In May 2000 JSME issued Rules on fitness-for-service for nuclear power plants, which define allowable flaw sizes at operating nuclear power plants, and based on evaluation against these rules, rational repairs were to be realized. According to results, rational in-situ repairs were urgently needed on aged nuclear power plants, and since underwater laser repairs met utilities requirements, the authors developed underwater YAG laser repair technology. 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 groove work piece. Metallurgical studies are ongoing.
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