Safety related investigations for the direct disposal of spent HTR fuel elements

The German strategy for managing the spent fuel from the two existing high-temperature gas-cooled power plants relies on the treatment of the fuel as waste without recovery of uranium and plutonium via reprocessing. The spent fuel elements will, after an interim period of storage at the reactor site, be suitably encapsulated in a gas-tight steel canister, and then placed in a deep mined rock salt repository either in a series of deep boreholes or alternatively stacked horizontally in sacrificial self-shielding transport and storage containers in the mine drift. Dry interim storage, encapsulation, and final test disposal are being studied for the spent spherical HTR fuel elements. Considerable progress has been achieved in safety related investigations concerning fuel element behaviour under normal operational conditions during interm and ultimate disposal as well as after the very unlikely event of accidental ingress of water into the salt mine repository. The salt brine thus formed would corrode the waste package and leach radionuclides from the fuel. A considerable body of data has been collected as a function of different parameters, e.g. brine composition, surface area, pressure and temperature. From the knowledge already available it can be concluded that a safe ultimate disposal of spent HTR fuel in a salt repository should be feasible