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Journal Articles

Development of prototype reactor maintenance, 3; Application to valves of sodium-cooled reactor prototype

Chikazawa, Yoshitaka; Takaya, Shigeru; Tagawa, Akihiro; Kubo, Shigenobu

Proceedings of 2019 International Congress on Advances in Nuclear Power Plants (ICAPP 2019) (Internet), 6 Pages, 2019/05

A maintenance management required to prototype nuclear power reactors has been developed. One of important mission of a prototype reactor is to develop maintenance program for commercial reactors step by step securing safety. Since operating experience at the early stage is limited, the maintenance program for the prototype reactor should be a progressive one. It has to be modified and improved frequently taking into account R&D insight and operation experiences. Additionally, the maintenance program has to consider features of the prototype reactor even at the early stage. To select maintenance grades on particular components/systems, risk informed and graded approaches are effective. And maintenance programs have to take into account degradation mechanism originally due to reactor features. In this paper, applications for maintenance program on sodium valves of prototype fast breeder reactor Monju are studied as an example of prototype sodium-cooled reactors (SFR).

Journal Articles

Proposal of maintenance management of nuclear power plants at R&D stage by taking account of their features

Takaya, Shigeru; Chikazawa, Yoshitaka; Hayashida, Kiichi; Tagawa, Akihiro; Kubo, Shigenobu; Yamashita, Atsushi

Hozengaku, 15(4), p.71 - 78, 2017/01

A maintenance management suitable to nuclear power plants (NPP) at R&D stage was discussed. Objectives of maintenance management of NPP at R&D stage was first clarified. Next, applicability of codes for maintenance management of commercial NPP to NPP at R&D stage was discussed. Then, requirements and consideration for maintenance management of NPP at R&D stage was proposed. Finally, an example that the proposal was applied to setting maintenance program of sodium-cooled fast reactor was presented.

JAEA Reports

Maintenance management of nuclear power reactors at the stage of research and development

Takaya, Shigeru; Chikazawa, Yoshitaka; Hayashida, Kiichi; Tagawa, Akihiro; Kubo, Shigenobu; Yamashita, Atsushi

JAEA-Research 2016-006, 66 Pages, 2016/07

JAEA-Research-2016-006.pdf:3.4MB

A maintenance management required to nuclear power reactors at the R&D stage was discussed. It is the most important to ensure safety of nuclear power plants by taking account of characteristics of nuclear power reactors at the R&D stage. In addition, it is needed to establish a system of maintenance management technologies suitable for reactor types. In this report, objectives of maintenance management of nuclear power reactors at the R&D stage was clarified. Next, requirements and consideration for maintenance management was discussed according to the objectives. "Codes for maintenance management of nuclear power plants" and "Guides for maintenance management of nuclear power plants" were refereed in the discussion. Then, a draft of codes for maintenance management of nuclear power plants at the R&D stage were newly proposed. Finally, an example that the draft codes were applied to components containing sodium, typical components of sodium-cooled fast reactor, was presented.

Journal Articles

Radioactivity decontamination in and around school facilities in Fukushima

Saegusa, Jun; Tagawa, Akihiro; Kurikami, Hiroshi; Iijima, Kazuki; Yoshikawa, Hideki; Tokizawa, Takayuki; Nakayama, Shinichi; Ishida, Junichiro

Mechanical Engineering Journal (Internet), 3(3), p.15-00609_1 - 15-00609_7, 2016/06

After the Fukushima nuclear accident, JAEA lead off demonstration tests to find out effective decontamination methods for various school facilities in Fukushima. It included (1) dose reduction measures at schoolyards, (2) purification of swimming pool water and (3) removal of surface contamination of playground equipments. Through these tests, they established practical methods suitable for each situation; (1) At school yards, dose rates were drastically reduced by removing topsoil which was then placed in trenches of 1 m deep; (2) For the purification of pool water, the flocculation-coagulation treatment was found to be effective for collecting radiocesium dissolved in the water; (3) Demonstration tests for playground equipments, such as horizontal bars and a sandbox wood frame, suggested that effectiveness of decontamination considerably varied depending on the material, paint or coating condition. This paper reviews these demonstrations.

