Takeshi Obana

Development of maintenance technology with underwater TIG welding for spent fuel storage pool

The core technology of an underwater TIG welding process has been developed and a welding equipment system has been manufactured for application to the maintenance of the spent fuel storage pool of Rokkasho reprocessing plant. Basic experiments for understanding the conditions of the dry area and the range of welding conditions was performed, and mock examination for simulation of the real environment by using the developed welding equipment was also carried out to judge the applicability of the system. For the purpose of selecting a water removing method for different spatial conditions of the parts to be maintained underwater, two kinds of welding equipment systems of Chamber type and Partition type were developed and manufactured. On the basis of fundamental experiments, the conditions of dry area formation and welding parameter range for high-reliability weld are discussed. Thus the proper condition of this process was able to be established. With the welding equipment systems of the Chamber type and Partition type, the practical use examination of underwater TIG welding process was executed by mock examination for simulating the real environment. As a result, it was confirmed that the underwater TIG welding could obtain the same reliability as a usual in-air TIG welding, and the operation and the control at remote distance were also possible. And the reliability of the patch-plate fillet weld could be evaluated by remote inspection with the expansion visual test.