Seismic fragility analysis of nuclear power plant systems considering the effect of the ground motion frequency content

Seismic fragility analysis has been extensively employed to evaluate the failure probabilities of equipment and individual components in nuclear power plants (NPPs). However, seismic fragility analysis at the system level of NPPs has received limited attention in existing studies. In this study, a system-level fragility analysis of an NPP is performed using a Gaussian Mixture Model (GMM). To improve the accuracy of the fragility analysis, eighteen individual intensity measures (IMs) are selected to develop the compound IM based on the correlation results between the candidate IMs and the engineering demand parameters (EDPs) of four critical components, using the Partial Least Squares Regression (PLSR) technique. The GMM-based Probabilistic Seismic Demand Models (PSDMs) are fitted using a multimodal log-normal distribution to model the probability densities of seismic demands for components. The results show that the compound IM outperforms single IMs in terms of efficiency, practicability, and proficiency while also demonstrating sufficiency with respect to ground motion (GM) characteristics. The concrete containment is identified as the critical component that governs the failure of the NPP system. The proposed approach offers valuable insights for enhancing the accuracy and predictive capability of fragility analysis for NPP systems, thereby contributing to the advancement of seismic safety assessment frameworks.