Katsunori Shiihara

Combination welding between CO2 laser beam and MIG arc

With the development of high power lasers in recent years, 45 kW class CO2 lasers are now employed on line in the steel industry for welding plates greater than 20 mm thick; in addition, in the automobile industry many 3-4 kW class YAG lasers are in practical use for high speed welding of thin sheets of approximately 3 mm or less. However, the practical application of laser welding in Japan remains small compared with that in the West and the following factors are often considered:

Underwater Laser Beam Welding for Nuclear Reactors

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.Copyright

Decreasing Waste of Laser Cutting by Metal Fume Capturing With Water

Decommissioning of aged nuclear reactors is planned, and cutting technologies for thick structure are necessary to reduce storage space of radioactive wastes. Though thermal cutting technology is suitable for cutting thick materials, radioactive fume is one of the problems due to increase the environmental dose. A water jet-guided laser cutting technology is one of the solutions for cutting irradiated materials, because radioactive fume is confined in the water and doze level won’t be increased. However, this technology was developed for precision machining like dicing and slotting of silicon wafers, cutting thick materials by using this process is very diffcult. In this study, cutting technology for thick material with a water jet-guided laser was discussed. Phenomenon during cutting thick stainless steel was observed by using high speed camera and optimum conditions for both water jet and laser cutting were derived. Finally, 50mm thick stainless steel plate was successfully cut by using this technology.© 2014 ASME