The results of a research project on thermal-hydrologic-airflow model development are reported in this paper, studying the coupled processes within waste emplacement drifts at the proposed nuclear waste repository at Yucca Mountain. Natural, convective air recirculation in a representative emplacement drift during post-closure is explicitly simulated, using the MULTIFLUX model and numerical code in conjunction with the TOUGH2 simulator. These results are compared to simplified models using an equivalent dispersion-type heat and moisture transport model approach. Results from the explicit convective velocity simulation model provide higher axial heat and moisture fluxes than those estimated from the simpler, equivalent-dispersion model, in addition to differences in temperature, humidity and condensation rate distributions along the drift length. The simulation results suggest that large-eddy turbulent flow, as opposed to small-eddy flow, dominate the drift air space for at least 5000 years following waste emplacement. The size of the largest, longitudinal eddy is equal to half of the drift length, providing a much stronger axial heat and moisture transport mechanism from the hot to the cold drift sections than what is currently and conservatively predicted by other approximate models using high estimates for the equivalent dispersion coefficient in the emplacement drift.
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