The Code of Federal Regulations, Title 10, Part 63 (10 CFR Part 63) for the proposed high-level nuclear waste disposal facility at Yucca Mountain, Nevada, USA, is risk-informed and performance-based. The regulations require demonstration of compliance with dose performance objectives for potential risk from natural hazards (e.g., earthquakes). Seismic risk can be evaluated by considering the ability of the structures, systems, and components (SSCs) that are relied on to prevent or mitigate seismically induced event sequences, to perform during a seismic event. Seismic risk or the mean probability of unacceptable performance of an SSC important to safety (ITS), is estimated by convolving the mean seismic hazard (i.e., mean annual probability of exceedance of ground motion level) and the SSC ITS mean fragility (i.e., the mean conditional probability of failure, given the ground motion level) curve. The seismic hazard curves at different sites can have substantially different characteristics (e.g., slopes). The mean fragility curve of an SSC for a defined failure mode or a specified limit state condition is typically defined as being lognormally distributed and can be expressed in terms of a median capacity level, and a composite log standard deviation. The seismic risk computations can be performed either by numerical integration or by a closed-form solution. This study aims at gaining insight on sensitivity of parameters that may affect the seismic risk of SSCs ITS. Effects of the following parameters on the seismic risk are discussed in this paper: (a) discretization steps in the numerical integration method; (b) low probability range of the seismic hazard curve; (b) slope of the hazard curve; and (d) log standard deviation of the fragility curve.
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