Study On The Scheme And Operation Characteristics Of Secondary Passive Residual Heat Removal System

During the period of the service in a floating nuclear power station,it is generally unable to obtain a stable off-site power supply.In case of the station black out(SBO)accident,energy can only be provided for the active safety system through power generation such as standby diesel engines.Once the diesel engine fails,the safety of the floating nuclear power station will be directly affected.Therefore,installing the passive safety system on a floating nuclear power station is necessary.Based on this background,two kinds of secondary passive residual heat removal systems(SPRHRS)are designed based on the system analysis program RELAP5.The affect of condenser geometric parameters on the performance of the SPRHRS is analyzed.Meanwhile,the startup mode and the opening speed of the isolation valve on the SPRHRS starting characteristics are studied.Then,the response characteristics of the two schemes within 24 hours after the SBO were simulated and analyzed.The operation characteristics of the SPRHRS under typical ocean conditions and the influence of ocean conditions on the operation characteristics of the scheme were studied based on the secondary development program RELAP5.The simulation results indicate that reducing the diameter of condenser heat pipe can increase the condenser heat transfer coefficient and enhance the heat removal capacity to a certain extent.Reducing the height of the vertical section of the C type heat transfer tube can also increase the heat removal capacity of the condenser,but reduce the stability of the system at the same time.The simulation results of the response characteristics of the two design schemes within 24 h after the SBO indicate that the schemes of intermediate water tank and the boiling water tank can both remove the residual heat of the core and maintain long-term cooling of the core effectively,but the effective cooling time of the scheme of boiling water tank is heavily dependent on the amount of water in the tank.In the scheme of intermediate water tank,since the cooling water in the tank is not evaporated and the sub-cooling degree is maintained above 36.9℃ all the time,the amount of water will not decrease.The heat exchanger can be immersed all the time to ensure that the heat is transferred to the sea water through the water tank,and the core cooling can be maintained all the time.In both designs,the flow in each loop of the system will fluctuate periodically due to the swaying.There is no significant change in the natural circulation capacity of the primary loop under the rolling condition.The heat removal capacity of the SPRHRS is affected by the rolling condition slightly.Under the condition of pitching,the smaller the pitching period means the smaller the primary loop natural circulation capacity and the weaker the ability of the SPRHRS to remove the residual heat from the core,taking the intermediate water tank scheme as an example,the total heat removal capacity of the SPRHRS is reduced by 13.3% at1 hour after the SBO accident under the condition that the pitching period is 5s.Under the swaying condition,the flow of seawater in the seawater loop of the scheme of intermediate tank is mainly driven by the centrifugal force in the flow direction.The natural circulation capacity of the primary loop is reduced by both heeling and leaning,and the heat removal capacity of the SPRHRS is also reduced by the tilting condition.The intermediate water tank scheme is better than the boiling tank scheme under the condition that the floating nuclear power station does not tilt for a long time.