Seismic fragility analysis of a piping structure in a nuclear power plant

The problem of predicting the fragility of a piping structure using computational models is considered. A framework for including uncertainties in load characteristics, structural properties and modeling is proposed. The earthquake input impinging on the primary structure is modeled as a vector of stationary Gaussian random processes. The piping response, conditioned on the structural and modeling uncertainties, is predicted by using standard random vibration theory. The study assumes linear structural behavior and neglects any possible interaction between the reactor containment structure and the piping structure. Failure criteria, in terms of exceedance of structural response in a given duration and over specified levels, are formulated based on extreme value theory of Gaussian random processes. The unconditional failure probability is computed using a newly developed gradient-board approximation. The proposed procedure is first validated by using Monte Carlo simulations on simple structures and subsequently applied to a realistic nuclear power plant piping structure. (author)