Investigating eutectic behavior and material relocation in BC-stainless steel composites using the improved MPS method

Ahmed, Z.*; Wu, S.*; Sharma, A.*; Kumar, R.*; 山野 秀将; Pellegrini, M.*; 横山 諒*; 岡本 孝司*

International Journal of Heat and Mass Transfer, 250, p.127343_1 - 127343_17, 2025/11

https://doi.org/10.1016/j.ijheatmasstransfer.2025.127343

The study aims to measure boron concentration through the unidirectional diffusion of boron within the stainless steel (SS) layers while evaluating the updated model ability to replicate melt relocation behavior and geometry. In the current MPS simulations, one scenario employed dummy walls as heat sources, while another scenario used SS surface particles as heat sources to avoid interference with the melt flow as it reached the bottom of the specimen.

Sorption mechanism of europium(III) onto metakaolin-based geopolymers

Yildirim, A. C.*; Mei, H.*; 戸田 賀奈子*; 青柳 登; 斉藤 拓巳*

Applied Clay Science, 274, p.107853_1 - 107853_9, 2025/09

https://doi.org/10.1016/j.clay.2025.107853

Metakaolin-based geopolymers (MKGPs) are ceramic-like materials used for nuclear waste stabilization. Therefore, understanding the sorption of ions on MKGPs is crucial where the cation exchange is considered as the main mechanism, yet the studies based on pH are limited. Thus, this study evaluates the effect of pH on the sorption mechanism of Eu(III) onto Na- and K-MKGPs. Here, time-resolved laser fluorescence spectroscopy (TRLFS) combined with parallel factor analysis, TRLFS in mixed DO/HO matrices, and extended X-ray absorption fine structure analysis. Eu(III) predominantly forms surface complexes with both MKGPs in the pH range of 4 11 at the open air environment, where three distinct surface species were identified at different pH values. The Eu(III) sorption mechanisms of both MKGPs are similar, involving ternary edge-sharing bidentate or monodentate inner-sphere surface complexation of Eu(III) with MKGP and silicate ions released from the MKGP up to pH 8, followed by the precipitation of europium tri-hydroxide within the pores of MKGP. The insights gained from this study will enhance the knowledge on MKGP for pollutant immobilization, thereby mitigating the spread of contaminants in the environment and expanding the potential application areas.

Microstructural evolution and mechanical instability of Mar-M509 superalloy fabricated by laser powder bed fusion under short-term thermal exposure

Cao, T.*; Wei, D.*; Gong, W.; 川崎 卓郎; Harjo, S.; 他10名*

Materials Science and Engineering A, 940, p.148534_1 - 148534_16, 2025/09

https://doi.org/10.1016/j.msea.2025.148534

The thermal stability of microstructure and mechanical performance is crucial for the industrial application of laser powder bed fusion (LPBF) superalloy components in gas turbines and jet engines. This work investigated the microstructural evolution and strengthening mechanism of LPBF Mar-M509 cobalt-based superalloy before and after thermal exposure at 1200 C using multi-scale microstructural characterization and in situ neutron diffraction tensile testing. The as-built Mar-M509 superalloy exhibited a heterogeneous microstructural features with coarse columnar and fine equiaxed grains, both containing dendritic and cellular substructures enriched with nanoscale carbides and high-density dislocations. The ultra high strength of the as-built sample was primarily attributed to dislocation-precipitation synergistic strengthening. After thermal exposure at 1200 C for 4 h, the dendritic and cellular substructures disappeared and the dislocation density decreased significantly. This study reveals the microstructural evolution and instability of LPBF Mar-M509 superalloy under high-temperature exposure and the impacts on mechanical properties, which provides critical support for the development of cobalt-based superalloys in high-temperature application fields.

Which radionuclides contribute most to seafood ingestion dose?

Johansen, M. P.*; Gwynn, J. P.*; Carpenter, J. G.*; Charmasson, S.*; 森 愛理; Orr, B.*; Simon-Cornu, M.*; Osvath, I.*; McGinnity, P.*

Journal of Environmental Radioactivity, 287, p.107706_1 - 107706_8, 2025/07

https://doi.org/10.1016/j.jenvrad.2025.107706

Radiological ingestion doses from eating seafood are regularly evaluated near coastal nuclear facilities, following accidents/events and frequently in national studies worldwide. However, a recent global review found that published seafood doses varied greatly depending on which radionuclides were selected for evaluation and that there has been a tendency to omit important radionuclides or focus on less significant ones. This indicates a need for clear guidance on which radionuclides to prioritise in such studies. Here, we use worldwide data for 16 key radionuclides contributing to typical background seafood ingestion dose. We account for the loss of radionuclides during cooking and the radioactive decay of the short-lived Po. Results indicate that for the typical world consumer, naturally-occurring radionuclides account for 99% of the total seafood ingestion dose, of which about 84% comes from Po and 8% from Pb. About 5% comes from Ra, a far greater proportion than the more frequently-assessed Ra (1%). Other Th- and U-series radionuclides provide far lower contributions (0.07%-0.70%), while C provides about 0.09%. In comparison, the contribution to total seafood ingestion dose from background anthropogenic radionuclides is 1%, with Cs contributing most (0.08%) and Sr, Tc, Ag and Pu adding a further 0.05% together. These percentage contributions to dose can vary somewhat depending on consumption patterns (e.g., differing proportions of fish, bivalves, etc.). However, Po is the dominant contributor irrespective of country-specific diets or restricted diet scenarios (fish-only, seaweed-only, etc.). Study results provide new guidance to improve the design, interpretation and communication of seafood ingestion dose assessments.

