Neutronic/thermal-hydraulic coupling analysis of natural circulation IPWR under ocean conditions

In this paper, a thermal-hydraulic analysis code under non-inertial system was developed based on a RELAP5/MOD3 code by establishing dynamic simulation models of typical ocean conditions. The simulation results under periodic force field were in good agreement with the reference data, proving the accuracy of the program. In order to analyze the reactor core flow distribution and power distribution under different ocean conditions, the thermal-hydraulic code was coupled with a two-group three-dimensional neutron kinetics code. Based on the modified RELAP5 code, the effects of heeling, heaving and rolling conditions on neutronic/thermal-hydraulic coupling characteristics of natural circulation integrated pressurized water reactor (IPWR) were studied. The results indicate that the uneven distribution of coolant flow increases with the increasing inclination angle, but the reactor power distribution is subject to little changes. This trend leads to an uneven distribution of coolant temperature at the core outlet. The flow or power fluctuation has a 180° phase difference under rolling conditions, and the reactor power and coolant flow oscillation increases with the increasing rolling period and amplitude. In the case of heaving motion, the peaks of the oscillation amplitude of the flow and power lying in the hottest channel as the additional forces on the fluid of each channel are spatially uniform. Furthermore, the impact of the heaving amplitude is more significant than the heaving period, whether on the flow or power.