SEISMIC FRAGILITY EVALUATION OF A MARK I SUPPRESSION CHAMBER INCLUDING FLUID-STRUCTURE INTERACTION ANALYSIS USING COMPUTER PROGRAM NASTRAN

摘要

The Muhleberg Nuclear Power Plant (KKM) in Switzerland is a single-unit Mark I boiling water reactor. BKW FMB Energie AG, who owns and operates KKM, recently updated the plant seismic probabilistic safety assessment (SPSA). Seismic fragility evaluation of the suppression chamber is an important element of the KKM SPSA and deterministic seismic evaluation, so realistic calculation of its seismic response is necessary. Previous seismic analyses considered all of the contained water to respond with the suppression chamber in the impulsive mode. For the seismic fragility evaluation, we performed the seismic response analysis accounting for fluid-structure interaction effects using computer program NASTRAN to eliminate excessive conservatism in the previous analyses. The seismic fragility for failure of the suppression chamber anchorage was obtained by comparison of median anchorage demand from the fluid-structure interaction seismic response analysis and median anchorage capacity. The High Confidence of a Low Probability of Failure (HCLPF) capacity exhibited significant margin above the mean 1.0E-04 uniform hazard spectrum (UHS), which is attributable to the more realistic seismic demands obtained by rigorous fluid-structure interaction analysis.