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Soma, Shu; Ishigaki, Masahiro*; Shibamoto, Yasuteru
Annals of Nuclear Energy, 219, p.111455_1 - 111455_12, 2025/09
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Shindo, Manami*; Ueoku, Aya*; Okamura, Wakana*; Kikuchi, Shin; Yamazaki, Atsushi*; Koga, Nobuyoshi*
Thermochimica Acta, 749, p.180021_1 - 180021_14, 2025/07
Times Cited Count：0 Percentile：0.00(Thermodynamics)Yamashita, Takuya
Fukushima Daiichi Nuclear Power Station Accident Information Collection and Evaluation (FACE) Project Annual Report 2023, p.55 - 62, 2024/11
Yamano, Hidemasa; Emura, Yuki; Takai, Toshihide; Kubo, Shigenobu; Quaini, A.*; Fossati, P.*; Delacroix, J.*; Journeau, C.*
Proceedings of International Conference on Nuclear Fuel Cycle (GLOBAL2024) (Internet), 4 Pages, 2024/10
This report mainly introduces trends in fast reactor development in Japan in addition to introducing overseas development trends for major developing countries. The paper describes major severe accident study results focusing on kinetics of interaction in core material mixtures, physical properties of core material mixtures, high temperature thermodynamic data for the uranium oxide (UO
)-iron (Fe)-boron carbide (B
C) system, experimental studies on BC-stainless steel (SS) kinetics and BC-SS eutectic material relocation (freezing), and BC-SS eutectic and kinetics models for severe accident code systems,
Kikuchi, Shin; Kondo, Toshiki; Doi, Daisuke; Seino, Hiroshi; Ogawa, Kengo*; Nakagawa, Takeshi*
Proceedings of 14th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation, and Safety (NTHOS-14) (Internet), 12 Pages, 2024/08
Shindo, Manami*; Ueoku, Aya*; Okamura, Wakana*; Kikuchi, Shin; Yamazaki, Atsushi*; Koga, Nobuyoshi*
Thermochimica Acta, 738, p.179801_1 - 179801_12, 2024/08
Times Cited Count：1 Percentile：34.56(Thermodynamics)Yamashita, Takuya; Shimomura, Kenta; Nagae, Yuji; Nagai, Eiichi*; Yasumatsu, Tomohiro*; Nakashima, Satoru*; Ogino, Shoya*; Mizokami, Shinya*
Proceedings of 11th European Review Meeting on Severe Accident Research Conference (ERMSAR 2024) (Internet), 11 Pages, 2024/05
Nemoto, Yoshiyuki
Kiho Enerugi Sogo Kogaku, 47(1), p.27 - 32, 2024/04
no abstracts in English
O
determined by aerodynamic levitationSun, Y.*; Takatani, Tomoya*; Muta, Hiroaki*; Fujieda, Shun*; Kondo, Toshiki; Kikuchi, Shin; Kargl, F.*; Oishi, Yuji*
International Journal of Thermophysics, 45(1), p.11_1 - 11_19, 2024/01
Times Cited Count：1 Percentile：35.22(Thermodynamics)no abstracts in English
Uchibori, Akihiro; Doda, Norihiro; Aoyagi, Mitsuhiro; Sonehara, Masateru; Sogabe, Joji; Okano, Yasushi; Takata, Takashi*; Tanaka, Masaaki; Enuma, Yasuhiro; Wakai, Takashi; et al.
Nuclear Engineering and Design, 413, p.112492_1 - 112492_10, 2023/11
Times Cited Count：2 Percentile：43.92(Nuclear Science & Technology)The ARKAIDA has been developed to realize automatic optimization of plant design from safety evaluation for the advanced reactors represented by a sodium-cooled fast reactor. ARKADIA-Design offers functions to support design optimization both in normal operating conditions and design basis events. The multi-level simulation approach by the coupled analysis such as neutronics, core deformation, core thermal hydraulics was developed as one of the main technologies. On the other hand, ARKAIDA-Safety aims for safety evaluation considering severe accidents. As a key technology, the numerical methods for in- and ex-vessel coupled phenomena during severe accidents in sodium-cooled fast reactors were tested through a hypothetical severe accident event. Improvement of the ex-vessel model and development of the AI technology to find best design solution have been started.
