Study on Depressurization Efficiency of Pressurizer Relief Valves

Based on SCDAP/RELAP5/MOD3.1,which may simulate the detail severe accident transient mechanism,this paper analyzes the progression and depressurization efficiency of postulated ATWS accident,initiated by the loss of main feed water（LOFW）,the loss of offsite power（LOOP） and uncontrolled rod cluster control assembly（RCCA） bank withdrawal.The results show that one train of pressurizer relief valves（PRV） is not sufficient to depressurize reactor coolant system（RCS）,and the primary pressure still remains above 10MPa;it brings a great potential risk of high-pressure core melt.The case adding one more train of PRV is analyzed and the results show that two trains of PRV could adequately reduce the primary pressure to about 3MPa,and the safety injection starts up and arrests the core melt progression,and thus reduce the risk of high-pressure core melt.It is also showed that the high pressure injection system has important contribution to RCS depressurization.