Jiaqi Zhang ^a, Akifumi Iwamoto ^a,b, Keisuke Shigemori ^a , Masanori Hara ^c , Kohei Yamanoi ^a

a Institute of Laser Engineering, Osaka University, Osaka 5650871, Japan
b National Institute for Fusion Science, National Institutes of Natural Sciences, Gifu 509-5202, Japan
c Academic Assembly, University of Toyama, Toyama 9308555, Japan

Abstract
A typical inertial confinement fusion target comprises a central deuterium-tritium (D-T) gas surrounded by a solid D-T layer inside an outer ablator shell. However, because of the isotope effect, fractionation of the hydrogen isotopologues can occur during the solidification process. This inhomogeneity in the solid D-T layer may lead to a deterioration in the fusion reaction. Thus, effective methods are required to characterize isotopologue distribution and homogeneity in solid D-T layers. The distribution of isotopologues in a solid hydrogen mixture can be simulated numerically using computational fluid dynamics. In this study, thermofluid simulations of the mixture’s solidification process were performed to investigate the mechanism behind component distribution and to analyze the factors affecting the homogeneity. A numerical simulation was conducted to model inhomogeneity formation during the solidification of hydrogen isotopologue mixtures in a 3D wedge-shaped cavity. The simulations revealed inhomogeneities in H₂-D₂, D₂-T₂, and D₂-DT-T₂ mixtures during solidification. For an H₂-D₂ mixture, the simulation showed good agreement with experimental results, validating the computational model. These simulation methods will be used for homogeneity analysis of the solid D-T layer in fuel pellets.

https://doi.org/10.1016/j.fusengdes.2025.114827
Accepted: 23 January 2025

Satoshi Akamaru, Kyosuke Miyake

Abstract
This study investigated the giant magnetoresistance (GMR) effect of a Fe/V(001) multilayer under different hydrogen concentrations in a hydrogen–nitrogen gas mixture to elucidate the effect of hydrogen absorption in the V layer on the exchange interactions between each Fe layer. The resistance against hydrogen concentration in the gas mixture revealed a phase boundary that was dependent on the V thickness in Fe/V, between hydrogen dissolved in the V metal and V hydride phases. The magnetoresistance in Fe/V with a V thickness of 1.7–2.0 nm demonstrated a GMR effect, which was reduced under low hydrogen concentration in the gas mixture, corresponding to the hydrogen dissolved phase in the V layer. However, Fe/V samples with V thicknesses within the range of 2.2–2.7 nm exhibited the GMR effect during the formation of the V hydride phase, although these samples did not display any GMR behavior under nitrogen gas. These behaviors were reversible to hydrogen concentration in the gas mixture. The dependence of the exchange coupling coefficient on the V layer thickness was estimated from the GMR behavior, revealing that the exchange coupling coefficient was governed by the change in the crystalline phase from the V metal to the hydride and not by the thickness of the V layer. In the V hydride phase, the GMR effect was gradually reduced following hydrogen absorption, suggesting that the induced structural disorder and/or stress in the V layer due to excess hydrogen absorption inhibited the exchange interactions between each Fe layer.

https://doi.org/10.1063/5.0250577
Published Online: 10 February 2025

Hidehisa Hagiwara,* Katsuaki Hayakawa, Kazuki Ishitsuka, Keisuke Awaya, Kazuto Hatakeyama,and Shintaro Ida

Abstract
To make full use of sunlight for water splitting reactions for hydrogen production, a visible-light-driven photocatalyst was developed by modifying TiO₂ nanosheets with Co(OH)₂. By adding an aqueous Co(NO₃)₂·6H₂O solution to a TiO₂ nanosheet suspension, the TiO₂ nanosheets aggregated and Co(OH)₂ was formed. In the ultraviolet−visible (UV−vis) diffuse reflectance spectrum of the photocatalyst, new absorption bands attributable to Co(OH)₂ and the interfacial charge transfer between Co(OH)₂ and the TiO₂ nanosheets appeared at around 600 and 400 nm, respectively. The photocatalytic activity of Co(OH)₂/TiO₂ nanosheets was evaluated in terms of the O₂ evolution reaction in an aqueous AgNO₃ solution, finding that the reaction proceeds under visible light. Furthermore, the investigation of the wavelength dependence of the photocatalytic activity revealed that the photocatalytic reaction on Co(OH)₂/TiO₂ nanosheets proceeds via Co(OH)₂ photocatalysis and interfacial charge transfer between Co(OH)₂ and the TiO₂ nanosheets under visible light irradiation.

https://doi.org/10.1021/acsomega.4c10161
Accepted:January 8, 2025

Makoto I. Kobayashi, Sachiko Yoshihashi, Kunihiro Ogawa, Mitsutaka Isobe, Tsukasa Aso, Masanori Hara, Siriyaporn Sangaroon, Sachie Kusaka, Shingo Tamaki, Isao Murata, Sho Toyama, Misako Miwa, Shigeo Matsuyama, Masaki Osakabe

Abstract
This paper presents the method to evaluate the fast neutron energy spectrum using the single crystal CVD diamond detector to be applicable on the radiation monitoring in advanced scientific/engineering systems usually characterized with mixed and high-dose radiation field. The pulse shape discrimination based on the shape and the width of a pulse was applied to extract events in which fast neutron hits at the specific depth of the single crystal diamond. Unfolding of the measured spectrum for extracted pulses could deduce the neutron energy spectrum. Experiments using mono-energetic neutron sources demonstrated the reliable capability of this method to evaluate the neutron energy spectrum quantitatively.

