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CPham V. H.; 倉田 正輝; 永江 勇二; 石橋 良*; 佐々木 政名*
Corrosion Science, 255, p.113098_1 - 113098_9, 2025/10
Being expected as materials for accident tolerant fuel cladding tube, oxidation behavior and kinetics of silicon carbide (SiC) under extreme conditions like severe accidents must be elucidated. In this study, oxidation tests of SiC at 1400-1600 C for 1-5 h, at atmospheric pressure, under two different flow rates of H
O/Ar gas mixture have been conducted to investigate the influence of steam flow rate on the formation of SiO scale and its subsequent volatilization. The oxidation tests were conducted via a newly developed test facility using laser as a heat source. Oxidation kinetics of SiC was evaluated via mass change of samples before and after the oxidation tests. Parabolic oxidation rate representative for SiO formation and linear volatilization rate reflecting its volatilization were calculated, based on these mass changes. The Arrhenius dependence of the parabolic oxidation and linear volatilization rate constants were then plotted. Results of this study indicated that SiC exhibits excellent performance under the conditions investigated. Steam flow rate has a significant influence on volatilization of SiO but has minor effects over its formation. Oxidation of SiC in steam at high temperature may follow mass gain or mass loss regime, depending on the steam flow rate. Two oxidation patterns were suggested and discussed. In the first oxidation pattern, the SiO formation is dominated over its volatilization. The second oxidation pattern (steady stage) is reached when the SiO formation rate is equivalent to its volatilization rate. Time to reach this steady stage was defined, based on the parabolic oxidation rate and linear volatilization rate.
和田 裕貴; 柴本 泰照; 日引 俊詞*
International Journal of Heat and Mass Transfer, 249, p.127219_1 - 127219_16, 2025/10
Two saturated boiling heat transfer correlations for downward flows in vertical circular pipes depending on wall superheat or wall heat flux as input parameters were developed based on a heat transfer experimental database. Owing to the absence of heat transfer correlations specifically developed for downward flows, existing heat transfer correlations for different flow directions were evaluated to determine their applicability to predicting the downward flow heat transfer coefficient. The results revealed that even the most accurate correlation showed a mean absolute percentage error (MAPE) of 66.5%, highlighting the need for improving predictive performance. In response, the downward flow heat transfer correlation was modeled by integrating a nucleate boiling heat transfer term and a forced convection heat transfer term. The Dong-Hibiki correlation, a two-component, two-phase heat transfer correlation for downward flows, was adopted for the forced convection heat transfer term. The Forster-Zuber correlation, developed as a wall superheat function, and the Cooper correlation, developed as a wall heat flux function, were used for the nucleate boiling term to develop the heat transfer correlations where either wall superheat or wall heat flux is known. Notably, the Dong-Hibiki correlation has been validated over a wide range of experimental conditions. A correction factor was applied to the nucleate boiling term to address errors caused by applying Foster-Zuber and Cooper correlations to downward flows. The two developed correlations achieved an MAPE value of approximately 20%, representing an improvement of roughly 40% over existing correlations of heat transfer coefficients.
Luu, V. N.; 谷口 良徳; 宇田川 豊; 勝山 仁哉
Nuclear Engineering and Design, 442, p.114222_1 - 114222_15, 2025/10
For near-term application, coated-Zr alloy claddings show potential for enhancing safety by providing better oxidation resistance and minimizing hydrogen absorption under design-basis accidents (DBA). This benefit could extend the burnup and operational cycles of fuel rods. In assessing safety, reactivity-initiated accidents (RIA) are considered as one of the DBA conditions. The current safety criteria for high-temperature oxidation failure, one of the failure modes linked to RIA, are defined by peak fuel enthalpy values that range from 205 to 270 cal/g. This wide variability presents challenges when attempting to generalize criteria for modified-Zr alloy claddings with superior oxidation resistance. Therefore, it may be more relevant to apply failure criteria based on embrittlement mechanisms, such as oxygen concentration in the 
-Zr phase. This study aimed to assess the failure based on both peak fuel enthalpy and cladding embrittlement by analyzing previous NSRR experiments conducted with conventional materials using the RANNS fuel performance code. The findings suggest that the failure criteria associated with cladding embrittlement can provide a rational evaluation of failure behavior compared to the existing criterion based on peak fuel enthalpy. The local failure criterion leading to the formation of through-wall cracks during quenching is consistent with Chung's proposal (NUREG/CR-1344): -Zr thickness of 
0.9 wt% oxygen is less than 0.1 mm, and this corresponds to approximately 35% BJ-ECR.
