Recommendation for a second access for the Yucca Mountain exploratory shaft facility

The Department of Energy (DOE) is conducting the Nevada Nuclear Waste Storage Investigations Project to determine the suitability of Yucca Mountain as a site for a repository for radioactive waste. An exploratory shaft facility (ESF) is planned to permit characterization of the tuff underlying Yucca Mountain. The ESF consists of a 12-foot-diameter, 1480-foot-deep exploratory shaft (ES) and associated surface facilities. This report responds to a request by DOE to study the inclusion of a second access in the ESF for the purposes of improving safety, providing flexibility in the scope and duration of geologic testing, and facilitating subsurface construction of the full repository. Eight options for a second access to the ESF are explored. These options include using the ES in combination with either a second shaft, a muck-handling ramp, or a waste-handling ramp. Some of these options also include enlarging the diameter of the ES to 16 feet. On the basis of the analysis performed for this study, a 16-foot-diameter ES and a muck-handling ramp are recommended as accesses to the ESF. Should budget or other considerations require a less expensive means of providing a second access, a 12-foot-diameter ES and a 6-foot-diameter second shaft would satisfy the requirement to improve safety