COMPARISON OF UNIFORM HAZARD SPECTRA AND CONDITIONAL SPECTRA APPROACH IN THE FRAMEWORK OF FRAGILITY CURVE DEVELOPMENT

摘要

Seismic Probabilistic Safety Assessment (PSA) studies are extensively implemented in risk assessment tools of nuclear power plants and primarily aim to estimate Core-Damage-Frequency (CDF) and Low-Early-Release-Frequency (LERF) based on the expected seismic hazard at a particular site. In the framework of seismic PSA studies, failure of a structure, system or component is estimated by means of a fragility (probabilistic failure curve), usually defined by means of a median seismic capacity A_m, an aleatory variability β_R and an epistemic uncertainty β_U, based on the Uniform Hazard Spectrum (UHS) of the underlying seismic hazard study. This paper wants to illustrate the intrinsic margins buried in the classical approach using UHS compared to when using earthquake scenario spectra (Conditional Spectra - CS) with realistic frequency content. In order to evaluate the benefit of conditional spectra, which on their turn need more computational effort as the traditional UHS based evaluation, a comparison for a (nuclear) structure is performed. The comparison of the UHS and CS approach in the framework of fragility curve development and the subsequent vulnerability analyses demonstrate the use and potential benefit of the CS. The use of more realistic ground motion input will be discussed in this paper in the context of improving the risk assessment of critical facilities, such as nuclear power plants.