Kinetic and thermodynamic controls on CsI-Mo gas-phase reactions under varying oxygen potentials

塩津 弘之

Progress in Nuclear Energy, 195, p.106300_1 - 106300_11, 2026/05

https://doi.org/10.1016/j.pnucene.2026.106300

The transport and release behavior of fission products (FPs) during nuclear power plant accidents is strongly influenced by their chemical forms, particularly gaseous species, which can lead to enhanced environmental release. For iodine, one of the most volatile FPs, condensable cesium iodide (CsI) has traditionally been regarded as the dominant chemical form in state-of-the-art source term evaluations. However, recent experiments have indicated that molybdenum (Mo), a semi-volatile FP, can promote the formation of gaseous iodine through gas-phase reactions with CsI. The key controlling factor of these reactions is the oxygen potential of the atmosphere. In the TeRRa experiments, CsI-Mo gas-phase reactions were observed at 1150 K under Ar-20%O-0.8%O conditions (-31.7 kJ/mol-O), whereas no reaction occurred under Ar-20%HO conditions (-149 kJ/mol-O). Nevertheless, the specific reactive conditions governing these reactions have not yet been fully clarified. In this study, the oxygen-potential dependence of gas-phase reactions between CsI and Mo vapors in the TeRRa-CsIMo series experiments was numerically investigated using chemical equilibrium, mass transport, and reaction kinetics analyses. Chemical equilibrium and transport analyses were performed using the VICTORIA code, while detailed kinetic analyses were conducted with the Cantera software and the ECUME database. The results demonstrate that although CsI-Mo gas-phase reactions are thermodynamically favorable under oxidizing conditions that stabilize Mo in the MoO form ( -158 kJ/mol-O), their contribution to gaseous iodine formation is strongly constrained by kinetic limitations under lower oxygen potential conditions, even at high temperatures around 1150 K. These findings suggest that both thermodynamic and kinetic effects must be considered for reliable evaluation of iodine source terms during severe accidents, particularly under oxygen-starved environments.

Simple technique for the preparation of uranium-impregnated porous silica particles and their application as working standard particles for analysis of the safeguards environmental samples

富田 純平; 富田 涼平; 鈴木 大輔; 安田 健一郎; 宮本 ユタカ

Journal of Nuclear Science and Technology, 63(4), p.443 - 454, 2026/04

https://doi.org/10.1080/00223131.2025.2557376

A simple method for preparing uranium particles by impregnating uranium into porous silica particles was developed for use as particulate isotopic working standards. Isotopic standard solutions of uranium were prepared by acid digestion of uranium isotopic standard powder (CRM U100 and U850 from NBL) and then impregnated into the porous silica particles. The impregnation of uranium into the porous silica particles was observed by scanning electron microscopy-energy dispersive X-ray spectroscopy and large-geometry secondary-ion mass spectrometry analyses. The abundances of uranium isotopes determined by multicollector thermal ionization mass spectrometry agreed with the certified values, and no significant bias was found between the measured and certified values. These results indicate this new method for preparing uranium-impregnated particles has the potential to be applied to the preparation of in-house particulate isotopic standards.

In situ study of growth mechanism of germanene segregated through Ag(111) thin films by Raman and X-ray photoelectron spectroscopy

