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Park, M.-H.*; 柴田 曉伸*; Harjo, S.; 辻 伸泰*
Acta Materialia, 292, p.121061_1 - 121061_13, 2025/06
被引用回数：1 パーセンタイル：79.44(Materials Science, Multidisciplinary)Dual-phase (DP) steel, composed of soft ferrite and hard martensite, offers excellent strength-ductility balance and low cost. This study found that refining the DP microstructure enhanced both yield strength and strain hardening, improving strength and ductility. Digital image correlation (DIC) revealed strain localization in ferrite, but refinement reduced strain differences between ferrite and martensite, suppressing crack initiation. More ferrite/martensite interfaces promoted plasticity in martensite via enhanced deformation constraint. 
neutron diffraction showed martensite bore higher phase stress, which increased with refinement. By combining 
-DIC and neutron data, individual stress-strain curves for ferrite and martensite were constructed for the first time, explaining the strength-ductility synergy through interphase constraint. These findings offer guidance for designing heterostructured materials to overcome the strength-ductility trade-off.
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
被引用回数：0 パーセンタイル：0.00Lattice 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.
林崎 康平; 廣岡 瞬; 山田 忠久*; 砂押 剛雄*; 村上 龍敏; 齋藤 浩介
Ceramics (Internet), 8(1), p.24_1 - 24_12, 2025/03
Zirconolite is a wasteform that can immobilize Pu. Herein, zirconolites comprising Ce as a Pu simulant and Al as a charge compensator of Ce/Pu were synthesized by sintering raw CaO, ZrO
, TiO, CeO, and AlO
powder mixtures at 1400
C in static air. The reduction behavior and phase transformation of zirconolites during their heat treatment in an Ar-H gas flow were investigated. All zirconolite compositions first underwent reduction at 
1050C by forming a small domain of perovskite phase. Ce-Al co-doped zirconolite showed a smaller fraction of phase transformation in perovskite than Ce-doped zirconolite, indicating the advantage of using a charge compensator to prevent perovskite formation.
Kim, M.*; Lee, C.*; 杉田 裕; Kim, J.-S.*; Jeon, M.-K.*
Geomechanics for Energy and the Environment, 41, p.100628_1 - 100628_9, 2025/03
被引用回数：1 パーセンタイル：81.46(Energy & Fuels)この研究では、DECOVALEX-2023プロジェクトの一環として幌延の地下研究施設で実施された実規模大の人工バリア試験の数値解析を使用して、非等温二相流のモデリングに対する主要変数の選択の影響を調査した。検証済みの数値モデルを使用して、人工バリアシステム内の不均質多孔質媒体の熱-水連成挙動を解析した。支配方程式を離散化する際の2つの異なる主要変数スキームを比較したところ、結果に大きな違いがあることが明らかになった。
北條 智彦*; 小山 元道*; 熊井 麦弥*; Zhou, Y.*; 柴山 由樹; 城 鮎美*; 菖蒲 敬久; 齋藤 寛之*; 味戸 沙耶*; 秋山 英二*
ISIJ International, 65(2), p.284 - 296, 2025/02
被引用回数：0Stress and plastic strain distributions and those partitioning behaviors of ferrite and retained austenite were investigated in the medium manganese (Mn) and the transformation-induced plasticity-aided bainitic ferrite (TBF) steels, and the martensitic transformation behaviors of retained austenite during Luders elongation and work hardening were analyzed using synchrotron X-ray diffraction at SPring-8. The stress and plastic strain of retained austenite and volume fraction of retained austenite were remarkably changed during Luders deformation in the medium Mn steel, implying that the medium Mn steel possessed inhomogeneous deformation at the parallel part of the tensile specimen. On the other hand, the distributions of the stress, plastic strain and volume fraction of retained austenite were homogeneous and the homogeneous deformation occurred at the parallel part of the tensile specimen at the plastic deformation regime with work hardening in the medium Mn and TBF steels. The martensitic transformation of retained austenite at uders deformation in the medium Mn steel was possessed owing to the application of high stress and preferential deformation at retained austenite, resulting in a significant increase in the plastic deformation and reduction of stress in the retained austenite. The martensitic transformation of retained austenite at the plastic deformation regime with work hardening was induced by the high dislocation density and newly applied plastic deformation in retained austenite in the medium Mn steel whereas the TBF steel possessed gradual transformation of retained austenite which is applied high tensile stress and moderate plastic deformation.
