Multihazard Fragility Analysis of a Nuclear Containment Structure under Sequential Earthquake–Tsunami Loading

Nuclear power plants are primarily situated in coastal regions, rendering them susceptible to multiple natural hazards, including tsunamis and earthquakes. However, research on the multihazard fragility analysis of containment structures under sequential earthquake–tsunami loading remains limited. This study proposes a fragility analysis framework for nuclear power plant containment structures subjected to sequential seismic and tsunami hazards, with a particular focus on the impact of earthquake-induced damage on postearthquake tsunami performance. A numerical model of the containment structure is developed, and nonlinear time-history analysis coupled with tsunami pushover analysis is employed to derive multihazard fragility curves under sequential earthquake–tsunami loadings. The results indicate that the sequential seismic-tsunami hazards significantly influence the fragility of containment structures. Specifically, following an earthquake with a peak ground acceleration of 0.4 g, probabilistic escalation ranges from 47% (slight damage) to 98.7% under earthquake–tsunami sequential events (16.4 m inundation depth, 9 m/s flow velocity), with severe damage probability increasing from 0.2% to 15.0%. These findings highlight that earthquake-induced damage exacerbates the risk of failure in containment structures subjected to tsunami loading.