does not apply to the actual measurement because of the counting loss caused by the restrictions of a finite solution and the wall of the counting vial (i.e., wall effect).PurposeThis study aims to analyze the influence of the wall effect on the computation of detection efficiency.MethodsThe transport process of emitted β from the solution to the vial wall was analyzed in sections. Thereby the relationship between the number of ?erenkov photons and the deposition energy spectra of emitted β with different energies in different matrices was obtained. This relationship was used to further improve the calculation model of the TDCR-?erenkov method. Subsequently, the calculation model was simplified to reduce the required time. Geant4 calculated the deposition spectra of emitted β in different matrices, subsequently, the efficiency of different nuclides was calculated using curves of the number of ?erenkov photons vs. the energy of the emitted β. To verify the accuracy of the improved calculation model, measurements were carried out on a variety of pure β-emitters.ResultsThe results derived from the improved TDCR-?erenkov method are in good agreement with those of the TDCR-LS method. Especially for high energy β-emitters, the relative deviation of the results between the TDCR-?erenkov and TDCR-LS methods is reduced from 0.47% for the original method to 0.02% (90Y), and 0.64% to -0.16% (32P).ConclusionsThe TDCR-?erenkov method is more accurate when considering the wall effect in the activity measurement of high-energy β-emitters.
BackgroundLost radioactive sources needs to be quickly retrieved, positioning of radioactive source in complex environment is the key to find the lost radioactive source. [Propose] This study aims to develope a novel approach for the rapid positioning of orphan sources using a NaI(Tl) array detection device.MethodFirst of all, by leveraging the shadow effect between array detectors, a response curve between gamma-ray incidence angles and counts was obtained through the use of Monte Carlo simulation software. Then, the support vector machine (SVM) method was employed to establish a predictive mathematical model for the counting rate of array detectors as a function of gamma-ray incidence angle, utilizing. Finally, a radioactive source localization physical experiment platform was constructed, and a series of incidence angle response experiments were conducted for the validation of this approach applied to radioactive source localization under varying conditions.ResultsEexperimental results demonstrate that, through the use of the SVM regression prediction model, the maximum average deviation of the angle is 9.21° whilst the minimum is 1.77° for the angle prediction of an orphan 137Cs point source.ConclusionsThis method can achieve rapid and accurate localization of an orphan radioactive source.
Neutron depth profiling (NDP) offers unique advantages in the measurement of element depth distributions, characterized by its high sensitivity and non-destructive nature. This article presents an overview of the principles and data processing methods employed in NDP technology, followed by a comprehensive comparison of various NDP devices and their corresponding parameters on a global scale. Furthermore, potential avenues for upgrades of NDP devices are explored. Given the remarkable sensitivity and non-destructive attributes of NDP technology in detecting 6Li, it proves particularly well-suited for in-situ measurements in lithium batteries, rendering it an invaluable tool for research in this field. The article underscores the application of NDP in lithium battery research whilst its utilization in high-temperature alloys, semiconductor materials, and nuclear materials is introduced as well.
With experimental facilities being developed globally, producing superheavy nuclei using heavy-ion collision has become feasible, which is essential for exploring charge and mass limits of nuclei and understanding the r-process in nuclear astrophysics. Fusion reactions are crucial for the synthesis of superheavy nuclei, yet only neutron-deficient superheavy nuclei get produced due to the limited neutron number of stable beams. Recent experiments suggest that multinucleon transfer reactions are promising for producing new neutron-rich superheavy nuclei. As a result, transport models are required for extracting physics information from these experiments and making predictions about incident energies and projectile-target combinations, to synthesize new super-heavy nuclei. In this article, we introduce the development of transport models such as the dinuclear system (DNS) model, quantum molecular dynamics (QMD) type model, Boltzmann type model, and Time-dependent Hatree-Fock (TDHF) type model, and conclude with their latest applications in the synthesis of superheavy nuclei, especially in fusion reactions and multinucleon transfer reactions. In addition, various international large-scale scientific facilities, as well as their scientific objectives, and future plans, are also summarized.
