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Kawasaki, Nobuchika
JAEA-Review 2025-043, 74 Pages, 2025/10
JAEA-Review-2025-043.pdf:2.45MB
Russia is one of the most advanced countries in the civilian use of nuclear energy. However, understanding the internal mechanisms of its nuclear program remains difficult due to various reasons. Therefore, this study presents a historical overview of Russia's nuclear energy utilization, fuel supply, fuel manufacturing capabilities, and concepts regarding reprocessing and the nuclear fuel cycle. From this overview, insights have been extracted and analyzed. These insights are then organized under two strategic perspectives: "Strategic diversity and continuity in developments and demonstrations" and "Diversity in utilizations and deployments," with considerations of implications for Japan, as below. Russia's nuclear energy policy strategically utilizes a variety of reactor types and fuel cycle technologies to expand nuclear power generation both domestically and internationally. Currently, nuclear power, centered on light-water reactors (VVER series), accounts for about 20% of Russia's electricity supply, and there are plans to increase this share to 25% by 2045. A wide range of reactors, from large-scale to medium and small modular reactors, are being constructed in Russia. Russia is also actively developing fast reactor technologies, and focusing on the reprocessing and recycling of spent fuel. Internationally, VVER-1200 reactors are under construction in several countries, and cooperation with China is deepening in the field of fast reactors. Notably, Russia offers an integrated, or selectively customizable, package of nuclear technology services on the international stage. These include not only reactor deployment, but also fuel supply, reprocessing, waste management, and even the provision of radioisotopes. Rather than simply exporting products or technology, Russia fosters long-term relationships and trust by flexibly responding to the conditions and needs of partner countries. For this reason, Russia promotes the technology developments in advance within the country in areas anticipated for future overseas deployment. It carefully selects target technologies and services and systematically rolls them out. This flexible strategy, combining "technological diversity" and "strategic consistency", enables cooperation with countries across various geopolitical contexts. For Japan, this strategic approach offers valuable lessons on how to engage in comprehensive international nuclear cooperation, not merely through technology exports, but through integrated approaches that encompass the entire fuel cycle, and by combining elements such as fast reactors and RI supply.
Miyata, Hokata*; Yoshida, Kenta*; Konashi, Kenji*; Du, Y.*; Kitagaki, Toru; Shobu, Takahisa; Shimada, Yusuke*
Microscopy, 74(4), p.293 - 302, 2025/01
Times Cited Count：0 Percentile：0.00(Microscopy)Yamada, Takeshi*; Li, X.; Yamashita, Takuya; Yamaji, Akifumi*
Proceedings of 31st International Conference on Nuclear Engineering (ICONE31) (Internet), 10 Pages, 2024/11
In this study, a new crust model is being developed to analyze MCCI, which involves continuous concrete ablation with presence of the crust layer between the corium and the concrete walls, which may gradually move with the slow concrete wall ablation process over long time. The new crust model must enable accumulation of physical displacement of the crust particle over long time (i.e., enable physical creeping) while preventing accumulation of numerical displacement of the crust particles over long time (i.e., preventing numerical creeping), Hence, in the new crust model, the PS has been effectively disabled for the crust particles. Qualitative validity of such numerical modeling was confirmed through some trial analyses of VULCANO-VBS test using a set of tentative calculation conditions and parameters, which should be carefully revised for future quantitative discussions including validation of the analysis results with experimental results.
Gunji, Satoshi; Araki, Shohei; Izawa, Kazuhiko; Suyama, Kenya
Proceedings of International Conference on Physics of Reactors (PHYSOR 2024) (Internet), p.227 - 236, 2024/04
It is considered that a large amount of fuel debris was generated in the TEPCO's Fukushima Daiichi Nuclear Power Station accident. In particular, the criticality characteristics of the fuel debris, including concrete components, which are products of molten core-concrete interaction (MCCI), have not been well investigated. In this study, to plan physical simulation in critical experiments at the critical assembly using pseudo fuel debris samples including concrete, we evaluated the sensitivity to the effective multiplication factor of the Si and Ca cross sections in the concrete-simulant sample based on the results of elemental analysis of the prototype. These sensitivity calculations were carried out for each sample loading method and composition. We focused on the energy profile of the sensitivity of the 
Ca capture reaction and confirmed that the shape of the sensitivity energy profile changed depending on the sample compositions and neutron moderation conditions. We could know the characteristics of each experimental method by clarifying the trends of sensitivity obtained in different experimental cases. It was found that increasing the amount of concrete in the samples and changing the neutron moderation conditions in the experimental core configurations produced similar changes in the shape of the sensitivity energy profile. This result shows the possibility of reproducing the characteristics of MCCI products through practical critical experiments using concrete materials that do not contain fissile materials.
