Quality control parameters for automatic welding of radioactive material containers

More than 30 commercial nuclear reactors are operating at present in Japan and a lot of spent nuclear fuels (hereafter called spent fuel) are generated from these nuclear reactors. After they have been temporarily stored at the storage pool within the nuclear power plant, these spent fuels are scheduled to be disposed of at a reprocessing plant in England or France, or at the domestic reprocessing plant planned for Shimokita. The residues generated when the spent fuel is subjected to reprocessing are scheduled to be solidified within stainless steel (SUH309) glass solidifying containers (canisters), shown in Fig. 1, and stored for several dozen years before disposal. Plasma arc welding using automatic remote operation is used to secure the canister cover; however, the oxidated scale or oil/grease which may adhere to the base material surface at the canister weld may adversely influence the welding when the molten glass is poured in the canister. However, it is difficult to perform a general non-destructive examination of the weld, and it is not possible to fully confirm the weld for soundness as the glass-solidified residue generates extremely high radioactivity. Consequently, strict quality control is required when performing the automatic remote welding. In this study, the stainless steel plate was fillet-welded and butt-welded to make a test weld and simulation of the canister flange. The weld was subjected to various examinations to evaluate the welding current, welding speed, surface condition of base material, and other conditions essential to sound welding from the view point of quality control