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Iijima, Kazuki
Enerugi, Shigen, 44(6), p.372 - 377, 2023/11
In the Fukushima Dai-ichi Nuclear Power Station accident, huge number of radioactive materials were released into the environment. We provided an overview of how issues have been tackled, with a focus on decontamination which was the pillar of large-scale reconstruction efforts.
Watanabe, So; Takahatake, Yoko; Ogi, Hiromichi*; Osugi, Takeshi; Taniguchi, Takumi; Sato, Junya; Arai, Tsuyoshi*; Kajinami, Akihiko*
Journal of Nuclear Materials, 585, p.154610_1 - 154610_6, 2023/11
Times Cited Count：0 Percentile：0.01(Materials Science, Multidisciplinary)
Cs supply from rivers to coastal waters off Fukushima considering human activitiesIkenoue, Tsubasa; Shimadera, Hikari*; Nakanishi, Takahiro; Kondo, Akira*
Water (Internet), 15(15), p.2734_1 - 2734_18, 2023/08
Times Cited Count：0 Percentile：0(Environmental Sciences)The Fukushima Daiichi Nuclear Power Plant accident caused an accumulation of Cs in coastal sediment. The Cs supply from rivers to the ocean can affect the long-term fate of Cs in coastal sediment. Since the Fukushima coastal river basins include large decontaminated and evacuation order areas, considering the decontamination work and resumption of agriculture is important for predicting the Cs supply. We conducted a 30-year prediction of the Cs supply from the Fukushima coastal rivers to the ocean using a distributed radiocesium prediction model, considering the effects of human activities. In river basins with decontaminated and evacuation order areas, human activities reduced the total Cs outflow from agricultural lands, urban lands, and forest areas to the rivers and the Cs supply to the ocean by 5.0% and 6.0%, respectively. These results indicated that human activities slightly impacted the Cs outflow and supply. The Cs supply from rivers impacted by the accident to the coastal sediment was estimated to correspond to 11-36% of the total Cs in the coastal sediment in the early phase of the accident. Therefore, the Cs supply from rivers to the ocean is important for the long-term behavior of Cs in coastal sediment.
Takahashi, Shigeo*; Sakurai, Daisuke*; Nagao, Fumiya; Kurikami, Hiroshi; Sanada, Yukihisa
Shimyureshon, 42(2), p.68 - 75, 2023/06
This paper introduces a case in which scientific knowledge on understanding the deposition process of radionuclides and evaluating the dose rate reduction due to decontamination work was obtained through visual analysis based on data on the spatio-temporal distribution of air dose rates accumulated through radiation monitoring after the accident. We will discuss the prospects for future efforts to effectively obtain important knowledge that will assist in the planning of policies for reconstruction from the nuclear power plant accident in the future.
Kusakabe, Kazuaki*; Watanabe, Masanori; Nishiuchi, Masashi*; Yamasaki, Takuhei*; Inoue, Hiromi*
Kankyo Hoshano Josen Gakkai-Shi, 11(1), p.15 - 23, 2023/03
The spread of radioactive materials caused by the Fukushima Daiichi Nuclear Power Plant accident that occurred in March 2011 contaminated a wide area that includes Fukushima Prefecture. Although air dose rates in Fukushima Prefecture have been steadily decreasing because of decontamination and the physical decay of radioactive materials, it is important to confirm the sustainability of decontamination effects in living areas and to predict future trends in air dose rates to reassure residents who are concerned regarding radiation exposure. This report aims to confirm the sustainability of the decontamination effects in public facilities after decontamination on a continuous and detailed basis, and to verify whether the future transition in air dose rates can be predicted using existing model. The air dose rates in public facilities after decontamination were measured via fixed-point and walking surveys, and the changes in air dose rates were clarified quantitatively for each facility. The measured values were compared with values obtained using existing model, and prediction accuracy was considered. The results showed that there was no evident recontamination after decontamination at any of the surveyed facilities, indicating that the decontamination effects were sustained. It was also confirmed that future trends in air dose rates at the facilities after decontamination could be accurately predicted by existing model. Key words: air dose rate, decontamination, future prediction, public facilities.
Yamamoto, Kosuke; Yanagihara, Satoshi*
Journal of Nuclear Science and Technology, 59(12), p.1527 - 1535, 2022/12
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)A series of work activities involved in clearance verification process was analyzed from the viewpoint of work efficiency at Fugen. As a result, decontamination required the most manpower expenditure. In addition, most of clearance candidate materials were very low contamination before the decontamination work. The analysis indicates that it will be effective for these lower radioactivity parts to reduce effort of decontamination activity or to skip the decontamination scenario considering that radioactivity was enough low. In addition, sample monitoring is possible scenario depending on the degree of contamination rather than to monitor all unit for clearance verification. When the manpower is evaluated based on the actual results of Fugen in consideration of these conditions, the clearance verification process could make the efficiency less than 37% in case of Fugen decommissioning.
