Risk-Informed, Performance-Based Design of a Seismic Isolation System for a Nuclear Power Plant

A methodology to achieve a user-specified performance target for a seismic base-isolation system for a nuclear power plant (NPP) is presented and demonstrated. The isolation system, composed of both isolators and damping devices, is treated as a structure, system, and component (SSC) per US nuclear practice. Acceptable performance is defined as sufficient horizontal displacement capacity of the isolators and dampers to achieve a user-specified target performance goal (TPG). The methodology involves the generation of a seismic displacement demand curve for the isolation system, expressed as the mean annual frequency of exceedance (MAFE) of a horizontal displacement, and a fragility function for the isolation system. Information is presented on the derivation of an isolation system fragility function. The methodology is described via application to six isolation systems installed beneath an advanced NPP, founded on two different soil domains, and located at Clinch River in East Tennessee, USA.