The Role of Smectite Clay Barriers for Isolating High-Level Radioactive Waste (HLW) In Shallow and Deep Repositories

AbstractThe major engineered barriers to migration of radionuclides from HLW in repositories are the canister and surrounding smectite clay. They interact physically and chemically by which the properties of both are changed, especially of the smectite “buffer” clay that is examined in the paper. The canisters are made of copper-lined iron according to the Swedish and Finnish concepts, steel being an alternative. The function of the host rock is of importance and the paper examines the role of two repository concepts with long subhorizontal or deep vertical holes for placing the waste.The hydraulic conductivity of the canister-embedding smectite clay can be significantly raised by high temperature and temperature gradients, which generate precipitation of salt and silica in different parts of the buffer clay. The impact of the degrading processes on the waste-isolating capacity is different for shallow repositories in permeable rock and for very deep disposal with higher temperature. The latter has stagnant groundwater as major barrier to the migration of radionuclides