Se concentration in concrete rubbleBanjarnahor, I. M.; Do, V. K.; 古瀬 貴広; 太田 祐貴; 田中 康介
Journal of Radioanalytical and Nuclear Chemistry, 10 Pages, 2025/00
Se has been conventionally measured via radiometry. However, measuring Se this way is difficult due to its low specific radioactivity. Moreover, the measurement is time-consuming and susceptible to the radioactive interferences from highly radioactive nuclides (
Sr, 
Cs, etc.) coexisting in the samples. ICP-MS/MS is widely known as a powerful technique to quantify difficult-to-measure radionuclides, which can effectively eliminate the interferences using a collision/reaction cell. In this research, a novel HCl-free chemical separation method was developed for separating Se from concrete matrices, followed by the selective measurement of Se concentration via ICP-MS/MS. Se was purified by stepwise chemical separation using anion exchange resin and activated alumina. The separation condition was optimized and evaluated. The chemical recovery of 
85% was achieved. Se concentration was determined via ICP-MS/MS at m/z = 79 using ammonia gas as the reaction gas, and possible interferences such as those from the Br isobar and argon gas were effectively mitigated. A method limit of detection of 0.1 Bq g
was achieved for the concrete rubble samples, making it a reliable tool for determining Se concentrations in concrete rubble collected from the Fukushima Daiichi Nuclear Power Station.
上澤 伸一郎; 吉田 啓之
Journal of Nuclear Science and Technology, 61(11), p.1438 - 1452, 2024/11
被引用回数：0 パーセンタイル：0.00(Nuclear Science & Technology)本研究では、重なり合う気泡の中から個々の気泡を検出・分割するために、Shifted window Transformer (Swin Transformer)を用いた深層学習ベースの気泡検出器を開発した。検出器の性能を検証するため、学習画像数を変えて平均適合率(AP)を計算した。APは、訓練画像の数が50枚以下の場合は、トレーニング画像の数の増加とともに増加したが、50枚を超える場合は一定であった。50枚以上ではSwin Transformerと一般的なCNNであるResNetのAPはほぼ同じであったが、学習画像が少ない場合はSwin TransformerのAPがResNetのAPを上回った。また、ボイド率が増加すると、Swin TransformerのAPはResNetの場合と同様の減少を示したものの、学習画像が少ない場合はSwin TransformerのAPが全てのボイド率においてResNetのAPを上回った。さらに、合成気泡画像で学習した検出器で、気泡流可視化実験の重なった気泡や変形気泡の検出が可能であることを確認した。このように、Swin Transformerを用いた新しい気泡検出器は、ResNetを用いた検出器よりも少ない学習画像で高いAPを得られることが確認された。
Brear, D. J.*; 近藤 悟; 曽我部 丞司; 飛田 吉春*; 神山 健司
JAEA-Research 2024-009, 134 Pages, 2024/10
JAEA-Research-2024-009.pdf:2.45MB
SIMMER-III/SIMMER-IVは液体金属高速炉の炉心崩壊事故(CDA)の解析に使用する計算コードである。CDAの事象進展は炉心物質間の熱伝達係数(HTC)により大きく影響される。溶融・固化、蒸発・凝縮といった質量移行現象も熱伝達により支配される。複雑な多相・多成分系においては、一つの流体成分と他の流体又は構造材表面との間での多数の異なるHTCを計算する必要がある。また、多相流の流動様式や構造材の配位に従って異なる伝熱モードを考慮する必要もある。結果として、各計算セルごとに数十のHTCが計算される。本報告書には、SIMMER-III/SIMMER-IVのHTCモデルの役割、選定したHTC相関式とその技術的背景、流動様式の取扱いとHTCの内挿方法、検証及び妥当性確認の成果概要を記載する。
Vauchy, R.; 廣岡 瞬; 堀井 雄太; 小笠原 誠洋*; 砂押 剛雄*; 山田 忠久*; 田村 哲也*; 村上 龍敏
Journal of Nuclear Materials, 599, p.155233_1 - 155233_11, 2024/10
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)U
Pu
O
(y=0.30および0.45)およびPuOにおける蛍石の溶出/再結合は、示差走査熱量測定を使用して調査された。結果は、プルトニアを除いて、文献データと比較的よく一致している。我々の値は、Pu-Oの混和ギャップの臨界温度が以前に報告されたものより3050K低いことを示している。最後に、体系的な実験手順により、低化学量論的U
0Pu
O、U
Pu
O、およびPuO二酸化物に存在するソルバスの軌跡を精密化することができた。
曽我部 丞司; 石田 真也; 田上 浩孝; 岡野 靖; 神山 健司; 小野田 雄一; 松場 賢一; 山野 秀将; 久保 重信; 久保田 龍三朗*; et al.
