Large-Scale in Situ Heater Tests for Hydrothermal Characterization at Yucca Mountain

by Thomas A. Buscheck, Lawrence Livermore Natl Lab, Livermore, United States,
Dale G. Wilder, Lawrence Livermore Natl Lab, Livermore, United States,
John J. Nitao, Lawrence Livermore Natl Lab, Livermore, United States,



Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1993

Abstract:

To safely and permanently store high-level nuclear waste, the potential Yucca Mountain repository site must mitigate the release and transport of radionuclides for tens of thousands of years. In the failure scenario of greatest concern, water would contact a waste package, accelerate its failure rate, and eventually transport radionuclides to the water table. Our analyses indicate that the ambient hydrological system will be dominated by repository-heat-driven hydrothermal flow for tens of thousands of years. In situ heater tests are required to provide an understanding of coupled geomechanical-hydrothermal-geochemical behavior in the engineered and natural barriers under repository thermal loading conditions. In situ heater tests have been included in the site characterization plan in response to regulatory requirements for site characterization and to support the validation of process models required to assess the total systems performance at the site. The success of the license application hinges largely on how effectively we validate the process models that provide the basis for performance assessment. Because of limited time, some of the in situ tests will have to be accelerated relative to actual thermal loading conditions. We examine the trade-offs between the limited test duration and generating hydrothermal conditions applicable to repository performance during the entire thermal loading cycle, including heating (boiling and dry-out) and cooldown (re-wetting). For in situ heater tests to be applicable to actual repository conditions, a minimum heater test duration of 6-7 yr (including 4 yr of full-power heating) is required. The parallel use of highly accelerated, shorter-duration tests may provide timely information for the LA, provided that the applicability of the test results can be validated against ongoing nominal-rate heater tests.

Subject Headings: Field tests | Radioactive wastes | HVAC | Thermal loads | Load tests | Site investigation | Thermal properties

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