The floating nuclear power plant (FNPP) is a vital energy supply method for future ocean exploitation and island construction. The typical fuel type of FNPP is similar to the onshore nuclear power plant, i.e., the rod bundle fuel assembly. Due to the effect of ocean waves and wind, the FNNP would be in continuous motion. Rolling is one of the most common types of motion. It can induce the periodical change of the inertial force field of the coolant and the change of flow and heat transfer characteristics of the rod bundle channel. Coupling with neutronic and thermohydraulic, as a result, the operation characteristics, safety, and economics of the FNPP can be affected.

This study aims to investigate the impact of neutronic-thermo-hydraulic coupling on natural circulation characteristics with the rod bundle channel under rolling motion condition.

A natural circulation system with a 5×5 square array basic rod bundles channel was taken as research object, and it was designed and built on a mechanical rolling platform. Then, based on the point reactor kinetic model, the coupling of neutronic-thermohydraulic-motion was achieved by real-time data acquisition of thermal parameters and calculation of real-time nuclear power, and the effects of fuel temperature feedback and coolant temperature feedback on single-phase natural circulation were considered. Finally, an experimental study on the low-pressure single-phase natural circulation under rolling motion condition was carried out.

Under static conditions, neutronic-thermo-hydraulic coupling makes the power fluctuate slightly, reactivity and power fluctuation amplitude increase with the increase of temperature feedback coefficient. When the feedback coefficient is lower than -5×10^-4 ℃^-1, fuel temperature feedback has a greater impact on power than coolant temperature feedback. Increasing the fuel temperature feedback coefficient reduces system stability. Under rolling motion conditions, the smaller the rolling amplitude or the shorter the rolling period, the smaller the amplitude of the introduced power fluctuations. During the initiation of the rolling motion, neutronic-thermo-hydraulic coupling significantly increases 50% of the time for the system to establish a new stable circulation.

These results provide a valuable application for further investigations of the FNNP's design and validation.