Role of SSI on seismic performance of nuclear reactors: A case study for a UK nuclear site

Abstract

The role of soil-structure interaction (SSI) on the risk of unacceptable performance of five non-structural components of a nuclear reactor is investigated through a representative case study consisting of a pressurized-water reactor sited at Holyhead, United Kingdom. The seismic hazard at the site is defined by a 10,000 years uniform hazard spectrum, and its corresponding design response spectrum computed for a target structural performance goal of 1 × 10−5. Nine hypothetical soil profiles, with shear wave velocities ranging from 300 m/s to 1,200 m/s, are considered. Non-linear site response analyses are performed to determine the input motion at the foundation level; seismic capacity and demand of the components are computed using response-history analyses. To obtain high-confidence performance estimates from a limited number of results, Monte-Carlo simulation is used to expand the seismic demand matrix. It is shown that the probability of unacceptable performance of the reactor is highly sensitive to SSI effects. Specifically, the beneficial effects induced by SSI on the seismic performance of the reactor are limited to models sited on stiffer soil deposits (ie, Vs ≥ 900 m/s), whereas, the median probability of unacceptable performance increases for medium-to-soft deposits.