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Suzuki, Seiya; Arai, Yoichi; Okamura, Nobuo; Watanabe, Masayuki
Journal of Nuclear Science and Technology, 60(7), p.839 - 848, 2023/07
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)The fuel debris, consisting of nuclear fuel materials and reactor structural materials, generated in the accident of Fukushima Daiichi Nuclear Power Plant can become deteriorated like rocks under the changes of environmental temperature. Although the fuel debris have been cooled by water for 10 years, they are affected by seasonal and/or day-and-night temperature changes. Therefore, in evaluating the aging behavior of the fuel debris, it is essential to consider the changes in environmental temperature. Assuming that the fuel debris are deteriorated, radioactive substances that have recently undergone micronization could be eluted into the cooling water, and such condition may affect defueling methods. We focused on the effect of repeated changes in environmental temperature on the occurrence of cracks, and an accelerated test using simulated fuel debris was carried out. The length of the crack increases with increasing number of heat cycle; therefore, the fuel debris become brittle by stress caused by thermal expansion and contraction. In conclusion, it was confirmed that the mechanical deterioration of the fuel debris is similar to that of rocks or minerals, and it became possible to predict changes in the length of the crack in the simulated fuel debris and environmental model.
Kitagaki, Toru; Krasnov, V.*; Ikeda, Atsushi
Journal of Nuclear Materials, 576, p.154224_1 - 154224_14, 2023/04
Times Cited Count：1 Percentile：49.51(Materials Science, Multidisciplinary)Zhou, Q.*; Saito, Takumi*; Suzuki, Seiya; Yano, Kimihiko; Suzuki, Shunichi*
Journal of Nuclear Science and Technology, 58(4), p.461 - 472, 2021/04
Times Cited Count：6 Percentile：70.8(Nuclear Science & Technology)Ikeuchi, Hirotomo; Yano, Kimihiko; Washiya, Tadahiro
Journal of Nuclear Science and Technology, 57(6), p.704 - 718, 2020/06
Times Cited Count：6 Percentile：59.94(Nuclear Science & Technology)To suggest efficient process of the fuel debris treatment after the retrieval from the Fukushima Daiichi Nuclear Power Plant (1F), thorough investigation is indispensable on potential source of U in the fuel debris. Estimation on the fuel debris accumulated in the reactor pressure vessel is specifically important due to its limited accessibility. The present study aims to estimate the chemical forms of U in the in-vessel fuel debris, especially in the minor phases such as metallic phases, by performing the thermodynamic calculation considering the material relocation and changing environment during the accident progression in the 1F Unit 2. Input conditions for the thermodynamic calculation such as composition, temperature, and oxygen amount were assumed mainly based on the results of severe accident analysis. The chemical form of U varied depending on the local amount of Fe and O. In regions of low steel content, the U-containing metallic phase was dominated by 
-(Zr,U)(O), while regions of high steel content were dominated by Fe
(Zr,U) (Laves phase). A few percent of U was transferred to the metallic phases under reducing conditions, raising challenging issues on the chemical removal of nuclear material from fuel debris.
Kitagaki, Toru; Ikeuchi, Hirotomo; Yano, Kimihiko; Brissonneau, L.*; Tormos, B.*; Domenger, R.*; Roger, J.*; Washiya, Tadahiro
Journal of Nuclear Science and Technology, 56(9-10), p.902 - 914, 2019/09
Times Cited Count：7 Percentile：61.18(Nuclear Science & Technology)Akagi, Yosuke*; Kato, Hiroyasu*; Tachi, Yukio; Sakamoto, Hiroyuki*
Progress in Nuclear Science and Technology (Internet), 5, p.233 - 236, 2018/11
A large amount of radioactive contaminated concrete will be generated from the decommissioning in the Fukushima Dai-ichi Nuclear Power Plant (NPP). For developing the plans of decommissioning and waste management including decontamination and disposal, it is important to estimate radionuclides inventory and concentration distribution in the concrete materials. In this study, effective diffusivities (De) and distribution coefficients (Kd) of HTO, Cs, I and U in OPC mortar were measured by through-diffusion and batch sorption experiments. De values derived were in the sequence of HTO, I, Cs, U, implying that cation exclusion effects may be important mechanisms in OPC mortar. Kd values derived by batch tests were higher by more than one order of magnitude than the diffusion-derived Kd values, indicating that crushing of samples had a strong influence on sorption. Diffusion and sorption mechanisms in OPC mortar were evaluated to predict the penetration behavior of these radionuclides.
