The current constraint at the middle plane of two emplacement drifts (drift pillars) in the Yucca Mountain repository is that the temperature there must be kept below 96 °C, the boiling point of the repository horizon, in order to maintain sub-boiling conditions. The rationale for this limit is that sub-boiling temperatures would maintain the open flow of condensate and infiltrating water that might otherwise collect above the repository and potentially drain into the drift. To test this rationale, the drift-scale coupled heat and mass transfer in the Yucca Mountain repository is analyzed under various infiltration, ventilation, and waste-loading conditions using both two- and three-dimensional models. The results reveal some physical phenomena of the drift pillars that indicate a more robust repository performance than achieved by the sub-boiling pillar concept.
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