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APPLICATION OF HOST ROCK CLASSIFICATION AND ACCEPTANCE CRITERIA FOR REPOSITORY LAYOUT AND THE SAFETY CASE

In Sweden and Finland the spent nuclear fuel will be disposed of in a KBS-3 type repository in crystalline rock. Extensive surface based studies at Forsmark and Laxemar sites by SKB in Sweden and at the Olkiluoto site by Posiva Oy in Finland show that the bedrock in general will provide suitable and sufficiently stable conditions for a repository. Still, there are certain site specific features, e.g.: extensive deformation zones, volumes of relatively low mechanical strength in relation to the rock stress, sparse occurrence of highly transmissive fractures or very highly saline groundwaters that may affect the safety of the repository. The KBS-3 concept aims at long-term isolation and containment of the spent fuel assemblies in the copper canisters. Consequently, the safety functions of the host rock are a) to isolate the waste from the biosphere, b) provide favourable mechanical, geochemical and hydrogeological conditions for the engineered barrier system and c) to limit and retard inflow to repository and releases of harmful substances from the repository. This paper presents an approach, how to derive the criteria for selecting suitable canister positions from the general safety functions of the host rock. An intermediate step is definition of the safety function indicators and related criteria, which consider properties and conditions under which the barriers will fulfil the safety functions. Examples of the current status of the development work are given highlighting the different aspects of applying such criteria for design, safety assessment and practical testing in tunnel conditions.