溶解槽燃料装荷バスケットの遠隔操作による肉厚測定

Remote wall thickness measurement of the fuel basket of the dissolver

横田 知; 畑中 聡; 藤森 真仁; 下山田 哲也; 中村 芳信

Yokota, Satoru; Hatanaka, Akira; Fujimori, Masahito; Shimoyamada, Tetsuya; Nakamura, Yoshinobu

せん断した使用済燃料を溶解する機器である溶解槽は、溶解部及び貯液部(材質:SUS310系)で構成される。溶解部に設置されている燃料装荷バスケット(材質:SUS304L)は、溶解槽での溶解後に溶け残った使用済燃料の被覆片を溶解槽から取り出すための機器である。溶解は高温, 高酸濃度下で行うため、溶解槽内は高い腐食環境であり、過去には腐食故障が生じたことから、遠隔補修装置を開発し、補修後は遠隔による溶解槽の肉厚測定を定期的に実施している。一方、燃料装荷バスケットは、更新時に破壊検査による肉厚測定を実施したのみであり、燃料装荷バスケットの腐食傾向の把握及び遠隔操作による非破壊検査方法の確立を目的に燃料装荷バスケットの肉厚測定の方法を検討し、その測定技術を確立した。

Three batch-type dissolvers in the Tokai Reprocessing Plant are a device for dissolving spent fuel. The dissolver is composed of one slab and two barrels (stainless steel 310s). Install a fuel basket (stainless steel 304L) in the barrel and accept the sheared spent fuel to dissolve it. The insoluble fuel cladding is taken out of the barrels with the basket. The dissolution time of operation for one batch is approximately 10 hours. During dissolution operation, nitric acid was added to the dissolver into the spent fuel in the basket with water. The solution was heated with steam. Corrosion failure has occurred in the past because the dissolver is exposed to a high corrosive environment (high temperature, high acid concentration). Therefore, we carry out the periodical wall thickness measurement of the barrel by the remote control. On the other hand, the wall thickness measurement of the fuel basket was carried out only once by destructive measurement at the time of renewal in 1999. The details of the corrosion tendency of the fuel basket are unknown, and it is urgent to establish a non-destructive measurement method by remote handling. Therefore, we examined the method of wall thickness measurement of the fuel basket and established the measuring technique.