Study on the minimum number of SRVs required for emergency depressurization in EOP of BWR power plants

The minimum number of safety/relief valves (SRVs) required for emergency depressurization (MNSRED) is an important reactor pressure vessel (RPV) parameter described in the appendix C of BWR Owners’ Group, Emergency Procedure Guidelines and Severe Accident Guidelines (BWROG, EPG/SAGs). It is directly related to the emergency depressurization if there are less SRVs available. MNSRED is always coupled with decay heat removal pressure (DHRP) in emergency depressurization. DHRP is used as the depressurization low-pressure end to ensure the decay heat can be removed.The purpose of this paper is to discuss their mathematical models in BWROG EPG/SAGs. After study, the vague concepts existed in these parameters are pointed out and clarified. The variables inappropriately used through their evaluations are revised. With improved modifications, the MNSRED turns out smaller than its original value and DHRP is larger than its previous one. These results affect the heat removal capability and the operation margin regarding emergency depressurization. At the end, the revised DHRP value is verified by MAAP5 code with the same plant status for the Kuosheng power station of Taiwan Power Company.