BackgroundNuclear science and technology are closely related to the lives of people. However, nuclear radiation may harm the health of the general public; hence, nuclear radiation monitoring must be strengthened. A wired nuclear radiation monitoring system has the characteristics of complex wiring, a long construction period, high cost, poor mobility, and more difficult troubleshooting.PurposeThis study aims to address the demand for convenient measurement and monitoring of gamma radiation fields.MethodsBased on the LoRa wireless communication technology, a γ radiation monitoring system using silicon photomultiplier (SiPM) tube-scintillator detector was designed. The main functions of the system included data collection from the detector, data processing and transmission using a STM32 single-core processor. The collected data packaging and transmission were processed in STM32 microcontroller using the LoRa wireless communication module. Considering the possible channel congestion in the monitoring system and the frequent data transmission, a dynamic optimal path communication algorithm was designed to find the optimal reconnection path and realize the priority allocation of data transmission.Results & ConclusionsThe test results show that the data transmission stability of γ radiation monitoring system based on LoRa is higher than 99.57%, and has the advantages of flexible networking, a further distance of transmission, low cost, and substantial expansion, hence has a broad reference prospect.
BackgroundIn the international fourth-generation nuclear power system, the lead-bismuth fast reactor is one of the most concerned technologies. However, insoluble particulate matter generated in the flow of liquid lead-bismuth alloys will collect locally in the flow channel and affect the operation of lead-bismuth fast reactors.PurposeThis study aims to find the motion deposition of particulate matter in the flow channel, understand its influence on the safe operation of small lead-bismuth fast reactors, and provide a reference for the safe design of lead-bismuth reactors.MethodsFirstly, based on the design scheme of 100 MWth small natural circulation lead cooled fast reactor SNCLFR-100, the particle deposition in the rod bundle channels that were divided into three types according to the relative position and wall conditions: triangle like channels, pentagon like channels and trapezoid like channels, was numerically simulated using ANSYS software, and the particle deposition movement was obtained. Then, the effects of particle type, particle size and particle velocity on particle deposition were obtained on the basis of grey correlation degree theory. Finally, the correlation degree of various factors affecting particle deposition rate was analyzed.ResultsThe results show that the particle deposition mainly occurs at the inlet stage,the surface of the inlet section is large area adhesion deposition,and the surface of the middle and rear sections is point-like deposition. With the increase of axial distance, the magnitude of turbulent kinetic energy is the main factor affecting the radial distribution of particulate matter. The increase of particle density and particle size will strengthen the deposition of particulate matter. The increase of particle velocity will reduce the particle deposition. The degree of influence on particle deposition is particle size>type> particle velocity.ConclusionsDuring the operation of lead-bismuth fast reactor, attention should be paid to the deposition of particles in the inlet section and to remove the particles with larger particle size.
BackgroundCurrently, the destructive puncture manometry method is used to measure helium pressure inside fuel rods. However, this method is expensive and does not guarantee 100% coverage. Hence the non-destructive testing (NDT) equipment is introduced for non-destructive measurement of helium pressure inside fuel rods.PurposeThis study aims to analyze the reliability of NDT testing method for the measurement of helium pressure inside fuel rods.MethodsThree standard rods with helium pressure values of 0.98 MPa, 1.76 MPa, 2.45 MPa, respectively, were selected for experimental test. The experimental fuel rods were first used to obtain the results comparison of heat transfer method and puncture manometry, then the control variates were employed to control the fuel rod temperature, the time interval of a single measurement, and the ambient temperature respectively, so as to determine influencing factors in the NDT method. Finally, reliability analysis of NDT method was performed according to experimental results.ResultsThe results of the NDT method are consistent with that of the puncture manometry method at a temperature range of 24~30 oC with less than 0.05 MPa deviation. Minimum repeat measurement time interval for NDT measuring helium pressure of the same standard rod or fuel rod is 2 min.ConclusionsThe NDT method for measuring the helium pressure of fuel rods is reliable, and the measurement results are stable in different environmental conditions.
