Residual stress relief effect in gradient structural steel and remaining life evaluation under stochastic fatigue loads

Qin, T. Y.*; Hu, F. F.*; 徐 平光; Zhang, R.*; Su, Y. H.; Ao, N.*; Li, Z. W.*; 篠原 武尚; 菖蒲 敬久; Wu, S. C.*

International Journal of Fatigue, 202, p.109233_1 - 109233_16, 2026/01

https://doi.org/10.1016/j.ijfatigue.2025.109233

The surface induction-hardened S38C medium carbon steel shows a good balance of strength and toughness, but complicates the evaluation of fatigue resistance, mainly because of gradient residual stress (RS) and grains. An integrated fatigue resistance assessment (AIFA) framework was proposed to consider the residual stress relief under stochastic loads. To this end, quasi-in situ neutron diffraction and Bragg-edge imaging were combined to probe the evolution of residual stress during crack propagation. Firstly, a rigid-flexible coupled vehicle dynamics model was adopted to obtain the time-domain variable amplitude loading spectrum. Then, Fortran subroutines were developed to assign these data into full-scale S38C axle model, and the remaining life was predicted using the damage tolerance approach. The results demonstrate that crack propagation would accelerate when residual stress is considered in the case of the crack depth exceeding 3.0 mm. It is, for the first time, found that 15 mm- and 5 mm-thickness fan-shaped specimens can retain the axial and hoop residual strain in terms of diffraction angle variation, respectively, for full-scale structural S38C steel axles. In the absence of RS, the remaining life of the axle decreases sharply from 624,800 to 51,300 km as the crack depth increases from 3.0 to 16 mm. Compared with the standard method under constant amplitude loading without residual stress relief, the present AIFA method provides the more accurate but conservative fatigue life prediction.

大規模イベント等のための核セキュリティ技術開発(共同研究)

高橋 時音; 持丸 貴則*; 小泉 光生; 吉見 優希*; 山西 弘城*; 若林 源一郎*; 伊藤 史哲*

JAEA-Review 2025-039, 34 Pages, 2025/11

JAEA-Review-2025-039.pdf:2.18MB

大規模イベント等において、核・放射性物質を用いたテロ行為を未然に防ぐために、それらの物質を持ち込ませない、あるいは、持ち込まれたとしても迅速に検知し対応するための監視技術の強化が求められている。従来は、イベント会場及びその周辺の要所にゲートモニターを設置し、通過する人や車両等を監視して、不審な物品の持ち込みがないことを確認する手法がとられてきたが、監視をすり抜ける場合を考慮すると、ゲート内のエリアを継続的にサーベイする補完的な技術が必要である。サーベイする領域が広い場合には、移動しながら放射線を測定し、各測定点の放射線量を地図上に記録していく放射線マッピングが有効である。複数の検出器を用いて並行して測定を進め、結果を集約することで、より効率的にサーベイを行うことができる。そこで本技術開発では、屋外で位置情報と放射線を同時に計測できる可搬型検出器を開発し、測定結果をネットワークで集約し、即時にマップ上で確認できる技術の開発を進めた。屋内においては、通過した場所の周辺環境地図を作成するSLAMに放射線測定結果を統合し、3次元地図を作成する技術を開発した。また、核物質を含む中性子源の迅速な検知のために、高速中性子検出器を用いた線源探索技術開発を進めた。本稿では、広域サーベイシステムのコンセプトについて述べるとともに、これまでの技術開発で得られた成果等について報告する。

Re-evaluation of nuclear criticality characteristics for infinite and finite heterogeneous lattice systems composed of uranium-zirconium hydride fuel rods used in the TRIGA annular core pulse reactor NSRR

柳澤 宏司; 求 惟子

JAEA-Research 2025-010, 197 Pages, 2025/11

JAEA-Research-2025-010.pdf:3.5MB

TRIGA燃料棒の臨界リスクの把握とその取扱いの安全対策の検討のため、NSRR燃料棒からなる無限及び有限非均質格子体系の臨界特性を、燃料棒の詳細な計算モデルを用いて再評価した。再評価には、最新バージョンのJENDL-5を含むJENDLライブラリとMVPバージョン3コードが使用された。臨界特性として、無限及び水反射有限体系の中性子増倍率の変化を、格子ピッチと減速材水の密度をパラメータとして詳細に調べた。再評価された臨界特性の結果から、JENDL-5ライブラリを用いて、水反射の六角格子体系の最小臨界燃料棒本数は46.80.2本と得られた。さらに、TRIGA燃料棒には水素化ジルコニウム減速材と黒鉛反射材が備わっているため、減速材及び反射材としての水が存在しない場合の臨界到達可能性を検討した。その結果、水が存在しない場合でも、NSRR標準炉心に装荷されている燃料棒の本数よりも少ない115.70.6本の燃料棒で臨界に到達することが可能であることが分かった。

Measurements of neutron capture cross-sections for nuclides of interest in decommissioning (V); Zr(n, )Zr and Zr(n, )Zr reactions at JRR-3