Journal Articles

Radioactivity decontamination in and around school facilities in Fukushima

Saegusa, Jun; Tagawa, Akihiro; Kurikami, Hiroshi; Iijima, Kazuki; Yoshikawa, Hideki; Tokizawa, Takayuki; Nakayama, Shinichi; Ishida, Junichiro

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 5 Pages, 2015/05

After the Fukushima nuclear accident, JAEA lead off demonstration tests to find out effective decontamination methods for various school facilities in Fukushima. It included (1) dose reduction measures at schoolyards, (2) purification of swimming pool water and (3) removal of surface contamination of playground equipments. Through these tests, they established practical methods suitable for each situation; (1) At school yards, dose rates were drastically reduced by removing topsoil which was then placed in trenches of 1 m deep; (2) For the purification of pool water, the flocculation-coagulation treatment was found to be effective for collecting radiocesium dissolved in the water; (3) Demonstration tests for playground equipments, such as horizontal bars and a sandbox wood frame, suggested that effectiveness of decontamination considerably varied depending on the material, paint or coating condition. This paper reviews these demonstrations.

Journal Articles

Application of natural linear polysaccharide to green resist polymers for electron beam and extreme-ultraviolet lithography

Takei, Satoshi*; Oshima, Akihiro*; Oyama, Tomoko; Ito, Kenta*; Sugahara, Kigen*; Kashiwakura, Miki*; Kozawa, Takahiro*; Tagawa, Seiichi*; Hanabata, Makoto*

Japanese Journal of Applied Physics, 53(11), p.116505_1 - 116505_7, 2014/11

 Times Cited Count:5 Percentile:67.42(Physics, Applied)

The application of natural linear polysaccharide to green resists was demonstrated for electron beam (EB) and extreme-ultraviolet (EUV) lithography. Because of the water solubility of natural polysaccharides, the water spin-coating and water-developable processes realize an environmentally friendly manufacturing process for next-generation electronic devices. The developed green resist with a weight-average molecular weight of 83,000 and 70 mol % hydroxyl groups was found to have acceptable properties such as spin-coat ability on 200 mm wafers, pillar patterns of 100-400 nm with a high EB sensitivity of 10 $$mu$$ C/cm$$^{2}$$, etch selectivity with a silicon-based middle layer in CF$$_{4}$$ plasma treatment, and high prediction sensitivity to EUV region.

JAEA Reports

Report for "FY 2013 Evaluation of Decontamination Technology Demonstrations Projects for the environmental remediation with radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant Accident" (Contract research)

Watanabe, Masahisa; Tagawa, Akihiro; Umemiya, Noriko; Maruyama, Noboru; Yoshida, Mami; Kawase, Keiichi; Noguchi, Shinichi; Sakazume, Yoshinori; Watanabe, Masanori; Hiraga, Hayato; et al.

JAEA-Review 2014-028, 184 Pages, 2014/10

JAEA-Review-2014-028.pdf:37.79MB

JAEA received technical proposals from private enterprise about techniques that can be used for decontamination work, and "Decontamination Technology Demonstrations Projects" was commissioned from the Ministry of the Environment to verifies the decontamination effect, economy feasibility, safety, and other factors. By the "FY 2013 Decontamination Technology Demonstrations Projects" JAEA carried out technical advice of demonstration test and evaluation of 11 technologies (e.g., decontamination of soils and green space and wastes and washing of fly ash).

Journal Articles

Organic solvent-free water-developable sugar resist material derived from biomass in green lithography

Takei, Satoshi*; Oshima, Akihiro*; Ichikawa, Takumi*; Sekiguchi, Atsushi*; Kashiwakura, Miki*; Kozawa, Takahiro*; Tagawa, Seiichi*; Oyama, Tomoko; Ito, Shoji*; Miyasaka, Hiroshi*

Microelectronic Engineering, 122, p.70 - 76, 2014/06

 Times Cited Count:20 Percentile:16.42(Engineering, Electrical & Electronic)

Biomass-derived branched sugar resist material was developed for environmentally-friendly electron beam lithography (EBL). The developed resist enables organic solvent-free water-developable process. The resist performance was evaluated using 75 keV EBL system. Lines of 50-200 nm were fabricated with high sensitivity of 7 $$mu$$C/cm$$^{2}$$. The resist is developable in pure water at 23 $$^{circ}$$C for 60 s, and it has acceptable CF$$_{4}$$ etch selectivity.

