Earthquake Response of Nuclear Power Facilities

Differences between design of nuclear facilities and conventional structures are noted. The seismic design process begins with site investigation. Two design earthquakes, the operating basis earthquake (OBE) and safe shutdown earthquake (SSE), are determined from a study of historical seismicity, geology, and tectonics. The OBE has a reasonable probability of occurrence during the facility design life. The SSE is based on maximum earthquake potential for the site. Conventional structures are commonly designed for earthquake levels corresponding to the OBE. Ductile inelastic behavior is considered acceptable response. Nuclear facilities are designed to remain elastic under the larger SSE loading. Seismic analysis is performed in phases beginning with overall analysis of structure and soil that determines gross motions. Soil-structure interaction is analyzed by either the impedance function approach or finite element method. Response from this analysis is used for more detailed analyses of structures or components. Ultimately all structures and components necessary for safety are seismically qualified by analysis or test.