Proceedings of International Conference on Nuclear Fuel Cycle (GLOBAL2024) (Internet), 4 Pages, 2024/10
日仏協力の枠組みにおいて、タンク型ナトリウム冷却高速を対象とした過酷事故の評価手法を定義し、解析評価を実施した。
福田 貴斉; 山下 晋; 吉田 啓之
Proceedings of 14th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation, and Safety (NTHOS-14) (Internet), 12 Pages, 2024/08
VOF法は移流界面を含む混相流解析に最も広く適用されているCFDの一種であり、高精度なVOF値の移流のために数多くの「界面捕獲スキーム」が開発されている。しかし、これらのスキームの性能は典型的に、空間的に規則的な速度場が時間固定された限られた数値問題に対してのみ評価されており、原子炉内の気液二相流などのより現実的で複雑な条件に対してこれらのスキームの性能を評価する研究はほとんど実施されていない。そこで本研究では、比較的近年開発されたTHINCおよびTHINC/WLICという界面捕捉スキームを用いて気泡流の3次元解析を実施し、その結果を、炉内ボイド率分布に影響するような気泡の数、体積、軌跡といったより工学的な指標を用いて評価する。これらの比較の結果は、界面捕獲スキームの選択によってはVOF値が著しく拡散し、気泡が数値的に分裂・消散する可能性を示した。
Harjo, S.; Gong, W.; 相澤 一也; 山崎 倫昭*; 川崎 卓郎
日本材料学会第58回X線材料強度に関するシンポジウム講演論文集, p.58 - 60, 2024/07
The experiment and analysis procedures for a sample exhibiting multimodal structures were outlined. The sample, a Mg
Zn
Y
alloy, initially comprised two phases: the HCP 
matrix (Mg) and the long-period stacking ordered phase (LPSO), constituting approximately 25% of the volume. Through hot extrusion at 623 K with an extrusion ratio (R) of 5.0, the alloy was rendered multimodal. Specifically, at an R value of 5.0, dynamic recrystallization occurred partially within the Mg phase, resulting in a bimodal microstructure. This microstructure consisted of a deformed Mg component and a recrystallized Mg component. An analysis employing Electron Backscatter Diffraction (EBSD) data facilitated multimodal characterization, enabling successful determination of stresses within the individual Mg components, as well as the LPSO phase stress.
Harjo, S.
