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Journal Articles

Chemical forms of uranium evaluated by thermodynamic calculation associated with distribution of core materials in the damaged reactor pressure vessel

Ikeuchi, Hirotomo; Yano, Kimihiko; Washiya, Tadahiro

Journal of Nuclear Science and Technology, 57(6), p.704 - 718, 2020/06

 Times Cited Count:0 Percentile:100(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 $$alpha$$-(Zr,U)(O), while regions of high steel content were dominated by Fe$$_{2}$$(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.

Journal Articles

Leaching behavior of prototypical Corium samples; A Step to understand the interactions between the fuel debris and water at the Fukushima Daiichi reactors

Nakayoshi, Akira; Jegou, C.*; De Windt, L.*; Perrin, S.*; Washiya, Tadahiro

Nuclear Engineering and Design, 360, p.110522_1 - 110522_18, 2020/04

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

Journal Articles

Material characterization of the VULCANO corium concrete interaction test with concrete representative of Fukushima Daiichi Nuclear Plants

Brissonneau, L.*; Ikeuchi, Hirotomo; Piluso, P.*; Gousseau, J.*; David, C.*; Testud, V.*; Roger, J.*; Bouyer, V.*; Kitagaki, Toru; Nakayoshi, Akira; et al.

Journal of Nuclear Materials, 528, p.151860_1 - 151860_18, 2020/01

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

Effect of quenching on molten core-concrete interaction product

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:1 Percentile:53.3(Nuclear Science & Technology)

Journal Articles

Knowledge obtained from dismantling of large-scale MCCI experiment products for decommissioning of Fukushima Daiichi Nuclear Power Station

Nakayoshi, Akira; Ikeuchi, Hirotomo; Kitagaki, Toru; Washiya, Tadahiro; Bouyer, V.*; Journeau, C.*; Piluso, P.*; Excoffier, E.*; David, C.*; Testud, V.*

Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR 2019) (Internet),  ( ), 4 Pages, 2019/05

Journal Articles

Large scale VULCANO molten core concrete interaction test considering Fukushima Daiichi condition

Bouyer, V.*; Journeau, C.*; Haquet, J. F.*; Piluso, P.*; Nakayoshi, Akira; Ikeuchi, Hirotomo; Washiya, Tadahiro; Kitagaki, Toru

Proceedings of 9th Conference on Severe Accident Research (ERMSAR 2019) (Internet), 13 Pages, 2019/03

Journal Articles

Current situation of OECD/NEA, Preparatory Study on Analysis of Fuel debris (PreADES) project

Nakayoshi, Akira; Bottomley, D.; Washiya, Tadahiro

Proceedings of 56th Annual Meeting on Hot Laboratories and Remote Handling (HOTLAB 2019) (Internet),  ( ), 3 Pages, 2019/00

Journal Articles

R&D strategy on mid- and long-term behavior of fuel debris

Yano, Kimihiko; Kitagaki, Toru; Washiya, Tadahiro; Miyamoto, Yasuaki; Ogawa, Toru

Progress in Nuclear Science and Technology (Internet), 5, p.225 - 228, 2018/11

According to the roadmap for decommissioning of Fukushima Daiichi NPS, fuel debris retrieval will start from 2021, after a decade from fuel debris generation. Fuel debris will stay in the reactors until the end of defueling. In addition, it is not hard to anticipate that storage is necessary for fuel debris removed from reactors. In order to consider such a post-accident operation for fuel debris, it is indispensable to discuss the states and characteristics of fuel debris during several decades. Therefore, JAEA directed R&D strategy on mid- and long-term behavior of fuel debris tentatively and is making a start of fundamental studies on this issue in corporation with the domestic universities and other research institutes.

