Seismic Fragility Evaluation of Main Steam Piping of Isolated APR1400 NPP Considering the Actual Failure Mode

Abstract

An isolation system installed in a nuclear power plant (NPP) could increase seismic safety during seismic events. On the other hand, a more significant relative displacement may occur due to the isolation system. The seismic risk could be increased in the case of an interface piping system that connects isolated and nonisolated structures. Therefore, it is necessary to consider the piping systems when evaluating the safety of isolated-NPPs. This study performed seismic fragility analysis with isolated APR1400 nuclear power plants with the main steam piping. The main steam piping is the interface pipe connecting the isolated auxiliary building and the turbine building. The failure mode for seismic fragility analysis was defined as cracks caused by leakage. The experimental and numerical analysis results quantified the leak-through crack point as a damage index. The seismic fragility curves are suggested based on peak ground acceleration and the relative displacement between the isolated and nonisolated buildings.