UNDERWATER LASER BEAM WELDING FOR NUCLEAR REACTORS

摘要

Toshiba has developed underwater laser beam welding (ULBW) technology as a maintenance measure for stress corrosion cracking. For an application to reactor vessel nozzles of PWR, ambient temperature temper bead welding technique and actual welding tools were developed. The ambient temperature temper bead welding technique can mitigate the degradation of toughness of low alloy steel of the nozzle due to high heat input of welding. Applicability of welding tools to actual PWR plants was confirmed through full-scale mockup tests in water tank at the depth of 10m. As ULBW dose not need to seal up and drain the work area, the new system can reduce the work period to less than half of the conventional system which needs draining. For an application of core shroud support of BWR, a prototype welding tool was developed to seal cracks and its performance was confirmed through mockup tests. ULBW enables significant reductions in radiation dose associated with maintenance efforts and also reduces impact on nuclear plant outage schedules. We will utilize this cutting-edge technology at nuclear plants both in Japan and abroad.