Inspection and repair techniques in reactor vessel of sodium cooled fast reactor, 5-1; Current status of in-vessel observation and repair techniques in Joyo

Sekine, Takashi ; Kitamura, Ryoichi; Maeda, Yukimoto; Chatani, Keiji

Since in-vessel observation for a sodium fast reactor has to be conducted under severe conditions that include high temperatures (approximately 200C) and high radiation doses (approximately 200 Gy/h). In addition, since the primary sodium coolant has to be always kept in the reactor vessel to remove the decay heat of fuel subassemblies. Therefore an in-vessel observation equipment has to be designed to not only stand the severe conditions but also be capable of being inserted into the sealed reactor vessel through the holes built into the rotating-plug. In Joyo, in-vessel inspections and repair technologies are developed and applied to observe the upper core structure and bent irradiation test subassembly. The detail design of the Joyo restoration work is now pushed forward based on the in-vessel observation results.