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Koike, Ayaka*; Takubo, Yusaku*; Anraku, Sohtaro; Kawakita, Ryohei
NUMO-TR-25-03, p.79 - 82, 2025/10
no abstracts in English
Abe, Yosuke; Tsuru, Tomohito; Fujita, Yohei*; Otomo, Masahide*; Sasaki, Taisuke*; Yamashita, Shinichiro; Okubo, Nariaki; Ukai, Shigeharu
Journal of Nuclear Materials, 606, p.155606_1 - 155606_12, 2025/02
Times Cited Count：6 Percentile：95.35(Materials Science, Multidisciplinary)We investigated the effect of Al addition on the formation of 
phase in Fe-Cr-Al model alloys by thermal aging. The Vickers hardness tests and a machine learning model indicate that the formation of the phase is promoted by low Al additions and suppressed by high Al additions. First-principles calculations, which indicate that Cr-Al-vacancy pairs are more stable than Cr-Cr pairs and that including Al atoms during phase nucleation may be energetically advantageous. On the other hand, the formation of Al-Al pairs was very unstable. The formation of Al-Al pairs near the interface can be avoided when the amount of Al addition is small. However, it is inevitable when the amount of Al addition is significant, leading to the instability of the phase.
Koike, Ayaka*; Takubo, Yusaku*; Anraku, Sohtaro; Kawakita, Ryohei
NUMO-TR-24-03, p.62 - 64, 2024/10
no abstracts in English
Sogabe, Joji; Ishida, Shinya; Tagami, Hirotaka; Okano, Yasushi; Kamiyama, Kenji; Onoda, Yuichi; Matsuba, Kenichi; Yamano, Hidemasa; Kubo, Shigenobu; Kubota, Ryuzaburo*; et al.
Proceedings of International Conference on Nuclear Fuel Cycle (GLOBAL2024) (Internet), 4 Pages, 2024/10
In the frame of France-Japan collaboration, the calculational methodologies were defined and assessed, and the phenomenology and the severe accident consequences were investigated in a pool-type sodium-cooled fast reactor.
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.
Yamano, Hidemasa; Kubo, Shigenobu; Sasa, Kyohei*; Shibata, Akihiro*; Hourcade, E.*; Dirat, J. F.*
Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 9 Pages, 2022/08
This paper describes coolability evaluations of a debris bed with a variety of decay heat removal system (DHRS) operating conditions with a whole vessel model assuming fuel accumulation on the core catcher in a short term. The evaluation tool is a one-dimensional plant dynamics code, Super-COPD, with a debris bed module. The coolability evaluations have indicated that the current core catcher design secures sufficient natural circulation flows around the core catcher to ensure the debris bed cooling when at least one circuit of DHRS was activated. Sensitivity analyses under a pessimistic condition have shown that the debris bed is coolable with at least one circuit of improved DHRS even if most of fuel accumulates on the core catcher in a short term.
Sonoda, Tetsu*; Katayama, Ichiro*; Wada, Michiharu*; Iimura, Hideki; Sonnenschein, V.*; Iimura, Shun*; Takamine, Aiko*; Rosenbusch, M.*; Kojima, Takao*; Ahn, D. S.*; et al.
Progress of Theoretical and Experimental Physics (Internet), 2019(11), p.113D02_1 - 113D02_12, 2019/11
Times Cited Count：1 Percentile：8.89(Physics, Multidisciplinary)An in-flight separator, BigRIPS, at RIBF in RIKEN provides each experiment with specific nuclides separated from many nuclides produced by projectile fragmentation or in-flight fission. In this process, nuclides other than separated ones are discarded on the slits in BigRIPS, although they include many nuclides interested from the view point of nuclear structure. In order to extract these nuclides for parasitic experiments, we are developing a method using laser ion-source (PALIS). A test experiment with 
Se beam from RIBF has been performed by using a gas cell set in BigRIPS. Unstable nuclides around 
Se were stopped in the gas cell in accordance with a calculation using LISE code. The stopping efficiency has been estimated to be about 30%. As a next step, we will establish the technique for extracting reaction products from the gas cell.
Matsuo, Eiji*; Sasa, Kyohei*; Koyama, Kazuya*; Yamano, Hidemasa; Kubo, Shigenobu; Hourcade, E.*; Bertrand, F.*; Marie, N.*; Bachrata, A.*; Dirat, J. F.*
Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 5 Pages, 2019/05
Discharged molten-fuel from the core during Core Disruptive Accident (CDA) could become solidified particle debris by fuel-coolant interaction in the lower sodium plenum, and then the debris could form a bed on a core catcher located at the bottom of the reactor vessel. Coolability evaluations for the debris bed are necessary for the design of the core catcher. The purpose of this study is to evaluate the coolability of the debris bed on the core catcher for the ASTRID design. For this purpose, as a first step, the coolability calculations of the debris beds formed both in short term and later phase have been performed by modeling only the debris bed itself. Thus, details of core catcher design and decay heat removal system are not described in this paper. In all the calculations, coolant temperature around the debris bed is a parameter. The calculation tool is the debris bed module implemented into a one-dimensional plant dynamics code, Super-COPD. The evaluations have shown that the debris beds formed both in short term and later phase are coolable by the design which secures sufficient coolant flow around the core catcher located in the cold pool.
