Development of phenomenological degradation models for Cr-Coated Zr alloy cladding under high-temperature oxidation conditions

谷口 良徳; Luu, V. N.; 田崎 雄大; 宇田川 豊; 勝山 仁哉

Annals of Nuclear Energy, 231, p.112177_1 - 112177_16, 2026/06

https://doi.org/10.1016/j.anucene.2026.112177

Advanced technology fuels (ATF) with improved oxidation resistance are under development to enhance the safety of light water reactors. Cr-coated Zr alloy cladding, a promising near-term ATF, exhibits excellent oxidation resistance below the Cr-Zr eutectic temperature. However, its gradual loss of protective effect over time, even without mechanical damage, indicates the need to understand its degradation mechanisms. This article presents a phenomenological model describing degradation due to high-temperature oxidation, focusing on Zr ingress into the Cr coating and the formation of oxygen pathways that accelerate oxygen uptake into the Zr matrix. The model was validated against experimental data at 1200C and 1300C, reproducing key trends such as oxide growth, weight gain, and oxygen concentration profiles. Applying the same parameters to a different PVD-coated cladding test gave reasonable agreement at 1200C, while discrepancies at 1300C suggest Cr-Zr eutectic reactions from local temperature variations, highlighting the model's sensitivity near the eutectic point.

Bayesian approach to model temperature dependence of Charpy absorbed energy and uncertainty evaluation of ductile-to-brittle transition temperature for reactor pressure vessel steel

高見澤 悠; 西山 裕孝

Journal of Pressure Vessel Technology, 148(3), p.031501_1 - 031502_12, 2026/06

https://doi.org/10.1115/1.4070725

原子炉圧力容器(RPV)鋼の中性子照射脆化は、プラント運転中の監視試験試験(シャルピー衝撃試験)で得られる延性‐脆性遷移温度(DBTT)を用いて評価されてきた。RPVの構造健全性評価の信頼性を確保するためには、監視試験に内包される不確かさを考慮した十分な安全余裕を考慮する必要がある。本研究では、日本と米国で製造された約1,900の未照射および照射済み材料のデータセットを用いて、シャルピー吸収エネルギー変動の温度依存性を評価するモデルを開発した。次に、モンテカルロサンプリングとベイズ推定を用いてシャルピー試験データの確率分布を推定し、41Jエネルギーレベル()におけるシャルピー延性‐脆性遷移温度の確率分布を評価した。試験片数との不確かさの関係を詳細に評価した結果、日本製鋼材と米国製鋼材のの不確かさはほぼ同等であり、中性子照射によっても変化がない(材料の不均質性に明確な変化がない)ことがわかった。一方、製造方法に関しては、母材と溶接金属のの不確かさはほぼ同等であったが、熱影響部(HAZ)の不確かさが大きいことが示された。

Non-invasiveness evaluation of gas-sheet beam profile monitor; Observation of emittance reduction due to space-charge neutralization

山田 逸平; 小島 邦洸; 地村 幹

Nuclear Instruments and Methods in Physics Research A, 1084, p.171261_1 - 171261_12, 2026/04

https://doi.org/10.1016/j.nima.2025.171261

大強度粒子加速器の安定運転には、非破壊型のビーム形状(プロファイル)モニタが不可欠であり、ガスを導入してビームとの相互作用で形状を測るモニタ開発を進めている。ガス導入型は、高い二次粒子収量により高速かつ高精度なプロファイル計測を可能にする一方、ビームと導入したガスの相互作用がビーム品質に影響を与える可能性があるため、その非破壊性の定量的な評価が必須である。本研究では、3MeV負水素イオンビームを用いて、導入ガス流量に対するビーム電流値及び位相空間分布の変化を評価した。ビーム電流値については、予想通り導入ガス流量に対して線形に減少し、その減少率は荷電変換断面積と一致した。位相空間分布については、ビームライン圧力が10 Pa未満の範囲では変化が見られず、10 Pa以上に増加させた場合には、逆に分布の広がりに約5%の減少が見られた。本測定結果を解析的および数値的に検証した結果、ビーム・ガス相互作用により生成された正イオンが水素負イオンビームの電気的斥力を中和し、負電荷同士の反発力を抑制したため、分布の広がりの相対的な減少を起こすことがわかった。以上により、開発したモニタは、使用に際してビームを広げることなく、逆にビーム品質を向上させる事が分かり、加速器の安定運転に貢献可能であると言える。

