Evaluation of Seepage during the Thermal Period at Yucca Mountain

Jens T. Birkholzer

Contact: 510/486-7134, jtbirkholzer@lbl.gov

Reserach Objectives
Predicting the amount of water that may seep into waste emplacement tunnels (drifts) is essential for assessing the performance of the geologic nuclear waste repository at Yucca Mountain, Nevada. At ambient temperatures, seepage from the unsaturated fractured tuff into the drifts is reduced by the capillary barrier behavior at the rock-drift interface. In addition, the fractured rock in the drift vicinity will be heated to maximum temperatures of more than 130 o C, caused by the radioactive decay of the nuclear waste, and water percolating down towards the repository will be subject to vigorous boiling during the first several hundred years following waste emplacement. Thus, the superheated fractured rock forms a vaporization barrier that may further limit the potential for seepage. To study the impact of the drift-scale thermal-hydrological (TH) perturbations, a TOUGH2 simulation model was developed for the prediction of "thermal seepage" (i.e., seepage during the time that flow is perturbed due to heating).

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