Seismic Fragility Analysis for Structures, Systems, and Components in Nuclear Power Plants

摘要

Seismic fragility analysis has been widely used to evaluate seismic capacities of structures,systems, and components (SSCs) in nuclear power plants. In the seismic fragility analysis, asingle ground motion parameter (GMP),such as peak ground acceleration (PGA), is chosento characterize the Review Level Earthquake (RLE) and represent the seismic capacity of anSSC.However, due to the use of a single GMP, problems have been observed in engineeringpractice.It is well known, from elastic structural dynamic analyses, structural responses underearthquake excitations depend primarily on spectral accelerations at its dominant naturalfrequencies. Choosing spectral accelerations at structural dominant natural frequencies asvector-valued GMPs (VGMPs) can more accurately characterize the input RLE and moreprecisely predict structural responses. The purpose of this study is to develop weightingseismic fragility analysis method that overcomes the problems in current seismic fragilityanalysis method. The proposed method mainly includes that1. vector-valued probabilistic seismic hazard analysis (VPSHA) is performed to determinethe weights of input ground response spectra (GRS);2. seismic fragility analysis considering VGMPs method is proposed to calculate seismicfragility based on VGMPs;3. weights of input GRS and seismic fragility are combined to obtain the weightingseismic fragility of an SSC.By using VGMPs, the proposed method resolves the problems in current seismic fragilityanalysis, thus it can obtain more accurate seismic capacities of safety-related SSCs. Inaddition, weighting seismic fragility curves and High Confidence and Low Probability ofFailure (HCLPF) seismic capacities are represented by a single GMP such as PGA, hencethey are readily incorporated into Seismic Probabilistic Risk Analysis and Seismic MarginAssessment (SMA).Based on weighting seismic fragility analysis method, an improved SMA procedure isproposed. The procedure combines the use of weighting and current seismic fragilityanalysis methods, i.e.,1. weighting seismic fragility analysis is performed to determine HCLPF seismic capacitiesof “weak link” SSCs, and2. current seismic fragility analysis is conducted to calculate HCLPF seismic capacitiesof less important SSCs.This ensures that more accurate plant seismic capacity is obtained, while computationalcost is acceptable. The proposed SMA procedure can save redesign cost of “weak link” SSCs.The proposed weighting seismic fragility analysis method is accurate and applicable,providing more accurate seismic capacity estimates of safety-related SSCs, thus savingredesign cost of “weak link” SSCs that do not satisfy seismic margin requirement.