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Journal Articles

Human resource development for decommissioning of JAEA's facilities

Takiya, Hiroaki

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 30(2), p.66 - 71, 2023/12

A half of unclear facilities in Japan Atomic Energy Agency (JAEA) has been transferred to decommissioning phase because of achieving the expected goals for the research and development, aging of buildings and equipment, etc. JAEA must safely, efficiently, and rationally implement back-end measures related to decommissioning, from the dismantling of nuclear facilities to the processing and disposal of radioactive waste generated by dismantling. The decommissioning and radioactive waste management head office collaborates with each JAEA's site to plan and promote comprehensive back-end measures and promote near surface disposal of low-level radioactive waste generated from research, medical, and industrial facilities, and to work on research and development aimed at solving common issues related to back-end measures, human resource development, etc. Since decommissioning is a long-term project, it is important to secure specialized human resources for the future. This article presents a summary of human resource development for decommissioning.

JAEA Reports

Strategic roadmap for back-end technology development

Nakazawa, Osamu; Takiya, Hiroaki; Murakami, Masashi; Donomae, Yasushi; Meguro, Yoshihiro

JAEA-Review 2023-012, 6 Pages, 2023/08

JAEA-Review-2023-012.pdf:0.93MB

The selection of back-end technology development issues to be prioritized and their schedule of the Japan Atomic Energy Agency (JAEA) have been put together as the "Strategic Roadmap for Back-end Technology Development." The results of questionnaires on development technologies (seeds) and technical issues (needs) within JAEA conducted in FY2022 were reflected in the selection. The issues were extracted from among those that match the seeds and needs, from the perspective of early implementation in the work front and the perspective of common issues, and nine themes were selected. We will build a cross-organizational implementation framework within JAEA and aim to implement the development results in the work front as well as social implementation.

JAEA Reports

Improvement of the Simplified Decommissioning Cost Estimation Code for Nuclear Facilities (DECOST)

Takahashi, Nobuo; Kubota, Shintaro; Takiya, Hiroaki; Sakaba, Ryosuke*; Sato, Koichi; Shichi, Ryo

JAEA-Testing 2021-002, 106 Pages, 2022/01

JAEA-Testing-2021-002.pdf:2.08MB

The Japan Atomic Energy Agency has various nuclear facilities such as reactor facilities and reprocessing facilities. Some aged facilities will be decommissioned after their original functions ended, and it is necessary to evaluate their decommissioning cost to formulate the initial decommissioning plans and the final decommissioning plans. We have developed an evaluation method called DECOST that can efficiently calculate the decommissioning cost in a short time based on factors such as features and similarity of the facilities and dismantling methods. The decommissioning of nuclear facilities has been implemented and new achievements and findings have been reported since the development of DECOST. These findings were reflected in DECOST. In consideration of the needs of DECOST users, DECOST has been improved so that the cost of dismantling the facility can be divided into the cost of releasing the controlled area and the cost of dismantling the facility building after the release of the controlled area. This report shows the improvement of DECOST, the concept of resetting the evaluation coefficient used in the cost evaluation formula, and the validity of the evaluation coefficient after resetting. In addition, the evaluation procedure of the improved DECOST is described, since the evaluation items and evaluation contents were partially changed due to the improvement.

JAEA Reports

Tritium removal of heavy water system and helium system in FUGEN

Takiya, Hiroaki; Kadowaki, Haruhiko; Matsushima, Akira; Matsuo, Hidehiko; Ishiyama, Masahiro; Aratani, Kenta; Tezuka, Masashi

JAEA-Technology 2020-001, 76 Pages, 2020/05

JAEA-Technology-2020-001.pdf:6.06MB

Advanced Thermal Reactor (ATR) FUGEN was operated for about 25 years, and now has been proceeding decommissioning after the approval of the decommissioning plan in Feb. 2008. The reactor, heavy water system and helium system are contaminated by tritium because of neutron absorption of heavy water, which is a moderator. Before dismantling these facilities, it is necessary to remove tritium from them for not only reducing the amount of tritium released to surrounding environment and the risk of internal exposure by tritium but also ensuring the workability. In first phase of decommissioning (Heavy Water and Other system Decontamination Period), tritium decontamination of the reactor, heavy water system and helium system started in 2008 and completed in 2018. This report shows the results of tritium decontamination of the reactor, heavy water system and helium system.