寺澤 知潮; 勝部 大樹*; 矢野 雅大; 小澤 孝拓*; 津田 泰孝; 吉越 章隆; 朝岡 秀人; 鈴木 誠也

Chemistry of Materials, 38(6), p.2933 - 2945, 2026/03

AA2025-0822.pdf:1.33MB

https://doi.org/10.1021/acs.chemmater.5c03462

Germanene, a honeycomb lattice of Ge atoms, has attracted attention for next-generation electronics and as a topological material. Among reported synthesis routes, the segregation method enables reproducible monolayer germanene formation on Ag(111) through simply annealing an Ag(111) thin film on a Ge(111) substrate. Despite this success, the physical origins of its monolayer selectivity and the mechanism for suppressing competing Ge phases remain unclear. Here, we investigate germanene formation via Ge segregation using in situ Raman spectroscopy and X-ray photoelectron spectroscopy to directly track Ge behavior during annealing and cooling. In situ observations revealed that annealing at 500C yielded no Ge-related byproducts, and the system reached a high-temperature surface equilibrium state, independent of the initial Ge amount. Cooling from this state produced a Ge-enriched surface that stabilizes the formation of monolayer germanene. In contrast, heating only to 300C produced three-dimensional Ge islands without Ge-enrichment, followed by Ge-Ag alloy formation upon subsequent cooling. By integrating the temperature-dependent diffusion length and the process-dependent diffusion direction, we established a unified description of Ge behavior on Ag/Ge(111) substrates, in which cooling-induced Ge-enrichment at the surface reproducibly stabilizes the selective formation of monolayer germanene.

Feasibility study on the production of Th as a long-life Ac generator using the experimental fast reactor Joyo

佐々木 悠人; 前田 茂貴; 深澤 哲生*; 高木 直行*

Journal of Nuclear Science and Technology, 63(2), p.154 - 165, 2026/02

https://doi.org/10.1080/00223131.2025.2558244

近年、核医学の分野では、がん細胞に選択的に集まる抗体やペプチドと結合させたAcを利用する標的線療法が注目されている。それに伴い、Acの需要が高まっているため、代替の製造方法の模索が不可欠となっている。著者らを含む複数の研究者が、Raを原料とする製造方法を模索しているが、Raの供給量が限られていること、取り扱いが難しいこと、定期的な照射が必要であることなどの課題が残っている。これらの課題に対処するため、われわれは、Thを原料とし、高速実験炉「常陽」を使用した長寿命のAc製造戦略の開発に焦点を当てた。照射後の化学処理、ターゲットの可用性、生産収率などについて詳細な調査を実施し、最尤値と関連する不確実性を含めた。その結果、原料の濃縮と長期照射が必要であるものの、Acは現在の世界供給量と同等の量で生産できることが明らかになった。さらに、本研究では、文献調査により、照射後の化学処理において、すでに実用化されているTHOREX法を適用することで、トリウムから核分裂生成物や放射性物質などの副生成物を効果的に分離できることが明らかになった。

Effect of nanoscale cellular structure on the mechanical properties of Inconel 718 with unique hierarchical structure fabricated by laser powder bed fusion

Cho, K.*; 山下 葵平*; 角谷 心之輔*; 齊藤 拓馬*; 佐々木 泰祐*; 澤泉 克彦*; 奥川 将行*; 小泉 雄一郎*; 眞山 剛*; 菊川 泰地*; et al.

Acta Materialia, 303, p.121696_1 - 121696_18, 2026/01

https://doi.org/10.1016/j.actamat.2025.121696

The deformation behavior and strengthening mechanism of Inconel 718 with a hierarchical structure composed of microscale crystallographic lamellar microstructure (CLM) and nanoscale cellular structure, fabricated by laser powder bed fusion, were clarified via nanoscale microstructural and in-situ neutron diffraction analyses. The CLM is a layered structure parallel to the building direction (BD) and consists of relatively wide main and narrow sub-layers with 110 and 100 orientations, respectively, with respect to BD. This is the first study to demonstrate that the yield stress of the alloys depends strongly on deformation stresses of the sub-layers, even though Schmid factors of the primary slip system for both layers are the same. The sub-layer continues to deform elastically even beyond the micro-yield point of the main layer, which results in the macroscopic strengthening at an early stage of deformation. On the other hand, the cellular structure is formed in both layers, associated with a dendritic cell growth along 100 direction, Nb segregation between the cells and an accumulation of dislocations to decrease a residual stress. The cell boundaries with numerous dislocations and Nb segregation act as a strong barrier to dislocation motion resulting in a stress increase through the Hall-Petch law, even though they are low-angle grain boundaries. The spacing and morphology of the cell boundary depend strongly on fabrication conditions. The optimized cellular structure provides significant strengthening comparable to or greater than that caused by large-angle grain boundaries, thereby increasing the macroscopic strength of the alloys through hardening of the sub-layer.