BackgroundThe annular fuel has a closely arranged structure, and the coolant flow at both the gap between the stringers and the near wall surface is small, which is unfavorable to the coolant mixing between the subchannels and the uniform circumferential temperature distribution.PurposeThis study aims to explore the effect of the ratio of gate spacing to gate diameter on the distribution of temperature along the circumference direction.MethodsBased on the software code ANSYS FLUENT, a computational fluid dynamics (CFD) analysis model for annular fuel assemblies was established. Then, the calculations in hydromechanics and the numerical simulation using operating parameters of typical pressurized water reactor (PWR) were performed to analyze the coolant flow and heat transfer characteristic when the annular fuels in square or hexagonal arrangement under different grid ratios. The circumferential non-uniformity of annular fuel outer temperature distribution was investigated under circumstances of various pitch-to-diameter ratio.ResultsComputational results show that an appropriate increase of grid ratio is beneficial to the uniform circumferential temperature distribution of stringers. The appropriate grid ratio of square component is between 1.07 and 1.09, and the non-uniformity of circumferential temperature distribution of triangle component is slightly lower than that of square component. Therefore, the appropriate grid ratio is between 1.06 and 1.09.ConclusionsThe temperature distribution at the bar gap is improved most obviously by increasing the grid ratio and the improvement in the near surface takes the second. The results of this study provide a reference for the subsequent optimization design of the grid ratio of annular fuel.
During the neutron detection process, owing to the effects of inelastic scattering and slow neutron capture, a neutron-gamma mixed radiation field is formed, which increases the complexity of neutron detection. Organic scintillators are widely used in neutron detection because of their high flashing efficiency, short decay time, and high detection efficiency. Pulse shape discrimination (PSD) is a key technology for discriminating neutrons and gamma rays according to the difference in pulse shape caused by the difference in particle decay time in organic scintillators. Traditional PSD methods include time-domain and frequency-domain discrimination methods. In recent years, various machine-learning techniques applied to neutron-gamma discrimination have achieved better results. To better use organic scintillators and the corresponding neutron-gamma discrimination methods in neutron detection, we conducted a comprehensive analysis of the glowing mechanism of organic scintillators, PSD principle, organic scintillator types, and neutron-gamma discrimination methods and investigated the performance evaluation indexes of organic scintillators and neutron-gamma discrimination methods. Finally, the future development directions of organic scintillators and neutron-gamma discrimination methods were examined.
BackgroundDiamond material demonstrates excellent temperature and radiation resistance properties, and detectors made from diamond exhibit good potential for use under harsh environments.PurposeThis study aims to analyze the structure and working principle of diamond thermal neutron detectors, and establish a physical model of such a detector applied to 2 MW thorium molten salt experimental reactor-liquid fueled (TMSR-LF1) radiation field by using MCNP program.MethodsFirst of all, 6Li and 10B were selected as neutron conversion materials considering the neutrons of TMSR-LF1 mainly concentrated in the 10-8~10-6 MeV energy range, and the Stopping and the Range of the Ions in Matter (SRIM) program was employed to calculate the range of secondary charged particles generated by the reaction in the neutron conversion layer and diamond layer. Then, the MCNP program was used to establish a physical model of diamond neutron detector applied to 2 MW TMSR-LF1 radiation field. Finally, the effects of the neutron conversion layer thickness (6LiF, 10B), diamond thickness, and γ screening threshold on the neutron detection efficiency, γ detection efficiency, and n/γ suppression ratio of the detector were determined through simulation results.ResultsThe results reveals that 6LiF is more suitable than 10B for use in the neutron conversion layer in neutron and γ mixed fields. With the increase of the 6LiF thickness, the neutron detection efficiency first increases and then decreases, and the optimal thickness of 6LiF is 25 μm. The n/γ discrimination performance of the detector deteriorates with the increase of diamond thickness, but the diamond thickness must be greater than 20 μm to ensure insensitivity of the detector to γ, hence a γ screening threshold is needed to prevent excessive γ interference for thick diamond layers.ConclusionThe influence of detector structural parameters on detector performance obtained by this study has guiding significance for the subsequent fabrication of and research on such detectors.
