Innovative method to authenticate copper canisters used for spent nuclear fuel based on the ultrasonic investigation of the friction stir weld

Sweden is planning to store nuclear spent fuel in long-term geological repositories. Copper canisters with a ductile iron insert will preserve the fuel for thousands of years at a depth of about 500 meters in Swedish bedrock. The IAEA (International Atomic Energy Agency) and EURATOM safeguards inspectorates have to maintain the Continuity of Knowledge (CoK) during transport and deposition of canisters from the encapsulation plant to the final repository. The aim of our research is then oriented to provide such CoK for canisters by an identification and authentication based on ultrasound. This paper describes an authentication method oriented to prevent falsification of copper canisters. According to the ultrasonic investigation of the Friction Stir Welding (FSW) process of the copper lid onto the cylindrical tube, the ultrasonic response of the remaining gap partially filled during the welding is used as a unique pattern for authentication. The analysis of various measurements made on angular sections of copper lids friction stir welded onto the tube revealed the feasibility of acquisition of a valuable signal from the reflection of the internal gap. Following the observations on this data set, a possible technical design is detailed where the identification and authentication methods can be combined with immersion probes.