パイロットADSの概念設計

西原 健司; 福島 昌宏; 阿部 拓海; 方野 量太; Yee-Rendon, B.; 岩元 大樹; 菅原 隆徳; 大林 寛生; 斎藤 滋

JAEA-Research 2025-013, 125 Pages, 2026/03

JAEA-Research-2025-013.pdf:4.68MB

マイナーアクチノイドの分離変換を目的とした商用加速器駆動未臨界システム(ADS)の前段階となるパイロットADSの概念設計を行った。パイロットADSの炉心出力は200MWとし、安全評価の結果、深い未臨界度と安全棒を備える設計とした。炉心設計、加速器設計、ターゲット設計、炉内機器設計を行い、具体的な概念を明らかにした。

Effect of coaxial HPGe detector structure on -ray beam measurements

Omer, M.; 静間 俊行*; 小泉 光生; 平 義隆*; Zen, H.*; 大垣 英明*; 羽島 良一*

Radiation Physics and Chemistry, 240, p.113467_1 - 113467_8, 2026/03

https://doi.org/10.1016/j.radphyschem.2025.113467

Coaxial high-purity germanium detectors are widely used in applications requiring high-resolution -ray spectroscopy. However, the internal structure of these detectors, particularly the geometry of the inactive volumes inside the detector core, can significantly influence their performance in beam detection configurations. This study investigates the impact of detector structure on the spectral response to pencil-like -ray beams, based on a comparison of -ray spectra measured with two coaxial high-purity germanium detectors that have similar active volumes but distinct internal geometries. Experimental measurements were conducted at the UVSOR synchrotron facility using collimated laser Compton scattered -ray beams with an energy of MeV. Monte Carlo simulations using the Geant4 toolkit were performed to refine the detector models and replicate experimental results. The results reveal that the front layer thickness and the presence of structural elements such as the cold finger strongly affect the spectral features, particularly the appearance of a coincidence sum peak of the annihilation radiation at 1.022 MeV. Off-axis irradiation significantly improves the detection efficiency and reduces undesired induced interactions within inactive volumes. Additionally, the observed pair production signatures are validated through the available theoretical cross section data, confirming the dominant role of internal structures in shaping the detector response under beam geometry. These findings are essential for optimizing detector configurations in precision -ray beam experiments. This work is a contribution of the Japan Atomic Energy Agency (JAEA) to the International Atomic Energy Agency (IAEA) under the agreement of the coordinated research program (CRP), J02015 (Facilitation of Safe and Secure Trade Using Nuclear Detection Technology - Detection of RN and Other Contraband). A part of this work was conducted at the BL1U of UVSOR Synchrotron Facility, Institute for Molecular Science (IMS program 23IMS6602).

再処理特別研究棟の解体廃棄物に対する廃棄体化を考慮した分別の導入

中嶋 瞭太; 酒井 達弥; 谷 陸; 半田 雄一; 砂押 瑞穂*; 井上 秀毅*; 山田 悟志; 清水 修

JAEA-Technology 2025-012, 39 Pages, 2026/01

JAEA-Technology-2025-012.pdf:2.31MB

再処理特別研究棟は1996年から廃止措置に移行し、施設内の設備・機器の解体作業を実施してきた。2022年10月からのグローブボックス等の解体撤去作業では、埋設施設へ処分する際に要求される技術上の基準に適合する廃棄体を作製することを目的として、「解体物分別マニュアル」を作成し、発生した解体廃棄物の分別・仕分け作業を実施した。本報告は、「解体物分別マニュアル」に従い実施したグローブボックス等の解体撤去作業で発生した解体廃棄物の分別・仕分けの結果及び得られた知見についてまとめたものである。

Effect of CaCl addition on decontamination of radioactive Cs in soil via heat treatment

下山 巖; 小暮 敏博*; 奥村 大河*; 馬場 祐治*

Journal of Environmental Management, 397, p.128239_1 - 128239_11, 2026/01

https://doi.org/10.1016/j.jenvman.2025.128239

大気条件および真空条件の両方で、放射性Csで汚染された福島土壌を熱処理し、NaCl添加の場合と比較することで、CaCl添加の熱的土壌除染に対する有効性を調査した。CaClを添加した場合、大気・真空いずれの条件下でも約740Cで95%を超える除染率が得られ、NaCl添加よりもやや高い効果を示した。風化黒雲母に吸着した非放射性Csの熱処理による除去においても、CaClはNaClより明確に高い効果を示した。NaClが真空条件下で土壌中の粘土鉱物に急速イオン交換(RIE)を引き起こすのに対し、CaClは大気条件および真空条件の両方で熱処理初期にRIEを誘起し、その後、粘土鉱物の分解と相変態を促進して放射性Csの除去に寄与することが明らかとなった。これらの結果から、CaClは単独でも熱処理に有効な添加剤であることが示された。

