Variation in multi-unit NPP seismic risk due to seismic failure correlation between structures, systems, and components (SSCs)

Seismic events affect a wide area; therefore, if such an event occurs at nuclear power plants on the same site, the impact will be similar. This correlation in seismic failure extends across structures, systems, and components (SSCs). This study performed a seismic probabilistic risk assessment for multi-units, incorporating the seismic failure correlations between SSCs, and investigated the variation in risk due to these correlations. The seismic failure correlation coefficients between SSCs were derived from probabilistic seismic response analyses. Furthermore, for comparative analysis, the seismic risk was assessed using the seismic failure correlation between SSCs for independence, partial dependence, and complete dependence. A partially dependent case for the same component was also investigated. The findings indicate significant variations in the seismic fragility and seismic risk of nuclear power plants when considering failure correlations between SSCs, highlighting the importance of including such interdependencies between SSCs in safety evaluations for multi-unit scenarios. This study provides insights for enhancing the seismic probability risk assessment of nuclear power plants, especially in areas with multi-unit issues.