HIGH WIND PRA FAILURE CALCULATIONS, ERROR ESTIMATES, AND USE OF CAFTA

摘要

Quantification of the top event in HW (High Wind) Probabilistic Risk Assessments (PRAs) involves thousands of computations of component and system failures with thousands of cutsets. The computation of component failure frequency from hazard and fragility curves is fundamental to HW plant response quantification. This paper examines failure frequency calculations using wind hazard and fragility functions. Multiple issues are investigated, including: (1) the number of wind speed intervals needed for accurate computation of component failures; (2) the wind speed range needed to accurately compute failure frequencies; (3) the differences in the computed failure frequency from the derived mean curve vs. its family of curves; (4) the tradeoffs in modeling single vs. multiple wind hazards; and, (5) the range of error bounds for perfectly positively and perfectly negatively correlated failure modes compared to statistically independent modes. We found many sources of potential errors, mostly ones of over estimation of failure frequency. Additional work is needed in HW modeling in order to develop improved understanding of HW PRA failure quantification.