Bayesian Approach for the Seismic Fragility Estimation of a Containment Shell Based on the Formation of Through-Wall Cracks

Abstract

The primary containment (PC) in a nuclear power plant provides the last barrier against radiation leakage to the environment. Design specifications fail to assess the performance of a seismically-damaged containment against accidental overpressure. The present work focuses on the seismic fragility estimation of a PC considering formation of through-wall cracks, which may lead to radiation leakage. This is significantly challenging, considering the computation involved in the integration over a multidimensional probability space, detailed numerical modeling of the containment including concrete damage, and nonlinear dynamic analyses of the structure. A Bayesian approach using a Markov chain Monte Carlo (MCMC) integration scheme is adopted, along with more traditional reliability algorithms (point estimate, first-order second moment (FOSM), and response surface), to address the issue of computation while estimating fragility considering both record-to-record variability and structural parameter uncertainty. The fragility based on through-wall cracks is found to be severe with a median acceleration capacity close to the design-basis intensity. The record-to-record variability dominates the total uncertainty. Structural parameter uncertainties can be excluded from fragility calculations to reduce computation.