Unveiling the effects of Mn, Cr, Al, and Si on the low-temperature tempering behaviors of high-carbon martensite

Zhang, Y.*; 丸澤 賢人*; 工藤 航平*; 諸岡 聡; Gong, W.; Harjo, S.; 宮本 吾郎*; 古原 忠*

Journal of Materials Science & Technology, 275, p.250 - 259, 2026/12

https://doi.org/10.1016/j.jmst.2026.04.015

This study examines how substitutional alloying elements (Mn, Cr, Al, and Si) influence low-temperature tempering reactions in high carbon martensitic steels. Through comprehensive experimental techniques including neutron diffraction et al., the work clarifies how alloying modifies tempering kinetics by affecting carbon diffusion and phase nucleation. Al and Cr strongly suppress martensite tetragonality reduction and carbon redistribution, while retained austenite decomposes in two stages that are selectively delayed by different alloying elements. Overall, the tempering sequence and kinetics are shown to be governed by alloying-dependent control of carbon mobility and phase transformations.

Implementation of ideal cascade model for uranium enrichment to nuclear fuel cycle simulator

阿部 拓海; 鈴木 大河*; 岡村 知拓*; 中瀬 正彦*

Annals of Nuclear Energy, 232, p.112224_1 - 112224_7, 2026/07

https://doi.org/10.1016/j.anucene.2026.112224

Reprocessed uranium is important for sustainable nuclear fuel use. It contains isotopes such as U-232, U-234, and U-236, which influence enrichment and later nuclear fuel cycle steps. To evaluate these effects, nuclear fuel cycle simulators require cascade models capable of handling multi-isotopic uranium. In this study, an ideal cascade model based on the matched abundance ratio cascade was implemented in a nuclear fuel cycle simulator NMB4, developed by the Institute of Science Tokyo and Japan Atomic Energy Agency. A three-component approximation was introduced to simplify calculations. Validation against numerical solutions and experimental data showed good agreement. Compared with the simple coefficient method, the ideal cascade model improved predictions for isotopes such as U-232 and U-236, which affect radiation, separative work, and actinide production. These results demonstrate that the new model enhances the accuracy of reprocessed uranium evaluation, aiding future fuel cycle planning.

令和6年度工務技術部年報

原子力科学研究所 工務技術部

JAEA-Review 2026-011, 97 Pages, 2026/06

JAEA-Review-2026-011.pdf:4.39MB

工務技術部は、原子力科学研究所及びJ-PARCの水、電気、蒸気、排水等のユーティリティ施設、原子炉施設、核燃料物質使用施設等の特定施設(受変電設備、非常用電源設備、気体・液体廃棄設備、圧縮空気設備)並びに一般施設の機械室設備の運転、保守管理を担っている。さらに、建物・設備の補修・改修工事及び点検・整備業務、電子装置及び機械装置の工作業務も担っている。本報告書は、令和6年度の当部の業務実績の概況、主な管理データ及び技術開発の概要を記録したものであり、今後の業務の推進に役立てられることを期待する。

令和6年度計算科学技術研究実績評価報告

システム計算科学センター

JAEA-Evaluation 2026-003, 41 Pages, 2026/06

JAEA-Evaluation-2026-003.pdf:1.08MB

システム計算科学センターでは、「国立研究開発法人日本原子力研究開発機構の中長期目標を達成するための計画(中長期計画)」に基づき、原子力分野における計算科学技術研究に関する研究開発を実施してきた。その計算科学技術研究の実績については、計算科学技術研究・評価委員会(以下「委員会」という。)により評価された。本報告は、システム計算科学センターにおいて実施された計算科学技術研究の、令和6年度における業務の実績及びそれらに対する委員会による評価結果をとりまとめたものである。

