HR: 0800h
AN: H21B-1334    [Abstracts]
TI: Effects of Natural Drift Degradation on In-Drift Moisture Distribution
AU: * Manepally, C
EM: cmanepally@swri.org
AF: Center for Nuclear Waste Regulatory Analyses - Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 United States
AU: Fedors, R W
EM: RWF@nrc.gov
AF: U.S. Nuclear Regulatory Commission, Two White Flint North 11545 Rockville Pike , Rockville, MD 20852 United States
AB: Understanding the complex thermohydrological processes at Yucca Mountain, Nevada, is essential for assessing the long-term performance of a potential high-level radioactive waste repository. This task is challenging as a result of the heterogeneity of the natural system, interactions between the engineered and natural systems, the unsaturated conditions at the repository horizon, and the potential for natural drift degradation in a thermally perturbed environment. Modeling in-drift thermohydrological processes to predict the temperature and relative humidity in the potential emplacement drift and in the near-field environment is vital to determine the composition of pore water that may contact the waste package and to evaluate the potential for corrosion of waste packages. Detailed process models will serve as a basis to model abstractions used in performance assessment. Degradation of the host rock may lead to rubble covering the engineered components in portions of the repository, which will markedly change in-drift thermohydrologic conditions. This poster presents a two-dimensional detailed process model that incorporates the temporal variation of in-drift and drift wall geometry as a result of drift degradation. At early times of the postclosure period, the heat generated by emplaced waste induces water vapor transport away from the drift, creating a dryout zone and redistributing pore fluids within a potentially large volume of host rock. At later times, after the thermal pulse has substantially dissipated, the thermohydrological conditions in the rubble strongly influence the amount of water that could contact the waste and contribute to the source release and in-drift transport of radionuclides. Moisture distribution in the rubble pile is dependent on its hydrologic properties, such as porosity and permeability, and the possible capillary barrier between the intact host rock and rubble. The hydrologic properties of the rubble are difficult to estimate because of uncertainty in packing and grain size distribution of the rubble pile, the latter of which can range from fine particulate matter to boulders. Sensitivity of the moisture distribution in the rubble and at the rubble-intact rock-interface to the rubble hydrologic properties will also be examined. This is an independent product of CNWRA and does not necessarily reflect the views or regulatory positions of NRC. The NRC staff views expressed here are preliminary and do not represent a final judgment or determination of the matters addressed or of the acceptability of a license application for a geologic repository at Yucca Mountain.
DE: 1829 Groundwater hydrology
DE: 1847 Modeling
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: Fall Meeting 2005