HR: 1330h
AN: H32A-0510    [PDF]
TI: Thermohydrologic Modeling of the Drift Scale Test in Partially Saturated Fractured Tuff at Yucca Mountain, Nevada
AU: * Lee, K H
EM: lee23@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94551-0808 United States
AU: Buscheck, T A
EM: buscheck1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94551-0808 United States
AU: Sun, Y
EM: sun4@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94551-0808 United States
AU: Glascoe, L G
EM: glascoe1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94551-0808 United States
AU: Gansemer, J
EM: gansemer1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94551-0808 United States
AB: Results of thermohydrologic modeling of the Drift Scale Test (DST) at Yucca Mountain show good agreement with field temperatures and liquid phase saturation during the heating as well as the cooling phases of the test. The DST is an ongoing large-scale thermal field test conducted by the US Department of Energy as part of the characterization of Yucca Mountain as a potential site of a geologic repository for high-level nuclear waste. The test location is 250 m below the ground surface, in fractured nonlithophysal Topopah Spring tuff, which is one of the host-rock units for the potential repository. The DST is one of a series of field-scale thermohydrologic tests designed to help investigators better understand the coupled thermohydrologic-mechanical-chemical processes that would occur in the host rock in response to the radioactive heat of decay from emplaced waste packages. The tests also provide data for the calibration and validation of numerical models used to analyze the thermohydrologic response of the near-field host rock and Engineered Barrier System (EBS). The rock was heated by nine floor heaters, placed along a 47.5-meter long heated drift, and arrays of wing heaters installed in horizontal boreholes on either side of the drift. A bulkhead separates the HD from the unheated section of the drift. Peak heater power during the heating phase was about 52 kW for the floor heaters and 135 kW for the wing heaters. The rock was heated for 4.1 years before all heaters were turned off on January 14, 2002. Monitoring of the cool-down phase is expected to last for at least four years. Using the NUFT code and the dual-permeability approach to representing fracture-matrix interaction, we utilize a half-symmetry model to simulate the thermohydrologic response of the rock to a heating and cooling cycle. The primary goals of the analysis were to study the heat-flow mechanisms and water redistribution patterns in the boiling and sub-boiling zones, and to compare model results with measured temperature and liquid-phase saturation data, and thereby evaluate rock property data sets available for modeling thermohydrologic behavior in the rock. We use a sensitivity analysis to examine the effect of data uncertainty on the results. We obtained a good match between model and observed temperatures, and found that the distinct dryout and condensation zones modeled above and below the heater level agreed fairly well with neutron measurements of liquid-phase saturation.
DE: 1800 HYDROLOGY
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2003 Fall Meeting