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In heated drifts such as those designated for emplacement of radioactive waste at the proposed geologic repository at Yucca Mountain, temperature gradients cause natural-convection processes that may significantly influence the moisture conditions in the drifts and in the surrounding fractured rock. Large-scale convection cells in the heated drifts would provide an effective mechanism for turbulent mixing and axial transport of vapor generated from evaporation of pore water in the nearby formation. As a result, vapor would be transported from the elevated-temperature sections of the drifts into cool end sections (where no waste is emplaced), would condense there, and subsequently would drain into underlying rock units. To study these processes, we have developed a new simulation method that couples existing tools for simulating thermal-hydrological conditions in the fractured formation with a module that approximates turbulent natural convection in heated emplacement drifts. The new method simultaneously handles (a) the flow and energy transport processes in the fractured rock, (b) the flow and energy transport processes in the cavity, and (c) the heat and mass exchange at the rock-cavity interface. An application is presented studying the future thermal-hydrological conditions within and near a representative waste emplacement drift at Yucca Mountain. Particular focus is on the potential for condensation along the emplacement section, a possible result of heat output differences between individual waste packages. [ABSTRACT FROM AUTHOR]

Thermally induced natural convection from the heat produced by emplaced waste packages is an important heat and mass transfer mechanism within the Yucca Mountain Project (YMP) drifts. Various models for analyzing natural convection have been employed. The equivalent porous medium approach using Darcy''s law has been used in many YMP applications. However, this approach has questionable fidelity, especially for turbulent flow conditions. Computational fluid dynamics (CFD), which is based on the fundamental Navier–Stokes equations, is currently being evaluated as a technique to calculate thermally induced natural convection in YMP. Data–model comparisons for turbulent flow conditions show good agreement of CFD predictions with existing experiments including YMP-specific data. [Copyright &y& Elsevier]