Laser technology for maintenance of nuclear pipe

A remote maintenance technology to process cooling pipes internally for the ITER (International Thermonuclear Experimental Reactor) has been developed. The fundamental welding properties of austenite stainless steel obtained by using high power YAG laser indicates the tendency of porosity increase as the welding depth increases. It is also found out that the occurrence of porosity was prevented when N-2 gas was used as a shielding gas and that the material strength of weld joint is kept unchanged. Furthermore, a processing equipment that can access the cooling pipe and consists of an focusing optics, clamping and driving mechanism, and an optical fiber. Operational experiments of this processing equipment is carried out and the basic verification experiments such as welding and cutting tests were conducted. As a result, a good quality of pipe welding joint was obtained without any defects.