Sato, Ikken
Enerugi Rebyu, 41(4), p.17 - 19, 2021/03
The accident progression behavior leading to core melting and after the start of the core melting at Fukushima Daiichi Nuclear Power Station Unit 3 were estimated based on data analysis mainly based on plant data such as pressure and knowledge obtained from existing analysis evaluations. In Unit 3, it is estimated that it took several hours for fuel debris to fall on to the pedestal floor, and it is likely that it was cooled by liquid coolant presented on the containment floor.
Gunji, Satoshi; Tonoike, Kotaro; Clavel, J.-B.*; Duhamel, I.*
Journal of Nuclear Science and Technology, 58(1), p.51 - 61, 2021/01
Times Cited Count：2 Percentile：14.69(Nuclear Science & Technology)The new critical assembly STACY will be able to contribute to the validation of criticality calculations related to the fuel debris. The experimental core designs are in progress in the frame of JAEA/IRSN collaboration. This paper presents the method applied to optimize the design of the new STACY core to measure the criticality characteristics of pseudo fuel debris that simulated Molten Core Concrete Interaction (MCCI) of the fuel debris. To ensure that a core configuration is relevant for code validation, it is important to evaluate the reactivity worth of the main isotopes of interest and their k
sensitivity to their cross sections. In the case of the fuel debris described in this study, especially for the concrete composition, silicon is the nucleus with the highest k sensitivity to the cross section. For this purpose, some parameters of the core configuration, as for example the lattice pitches or the core dimensions, were adjusted using optimization algorithm to find efficiently the optimal core configurations to obtain high sensitivity of silicon capture cross section. Based on these results, realistic series of experiments for fuel debris in the new STACY could be defined to obtain an interesting feedback for the MCCI. This methodology is useful to design other experimental conditions of the new STACY.
Washiya, Tadahiro; Koyama, Shinichi; Takano, Masahide; Mitsugi, Takeshi
Denki Hyoron, 105(9), p.64 - 71, 2020/09
For the retrieval of fuel debris in the 1F decommissioning, a retrieval tool and a retrieval method according to the characteristics of fuel debris are being studied. In addition, for stable storage, treatment, and disposal after retrieval, it is necessary to fully understand the characteristics and chemical stability of fuel debris and select appropriate measures. In this paper, we will introduce the characteristics of fuel debris that have been discovered in the previous studies and the problems in handling them.
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：17 Percentile：80.96(Nuclear Science & Technology)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：9 Percentile：58.71(Nuclear Science & Technology)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
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
MoO
, in severe accident conditions, 1; Partitioning of Cs and Mo among gaseous speciesDo, Thi Mai Dung*; Sujatanond, S.*; Ogawa, Toru
Journal of Nuclear Science and Technology, 55(3), p.348 - 355, 2018/03
Times Cited Count：8 Percentile：52.83(Nuclear Science & Technology)In order to better understand the behavior of cesium in the severe accident of the LWR, the high-temperature chemistry of CsMoO in HO+H gas was studied. The pseudo-binary system, CsMoO-MoO
, was thermochemically modeled with Redlich-Kister formulation to form a basis to analyze the high-temperature behavior of CsMoO. The model prediction was compared with the thermogravimetric measurements of CsMoO in dry and humid argon, which revealed that the mass-loss rate was enhanced in the humid atmosphere. Thermochemical model was further applied to predict the partitioning of cesium and molybdenum among gaseous species in the BWR core degradation condition typical of Short-Term Station Blackout.
Gunji, Satoshi; Tonoike, Kotaro; Izawa, Kazuhiko; Sono, Hiroki
Progress in Nuclear Energy, 101(Part C), p.321 - 328, 2017/11
Times Cited Count：4 Percentile：30.47(Nuclear Science & Technology)Criticality safety of fuel debris, particularly MCCI (Molten-Core-Concrete-Interaction) products, is one of the major safety issues for decommissioning of Fukushima Daiichi Nuclear Power Station. Criticality or subcriticality condition of the fuel debris is still uncertain; its composition, location, neutron moderation, etc. are not yet confirmed. The effectiveness of neutron poison in cooling water is also uncertain for use as a criticality control of fuel debris. A database of computational models is being built by Japan Atomic Energy Agency (JAEA), covering a wide range of possible conditions of such composition, neutron moderation, etc., to facilitate assessing criticality characteristics once fuel debris samples are taken and their conditions are known. The computational models also include uncertainties which are to be clarified by critical experiments. These experiments are planned and will be conducted by JAEA with the modified STACY (STAtic experiment Critical facilitY) and samples to simulate fuel debris compositions. Each of the samples will be cladded by a zircalloy tube whose outer shape is compatible with the fuel rod of STACY and loaded into an array of the fuel rods. This report introduces a study of experimental core configurations to measure the reactivity worth of samples simulating MCCI products. Parameters to be varied in the computation models for the experimental series are:(1) Uranium dioxide with 
U enrichments of 3, 4, and 5 wt.%; (2) Concrete volume fraction in the samples of 0, 20, 40, 60, and 80%; and (3) Porosity of the samples filled from 0 to 80% where the sample void is filled with water. It is concluded that the measurement is feasible in both under- and over-moderated conditions. Additionally, the required amount of samples was estimated.
