The U.S. Geological Survey's program for geologic and hydrologic evaluation of physiographic provinces to identify areas potentially suitable for locating repository sites for disposal of high-level nuclear wastes was announced to the Governors of the eight States in the Basin and Range Province on May 6, 1981. Representatives of Arizona, California, Idaho, New Mexico, Nevada, Oregon, Texas, and Utah, were invited to cooperate with the Federal Government in the evaluation process.

The Lake Superior region (Wisconsin, the Upper Peninsula of Michigan, and Minnesota) contains 41 Precambrian crystalline (medium- to coarse-grained igneous and high-grade mstamorphic) rock complexes comprising 64 individual but related rock bodies with known surface exposures. Each complex has a map area greater than 78 km2. About 54% of the rock complexes have areas of up to 500 km2, 15% fall between 500 km2 and 1000 km2, 19% lie between 1000 km2 and 2500 km2, and 12% are over 2500 km2. Crystalline rocks of the region vary widely in composition, but they are predominantly granitic.

Fifty-four objectives were identified to guide the screening of the Nevada Research and Development Area of the Nevada Test Site for relatively favorable locations for the disposal of nuclear waste in a mined geologic repository. The objectives were organized as a hierarchy composed of 4 upper-level, 12 middle-level, and 38 lower-level objectives. The four upper-level objectives account for broad national goals to contain and isolate nuclear waste in an environmentally sound and economically acceptable manner.

Repository performance assessment is analysis that identifies events and processes that might affect a repository system for isolation of radioactive waste, examines their effects on barriers to waste migration, and estimates the probabilities of their occurrence and their consequences. In 1983 Battelle Memorial Institute's Office of Nuclear Waste Isolation (ONWI) prepared two plans — one for performance assessment for a waste repository in salt and one for verification and validation of performance assessment technology. At the request of the U.S.

Geologic repositories for radioactive waste are evolving<br/>from conceptualization to the development of specific<br/>designs. Estimates of long-term hazards must be based<br/>upon quantitative predictions of environmental releases<br/>over time periods of hundreds of thousands of years and<br/>longer.

Comments contained in this document were received by the U.S. Department of Energy (DOE) on the Report of Early Site Suitability Evaluation (ESSE) of the Potential Repository Site at Yucca Mountain, Nevada, (Younker et al., 1992, SAIC 91/8000). Comments were received from the U.S. Department of Interior, the U.S. Nuclear Regulatory Commission, the State of Nevada, and several local affected governments in Nevada. No comments were received from members of the public.

The Nuclear Regulatory Commission (NRC) is publishing technical criteria for disposal of high-level radioactive wastes (HLW] in geologic repositories, as required by the Nuclear Waste Policy Act of 1982. The criteria address siting, design, and performance of a geologic repository, and the design and performance of the package which contains the waste within the geologic repository. Also included are criteria for monitoring and testing programs, performance confirmation, quality assurance, and personnel training and certification.

Deep geologic repositories are being widely studied as the most favored method of disposal of nuclear waste. Scientists search for repository sites in salt, basalt, tuff and granite that are geologically and hydrologically suitable. The systematic evaluation of the safety and reliability of deep geologic disposal centers around the concept of interacting multiple barriers. The simplest element to describe of the geologic barrier is the physical isolation of the waste in a remote region at some depth within the rock unit.

The National Plan for Siting High-Level Radioactive Waste Repositories describes the process the Department of Energy (DOE) is using to find sites suitable for disposal of high-level radioactive waste.