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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：0
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.
Iwasa, Toma; Takano, Masahide
Progress in Nuclear Science and Technology (Internet), 8, p.291 - 295, 2025/09
We have developed the external gelation technology for the fabrication of MAs nitride particles in high-performance heterogeneous fuel. Although the particle fabrication technology using external gelation methods has been developed, there has been almost no study targeting MAs nitrides fuel. Previously study suggested that the size of particle was required to be smaller than 250 
m to avoid the degradation of thermophysical properties. The purpose of this study is to optimize the external gelation conditions for spherical gel particle smaller than 500 m because the particle shrank less than half size by calcination and nitridation. The external gelation tests were performed with the viscosity and pressure of dropping solution as parameters. The results show that the smaller particle with higher sphericity was obtained at the higher pressure of 350-500kPa at each viscosity of 30-50cP with positive correlation.
Sudo, Ayako; Sato, Takumi; Takano, Masahide
Journal of Nuclear Science and Technology, 62(6), p.573 - 581, 2025/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)During the progression of the severe accident at the Fukushima Daiichi Nuclear Power Station, seawater flowed down and was predicted to react with molten corium and concrete. For the removal and storage of fuel debris, knowing the effects of seawater components on the characteristics of reaction products in the fuel debris is crucial. To understand changes in the microstructure of fuel debris, a reaction test was conducted by introducing sea salt to simulated corium and concrete under a temperature gradient. Among the components of sea salt, sulfur formed iron sulfide during metallic precipitation. Analysis of vaporized species indicated that most of Cl, some Na and K in the sea salt might volatilize during heating rather than react with simulated corium and concrete. Calcium and a small amount of Mg, Na, and K in the sea salt might be trapped in the silicate glass.
Nakamura, Satoshi; Ishii, Sho*; Kato, Hitoshi*; Ban, Yasutoshi; Hiruta, Kenta; Yoshida, Takuya; Uehara, Hiroyuki; Obata, Hiroki; Kimura, Yasuhiko; Takano, Masahide
Journal of Nuclear Science and Technology, 62(1), p.56 - 64, 2025/01
Times Cited Count：1 Percentile：20.46(Nuclear Science & Technology)A dissolution method for analyzing the elemental composition of fuel debris using the sodium peroxide (NaO) fusion technique has been developed. Herein, two different types of simulated debris materials (such as solid solution of (Zr,RE)O and molten core-concrete interaction products (MCCI)) were taken. At various temperatures, these debris materials were subsequently fused with NaO in crucibles, which are made of different materials, such as Ni, AlO
, Fe, and Zr. Then, the fused samples are dissolved in nitric acid. Furthermore, the effects of the experimental conditions on the elemental composition analysis were evaluated using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), which suggested the use of a Ni crucible at 923 K as an optimum testing condition. The optimum testing condition was then applied to the demonstration tests with Three Mile Island unit-2 (TMI-2) debris in a shielded concrete cell, thereby achieving complete dissolution of the debris. The elemental composition of TMI-2 debris revealed by the proposed dissolution method has good reproducibility and has an insignificant contradiction in the mass balance of the sample. Therefore, this newly developed reproducible dissolution method can be effectively utilized in practical applications by dissolving fuel debris and estimating its elemental composition.
and Fe-Zr meltNakajima, Kunihisa; Takano, Masahide
Journal of Nuclear Science and Technology, 62(1), p.78 - 85, 2025/01
Times Cited Count：4 Percentile：55.60(Nuclear Science & Technology)At TEPCO's Fukushima Daiichi Nuclear Power Station, it is estimated that considerable amounts of cesium still remain in the reactors from the analysis results using the severe accident analysis codes and the reverse analysis from contaminated water. Since cesium is known to form stable compounds with uranium and zirconium, chemisorption experiments with uranium dioxide pellets and iron-zirconium melts for cesium hydroxide vapor were carried out. As the results, formations of cesium uranate, CsUO
, and cesium zirconate, CsZrO, were confirmed, indicating that cesium was chemisorbed on both of the uranium dioxide pellets and the iron-zirconium melts in an Ar-H-HO flow and an Ar-H flow, respectively. Therefore, it was considered that cesium released from fuel might be trapped by chemisorption with fuels and/or iron-zirconium melts during light water reactor severe accidents.