JAEA Reports

Report for "Decontamination Pilot Projects for the environmental remediation of evacuation areas contaminated with radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant accident; Decontamination Technology Demonstrations Projects" (Contract research)

Watanabe, Masahisa; Tagawa, Akihiro

JAEA-Review 2013-053, 84 Pages, 2014/03

JAEA-Review-2013-053.pdf:48.63MB

To discover technologies that can be utilized for decontamination work and verify their effects, economic feasibility, safety, and other factors, the Cabinet Office, Government of Japan launched the FY2011 Decontamination Technology Demonstrations Project to publicly solicit decontamination technologies that would be verified in demonstration tests and adopted 25 candidates. JAEA was commissioned by the Cabinet Office, Government of Japan to provide technical assistance related to these demonstrations. JAEA carried out a demonstration test and evaluation of 25 technologies (e.g., decontamination technology of soil classifiers, ultra-high pressure water jets and volume reduction of organic materials) to perform decontamination of the environment

JAEA Reports

Report for "FY 2012 Evaluation of Decontamination Technology Demonstrations Projects for the environmental remediation with radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant Accident" (Contract research)

Watanabe, Masahisa; Umemiya, Noriko; Tagawa, Akihiro; Kawase, Keiichi; Noguchi, Shinichi; Sakazume, Yoshinori; Watanabe, Masanori; Tokizawa, Takayuki

JAEA-Review 2013-052, 232 Pages, 2014/03

JAEA-Review-2013-052.pdf:26.42MB

To discover technologies that can be utilized for decontamination work and verify their effects, economic feasibility, safety, and other factors, the Cabinet Office, Government of Japan launched the FY2012 Decontamination Technology Demonstrations Project to publicly solicit decontamination technologies that would be verified in demonstration tests and adopted 15 candidates. JAEA was commissioned by the Ministry of the Environment, Government of Japan to provide technical assistance related to these demonstrations. JAEA carried out technical advice of demonstration test and evaluation of 15 technologies (e.g., decontamination technology of Burned ash washing and Pond Dredging) to perform decontamination of the environment.

JAEA Reports

Report for "FY 2011 Evaluation of Decontamination Technology Demonstrations Projects for the environmental remediation with radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant accident" (Contract research)

Watanabe, Masahisa; Tagawa, Akihiro

JAEA-Review 2013-051, 244 Pages, 2014/03

JAEA-Review-2013-051.pdf:34.73MB

To discover technologies that can be utilized for decontamination work and verify their effects, economic feasibility, safety, and other factors, the Cabinet Office, Government of Japan launched the FY2011 Decontamination Technology Demonstrations Project to publicly solicit decontamination technologies that would be verified in demonstration tests and adopted 22 candidates. JAEA was commissioned by the Ministry of the Environment, Government of Japan to provide technical assistance related to these demonstrations. JAEA carried out technical advice of demonstration test and evaluation of 22 technologies (e.g., decontamination technology of Thermal decomposition, Bottom sediment of Pond and volume reduction of organic materials using biomass technologies) to perform decontamination of the environment.

Journal Articles

Positive-negative dual-tone sensitivities of ZEP resist

Oyama, Tomoko; Nakamura, Hirotaka*; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*

Applied Physics Express, 7(3), p.036501_1 - 036501_3, 2014/03

 Times Cited Count:4 Percentile:73.54(Physics, Applied)

A chlorinated polymer ZEP is a main-chain scission type (positive-tone) high-sensitivity resist. However, we found that ZEP changes to negative-tone with a high dose of electron beam irradiation. The sensitivities to a 100 kV electron beam as a dual-tone are evaluated with various developers. Owing to different solvation strengths, the resist sensitivity varied with different developers in the positive-tone region. On the other hand, it was found that the threshold dose for the positive-negative inversion is independent of the developer. According to an analysis using X-ray photoelectron spectroscopy and NMR spectroscopy, we found that the amount of chlorine atoms and terminal double bonds generated by chain scission determines the threshold of the P-N inversion. This result provides important information for possible ZEP applications such as a dual-tone resist.

