Durability of U-Zr oxide solid solution in aqueous HO solution

Kumagai, Yuta; Kusaka, Ryoji; Takano, Masahide; Watanabe, Masayuki

Journal of Nuclear Materials, 625, p.156553_1 - 156553_7, 2026/04

https://doi.org/10.1016/j.jnucmat.2026.156553

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.

Temperature effect on radiolytically generated hydrogen yield from a plutonium nitric acid aqueous solution

Toigawa, Tomohiro; Hotoku, Shinobu; Kumagai, Yuta; Abe, Yuma*; Oyama, Kanichi*; Fukaya, Hiroyuki; Ban, Yasutoshi; Kida, Takashi; Hasegawa, Satoshi*; Nakano, Masanao*; et al.

Journal of Nuclear Science and Technology, 63(3), p.322 - 327, 2026/03

https://doi.org/10.1080/00223131.2025.2541067

The effect of temperature on hydrogen production generated from radiolysis was investigated to determine the associated implications for nuclear fuel reprocessing safety. The hydrogen yield from radiolysis of plutonium nitric acid solution was measured at temperatures up to the boiling temperature of the solution. The results showed no notable temperature dependence even under boiling conditions. The impact of solution agitation on hydrogen production was also assessed, which revealed minor differences in the hydrogen yield between static and agitated conditions at room temperature. These findings suggest that high temperatures or boiling the solution do not considerably enhance hydrogen generation, and provide crucial information for accurately modeling hydrogen risks under severe accidents.

Effect of temperature on radiolytically generated hydrogen yield from actual nuclear fuel-derived solution

Toigawa, Tomohiro; Hotoku, Shinobu; Kumagai, Yuta; Abe, Yuma*; Oyama, Kanichi*; Fukaya, Hiroyuki; Tsubata, Yasuhiro; Ban, Yasutoshi; Kida, Takashi; Hasegawa, Satoshi*; et al.

Journal of Nuclear Science and Technology, 7 Pages, 2026/00

https://doi.org/10.1080/00223131.2026.2637453

The effect of temperature on hydrogen generated from radiolysis was investigated to determine the safety implications in nuclear fuel reprocessing. Radiolytic hydrogen production poses a risk due to its flammability, especially when it accumulates in confined spaces without ventilation. Herein, generation of radiolytic hydrogen from an actual nuclear fuel-derived solution is investigated. Compared to previous studies using a plutonium nitric acid solution, this study evaluates radiolytic hydrogen yield under more realistic conditions, reflecting post-irradiation fuel composition. G-values of H are determined at multiple temperatures, and the impact of alpha, beta, and gamma radiation doses is evaluated using PHITS-based simulations. Findings from this study confirmed a reduction in hydrogen yield due to scavenging effects of high-concentration nitric acid and metal ions dissolved in the solution, and temperature dependence appeared to be minor. A weak decreasing trend of G-values with temperature under agitated conditions might be related to hydrogen consumption by palladium species.

Fukushima Daiichi Nuclear Power Plant Unit 2 Accident analysis considering the thermal stratification and containment leakage

Nakamura, Yuki*; Kojima, Yoshihiro*; Yamashita, Takuya; Shimomura, Kenta; Mizokami, Shinya

Journal of Nuclear Science and Technology, 62(12), p.1226 - 1230, 2025/12

https://doi.org/10.1080/00223131.2025.2570371

Development trends of advanced reactor with a focus on fast reactor and high temperature gas-cooled reactor, 3; Development trends of high temperature gas-cooled reactor

Sakaba, Nariaki; Ohashi, Hirofumi; Sato, Hiroyuki

Nihon Genshiryoku Gakkai-Shi ATOMO, 67(10), p.593 - 597, 2025/10

https://doi.org/10.3327/jaesjb.67.10_593

no abstracts in English

neutron diffraction study on the strength and ductility enhancement mechanism of hydrogen-charged SUS310S stainless steel

Ito, Tatsuya; Ogawa, Yuhei*; Gong, W.; Mao, W.*; Kawasaki, Takuro; Okada, Kazuho*; Shibata, Akinobu*; Harjo, S.