Journal Articles

Technology demonstration of sampling from reactor core structure of FUGEN Decommissioning Engineering Center

Iwai, Hiroki; Soejima, Goro; Takiya, Hiroaki; Awatani, Yuto; Aratani, Kenta; Miyamoto, Yuta; Tezuka, Masashi

Dekomisshoningu Giho, (61), p.12 - 19, 2020/03

FUGEN Decommissioning Engineering Center received the approval of the decommissioning plan in 2008, and we have been progressing the decommissioning. The first phase of decommissioning (Heavy Water and Other System Decontamination Period) finished in March 2018, and FUGEN has entered into the second phase of decommissioning (Reactor Periphery Facilities Dismantling Period). This report outlines the technology demonstration of sampling from reactor core structure of FUGEN that to prepare for reactor dismantlement in the third phase.

Journal Articles

Result of dismantlement on the turbine systems in FUGEN

Aratani, Kenta; Takiya, Hiroaki; Koda, Yuya; Ishiyama, Masahiro; Tezuka, Masashi; Mizui, Hiroyuki

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 5 Pages, 2019/05

The prototype advanced thermal reactor FUGEN is the heavy water-moderated, boiling light water-cooled, pressure tube-type reactor, and has progressing the decommissioning since 2008. The most of facilities such as turbine system have the system structure and the operating conditions similar to those of BWR, although FUGEN has the characteristic structure of reactor core and the heavy water treatment facilities. In Japan, the knowledge and findings from FUGEN decommissioning activities are very important and valuable to perform BWR decommissioning in future, because the decommissioning of FUGEN is research and development as the first decommissioning of real-scale reactor. In the first phase of FUGEN decommissioning activities, the dismantlement project of reactor core cooling system started. By 2017, the low-level contaminated equipment such as the condensers of turbine system and the main-steam pipes of main-steam system was dismantled, and the management data was accumulated. The knowledge and findings from the 10 years of dismantlement experience will be reflected to the future dismantlement of higher contaminated facilities.

Journal Articles

Status of decommissioning of FUGEN Decommissioning Engineering Center

Takiya, Hiroaki; Aratani, Kenta; Awatani, Yuto; Ishiyama, Masahiro; Tezuka, Masashi; Mizui, Hiroyuki

Dekomisshoningu Giho, (59), p.2 - 12, 2019/03

FUGEN Decommissioning Engineering Center received the approval of the decommissioning program in 2008, and we have been progressing the decommissioning. The first phase of decommissioning (Heavy Water and Other system Decontamination Period) finished in May 2018, and FUGEN has entered into the second phase of decommissioning (Reactor Periphery Facilities Dismantling Period). This report outlines the results obtained in the first phase of decommissioning of FUGEN.

Journal Articles

Pipe cutting method at high radiation area in FUGEN

Takiya, Hiroaki; Ishiyama, Masahiro; Tezuka, Masashi; Kitayama, Naoki

Proceedings of International Conference on Dismantling Challenges; Industrial Reality, Prospects and Feedback Experience (DEM 2018) (Internet), 8 Pages, 2018/10

In FUGEN, we had isolated the reactor core by cutting pipes of the periphery systems (e.g. reactor cooling system, heavy water system, and helium system) between 2015 and 2017, as preparation for dismantling the reactor core and taking some samples from the reactor core structures. There are three issues to be solved at this isolation work; (1) to shorten the working time at high radiation area which is 1-5mSv/h at air and 10mSv/h at contact, (2) to prevent tritium spreading to working area at cutting work because tritium air is existing with 20-30Bq/cm$$^{3}$$ inside of the heavy water system and helium system, and (3) to minimize the influence of contaminated fume for the accurate radioactivity evaluation of reactor core structure. In this study, considering these problems, we discussed the method for cutting the pipes of heavy water system and helium system at the high radiation area and carried out the pipe cutting in the way.