Sakasegawa, Hideo; Nomura, Mitsuo; Sawayama, Kengo; Nakayama, Takuya; Yaita, Yumi*; Yonekawa, Hitoshi*; Kobayashi, Noboru*; Arima, Tatsumi*; Hiyama, Toshiaki*; Murata, Eiichi*
Progress in Nuclear Energy, 153, p.104396_1 - 104396_9, 2022/11
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)When dismantling centrifuges in uranium-enrichment facilities, decontamination techniques must be developed to remove uranium-contaminated surfaces of dismantled parts selectively. Dismantled uranium-contaminated parts can be disposed of as nonradioactive wastes or recycled after decontamination appropriate for clearance. previously, we developed a liquid decontamination technique using acidic electrolyzed water to remove uranium-contaminated surfaces. However, further developments are still needed for its actual application. Dismantled parts have various uranium-contaminated surface features due to varied operational conditions, inhomogeneous decontamination using iodine heptafluoride gas, and changes in long-term storage conditions after dismantling. Here, we performed liquid decontamination on specimens with varying uranium-contaminated surfaces cut from a centrifuge made of low-carbon steel. From the results, the liquid decontamination can effectively remove the uranium-contaminated surfaces, and radioactive concentrations fell below the target value within twenty minutes. Although the required time should also depend on dismantled parts' sizes and shapes in their actual application, we demonstrated that it could be an effective decontamination technique for uranium-contaminated steels of dismantled centrifuges.
Kam, D. H.*; Grabaskas, D.*; Starkus, T.*; Bucknor, M.*; Uchibori, Akihiro
Transactions of the American Nuclear Society, 126(1), p.536 - 539, 2022/06
Removal of gaseous radionuclides from the bubbles released into the sodium pool is an important consideration of fuel pin failure accident in sodium-cooled fast reactors. To support modeling of this phenomenon as a part of development of the SRT (Simplified Radionuclide Transport) code in Argonne National Laboratory, numerical analysis of experiment on Iodine gas transport to sodium pool was performed. A proposed evaluation method can be regarded to be reasonably predicting the measured decontamination factors.
Kawase, Keiichi
Kankyo Hoshano Josen Gakkai-Shi, 9(4), p.171 - 172, 2021/12
no abstracts in English
Saegusa, Hiromitsu*; Funaki, Hironori; Kurikami, Hiroshi; Sakamoto, Yoshiaki; Tokizawa, Takayuki*
Insights Concerning the Fukushima Daiichi Nuclear Accident, Vol.4; Endeavors by Scientists, p.170 - 187, 2021/10
Removed contaminants including soil, grass and trees are to be stored safely at temporary storage facilities for several years, after which they will be transferred to a planned interim storage facility. The decontamination pilot project was carried out in both the restricted and planned evacuation areas in order to assess decontamination methods and demonstrate measures for radiation protection of workers. Fourteen temporary storage facilities of different technical specifications were designed and constructed under various topographic conditions and land use. In order to support the design, construction and monitoring of temporary storage facilities for removed contaminants during the full-scale decontamination within the prefecture of Fukushima, technical know-how obtained during the decontamination pilot project has been identified and summarized in this paper.
Sun, Haomin; Shibamoto, Yasuteru; Hirose, Yoshiyasu; Kukita, Yutaka
Journal of Nuclear Science and Technology, 58(9), p.1048 - 1057, 2021/09
Times Cited Count：4 Percentile：56.94(Nuclear Science & Technology)no abstracts in English
Plutonium Fuel Development Center
JAEA-Review 2021-007, 61 Pages, 2021/06
JAEA-Review-2021-007.pdf:7.56MB
The contamination incident in an operation room (Room No. A-103) of Plutonium Fuel Fabrication Facility (PFFF) in Japan Atomic Energy Agency (JAEA), Nuclear Fuel Cycle Engineering Laboratory occurred on January 30, 2019 during replacement of the double plastic bags which enclose a storage container containing nuclear material. At this time, some of nuclear materials spread all over the room. Nine workers in the room were contaminated with plutonium, but internal exposure of them was not confirmed. In order to restore the Room No. A-103 of PFFF, the Restoration Activity Team organized in JAEA carried out the decontamination work after the investigation of the contamination level in the room. The team had decontaminated the surface of walls, ceiling, gloveboxes and other instruments. Suitable decontamination methods were selected depending on the contamination distribution and installation state of the instruments. In addition to the manual wiping using wet wipes, the exfoliation method using a microfiber mop was applied for narrowed areas. As a result, the loose alpha-contamination level throughout the room fell below the detection limit. On other hand, the fixed alpha-contaminations were confined by painting after the decontamination. This report shown detail restoration activities for this time incident. This information is useful for making a manual on restoration activities and performing practice for the largescale contamination incident. We hope this report will be used for other facilities handled alpha-radioactive materials such as plutonium.