Journal Articles

Characterization of the VULCANO test products for fuel debris removal from the Fukushima Daiichi Nuclear Power Plant

Kitagaki, Toru; Ikeuchi, Hirotomo; Yano, Kimihiko; Ogino, Hideki; Haquet, J.-F.*; Brissonneau, L.*; Tormos, B.*; Piluso, P.*; Washiya, Tadahiro

Progress in Nuclear Science and Technology (Internet), 5, p.217 - 220, 2018/11

Journal Articles

Thermodynamic evaluation of the solidification phase of molten core-concrete under estimated Fukushima Daiichi Nuclear Power Plant accident conditions

Kitagaki, Toru; Yano, Kimihiko; Ogino, Hideki; Washiya, Tadahiro

Journal of Nuclear Materials, 486, p.206 - 215, 2017/04


 Times Cited Count:9 Percentile:11.84(Materials Science, Multidisciplinary)

JAEA Reports

Study of treatment method for damaged fuel removed from the spent fuel pool; Outline of annual report for JFY 2013 and 2014 (Contract research)

Iijima, Shizuka; Uchida, Naoki; Taguchi, Katsuya; Washiya, Tadahiro

JAEA-Review 2015-018, 39 Pages, 2015/11


There is a possibility that the fuel assemblies stored in the spent fuel pool (SFP) at Fukushima Daiichi NPS (or Nuclear Power Station) are not only exposed to seawater and concrete fragments, but also damaged by fallen rubbles. We checked the reprocessing experiences of leak fuels at Tokai Reprocessing Plant and overseas reprocessing facilities, and the storage conditions and the checked and inspected results of the fuel stored in the SFP at Fukushima Daiichi NPS, after that, we listed up the technological problems with reprocessing damaged nuclear fuels and selected elements of the research for the purpose of drawing indicators to make a judgmental decision of the possibility of damaged nuclear fuels reprocessing. And we drew the indicators to make a judgmental decision on the possibility of reprocessing based on the results of the examination and the study about elements of the research.

Journal Articles

Study of treatment scenarios for fuel debris removed from Fukushima Daiichi NPS

Washiya, Tadahiro; Yano, Kimihiko; Kaji, Naoya; Yamada, Seiya*; Kamiya, Masayoshi

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 7 Pages, 2015/05

On March 11, 2011, a severe nuclear accident occurred at Tokyo Electric Power Company (TEPCO)'s Fukushima Daiichi Nuclear Power Plant (hereinafter called as F1). After the accident, the Council for the Decommissioning was established, mainly by the government and TEPCO, and a road map for the F1 decommissioning was drawn up. In the road map, the fuel debris removal from the reactors is scheduled to launch around 2020. In this study, the characteristics and technological issues of each potential treatment scenario were extracted, and the scenarios were prioritized in advance of formal evaluations in the future. The preliminary evaluation results show that long term storage and direct disposal have more positive aspects in terms of economic efficiency and radioactive waste generation. On the other hand, stabilizing processing, aqueous processing, and pyrochemical processing have been estimated to have more disadvantages in such aspects.

Journal Articles

Property measurements and inner state estimation of simulated fuel debris

Hirooka, Shun; Kato, Masato; Morimoto, Kyoichi; Washiya, Tadahiro

Proceedings of 19th Pacific Basin Nuclear Conference (PBNC 2014) (USB Flash Drive), 8 Pages, 2014/08

Since the severe accident at Fukushima Daiichi Nuclear Power Station, technologies to remove fuel debris from the damaged core have been developed. However, many subjects such as how to access to the core, cut the fuel debris, control criticality safety, estimate fissile materials, store removed debris and so on are still in existence. Purpose of this work is to evaluate the fuel debris properties by using analysis of simulated fuel debris and to estimate the inner state such as temperature profile and density profile which depend on elapsed time after the accident. The reported properties such as melting temperature, thermal conductivity and thermal expansion were obtained by the simulated fuel debris manufactured from UO$$_2$$ and zircaloy.

Journal Articles

Dissolution behavior of (U,Zr)O$$_{2}$$-based simulated fuel debris in nitric acid

Ikeuchi, Hirotomo; Ishihara, Miho; Yano, Kimihiko; Kaji, Naoya; Nakajima, Yasuo; Washiya, Tadahiro

Journal of Nuclear Science and Technology, 51(7-8), p.996 - 1005, 2014/07

 Times Cited Count:5 Percentile:51.05(Nuclear Science & Technology)

Journal Articles

Suggestion of typical phases of in-vessel fuel-debris by thermodynamic calculation for decommissioning technology of Fukushima-Daiichi Nuclear Power Station

