Feasibility study of reactor radiation photon spectroscopy in Fugen for nuclear decommissioning

Kaburagi, Masaaki; Miyamoto, Yuta; Mori, Norimasa; Iwai, Hiroki; Tezuka, Masashi; Kurosawa, Shunsuke*; Tagawa, Akihiro; Takasaki, Koji

Journal of Nuclear Science and Technology, 62(3), p.308 - 316, 2025/03

https://doi.org/10.1080/00223131.2024.2417786

The Great East Japan Earthquake; What has JAEA done?

Tagawa, Akihiro

Hoshasen (Internet), 49(1), p.2 - 4, 2024/03

https://doi.org/10.11470/houshasen.49.1_2

The Great East Japan Earthquake occurred on March 11, 2011, and the accident at TEPCO's Fukushima Daiichi Nuclear Power Station caused widespread contamination in Fukushima Prefecture and elsewhere. JAEA started its activities on the day of March 11 when it was dispatched by a Self-Defense Forces helicopter from Hyakuri Air Base in Ibaraki Prefecture to the Okuma Town Off-Site Center. The activities included physical survey, health consultation telephone counter, temporary return home response for residents, whole body measurement of TEPCO employees and Fukushima Prefecture residents, environmental radiation monitoring, and others. The lecture reviewed the various events that took place during the first year after the disaster and introduced the dilemma under which JAEA has been working through simulated experiences.

Testing of multistep soil washing for radiocesium-contaminated soil containing plant matter

Funakawa, Masashi*; Tagawa, Akihiro; Okuda, Nobuyasu*

Insights Concerning the Fukushima Daiichi Nuclear Accident, Vol.4; Endeavors by Scientists, p.125 - 137, 2021/10

https://doi.org/10.15669/fukushimainsights.Vol.4.125

The current study subjected 4 types of contaminated soil with different properties to multistep soil washing under the same conditions. This study also determined the effectiveness of radiocesium decontamination and the extent to which the amount of contaminated soil was reduced. In addition, the effectiveness of plant matter separation, adsorbent addition, and grinding as part of multistep soil washing was determined using the same contaminated soil. Results of testing indicated that the rate of radiocesium decontamination ranged from 73.6 to 89.2% and the recovery rate ranged from 51.5 to 84.2% for twice-treated soil, regardless of the soil properties or cesium level. Plant matter in soil had a high radiocesium level. However, there was little plant matter in our soil sample. Therefore, plant matter separation had little effect on the improvement in the percentage of radiocesium decontamination of twice-treated soil. Soil surface grinding improved the radiocesium decontamination of twice-treated soil. However, radiocesium in soil tightly bound with minerals in the soil thus, the addition of an adsorbent also failed to improve radiocesium decontamination.

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).

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.

Communication activity for residents to understand radiation after the accident of Fukushima Daiichi Nuclear Power Station

Itabashi, Kiyoshi; Tagawa, Akihiro; Sugiyama, Kenji; Yamamoto, Tomoyo

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

https://doi.org/10.1299/jsmeicone.2015.23._ICONE23-2_50

Kotaeru kai for questions about radiation (below is called Kotaeru kai) has started since July 2011 in Fukushima prefecture which influenced especially after the accident of Fukushima Daiichi Nuclear Power Station on 11st March 2011. The purpose is to have mainly parents and educators (such as of kindergartens, nursery schools etc.) understand correctly about radiation and the influence to health. Receiving requests from educators in Fukushima prefecture, about 4 staff members teamed up to explain. They were selected from 500 JAEA staffs entered beforehand. The members explain about radiation and the influence to health by using illustrations and metaphors in materials and answer questions asked in advance at schools or so which require explain. When they explain, they place much vale for communication with participants. Until the end of September 2014, Kotaeru kai have enforced 237 times for about 20 thousand of participants. According to 7,613 participants' questionnaires (which were collected from July 2011 to the end of 2012), it seems that participants understood well about radiation and the influence to health. Certain junior high school requested to explain for students, and JAEA will continue this activity in order to meet these expectations and requirements.

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

https://doi.org/10.7567/JJAP.53.116505

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 C/cm, etch selectivity with a silicon-based middle layer in CF plasma treatment, and high prediction sensitivity to EUV region.

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

https://doi.org/10.1016/j.mee.2014.02.026

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 C/cm. The resist is developable in pure water at 23 C for 60 s, and it has acceptable CF etch selectivity.

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.

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

https://doi.org/10.7567/APEX.7.036501

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.