Journal Articles

Pulse radiolysis study on a highly sensitive chlorinated resist ZEP520A

Hosaka, Yuji*; Oyama, Tomoko; Oshima, Akihiro*; Enomoto, Satoshi*; Washio, Masakazu*; Tagawa, Seiichi*

Journal of Photopolymer Science and Technology, 26(6), p.745 - 750, 2013/12

 Times Cited Count:7 Percentile:67.05(Polymer Science)

ZEP520A is one of the most popular positive electron beam (EB) resists used in research and photomask fabrication owing to its excellent properties. Herein, EB-induced initial reactions of ZEP520A were investigated via pulse radiolysis (EB energy: 28 MeV, time resolution: 10 ns). Dissociative electron attachment and formation of a charge transfer complex were definitive contributing factors to the efficient degradation of ZEP520A. Furthermore, products induced by direct ionization of ZEP520A were observed in a highly concentrated ZEP520A solution in tetrahydrofuran, suggesting that initial reactions in the ZEP520A solid film that are induced only by direct ionization could be simulated via pulse radiolysis in specific solutions.

Journal Articles

Micro/nanofabrication of poly($$_{L}$$-lactic acid) using focused ion beam direct etching

Oyama, Tomoko; Hinata, Toru*; Nagasawa, Naotsugu; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*; Taguchi, Mitsumasa

Applied Physics Letters, 103(16), p.163105_1 - 163105_4, 2013/10

 Times Cited Count:6 Percentile:64.35(Physics, Applied)

Micro/nanofabrication of biocompatible and biodegradable poly($$_{L}$$-lactic acid) (PLLA) was evaluated using focused Ga ion beam direct etching. The fabrication performance was determined with different ion fluences and fluxes. It was found that the etching speed and fabrication accuracy were affected by irradiation-induced heat because the resistance of PLLA to thermal deformation is decreased when above its glass transition temperature (approximately 60$$^{circ}$$C). By controlling the irradiation conditions, controlled micro/nanostructures of PLLA were fabricated, such as holes ($$phi$$80 nm) and alphabets (width: 100 nm). Moreover, focused ion beam (FIB)-irradiated surfaces were analyzed using micro-area X-ray photoelectron spectroscopy. Owing to reactions such as the physical sputtering of atoms and radiation-induced decomposition, PLLA was gradually carbonized with increasing C=C bonds expected to have good cell attachment properties.

Journal Articles

Demonstration test results of organic materials' volumetric reduction using bio-ethanol, thermal decomposition and burning

Tagawa, Akihiro; Watanabe, Masahisa

Proceedings of 15th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2013) (CD-ROM), 6 Pages, 2013/09

Journal Articles

Method of predicting resist sensitivity for 6.x nm extreme ultraviolet lithography

Oyama, Tomoko; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*

Journal of Vacuum Science and Technology B, 31(4), p.041604_1 - 041604_5, 2013/07

Journal Articles

Demonstration test on concrete with epoxy resin coating using ultra-high pressure water jet decontamination technology

Tagawa, Akihiro; Tezuka, Masashi; Terakura, Yoshihiro*; Naito, Masayuki*; Miyajima, Kenji*

Proceedings of 21st International Conference on Nuclear Engineering (ICONE-21) (DVD-ROM), 6 Pages, 2013/07