BackgroundThe extraction of uranium (U) and its alternative resources, such as thorium (Th) and plutonium (Pu), from seawater is essential to address the scarcity of terrestrial U resources. The development of a separation material with high adsorption properties is the key to solving this problem.PurposeThis study aims to reveal the adsorption behavior of actinides (U, Th, and Pu) on the surface of a two-dimensional metal material, antimonene.MethodsThe Hubbard U values, Ueff, were determined for the on-site Coulomb interactions of 5f electrons of U and Pu atoms using the linear response method. Furthermore, the adsorption energy, adsorption configuration, electronic structures, charge transfer, and highest occupied molecular orbital wavefunction of a U, Th, or Pu atom adsorbed on the surface of monolayer antimonene were analyzed using the DFT+U approximation. The variation of the adsorption rate with temperature was further calculated by the equilibrium adsorption rate equation.ResultsThe calculated Ueff values of U and Pu atoms are 2.24 eV and 2.84 eV, respectively. The Pu atom is energetically unfavorable to be adsorbed on antimonene (with a negative adsorption energy for each adsorption site), whereas the U and Th atoms exhibit strong chemical adsorption on its surface. Antimonene also offers abundant surficial stable adsorption sites for the U and Th adatoms. The most energetically stable sites for the U and Th adatoms are the B (Bridge)-H (Hollow) site and H (Hollow) site, with adsorption energies of 4.40 eV and 3.62 eV, respectively. The impurity states are generated in the band gap of antimonene upon the adsorption of the U or Th atom, and the strong p-d coupling between the U or Th adatom and antimonene in the impurity states contributes to the strong adsorption of the adatoms. The desorption temperatures of U and Th on the surface of antimonene reach 837 K and 660 K, respectively.ConclusionsThe results indicate that antimonene is an excellent two-dimensional adsorbent material for U and Th and has potential for several applications such as in the extraction of actinides from seawater.
BackgroundTraditional X-ray fluorescence spectrum analysis has the limitations of poor accuracy of the characteristic peak counting rate and shadow peak.PurposeThis study aims to propose a long and short term memory (LSTM) neural network model based on deep learning for the loss correction of the characteristic peak count rate and shadow peak.MethodsFirstly, a LSTM neural network model based on deep learning was proposed to estimate accurately the amplitudes of nuclear pulse signals by learning samples. Then, a convolutional neural network (CNN) with unique convolutional kernel structure was introduced to deal with the challenges of large sample size of the nuclear pulse signal and the low training efficiency of the model by extracting the sample features layer by layer, thereby effectively reducing the number of samples and the complexity of model training. Finally, a series of offline nuclear pulse sequences of powdered iron ore samples were used to generate the dataset required for model training. Among the 64 000 entries in this dataset, 44 800 were used as training sets, 12 800 were used as validation sets, and the remaining 6 400 were used as testing sets.ResultsThe trained CNN-LSTM model saves considerable training time, overcomes the defects of local convergence of traditional methods, and accurately estimates the parameters of input pulse under different degrees of distortion. Results show that the accuracy rate of the training and verification sets is greater than 99%. An analysis of the count repair results reveals that the average value of the correction ratio of the three shadow peaks, that is, the correction ratio of the depth learning model trained in this study to the count loss derived from the distorted pulses, is 91.52%.ConclusionsThe CNN-LSTM model can effectively correct the shadow peaks derived from the amplitude loss of distorted pulses and improve the accuracy of the characteristic peak count rate in X-ray fluorescence spectra. The model is shown to have high application value for the field of X-ray fluorescence spectroscopy.
