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Toyama, Shinichi; Minehara, Eisuke*
Dekomisshoningu Giho, (56), p.55 - 65, 2017/09
Development of the steel cutting technology which employs high power fiber laser for the industrial applicability of the laser technology has been carried out at The Wakasa Wan Energy Research Center (WERC). At present, the laser technologies for dismantling and decontamination are concurrently being developed to the application measure of nuclear dismantling for domestic nuclear power plants in the future. Dismantling of nuclear facilities is now under the development in the world. The necessity of the technology is increasing and the development is strongly expected. Beside the relative easiness to handle compared with other laser system, suppression of production of secondary radioactive waste and dose exposure can be realized by the dramatic improvement by excelled thermal density of fiber laser. This paper provides recent results from cutting technology for thick steels aiming disassembling nuclear pressure vessel, and decontamination machine technology which works under high radiation dose, explaining the results from cutting experiment of steels and the actual equipment and from the radiation resistance experiment for component devices.
Tamura, Koji; Ishigami, Ryoya*
no journal, ,
The laser cutting of thick steel plates with 30 kW fiber laser has been developed. Output of the introduced fiber laser (30 kW, IPG YLS-30000) was collimated with a pair of focusing lens, and was irradiated to stainless steel and carbon steel plates, which were transferred at a constant speed. Assist gas of air at a flow rate of about 500 l/min was used. It was demonstrated in this experiment that thick stainless steel plates up to 300 mm and carbon steel plates up to 300 mm were successfully cut. These results are quite promising for the application of laser cutting to the actual nuclear decommissioning.
-raysMori, Michiaki; Kosuge, Atsushi*; Hajima, Ryoichi; Nagashima, Keisuke; Kondo, Kiminori; Kiriyama, Hiromitsu
no journal, ,
We report on a high average power Yb-fiber CPA laser system. The system can produces an average power of 100 W class at 160 MHz in a 
5 ps pulse with narrow bandwidth of 0.4 nm in full-width-half-maximum. The bandwidth of the laser beam can be varied (from 0.4 nm to 2 nm) easily by changing the configuration of a spectrum mask at a secondary pulse stretcher. The power fluctuation is only 0.6% (rms value), which was measured over a period of 10 hours. The excellent beam profile is preserved over the full range of average power. The reliable, efficient, and compact our fiber laser system is currently being applied to realize intense LCS -ray source.
Nishimura, Akihiko
no journal, ,
no abstracts in English
Kosuge, Atsushi; Minehara, Eisuke*; Saruta, Koichi
no journal, ,
Decontamination is required when disposing of equipment contaminated by the accident at TEPCO's Fukushima Daiichi Nuclear Power Station. The decontamination method generally used at present has a problem that a large amount of secondary waste is generated. Decontamination using a laser is non-contact and can significantly suppress the generation of secondary waste. In this study, we used a method of instantly evaporating and peeling using a continuous wave fiber laser, and observed the time change of peeling of the metal surface using a high-speed camera.
Nishimura, Akihiko; Kitagawa, Yoshihiro
no journal, ,
no abstracts in English
Kosuge, Atsushi; Minehara, Eisuke*; Saruta, Koichi
no journal, ,
Decontamination is required when disposing of equipment contaminated by the accident at TEPCO's Fukushima Daiichi Nuclear Power Plant. The decontamination method generally used at present has a problem that a large amount of secondary waste is generated. Decontamination using a laser is non-contact and can significantly suppress the generation of secondary waste. In this study, we used a method of instantly evaporating and peeling using a continuous wave fiber laser, and observed the time change of peeling of the metal surface using a high-speed camera. Furthermore, a decontamination test was conducted using this laser decontamination method for the parts of the analyzer installed in Minamisoma City, Fukushima Prefecture, which was contaminated with radioactive substances.
Nishimura, Akihiko
no journal, ,
no abstracts in English
Miyabe, Masabumi
no journal, ,
We have studied the applicability of spectroscopic technique for obtaining process information needed for laser decommissioning and other various laser processing techniques. When a material is irradiated with intense laser pulses, atomic species eject from the surface which absorbing the light energy via inverse Bremsstrahlung process and laser plasma grows rapidly. Thus various properties of the generated laser plasma strongly depend on the duration of the laser irradiation. Although previous studies have reported differences in emission characteristics between Nd:YAG lasers with about 10 ns-pulse and long-pulse lasers with about 100 ns-pulse, little is known about the emission and/or absorption characteristics of the plasma produced through the irradiation of longer than 10 ms duration, which is common in current laser processing. In this study, we investigated the emission characteristics of the laser plasma produced in atmospheric air using a QCW (Quasi Continuous Wave) fiber laser. As a result, it was found that the emission intensity of oxide molecules is enhanced. Also, only for zirconia and gadolinia targets, strong emission lines of atomic species were observed. From the images recorded during laser ablation process, it was observed that the sputtered materials were burned while floating in the air and this might contribute to strong emission signal of atomic species. This study demonstrated the possibility of applying emission spectroscopy to laser processing to evaluate elemental composition of the processed materials.
Kisohara, Naoyuki; Aoyagi, Yuji*; Taguchi, Toshihiro
no journal, ,
Decontamination technologies, which remove radioactive substances from material surfaces, are significant to reduce radioactive wastes and recycle materials in decommissioning. Laser decontamination provides advantages such as remote processing and less produced secondary waste. The JAEA's experimental study has revealed that high-power density and high-speed Laser scanning irradiations achieve high decontamination efficiency by surface metal vaporization. The JAEA's computer code has been used to understand the phenomena induced by laser heating. This computer code has physical models including thermal conduction, metal melting, vaporization and radiation. The transient calculation is applied to simulate moving heat source by Laser scanning. The computer results have clarified surface melting, vaporization and solidification, explaining the relation between measured delamination depth and Laser irradiation conditions well.