Seismic Qualification of Equipment: A PRA-Consistent Framework Available to Purchase

The seismic probabilistic risk assessment (SPRA) for a nuclear power plant involves the estimation of fragility curves for plant equipment. The seismic qualification of an equipment based on testing requires the equipment to continue to function when subjected to a specific test response spectrum (TRS). Broad banded ground motions have been found to cause more damage to equipment than the filtered narrow banded excitations. As a result, the definition of acceleration capacity used in the fragility models use clipped response spectra for both test response spectrum (TRS) and required response spectrum (RRS). The main purpose of the clipping factors is to convert a narrow banded response spectrum to a broad banded spectrum. The broadband correction factor and the modal interaction correction factors together contribute to the definition of clipping factor. The current study involves reconciliation with previous research by generating the mean response factor for different waveforms and subsequently the root-mean-square (RMS) severity ratio as a function of bandwidth. This ratio can be estimated for real earthquakes from their peak-to-rms values and the peak spectral values. In addition it can be shown that in case of real narrow banded earthquakes, this ratio is even lower and therefore the clipping would be greater. The modal interaction correction factor which considers the effect of interaction between different modes in case of broad banded time histories has also been investigated. The primary objective of this work is to study the existing Conservative Deterministic Failure Margin (CDFM) and Probabilistic approaches for estimating these factors as per the guidelines of EPRI [2] and apply the same to real life ground motions. It has been observed that the recommended practices are based on studying the behavior of random ground motions generated artificially for different bandwidths and center frequencies. The present study aims towards a more realistic fragility estimation of equipment by studying the spectral response of equipment based on actual ground motions. The purpose is to evaluate clipping factors that are consistent with Seismic Probabilistic Risk Assessment.