-ray imager mounted on a multicopter droneSato, Yuki; Ozawa, Shingo*; Terasaka, Yuta; Kaburagi, Masaaki; Tanifuji, Yuta; Kawabata, Kuniaki; Miyamura, Hiroko; Izumi, Ryo*; Suzuki, Toshikazu*; Torii, Tatsuo
Journal of Nuclear Science and Technology, 55(1), p.90 - 96, 2018/01
Times Cited Count：43 Percentile：98.12(Nuclear Science & Technology)Mizukoshi, Seiji; Oshima, Soichiro; Shimada, Taro
JAERI-Tech 2005-011, 122 Pages, 2005/03
JAERI-Tech-2005-011.pdf:13.25MB
The radiological and physical characteristic on decommissioning, such as component and structure weights and radioactivity of the 1.1 MWe class reference nuclear power plants summarized in the NUREG reports of the US NRC were classified,arranged and compared with the domestic commercial nuclear power plants and JPDR from a view point of dismantling plan and waste management for decommissioning. As the results, it was found that the radioactive component and structure weights was about 28,000ton、and non-radioactive structure weights was about 124,000ton less than the domestic commercial BWR. And it was found that this differences has mainly influenced dismantling costs for decommissioning. Farther, it was found that the concrete element composition rates of B, Ni, Nb and so were differerence of one or more figures btween the reference nuclear power plants and the domestic commercial PWR or JPDR.Also,it was found that the this difference became about two or three times by radioactivity concentration and has mainly influenced transport and disposal costs for decommissioning.
Nakamura, Hisashi; Nakashima, Mikio
JAERI-Tech 2002-006, 58 Pages, 2002/03
JAERI-Tech-2002-006.pdf:2.56MB
Radiation exposure was estimated on production and utilization of recycled items using dismantling waste by assuming that their usage are restricted to nuclear facilities. The radiation exposure attributed to production of a steel-plate cast iron waste container, a receptacle for slag, and a drum reinforcement was calculated to be in the range of several 
Sv to several tens of Sv even in recycling contaminated metal waste of which radioactivity concentration of Co-60 is higher than the clearance level by a factor of two figures. It is also elucidated that casting of a multiple casting waste package meets the standards of dose equivalent rate for the transport of a radioactive package and the weight of the package will be able to kept around 20 tons for the convenience of the handling, in case of disposal of metal waste less than 37MBq/g with the steel-plate cast iron waste container. As the results, from the radiological exposure's point of view, it should be possible to use slightly contaminated metal for recycled items in waste management.
Department of Decommissioning and Waste Management
JAERI-Review 2000-013, 49 Pages, 2000/09
JAERI-Review-2000-013.pdf:3.26MB
no abstracts in English
E.J.Claude*; Nakamura, Hisashi; D.M.Chapin*; J.W.Simons*; H.Seneviratne*
Proceedings of 7th International Conference on Nuclear Engineering (ICONE-7) (CD-ROM), 10 Pages, 1999/00
no abstracts in English
Yanagihara, Satoshi;
JAERI-M 94-005, 61 Pages, 1994/02
no abstracts in English
Yanagihara, Satoshi; ; ; Fujiki, Kazuo
1st JSME/ASME Joint Int. Conf. on Nuclear Engineering, p.65 - 70, 1991/00
no abstracts in English
Sato, Yuki; Kaburagi, Masaaki; Terasaka, Yuta; Saegusa, Jun; Kawabata, Kuniaki; Wakaida, Ikuo; Torii, Tatsuo
no journal, ,
Nakamura, Hironobu; Kitao, Takahiko; Shimizu, Yasuyuki; Takeda, Seiichi; Yamaguchi, Katsuhiro*
no journal, ,
Based on the DIQ guideline discussed and summarized at the 1st consultancy meeting, since JAEA made an example of DIQ for the reprocessing considering the decommissioning stages as Japan's task, we explain the contents and submit it to IAEA in the 2nd consultancy meeting. Basically, as the information regarding decommissioning stage, date of decommissioned, facility decommissioning plan, nuclear material recovery and removing or rendering inoperable of "essential equipment" with example are additionally described in the DIQ. We hope that this material could be helped to make a reprocessing DIQ (PUREX) in the world.
Saruta, Koichi; Kamei, Naomitsu; Sato, Yuji; Muramatsu, Toshiharu
no journal, ,
Dohi, Terumi; Di Palma, A.*; Fujiwara, Kenso; Adamo, P.*; Kusano, keiichi*; Kimura, Shigeru*; Kanno, Futoshi*; Iijima, Kazuki
no journal, ,
In the surrounding area of the FDNPS, dust samplers have been used as a means of monitoring the radionuclides concentration in the air. However, the installation of dust samplers requires a power supply, which limits the number and location of the samplers. We aim to establish a method to evaluate the radiocaesium concentration and behavior in the air using moss bags, which have been used in air pollution research. Since the moss bags can be easily installed at any place and time, the establishment of the evaluation method using the moss bags will be effective in creating a sense of security among the local governments and their residents around the FDNPS. In this study, we investigated the applicability of moss bags to the evaluation of the concentration and behavior of radiocaesium in the air.