Cs outflow from forest floor adjacent to a residential area; Comparison of decontaminated and non-decontaminated forest floorNiizato, Tadafumi; Watanabe, Takayoshi
Global Environmental Research (Internet), 24(2), p.129 - 136, 2021/06
The 3-years monitoring of Cs outflow associated with soil erosion in the decontaminated and no decontaminated sites using experimental plot was conducted in the forest of Fukushima during the rainy season. The Cs outflow in the decontaminated site was 10 to 14 times larger than that of no decontaminated site. However, the outflow in the decontaminated site decreased from 3.24% to 0.61% in corresponding with the recovery of the forest floor cover. When reaching of the forest floor cover to 60% and over, the Cs outflow in the decontaminated site turned into relatively minor fluctuations and similar level to the no decontaminated site. The decrease in the Cs outflow corresponding to the restoration of the forest floor cover was owing to the recovering of the protective effect of forest floor against the raindrop splash and decrease in ratio of the soil component with relatively high Cs activity in the particulate matter.
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.
Sun, Haomin; Shibamoto, Yasuteru; Okagaki, Yuria; Yonomoto, Taisuke
Science and Technology of Nuclear Installations, 2019, p.1743982_1 - 1743982_15, 2019/06
Times Cited Count：13 Percentile：82.61(Nuclear Science & Technology)Nakayama, Takuya; Nomura, Mitsuo; Mita, Yutaka; Yonekawa, Hitoshi*; Bunbai, Misako*; Yaita, Yumi*; Murata, Eiichi*; Hosaka, Katsumi*; Sugitsue, Noritake
Proceedings of 2019 International Congress on Advances in Nuclear Power Plants (ICAPP 2019) (Internet), 8 Pages, 2019/05
Clearance of contaminated metal is important for recycling and volume reduction of radioactive waste. Among applicable decontamination technologies, immersion method with ultrasonic cleaning is considered to be effective for metal materials having various shapes. in this study is to demonstrate decontamination of carbon steel contaminated by uranium hexafluoride to the target level for clearance (less than 0.04 Bq/cm
), and minimize secondary waste. In this test, acidic electrolytic water, dilute hydrochloric acid, dilute sulfuric acid and ozone water with various pH and redox potential were used as decontamination solutions to be tested. We found that acidic electrolytic water is effective solution for decontamination of carbon steel contaminated by uranium hexafluoride. It could be decontaminate less than target level for clearance, and reduced secondary waste relatively.
Malins, A.; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko
Remediation Measures for Radioactively Contaminated Areas, p.259 - 272, 2019/00
Sakamoto, Hiroyuki*; Akagi, Yosuke*; Yamada, Kazuo*; Tachi, Yukio; Fukuda, Daisuke*; Ishimatsu, Koichi*; Matsuda, Mikiya*; Saito, Nozomi*; Uemura, Jitsuya*; Namihira, Takao*; et al.
Nihon Genshiryoku Gakkai Wabun Rombunshi, 17(2), p.57 - 66, 2018/05
Concrete debris contaminated with radioactive cesium and other nuclides have been generated from the accident in the Fukushima Dai-ichi Nuclear Power Plant and there will be generated due to the decommissioning of nuclear power plants in the future. Although conventional decontamination techniques are effective for flat concrete surfaces such as floors and walls, it is not clear what techniques to apply for decontaminating radioactive concrete debris. In this study, focusing on a pulsed power discharge technique, fundamental experimental works were carried out. Decontamination of concrete by applying the aggregate recycling technique using the pulsed power discharge technique was evaluated by measuring radioactivity of aggregate and sludge separated from the contaminated concrete. The results suggest that the separation into aggregate and sludge of the contaminated concrete debris could achieve decontamination and volume reduction of the radioactive concrete debris.
Nagasu, Ryosuke*; Tanabe, Daijiro*; Yokotsuka, Satoshi*; Kumazawa, Noriyuki*; Ajiki, Takaya*; Aizawa, Yusuke*; Naganawa, Hirochika; Nagano, Tetsushi; Yanase, Nobuyuki*; Mitamura, Hisayoshi*; et al.
Kankyo Joka Gijutsu, 17(2), p.58 - 61, 2018/03
A new technology to suppress cesium migration from forests has been developed collaboratively by Ibaraki University, Kumagai-gumi Co., Ltd. and its group company, Technos, and JAEA. The new technology utilizes polyelectrolytes (polymers with electric charges) and clay minerals to control Cs migration with the aid of natural forces such as rainfall and rainwater runoff. In Imitate-mura, Fukushima, verification tests of the new technology have been performed and its effect on controlling Cs migration from forests to grass farm adjoining the forests has been proven.
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.
