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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.