望月 陽人; 松井 裕哉; 中山 雅; 坂本 亮*; 柴田 真仁*; 本島 貴之*; 城 まゆみ*
Case Studies in Construction Materials, 22, p.e04648_1 - e04648_20, 2025/07
被引用回数：0放射性廃棄物の地層処分で使用される低アルカリ性セメントは、長期にわたる処分場の操業期間中に大気中の二酸化炭素による炭酸化や地下水との接触によってその特性が変化する可能性がある。本研究では、フライアッシュとシリカヒュームを混合した低アルカリ性セメント(HFSC)を用いた吹付けコンクリートの化学的特性、微細構造ならびに輸送特性に対して大気中での炭酸化および地下水との接触が与える影響を、幌延の地下研究施設において16年間にわたり調査した。HFSC吹付けコンクリートの炭酸化領域と溶出領域のいずれにおいても、直径約300nm未満の細孔の毛細管空隙率が増加し、全空隙率は非変質領域よりも高くなった。これらの空隙構造の変化は、ケイ酸カルシウム水和物(C-S-H)の脱灰とエトリンガイトの分解に関連していると考えられる。このような変化は、OPC吹付けコンクリートの変質領域では軽微であったことから、本研究の調査条件下において、HFSC吹付けコンクリートは炭酸化や地下水溶出に対する抵抗性が相対的に低いことが示された。しかしながら、HFSCの透水係数は、地層処分に用いられる低pHセメントに求められる機能要件を満たす程度に低かった。
Gu, G. H.*; Jeong, S. G.*; Heo, Y.-U.*; Harjo, S.; Gong, W.; Cho, J.*; Kim, H. S.*; 他4名*
Journal of Materials Science & Technology, 223, p.308 - 324, 2025/07
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)Face-centered cubic (FCC) equi-atomic multi-principal element alloys (MPEAs) exhibit excellent mechanical properties from cryogenic to room temperatures. At room temperature, deformation is dominated by dislocation slip, while at cryogenic temperatures (CTs), reduced stacking fault energy enhances strain hardening with twinning. This study uses in-situ neutron diffraction to analyze the temperature-dependent deformation behavior of Al
(CoNiV)
, a dual-phase (FCC/BCC) medium-entropy alloy (MEA). At liquid nitrogen temperature (LNT), deformation twinning in the FCC matrix leads to additional strain hardening through the dynamic Hall-Petch effect, giving the appearance of improved strengthening at LNT. In contrast, BCC precipitates show dislocation slip at both 77 K and 298 K, with temperature-dependent lattice friction stress playing a significant role in strengthening. The study enhances understanding of deformation behaviors and provides insights for future alloy design.
Hamdani, A.; 相馬 秀; 安部 諭; 柴本 泰照
Progress in Nuclear Energy, 185, p.105771_1 - 105771_13, 2025/07
被引用回数：0 パーセンタイル：0.00(Nuclear Science & Technology)This study, motivated by previous TEPSYS analysis, examined how different temperatures on the 4th and 5th floors of the Fukushima Daiichi Unit 3 reactor building (R/B) influenced non-condensable gas distribution during the 2011 severe accident. Understanding this is vital for assessing risks related to gas accumulation, especially since the hydrogen explosion may have involved multiple stages. An experimental study was conducted using the CIGMA facility, designed to mimic the R/B structure, where steam and helium (as a substitute for hydrogen) were injected for 10,000 seconds to simulate leakage. Two cooling conditions were tested: 50C (Case 1) and 90C (Case 2). Results showed that the highest concentration of non-condensable gases was often found downstream rather than near the injection point. In Case 1, after 10,000 seconds, helium concentration reached 65% in the middle region (4th floor) and 45% in the top region (5th floor). Analysis indicated that the gas mixture in the middle region posed a potential detonation risk. This study offers crucial insights for enhancing safety measures and risk mitigation strategies in nuclear reactor designs.
Mao, W.*; Gong, W.; 川崎 卓郎; Gao, S.*; 伊東 達矢; 山下 享介*; Harjo, S.; Zhao, L.*; Wang, Q.*
Scripta Materialia, 264, p.116726_1 - 116726_6, 2025/07
被引用回数：0An ultrafine-grained 304 austenitic stainless steel exhibited pronounced serrated Luders deformation at 20 K, with stress and temperature oscillations reaching 200 MPa and 20 K. 
neutron diffraction and digital image correlation revealed discontinuous Luders band propagation and burst martensite formation. During deformation, austenite phase stress remained lower than at upper yielding, indicating elastic behavior. Notably, martensite phase stress stayed lower than austenite until fracture, likely due to stress relaxation from burst martensitic transformation at 20 K. The low martensite stress delayed brittle fracture until austenite plastically yielded during uniform deformation.