Isotope News, (793), p.13 - 16, 2024/06
高強度マグネシウム(Mg)合金の高温押出加工による大幅な強度増加の機構を引張変形その場中性子回折実験によってどのように解明したかについて紹介する。高温押出加工の条件により組織が複雑化し、構成相それぞれの組織からの強度への寄与について解説する。
小野 綾子; 岡本 薫*; 牧野 泰*; 細川 茂雄*; 吉田 啓之
Proceedings of Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal-Hydraulics and Severe Accidents (SWINTH-2024) (USB Flash Drive), 13 Pages, 2024/06
原子力機構では、先進的な核熱連成解析コードの開発を進めている。連成解析コードでは、界面捕捉法に基づく詳細熱流動解析コード(JUPITER又はTPFIT)を採用し、燃料バンドル内の熱流動解析を行う。JUPITER/TPFITの妥当性確認のためには、燃料バンドル内の二相流に関する実験データや知見が必要である。本研究では、レーザードップラー流速計とフォトダイオードを組合せた気泡流計測手法を開発し、計測の妥当性については導電プローブを用いた計測により確認した。そして、模擬燃料集合体サブチャンネルなどの狭隘流路における気泡流計測に適用し、燃料バンドル内の気泡挙動および流速データを取得した。
石田 真也; 深野 義隆; 飛田 吉春; 岡野 靖
Journal of Nuclear Science and Technology, 61(5), p.582 - 594, 2024/05
被引用回数：1 パーセンタイル：22.00(Nuclear Science & Technology)To improve the safety of future SFRs, the development of SFRs with low void reactivity has been promoted. Small SFRs can have a negative void coefficient of reactivity, so the analysis of the CDA event sequence in small SFRs is valuable for the investigation of the reactor characteristics for the future research and development of SFRs. In this study, the typical initiating events of a CDA in small SFRs were evaluated with the computational code, SAS4A. The event progression of ULOF and UTOP in the low void reactivity reactor is found to be slow due to the effective operation of the negative reactivity feedback and the absence of significant positive reactivity insertion. No power excursion occurs in the initiating phase. In ULOF, the cladding melt and relocation behavior becomes more important for the evaluation of the event progression due to its positive reactivity.
Li, X.*; Zhu, R.*; Xin, J.*; Luo, M.*; Shang, S.-L.*; Liu, Z.-K.*; Yin, C.*; 舟越 賢一*; Dippenaar, R. J.*; 肥後 祐司*; et al.
CALPHAD; Computer Coupling of Phase Diagrams and Thermochemistry, 84, p.102641_1 - 102641_6, 2024/03
被引用回数：0 パーセンタイル：0.00(Thermodynamics)The phase transformations and pressure-volume dependencies of the Ti-45Al alloy with respect to pressure have been investigated by means of in-situ observation using multi anvil-type high-pressure devices and synchrotron radiation. Under hydrostatic compression from 0 to 10.1 GPa, about 2.3 vol. % of 
transforms continuously to 2. Lattice parameters as well as volume fractions of these two phases have been determined as a function of pressure. Bulk moduli estimated using Birch-Murnaghan's equation of state are 148 GPa for the phase, 138 GPa for the 2 phase, and 149 GPa for their two-phase mixture of Ti-45Al alloy. First-principles have also applied to investigate bulk moduli of two single phases, and the deviation between calculations and measurements is discussed and attributed to mainly phase transformation. The presently study provides useful insights into thermodynamics of 2 and phases under high pressure.
萩原 幸司*; 眞山 剛*; 山崎 倫昭*; Harjo, S.; 徳永 透子*; 山本 和輝*; 杉田 三佳*; 青山 海琳*; Gong, W.; 西本 宗矢*
International Journal of Plasticity, 173, p.103865_1 - 103865_21, 2024/02
被引用回数：24 パーセンタイル：99.22(Engineering, Mechanical)The unique control mechanisms of the plastic deformation of two-phase extruded alloy composed of Mg and long-period stacking ordered (LPSO) phase were clarified by comparison with those of other Mg solid-solution alloys, focusing on the question of why do the Mg/LPSO two-phase alloys exhibit both large elongation and high strength? The stress-strain curves for each grain in the alloys could be imaginary estimated using neutron diffraction analysis during the tensile test. The results demonstrate that the deformation behaviors of the worked and recrystallized grains are significantly different in all the Mg-extruded alloys owing to the strong plastic anisotropy in Mg with hexagonal close-packed (hcp) structure. Therefore, the deformation behavior is controlled by a composite-like deformation mechanism, even in single-phase Mg solid-solution alloys.