Shibata, Hiroki; Saito, Hiroaki; Hayashi, Hirokazu; Takano, Masahide
Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 23(3), p.74 - 80, 2024/08
Partitioning and transmutation of minor actinides techniques have been developed to reduce the radiotoxicity and volume in the high-level radioactive wastes. Minor actinide nitride fuel has been chosen as a candidate for transmutation of long-lived nuclides by accelerator-driven system. Understanding irradiation behavior of nitride fuel is important for its design and development, however, experimental data on irradiation tests of actinide nitrides and these solid solutions are scarce. Recently, in JAEA, nitride fuel performance analysis module based on light water reactor fuel performance code, FEMAXI-7, has been developed to simulate irradiation behavior of the nitride fuel. In this study, performance analysis was carried out focusing on the pellet-cladding mechanical interaction (PCMI), which was pointed out as the most effective factor for the fuel safety during irradiation. Simulation results show that PCMI does not cause the creep rupture of the cladding.
Miyazaki, Kanako*; Takehara, Masato*; Minomo, Kenta*; Horie, Kenji*; Takehara, Mami*; Yamasaki, Shinya*; Saito, Takumi*; Onuki, Toshihiko*; Takano, Masahide; Shiotsu, Hiroyuki; et al.
Journal of Hazardous Materials, 470(15), p.134104_1 - 134104_11, 2024/05
Times Cited Count：4 Percentile：36.55(Engineering, Environmental)
observation of radiation-induced defects in ZrN under electron irradiation in HVEMRahman, M. M.*; Yamamoto, Tomokazu*; Matsumura, Sho*; Takaki, Seiya; Takano, Masahide; Costantini, J. M.*; Yasuda, Kazuhiro*
Nuclear Instruments and Methods in Physics Research B, 549, p.165289_1 - 165289_8, 2024/04
Times Cited Count：5 Percentile：74.74(Instruments & Instrumentation)Nucleation-and-growth process of radiation-induced defects in zirconium nitride (ZrN) has been investigated 
under electron irradiation by using a high voltage transmission electron microscope (HVEM) under electron irradiation by using a high voltage transmission electron microscope (HVEM).
Sato, Nobuaki*; Kirishima, Akira*; Sasaki, Takayuki*; Takano, Masahide; Kumagai, Yuta; Sato, Soichi; Tanaka, Kosuke
Current Location of Fuel Debris Chemistry, 178 Pages, 2023/11
Considerable efforts have been devoted to the decommissioning of the TEPCO's Fukushima Daiichi Nuclear Power Station (1F) and now the retrieval of fuel debris is being proceeded on a trial basis. It can be said that the succession of science and technology related to debris, that is, human resource development, is important and indispensable. For that reason, we thought that a specific textbook on decommissioning is necessary. Regarding the 1F fuel debris, we still do not know enough, and it would be difficult to describe the details. However, 12 years have passed since the accident, and we have come to understand the situation of 1F to a certain extent. At this stage, it is essential for future development to organize the current situation by combining examples of past severe accidents. Therefore, we presented in this book the current state of fuel debris chemistry research from the perspectives of solid chemistry, solution chemistry, analytical chemistry, radiochemistry, and radiation chemistry.
Koyama, Shinichi; Ikeuchi, Hirotomo; Mitsugi, Takeshi; Maeda, Koji; Sasaki, Shinji; Onishi, Takashi; Tsai, T.-H.; Takano, Masahide; Fukaya, Hiroyuki; Nakamura, Satoshi; et al.
Hairo, Osensui, Shorisui Taisaku Jigyo Jimukyoku Homu Peji (Internet), 216 Pages, 2023/11
In FY 2021 and 2022, JAEA perfomed the subsidy program for "the Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris (Development of Technologies for Enhanced Analysis Accuracy, Thermal Behavior Estimation, and Abbreviated Analysis))" started in FY 2021. This presentation material summarized the results of the project, which will be available shortly on the website of Management Office for the Project of Decommissioning, Contaminated Water and Treated Water Management.
Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Aoyagi, Noboru; Mei, H.; Takano, Masahide; Kozai, Naofumi
Journal of Nuclear Science and Technology, 60(8), p.1002 - 1012, 2023/08
Times Cited Count：1 Percentile：12.78(Nuclear Science & Technology)Yoneda, Yasuhiro; Tsuji, Takuya; Matsumura, Daiju; Okamoto, Yoshihiro; Takaki, Seiya; Takano, Masahide
Physica B; Condensed Matter, 663, p.414960_1 - 414960_9, 2023/08
Times Cited Count：0 Percentile：0.00(Physics, Condensed Matter)We performed various synchrotron X-ray measurements to extract local and average structures of DyN-ZrN solid solutions. We performed the nanoscale structural analysis by combining X-ray absorption fine structure and high-energy X-ray diffraction. The DyN-ZrN solid solution has a rock-salt type cubic crystal structure, and there are instabilities such as the chemical order of the metal site and the distribution of the bond length of the nitrogen site.
Onuki, Toshihiko*; Ye, J.*; Kato, Tomoaki; Liu, J.; Takano, Masahide; Kozai, Naofumi; Utsunomiya, Satoshi*
Environmental Science; Processes & Impacts, 25(7), p.1204 - 1212, 2023/07
Times Cited Count：2 Percentile：11.86(Chemistry, Analytical)To elucidate chemical forms of Cs and I in microparticles produced via the Fukushima Daiichi Nuclear Power Plant accident and released into the atmosphere, we analyzed Cs and I in condensed vaporized particles (CVP) produced by melting experiments using nuclear fuel components containing CsI with concrete. CVPs consisted of many round particles containing Cs and I of diameters less than several tens of micrometers. Two kinds of particles were present: one containing large amounts of Cs and I, suggesting the presence of CsI, and the other containing small amounts of Cs and I with large Si contents. Most of CsI from both particles were dissolved in water. On the contrary, some fractions of Cs remained from the latter particles. These results suggest that Cs was incorporated in CVPs along with Si to form water low-soluble CVPs
Ikeuchi, Hirotomo; Koyama, Shinichi; Osaka, Masahiko; Takano, Masahide; Nakamura, Satoshi; Onozawa, Atsushi; Sasaki, Shinji; Onishi, Takashi; Maeda, Koji; Kirishima, Akira*; et al.
JAEA-Technology 2022-021, 224 Pages, 2022/10
JAEA-Technology-2022-021.pdf:12.32MB
A set of technology, including acid dissolving, has to be established for the analysis of content of elements/nuclides in the fuel debris samples. In this project, a blind test was performed for the purpose of clarifying the current level of analytical accuracy and establishing the alternative methods in case that the insoluble residue remains. Overall composition of the simulated fuel debris (homogenized powder having a specific composition) were quantitatively determined in the four analytical institutions in Japan by using their own dissolving and analytical techniques. The merit and drawback for each technique were then evaluated, based on which a tentative flow of the analyses of fuel debris was constructed.
/Fe(0) by bacteriaLiu, J.; Dotsuta, Yuma; Kitagaki, Toru; Takano, Masahide; Onuki, Toshihiko; Kozai, Naofumi
Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR2022) (Internet), 2 Pages, 2022/10
Nuclear fuel debris, consisting primarily of nuclear fuel and structural material, was formed during the Fukushima Daiichi NPP accident and exists in the cooling water accumulated in the primary containment vessels. Microorganisms living in groundwater may come into contact with the fuel debris and react with it. To assess the degradation of fuel debris, it is necessary to evaluate the interactions between microorganisms and fuel debris. Here we performed an experimental study on bacterial degradation. A mixed powder of UO and Fe(0) was used as a fuel debris simulant. Bacillus subtilis, which is widespread bacteria in nature and thought to be present at the accident site, was used. The mixed powder was exposed to the Bacillus subtilis in a liquid medium for some days. It was found that the oxidative dissolution of the U(IV) and Fe(0) was accelerated by B. subtilis. A fraction of the dissolved U(VI) was precipitated together with iron precipitates which are probably amorphous Fe(III) hydroxides. The study indicates that microorganisms would cause the degradation of fuel debris.
temperature measurement for lamp-based heating deviceSumita, Takehiro; Sudo, Ayako; Takano, Masahide; Ikeda, Atsushi
Science and Technology of Advanced Materials; Methods (Internet), 2(1), p.50 - 54, 2022/02
CSumita, Takehiro; Kobata, Masaaki; Takano, Masahide; Ikeda, Atsushi
Materialia, 20, p.101197_1 - 101197_11, 2021/12
