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under high temperatures and various water vapor concentrationsMohamad, A. B.; Nakajima, Kunihisa; Imoto, Jumpei*; Takano, Masahide
Journal of Nuclear Materials, 631, p.156826_1 - 156826_12, 2026/09
Times Cited Count：0Abe, Takumi; Suzuki, Taiga*; Okamura, Tomohiro*; Nakase, Masahiko*
Annals of Nuclear Energy, 232, p.112224_1 - 112224_7, 2026/07
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)
Minami, Shoko*; Matsuno, Haruki*; Morita, Kyohei*; Matsuki, Rintaro*; Kotegawa, Hisashi*; Harima, Hisatomo*; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika*; Tou, Hideki*
Journal of the Physical Society of Japan, 95(7), p.074711_1 - 074711_11, 2026/07
Batsaikhan, M.; Oba, Hironori*; Karino, Takahiro; Akaoka, Katsuaki; Wakaida, Ikuo*; Iwata, Yoshihiro; Sakamoto, Kan*
Journal of Analytical Atomic Spectrometry, 41(4), p.1324 - 1335, 2026/04
Times Cited Count：0 Percentile：0.00(Chemistry, Analytical)
O solutionKumagai, Yuta; Kusaka, Ryoji; Takano, Masahide; Watanabe, Masayuki
Journal of Nuclear Materials, 625, p.156553_1 - 156553_7, 2026/04
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Uranium-zirconium oxide solid solution, (U, Zr)O, is a representative matrix phase found in fuel debris formed during severe nuclear reactor accidents. Understanding its chemical behavior in oxidative aqueous environments is important for evaluating the potential release of radionuclides during water contact. In this study, we investigated the reactivity of (U, Zr)O with hydrogen peroxide (HO) in pure water to assess its resistance to oxidative dissolution, because HO is the dominant oxidant produced by water radiolysis. The dissolution behavior of uranium and zirconium was monitored through repeated HO exposure experiments, and the solid phases were characterized using Raman micro-spectroscopy and X-ray diffraction. Kinetic modeling was performed to interpret experimental data. The results showed that uranium dissolution occurred initially but decreased significantly upon repeated HO exposure, while zirconium dissolution proceeded more slowly. Raman analysis revealed only minor surface changes, with limited formation of uranyl peroxide phases. The kinetic simulation reproduced the experimental trends by assuming a small fraction of redox-active surface sites. These findings suggest that the observed durability of (U, Zr)O against HO-induced oxidative dissolution is not due to the formation of a protective surface layer, but rather reflects the limited redox reactivity of most of the surface. This study provides a quantitative basis for understanding the HO-induced oxidation of (U, Zr)O in water, relevant to the long-term behavior of fuel debris.
Tomita, Jumpei; Tomita, Ryohei; Suzuki, Daisuke; Yasuda, Kenichiro; Miyamoto, Yutaka
Journal of Nuclear Science and Technology, 63(4), p.443 - 454, 2026/04
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Yanagisawa, Hiroshi; Motome, Yuiko
JAEA-Research 2025-010, 197 Pages, 2025/11
JAEA-Research-2025-010.pdf:3.5MB
For understandings of nuclear criticality risks of TRIGA fuel rods and review of safety measures for handling them, nuclear criticality characteristics for infinite and finite heterogeneous lattice systems composed of the NSRR fuel rods were re-evaluated with the use of a detailed computational model for the fuel rod. The MVP version 3 code was used with the JENDL libraries including the latest version, JENDL-5, for the re-evaluation. As the criticality characteristics, variations of neutron multiplication factors of the infinite and water-reflected finite systems were examined in detail with parameters of the lattice pitch and density of moderator water. From the results of the re-evaluated criticality characteristics, the minimum critical number of fuel rods for the water-reflected hexagonal shaped lattice system was obtained to be 46.8 
0.2 using the JENDL-5 library. Moreover, the attainability of criticality without the water as moderator and reflector was examined because the zirconium hydride moderator and graphite reflector are equipped with the TRIGA fuel rod. It was found that the criticality is possible to be attained by 115.7 0.6 of the number of fuel rods, which is the smaller number of fuel rods than loaded in the NSRR standard core, even though no water exists.