吉田 啓之; 堀口 直樹; 古市 肇*; 上遠野 健一*
Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 7 Pages, 2023/05
About the boiling transition (BT) that determines the maximum thermal output of the BWR, it is considered that the spacers have significant effects on the occurrence of the BT. The occurrence conditions of the BT can be changed by devising the spacer shapes because it will affect to entrainment and deposition behaviors of droplets. In the light water cooled fast reactor: RBWR, thermal-hydraulics conditions are more challenging than in the current BWR. Then, the effect of the spacer on the BT should be sufficiently utilized in the RBWR. In the thermal-hydraulics design for the current BWR, large-scale tests were carried out and used to evaluate BT conditions. The RBWR is still in the design stage, and there is room to be changed to many parameters. Then, it is not reasonable to determine the shape of the spacer only by large-scale tests but also by local effect on droplet entrainment and deposition. On the other hand, by applying a two-phase CFD method with remarkable development in recent years, we can develop a model that can predict the effect of the spacers mechanistically. This research used the detailed two-phase flow simulation code TPFIT developed by JAEA to simulate annular dispersed flow in RBWR subchannels. In the occurrence of the BT, it is considered that the two-phase flow pattern is the annular dispersed flow, and we want to evaluate the effects of the spacer on annular dispersed flow in the RBWR subchannels. We performed numerical simulations of annular dispersed flow in the simplified subchannel of the RBWR. As a simulation parameter, we choose the existence of the spacer. The spacer in the simulation has a simplified shape and the same blockage ratio as the RBWR. In addition, we performed data analysis of numerical data and identified the occurrence and disappearance points of each droplet. We evaluate entrainment and deposition rate distribution in and around the spacer based on these data.
Song, K.*; 伊藤 啓*; 伊藤 大介*; 大平 直也*; 齊藤 泰司*; 松下 健太郎; 江連 俊樹; 田中 正暁
Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 10 Pages, 2023/05
自由表面渦によるガス巻込み現象はナトリウム冷却高速炉の炉出力を擾乱させる原因となり得る。そのため、ナトリウム冷却高速炉の実用的な安全設計のために、ガス巻込み現象によるガス巻込み流量を正確に評価する必要がある。本研究では、ガス巻込み現象の正確な評価のためのCFD解析の適用性について検討することを目的に、吸い込み管を有する円筒容器における自由表面渦およびそれに伴うガス巻込み現象のシミュレーションにCFD解析を適用し、CFD解析結果とガス巻込み現象の実験データとを比較した。その結果、CFD解析結果と実験結果とで吸い込み管内部の二相流形態がよく一致し、かつ自由液面における渦のガスコアの形状もよく一致した。よって、CFD解析によって、自由表面渦によって引き起こされるガス巻込み現象を許容誤差の範囲内で適切かつ正確に予測できることが確認された。
Kwon, H.*; Sathiyamoorthi, P.*; Gangaraju, M. K.*; Zargaran, A.*; Wang, J.*; Heo, Y.-U.*; Harjo, S.; Gong, W.; Lee, B.-J.*; Kim, H. S.*
Acta Materialia, 248, p.118810_1 - 118810_12, 2023/04
被引用回数：54 パーセンタイル：99.37(Materials Science, Multidisciplinary)Maraging steels, known for ultrahigh strength and good fracture toughness, derive their superior properties from lath martensite structure with high-density nanoprecipitates. In this work, we designed a novel Fe-based medium-entropy alloy with a chemical composition of Fe
Co
Ni
Mo
in atomic% by utilizing the characteristics of the maraging steels. By a single-step aging of only 10 min at 650 C, the alloy showed microstructures consisting of a very high number density of (Fe, Co, Ni)
Mo
-type nanoprecipitates in lath martensite structure and reverted FCC phase, which led to ultrahigh yield strength higher than 2 GPa. This work demonstrates a novel direction to produce strong and ductile materials by expanding the horizons of material design with the aid of high-entropy concept and overcoming the limits of conventional materials.
