Risk-based decision on configuration of AAC DGs in multi-units site

Since a domestic nuclear plant site different from overseas has 6 units in a site, it is necessary to consider deeply a mitigating measure to station blackout accident (SBO). Currently it is proposed the installation of additional diesel generator to ensure an alternative AC power source, but it has not been decided yet how many diesel generators should be installed in a multi-units site: one or two. In this paper, risk-based decision making method, which evaluates reliability, core damage frequency, and average of core damage frequencies of nuclear power plants, is introduced to draw up the suitable number of diesel generator. The results shows that installing two diesel generators increases 1.4% of average of core damage frequencies as compared with installing one diesel generator but for both cases 4.5% of reliability of the electrical system equally increases. In the light of risk - informed decisions in regulatory guide 1.174, there is no difference of safety between two alternatives. It is concluded that one additional diesel generator sufficiently guarantees safety against station black out of nuclear power plants in multi-units site