A critical component of a nuclear waste repository is the cut-off seal, which will mitigate flow and gas migration along the excavation surface and damage zone. This paper examines a thin to wide slot cut-off geometry under fixed stress (an upper bound) and sedimentary rock properties. Volumetric extensile strain was used as an indicator of the extent of excavation damage prior to and after the construction of the cut-off. Using the volumetric extensile strain to plastic yield zone area ratio the cut-off performance for thickness to depth ratios between 0.05 and 0.7 were examined. It was found that for a cut-off with a thickness to depth ratio of less than 0.13 a complete disconnect could be established across the cut-off slot, indicating that a slender slot is optimum under the conditions modelled. Further modelling with different stresses and properties will establish if these results are applicable for a wider range of possible repository settings.
A nuclear waste repository requires a system of barriers, natural and man-made, acting together to isolate the waste from the surrounding hydrosphere and biosphere. The conceptual components of a repository include access and ventilation shafts or ramps, horizontal adits, and placement drifts, caverns or boreholes. The access and ventilation shafts or ramps pass from surface, through the isolating rock mass, and end in the host rock. The horizontal adits are long tunnels for access and from which large-diameter boreholes are drilled or caverns can be excavated to provide the waste canister receptacles. The canister itself is an isolating component, designed to withstand high compressive stresses and to minimize the rate of corrosion of the canister. For the case of high level waste storage; the canister will typically be surrounded by a highly compact bentonite, which will act as the first barrier in the event the canister is breached. The interface between the bentonite and the rock mass, as well as the excavation damage zone (EDZ) represent a potential pathway for radionuclide migration if the canister is breached.
