None

Yokozuka, Eri*; Seito, Hajime*; Oka, Toshitaka; Kumagai, Yuta; Nagasawa, Naotsugu*

Isotope News, (801), p.46 - 48, 2025/10

no abstracts in English

Fabrication of low-O/M fast reactor MOX fuel and analysis on its oxygen potential behaviors

Hirooka, Shun; Vauchy, R.; Horii, Yuta; Sunaoshi, Takeo*; Saito, Kosuke

Proceedings of TopFuel 2025; Nuclear Reactor Fuel Performance Conference (Internet), 10 Pages, 2025/10

Reducing the oxygen-to-metal (O/M) ratio in MOX fuels plays an important role in suppressing the corrosion depth in the cladding due to fuel-cladding chemical interaction (FCCI), which is the key to determining the lifetime of fast reactor MOX fuels. Owing to a number of irradiation and post-irradiation experiments, a clear decreasing trend in the corrosion depth with lower O/M ratio in the as-fabricated MOX pellet was reported, whereas a significant redistribution of the O/M ratio in a pellet driven by the radial temperature gradient during irradiation could supply a higher oxygen potential near the pellet periphery where the FCCI should occur. The reduction of the O/M ratio in the MOX pellet fabrication processes can be achieved by heat treatment by taking high temperature, longer time, and lower oxygen partial pressure in the gas into account; the properties governing the reduction are not sufficiently studied. This study demonstrated the variation of O/M ratio in MOX pellets and the in-situ O/M ratio during the heat treatment was analyzed by using a thermogravimeter, which revealed a decreasing behavior during heating and dwell as well as an increasing behavior in the O/M ratio during the cooling step. Furthermore, the redistribution of O/M ratio, analyzed by Sari's model, was discussed to investigate the O/M ratio and the oxygen potential near the pellet periphery which is likely to have a more direct influence on the FCCI than the as-fabricated O/M ratio. By using the recent oxygen potential data on MOX, it is found that the oxygen potential profile in the radial direction is especially drastic near the pellet periphery and is sensitive to the as-fabricated O/M ratio.

Upper limit for the Cm(Ti,xn)Og reaction cross section

Gall, B. J.-P.*; Asai, Masato; Ito, Yuta; Toyoshima, Atsushi*; 30 of others*

Journal of the Physical Society of Japan, 94(9), p.094201_1 - 094201_9, 2025/09

https://doi.org/10.7566/JPSJ.94.094201

An experiment to search for Og isotopes using the Ti beam impinging on Cm target was performed at RIKEN Nishina Center. The optimal beam energy was determined from the quasielastic barrier distribution extracted from the excitation function of quasielastic backscattering. As a result, no Og decay was found, enabling only an estimation of the sensitivity for one event of 0.27 pb, and the 1 cross section upper limit of 0.50 pb.

Control and irradiation behaviors of oxygen potential of MOX fuel

Hirooka, Shun; Vauchy, R.; Horii, Yuta; Sunaoshi, Takeo*; Saito, Kosuke; Ozawa, Takayuki

Proceedings of Workshop on Fuel Performance Assessment and Behaviour for Liquid Metal Cooled Fast Reactors (Internet), 8 Pages, 2025/07

no abstracts in English

Diffusion of Cs, I and HDO onto pre-Neogene sedimentary rocks

Hou, L.*; Fukatsu, Yuta; Okamoto, Shunichi*; Toda, Kanako*; Nakata, Kotaro*; Nohara, Shintaro*; Ishidera, Takamitsu; Saito, Takumi*

Journal of Nuclear Science and Technology, 14 Pages, 2025/00

https://doi.org/10.1080/00223131.2025.2528482

Pulsed muon facility of J-PARC MUSE

Shimomura, Koichiro*; Koda, Akihiro*; Pant, A. D.*; Sunagawa, Hikaru*; Fujimori, Hiroshi*; Umegaki, Izumi*; Nakamura, Jumpei*; Fujihara, Masayoshi; Tampo, Motonobu*; Kawamura, Naritoshi*; et al.

Interactions (Internet), 245(1), p.31_1 - 31_6, 2024/12

https://doi.org/10.1007/s10751-024-01863-8

Creep deformation and rupture behavior of 9Cr-ODS steel cladding tube at high temperatures from 700C to 1000C

Imagawa, Yuya; Hashidate, Ryuta; Miyazawa, Takeshi; Onizawa, Takashi; Otsuka, Satoshi; Yano, Yasuhide; Tanno, Takashi; Kaito, Takeji; Onuma, Masato*; Mitsuhara, Masatoshi*; et al.

Journal of Nuclear Science and Technology, 61(6), p.762 - 777, 2024/06

https://doi.org/10.1080/00223131.2023.2269178

The Japan Atomic Energy Agency has been developing 9Cr-oxide dispersion strengthened (ODS) steel as a fuel cladding material for sodium-cooled fast reactors (SFRs). Previous studies have formulated the creep rupture equation for 650C to 850C. However, little data have been obtained above 850C, and no equation has been formulated. This study conducted creep tests to evaluate creep strength at 700C to 1000C. Two creep test methods, the internal pressure and ring creep tests under development, were used, and the validation of the ring creep test method was conducted. The results showed that 9Cr-ODS steel undergoes almost no strength change due to the matrix's phase transformation, and a single equation can express a creep rupture strength from 700C to 1000C. In validating the ring creep test method, analysis clarified the effect of stress concentration on the specimen. Plastic deformation occurs at high initial stress and may lead to early rupture. The results will be essential for future creep testing and evaluation of neutron-irradiated 9Cr-ODS steel.

Multiscale observation of nano-oxide particles in oxide-dispersion-strengthened Cu alloys

Saito, Toshiki*; Yu, H.*; Gao, Z.*; Inoue, Koji*; Kondo, Sosuke*; Kasada, Ryuta*; Nagai, Yasuyoshi*; Oba, Yojiro*; Hiroi, Kosuke

Journal of Alloys and Compounds, 983, p.173852_1 - 173852_12, 2024/05

https://doi.org/10.1016/j.jallcom.2024.173852

Mass measurements of neutron-rich nuclei constrain element abundances

Xian, W.*; Ito, Yuta; 30 of others*

Physical Review C, 109(3), p.035804_1 - 035804_10, 2024/03

https://doi.org/10.1103/PhysRevC.109.035804

First direct mass measurement for neutron-rich Mo with the new ZD-MRTOF mass spectrograph system

Hou, D. S.*; Ito, Yuta; 30 of others*

Physical Review C, 108(5), p.054312_1 - 054312_10, 2023/11

https://doi.org/10.1103/PhysRevC.108.054312

The atomic masses of Ag, Pd, Rh, Ru, and Mo have been measured with the ZeroDegree multi-reflection time-of-flight Mass Spectrograph (ZDMRTOF-MS) at the RIKEN RI beam factory. In most cases, good agreements between our results and available experimental data as well as the evaluated masses in AME2020. From the present results, we conclude that up to Mo there is no stabilizing shell effect corresponding to the harmonic oscillator gap at N = 70.