中村 詔司; 木村 敦; 遠藤 駿典; Rovira Leveroni, G.; 芝原 雄司*

Journal of Nuclear Science and Technology, 14 Pages, 2025/11

https://doi.org/10.1080/00223131.2025.2586632

Decommissioning of nuclear facilities generates a wide variety of wastes in large quantities. To make matters more complicated, they are radioactive wastes due to neutron activation. Thus, the neutron capture cross-sections of decommissioned nuclides are required to evaluate the produced radioactivity. This study selected Zr and Zr nuclides from the nuclides targeted for decommissioning, and aimed to measure the thermal-neutron capture cross-sections of Zr and Zr, which contribute to the production of Zr and Zr, respectively. Considering the relatively small cross-sections of Zr isotopes, measurements were performed by a neutron activation method using the pneumatic tube PN-3 of the Japan Research Reactor-3 (JRR-3) because its thermal-neutron flux is 250 times larger than that of the graphite thermal column of the Kyoto University Research Reactor. A natural Zr foil was irradiated in the PN-3 and subjected to -ray spectrometry. The thermal-neutron capture cross-sections were derived according to Westcott's convention to be 50.90.6 millibarns for the Zr(n,)Zr reaction, and 21.90.3 millibarns for the Zr(n,)Zr reaction. These results are consistent with recent evaluation and experimental data. It was demonstrated that the thermal-neutron capture cross-section of the order of millibarns could be straightforwardly measured by using the PN-3 of JRR-3.

スピンコントラスト変調中性子小角散乱法と反射率法を用いた複合材料のナノ構造解析

熊田 高之

水素科学技術の将来のために, 3(1), p.2 - 6, 2025/10

Spin-contrast variation (SCV) is a technique that exploits the strong dependence of the coherent scattering length of thermal and cold neutrons from protons on their relative spin orientation. By analyzing the proton-polarization dependent scattering of polarized neutrons, SCV enables the elucidation of the structure of individual components as well as the degree of interpenetration between them in composite materials. Recently, we applied SCV small-angle neutron scattering (SCV-SANS) to determine the nanostructure of ice crystals formed in rapidly frozen sugar solutions. We also employed SCV neutron reflectivity (SCV-NR) to reveal the interpenetration between a silane coupling agent layer on inorganic substrates and rubber, which plays a crucial role in their adhesion.

Neutron diffraction-assisted constitutive modeling of directed energy deposited CoCrFeMnNi high entropy alloy

Jeong, S. G.*; Kwon, J.*; Kim, E. S.*; Prasad, K.*; Harjo, S.; Gong, W.; 川崎 卓郎; Estrin, Y.*; Bouaziz, O.*; Hong, S. I.*; et al.

Materials Science & Engineering A, 942, p.148712_1 - 148712_11, 2025/10

https://doi.org/10.1016/j.msea.2025.148712

The cellular structure plays a key role in determining the mechanical properties of metal additive manufacturing (MAM) components. This study presents in situ neutron diffraction and dislocation density-based modeling for a CoCrFeMnNi high-entropy alloy (HEA) made via directed energy deposition (DED). A constitutive model based on the Kocks-Mecking-Estrin framework was used to represent the cellular structure. Parametric analysis showed lower dislocation accumulation and annihilation rates in the as-built sample (with cellular structure) than in the heat-treated one. These differences are linked to dislocation forest networks and local stacking fault energy variations. Dislocation density across cell interiors and walls was also compared with deformation-induced dislocation cells.

Neutron emission during fission and its impact on fission-fragment mass distribution studied by a Langevin model

高木 慎弥*; 原田 壮太*; 有友 嘉浩*; 廣瀬 健太郎; 西尾 勝久

Physical Review C, 112(4), p.044607_1 - 044607_9, 2025/10

https://doi.org/10.1103/ml4c-3k8t

Actinide nucleus shows mass-asymmetric fission in low energy due to shell structure. The fission fragment mass distributions at high energy tend to have a symmetric shape due to smearing of the shell. On the other hand, the distribution can be changed by the neutron emission before fission, as it decreases the excitation energy of fissioning nucleus, thus revives the shell structure. In the so called multichance fission, neutron emission is considered at the ground state shape, and competition between fission and neutron emission is determined in the framework of statistical model. In the present work, we describe fission in the Langevin equations, and the neutron emission is treated all over the fission process. The calculation demonstrated experimentally observed mass distribution, characterized by the peak-to-valley ratio, for wide range of initial compound-nucleus excitation energy up to 60MeV. The results show that, while neutron emission dominates at the ground state shape, it occurs along the shape evolution down to the scission point.

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.

その場中性子回折を用いたSUS310Sステンレス鋼の水素添加による強さ・伸び向上メカニズムの解明

伊東 達矢; 小川 祐平*; Gong, W.; Mao, W.*; 川崎 卓郎; 岡田 和歩*; 柴田 曉伸*; Harjo, S.

波紋, 35(3), p.129 - 133, 2025/08

Recent studies have shown that the addition of hydrogen to SUS310S stainless steel (Fe-24Cr-19Ni, mass%) simultaneously enhances both strength and ductility, indicating a phenomenon contrary to the conventional understanding of hydrogen embrittlement. In this study, we investigated the underlying mechanism through neutron diffraction experiments during tensile deformation using TAKUMI at the MLF of J-PARC. The results revealed that solid-solution strengthening by hydrogen plays the most significant role in improving the mechanical properties. Solute hydrogen atoms distort the lattice to suppress dislocation motion, thereby increasing the strength. The raised stress in the hydrogen charged sample enables the onset of deformation twinning at a smaller strain compared to the non-hydrogen charged sample. Consequently, the twinning-induced plasticity effect contributes more significantly to work hardening and the improvement of uniform elongation due to the solid-solution strengthening by hydrogen. These findings suggest a new pathway for the effective utilization of hydrogen in austenitic steels.

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.