Development of observation techniques in reactor vessel of experimental fast reactor Joyo

Takamatsu, Misao ; Imaizumi, Kazuyuki ; Nagai, Akinori; Sekine, Takashi ; Maeda, Yukimoto

During the investigation of an incident in Joyo, in-vessel observations using a Video Camera (VC) and a Radiation-Resistant Fiberscope (RRF) took place at (1) the top of the Sub-Assemblies (S/As) and the In-Vessel Storage rack (IVS), (2) the bottom face of the Upper Core Structure (UCS). A simple 6 m overhead view of each S/A was photographed using a VC fixed to the rotating-plug for making observations of the top of S/As and IVS. A resolution was estimated to be approximately 1mm. In order to observe the bottom face of the UCS, a remote handling device equipped with RRFs was specifically developed for Joyo with a tip that can be bent into an L-shape and inserted into the 70 mm gap between the top of the S/As and the bottom of the UCS. The sodium flow regulating grid of 0.8mm in thickness could be discriminated. These experiments provided valuable insights for use in further improving and verifying in-vessel observation techniques in sodium cooled fast reactors.