HR: 1330h
AN: H13B-12    [Abstracts]
TI: Natural Barriers of the Geosphere at Yucca Mountain, Nevada
AU: * Arlt, H
EM: hda@nrc.gov
AF: U.S. Nuclear Regulatory Commission, Two White Flint North, 11545 Rockville Pike, Rockville, MD 20852-2738 United States
AU: Kotra, J
EM: jpk@nrc.gov
AF: U.S. Nuclear Regulatory Commission, Two White Flint North, 11545 Rockville Pike, Rockville, MD 20852-2738 United States
AU: Mohanty, S
EM: smohanty@cnwra.swri.edu
AF: Center for Nuclear Waste Regulatory Analyses, A Division of Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228-5166 United States
AU: Winterle, J
EM: jwinterle@cnwra.swri.edu
AF: Center for Nuclear Waste Regulatory Analyses, A Division of Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228-5166 United States
AB: Geological repositories designed to isolate high-level radioactive waste need natural and engineered barriers that prevent or slow the release of radioactive elements into the accessible environment to acceptable regulatory limits. Under the U.S. Nuclear Regulatory Commission's (NRC's) regulations, a barrier is any material, structure, or feature that prevents or substantially reduces the rate of movement of water or radionuclides from the repository to the accessible environment. In 1982, Congress passed the Nuclear Waste Policy Act which directed the NRC to include multiple barriers in regulating geologic disposal of high-level radioactive waste. Accordingly, as provided in 10 CFR Part 63, the NRC's regulations for Yucca Mountain require a repository to include multiple barriers to ensure the system is robust and not wholly dependent on any single barrier. Any potential license application to construct a repository at Yucca Mountain must identify the multiple barriers (both natural and engineered), describe the capabilities of each barrier, and provide the technical bases for the capabilities of the barriers. The NRC believes that understanding the capability of the repository's component barriers improves understanding of the overall system. The objective of this paper is to discuss potential natural barriers of the geosphere at Yucca Mountain and describe the NRC regulatory requirements for such barriers. To better understand the natural barriers of the geosphere, it helps to divide the barriers into groups of features and their associated processes. Natural barriers, i.e., barriers not constructed by man, ideally include processes that delay the transport of radionuclides from reaching the accessible environment or limit the amount of water that can seep from a ground surface to the depth of an underground repository. Natural barriers at Yucca Mountain may include: topographic influences on precipitation runoff; soil and plants influences on evaporation and transpiration; effect of surface bedrock characteristics on infiltration; influences of unsaturated zone rocks above the repository on quantity and characteristics of downward flowing water; and the effects of the repository tunnel wall geometry and rock characteristics on seepage into the tunnels. Unsaturated zone rocks below the repository may influence water and radionuclide migration into either fractures or the rock matrix, where processes such as matrix diffusion and sorption can retard radionuclide movement. Properties of different saturated zone rock units may slow the radionuclide flow rate while structural features within the saturated zone rocks (faults, heterogeneities) control water flow rate and direction. The saturated zone alluvium may reduce the water velocity while radionuclides sorption onto the alluvium can further delay radionuclides from reaching the accessible environment.
DE: 1899 General or miscellaneous
SC: Hydrology [H]
MN: 2005 Joint Assembly