Lab Testing of Method for Clay Isolation of Spent Reactor Fuel in Very Deep Boreholes

In Sweden and Finland and some other countries, two fundamentally different multi barrier concepts for disposal of spent reactor fuel (HLW) are the often cited as KBS-3 methods and Very Deep Boreholes methods (VDH) on which the paper is focused. These concepts have engineered barriers in the form of clay-embedded canisters with spent reactor fuel. The clay, placed around the canisters and between them, provides ductility and tightness for minimizing the risk of canister breakage. The large-diameter VDH holes have dense clay seals of smectite-rich material in combination with clay mud for stabilization of the rock. In this paper, clay mud of smectite-rich Danish Holmehus clay was investigated for evaluation of the physical interaction with the dense clay blocks. The possibility of solving the problem of rapid hydration of the blocks, which can make the resistance to insertion of the units of dense clay and canisters (“supercontainers”) in the mud difficult, was investigated by using pre-wetted dense clay blocks prepared by a new method (“DW” technique). The laboratory experiments, which were made with model versions to simulate the installation of super containers in clay mud have given promising results.