Compact YAG laser welding system and its in-process monitoring in sleeving technology

With respect to laser sleeve repairing by YAG laser welding for damaged sections of S/G tubes in nuclear power plants, about 40,000 sleeves have already been welded up to now. After replacement of S/Gs, it is considered that the quantity of such large-scale working will decrease and small-scale working will be carried out. Therefore, the authors have developed utilization of a 1kW YAG laser oscillator of a compact single-rod type mountable in reactor containment vessels, together with a small-diameter tube welding tool of 12mm in O.D. applicable to heat exchanger tubes of 3/4 in. Further, they have put such a system to practical use that can monitor deterioration of optical parts and welding conditions in process during welding by extracting the radiation intensity of the welded area with monitoring fibers. In this paper, they will report the results of study