Site characterization of the Yucca Mountain disposal system for spent nuclear fuel and high-level radioactive waste

This paper summarizes the investigations conducted to characterize the geologic barrier of the Yucca Mountain disposal system. Site characterization progressed through (1) non-intrusive evaluation and borehole completions to determine stratigraphy for site identification; (2) exploration from the surface through well testing to evaluate the repository feasibility; (3) underground exploration to study coupled processes to evaluate repository suitability; and (4) reporting of experimental conclusions to support the repository compliance phase. Some of the scientific and technical challenges encountered included the evolution from a small preconstruction characterization program with much knowledge to be acquired during construction of the repository to a large characterization program with knowledge acquired prior to submission of the license application for construction authorization in June 2008 (i.e., the evolution from a preconstruction characterization program costing <$0.04×109 as estimated by the Nuclear Regulatory Commission in 1982 to a thorough characterization, design, and analysis program costing $11×109—latter in 2010 constant dollars). Scientific understanding of unsaturated flow in fractures and seepage into an open drift in a thermally perturbed environment was initially lacking, so much site characterization expense was required to develop this knowledge. - Highlights: • Progression of site characterization through four phases is described for a geological repository at Yucca Mountain. • Well testing from the surface to determine hydraulic flow properties in the saturated and unsaturated zones is summarized. • Investigation of infiltration in a desert climate is summarized. • Underground testing to evaluate coupled hydrologic–thermal processes and determine seepage into disposal drifts is summarized