Study on laser surface modification and repair welding techniques for neutron irradiated austenitic stainless steels

Abstract

The deterioration of weldability caused by helium is an important issue to be addressed in planning of proactive maintenance of light water reactor core internal components. Helium concentration, generated by neutron irradiation, was calculated to be about 20 appm in a core shroud after the 40-years nuclear power plant operation. The helium bubbles in grain boundaries (GBs) of the weld heat affected zone is one of the causes of weld cracking. In fact, there are some reports that application of conventional Gas Tungsten Arc Welding (GTAW) for neutron irradiated austenitic stainless steels caused cracks1,2. Yttrium-Aluminum-Garnet (YAG) Laser technique is one of the candidate method for surface modification and repair welding of the irradiated stainless steels, because the cooling rate of YAG Laser technique is fairly fast, the helium bubbles could not grow enough in grain boundary during process. Therefore, in the s study, the test of Laser surface modification (LSM) treatment, which is same as Laser de-sensitized treatment (LDT) and Laser repair welding (LRW) for neutron irradiated Type 304 and Type 316L austenitic stainless steels, were conducted. The applicability of LSM and LRW with optimized condition for neutron irradiated to 5E24 n/m2 (>1MeV) was demonstrated. The present study was carried out by the Japan Power Engineering and Inspection Corporation (JAPEIC) as one of the research works entrusted by the Ministry of Economy, Trade and Industry (METI).The deterioration of weldability caused by helium is an important issue to be addressed in planning of proactive maintenance of light water reactor core internal components. Helium concentration, generated by neutron irradiation, was calculated to be about 20 appm in a core shroud after the 40-years nuclear power plant operation. The helium bubbles in grain boundaries (GBs) of the weld heat affected zone is one of the causes of weld cracking. In fact, there are some reports that application of conventional Gas Tungsten Arc Welding (GTAW) for neutron irradiated austenitic stainless steels caused cracks1,2. Yttrium-Aluminum-Garnet (YAG) Laser technique is one of the candidate method for surface modification and repair welding of the irradiated stainless steels, because the cooling rate of YAG Laser technique is fairly fast, the helium bubbles could not grow enough in grain boundary during process. Therefore...