Review of In-Service Inspection and Repair Technique Developments for French Liquid Metal Fast Reactors

In-service monitoring of nuclear plants is indispensable for both the Operator and the Regulator. The notion of in-service monitoring ranges from the continuous monitoring of the reactor in operation to the thorough in-service reactor inspection during programmed shutdowns. However, the highly specific environment found in French liquid metal fast reactor plants - Phénix and Superphénix - makes monitoring and inspection complicated because of the use of a sodium coolant that is hot, opaque, and difficult to drain. The Commissariat à lʹEnergie Atomique, in collaboration with its traditional French partners, Electricité de France utilities and FRAMATOME/Novatome Engineering, decided to conduct a 6-yr research and development program (1994-2000) to explore this problem vis-à-vis Superphénix, as well as the possibilities of intervening within the reactor block or on components in a sodium environment. Furthermore, the safety reevaluation of Phénix, conducted between 1994 and 2003, represented an excellent "test bench" during which the limits of inspection processes - applied to an integrated reactor concept - were surpassed using techniques such as fuel subassembly head scanning, ultrasonic examination of the core support, and visual inspection of the cover-gas plenum following a partial sodium draining. Repair techniques were investigated for cleaning of sodium wet structure surfaces, cutting of damaged parts, and welding in sodium aerosol atmosphere. Both conventional and laser processes were tested.