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Yamada, Tomonori; Shobu, Takahisa; Nishimura, Akihiko; Yonemoto, Yukihiro; Yamashita, Susumu; Muramatsu, Toshiharu
Journal of Laser Micro/Nanoengineering, 7(3), p.244 - 248, 2012/11
Times Cited Count：21 Percentile：69.68(Nanoscience & Nanotechnology)Small size and high-performance fiber lasers enable in-situ flaw sizing and repairs at nuclear power plants. In quantum beam science directorate, the new probing system was developed to treat micro cracks at the welded section of heat exchanger tubes, where a fiber laser beam passed through a composite-type optical fiber scope. Molten pool's diameter by laser welding gradually expanded more than the width of the micro crack's crevice caused by stress corrosion cracking. In this work, we have carried out in-situ X-ray observation of inside materials during laser welding. In-situ observation of inside materials during fiber laser welding provides a useful knowledge of repair welding because bubbles and cracks which cause the poor weld was clearly observed in non-destructive. This is very effective for control of weld defect and investigation of the mechanisms. As a result, we are able to confirm the molten pool depth of butt welding for heat exchanger units using the new probing system.
Nishimura, Akihiko; Terada, Takaya; Shimada, Yukihiro; Yonemoto, Yukihiro*; Yamada, Tomonori
Proceedings of 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference (ICONE-20 & POWER 2012) (DVD-ROM), 5 Pages, 2012/07
Instrumentation devices using laser technologies were developed for maintenance of coolant piping system. For instrumentation devices, seismic monitoring by optical fiber sensors was able to detect vibration of piping system. X-ray absorption contrast by synchrotron radiation clarified convection motion inside a molten pool produced by laser welding. For surface control technologies, a new probing system was under development for heat exchanger tubes by laser cladding. And laser ablation could be used for surface cleaning. These technologies are expected for maintenance of the piping system of nuclear power plants.
Yamashita, Susumu; Yonemoto, Yukihiro; Yamada, Tomonori; Kunugi, Tomoaki*; Muramatsu, Toshiharu
Yosetsu Gakkai Rombunshu (Internet), 29(3), p.48s - 52s, 2011/08
Quantitative evaluation and controlling the residual stress which is induced by laser welding is of important problem for a life extension of FBRs (Fast Breeder Reactors) and the guarantee of the reliability of the repair processes. Numerical simulation is an effective tool for deep understanding of their problems and it needs to have high accuracy, robustness and reliability. We have recently constructed the fully parallelized laser welding simulation code which satisfies above aspects using some advanced numerical models. Concretely, VSIAM3 numerical model as the spatial discretization, an efficient free surface capturing scheme, THINC scheme, and FAVOR method as the solid phase expression has been applied to the code. We have conducted laser welding simulations and obtained some reasonable results. Therefore, the numerical model will be contributed to the repairing technology of a laser welding.
Yamada, Tomonori; Yonemoto, Yukihiro; Yamashita, Susumu; Muramatsu, Toshiharu; Komizo, Yuichi*
Yosetsu Gakkai Rombunshu (Internet), 29(3), p.86s - 89s, 2011/08
It is known that residual stress is important to keep the structural integrity. Laser welding is effective for the residual stress decrease because heat input is smaller and heats have a very small effect. Therefore, the repairing technology by laser welding has draw wide attention for a life extension of FBRs (Fast Breeder Reactors). To establish the laser repair technology, special attentions should be paid to the morphological developments. In the present work, morphological developments were directly observed using laser scanning conforcal microscopy during laser weld cooling.
Yonemoto, Yukihiro; Kunugi, Tomoaki*
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Yamashita, Susumu; Yonemoto, Yukihiro; Yamada, Tomonori; Kunugi, Tomoaki*; Muramatsu, Toshiharu
no journal, ,
Quantitative evaluation and controlling the residual stress which is induced by laser welding is of important problemfor a life extension of FBRs (Fast Breeder Reactors) and the guarantee of the reliability of the repair processes. Numerical simulation is an effective tool for deep understanding of their problems and it needs to have high accuracy, robustness and reliability. We have recently constructed the fully parallelized laser welding simulation code which satisfies above aspects using some advanced numerical models. Concretely, VSIAM3 (Volume and Surface Integrated Average based Multi Moment Method) numerical model as the spatial discretization, an efficient free surface capturing scheme, THINC scheme, and FAVOR method as the solid phase expression has been applied to the code. We have conducted modest large-scale laser welding simulations by using a supercomputer in Japan Atomic Energy Agency and obtained some preliminary results. And reasonable results were obtained.
Yamashita, Susumu; Yamada, Tomonori; Yonemoto, Yukihiro; Kunugi, Tomoaki*; Muramatsu, Toshiharu
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no abstracts in English
Yamada, Tomonori; Shobu, Takahisa; Yonemoto, Yukihiro; Yamashita, Susumu; Nishimura, Akihiko; Muramatsu, Toshiharu
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Yonemoto, Yukihiro; Kunugi, Tomoaki*; Yamada, Tomonori; Yamashita, Susumu; Nishimura, Akihiko; Daido, Hiroyuki; Muramatsu, Toshiharu
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Yonemoto, Yukihiro; Nishimura, Akihiko
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Yonemoto, Yukihiro; Nishimura, Akihiko; Shimada, Yukihiro
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Nishimura, Akihiko; Yonemoto, Yukihiro; Shimada, Yukihiro
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Femtosecond laser pulses ablated a thin layer on the stainless steel surface where tensile stress had been mechanically induced. Thermal damage was strongly restricted by femtosecond laser pulses. The surface condition after laser ablation turned to be compressive gradually, which indicated a tolerance for Stress Corrosion Cracking. The laser processing application successfully produced two research directions for maintenance of nuclear power plants. One research direction was the fabrication of fiber Bragg grating. The other research direction was the development of prototype new probing system for heat exchanger by laser micro welding. It is the prototype probing system. Up to now, we have been working on both research directions in the new organization in Tsuruga since November 2009.
Yamada, Tomonori; Shobu, Takahisa; Yonemoto, Yukihiro; Yamashita, Susumu; Nishimura, Akihiko; Muramatsu, Toshiharu
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Nishimura, Akihiko; Yonemoto, Yukihiro; Shimada, Yukihiro
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Yonemoto, Yukihiro; Nishimura, Akihiko; Shimada, Yukihiro
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Yonemoto, Yukihiro; Nishimura, Akihiko; Shimada, Yukihiro; Terada, Takaya
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Shimada, Yukihiro; Yonemoto, Yukihiro; Nishimura, Akihiko; Suzuki, Hirokazu*; Ishibashi, Hisayoshi*; Kawahara, Hirotaka; Ito, Chikara; Yoshida, Akihiro
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Ito, Fuyumi; Nishimura, Akihiko; Yonemoto, Yukihiro*; Terada, Takaya; Shimada, Yukihiro
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Development of inspection repair technology for tube inner wall of aging nuclear power plants was described. Three functions of the pulse laser, observation by the composite-type optical fiber scope, and laser-induced breakdown spectroscopy (LIBS) are built into a coupling device. In addition, to facilitate the observation of the cracks, we adopted the magnetic particle testing (MT). And to remove the dispersed magnetic particle liquid from cracks after MT, we manufactured a microcapsule containing the magnetic particle liquid. Furthermore, pulse laser ablation with LIBS can clean up the oxide layer of the inner wall of heat exchanger tubes. Applying LIBS on tube inner wall before MT can give us the information about cracks and defects.