廃炉環境国際共同研究センター; 東京大学*
JAEA-Review 2025-001, 94 Pages, 2025/06
JAEA-Review-2025-001.pdf:6.21MB
日本原子力研究開発機構(JAEA)廃炉環境国際共同研究センター(CLADS)では、令和5年度英知を結集した原子力科学技術・人材育成推進事業(以下、「本事業」という。)を実施している。本事業は、東京電力ホールディングス株式会社福島第一原子力発電所の廃炉等をはじめとした原子力分野の課題解決に貢献するため、国内外の英知を結集し、様々な分野の知見や経験を、従前の機関や分野の壁を越えて緊密に融合・連携させた基礎的・基盤的研究及び人材育成を推進することを目的としている。平成30年度の新規採択課題から実施主体を文部科学省からJAEAに移行することで、JAEAとアカデミアとの連携を強化し、廃炉に資する中長期的な研究開発・人材育成をより安定的かつ継続的に実施する体制を構築した。本研究は、令和元年度に採択された研究課題のうち、「燃料デブリ取り出し時における炉内状況把握のための遠隔技術に関する研究人材育成」の令和元年度から令和5年度分の研究成果について取りまとめたものである。本研究は、燃料デブリ取り出し時における炉内状況把握のためのモニタリングプラットフォームの構築及びプラットフォーム上を移動するセンサによる計測・可視化に関する研究開発を行う。また、このような研究課題に参画することによる研究教育、講義等の座学、施設見学の3つの柱で研究人材を育成することを目的とする。令和5年度は、各システムの検証とともに、模擬環境においてモニタリングプラットフォーム上の移動カメラから取得された画像を用いて立体復元モデルを生成し、可視化対象に対して最適視点からの映像提示が可能であることを、各研究項目協力のもと統合実験として実施した。
吉田 一雄; 桧山 美奈*; 玉置 等史
JAEA-Research 2025-003, 24 Pages, 2025/06
JAEA-Research-2025-003.pdf:2.06MB
再処理施設の過酷事故の一つである高レベル放射性廃液貯槽の冷却機能喪失による蒸発乾固事故では、沸騰により廃液貯槽から発生する硝酸-水混合蒸気とともにルテニウム(RuO
)の揮発性の化学種が放出される。このためリスク評価の観点からは、Ruの定量的な放出量の評価が重要な課題である。揮発性Ruは施設内を移行する過程で床面に停留するプール水中の亜硝酸によって化学吸収が促進されることが想定され、施設内の硝酸-水混合蒸気の凝縮水量がRuの施設内での移行に重要な役割を担う。当該事故の施設内の熱流動解析では、水の熱流動を解析対象とするMELCORコードを用いている。解析では、凝縮の支配因子である蒸発潜熱が、事故時での施設内の温度帯域で同程度であることから硝酸をモル数が等しい水として扱っている。本報では、この解析モデルの妥当性を確認するために、MELCORの制御関数機能を用いて硝酸-水混合蒸気を水蒸気で近似することによって生じる誤差を補正する解析モデルを作成し解析を実施し補正効果を比較することで従来の解析モデルの妥当性を確認した。その結果、補正解析モデルの適用によって各区画のプール水量の分布は変化するものの施設内のプール水量の総和には影響しないことを確認した。
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：1Dual-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.
杉田 裕; 大野 宏和; Beese, S.*; Pan, P.*; Kim, M.*; Lee, C.*; Jove-Colon, C.*; Lopez, C. M.*; Liang, S.-Y.*
Geomechanics for Energy and the Environment, 42, p.100668_1 - 100668_21, 2025/06
国際共同プロジェクトDECOVALEX-2023は、数値解析を使用してベントナイト系人工バリアの熱-水-応力(または熱-水)相互作用を研究するためのタスクDとして、幌延人工バリア性能確認試験を対象とした。このタスクは、モデル化のために、1つの実物大の原位置試験と、補完的な4つの室内試験が選択された。幌延人工バリア性能確認試験は、人工的な地下水注入と組み合わせた温度制御非等温の試験であり、加熱フェーズと冷却フェーズで構成されている。6つの研究チームが、さまざまなコンピューターコード、定式化、構成法則を使用して、熱-水-応力または熱-水(研究チームのアプローチによって異なる)数値解析を実行した。
Birkholzer, J. T.*; Graupner, B. J.*; Harrington, J.*; Jayne, R.*; Kolditz, O.*; Kuhlman, K. L.*; LaForce, T.*; Leone, R. C.*; Mariner, P. E.*; McDermott, C.*; et al.