Small-scale experiments on melt spreading and deposition via melt-jet impingement on a dry substrate; Evaluation of empirical correlations for deposition area of continuous layered debris

岩澤 譲; 柴本 泰照; 丸山 結

Nuclear Engineering and Design, 446(Part B), p.114599_1 - 114599_16, 2026/01

https://doi.org/10.1016/j.nucengdes.2025.114599

Continuous layered debris deposited due to the molten core (melt) spreading across the floor of a containment vessel can pose a serious threat to containment integrity during severe accidents in light water reactors. The present study conducted small-scale experiments to investigate melt spreading process and subsequent deposition of continuous layered debris via melt-jet impingement onto a floor. The small-scale experiments were conducted using a low-melting-point metal under dry conditions without coolant water. High-speed imaging and image processing techniques were employed to elucidate the influence of melt injection conditions on melt spreading and subsequent deposition of continuous layered debris. The use of larger nozzle sizes and more highly superheated melts enabled the expansion of the experimental database. Based on the experimental results, we identified appropriate correlations from those proposed in previous studies to estimate the debris deposition area and evaluated their predictive accuracies. These correlations were then applied to estimate the potential spreading area of the relocated melt under anticipated reactor-scale conditions. The analysis revealed that thermal effects, such as heat transfer to the floor, influence the potential spreading area, could be incorporated into the correlations for applications under the anticipated reactor-scale conditions.

Possible transition from silandic to aluandic andosols with acidification as evidenced by detailed profile investigation of two well-preserved forest andosols in Japan

Alam, M. M.*; 山北 絵理*; 井上 弦*; 小嵐 淳; 安藤 麻里子; 阿部 有希子; 中山 浩成; 森 裕樹*; 平舘 俊太郎*

Soil Science and Plant Nutrition, 72(1), p.55 - 66, 2026/01

https://doi.org/10.1080/00380768.2025.2511803

Andosols are one of the major soil types in Japan. Andosols have been grouped into two distinct categories: Silandic and Aluandic, but their formation has not been well investigated. To clarify the formation process of the Andosols, two soil profiles were collected from natural forest sites at Aya (Sil-A) and Shiiba (Alu-A) in Miyazaki. The soil samples were analyzed for carbon stock, and chemical and mineralogical properties. Based on the analytical data, Sil-A was classified as a Silandic Andosol and an Allophanic Andosol, whereas Alu-A was classified as an Aluandic/Silandic Andosol and a Non-allophanic Andosol. The changes in the chemical and mineralogical properties with depth suggested that acidification had happened from upper layers, resulting in dissolution of the allophanic materials and formation of Al-humus complexes in both soils, and Alu-A would have been more deeply affected by this process than Sil-A. Therefore, we conclude that Silandic Andosols can be transformed into Aluandic Andosols with acidification.

Relationships among non-allophanic/allophanic indicators in six Japanese forest Andosol profiles; Implications for soil classification and genesis

Alam, M. M.*; 山北 絵理*; Tamanna, S.*; Thae, E. P.*; 小嵐 淳; 安藤 麻里子; 阿部 有希子; 中山 理智; 森 裕樹*; 平舘 俊太郎*

Soil Science and Plant Nutrition, 12 Pages, 2026/00

https://doi.org/10.1080/00380768.2026.2616655

Andic Andosols, prevalent in Japan, have been classified as Allophanic or Non-allophanic, based on indicators: oxalate-extractable silicon (Sio), the ratio of pyrophosphate- to acid-oxalate-extractable aluminum (Alp/Alo), and exchangeable acidity (y1), in the Fifth Committee for Soil Classification and Nomenclature 2017 (FCSCN 2017). This study investigated chemical and mineralogical properties in six forested Andosol profiles to assess the consistency of these indicators and their link to soil formation. While FCSCN 2017 classified two profiles as Allophanic and four as Non-allophanic, inconsistencies were found among the indicators. Sio content is proposed as a more reliable indicator of allophanic material richness than the Alp/Alo ratio, which is influenced by organic matter content. Sio and y1 are suggested as informative parameters for diagnosing allophanic content and soil acidity, respectively. The findings contribute to refining Andosol classification and enhancing our understanding of Andosol formation under forests.