Key Component Selection and Multiobjective Optimization for Improving Seismic Performance of Nuclear Power Plants Considering Correlations Among SSCs

Owing to the increasing frequency and magnitude of earthquakes, it is necessary to improve the seismic capacity of nuclear power plants (NPPs) by strengthening systems, structures, and components (SSCs). Seismic probabilistic safety assessment is a widely used method for evaluating seismic performance, but it often does not consider correlations between component failures. In this study, a method to enhance seismic safety by considering such correlations is proposed. First, a seismic risk model that includes failure correlations between components was developed. Then, key components that have a significant impact on seismic risk were identified through sensitivity analysis. Multiobjective optimization was performed using the strengthening cost and seismic risk as objective functions. The OPR1000, a Korean standard NPP model, was used for the case study because it is the most widely used reactor type in Korea. The multiobjective gray wolf optimizer was applied for the multioptimization. The results show that the key components were the same regardless of whether correlations were considered. However, when correlations were included, greater risk reduction was achieved with less strengthening. This is because the loss of essential power, which accounts for the largest portion of the seismic risk in OPR1000, is primarily structured with OR gates. These findings indicate that while the selection of important SSCs is not affected by the inclusion of correlations, incorporating them is crucial for accurate seismic risk assessment, enabling more effective strategies for seismic performance enhancement.