The single heater test (SHT) is up to an eighteen-month-long heating and cooling experiment begun in August, 1996, located underground within the unsaturated zone near the potential geologic repository at Yucca Mountain, Nevada. Experimental measurements at the test site include temperature measurements made at various radial locations and along the length of the heater, moisture concentration measurements around the heater zone, and rock displacement measurements resulting from the development of thermal stresses.
Three-dimensional thermal-hydrologic calculations were performed with an integrated finite difference code. This computer code determines the simultaneous transport of heat and mass in response to a thermal perturbation resulting from an emplaced heat source. The working range in rock permeability (5.1 millidarcy to 5.3 darcy) results in predicted temperature differences of approximately 10°C or less. The high permeability simulations resulted in lower predicted temperatures around the heater along with the formation of an asymmetrical dry-out zone resulting from the development of buoyant gas-phase convection cells. The low bulk permeability simulations resulted in higher predicted temperatures and a symmetrical dry-out zone.
Three-dimensional, elastic thermal-mechanical calculations were performed with a finite element nonlinear structural mechanics computer code. The temperature predictions from the thermal-hydrologic calculations were used as the input temperatures for the thermal-mechanical calculations. Total displacements along the multi-point borehole extensometers (MPBX’s) are predicted to be no more than ∼3 mm for the conditions and properties used.