Non-destructive evaluation of the spent nuclear fuel disposal canisters

The Finnish concept of high activity nuclear waste disposal is based on deep geological storage in copper canisters with cast iron inserts. The development of disposal concept and final disposal in Finland is managed and organised by Posiva Oy. Disposal canisters will be embedded in Olkiluoto bedrock at a depth of approximately 400 metres. Therefore it is essential to inspect the canisters with non-destructive testing (NDT) methods as well as possible before the final disposal. The lid of the copper disposal canister for high activity nuclear waste is sealed with a weld. Before accepting the canister to the final disposal the weld is planned to be inspected by four non-destructive testing methods. These methods are ultrasonic testing (UT), radiographic testing (RT), eddy current testing (ET) and remote visual testing (VT) using cameras. The copper overpack and the lid are also inspected with multiple NDT methods; UT, ET and VT. The nodular cast iron insert is inspected with UT and VT. In this paper the four NDT inspection methods (UT, RT, ET, VT) for inspection of different parts of the disposal canister are presented in brief. All information in this paper is collected and summarised from public reports and from the procedures of each method and inspection records. All of the four NDT methods detect defects in slightly different directions and based on different physical principles. The four methods are therefore supplements to each other in inspection of different parts of the disposal canister.