Geomechanics for Energy and the Environment, 42, p.100685_1 - 100685_17, 2025/06
The DECOVALEX initiative is an international research collaboration (www.decovalex.org), initiated in 1992, for advancing the understanding and modeling of coupled thermo-hydro-mechanical-chemical (THMC) processes in geological systems. DECOVALEX stands for "DEvelopment of COupled Models and VALidation against EXperiments". DECOVALEX emphasizes joint analysis and comparative modeling of the complex perturbations and coupled processes in geologic repositories and how these impact long-term performance predictions. More than fifty research teams associated with 17 international DECOVALEX partner organizations participated in the comparative evaluation of eight modeling tasks covering a wide range of spatial and temporal scales, geological formations, and coupled processes. This Virtual Special Issue on DECOVALEX-2023 provides an in-depth overview of these collaborative research efforts and how these have advanced the state-of-the-art of understanding and modeling coupled THMC processes. While primarily focused on radioactive waste, much of the work included here has wider application to many geoengineering topics.
武井 早憲
Journal of Nuclear Science and Technology, 45 Pages, 2025/06
日本原子力研究開発機構では、マイナーアクチニドを効率的に核変換する加速器駆動核変換システム(ADS)の研究開発を行っている。このシステムは、未臨界炉と大強度超伝導陽子線形加速器(ADS用陽子加速器)の組み合わせである。ADS用陽子加速器の開発を困難にしている要因の一つは、熱サイクル疲労を誘因するビームトリップ事象であり、この事象によって未臨界炉の機器が損傷するからである。ADS用陽子加速器は大強度陽子加速器の一つであるJ-PARCリニアックと比べて電流比で32倍の差がある。従って、開発段階に応じてADS用陽子加速器のビームトリップ頻度と許容ビームトリップ頻度を比較することが必要になる。今回、J-PARCリニアックの運転データに基づく信頼度関数を使ったモンテカルロ法のプログラムを作成し、ADS用陽子加速器のビームトリップ頻度を推測した。モンテカルロ法のプログラムにより、従来の解析手法では得られなかったビームトリップ事象の時間分布が得られた。その結果、許容ビームトリップ頻度を満足するには、ビームトリップ時間が5分以上のビームトリップ頻度を現状の27%に低減しなければならないことがわかった。
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
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。
福島 昌宏; 安藤 真樹; 長家 康展
Nuclear Science and Engineering, 199(6), p.1029 - 1043, 2025/06
被引用回数：0 パーセンタイル：0.00(Nuclear Science & Technology)A series of simulated experiments were conducted at the FCA to simulate a light water reactor core with a tight lattice cell containing highly enriched MOX fuel with a fissile Pu ratio 
15%. The prediction accuracy of the neutron computation codes and nuclear data libraries in a wide range of neutron spectra was evaluated by constructing three experimental configurations of the FCA-XXII-1 assembly with different void fractions (45%, 65%, and 95%) of the moderator material. In a previous paper, we reported the criticality and reactivity worths measured in these experiments. This paper provides the experimental results for the central reaction rate ratios and fission distributions as follows. The fission rate ratios of 
U and 
Pu relative to 
U were measured at the core centers using three calibrated fission chambers, and the U capture reaction rate ratio relative to U fission was measured using depleted uranium foils. Reaction rate distributions were also obtained by traversing four micro fission chambers of HEU, NU, Pu, and Np through each core region in the radial and axial directions. The experimental analyses were performed using detailed models of the Monte Carlo code MVP3 with JENDL-4.0. Most calculation results agreed well with the experiments, whereas those for the fission rate ratio of Pu to U were underestimated by up to 6% with the softening neutron spectrum.
Go, G.*; Goli, D. P.*; 江崎 蘭世; Tserkovnyak, Y.*; Kim, S. K.*
Physical Review Research (Internet), 7(2), p.L022066_1 - L022066_7, 2025/06
It remains an open question whether or not the scalar spin chirality itself can exhibit a Hall-type transport. In this work, we show that the answer is yes: The scalar spin chirality is Hall-transported in Kagome ferromagnets and antiferromagnets under an external bias, engendering a phenomenon which we dub the scalar spin chirality Nernst effect. Our findings call for the need to lift the conventional assumption that the scalar spin chirality is a static quantity in order to discover the active roles of the scalar spin chirality in transport properties.
