Evaluating the Seismic Hazards and Developing Design Ground Motions for Yucca Mountain, Nevada, U.S.A.

Abstract eng:
Yucca Mountain, Nevada has been recommended and approved for development as the site of the United States’ first permanent repository for the disposal of spent nuclear fuel and high-level radioactive waste. As part of the development process, a license application has been prepared and submitted to the U.S. Nuclear Regulatory Commission. The license application describes earthquake ground-motion parameters for the subsurface waste emplacement facility (repository block) and for surface facilities. The ground-motion parameters are used for design of the subsurface and surface facilities, to evaluate safety during the preclosure period, and to assess repository performance during the postclosure period. Development of the ground motion parameters has been performed in three phases: (1) probabilistic seismic hazard analyses (PSHA) for both ground shaking and fault displacement; (2) geotechnical, geophysical, and geologic site characterization of the repository block and Surface Facility Area (SFA) to acquire site-specific data for site-response analysis; and (3) site-response analyses to modify reference rock outcrop ground motions from the PSHA to site-specific conditions and to develop design ground motions. The PSHA was the largest and most comprehensive analysis ever conducted for ground-shaking hazard and was a first-of-a-kind assessment of probabilistic fault displacement hazard. Formal expert elicitation was used to develop inputs for the PSHA. The hazard from the PSHA was conditioned to establish an upper range of extreme ground motions based on geologic and seismological arguments. An integrated program of borehole logging, geophysics, and velocity surveys, spectral-analysis-of-surface-wave surveys, and dynamic laboratory testing was performed to characterize the lithologic, velocity, and dynamic material properties for input into the site-response analysis. Variabilities in site properties were quantified and are accommodated in the ground-motion estimates. Site-response analyses were performed to calculate hazard-consistent ground motions using a random vibration theory-based equivalent-linear approach. Response spectra, time histories, and strain-compatible properties (SFA only) for preclosure analyses were calculated for mean annual frequencies of exceedance (AFE) of 10-3, 5x10-4, and 10-4. For postclosure analyses, ground motions were calculated for mean AFEs between 10-4 and 10-8.

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