Identification of copper canisters for spent nuclear fuel: the ultrasonic method

The long-term storage of spent nuclear fuel in geological repositories has introduced the need to develop new safeguards procedures, measures and technologies. For the proposed Swedish disposal process, the Continuity of Knowledge (CoK) of fuel during transport from Oskarshamn and deposition of the same copper canisters at Forsmark is a challenging topic. Several Containment and Surveillance (C/S) measures could be used for this purpose; among them, the identification and authentication of copper canisters could be useful to trace canisters during transport. Ultrasonic techniques are used by authors to acquire unique fingerprints from each container. The ultrasonic amplitude response of a series of chamfers machined in the inner part of the copper lid can be used as a unique signature readable from outside the canister. In addition, canisters can be authenticated by investigating the welding area between the lid and the canister itself. The robustness of this approach is guaranteed by the angular matching between the identification and authentication fingerprints to produce a  third unique fingerprint, more reliable than the other two. Several experimental tests are performed to validate the approach and optimize the design of a device for the acquisition of ultrasonic fingerprints. A potential implementation of this device within the Swedish disposal process is also studied. The acquisition of ultrasonic references could be carried out after canisters’ final machining at the encapsulation plant and the process could be completely automated. The reduced cost of realization and its ease of use are the main advantages of the method. However, the machining of chamfers on copper lids requires the introduction of further steps in the manufacturing process of containers.