Interaction of millisecond kW-class laser pulses with metals and metal oxides; Fundamentals of processing

Daido, Hiroyuki*; Yamada, Tomonori

ILT-APR-34; ILT 2023 Nempo (Internet), p.1 - 5, 2023/07

The decommissioning of Fukushima and the contribution to reconstruction have become national issues. The authors participated in the "Analysis of fine particles generated by laser processing and development of nuclide identification method" (represented by Professor Shuichi Hasegawa of the University of Tokyo), which was adopted as one of the JAEA's publicly solicited projects for this purpose, from FY 2018 to FY 2021 as a subcontractor, The authors conducted research on the observation, evaluation and analysis of the interaction between lasers and various laser-irradiated targets. This report outlines the results of the research in which the authors took part. In the experiments, laser irradiation was carried out on test specimens set up in an irradiation chamber, and shadowgraphs were taken using a high-speed camera and a He-Ne laser. As an example of the experimental results, shadowgraphs of metal (stainless steel) and metal oxide (zirconia), irradiation traces after laser irradiation, and the relationship between laser irradiation power and jet mass are shown, and the interaction between the laser and the metal or metal oxide is discussed. The results will not only contribute to the decommissioning technology of the Fukushima Daiichi NPP, but also to laser processing technology and laser interaction research.

Internal strain distribution of laser lap joints in steel under loading studied by high-energy synchrotron radiation X-rays

Shobu, Takahisa; Shiro, Ayumi*; Kono, Fumiaki*; Muramatsu, Toshiharu; Yamada, Tomonori; Naganuma, Masayuki; Ozawa, Takayuki

Quantum Beam Science (Internet), 5(2), p.17_1 - 17_9, 2021/06

https://doi.org/10.3390/qubs5020017

The automotive industries employ laser beam welding because it realizes a high energy density without generating irradiation marks on the opposite side of the irradiated surface. Typical measurement techniques such as strain gauges and tube X-rays cannot assess the localized strain at a joint weld. Herein high-energy synchrotron radiation X-ray diffraction was used to study the internal strain distribution of laser lap joint PNC-FMS steels (2- and 5-mm thick) under loading at a high temperature. As the tensile load increased, the local tensile and compressive strains increased near the interface. These changes agreed well with the finite element analysis results. However, it is essential to complementarily utilize internal defect observations by X-ray transmission imaging because the results depend on the defects generated by laser processing.

Development of a laser chipping technique combined with water jet for retrieval of fuel debris at Fukushima Daiichi Nuclear Power Station

Yamada, Tomonori; Takebe, Toshihiko*; Ishizuka, Ippei*; Daido, Hiroyuki*; Hanari, Toshihide; Shibata, Takuya; Omori, Shinya*; Kurosawa, Koichi*; Sasaki, Go*; Nakada, Masahiro*; et al.

Journal of Nuclear Science and Technology, 56(12), p.1171 - 1179, 2019/12

https://doi.org/10.1080/00223131.2019.1647890

We describe a new chipping technique combined with a water-jet technique as one of the candidate techniques for the retrieval of fuel debris and support structures as part of the decommissioning of the Fukushima Daiichi Nuclear Power Station. We performed proof-of-principle experiments to demonstrate the removal capability of metal parts, where we focused on the observation of removal processes from a metallic sample using a 5.5-kW continuous wave fiber laser combined with continuous and pulsed water jets.

Development on laser cutting technique to suppress spatter particles aiming at disposal of radio-active waste

Naoe, Takashi; Teshigawara, Makoto; Futakawa, Masatoshi; Mizutani, Haruki; Muramatsu, Toshiharu; Yamada, Tomonori; Ushitsuka, Yuji*; Tanaka, Nobuatsu*; Yamasaki, Kazuhiko*

Proceedings of 8th International Congress on Laser Advanced Materials Processing (LAMP 2019) (Internet), 5 Pages, 2019/05

Laser cutting is one of the options in the disposal of radio-active waste, such as spallation neutron target vessel in J-PARC, etc. Due to unique characteristic of laser, such as non-contact system, it is more easily to provide remote-controlled system in comparison with conventional one, such as mechanical cutting machine, etc. However, a demerit of laser cutting is the sputter and fume caused by laser cutting, resulting in contamination with radio-active materials its surroundings. Recently it was developed that the spatter suppression technique by controlling laser beam profile in laser welding process. In order to apply this suppression technique to laser cutting, first of all, we attempted to observe the phenomenon at melting area during laser cutting using a high-speed video camera in order to make the physical model. The result showed that the appearance of fume and sputter were independently confirmed in the time evolution.

