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Review of DOE's Site Characterization Process

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DOE's Site Characterization Process
The NRC's Role

DOE’s Site Characterization Process

The 1988 Site Characterization Plan for Yucca Mountain, developed by the U.S. Department of Energy (DOE), established the initial basis for the many engineering and scientific investigations of the site. Under that plan, DOE has conducted a variety of site characterization activities to evaluate the waste isolation capabilities of the Yucca Mountain site.

In 1991, the State of Nevada granted DOE the permits necessary to proceed with excavating test pits and trenches, drilling bore holes, and monitoring ground water. Then, in September 1994, DOE began excavating the exploratory studies facility using a tunnel boring machine. The initial design called for a continuous tunnel with a diameter of 7.6 meters (25 feet). Completed in April 1997, the tunnel begins at the North Portal and extends approximately 2,000 meters (1.24 miles) to the northwest. The tunnel then transitions into a turn of approximately 60 degrees to the south. The section from the North Portal to the 60-degree turn is known as the North Ramp. The turn from the North Ramp leads to a main tunnel 300 meters (984 feet) below the surface. The main tunnel has a north-south alignment and extends approximately 3,000 meters (1.86 miles) to the south. The main tunnel ends in a 90-degree turn, from which the tunnel travels east about 1,300 meters (0.8 miles) and emerges at the South Portal. (For additional information, see the Conceptual Design of the Yucca Mountain Disposal Plan.)

In excavating the exploratory studies facility, the tunnel boring machine has bored through a series of geologic features, including a structural feature known as the Bow Ridge Fault. Within the tunnel are seven testing alcoves and four test niches that are being used to investigate the hydrologic, hydrochemical, and thermomechanical properties of the rocks underlying Yucca Mountain.

In December 1997, DOE began excavatinga smaller exploratory tunnel (5.5 meters/18 feet) across the main tunnel. This smaller tunnel is known as the "east-west" or "cross" drift, and runs almost perpendicular to the North Ramp. The "cross" drift begins to the west of the Bow Ridge Fault and crosses over and above the north-south main tunnel. It is about 2,600 meters (1.6 miles) long and ends near the Solitario Canyon Fault. The "cross" drift will also contain instrumentation for scientific tests, and should provide additional data on the sub-surface geology of Yucca Mountain to the west of the main tunnel.

The NRC's Role

In reviewing DOE's site characterization process, the primary objective of the U.S. Nuclear Regulatory Commission (NRC) was to identify any specific concerns that may impact licensing of the repository. Toward that end, the NRC staff observed DOE's site characterization activities, including exploratory drilling and tunneling. The staff also observed and commented on DOE's quality assurance program. See Resolution of Key Technical Issues for High-Level Waste Disposal for more information about the NRC's activities to review DOE's site characterization program.