The Development Of A Thermal Hydraulic Analysis Code Of Nuclear Reactor Under Ocean Conditions

As an important operation scheme of marine PWR,natural circulation has the advantages of enhancing the inherent safety of the reactor and reducing navigation noise.However,the unsteady force field introduced by the ocean conditions changes the thermal-hydraulics characteristics of the system,and significantly affects the stability and safety of the natural circulation operation.Meanwhile,under the combined impacts of ocean conditions and coupled neutronics/thermal-hydraulics,the natural circulation flow and power distributions of the core exhibit complex characteristics.Therefore,it is necessary to fully assess the effects of ocean conditions on the natural circulation and coupled neutronics/thermal-hydraulics of the reactor by simulation method.In this paper,a thermal-hydraulics analysis code of non-inertial system was developed by establishing dynamic simulation models of typical ocean conditions and modifying RELAP5 code.The simulation results under the periodic force field were in good agreement with the reference data,which verified the credibility of the analysis code.Based on the modified code,the effects of the inclination,fluctuation and rolling conditions on the natural circulation characteristics of an integrated PWR-200(IP200)were studied.The dynamic input and output interface models of RELAP5 were further established,and RELAP5 was coupled with a two-group three-dimensional neutron kinetics code REMARK to realize the improvement of nuclear feedback module in thermal hydraulic code.The coupled neutronics/thermal-hydraulics of a plate-type fuel reactor under ocean conditions were simulated.The distributions of core flow and power under different motions were analyzed.The calculation results of each condition conclude that,the inclination will cause the offset of loop flow,core flow and power distributions.The larger the inclination angle is,the more obvious the offset characteristic is.A large angle of inclination can lead to lower undercooling at core exit,which is adverse to the safe operation of the reactor.Rolling period,amplitude,operating power and other factors are driven by changing the pressure head or additional pressure drop to affect the natural circulation flow fluctuations.The additional loop pressure drop is mainly contributed by the tangential force.The off-center roll axis location can break the thermal-hydraulics symmetry among different loops and enlarge fluctuationamplitude of the core flow rate.The assembly channels away from the rolling axis are subject to stronger additional forces,so the peaks of the flow and power fluctuation amplitude appear on both sides of the rolling axis.In the larger heaving amplitude and period,the heaving motion can significantly damage the stability of natural circulation operation.The impact of the heaving amplitude is more significant than period whether on the flow or power.The additional force under heaving conditions is spatially uniform,with the peaks of the oscillation amplitude of the flow and power lying in hottest channel.The code developed in this paper has the functions of modeling ocean conditions and three-dimensional coupled neutronics/thermal-hydraulics,and can be used as a simulation tool for marine PWR.The results of this research can deepen the understanding of the natural circulation operation characteristics of the reactor under ocean conditions.