Through the use of the accelerator facilities at home and abroad, the nuclear reaction group of the China Institute of Atomic Energy has made many remarkable achievements in the study of fusion-fission dynamics, fusion-enhancement mechanisms at sub-barrier energies, reaction dynamics induced by exotic nuclei, and the related exotic nuclear structure and proton decay. In this study, some representative achievements are reviewed briefly. (1) The fusion mechanisms at near-barrier energies were investigated systematically, and a self-consistent method to evaluate the coupled-channel effects was proposed. (2) Nuclear deformation parameters were extracted from backward quasi-elastic scattering, which offered evidence for hexadecapole shapes. (3) A surrogate capture method was developed, based on which the first 239Pu(n,2n) excitation function developed in China was derived. (4) Systematic studies of exotic decay spectroscopies for proton-rich nuclei in the sd-shell were performed, following which a β2p decay of 22Si and a large isospin-asymmetry decay were discovered, and a strongly isospin-mixed doublet in 26Si was revealed. (5) Systematic studies of reaction mechanisms induced by exotic nuclei at energies close to the Coulomb barrier were performed, providing evidence for the failure of the dispersion relation in the optical potential of 6He+209Bi, and the reaction dynamics of proton drip-line nuclei of 8B and 17F were investigated. Future research based on the new HiTOF and BRIF facilities is discussed as well.
BackgroundSilicon carbide (SiC) composite claddings are candidate solutions for accident resistant fuel claddings in light water reactors.PurposeThis study aims to estimate the failure probability of a double-layer structured SiC cladding under a loss-of-coolant accident (LOCA).MethodsBased on a failure probability calculation method for SiC composite cladding, a quasi-steady state method was used to simulate and calculate the SiC composite cladding failure probability under transient conditions. Sensitivity analysis of the two characteristic parameters of Weibull distribution was performed by analyzing the proportion of various stresses under accident conditions. The effects of different burn-up conditions on the failure probability were investigated, and the failure probability of the cladding under different layer thickness ratios was simulated.Results & ConclusionsSimulation results indicate that the transient failure probability of SiC composite claddings is significantly affected by changes in the proportion of the composite layer and Weibull parameter, as well as the occurrence of LOCAs under different burn-up conditions. This study makes contribution to the development and design of accident resistant fuel claddings, providing reference for further investigations on the failure probability of SiC composite claddings.
China Jinping Underground Laboratory (CJPL) has the deepest rock overburden in the world, which considerably shields the detectors from muons. Thus, it has ultra-low radiation background level and is useful for experiments investigating rare physical events. Previously, experiments including the CDEX (China Dark matter EXperiment), PandaX (Particle and Astrophysical Xenon Experiments), JUNA (Jinping Underground Nuclear Astrophysics Experiment), and neutrino experiment have been carried out at CJPL and have given good results in dark matter detection, neutrinoless double beta decay, and more. This review introduces the construction process of CJPL, and introduces the facilities, results, and future plans of the aforementioned experiments. The CDEX used a high-purity germanium detector array for the dark matter detection and neutrinoless double-beta decay searches; whereas, for the same searches, PandaX used a dual-phase liquid xenon time projection chamber detector. A proton and helium accelerator was used by JUNA to simulate four nuclear reactions that occur in the Universe. A 103-kg prototype was constructed for feasibility verification by the neutrino experiment. The CDEX, PandaX, and JUNA collaboration groups give their latest results, all of which have approached or replaced the best results in the world. These experiments verify the extraordinary experimental conditions at CJPL. With the construction of CJPL-II, we expect an increase in the number of experiments based in Jinping and for further significant results to be achieved.
The nucleus is a quantum many-body complex system governed by the nuclear force, and it is prone to global changes such as deformation, rotation, vibration, fission, and clustering. In the past >30 a, we have witnessed the rapid expansion of the experimentally attainable nuclear chart and new discoveries and breakthroughs in studies on unstable nuclei. Examples include the halo nuclei and the associated exotic structural phenomena, the shell evolution observed using in-beam γ spectroscopy through the application of the achromatic magnetic spectrometer, the measurement of the basic properties of unstable nuclei, and the discovery of new magic numbers and rich phenomena in multi-nucleon correlations along with the formation of clusters and molecules. In the coming years, the expanded area of the nuclear chart—particularly the medium-heavy-mass neutron-rich region—will be the host of extreme exotic structures, the astrophysical r-process, and the reaction pathways to reach the superheavy island. Therefore, many new-generation radioactive ion-beam facilities are under development worldwide, and essential breakthroughs are foreseen.