方野 量太; 阿部 拓海; Cibert, H.*
JAEA-Research 2024-019, 22 Pages, 2025/05
JAEA-Research-2024-019.pdf:1.03MB
マイナーアクチノイドの核変換を目的とする加速器駆動システム(ADS)は未臨界状態で運転される。ADSの未臨界度管理においては、燃焼反応度の予測が重要であるが、予測精度の検証のためには、特に第一サイクル運転時では燃焼反応度を精度良く測定する必要がある。本検討では、燃焼反応度測定手法としてCurrent-To-Flux(CTF)法に着目し、連続エネルギーモンテカルロ計算コードSERPENT2を用いて固定源燃焼計算を実施し、炉内に配置する核分裂計数管を模したタリーを用いることで、CTF法によるADS通常運転時の燃焼反応度測定のシミュレーションを実施した。シミュレーション結果から測定手法起因の燃焼反応度測定不確かさの推定を行い、燃焼期間に依らず燃焼反応度に対して10%程度のバイアスが生じ、その検出器位置依存性が体系外側で小さいことを明らかにした。
Auh, Y. H.*; Neal, N. N.*; Arole, K.*; Regis, N. A.*; Nguyen, T.*; 小川 修一*; 津田 泰孝; 吉越 章隆; Radovic, M.*; Green, M. J.*; et al.
ACS Applied Materials & Interfaces, 17(21), p.31392 - 31402, 2025/05
MXenes are a promising class of 2D nanomaterials and are of particular interest for gas barrier application. However, MXene nanosheets naturally bear a negative charge, which prevents assembly with negatively charged polymers, such as polyacrylic acid (PAA), into gas barrier coatings. Here, we present MXene- and PAA-based layer-by-layer (MXene/PAA LbL) multilayers formed by leveraging hydrogen bonding interactions. When assembled in acidic conditions, MXene/PAA LbL films exhibit conformal, pin-hole free, nacre-like structures. The MXene/PAA LbL films yield high blocking capability and low permeability (0.14
0.01 cc mm m
day
MPa) for hydrogen gas. These nacre-like structures are also electronically conductive (up to 37030 S cm). Specifically, the reversible deconstruction of these films under basic conditions is experimentally verified. This study shows that hydrogen bonding interactions can be leveraged to form MXene LbL multilayers as gas barriers, electronically conducive coatings, and deconstructable thin films via pH control.
青山 高士; 上野 文義; 佐藤 智徳; 加藤 千明; 佐野 成人; 山下 直輝; 大谷 恭平; 五十嵐 誉廣
Annals of Nuclear Energy, 214, p.111229_1 - 111229_6, 2025/05
被引用回数：0 パーセンタイル：0.00(Nuclear Science & Technology)To elucidate the effect of dissolved radionuclides on corrosion of carbon steels and on formation of corrosion products of carbon steel, corrosion tests and imaging plate analysis were conducted. Carbon steel samples immersed in 10 mM NaCl containing 
Sr and 
Cs were analyzed using an imaging plate. As a result, the distribution of Sr or Cs in the corrosion products formed on carbon steel was successfully visualized. Furthermore, the radioactivity of the corroded specimens was calculated from calibration curves prepared using a Sr standard.
Li, X.; 山路 哲史*; 佐藤 一憲*; 山下 拓哉
Annals of Nuclear Energy, 214, p.111217_1 - 111217_13, 2025/05
被引用回数：0 パーセンタイル：0.00(Nuclear Science & Technology)The decommissioning of Fukushima Daiichi NPP Unit-2 requires understanding of reactor damage and fuel debris distribution for effective debris retrieval. This study numerically analyzes potential Reactor Pressure Vessel (RPV) boundary failure due to eutectic melting of Control Rod Drive (CRD) housings during reheating after debris bed dryout. The Moving Particle Semi-implicit (MPS) method, with an enthalpy-based temperature algorithm and Boussinesq approximation, is applied to simulate melt/solid interactions in a 2-D model of the lower plenum. The CRD housing melting temperature is set at 1523 K based on a quasi-binary phase diagram of 304 Stainless Steel (SS) and Zirconium (Zr) and ELSA experiments. Results suggest local RPV failure at CRD housings, leading to melt release and refreezing. The estimated failure occurs 8-12 hours post-dryout (ca. 12:00-16:00 on 3/15/2011), providing insights into melt progression and boundary breach scenarios in Unit-2.