Yomogida, Takumi; Scaria, J.*; Fablet, L.*; Tokunaga, Kohei; Dei, Shuntaro; Higashi, Kotaro*; Kawamura, Naomi*; Takahashi, Yoshio*; Marsac, R.*
Chemical Communications, 61(91), p.17926 - 17929, 2025/11
Times Cited Count：0 Percentile：0.00(Chemistry, Multidisciplinary)This paper presents insights into the influence of magnetite stoichiometry (0 
R = Fe(II)/Fe(III) 0.5) on the surface reduction of U(VI) to U(V) and U(IV), as a key parameter controlling U redox speciation in natural settings. Although R can readily change due to the oxidation of structural Fe(II) or proton/ligand-promoted dissolution, prior studies have not quantified U(V) when assessing these effects. We employed U L
-edge HERFD-XANES spectroscopy to investigate the electronic structure of U on magnetite with varying stoichiometries and observed a peak splitting of U(V) on magnetite. Our results demonstrate the high stability of U(V) species under a wide range of conditions, and after 10 days on magnetite by the combination of MCR-ALS analysis. A key finding is that structural Fe(II), whose abundance depends on pH and redox conditions, plays a critical role for in the stabilization of U(V) on magnetite.
Yamamoto, Masahiko; Horigome, Kazushi; Goto, Yuichi; Taguchi, Shigeo; Kuno, Takehiko
Progress in Nuclear Science and Technology (Internet), 8, p.387 - 392, 2025/09
Flush-out of Tokai Reprocessing Plant was completed in February, 2024 for the preparation of process decontamination. Since remaining nuclear materials were contained in main process, purpose of the activities was to recover nuclear materials by transferring them to the highly radioactive liquid waste storage tank and converting uranium solution into uranium trioxide, and to rinse all related processes with nitric acid and water. During this activity, analysis of U and Pu was conducted for nuclear material control and accountancy. Appropriate analytical methods such as isotope dilution mass spectrometry, gravimetric method, spectrophotometry and alpha-ray counting methods were selected depending on the status of flush-out. Also, gamma-ray emitted nuclides in rinsing solution were detected by highly purified germanium detector. This paper describes analysis and its results related to flush-out activities of decommissioning in reprocessing plant.
Ouchi, Kazuki; Ueno, Katsuhiro; Watanabe, Masayuki
Scientific Reports (Internet), 15, p.18515_1 - 18515_7, 2025/05
Times Cited Count：1 Percentile：37.05(Multidisciplinary Sciences)We first demonstrate a nonaqueous rechargeable battery using uranium and iron as active materials. This uranium-iron battery achieves an open-circuit voltage of approximately 1.3 V, exhibits stable cycling performance, and delivers a good Coulombic efficiency of 862%. These characteristics suggest a promising avenue for utilizing depleted uranium in innovative applications.
Tanabe, Kosuke*; Komeda, Masao; Toh, Yosuke; Kitamura, Yasunori*; Misawa, Tsuyoshi*
Nihon Genshiryoku Gakkai-Shi ATOMO
, 67(3), p.198 - 202, 2025/03
no abstracts in English
Maeda, Mizuho*; Matsuda, Tatsuma*; Haga, Yoshinori; Shirasaki, Kenji*; Kimura, Noriaki*
Journal of the Physical Society of Japan, 94(2), p.024707_1 - 024707_6, 2025/01
Times Cited Count：0 Percentile：0.00(Physics, Multidisciplinary)
U/
U isotope ratios in deep groundwater and its potential application as a groundwater mixing indicatorKuribayashi, Chika*; Miyakawa, Kazuya; Ito, Akane*; Tanimizu, Masaharu*
Geochemical Journal, 59(2), p.35 - 44, 2025/00
Times Cited Count：2 Percentile：62.57(Geochemistry & Geophysics)no abstracts in English
Vali
ka, M.*; Haidamak, T.*; Cabala, A.*; Posp
il, J.*; Bastien, G.*; Sechovsk
, V.*; Prokleka, J.*; Yanagisawa, Tatsuya*; Opletal, P.; Sakai, Hironori; et al.