BackgroundFeCrAl alloy cladding, as an accident tolerant fuel (ATF) mid-term commercial technology approach, has received extensive attention.PurposeThis study aims to investigate the effect of trace Y on the internal pressure burst and oxidation properties of FeCrAl alloy cladding.MethodsFirstly, the crystalline grain size and micro-morphologies of FeCrAl and FeCrAlY alloy cladding samples were observed by optical microscope. Internal pressure burst and high temperature oxidation tests were carried out by burst test equipment and thermo-gravimetric analyzer with a moisture generator. Then, X-ray diffractometry (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were employed to analyze the composition of oxidation products, surface and cross-sectional micro-morphologies of FeCrAl and FeCrAlY alloy cladding samples before and after high-temperature stream oxidation and the distribution of elements on the surface oxidation products.ResultsThe results show that trace Y is mainly dissolved in the FeCrAl alloy matrix, and no Fe-Y phase is formed. The inclusion of Y do not change the burst strength and the rupture opening morphology at room temperature (RT) to 1 000 ℃, and the high-temperature steam oxidation resistance of FeCrAl alloy cladding is significantly improved by the trace Y. Under the condition of steam oxidation at 800 ℃, 1 000 ℃ and 1 200 °C for 8 h, the oxidation weight gain of FeCrAlY alloy cladding decrease by 65.1%, 60.0% and 31.5%, respectively. Compared with the single Al2O3 oxide film on the surface of FeCrAl alloy cladding, the Y-containing composite oxide film with lower internal stress, higher compactness and better adhesion with the substrate is formed on the surface of FeCrAlY alloy cladding.ConclusionsTherefore, the addition of trace Y do not change the burst properties of FeCrAl alloy cladding, however, the high-temperature steam oxidation resistance of FeCrAl alloy cladding is significantly improved.
BackgroundIn order to accurately predict the friction pressure drop characteristics of liquid lead bismuth in the cross-section of the fuel assembly rod bundle, a suitable friction pressure drop model should be selected.PurposeThis study aims to investigate Friction pressure drop model for wire-wrapped rod bundles in full flow.MethodsEight different frictional pressure drop models within wire-wrapped rod bundles were evaluated their applicability by using statistical analysis. The prediction accuracy of experimental data from different models in different flow regimes was explored corresponding to laminar flow, transitional flow, and turbulence.ResultsThe analysis results show that the friction coefficient is not only related to the number of rod bundles (Nr) and the pitch-to-diameter ratio (P/D), but also related to the wire lead length-to-diameter ratio (H/D). The modified BDD model in the laminar flow range and this work model are more consistent with the experimental data. The modified BDD model, CTD model and this work model are relatively consistent with the experimental data in the transition flow range. The Rehme model, the UCTD model and this work model in the turbulent range are more consistent with the experimental data.ConclusionsTherefore, the model presented in this study is suitable for predicting friction pressure drop in the cross-section of the fuel assembly bundle in the full flow state.
Silicon carbide (SiC) crystal can be used as a passive monitor to measure the neutron irradiation temperature in nuclear reactors, which has significant application prospects for advanced reactors operating in high-temperature intense irradiation environments. Since the SiC temperature measurement technique was proposed in the 1960s, various temperature measurement methods have been developed on basis of neutron irradiation effects in the structural, thermal and electrical properties of SiC. These methods involve measuring changes in macro-size, density, thermal diffusivity or the electrical resistivity of SiC. This study summarizes the fundamental principles and characteristics of these methods firstly, then the research progress on SiC temperature measurement system required for advanced nuclear reactors at the China Institute of Atomic Energy (CIAE) is emphatically reported, and the measurement accuracy of SiC monitor is analyzed by calculating the lattice swelling rate of the neutron-irradiated SiC using a theoretical model, which verified the reliability of the temperature measurement results of the system. Finally, experimental methods for further improving measurement efficiency of SiC monitor are discussed.