Hamon, 35(3), p.129 - 133, 2025/08

Experimental verification to developing safety technology for liquefied hydrogen in the project "STACY"

Tanaka, Hirohisa*; Matsumura, Daiju; 10 of others*

International Journal of Hydrogen Energy, 141, p.1088 - 1097, 2025/06

https://doi.org/10.1016/j.ijhydene.2025.01.284

Synthesis of BaSiH hydridosilicate at high pressures; A Bridge to BaSiH polyhydride

Beyer, D. C.*; Spektor, K.*; Vekilova, O. Y.*; Grins, J.*; Barros Brant Carvalho, P. H.*; Leinbach, L. J.*; Sannemo-Targama, M.*; Bhat, S.*; Baran, V.*; Etter, M.*; et al.

ACS Omega (Internet), 10(15), p.15029 - 15035, 2025/04

https://doi.org/10.1021/acsomega.4c10502

Hydridosilicates featuring SiH octahedral moieties represent a rather new class of compounds with potential properties relating to hydrogen storage and hydride ion conductivity. Here, we report on the new representative BaSiH obtained from reacting the Zintl phase hydride BaSiH with H fluid at pressures above 4 GPa and subsequent decompression to ambient pressure. It consists of complex SiH ions, which are octahedrally coordinated by Ba counterions. The arrangement of Ba and Si atoms deviates only slightly from an ideal fcc NaCl structure. IR and Raman spectroscopy showed SiH bending and stretching modes in the ranges 800-1200 and 1400-1800 cm, respectively. BaSiH is thermally stable up to 95C above which decomposition into BaH and Si takes place. DFT calculations indicated a direct band gap of 2.5 eV. The discovery of BaSiH consolidates the compound class of hydridosilicates, accessible from hydrogenations of silicides at gigapascal pressures (10 GPa). The structural properties of BaSiH suggest that it presents an intermediate (or precursor) for further hydrogenation at considerably higher pressures to the predicted superconducting polyhydride BaSiH.

Handbook of Advanced Nuclear Hydrogen Safety (2nd Edition); Development of hydrogen behavior integrated analysis system and application to actual PWR

Terada, Atsuhiko; Thwe Thwe, A.; Hino, Ryutaro*

JAEA-Review 2024-049, 400 Pages, 2025/03

JAEA-Review-2024-049.pdf:13.94MB

In the aftermath of the Fukushima Daiichi Nuclear Power Station accident, safety measures against hydrogen in severe accident has been recognized as a serious technical problem in Japan. As one of efforts to form a common knowledge base between nuclear engineers and experts on combustion and explosion, we issued the "Handbook of Advanced Nuclear Hydrogen Safety (1st edition)" in 2017. For improvement of the rational advancement of hydrogen safety measures and further reliability of hydrogen safety evaluation, a CFD analysis is highly expected to produce more precisely and quantitative results. We have been developing an integrated CFD analysis code system which can analyze hydrogen diffusion, explosion-combustion and structural integrity at the severe accident especially for pressurized water reactors (PWRs). We organized the role of LP and the CFD analyses and their utilization examples of hydrogen safety validation. Based on these results, we made the "Handbook of Advanced Nuclear Hydrogen Safety (2nd volume)". The analysis results of real scale PWR described in 2nd volume are confirmed by cross-analysis models and existing data obtained through representative small, medium and large-scale tests.

High-pressure neutron diffraction study on -FeOOH; The Spin-reorientation transition and hydrogen-bond symmetrization

Ikeda, Osamu*; Yamamoto, Hajime*; Sano, Asami; Sakamaki, Tatsuya*; Kuribayashi, Takahiro*; Noda, Yukio*; Suzuki, Akio*

Journal of the American Chemical Society, 147(5), p.4005 - 4016, 2025/02

https://doi.org/10.1021/jacs.4c11982

The compression behavior of iron oxyhydroxide -FeOOH is complex, with variations in its magnetic property and bonding character. In this study, in situ powder neutron diffraction experiments were conducted on -FeOOH and -FeOOD up to pressures exceeding 20 GPa to investigate a spin-reorientation transition, hydrogen-bond symmetrization, and their correlation. The magnetic transition was observed at 8 GPa in both -FeOOH and -FeOOD. The crystal symmetry and H-bonds of -FeOOH transitioned from P21nm with asymmetric H-bonds to Pnnm with disordered H-bonds at 17.90 GPa, while -FeOOD remained asymmetric. The pressure evolution of the interatomic angles and distances indicates that the coordinate geometry of Fe transitioned toward H-bond symmetrization and would have affected the magnetic anisotropy.