Assessing Effects of Thermal Loading on the Stability of Emplacement Drifts

Thermal-mechanical analyses were performed to assess the effects of thermal loading on the stability of emplacement drifts used for nuclear waste disposal. The analyses focused on a U.S. Department of Energy design concept and the rock-mass properties for a potential Yucca Mountain repository. The design concept includes using forced ventilation to reduce the amount of waste-generated heat transmitted into the rock during the operational period. The analyses indicate that thermally induced stress during the forced-ventilation period would be insufficient to cause instability of the drifts. Thermal stresses, however, would increase rapidly after forced ventilation is terminated and would cause overstress of rock near the perimeter of the drifts. Such overstress would not cause instability if the drifts are provided with effective ground support. The overstress, however, would persist for a long time and indicates a potential for progressive spallation of the drift perimeter after any installed ground support loses effectiveness. Progressive degradation of drifts and the accumulation of rock rubble inside the drift openings would result from such spallation.