Diffusion and sorption of Cs in the mudstone matrix at the Horonobe URL; Comparative experimental and modeling analysis between in situ and laboratory conditions

武田 匡樹; 大野 宏和; 伊藤 剛志*; 四辻 健治*; 深津 勇太; 佐藤 智文*; 舘 幸男

Journal of Nuclear Science and Technology, 63(9), p.1071 - 1085, 2026/09

https://doi.org/10.1080/00223131.2026.2659269

Diffusion and sorption of radionuclides in potential host rocks are key processes controlling the safe geological disposal of radioactive waste. To set reliable parameters of diffusion and sorption relevant to safety assessment, it is necessary to understand these processes under laboratory and in situ conditions, and to confirm the consistency or the relationship of these parameters (e and d) between both conditions. This paper focused on comparative experiments and modeling of diffusion and sorption of Cs for both in situ and laboratory conditions in siliceous mudstone in 350 m Gallery at the Horonobe Underground Research Laboratory (URL) in northern Hokkaido, Japan. The e values for Cs were consistent between in situ and laboratory results, indicating typical cation excess and porewater salinity effects. The effect of the diffusion direction, parallel or perpendicular to the bedding plane was not significant. The d values for Cs were also consistent between in situ and laboratory results, indicating the porewater salinity effect. The clay-based modeling approach, which considers the major contributions of clay minerals through cation excess diffusion by electrostatic interaction at the clay surface, and the component additive cation exchange reactions, could interpret the diffusion and sorption behavior of Cs under different salinity conditions and for both in situ and laboratory conditions.

Superior TRIP effect in a duplex stainless steel and its mechanism studied by neutron diffraction experiments

土田 紀之*; 藤田 晃徳*; 平川 直樹*; 濱田 純一*; 石丸 栄一郎*; Gong, W.; 川崎 卓郎; Harjo, S.

Materials Characterization, 236, p.116436_1 - 116436_13, 2026/06

https://doi.org/10.1016/j.matchar.2026.116436

This study investigated the transformation-induced plasticity (TRIP) effect in duplex stainless steel (DSS), focusing on the influence of deformation temperature on the mechanical properties of 24Cr-5Ni-0.18N DSS. The steel showed an excellent balance of tensile strength and uniform elongation below 183 K due to deformation-induced martensitic transformation (DIMT) of the austenite () phase. The superior TRIP effect was attributed not only to DIMT and enhanced stress and work hardening at lower temperatures, but also to changes in phase interactions and texture evolution. DIMT suppressed crystal rotation, altered stress partitioning among constituent phases, and weakened the texture of the and ' phases. In JIS-SUS329J4L, phase stress, work hardening, and KAM values increased with decreasing temperature, while the texture weakened.

International benchmark on radionuclide solubility and speciation for the Long-term In-situ Test (LIT) at Grimsel Test Site (GTS, Switzerland)

Noseck, U.*; Schfer, T.*; Alonso, U.*; 浜本 貴史*; Havlova, V.*; Hibberd, R.*; 石寺 孝充; 北村 暁; Klajmon, M.*; Missana, T.*; et al.

Applied Geochemistry, 201, p.106762_1 - 106762_23, 2026/04

https://doi.org/10.1016/j.apgeochem.2026.106762

グリムゼル試験場(GTS)での長期原位置試験(LIT)および対応するモックアップ実験において、地球化学的条件が変化する環境でのSe(VI)、Tc(VII)、U(VI)、Np(V)、Am(III)、Th(IV)およびPu(IV)の挙動をより深く理解するために、熱力学ベンチマーク計算を実施した。本計算では、これらの元素の地球化学的な溶存状態評価モデルとデータベースの状況を確認することも目的としている。これらの実験は、結晶質岩石中に設置されたベントナイト人工バリアを含む放射性廃棄物処分場概念における廃棄体近傍の場をシミュレートしており、その知見は放射性廃棄物処分場の長期安全性評価に貢献する。

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.

水中での放射線測定技術の開発(ROV、PSF)

越智 康太郎

環境創造センター調査研究成果報告書; 平成27年度(2015)令和6年度(2024)(インターネット), P. 24, 2025/10

ダム湖やため池に蓄積したCs及びCs(放射性セシウム)の分布を評価する際には、底質試料の採取が必要だが、試料の前処理や放射能測定に時間がかかり、広域の分布評価が煩雑であった。本研究では、水底における放射性セシウム分布を迅速に評価するためのin-situ測定手法を開発した。従来の底質試料の採取と放射能測定では、ダム湖で30地点の底質試料中放射性セシウムインベントリーを評価する際に、20日程度時間がかかっていた。無人潜水艦(ROV)によるin-situ測定では、4日間で評価を完了したため、広域の放射性セシウムインベントリー分布を迅速に評価することが可能となった。ため池では、ダム湖に比べて水底の起伏が大きいことから、形状を任意に変更可能なプラスチックシンチレーションファイバー(PSF)を適用することで、複雑な地形の放射性セシウム濃度分布を迅速に評価できるか検討した。PSFにより網羅的にため池全体を迅速に測定することが可能となり、浚渫が必要な放射性セシウム濃度が高い場所を迅速に把握できた。

