Seismic Soil-Containment Interaction: Pipe Safety

The integrity of pipes penetrating the containment wall of a nuclear power plant may be threatened by seismic motions of the containment vessel. Within the context of an integrated accident and seismic containment reliability study, a methodology is presented for the determination of the probability of failure of a single pipe and of a system of pipes, as a function of the causative ground acceleration. Extreme rocking displacements of the containment under earthquake intensities well beyond the design level are estimated by means of simple model that takes into account the possibility for soil-base separation and the multidirectionality of the ground motion. The final reliability estimates reflect a large number of uncertainties, most of which are of statistical nature, i.e., stemming from the limited information about soil properties, details of the seismic motion, and resistance of the pipes. The correlation between failures of apparently redundant pipes that is introduced by the common dependence on system-wide uncertainties is illustrated.