Research On Technical Scheme Of Core Melt Retention In Pressurized Water Reactor Nuclear Power Plant

Because of its clean and efficient characteristics,nuclear power generation has been paid attention by all countries.However,the commercial nuclear power project has not yet achieved intrinsic safety in design,especially a series of major accidents such as Three Mile Island,Chernobyl and Fukushima nuclear accidents,which have a huge impact on nuclear power construction.On the one hand,we should continue to explore ways to achieve intrinsic safety under the existing technical conditions at home and abroad;on the other hand,combined with previous nuclear accidents,we put forward a feasible goal under the current technology,that is,to actually eliminate the release of a large number of radioactive substances.No matter what kind of event sequence,the release of a large number of radioactive materials in a nuclear accident will experience the melting of the reactor core,the collapse of the molten materials to the lower head,and then the failure of the pressure vessel.Because of the overpressure of containment or the reaction of melts with the bottom plate of containment,the integrity of containment is threatened,resulting in the release of a large number of radioactive materials.In order to cope with this extreme situation,different technical schemes have been adopted in the design of nuclear power plants at home and abroad.At present,the schemes adopted by the mainstream PWR nuclear power can be divided into two categories: 1)keeping the core melt inside the pressure vessel(IVR),and the main application types are AP1000,hualong-1 and the domestic second generation nuclear power transformation project;2)The main application of core melt capture outside the reactor is Russian VVER series units and French EPR units.Based on the study of severe accident management and the construction and operation of nuclear power projects,this paper makes a comparative analysis of IVR technology and core melt capture technology.The research shows that the core melt capture technology has advantages in reliability and success rate for the second generation nuclear power plant.A detailed comparative analysis is made on the water injection scheme of each type of reactor cavity.It is found that there is room for further optimization of IVR technology in the current generation II nuclear power plant project,and suggestions for optimization are put forward.Taking the second generation nuclear power project as the analysis object,some key problems in the implementation of IVR are analyzed,such as the integrity of pressure vessel under the condition of misinjection,the effectiveness of cavity water injection,the influence of the lower boss of pressure vessel on the critical heat flux(CHF)and the response time of passive core water injection technology.The analysis shows that even under the condition of misinjection,the integrity of the pressure vessel can be maintained.The test and calculation show that the effective injection flow and water level can be guaranteed,and the retention of the core melt can be realized.The boss of the second generation nuclear pressure vessel has a certain adverse effect on CHF,but it will not lead to the failure of IVR.