BackgroundDouble perovskites have become a research hotspot in recent years due to their flexible structure, easy doping, and good thermal stability. Photoluminescence (PL) of rare-earth-doped double perovskite materials has been frequently reported, but few studies on thermoluminescence (TL) have been conducted.PurposeThis study aims to investigate the TL characteristics of Y2-x-yBixEuyMgTiO6 (0≤x<1, 0≤y<1) phosphors.MethodBi3+ and Eu3+ co-doped Y2MgTiO6 samples were synthesized by a high-temperature solid phase method, and the X-ray diffraction (XRD), PL, and TL of the samples were measured.ResultsXRD analysis results show that the crystal structures of all samples are monoclinic P21/n, and Bi3+ and Eu3+ are doped into Y2MgTiO6 by substituting Y3+. The PL results show that Y1.79Bi0.01Eu0.20MgTiO6 has a strong red emission near 620 nm (corresponding to the 5D0→7F2 transition of Eu3+), which is accompanied by a long afterglow. The TL curves of the samples doped with different concentrations of Bi and Eu ions show that Y1.79Bi0.01Eu0.20MgTiO6 has the highest TL sensitivity, and the samples exhibits two significant TL peaks near 510 K and 610 K. The TL spectrum is more abundant than the fluorescence spectrum, and the 5D0→7FJ (J =1,2,3,4) transition of Eu3+ can be observed. The TL intensity of the sample has a good linear relationship with the irradiation dose in the range of 2~1 000 Gy. The TL kinetic parameters of the samples are analyzed using two methods under different preheating temperatures (Tm and Tstop) and glow curve deconvolution. The analysis results show that the depth of the TL trap in the sample extends from 0.80 eV to 1.40 eV.ConclusionsThe results of this study indicate that the TL spectrum is richer than the PL spectrum and that Y1.79Bi0.01Eu0.20MgTiO6 may be used as TL dosimeter material for large dose detection.
The first radioactive ion beam line, GIRAFFE, has been built at the CIAE HI-13 tandem accelerator in China. A total of eleven types of radioactive ion beam, including 6He, 7Be, and 8Li, have been generated. Several significant reactions in nuclear astrophysics have been indirectly measured via transfer reactions, and research on nuclear structure, relevant to nuclear astrophysics, has been performed using charge exchange reactions and thick-target experimental methods. A series of single nucleon or α cluster transfer reactions have been measured using a Q3D magnetic spectrometer, and the astrophysical S-factors and reaction rates for essential reactions have been obtained. The obtained results serve as a crucial experimental foundation for research involving element abundance and celestial body models.
BackgroundMany existing studies have shown that the use of suitable surface modification methods can enhance the boiling heat transfer effect of metal components, making it have a broad potential application prospect in the pressurized water reactor. However, for the weak alkaline environment of high temperature and high pressure in the reactor, little literature is reported on whether this enhanced effect can be maintained for a long time.PurposeThis study aims to explore the effect of corrosion on boiling heat transfer characteristics of metal specimens with micro-structure surface.MethodsFirst of all, three micro-structures of micro-groove, micro-porous and micro-columns were processed on the surface of stainless steel plate specimens by laser processing. Then the specimens were placed in the high-temperature and high-pressure environment simulating the actual reactor conditions to carry out corrosion experiments for up to 200 d. Finally, the pool boiling experiment and visualization study of the specimens before and after corrosion were carried out for comparison.ResultsThe results show that the surface critical heat flux (CHF) of the three micro-structured metal specimens increases and then decreases with the increase of corrosion time, among which the micro-pores specimens have the largest bubble generation rate at the beginning of nuclear boiling, and the micro-groove specimens have the highest CHF.ConclusionsThe influence law and mechanism of long-term corrosion in pressurized water reactor on the enhanced heat transfer effect of different micro-structure surfaces are partially revealed by this study.