酸化物燃料ナトリウム冷却高速炉のシビアアクシデントに係る研究,1; プロジェクト全体概要及び令和7年度までの進捗

山野 秀将; 松場 賢一; 佐々 京平*; 木下 円機*; 守田 幸路*; 齊藤 泰司*; 伊藤 啓*; 鈴木 徹*

第30回動力・エネルギー技術シンポジウム講演論文集(インターネット), 5 Pages, 2026/06

A research project on severe accidents of oxide-fueled core has been started since 2024 as research and development in a conceptual design stage of demonstration sodium-cooled fast reactors in Japan. It is necessary to develop analytical methodologies and technical bases to confirm the effectiveness of various design measures, which are introduced to the demonstration reactor in order to achieve recriticality elimination and in-vessel retention. The project implements element testing, integral testing, analytical methodology development and reactor application analyses, in which involved are important phenomena of fuel discharge behavior, core residual fuel coolability, and debris-bed formation behavior and coolability. This paper describes the project overview and progress until 2025.

Investigation of differences in the mean time between beam trips between normal-conducting and superconducting acceleration cavities

武井 早憲

JPS Conference Proceedings (Internet), 45, p.011175_1 - 011175_7, 2026/06

https://doi.org/10.7566/JPSCP.45.011175

原子力機構(JAEA)はマイナーアクチニドを効率的に核変換するADSの研究開発を行っている。JAEAが提案するADSは、未臨界炉と大強度超伝導陽子線形加速器の組み合わせである。ADS用陽子加速器の開発課題の一つとしてビームトリップ事象の低減がある。すなわち、ビームトリップ事象により未臨界炉の機器が熱サイクル疲労で損傷するおそれがあるからである。この損傷を防ぐため、ADS用陽子加速器のビームトリップ頻度を許容ビームトリップ頻度以下まで低減させる必要がある。武井らはADS用陽子加速器の許容ビームトリップ頻度を算出するとともに、J-PARCリニアックの運転データを用いてADS用陽子加速器のビームトリップ頻度を推測した。推測では、J-PARCリニアックのイオン源、RFQ、常伝導加速空洞における5年分の運転データを用いた。その結果、ビームトリップ時間が10秒を超えるビームトリップ頻度は許容ビームトリップ頻度を満たさないことがわかった。ところで、大強度陽子リニアックの一つであるSNSの超伝導加速空洞におけるビームトリップ事象のデータが公表された。このデータは超伝導空洞を用いるADS用陽子加速器のビームトリップ頻度を推測するうえで重要となる。そこで、本研究では、J-PARCリニアックにおける常伝導加速空洞とSNSリニアックの超伝導加速空洞における平均ビームトリップ間隔を比較し、両者の相違などについて述べる。

LLRF requirements for the JAEA-ADS linac

Yee-Rendon, B.; 近藤 恭弘; 田村 潤; 明午 伸一郎; 前川 藤夫

JPS Conference Proceedings (Internet), 45, p.011173_1 - 011173_7, 2026/06

https://doi.org/10.7566/JPSCP.45.011173

日本原子力研究開発機構(JAEA)は、核変換用加速器駆動システム(ADS)の研究開発を行っている。JAEA-ADSは、30MWのCW超伝導陽子リニアックと未臨界炉心から構成される。このリニアックは、20mAの陽子ビームを最終エネルギー1.5GeVまで加速する。リニアックの常伝導部で2.5MeVまで加速し、残りは超伝導部で加速する。300以上のLLRFシステムが、リニアックを構成するRF構造が、ビーム進行方向のパラメータを制御する。JAEA-ADSのLLRFシステムは、リニアックの効率化のためのRFの安定性を確保することに加え、ADS運転における大きな課題であるリニアックの稼働率向上のための耐故障補償も可能にする。本研究では、ADS LLRFの必要な条件について議論し、これらの要求を満たすモデル案を提示する。

Transient behavior of a boiling water reactor-type offshore floating nuclear power plant during platform motion