Journal Articles

Preliminary re-conditioning test of the bituminization for radioactive wastes

Soejima, Goro; Takiya, Hiroaki; Mizui, Hiroyuki; Fujita, Yoshihiko*; Akari, Eisaku*; Endo, Nobuyuki*; Kume, Kyo*

Heisei-27-Nendo Koeki Zaidan Hojin Wakasawan Enerugi Kenkyu Senta kenkyu Nempo, 18, P. 14, 2016/10

We have performed the preliminary re-conditioning test of the bituminization for radioactive wastes applying to the technical criteria by non-radioactive samples. As a result, we have confirmed the applicability to secure homogeneity that is a part of the technical criteria by evaluating sample properties.

Journal Articles

Dipole tracer migration and diffusion tests in fractured sedimentary rock at Horonobe URL

Tanaka, Shingo*; Yokota, Hideharu; Ono, Hirokazu; Nakayama, Masashi; Fujita, Tomoo; Takiya, Hiroaki*; Watanabe, Naoko*; Kozaki, Tamotsu*

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05

Oral presentation

Dependence of water diffusion on water to cement ratio in ordinary portland cement pastes

Takiya, Hiroaki*; Tanaka, Shingo*; Noda, Natsuko*; Sato, Seichi*; Kozaki, Tamotsu*; Sato, Haruo; Hatanaka, Koichiro

no journal, , 

It is important to clarify the behaviour of cement porewater for performance assessment of radioactive waste disposal. In this study, we measured apparent self-diffusion coefficients of water in Ordinary Portland Cement pastes with various water-cement ratios (W/C) as the part. The diffusion experiments were carried out as a function of W/C ratio in a range of 0.4-0.8, and O-18 was used as a tracer of water. The apparent diffusion coefficient increased with W/C. All penetration profiles of O-18 showed a tendency to shift from simple diffusion profile with increasing diffusion depth. It was indicated existence of some different diffusion pathways.

Oral presentation

Study on the method for cutting pipes in high radiation area for the isolation of reactor core from other systems in FUGEN

Takiya, Hiroaki; Matsushima, Akira; Ishiyama, Masahiro; Okuzawa, Kazuhiro

no journal, , 

no abstracts in English

Oral presentation

Development of the electrolytic decontamination machine for pipes, 2; Result of decontamination test

Aratani, Kenta; Matsushima, Akira; Takiya, Hiroaki; Awatani, Yuto; Sasaki, Katsuya*; Maehata, Hidehiko*; Maruyama, Akira*

no journal, , 

no abstracts in English

Oral presentation

Trial manufacture of the rubber lining separation machine from rubber-lined pipes

Takiya, Hiroaki

no journal, , 

no abstracts in English

Oral presentation

Specialized training on decommissioning

Matsushima, Akira; Nakayama, Tamotsu; Soejima, Goro; Takiya, Hiroaki; Isomi, Kazuhiko

no journal, , 

no abstracts in English

Oral presentation

Analysis of technical problems on decommissioning work-site activities

Tanabe, Kazuhiro*; Yanagihara, Satoshi*; Iguchi, Yukihiro; Takiya, Hiroaki; Narikawa, Isao*; Kobashi, Hiroaki*; Aoyama, Yoshiharu*; Iida, Keiichi*; Yanagida, Akihiro*; Murayama, Kazunari*; et al.

no journal, , 

In order to make safer and more rational efforts possible for a decommissioning project that is about to begin in full swing, we organized our experience, achievements and knowledge, including maintenance and dismantling work in the plant, and evaluated basic issues for decommissioning.

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