Tsuchikawa, Yusuke; Kai, Tetsuya; Abe, Yuta; Oikawa, Kenichi; Parker, J. D.*; Shinohara, Takenao; Sato, Ikken
Journal of Physics; Conference Series, 2605, p.012022_1 - 012022_6, 2023/10
We developed a method to obtain the areal density distribution of boron, which has a large neutron cross section, by means of an energy resolved neutron imaging. Commonly in a measurement of elements with very high neutron sensitivity, the quantitative measurement becomes more difficult with the amount of element due to the neutron self-shielding effect. To avoid this effect, an energy-resolved method using known cross section data was attempted, and a quantitative imaging of such elements was demonstrated at the MLF of J-PARC. This presentation introduces a measurement of melted simulated-fuel assemblies obtained in the research of the Fukushima Daiichi Nuclear Power Plant after the severe accident. Energy-dependent neutron transmission rates of the samples were measured by a neutron imaging detector, and were analyzed to obtained the areal density of boron at each position.
Bando, Yamato*; Yamaji, Akifumi*; Yamashita, Takuya
Proceedings of International Conference on Environmental Remediation and Radioactive Waste Management (ICEM2023) (Internet), 9 Pages, 2023/10
O)
-(SiO)
measured by aerodynamic levitationKondo, Toshiki; Toda, Taro*; Takeuchi, Junichi*; Kikuchi, Shin; Kargl, F.*; Muta, Hiroaki*; Oishi, Yuji*
High Temperatures-High Pressures, 52(3-4), p.307 - 321, 2023/06
Times Cited Count：0 Percentile：0.00(Thermodynamics)In order to establish an evaluation method/numerical simulation for nuclear reactor safety under severe accidental conditions, it is necessary to obtain the physical properties, especially fluidity of the relevant molten materials at very high temperatures. In this study, thermophysical properties such as density and viscosity were obtained for (FeO)-(SiO), which is a representative composition in the early stage of severe accident. (FeO)-(SiO) is produced by the contact between the molten oxide of steel, which is the main component of the reactor, and SiO, which is the main component of concrete. As a result, the physical properties of the (FeO)-(SiO) mixture were almost the same as those of FeO obtained in previous studies, and it could be concluded that a small amount of SiO (about 5 mol.%) did not significantly affect the fluidity of FeO.
and Zr at precisely controlled high temperaturesShirasu, Noriko; Sato, Takumi; Suzuki, Akihiro*; Nagae, Yuji; Kurata, Masaki
Journal of Nuclear Science and Technology, 60(6), p.697 - 714, 2023/06
Times Cited Count：2 Percentile：43.92(Nuclear Science & Technology)Interaction tests between UO and Zr were performed at precisely controlled high temperatures between 1840 and 2000 
C to understand the interaction mechanism in detail. A Zr rod was inserted in a UO crucible and then heat-treated at a fixed temperature in Ar-gas flow for 10 min. After heating in the range of 1890 to 1930 C, the Zr rod was deformed to a round shape, in which the post-analysis detected the significant diffusion of U into the Zr region and the formation of a dominant 
-Zr(O) matrix and a small amount of U-Zr-O precipitates. The abrupt progress of liquefaction was observed in the sample heated at around 1940 C or higher. The higher oxygen concentration in the -Zr(O) matrix suppressed the liquefaction progress, due to the variation in the equilibrium state. The U-Zr-O melt formation progressed by the selective dissolution of Zr from the matrix, and the selective diffusion of U could occur via the U-Zr-O melt.