Concrete cutting technology with lasers

Daido, Hiroyuki*; Yamada, Tomonori

Oputoronikusu, 37(12), p.67 - 71, 2018/12

no abstracts in English

Demonstration of laser processing technique combined with water jet technique for retrieval of fuel debris at Fukushima Daiichi Nuclear Power Station

Hanari, Toshihide; Takebe, Toshihiko*; Yamada, Tomonori; Daido, Hiroyuki; Ishizuka, Ippei*; Omori, Shinya*; Kurosawa, Koichi*; Sasaki, Go*; Nakada, Masahiro*; Sakai, Hideaki*

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 3 Pages, 2017/04

In decommissioning of Fukushima Daiichi Nuclear Power Station, a retrieval process of fuel debris in the Primary Containment Vessel by a remote operation is one of the key issues. In this process, prevention of spreading radioactive materials is one of the important considerations. Furthermore, an applicable technique to the process requires keeping of reasonable processing-efficiency. We propose to use the combined technique including a laser light and a water jet as a retrieval technique of the fuel debris. The laser processing technique combined with a repetitive pulsed water jet could perform an efficient retrieval processing. Our experimental result encourages us to promote further development of the technique towards a real application at Fukushima Daiichi Nuclear Power Station.

A Study on laser welding of ferritic/martensitic steel (PNC-FMS) for fast reactor fuel assemblies

Kono, Fumiaki; Sogame, Motomu; Yamada, Tomonori; Shobu, Takahisa; Naganuma, Masayuki; Ozawa, Takayuki; Muramatsu, Toshiharu

JAEA-Technology 2015-004, 57 Pages, 2015/03

JAEA-Technology-2015-004.pdf:20.87MB

Laser welding of ferritic/martensitic steel (PNC-FMS) sheets with different thicknesses (2 mm and 5 mm) was examined to investigate the weldability between the inner and outer duct in fast reactor fuel assemblies with inner duct structure (FAIDUS); the objective of the inner duct is to avoid the re-criticality in case of the core melting accident. Laser-spot and melt-run welding was performed at various laser powers, welding times and velocities to find out the appropriate welding conditions with few defects and enough penetration depth. As for the spot welding, furthermore, slow cooling rate or pulsed laser irradiation could reduce the crack and porosity in the welded zone. The strain of the welded zone almost disappeared and the hardness was comparable with that of the base metal by applying post welding heat treatment at 690 C for 103 min. In addition, the shear strength of welded joints was confirmed to be sufficiently higher than the provisional allowance shear stress. These results indicate that laser welding would be probably applied to the PNC-FMS inner and outer ducts.

Research on removal technologies of fuel debris and in-vessel structures using laser light (II); Research activities on FY2013

Muramatsu, Toshiharu; Yamada, Tomonori; Hanari, Toshihide; Takebe, Toshihiko; Nguyen, P. L.; Matsunaga, Yukihiro

JAEA-Research 2014-018, 41 Pages, 2014/09

JAEA-Research-2014-018.pdf:42.21MB

In decommissioning works of the Fukushima Daiichi Nuclear Power Plants, it is required that fuel debris solidifying mixed materials of fuels and in-vessel structures should be removed. The fuel debris is considered to have characteristics, such as indefinite shapes, porous bodies, multi-compositions, higher hardness, etc. from the knowledge in the U.S. and the Three Mile Island nuclear power plant. Laser lights are characterized by higher power density, local processability, remote controllabilitiy, etc. and can be performed thermal cutting and crushing-up for various materials which does not depend on fracture toughness. This report describes a research program and research activities in FY2013 aiming at developing removal system of fuel debris by the use of laser lights.

Numerical simulation of laser processing

Yamada, Tomonori; Yamashita, Susumu; Sugihara, Kenta; Muramatsu, Toshiharu

Purazuma, Kaku Yugo Gakkai-Shi, 89(7), p.500 - 506, 2013/08

http://www.jspf.or.jp/Journal/PDF_JSPF/jspf2013_07/jspf2013_07-500.pdf

no abstracts in English

In-situ X-ray observation of molten pool depth during laser micro welding

Yamada, Tomonori; Shobu, Takahisa; Nishimura, Akihiko; Yonemoto, Yukihiro; Yamashita, Susumu; Muramatsu, Toshiharu

Journal of Laser Micro/Nanoengineering, 7(3), p.244 - 248, 2012/11

https://doi.org/10.2961/jlmn.2012.03.0002

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.