Temperature effect on radiolytically generated hydrogen yield from a plutonium nitric acid aqueous solution

樋川 智洋; 宝徳 忍; 熊谷 友多; 阿部 侑馬*; 小山 幹一*; 深谷 洋行; 伴 康俊; 木田 孝; 長谷川 聡*; 中野 正直*; et al.

Journal of Nuclear Science and Technology, 63(3), p.322 - 327, 2026/03

https://doi.org/10.1080/00223131.2025.2541067

燃料再処理施設における水素安全に資するため、放射線分解により生成する水素発生に対する温度の影響を調べた。プルトニウム硝酸水溶液の放射線分解による水素発生量を、室温から溶液の沸騰温度までの温度について実験的に取得した。その結果、沸騰条件まで温度を上昇させても有意な水素発生量の上昇は見られなかった。さらに溶液の撹拌が水素生成に与える影響についても検討したところ、室温での静的条件と混合条件の間で水素生成に違いがみられなかった。これらの知見は、溶液の温度上昇や沸騰が水素生成を大幅に増加させないことを示唆しており、重大事故時の水素リスク評価に貢献する。

High-temperature oxidation failure in reactivity-initiated accidents; An Evaluation of failure criteria based on oxygen concentration from the previous NSRR experiments

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

https://doi.org/10.1016/j.nucengdes.2025.114222

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.

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.

Unique deformation behavior of ultrafine-grained 304 stainless steel at 20 K

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

https://doi.org/10.1016/j.scriptamat.2025.116726

An 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.

クリープ破断時間および高温引張強度予測モデルの連合学習

櫻井 惇也*; 鳥形 啓輔*; 松永 学*; 高梨 直人*; 日比野 真也*; 木津 健一*; 森田 聡*; 井元 雅弘*; 下畠 伸朗*; 豊田 晃大; et al.

鉄と鋼, 111(5), p.246 - 262, 2025/04

https://doi.org/10.2355/tetsutohagane.TETSU-2024-124

Creep testing is time-consuming and costly, leading institutions to limit the number of tests conducted to the minimum necessary for their specific objectives. By pooling data from each institution, it is anticipated that predictive models can be developed for a wide range of materials, including welded joints and degraded materials exposed to service conditions. However, the data obtained by each institution is often highly confidential, making it challenging to share with others. Federated learning, a type of privacy-preserving computation technology, allows for learning while keeping data confidential. Utilizing this approach, it is possible to develop creep life prediction models by leveraging data from various institutions. In this paper, we constructed global deep neural network models for predicting creep rupture life of heat-resistant ferritic steels in collaboration with eight institutions using the federated learning system we developed for this purpose. Each institution built a local model using only its own data for comparison. While these local models demonstrated good predictive accuracy for their respective datasets, their predictive performance declined when applied to data from other institutions. In contrast, the global model constructed using federated learning showed reasonably good predictive performance across all institutions. The distance between each institution's data was defined in the space of explanatory variables, with the NIMS data, which had the largest dataset, serving as the reference point. The global model maintained high predictive accuracy regardless of the distance from the NIMS data, whereas the predictive accuracy of the NIMS local model significantly decreased as the distance increased.

Applicability of mechanistic analysis code seraphim to sodium-water reaction in tube bundle system

小坂 亘; 内堀 昭寛; 渡部 晃*; 椎名 祥己*

Proceedings of 10th Workshop on Computational Fluid Dynamics for Nuclear Reactor Safety (CFD4NRS-10) (Internet), 12 Pages, 2025/00

In a steam generator (SG) of a sodium-cooled fast reactor, water leakage caused by heat transfer tube failure in an SG makes a high-temperature, high-velocity, and corrosive jet with sodium-water reaction (SWR). The reacting jet may cause further tube failure and the expansion of the affected area in an SG. A mechanistic analysis code SERAPHIM has capability to evaluate the reacting jet considering multi-component, multiphase and compressive flow with SWR. By comparing analysis and experimental results, SERAPHIM code has been validated from the case of a free jet to the reacting jet in a tube bundle system with an average water leak rate of 0.15 kg/s. In this paper, as one of the validation analysis series of SERAPHIM code, we performed numerical analysis for the reacting jet in a tube bundle system with larger average water leak rate, i.e. 1.85 kg/s. Similar to previously reported results, the gas phase expanded in the system immediately after the discharging and then flowed in the direction of buoyancy force. It was confirmed the occurrence of an underexpanded jet and the limitation of the maximum temperature, which are consistent with the knowledge of the SWR phenomena in an SG. The low and high-temperature regions were wider than in previous reports due to the larger average water leak rate. The high-temperature region obtained by the analysis agreed with the representative characteristics appeared in the experimental result such as location and shape of the temperature distribution. The analysis results were consistent with previous knowledge. The representative characteristics that appeared in the experimental result were also reproduced. SERAPHIM code was applicable to the selected average water leak rate in the tube bundle system.

