Severe core damage frequency and insights from CANDU 6 level 1 probabilistic safety assessment

An internal events Level 1 probabilistic safety assessment (PSA) of a CANDU 6 nuclear power plant (NPP) was conducted by AECL and KAERI, with Wolsong NPP 2/3/4 in Korea taken as the reference plant. Wolsong NPP 2/3/4 is an enhanced design of Wolsong NPP Unit 1, which has been operating successfully since 1983. The reference plant has a number of safety and design improvements compared to Wolsong NPP 1. Based on the PSA, the summed severe core damage frequency for Wolsong NPP 2/3/4 is estimated to be 6.1E-6 events per year for internal events. Initiating events that dominate the severe core damage frequency are loss of Class 1V electrical power, dual digital computer control failure, loss of end shield cooling and loss of service water. They contribute 24%, 17%, 16% and 12% respectively to the summed severe core damage frequency. The results of this PSA confirm a low severe core damage frequency. (author)