The role of crystalline rock for disposal of high-level radioactive waste (HLW)

The stress conditions in the host rock of HLW repositories, altered by construction and heat generated by the waste can cause large changes in groundwater flow, and failure of the repository. These shortcomings reduce the barrier role of the rock and the required effective isolation of HLW has to be provided by engineered barriers of which clay-embedded metal canisters are most important. The paper describes the performance of the nearfield rock of HLW packages according to two types of repositories: very long subhorizontal holes with large diameter (1.9 m) bored or blasted at 400-600 m depth, and bored 4 km deep holes with clay/concrete seals in the upper 2 km parts and HLW packages separated by clay/concrete seals in the lower 2 km parts. The most important difference between the two concepts is the much higher groundwater transmissivity of the rock in the shallow repository. A common feature is the need for rock support by filling the space between waste containers and rock with clay mud after installing the containers in shallow repositories, and by keeping the holes in deep repositories filled with clay mud from the start of boring the holes and throughout the installation of clay/concrete seals. Focus is on the role of rock discontinuities on the hydraulic and mechanical performances of the repository host rock at construction and under seismic and tectonic impact. Comparison of the two concepts shows that the one implying deep-disposal is superior but requires preparative steps in the waste placement phase. Validerad; 2015; Nivå 1; 20150720 (tinyan); Konferensartikel i tidskrift