Semi-Analytic Stereological Analysis of Waste Package/Fracture Intersections in a Granitic Rock Nuclear Waste Repository

Abstract

In Sweden, spent nuclear fuel is planned to be placed in copper/iron canisters and deposited at a depth of approximately 500 m in granitic rock. Earthquakes may induce secondary shear movements in fractures intersecting canister deposition holes, thereby threatening the integrity of the canisters. The extent of a secondary movement is related to earthquake magnitude and to the size of the intersecting fracture. This paper analyses the likelihood of a canister being intersected by a fracture exceeding a certain radius, for given fracture size and orientation distributions, and under the assumption that such fractures are not detected and avoided at canister deposition. The stereological analysis is analytic but requires numerical evaluation of a simple integral for detailed results. It is demonstrated that the likelihood of critical intersections is a few percent for typical fracture populations determined from field observations at a candidate site for a spent nuclear fuel repository in Sweden. Sensitivities to a number of parameters in the description of the fracture distributions are explored, demonstrating that the results are more sensitive to uncertainties in parameters relating to the fracture size distributions than to those relating to the orientation distributions. The analytical result is verified by numerical simulations of canister/fracture intersections with excellent agreement.