福田 航大; 小原 徹*

Nuclear Technology, 212(6), p.1567 - 1578, 2026/06

https://doi.org/10.1080/00295450.2025.2502266

Offshore floating nuclear power plants (OFNPs) are gaining attention as safe and location-flexible means for nuclear energy utilization. Although platform motion in the marine environment may affect reactor kinetics, particularly in boiling water reactors (BWRs), BWR-type OFNPs are expected to have high economic efficiency. This study investigated the reactor power behavior of a BWR-type OFNP using three-dimensional transient neutronics-thermal hydraulics coupled analysis. Heave and pitch motions were considered under realistic wave conditions using a typical BWR model. The results show that the reactor power and its distribution can vary because of the wave-induced platform motion; however, the amplitude of these variations is sufficiently small to ensure normal operation, even under the extreme wave conditions of a one-in-10,000-year storm. Although the results of the present study demonstrate the ability of BWR-type OFNPs to provide a safe and stable energy supply, they also suggest the need for further research. Further studies are needed to address the complex wave conditions and assess the effects of the platform motion on ancillary systems, such as recirculation systems.

Hydraulic modeling of saltwater infiltration with various concentrations into unsaturated bentonite-based buffer material

田窪 勇作*; 高山 裕介*; 杉田 裕; 生越 季理; 石田 圭輔*

Environmental Earth Sciences, 85(9), p.229_1 - 229_19, 2026/05

https://doi.org/10.1007/s12665-026-12955-9

In this study, sensitivity analysis was conducted to identify key parameters that strongly influence infiltration assessment. The results indicate that the intrinsic permeability and the water retention function have a significant impact on the simulation of liquid saturation as key parameters to be focused on the hydraulic modelling. Furthermore, the results of hydraulic analysis for saltwater infiltration with various concentrations suggest that the hydraulic analysis model is applicable for evaluating infiltration behaviour, by setting several analysis cases focused on variabilities of key parameters. This modeling approach, which focuses on the key parameters, has the potential to be a simple method to predict the hydraulic state transition of the buffer material during re-saturation period.

Kinetic and thermodynamic controls on CsI-Mo gas-phase reactions under varying oxygen potentials

塩津 弘之

Progress in Nuclear Energy, 195, p.106300_1 - 106300_11, 2026/05

https://doi.org/10.1016/j.pnucene.2026.106300

The transport and release behavior of fission products (FPs) during nuclear power plant accidents is strongly influenced by their chemical forms, particularly gaseous species, which can lead to enhanced environmental release. For iodine, one of the most volatile FPs, condensable cesium iodide (CsI) has traditionally been regarded as the dominant chemical form in state-of-the-art source term evaluations. However, recent experiments have indicated that molybdenum (Mo), a semi-volatile FP, can promote the formation of gaseous iodine through gas-phase reactions with CsI. The key controlling factor of these reactions is the oxygen potential of the atmosphere. In the TeRRa experiments, CsI-Mo gas-phase reactions were observed at 1150 K under Ar-20%O-0.8%O conditions (-31.7 kJ/mol-O), whereas no reaction occurred under Ar-20%HO conditions (-149 kJ/mol-O). Nevertheless, the specific reactive conditions governing these reactions have not yet been fully clarified. In this study, the oxygen-potential dependence of gas-phase reactions between CsI and Mo vapors in the TeRRa-CsIMo series experiments was numerically investigated using chemical equilibrium, mass transport, and reaction kinetics analyses. Chemical equilibrium and transport analyses were performed using the VICTORIA code, while detailed kinetic analyses were conducted with the Cantera software and the ECUME database. The results demonstrate that although CsI-Mo gas-phase reactions are thermodynamically favorable under oxidizing conditions that stabilize Mo in the MoO form ( -158 kJ/mol-O), their contribution to gaseous iodine formation is strongly constrained by kinetic limitations under lower oxygen potential conditions, even at high temperatures around 1150 K. These findings suggest that both thermodynamic and kinetic effects must be considered for reliable evaluation of iodine source terms during severe accidents, particularly under oxygen-starved environments.