Validation of the Multiscale Thermohydrologic Model used for analysis of a proposed repository at Yucca Mountain

Abstract Performance assessment and design evaluation of the proposed repository at Yucca Mountain are facilitated by a thermohydrologic modeling tool that simultaneously accounts for processes occurring at a scale of a few tens of centimeters around individual waste packages and emplacement drifts, and accounts for processes at the multi-kilometer scale of the mountain. The most straightforward approach is to account for the 3-D drift- and mountain-scale dimensionality all within a single monolithic thermohydrologic model. This approach is too computationally expensive to be a viable simulation tool capable of addressing all waste-package locations in the repository. The Multiscale Thermohydrologic Model (MSTHM) is a computationally efficient alternative to addressing these modeling issues. In this paper, we describe the principal calculation stages to predict temperature, relative humidity, and liquid-saturation, as well as other thermohydrologic variables, in the drifts and in the host rock. Using a three-drift repository example (which is a scaled-down version of the proposed repository), we demonstrate the validity of the MSTHM approach against a nested monolithic thermohydrologic model.