Physical Review Materials (Internet), 8(9), p.094415_1 - 094415_9, 2024/09
Times Cited Count：2 Percentile：16.66(Materials Science, Multidisciplinary)
Cf rotation method with a water Cherenkov neutron detectorTanabe, Kosuke*; Komeda, Masao; Toh, Yosuke; Kitamura, Yasunori*; Misawa, Tsuyoshi*; Tsuchiya, Kenichi*; Sagara, Hiroshi*
Scientific Reports (Internet), 14, p.18828_1 - 18828_10, 2024/08
Times Cited Count：1 Percentile：20.46(Multidisciplinary Sciences)Suetsugu, Shota*; Sakai, Hironori; Opletal, P.; Tokiwa, Yoshifumi; Haga, Yoshinori; 12 of others*
Science Advances (Internet), 10(6), p.eadk3772_1 - eadk3772_6, 2024/02
Times Cited Count：36 Percentile：97.69(Multidisciplinary Sciences)Horii, Yuta; Hirooka, Shun; Uno, Hiroki*; Ogasawara, Masahiro*; Tamura, Tetsuya*; Yamada, Tadahisa*; Furusawa, Naoya*; Murakami, Tatsutoshi; Kato, Masato
Journal of Nuclear Materials, 588, p.154799_1 - 154799_20, 2024/01
Times Cited Count：8 Percentile：78.42(Materials Science, Multidisciplinary)The thermal conductivities of near-stoichiometric (U,Pu,Am)O doped with NdO
/SmO, which is major fission product (FP) generated by a uranium-plutonium mixed oxides (MOX) fuel irradiation, as simulated fission products are evaluated at 1073-1673 K. The thermal conductivities are calculated from the thermal diffusivities that are measured using the laser flash method. To evaluate the thermal conductivity from a homogeneity viewpoint of Nd/Sm cations in MOX, the specimens with different homogeneity of Nd/Sm are prepared using two kinds of powder made by ball-mill and fusion methods. A homogeneous Nd/Sm distribution decreases the thermal conductivity of MOX with increasing Nd/Sm content, whereas heterogeneous Nd/Sm has no influence. The effect of Nd/Sm on the thermal conductivity is studied using the classical phonon transport model (A+BT)
. The dependences of the coefficients A and B on the Nd/Sm content (C
and C
, respectively) are evaluated as: A(mK/W)=1.70 
10
+ 0.93C + 1.20C, B(m/W)=2.39 10
.
Eaton, A. G.*; Weinberger, T. I.*; Popiel, N. J. M.*; Wu, Z.*; Hickey, A. J.*; Cabala, A.*; Pospil, J.*; Prokleka, J.*; Haidamak, T.*; Bastien, G.*; et al.
Nature Communications (Internet), 15, p.223_1 - 223_10, 2024/01
Times Cited Count：46 Percentile：98.53(Multidisciplinary Sciences)
McGrady, J.; Kumagai, Yuta; Watanabe, Masayuki; Kirishima, Akira*; Akiyama, Daisuke*; Kimuro, Shingo; Ishidera, Takamitsu
Journal of Nuclear Science and Technology, 60(12), p.1586 - 1594, 2023/12
Times Cited Count：2 Percentile：27.37(Nuclear Science & Technology) dissolution in bicarbonate solution with HO; The Effect of temperatureMcGrady, J.; Kumagai, Yuta; Kitatsuji, Yoshihiro; Kirishima, Akira*; Akiyama, Daisuke*; Watanabe, Masayuki
RSC Advances (Internet), 13(40), p.28021 - 28029, 2023/09
Times Cited Count：4 Percentile：18.03(Chemistry, Multidisciplinary)Upon nuclear waste canister failure and contact of spent nuclear fuel with groundwater, the UO matrix of spent fuel will interact with oxidants in the groundwater generated by water radiolysis. Bicarbonate (HCO
) is often found in groundwater, and the HO induced oxidative dissolution of UO in bicarbonate solution has previously been studied under various conditions. Temperatures in the repository at the time of canister failure will differ depending on the location, yet the effect of temperature on oxidative dissolution is unknown. To investigate, the decomposition rate of HO at the UO surface and dissolution of U
in bicarbonate solution (0.1, 1, 10 and 50 mM) was analysed at various temperatures (10, 25, 45 and 60 
C). At [HCO] 
1 mM, the apparent equilibrium concentration of U decreased with increasing temperature. This was attributed to the formation of U-bicarbonate species at the surface and a change in the mechanism of HO decomposition from oxidative to catalytic. At 0.1 mM, no obvious correlation between temperature and U dissolution was observed, and thermodynamic calculations indicated this was due to a change in the surface species. A pathway to explain the observed dissolution behaviour of UO in bicarbonate solution as a function of temperature was proposed.