高速炉燃料用SUS316相当鋼の高温強度及び照射特性評価

宮澤 健; 上羽 智之; 矢野 康英; 丹野 敬嗣; 大塚 智史; 鬼澤 高志; 安藤 勝訓; 皆藤 威二

JAEA-Technology 2024-009, 140 Pages, 2024/10

JAEA-Technology-2024-009.pdf:8.03MB

SUS316相当鋼を用いた高速炉燃料設計の高信頼性化に向けて、SUS316相当鋼被覆管及びラッパ管の高温強度及び照射データを材料学的及び統計学的な観点で評価・解析することで、高温強度及び高照射量までの照射特性に係る設計用強度式を導出した。異常な過渡変化の上限温度を超える900CまでのSUS316相当鋼被覆管及びラッパ管(非照射材)の高温引張試験データ及び高温クリープ試験データを拡充し、0.2%耐力、引張強さ、クリープ破断強度の最適近似式と下限式並びに熱クリープひずみの最適近似式と上下限式を導出した。また、高速実験炉「常陽」、仏国・高速原型炉Phenix及び米国・FFTFで高照射量まで中性子照射したSUS316相当鋼被覆管及びラッパ管の照射後引張試験データ及びSUS316相当鋼被覆管の炉内クリープ破断試験データを解析することで、炉内Na中照射による引張強度及びクリープ強度の低下を表す強度補正係数を導出した。導出した式を実測値と比較することで、その妥当性を確認した。

Development of failure mitigation technologies for improving resilience of nuclear structures

笠原 直人*; 山野 秀将; 中村 いずみ*; 出町 和之*; 佐藤 拓哉*; 一宮 正和*

International Journal of Pressure Vessels and Piping, 211, p.105298_1 - 105298_6, 2024/10

https://doi.org/10.1016/j.ijpvp.2024.105298

Passive safety structures were applied to next-generation fast reactors, subject to high temperature and low-pressure conditions. In the case of loss-of-heat-removal accidents, high temperature conditions accelerate the creep deformation of structures. When deformation redistributes loadings and reduces stresses at important positions such as coolant boundaries, progression to creep rupture of boundaries can be mitigated. When an excessive earthquake occurs, plastic deformation and buckling become dominant, due to low pressure and, therefore, a thin-wall structure. The above-mentioned failure modes reduce rigidity and natural frequency. When the natural frequency becomes lower than the input frequency, vibration energy is hardly transferred to structures and the subsequent failures of structures, such as collapse and break, are mitigated.

消防自動車を用いたHTTRのBDBA拡大防止対策

島崎 洋祐; 地代所 達也; 石井 俊晃; 猪井 宏幸; 飯垣 和彦

JAEA-Technology 2024-005, 23 Pages, 2024/06

JAEA-Technology-2024-005.pdf:5.53MB

HTTRでは、新規制基準への対応の一環として新たに多量の放射性物質等を放出するおそれのある事故(BDBA)の想定を行うとともに、BDBAの拡大防止対策を定めた。このうち、使用済燃料貯蔵プールに係る冷却水漏洩によって発生するBDBAの拡大防止対策においては、大洗研究所の消防自動車をBDBAの拡大防止対策機器として選定し、揚水性能等の要求性能を定めて検査で確認した。これにより、消防自動車は使用前事業者検査に合格し、HTTRの運転再開に貢献した。

Formulation of high-temperature strength equation of 9Cr-ODS tempered martensitic steels using the Larson-Miller parameter and life-fraction rule for rupture life assessment in steady-state, transient, and accident conditions of fast reactor fuel

宮澤 健; 丹野 敬嗣; 今川 裕也; 橋立 竜太; 矢野 康英; 皆藤 威二; 大塚 智史; 光原 昌寿*; 外山 健*; 大沼 正人*; et al.

Journal of Nuclear Materials, 593, p.155008_1 - 155008_16, 2024/05

https://doi.org/10.1016/j.jnucmat.2024.155008

This paper discusses the applicability of J.L. Straalsund et al.'s technique for combining the Larson-Miller parameter (LMP) and life-fraction rule to form a single high-temperature strength equation for 9Cr- oxide-dispersion-strengthened (ODS) tempered martensitic steels (TMS). It uses the extensive dataset on creep rupture, tensile, and temperature-transient-to-burst tests of 9Cr-ODS TMS cladding tubes in the -phase, /-duplex, -phase matrices, which are accumulated by the Japan Atomic Energy Agency so far. The technique is adequately applicable to 9Cr-ODS TMS cladding tubes. A single high-temperature strength equation expressing the mechanical strength in different deformation and rupture modes (creep, tensile, temperature-transient-to-burst) is derived for 9Cr-ODS TMS cladding tubes. This equation can predict the rupture life of the cladding tubes under various stresses and temperatures over time. The applicable range of the high-temperature strength equation is specified in this study and the upper limit temperature for the equation is found to be 1200C. At temperatures higher than 1200C, the coarsening and aggregation of nanosized oxide particles and the to phase transformation are reported in previous studies. The high-temperature strength equation can be well applied to the creep and tensile strength in the -phase matrix, the creep strength in the -phase matrix and the temperature-transient-to-burst strength in both phases except for the low equivalent stress (43 MPa) at temperatures exceeding 1050C. The mechanism of the notable consistency between creep and tensile strength in the -phase matrix is discussed by analyzing the high-temperature deformation data in the light of existing deformation models.