Zn
Cr
Se
Iikubo, Satoshi*; Yasui, Yukio*; Oda, Keisuke*; Ono, Yohei*; Kobayashi, Yoshiaki*; Sato, Masatoshi*; Kakurai, Kazuhisa
Journal of the Physical Society of Japan, 71(11), p.2792 - 2799, 2002/11
Times Cited Count：11 Percentile：56.06(Physics, Multidisciplinary)no abstracts in English
Ogawa, Tsuyoshi; Takahatake, Yoko; Koma, Yoshikazu; Nakajima, Yasuo; Sano, Kyohei*; Arai, Tsuyoshi*; Hashimoto, Jun*; Kubo, Kaname*; Kaneko, Masashi*
no journal, ,
no abstracts in English
Nakai, Kei*; Yamamoto, Yohei*; Yamamoto, Tetsuya*; Yoshida, Fumiyo*; Matsumura, Akira*; Koka, Masashi; Yamada, Naoto; Kitamura, Akane; Sato, Takahiro; Yokoyama, Akihito; et al.
no journal, ,
no abstracts in English
Abe, Yosuke; Sasaki, Taisuke*; Tsuru, Tomohito; Kubo, Atsushi; Yamashita, Shinichiro; Okubo, Nariaki; Fujita, Yohei*; Otomo, Masahide*; Ukai, Shigeharu
no journal, ,
In oxide dispersion strengthened Fe-Cr-Al alloys being developed as accident-resistant fuel cladding materials for light water reactors, it has been a challenge to elucidate and predict the embrittlement behavior caused by the formation of Cr-rich precipitates (Cr-Rich Precipitates: CrRP). However, the effects of irradiation and Al addition on the formation of CrRPs are not well understood. In this study, CrRP formation behavior by self-ion irradiation was systematically investigated for 14 Fe-Cr-Al alloys with different compositions, and the effect of each experimental variable on the CrRP-related amount was quantitatively evaluated by multiple regression analysis. The effect of Al addition on the stability of CrRP formation was also investigated by first-principles calculations, and the results showed that the dependence of Al addition on the stability of CrRP is consistent with the results of ion irradiation experiments.
Ukai, Shigeharu; Abe, Yosuke; Geng, D.*; Kubo, Atsushi; Sasaki, Taisuke*; Mohamad, A. B.; Fujita, Yohei*; Okubo, Nariaki; Yamashita, Shinichiro; Yu, H.*; et al.
no journal, ,
A combinatorial specimen with a continuous compositional gradient of Cr and Al in FeCrAl alloys was fabricated, and by integrating an ion irradiation with continuous stiffness nanoindentation measurement, high-throughput dataset was created. It was clarified for the first time, that alpha-prime precipitation occurs within subtle two-dimensional (Cr, Al) composition; about 5 at.% Al addition accelerates alpha-prime formation, and spinodal decomposition becomes dominant at more than 30 at.% Cr. It was also clarified that alpha-prime precipitation reaches saturation at an irradiation dose as low as 1.44 dpa (0.64 dpa).
Takahatake, Yoko; Shibata, Atsuhiro; Koma, Yoshikazu; Nakajima, Yasuo; Sano, Kyohei*; Arai, Tsuyoshi*; Hashimoto, Jun*; Kubo, Kaname*; Kaneko, Masashi*
no journal, ,
no abstracts in English
Kiyohara, Keita*; Murakawa, Hideki*; Sugimoto, Katsumi*; Kubo, Yohei*; Kurita, Keisuke; Iikura, Hiroshi; Asano, Hitoshi*
no journal, ,
Boiling two-phase flows in mini-channel cross-flow vaporizer had been visualized by two methods, neutron radiography and the method by replacing the outer wall with a transparent wall.
Nakaya, Atsushi*; Tada, Hiroyuki*; Okuyama, Yasuji*; Iwasaki, Masahiro*; Kusano, Takashi*; Kubo, Yohei*; Yamawaki, Hiroyuki; Sato, Toshinori
no journal, ,
no abstracts in English
Abe, Yosuke; Sasaki, Taisuke*; Tsuru, Tomohito; Fujita, Yohei*; Otomo, Masahide*; Yamashita, Shinichiro; Okubo, Nariaki; Ukai, Shigeharu
no journal, ,
This study examines CrRP formation behavior through 10.5 MeV self-ion irradiation at 350
C on 14 Fe-Cr-Al alloy compositions, with doses of 0.24 and 0.64 dpa and three damage rates differing by two orders of magnitude. Using a three-dimensional atom probe, we analyzed CrRPs in irradiated samples and evaluated the effects of different variables with a correlation matrix and multiple regression model. We found that the number density, volume fraction, and internal Cr concentration of CrRPs increased with higher Cr levels, lower Al levels, and reduced damage rates. To better understand the atomic-level mechanisms, we also explored the effect of Al addition on CrRP formation using first-principles calculations, analyzing atomic arrangement energy and short-range order parameters alongside experimental data.
