Development of on-site detection system for concealed nuclear materials

Tanabe, Kosuke*; Komeda, Masao; Toh, Yosuke; Kitamura, Yasunori*; Misawa, Tsuyoshi*

Nihon Genshiryoku Gakkai-Shi ATOMO, 67(3), p.198 - 202, 2025/03

https://doi.org/10.3327/jaesjb.67.3_198

no abstracts in English

Large disequilibrium of U/U isotope ratios in deep groundwater and its potential application as a groundwater mixing indicator

Kuribayashi, Chika*; Miyakawa, Kazuya; Ito, Akane*; Tanimizu, Masaharu*

Geochemical Journal, 59(2), p.35 - 44, 2025/00

https://doi.org/10.2343/geochemj.GJ24028

no abstracts in English

Compact and transportable system for detecting lead-shielded highly enriched uranium using Cf rotation method with a water Cherenkov neutron detector

Tanabe, Kosuke*; Komeda, Masao; Toh, Yosuke; Kitamura, Yasunori*; Misawa, Tsuyoshi*; Tsuchiya, Kenichi*; Sagara, Hiroshi*

Scientific Reports (Internet), 14, p.18828_1 - 18828_10, 2024/08

https://doi.org/10.1038/s41598-024-69526-w

Thermal conductivity measurement of uranium-plutonium mixed oxide doped with Nd/Sm as simulated fission products

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

https://doi.org/10.1016/j.jnucmat.2023.154799

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.

UO dissolution in bicarbonate solution with HO; The Effect of temperature

McGrady, J.; Kumagai, Yuta; Kitatsuji, Yoshihiro; Kirishima, Akira*; Akiyama, Daisuke*; Watanabe, Masayuki

RSC Advances (Internet), 13(40), p.28021 - 28029, 2023/09

https://doi.org/10.1039/D2RA08131H

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.

Uranium hydroxide/oxide deposits on uranyl reduction

Ouchi, Kazuki; Matsumura, Daiju; Tsuji, Takuya; Kobayashi, Toru; Otobe, Haruyoshi; Kitatsuji, Yoshihiro

RSC Advances (Internet), 13(24), p.16321 - 16326, 2023/05

https://doi.org/10.1039/D3RA02899B

We clarified the chemical state transformation of deposits following the reduction of uranyl ion (UO) from the results of electrochemical quartz crystal microbalance, impedance spectra and X-ray absorption fine structure measurements. We propose the following deposition mechanism: (1) U is formed by the disproportionation of U. (2) U forms U hydroxide deposits, and (3) finally, the hydroxide deposits transform into U oxide, generally having a larger electrical resistance than the former.

Nuclear criticality benchmark analyses on TRIGA-type reactor systems by using continuous-energy Monte Carlo code MVP with JENDL-5

Yanagisawa, Hiroshi; Umeda, Miki; Motome, Yuiko; Murao, Hiroyuki

JAEA-Technology 2022-030, 80 Pages, 2023/02

JAEA-Technology-2022-030.pdf:2.57MB
JAEA-Technology-2022-030(errata).pdf:0.11MB

Nuclear criticality benchmark analyses were carried out for TRIGA-type reactor systems in which uranium-zirconium hydride fuel rods are loaded by using the continuous-energy Monte Carlo code MVP with the evaluated nuclear data library JENDL-5. The analyses cover two sorts of benchmark data, the IEU-COMP-THERM-003 and IEU-COMP-THERM-013 in the International Criticality Safety Benchmark Evaluation Project (ICSBEP) Handbook, and effective neutron multiplication factors, reactivity worths for control rods etc. were calculated by JENDL-5 in comparison with those by the previous version of JENDL. As the results, it was confirmed that the effective neutron multiplication factors obtained by JENDL-5 were 0.4 to 0.6% greater than those by JENDL-4.0, and that there were no significant differences in the calculated reactivity worths by between JENDL-5 and JENDL-4.0. Those results are considered to be helpful for the confirmation of calculation accuracy in the analyses on NSRR control rod worths, which are planned in the future.

Oxygen potential, oxygen diffusion, and defect equilibria in UO

Watanabe, Masashi; Kato, Masato

Frontiers in Nuclear Engineering (Internet), 1, p.1082324_1 - 1082324_9, 2023/01

https://doi.org/10.3389/fnuen.2022.1082324

Since the oxygen potential and the oxygen coefficient of UO have a significant impact on fuel performance, many experimental data have been obtained. However, experimental data of the oxygen potential and the oxygen diffusion coefficient in the high temperature region above 1673 K are very limited. In the present study, we aimed to obtain these data and analyze them by defect chemistry. The oxygen potentials and the oxygen chemical diffusion coefficient of UO were measured by the gas equilibrium method in the near stoichiometric region at temperatures ranging from 1673 to 1873 K. A data set of oxygen potentials was made together with literature data and analyzed by defect chemistry. The oxygen potential of UO was determined as a function of O/U ratio and temperature, and an equation representing the relationship was derived. The oxygen chemical diffusion coefficient values obtained in this study were reasonably close to the literature values. The oxygen partial pressure dependence of the oxygen chemical diffusion coefficients was predicted from the evaluated results of the oxygen potential data, but no clear dependence was observed.

Development of tailor-made adsorbents for uranium recovery from seawater on the basis of uranyl coordination chemistry (Contract research); FY2021 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Tokyo Institute of Technology*

JAEA-Review 2022-028, 54 Pages, 2022/11

JAEA-Review-2022-028.pdf:2.97MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2021. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2019, this report summarizes the research results of the "Development of Tailor-made Adsorbents for Uranium Recovery from Seawater on the Basis of Uranyl Coordination Chemistry" conducted from FY2019 to FY2021. Since the final year of this proposal was FY2021, the results for three fiscal years were summarized. The present study aims to develop a new ligand class for efficient and selective capture of uranium from seawater. On the basis of deep understanding on uranyl coordination chemistry, we design molecular structures of pentadentate ligands as functional moieties for uranium adsorption from seawater and study fundamental coordination chemistry of uranyl ion with those ligands in order to resolve current problems in uranium recovery technology …

Study on identification of materials in fuel debris and waste by neutron induced gamma ray spectroscopy

Nauchi, Yasushi*; Nomi, Takayoshi; Suzuki, Risa; Kosuge, Yoshihiro*; Shiba, Tomooki; Takada, Akira*; Kaburagi, Masaaki; Okumura, Keisuke

Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR2022) (Internet), 4 Pages, 2022/10