Ikeuchi, Hirotomo; Kondo, Yoshikazu*; Noguchi, Yoshihiro*; Yano, Kimihiko; Kaji, Naoya; Washiya, Tadahiro

Proceedings of International Nuclear Fuel Cycle Conference; Nuclear Energy at a Crossroads (GLOBAL 2013) (CD-ROM), p.1349 - 1356, 2013/09

Journal Articles

Direction on characterization of fuel debris for defueling process in Fukushima Daiichi Nuclear Power Station

Yano, Kimihiko; Kitagaki, Toru; Ikeuchi, Hirotomo; Wakui, Ryohei; Higuchi, Hidetoshi; Kaji, Naoya; Koizumi, Kenji; Washiya, Tadahiro

Proceedings of International Nuclear Fuel Cycle Conference; Nuclear Energy at a Crossroads (GLOBAL 2013) (CD-ROM), p.1554 - 1559, 2013/09

Journal Articles

Dissolution behavior of irradiated mixed oxide fuel with short stroke shearing for fast reactor reprocessing

Ikeuchi, Hirotomo; Sano, Yuichi; Shibata, Atsuhiro; Koizumi, Tsutomu; Washiya, Tadahiro

Journal of Nuclear Science and Technology, 50(2), p.169 - 180, 2013/02

 Times Cited Count:5 Percentile:52.48(Nuclear Science & Technology)

An efficient dissolution process was established for future reprocessing in which MOX fuels with high plutonium contents and dissolver solution with high heavy-metal concentrations will be treated. This dissolution process involves short stroke shearing of fuels (10 mm in length). The dissolution kinetics of irradiated mixed-oxide fuels and the effects of the Pu content, heavy-metal concentration and fuel form on the dissolution rate were investigated. Irradiated fuel was decreased with increasing Pu content. Kinetic analysis based on the fragmentation model indicated that the dissolution rate of irradiated fuel was affected not only by the volume ratio of liquid to solid ($$L/S$$ ratio), but also by the exposed surface area ($$A/m$$ ratio). The penetration rate of nitric acid is expected to be decreased at high heavy-metal concentrations by a reduction in the $$L/S$$ ratio, but enhanced by shearing the fuel pieces with short strokes and thus enlarging the $$A/m$$ ratio.

Journal Articles

Applicability of single mode fiber laser for wrapper tube cutting

Wakui, Ryohei; Kitagaki, Toru; Higuchi, Hidetoshi; Takeuchi, Masayuki; Koizumi, Kenji; Washiya, Tadahiro

Proceedings of 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference (ICONE-20 & POWER 2012) (DVD-ROM), 7 Pages, 2012/07

Journal Articles

FaCT Phase-I evaluation on the advanced aqueous reprocessing process, 3; Highly effective dissolution technology for FBR MOX fuels

Ikeuchi, Hirotomo; Katsurai, Kiyomichi*; Sano, Yuichi; Washiya, Tadahiro

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 5 Pages, 2011/12

Journal Articles

FaCT Phase I evaluation on the advanced aqueous reprocessing process, 5; Research and development of uranium crystallization system

Shibata, Atsuhiro; Yano, Kimihiko; Sambommatsu, Yuji; Nakahara, Masaumi; Takeuchi, Masayuki; Washiya, Tadahiro; Nagata, Masanobu*; Chikazawa, Takahiro*

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 6 Pages, 2011/12

JAEA has been developing a U crystallization process. The development targets were DFs of over 100, confirmation of mechanical performance of crystallizer, and so on. Fundamental data were obtained by beaker-scale experiments with actual dissolver solution. DFs for most of the FPs are improved by washing. However the formation of Pu-Cs double salt causes low DF of Cs. To confirm the mechanical performance of an annular type crystallizer and a crystal separator, some experiments were carried out. The crystallizer and the separator have good performance. However washing of UNH crystals by the separator did not have the intended effect for solid impurities. We discussed the application of crystal purification technology to improve the purity and selected KCP. UNH crystal purification tests were carried out using bench-scale KCP apparatus with simulated solid impurities. The purifier has good performance on the decontamination of not only liquid impurities but also solid impurities.

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