Underwater laser welding by 4 kW CWYAG laser

In May 2000 JSME issued Rules on fitness-for-service for nuclear power plan ts, which define allowable flaw sizes at operating nuclear power plants, an d based on evaluation against these rules, rational repairs were to be real ized. According to results, rational in-situ repairs were urgently needed o n aged nuclear power plants, and since underwater laser repairs met utiliti es requirements, the authors developed underwater YAG laser repair technolo gy. Hitachi installed the equipment at JAPEIC (Japan Power Engineering and Inspection Corporation) in 1998 and implemented 0.3MPa underwater YAG laser welding in both downward and horizontal direction repairs, even in a U gro ove work piece. Metallurgical studies are ongoing.