It is one of the most urgent issues to remediate the nuclear power plants contaminated by radioactive materials discharged following the accident at the TEPCO's Fukushima Daiichi NPS. Concrete walls of nuclear power plants in Japan are coated an epoxy resin coating for easily performing decontamination. We experimented a cutting test in Fugen Decommissioning Engineering Center using maximum 280 MPa pressure and 30 L/min water quantity, ultra-high pressure water jet system and 40 m$$^{3}$$/min air quantity vacuum system. We are conducting a study of decontamination technology in environmental pollution using this decontamination system. This decontamination system has achieved a decontamination factor 10 to 100. Thus, we have confirmed the change in a cutting ability by changing parameters. Parameters are the water pressure, the water quantity and air quantity. The impact force for water jet is a function that contains the test parameters. We have considered it using this function. The results of the test showed that there is a correlation between the impact force for water jet and a cutting capability. This decontamination technology can decontaminate radioactive material of the surface adhesion contamination and reduce the amount of waste generated for a thin cutting. In addition, we have experimented that the water can be recycled by chemical precipitation. After we experimented flocculation test using aluminum sulfate and zeolite flocculant, we have confirmed that it can clean water up to the level of suspended solids 5 mg/L, in turbid water using zeolite flocculant. This suspended solids concentration can be passed to the water processing system in nuclear power plant. From the test results, we found that ultra-high pressure water jet decontamination technology has a possibility that it can be used for decontamination of Fukushima Daiichi Nuclear Power Plant.

Journal Articles

Environmental remediation following the Fukushima-Daiichi accident

Tagawa, Akihiro; Nakayama, Shinichi; Miyahara, Kaname

Proceedings of International Nuclear Fuel Cycle Conference; Nuclear Energy at a Crossroads (GLOBAL 2013) (CD-ROM), p.944 - 951, 2013/03

A wide area of Fukushima Prefecture was contaminated with radioactivity released by the Fukushima Daiichi nuclear accident. Japan Atomic Energy Agency (JAEA) has been involved in mitigating the effects of the accident in a diversifying ways from the emergency dispatch of radiation experts immediately after the accident and radiation monitoring in the affected areas to demonstrate of decontamination for a variety of targets, public affairs with evacuated populations, and research and development activities for environmental remediation. The decontamination related activity is one of the major contributions of JAEA to environmental remediation, providing technical supports to the unprecedented regional decontamination in Fukushima that have been carried out by the central and local governments of Japan. JAEA's experiences and expertise obtained are overviewed in this paper focusing on the decontamination pilot project.

Journal Articles

Synthesis of arsenic graft adsorbents in pilot scale

Hoshina, Hiroyuki; Kasai, Noboru; Shibata, Takuya*; Aketagawa, Yasushi*; Takahashi, Makikatsu*; Yoshii, Akihiro*; Tsunoda, Yasuhiko*; Seko, Noriaki

Radiation Physics and Chemistry, 81(8), p.1033 - 1035, 2012/08

 Times Cited Count:2 Percentile:76.11(Chemistry, Physical)

Journal Articles

Effects of ground surface decontamination on the air radiation dose rate; Results of a decontamination trial at a playground lot in a Fukushima residential area

Tagawa, Akihiro

Nippon Genshiryoku Gakkai Wabun Rombunshi, 11(2), p.111 - 117, 2012/05

The Japan Atomic Energy Agency decontaminated schools, playgrounds, swimming pools, and houses in non-evacuated, less-contaminated areas in Fukushima for the environmental restoration. A small, 150 m$$^{2}$$ playground lot in the residential area was chosen for the decontamination demonstration, which used routinely available tools and commodities to carry out the work. The surfaces of playground lot equipment such as swings, slides, and horizontal iron bars were completely decontaminated by brushing with water and/or detergent. Side gutters around the playground lot were cleaned up by removing mud, then they were brushed and washed with a high-pressure water jet 7 MPa. The air dose rate at the playground lot was dominated by radiation from the ground surface and from adjacent surroundings such as apartments and rice fields. Two or three centimeters of the surface soil contaminated with cesium were removed manually with shovels, hoes and other gardening tools. This resulted in a significant decrease in the average air dose rate of the entire playground lot from 1.5 $$mu$$Sv/hr before decontamination to 0.6 $$mu$$Sv/hr. These results showed that ground surface decontamination can contribute measurably to a reduction in the air dose rate in relatively small areas in residential areas.

102 (Records 1-20 displayed on this page)