Validating the Multiscale Thermohydrologic Model Using an Alternative Model of the Proposed Repository at Yucca Mountain
Abstract
The MultiScale ThermoHydrologic Model (MSTHM) is used in the total system performance assessment (TSPA) for the proposed nuclear-waste repository at Yucca Mountain. The MSTHM uses the Nonisothermal Unsaturated Flow and Transport (NUFT) code to represent thermal-hydrologic (TH) processes occurring at scales from a few tens of centimeters around individual waste packages and emplacement drifts (tunnels) all the way to the kilometer scale for heat flow through the mountain. The MSTHM is computationally more efficient than a monolithic 3-D TH model because it breaks the problem into smaller tractable pieces. An MSTHM simulation is constructed with NUFT-submodel calculations of various levels of coupled-process detail and scale, by superposing results of 3-D mountain- and drift-scale thermal submodels onto those of 2-D drift-scale TH submodels. The MSTHM was previously validated against an alternative (monolithic) 3-D TH model for a test problem at a scale smaller than the Yucca Mountain repository. Good agreement with the alternative model was obtained for temperature, relative humidity, and liquid saturation. A parallel-CPU version of NUFT handles much larger and more computationally demanding problems. This version is applied to an alternative (monolithic) 3-D "pillar-scale" TH model to simulate near-field and in-drift TH behavior along a full-scale (~1000-m long) emplacement drift. Results from the alternative model are compared to corresponding MSTHM results. Agreement with the alternative model builds confidence in the MSTHM applied at the scale of the Yucca Mountain repository. This study justifies key assumptions used in the MSTHM, such as that of negligible vapor flow along emplacement drifts. The pillar-scale model is also used to conduct a sensitivity study of parameters that control the magnitude of vapor flow and condensation along emplacement drifts. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.H51F0849H
- Keywords:
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- 1829 Groundwater hydrology;
- 1846 Model calibration (3333);
- 1847 Modeling