Comparison of CFD Natural Convection and Conduction-Only Models for Heat Transfer in the Yucca Mountain Drifts

A CFD analysis was conducted comparing turbulent natural convection and conduction-only models used for heat and fluid flow simulations in the drifts of the Yucca Mountain Project. The conduction-only model represents open spaces in the drifts using effective air thermal conductivities. The FLUENT code was used for both simulations with heat generation boundary condition at the waste package and constant temperature boundary condition 5 meters into the host rock formation. Comparisons were made of temperature contours in the drift air and temperature profiles at surfaces of the different engineered components using the two approaches. The results show that for the two-dimensional YMP geometry considered, the average surface temperatures of the CFD natural convection and conduction-only using the equivalent thermal conductivity are similar and the maximum local temperature differences for the different surfaces were within two 2°C. The differences in temperature profiles reflect the use of a single average equivalent thermal conductivity. The effect of the differences on repository performance is discussed.