Development of a new THINC/WLIC method based on a separate evaluation of the geometrical fidelity and the interface sharpness

福田 貴斉; 山下 晋; 吉田 啓之

Journal of Computational Physics, 545, p.114485_1 - 114485_32, 2026/01

https://doi.org/10.1016/j.jcp.2025.114485

本論文では、界面捕獲法の形状再現性と界面のシャープさを別々に定量的に評価する新しいアプローチを提案する。この新しい評価により、既存の界面捕獲法であるTHINC法とTHINC/WLIC法の間の形状再現性と界面のシャープさのトレードオフ関係が明らかになった。このトレードオフ関係の原因を解明し解決することで、THINC法やTHINC/WLIC法と同程度に簡潔なアルゴリズムを採用しながらも、形状再現性と界面のシャープさの両方において高い性能を発揮する新しいTHINC法ベースのスキームを開発した。THINC/Advanced WLIC (THINC/AWLIC)法と名付けられたこの新しいスキームは、先行するTHINC/WLIC法の重み関数を、1次風上フラックスの寄与を調整できるように再定義することによって開発された。2次元と3次元の複数のベンチマークテストの結果、THINC/AWLIC法は形状再現性と界面のシャープさの両方の観点で既存のTHINC/WLIC法より優れている。さらに、THINC/AWLIC法のアルゴリズムはTHINC/WLIC法と同様に非常で簡潔であるにもかかわらず、その形状誤差はアルゴリズムが複雑な既存の幾何学的スキームの誤差と同等程度である。

2D iron oxide at the graphene/SiC(0001) interface

榊原 涼太郎*; 寺澤 知潮; 河内 泰三*; 福谷 克之; 伊藤 孝寛*; 乗松 航*

Small Methods, 12 Pages, 2026/00

https://doi.org/10.1002/smtd.202501889

Fabrication of two-dimensional (2D) transition metal oxides has gained considerable attention due to their unique crystal structures and physical properties distinct from their bulk counterparts. Intercalation of foreign elements into the graphene/SiC(0001) interface is a possible approach for achieving this, as it enables the confinement and arrangement of atoms within the 2D interface. However, while various 2D metals and their compounds have been synthesized at the graphene/SiC interface, the fabrication of 2D transition metal compounds remains challenging. This difficulty arises from the high reactivity of transition metals such as Fe, Co, and Ni, which readily form carbides and silicides with the host material. In this work, the successful fabrication of a uniform 2D iron oxide at the graphene/SiC interface is demonstrated through the simultaneous intercalation of Fe and O. Direct observation using atomic-resolution electron microscopy revealed that the crystalline 2D iron oxide is encapsulated by graphene and forms a sharp interface with the SiC substrate. Mssbauer spectroscopy measurements suggest that the 2D iron oxide exhibits a magnetic ordering at low temperatures. These findings suggest another strategy for synthesizing 2D transition metal oxides, opening new avenues for the advancement of 2D magnetic materials.