BackgroundThe solar X-ray detector (SXD) is the main scientific instrument onboard the Macau Science Satellite-1B (MSS-1B). It consists of two parts—a soft X-ray detection unit and a hard X-ray detection unit—with a dual-channel design comprising a silicon drift detector (SDD) and a cadmium zinc telluride detector (CZT). Both the precise energy spectrum and intensity of the Sun can be simultaneously obtained by the SXD, hence to quantify the level of solar flares and study their evolutionary process.PurposeThis study aims to calibrate the detection efficiencies of the SDD and CZT, so as to invert the observed data for obtaining real solar X-ray data.MethodsThe Monte Carlo code MCNP5 (Monte Carlo N-Particle 5) was employed to calculate the SDD and CZT efficiencies by simulation. Soft and hard X-ray detection efficiency calibration experiments were performed using a monochromatic X-ray ground calibration facility via relative measurement methods.ResultsThe experimental results for the SDD-1 and CZT-1 efficiency calibration agree well with the predicted results of the simulation. In particular, the maximum relative error between the experimental and simulated efficiencies of SDD-1 dose not exceed 3.59%@16 keV, and the maximum relative error between the experimental and simulated efficiencies of CZT-1 dose not exceed 9.54%@120 keV. The relative expanded uncertainty of the monochromatic X-ray flow intensity measurement is 3.8% (k=2), and the uncertainty of the simulation results for the SXD is 0.12%.ConclusionsThis study provides not only data support for SXD onboard MSS-1B satellite, but also valuable guidance for the calibration of other astronomical satellites' detectors in the future.
BackgroundThe passive residual heat removal (PRHR) system is an important innovative design of the advanced pressurized water reactor technology. Under accident conditions, PRHR system can transport decay heat in the form of natural circulation to ensure core cooling. However, the heat exchange function of PRHR system will be lost when the PRHR pipeline breaks. With development of the accident process, the coupling effect between different safety equipments of the passive core cooling system (PXS) will be affected. Besides, thermal hydraulic state of the reactor coolant system (RCS) will also be affected via complex interaction mechanism. As a result, the new thermal hydraulic phenomena occur, and thus ultimately affecting the accident mitigation capacity of the PXS.PurposeThis study aims to confirm the safety characteristics of PXS and identify the new thermal hydraulic phenomena of advanced passive nuclear power plant during accident with multiple failures.MethodsA series of integral effect tests of loss of coolant accident (LOCA) were conducted on the advanced core-cooling mechanism experiment (ACME) facility. The influence of failure of PRHR HX flow and heat exchanging function on LOCA accident process were investigated on the basis of the test cases including PRHR pipeline break and cold leg (CL) break. The unique thermal hydraulic phenomena occurred during PRHR LOCA were explored, and their influence laws on the coupling effect among PXS safety equipments, and the influence laws on thermal hydraulic state of RCS were obtained.ResultsThe results show that there is a momentary reverse flow and heat transfer process in PRHR HX at the beginning of PRHR LOCA compared with typical CL LOCA. Besides, the natural circulation process between the core and steam generators (SGs) plays a critical role in cooling and depressurization of RCS, and its corresponding time-averaged heat transfer power is increased by about 30%. Besides, the asymmetric arrangement of PXS leads to a significant difference of transient thermal hydraulic state between the RCS branches, namely the PRHR cools the coolant via one RCS loop while two core makeup tanks (CMTs) inject the cold water to the core via the other RCS loop, and the pipeline resistance distribution shows a significant impact on the injection performance of safety equipment with low driven head such as CMTs.ConclusionsThe unique and important thermal hydraulic phenomena in the early stage of the accident, namely reverse flow and heat transfer process in PRHR HX and natural circulation process between core and SGs, are identified. The asymmetric arrangement effect will be more noticeable when the break occurs in PRHR pipeline.