Study On Transient Response Characteristics Of Natural Circulation In Coupled Loops Under Ocean Condition

Marine nuclear power plants are far from land and lack of adequate external support under accident condition.As a result,passive safety technology can significantly enhance the inherent safety of marine nuclear power plants.Passive residual heat removal system and reactor primary and secondary circuit systems are in a coupling state of multi-natural circulation loops under accident conditions.The influencing factors of the circuits interact with each other and have obvious feedback effects.In addition,the influence of ocean condition has a strong multi-factor coupling and nonlinear characteristics,which make response characteristics of multi-loop natural circulation in residual heat removal system extremely complex.Therefore,in this paper,a combination of experimental and numerical methods are used to study the transient response characteristics of natural circulation in coupled loops under ocean condition.Based on the two sets of coordinate systems needed to study the influence of ocean condition,this paper gives the rotational coordinate matrix needed for ocean condition modeling,and confirms the momentum conservation equation in non-inertial system.The basic idea of secondary development of RELAP5 program under the ocean condition is summarized.Mathematical model of oceanic condition,additional inertial force model and internal model of RELAP5 system are combined successfully.The secondary development of RELAP5 is initially completed.Using deionized water as working fluid,the experimental research on single-phase natural circulation flow rate and temperature fluctuation under the single-loop rolling condition and multi-loop were carried out,and the system was simulated by the modified RELAP5 code.The comparative analysis shows that the calculated results are in good agreement with the experimental data.It is considered that the RELAP5 program after secondary development can be used to simulate single-phase flow in a low-pressure natural circulation system under ocean conditions.On this basis,the impact of inclination,heaving and rolling conditions to the natural circulation system in coupled loop under rated power operation condition or the power jump condition was carried out by numerical simulation.The simulation results show that:Under the rated power condition,the rolling motion caused the violent fluctuation of the flow and heat exchange.The impact of pitching motion to parameters under the rated power operation can be negligible.Heaving motion will cause the first and second circuit flow and heat transfer fluctuations,but the effect to system pressure and temperature is samll.Under the condition of power jump and inclination,the response time of each parameter of the system decreases with the increase of the height difference of cooling and heating source.Under the heaving condition involved in this paper,the response time of each parameter in the multi-loop natural circulation system will not be affected.The response time of the condition of rolling at 20°/0.05 and the condition of rolling at 15°/0.05 is basically the same as that under static condition,but the response time of power jump is obvious less when the flow oscillation is more violent at 15°/0.1 than static conditions and other roll conditions.The effect of pitching motion on the response time of multi-loop natural circulation system is basically negligible.