Rapid Postearthquake Fragility Assessment of Operating Nuclear Structures Using a Parametric Reduced‐Order Model

This study proposes a rapid fragility‐reassessment framework to support postearthquake operational decision‐making in nuclear power plants. Design‐stage fragility assessments often require extensive nonlinear analyses and cannot be readily recomputed to reflect changes in the in‐service structural condition. To address this limitation, the proposed framework integrates parametric reduced‐order modeling with piecewise‐linear dynamic analysis, focusing on a slight‐damage limit state relevant to operational early‐damage assessment. The framework adopts an offline–online structure, in which a reduced‐order representation is constructed in advance and then activated using monitoring‐informed parameters for fast seismic response evaluation. The approach is demonstrated using a high‐fidelity model of a nuclear containment structure. The reduced model enables each seismic simulation to be completed within seconds, allowing 30 ground motions across 15 intensity levels to be analyzed within approximately 30 min. The results show that the structural capacity decreases with stiffness degradation, confirming that the proposed framework provides fast, physics‐based, and condition‐informed fragility estimates for operational early‐damage assessment and timely postearthquake decision support within the considered slight‐damage regime.