Cutoff Modeling for Drift Sealing in Underground Nuclear Waste Repositories

Different types of barriers are used in an underground nuclear waste repository to isolate the waste, including engineered barriers and the natural geological environment. Cutoff seals are one component of the engineered barrier design used in drifts and shafts at specific locations in a repository. In this study, rectangle, triangular and trapezoidal cutoff shapes for drift sealing are numerically modeled. The extent of the excavation damaged zone in crystalline rock is predicated for changes in the shape and size of these cutoffs. The excavation damaged zone dimensions are determined based on plastic yielding and the volumetric strain in these model simulations. The influence of the stress to strength ratio on the extension of the excavation damage zone due to cutoff construction is also examined. The mechanical response of the rock around the drifts showed that the extension of the excavation damage zone beyond the cutoff is dependent on rock properties and the geometry of the cutoff. The rectangular shaped cutoff dimensions were optimized, and it was determined that leads to the smallest increase in the depth of the excavation damage zone associated with cutoff construction.