Sato, Ikken; Yoshikawa, Shinji; Yamashita, Takuya; Cibula, M.*; Mizokami, Shinya*
Nuclear Engineering and Design, 404, p.112205_1 - 112205_21, 2023/04
Times Cited Count：10 Percentile：94.74(Nuclear Science & Technology)Based on updated knowledge from plant-internal investigations, experiments and model simulations until now, the in-vessel phase of Fukushima-Daiichi Nuclear Power Station Unit 2 was analyzed using the MAAP code. In Unit 2, it is considered that the core material enthalpy was relatively low when it relocated to the lower plenum of the pressure vessel, then, cooled by the coolant and solidified there. Although the MAAP code tended to underestimate the degree of core-material oxidation during the relocation, this probable underestimation was compensated for by an existing study that was considered more reliable, so that more realistic debris conditions in the lower plenum could be obtained. Basic validity of the former prediction of the Unit 2 accident progression behavior was confirmed and detailed boundary condition for the later phase was provided. This boundary condition should be utilized for future studies addressing debris reheating process leading to lower head failure and debris relocation toward the pedestal.
Madokoro, Hiroshi; Yamashita, Takuya; Gaus-Liu, X.*; Cron, T.*; Fluhrer, B.*; Sato, Ikken; Mizokami, Shinya*
Nuclear Technology, 209(2), p.144 - 168, 2023/02
Times Cited Count：2 Percentile：28.39(Nuclear Science & Technology)Takano, Kazuya; Oki, Shigeo; Ozawa, Takayuki; Yamano, Hidemasa; Kubo, Shigenobu; Ogura, Masashi*; Yamada, Yumi*; Koyama, Kazuya*; Kurita, Koichi*; Costes, L.*; et al.
EPJ Nuclear Sciences & Technologies (Internet), 8, p.35_1 - 35_9, 2022/12
The France and Japan teams have carried out collaborative works to have common technical views regarding a sodium-cooled fast reactor concept. Japan has studied the feasibility of an enhanced high burnup low-void effect (CFV) core and fuel using oxide dispersion-strengthened steel cladding in ASTRID 600. Regarding passive shutdown capabilities, Japan team has performed a preliminary numerical analysis for ASTRID 600 using a complementary safety device, called a self-actuated shutdown system (SASS), one of the safety approaches of Japan. The mitigation measures of ASTRID 600 against a severe accident, such as a core catcher, molten corium discharge assembly, and the sodium void reactivity features of the CFV core, are promising to achieve in-vessel retention for both countries. The common design concept based on ASTRID 600 is feasible to demonstrate the SFR core and safety technologies for both countries.
Nakamura, Hironori*; Hayakawa, Satoshi*; Shibata, Akihiro*; Sasa, Kyohei*; Yamano, Hidemasa; Kubo, Shigenobu
Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 7 Pages, 2022/10
In order to evaluate long-term coolablity of the debris-bed with decay heat, a three-dimensional calculation method coupled with the debris bed module was developed in this study. The coupled code calculation results show that natural circulation of the coolant between the hot pool and the cold pool is established through the four intermediate heat exchangers after the activation of the dipped direct heat exchangers. The cold pool with the debris-bed is continually cooled not only by the natural circulation flow, but also by heat transfer to the hot pool through the plenum separation plate between the hot pool and the cold pool. The effect of the three-dimensional flow field around the core catcher on the temperature in the debris-bed is about 20K under the current calculation condition.
, (FeO)
-(ZrO)
and (FeO)-(UO)Kondo, Toshiki; Toda, Taro*; Takeuchi, Junichi*; Kargl, F.*; Kikuchi, Shin; Muta, Hiroaki*; Oishi, Yuji*
Journal of Nuclear Science and Technology, 59(9), p.1139 - 1148, 2022/09
Times Cited Count：1 Percentile：14.04(Nuclear Science & Technology)no abstracts in English
Yamano, Hidemasa; Kubo, Shigenobu; Kan, Taro*; Shibata, Akihiro*; Hourcade, E.*; Dirat, J. F.*
Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 10 Pages, 2022/08
In this paper, the approach to event tree development and the scope of the event tree analysis were described with key points on core catcher loading. For the analytical conditions, two core catcher loading conditions were given as bounding and conservative cases. For important heading of the event tree, key important phenomena were included: strong back design, fuel-coolant interaction and quench in the sodium plenum design, jet attack, criticality and coolability on the core catcher. In this paper, preliminary trial quantification was attempted using a probability ranking table which is based on engineering judgement. This event tree analysis has identified the dominant sequence, and clarified the effect of the core catcher loading and effectiveness of design measures. This study suggests that the criticality measure is very important for the core catcher study.