Kitagaki, Toru; Yano, Kimihiko; Ogino, Hideki; Washiya, Tadahiro
Journal of Nuclear Materials, 486, p.206 - 215, 2017/04
Times Cited Count：38 Percentile：94.40(Materials Science, Multidisciplinary)Gunji, Satoshi; Tonoike, Kotaro; Izawa, Kazuhiko; Sono, Hiroki
Proceedings of International Conference on the Physics of Reactors; Unifying Theory and Experiments in the 21st Century (PHYSOR 2016) (USB Flash Drive), p.3927 - 3936, 2016/05
Criticality safety of fuel debris including MCCI products is one of the major safety is-sues for decommissioning of Fukushima Daiichi Nuclear Power Station. Criticality or subcriticality condition of the fuel debris is still uncertain since its composition, location, neutron moderation, etc. are not confirmed. Also uncertain in criticality control of fuel debris is the effectiveness of neutron poison in cooling water. A database is being built by computation in JAEA, covering a wide range of possible conditions of such composition, neutron moderation, etc., to facilitate assessing criticality characteristics when fuel debris samples are taken and their conditions are known. The computation also has uncertainties to be clarified by critical experiments, which is planned by JAEA to be conducted with the modified STACY and samples simulating fuel debris compositions. This report introduces a study of experimental core configurations for reactivity worth measurements of samples simulating MCCI products. It is concluded that the measurement is feasible in both under- and over-moderated conditions. Additionally, required amount of samples was estimated.
Tonoike, Kotaro; Okubo, Kiyoshi; Takada, Tomoyuki*
Proceedings of International Conference on Nuclear Criticality Safety (ICNC 2015) (DVD-ROM), p.292 - 300, 2015/09
The damaged Unit 1-3 reactors of the Fukushima Daiichi Nuclear Power Station may contain fuel debris of a significant amount that is in a form of molten-core-concrete-interaction (MCCI) product with porous structure. Such low density MCCI product including fissile material is a great concern for its criticality control, especially under submerged condition, due to its fairly good neutron moderation. This report shows computation results of basic criticality characteristics of the MCCI product, which will facilitate criticality risk assessments during decommissioning of the reactors. The results imply that water bound in concrete may raise the risk from the viewpoints of possibility of criticality events and of effectiveness of mitigation measures such as neutron poison injection into coolant water.
Washiya, Tadahiro; Yano, Kimihiko; Ikeuchi, Hirotomo; Kaji, Naoya; Takano, Masahide; Morimoto, Kyoichi
Proceedings of 2014 Water Reactor Fuel Performance Meeting/ Top Fuel/ LWR Fuel Performance Meeting (WRFPM 2014) (CD-ROM), 6 Pages, 2014/09
On March 11, 2011, the Great East Japan Earthquake caused the severe accident at Fukushima Daiichi NPS (F1). In the reactors of unit 1-3, large amount of fuel debris was generated. Thermodynamic equilibrium (TDE) calculations based on results of MAAP code analysis was carried out and typical debris phases were predicted. Experimental studies were also carried out using simulated fuel debris, and verify the expected properties. The F1 accident differs from the past severe accidents. Specific factors in the F1 accident to be considered in this study are fuel assembly and control rod materials, core configuration and accident sequence. Further specific factors are high zirconium and iron contents, BC and sea water effects and molten core concrete interaction (MCCI). Mechanical properties were identified as important properties. Mechanical properties have been obtained experimentally using simulated debris as based on (U,Zr)O
and (U,Zr,Fe)O materials.
V.Balek*; Z.Malek*; Mitamura, Hisayoshi; Bamba, Tsunetaka
Proc. of 7th Int. Conf. on Radioactive Waste Management and Environmetnal Remediation (ICEM'99)(CD-ROM), 4 Pages, 1999/00
no abstracts in English
Nariai, Hideki*; Sugiyama, Kenichiro*; Kataoka, Isao*; Mishima, Kaichiro*; ; Monde, Masanori*; Sugimoto, Jun; ; Hidaka, Akihide; ; et al.
Nihon Genshiryoku Gakkai-Shi, 39(9), p.739 - 752, 1997/00
Times Cited Count：1 Percentile：8.11(Nuclear Science & Technology)no abstracts in English
Sugimoto, Jun
Dennetsu Kenkyu, 34(133), p.52 - 59, 1995/04
no abstracts in English