Enhanced work hardening in ferrite and austenite of duplex stainless steel at 200 K; neutron diffraction study

山下 享介*; 古賀 紀光*; Mao, W.*; Gong, W.; 川崎 卓郎; Harjo, S.; 藤井 英俊*; 梅澤 修*

Materials Science & Engineering A, 941, p.148602_1 - 148602_11, 2025/09

https://doi.org/10.1016/j.msea.2025.148602

Ferrite-austenite duplex stainless steels offer excellent strength and ductility, making them suitable for extreme environments. In this study, neutron diffraction during tensile testing at 293 K and 200 K was used to investigate stress partitioning and phase-specific deformation. Phase stress was calculated using a texture-compensated method. At both temperatures, ferrite showed higher phase stress than austenite, acting as the harder phase. At 200 K, both phases exhibited increased strength and work hardening. Austenite showed significant stacking fault formation alongside dislocation migration, while ferrite retained its dislocation-based deformation mode, becoming more effective. Stress contributions from both phases were comparable. No martensitic transformation occurred. Strengthening and enhanced work hardening in both phases led to high strength at 200 K, with ductility similar to that at 293 K.

Change in dislocation density via ausforming in Fe-5%Mn-C alloy with lath martensitic structure

高梨 美咲*; 日高 僚太*; 大久保 亘太*; 増村 拓朗*; 土山 聡宏*; 諸岡 聡; 前田 拓也*; 中村 修一*; 植森 龍治*

ISIJ International, 65(9), p.1384 - 1393, 2025/08

https://doi.org/10.2355/isijinternational.ISIJINT-2025-090

This study investigates the strengthening mechanism of ausforming in martensitic steels, focusing on the role of dislocation inheritance from austenite. By analyzing Fe-5%Mn-C alloys, the researchers quantified dislocation densities before and after ausforming and examined how carbon content affects hardening. Results show that both hardness and dislocation density of ausformed martensite increase with greater deformation in austenite and higher carbon content. The findings support that ausforming strengthens martensite through dislocation accumulation, consistent with the Bailey-Hirsch relationship. neutron diffraction revealed that dislocation inheritance occurs only in steels with sufficient carbon, while additional dislocations are introduced during martensitic transformation.

幌延国際共同プロジェクトの現状と今後の展開

青柳 和平; 尾崎 裕介; 早野 明; 大野 宏和; 舘 幸男

日本原子力学会誌ATOMO, 67(6), p.354 - 358, 2025/06

https://doi.org/10.3327/jaesjb.67.6_354

日本原子力研究開発機構は、幌延深地層研究センターの地下施設を活用した"幌延国際共同プロジェクト(Horonobe International Project: HIP)"を開始した。本プロジェクトの主要な目的は、地層処分のための先進的な安全評価技術や工学技術に関わる研究開発の成果の最大化や、次世代の研究者や技術者の育成と知識の継承である。本解説では、日本原子力学会2024年秋の大会におけるバックエンド部会の企画セッション"幌延国際共同プロジェクトの現状と今後の展開"の流れに沿って、本プロジェクトの概要を紹介する。

Experimental investigation of phase transformations in steel using X-ray and neutron diffraction

友田 陽*; Harjo, S.; 徐 平光; 諸岡 聡; Gong, W.; Wang, Y.*

Metals, 15(6), p.610_1 - 610_19, 2025/05

https://doi.org/10.3390/met15060610

Lattice parameters of product and matrix phases in steels have been measured using in situ X-ray and neutron diffraction during forward and reverse transformations. These parameters are influenced by temperature, transformation-induced internal stresses, alloying element partitioning, crystal defects, and magnetic strains. Disentangling these contributions is essential for understanding lattice behavior. This review explores internal strain (stress) associated with ferrite, pearlite, bainite, martensite, and reverse austenite transformations, emphasizing the distinction between diffusional and displacive mechanisms. It also examines how plastic deformation of austenite affects subsequent bainite or martensite formation. The roles of dislocations and vacancies are identified as critical areas for further research.

Modeling of coupled processes in full-scale engineered barrier system performance experiment at Horonobe Underground Research Laboratory, Japan

大野 宏和; 高山 裕介*

Geomechanics for Energy and the Environment, 41, p.100636_1 - 100636_14, 2025/03

https://doi.org/10.1016/j.gete.2025.100636

In the geological disposal of high-level radioactive waste, the overpack lifetime and initial conditions of radionuclide migration are essential considerations along with the assessments of the environmental conditions, including study of the evolution of near-field thermal, hydrological, mechanical, and chemical processes following the emplacement of an engineered barrier system. In this study, experimental data from an in situ full-scale engineered barrier experiment at Horonobe Underground Research Laboratory were used to assess the applicability of a simulation model to evaluate near-field coupled processes.