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

Abstract

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.

Keywords:

• spent fuel storage pool
• underwater welding
• TIG welding
• patch plate welding
• welding equipments system

Acknowledgements

We would like to express our profound gratitude for the valuable advice given to us during this research by Dr Fukuhisa Matsuda, Professor Emeritus of Osaka University, Dr Shigeo Tsujikawa, Professor Emeritus of Tokyo University, Mr Takamichi Yamanouchi, former Technical Consultant to the Nuclear Power Safety Association of the Cabinet Office, Mr Masayoshi Abe, Director of the Radiation Measurement Association, Dr Kiichi Ooka, Japan Welding Society and Mr Kazutoshi Fujioka, Chairman of the Western Japan Branch of the Japan Power Engineering and Inspection Corporation