簡易粘弾性評価モデルを用いた炉内黒鉛構造物の応力挙動の解析的検討

西條 友章; 島崎 洋祐; 石原 正博

JAEA-Technology 2025-010, 126 Pages, 2025/12

JAEA-Technology-2025-010.pdf:12.52MB

HTTR(高温工学試験研究炉)の運転中には、黒鉛構造物に熱応力が発生する。また、黒鉛材料は中性子照射により収縮挙動を示すとともに、クリープ現象が発生するため、原子炉停止時には黒鉛構造物に残留応力が発生する。そこで、HTTR炉心黒鉛構造物の設計においては、有限要素法応力解析コード「VIENUS」を用いた黒鉛構造物の応力解析を行ってきた。HTTRの黒鉛構造物は配置場所によって照射される温度域が400Cから1200Cと大きく異なるため、材料物性値や照射収縮などの照射挙動も黒鉛構造物ごとに異なる。一方、VIENUSコードは熱流動・熱伝導解析結果を解析条件として入力し応力を評価する解析コードであるため、温度条件や材料物性値をパラメータとした検討には向かない。そこで、本報告書ではVIENUSコードよりもパラメータスタディを効率的に実施できる2本のはり要素からなる簡易粘弾性評価モデルを用いて、400Cから1200Cの温度域にある黒鉛構造物の照射挙動が応力挙動に与える影響を解析し、運転時応力は黒鉛構造物の照射収縮の影響により、照射温度800Cを境に2つの異なる挙動を示すことを明らかにした。また、原子炉停止時の残留応力は熱応力に漸近するため、照射収縮が大きくなった場合でも過度に大きくならないことがわかった。さらに、簡易粘弾性評価モデルとVIENUSの応力解析結果を比較した結果、応力挙動の傾向が一致し、簡易粘弾性評価モデルは応力挙動の把握に有用であることが明らかとなった。

Effects of thoron inhalation and cyclosporin A treatment on dextran sulfate sodium-induced oxidative damage in mice

田中 歩*; 直江 翔太*; 竹中 伶樹*; 神崎 訓枝; 迫田 晃弘; 山岡 聖典*; 片岡 隆浩*

Acta Medica Okayama (Internet), 79(6), p.421 - 429, 2025/12

https://doi.org/10.18926/AMO/69844

Radon (Rn) or thoron (Rn, Tn) inhalation enhances the antioxidant activity in some organs. However, the effects of thoron on the colon have not been reported. This study aimed to clarify the effects of thoron inhalation, alone and in combination with Cyclosporin A (CsA), on oxidative stress and colitis induced by dextran sulfate sodium (DSS) in mice. The mice were subjected to 8-day thoron inhalation (c-Tn) or thoron inhalation every other day (f-Tn) at a concentration of 500 Bq/m. The mice were then administered a combination of 3% DSS and CsA or vehicle for 7 d. Although the disease activity index (DAI) reduced significantly by day 2 in the c-Tn group, the score was significantly higher than that in the f-Tn group. Superoxide dismutase activity in the colons of both the c-Tn and f-Tn group mice and catalase activity in the c-Tn group mice were significantly higher than those in the sham groups. These observations suggest that DSS-induced colitis was effectively inhibited in the earlier stages by the c-Tn mode of inhalation than by the f-Tn mode. This could be attributed to the activation of antioxidant functions by c-Tn inhalation. Furthermore, thoron inhalation and CsA treatment showed no combined effects.

Evaluation of interface capturing schemes of VOF method through application to bubble flow with single orifice

福田 貴斉; 山下 晋; 吉田 啓之

Journal of Nuclear Science and Technology, 62(12), p.1264 - 1278, 2025/12

https://doi.org/10.1080/00223131.2025.2581248

この研究では、VOF法に基づく多相流シミュレーションの3つの界面捕捉スキーム(PLIC法、オリジナルTHINC法、THINC/WLIC法)を、気泡体積の保存に焦点を当てて比較検討した。単一気泡流と単孔連続気泡流の解析の結果により、THINC/WLIC法は著しいVOF拡散を示し総気泡体積を過小評価したのに対し、オリジナルTHINC法とPLIC法は気泡の体積を保存することがわかった。また、新しい視覚化アプローチに基づく分析により、THINC/WLIC法ではVOF値の一部が界面周辺のせん断力によって「引き剥がされ」てしまうことが明らかになり、同法は沸騰水型原子炉等での正確なボイド率の予測には適していないことを示した。一方、オリジナルTHINC法は、気泡体積保存の観点では、高い精度で知られるPLIC法の実装が困難である際の代替手法として有効であることが示された。