Keywords:single crystal CVD diamond detector, neutron, pulse shape discrimination
http://hdl.handle.net/10655/0002000878

Hanns Gietl^{1, *}, Chase N. Taylor¹, Yuji Hatano², Yasuhisa Oya³, Masashi Shimada¹

1Fusion Safety Program, Idaho National Laboratory, Idaho Falls, ID 83415, USA
2Hydrogen Isotope Research Center, University of Toyama, Toyama 930-8555, Japan
3Graduate School of Integrated Science and Technology, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan

The effect of mixed spectra and thermal neutron shielded irradiation on tungsten was evaluated with plasma exposure in the tritium plasma experiment followed by thermal desorption spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The two different irradiation campaigns were performed at the High Flux Isotope Reactor to 0.39-0.74 isplacement per atom (dpa) in the 894–1379 K temperature range. A neutron spectrum influence on the void size and void number density was not observed. However, a strong correlation was found between void size and void number density with temperature, but not with dpa in the limited dpa range of this study. Thermal neutron shielding significantly reduced the transmutation to Re+Os. Higher irradiation temperature will lead to larger voids with lower number density, which reduces deuterium retention. Grain growth was also observed for high-temperature irradiation of over ~1300 K within the limited grains visible in the transmission electron microscopy specimens.

Keywords: tungsten, neutron irradiation, deuterium retention

Azusa Matsumoto ^a,b,*, Yuji Hatano ^a,c

a Graduate School of Engineering, Tohoku University, 6-6-01-2 Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8579, Japan
b Graduate School of Science and Engineering, University of Toyama, Toyama 930-8555, Japan
c Hydrogen Isotope Research Center, University of Toyama, Toyama 930-8555, Japan

Abstract
Tritium (T) permeation through steam generator piping from the primary to the secondary side of a water-cooled breeding blanket system increases a risk of exposure of workers and members of the public. From this viewpoint, the T permeation through Inconel 600, a candidate material of steam generator piping, under exposure to tritiated water was examined at 280 ℃ and 6.4 MPa by focusing attention on the influence of oxidation of coexisting materials and that of H₂ and O₂ gas addition. The T permeation rate through Inconel 600 sample was sensitively dependent on the oxidation rate of coexisting material, and a high permeation rate was observed with a material with high oxidation rate. The H₂ gas addition also resulted in a remarkable increase in T permeation rate, while the O₂ gas addition led to clear reduction. These observations indicated that HT generated by the oxidation of coexisting material by HTO and the isotope exchange reaction between HTO and H₂ gas (HTO + H₂ → H₂O + HT) contributed to the permeation. Reduction in T permeation in a steam generator appears possible by minimizing oxidation of coexisting materials in the primary loop and/or continuous O₂ gas supply.

https://doi.org/10.1016/j.fusengdes.2025.114896
Accepted:19 February 2025

Yuzuka Hoshino ^a,*, Fei Sun ^b, Makoto I. Kobayashi c,d, Takeshi Toyama ^e, Robert Kolasinski ^f,Chase N. Taylor ^g , Masashi Shimada ^g , Yuji Hatano ^e, Yasuhisa Oya ^a

a Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, Japan
b Hefei University of Technology, Hefei, China
c National Institute for Fusion Science, Gifu, Japan
d The Graduate University for Advanced Studies, SOKENDAI, Japan
e Tohoku University, Ibaraki, Japan
f Sandia National Laboratories, Livermore, CA, United States of America
g Idaho National Laboratory, Idaho Falls, ID, United States of America

Abstract
Hydrogen and deuterium permeation behavior for neutron damaged W and W-3 %Re was evaluated using a Plasma Driven Permeation device. For neutron damaged W-3 %Re at 773 K and 1473 K, precipitation of Re and Os was observed by atom probe tomography. Neutron irradiation introduced defect damage throughout the sample and enhanced H and D diffusion toward downstream side. The existence of irradiation damage by neutron irradiation was found to increase hydrogen isotope permeation. Moreover, the existence of Re has suppressed the formation of irradiation defects for hydrogen isotope trapping sites. The recovery of irradiation defects by increasing the irradiation temperature led to the structural changes due to the diffusion of Re and Os, which also affected the hydrogen isotope permeation behavior.

https://doi.org/10.1016/j.fusengdes.2024.114769
Accepted:9 December 2024