Non-condensable gas accumulation and distribution due to condensation in the CIGMA Facility; Implications for Fukushima Daiichi Unit 3 (1F3)

Hamdani, A.; 相馬 秀; 安部 諭; 柴本 泰照

Progress in Nuclear Energy, 185, p.105771_1 - 105771_13, 2025/07

https://doi.org/10.1016/j.pnucene.2025.105771

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.

Complementary layer thickness effects of Q235 and SUS304 layers of multilayered steels for improving of tensile strength and plasticity simultaneously

Lin, Z. M.*; Liu, B. X.*; Ming, K. S.*; 徐 平光; Yin, F. X.*; Zheng, S. J.*

Scripta Materialia, 263, p.116692_1 - 116692_7, 2025/07

https://doi.org/10.1016/j.scriptamat.2025.116692

Complementary layer thickness effects on strength and plasticity in Q235 and SUS304 steels provide a novel strategy to realize high strength and high plasticity of heterogeneous Q235/SUS304 multilayered steel. In this work, the tensile deformation behaviors and fracture characteristics of vacuum hot-rolled Q235/SUS304 multilayered steel with various layer thicknesses ranging from 223 m to 5 m were deeply investigated. The tensile strength improved with the reduction of layer thickness, and the uniform elongation were first increasing and then decreasing with the decrease of layer thickness, and the peak value appeared at the layer thickness of 20 m. Interestingly, the fracture elongation forms a high plateau value within the 1020 m range. Further analysis reveals that the severe strain localization in the brittle SUS304 thin layers is delayed by the ductile Q235 layers, which is mainly attributed to the different texture evolution and dislocation configuration characteristics during tensile deformation.

Methods for regulating depth of corrosion fissures in simulated fastener holes of 7050-T7451 aluminum alloy

青山 高士; Choudhary, S.*; Pandaleon, A.*; Burns, J. T.*; Kokaly, M.*; Restis, J.*; Ross, J.*; Kelly, R. G.*

Corrosion, 81(6), p.609 - 621, 2025/06

https://doi.org/10.5006/4739

This study presents a new test method for inducing controlled corrosion damage within simulated fastener holes of aluminum alloys, aimed at pretreating fatigue test specimens. The method involves insulating the outer surface while exposing the fastener hole surface to electrolytes containing 0.66 M NaCl + 0.1 M AlCl with varying concentrations of K S O . The evolution of corrosion damage within the fastener hole was examined as a function of exposure duration, electrolyte composition, and volume, as well as the effect of galvanic coupling with a SS316 cathode. Results indicate that fissure depth increases with an increase in K S O concentration but does not progress further after 24-48 hours of exposure in the chemical, or freely-corroding, exposure test. In contrast, galvanic coupling with a SS316 plate significantly accelerates corrosion, leading to much deeper fissures in a shorter time. The importance of electrolyte replenishment has been explored using electrochemical measurements, revealing the impact of evolving electrolyte chemistry. Beyond its application in fatigue specimen pretreatment, this method provides a simple yet effective approach for studying localized corrosion and evaluating mitigation strategies for fastener holes in aerospace structures.

Characterization of micelles of the thermo-responsive zwitterionic surfactant, 3-(-nonyl N,N-dimethylammonio)-propyl sulfate, present in isotropic solutions above its upper critical solution temperature

丹治 珠緒*; 楠 裕翔*; 中川 太一; 高瀬 つぎ子*; 上田 祐生; 元川 竜平; Hinze, W. L.*; 高貝 慶隆*

Langmuir, 41(21), p.13184 - 13191, 2025/06

https://doi.org/10.1021/acs.langmuir.5c00818

The thermosensitive zwitterionic surfactant, CAPSO, in solution displays a liquid-liquid miscibility gap exhibiting an upper critical solution temperature (UCST) in contrast to the lower critical temperature as is characteristic of nonionic surfactants. In this study, the micellar and aggregational properties of this surfactant in its homogeneous isotropic one phase region above the UCST was examined using surface tension and small-angle neutron scattering (SANS) measurements. The critical micelle concentration (CMC) of CAPSO was determined in both HO and DO at 40 and 70C as well as the cloud point temperature determined over a surfactant concentration range of 0.05-0.70 M. The CMC values were in the range of 48-55 mM (40C) and 61-65 mM (70C), respectively. The SANS data was analyzed using a core-shell model in which the CAPSO is represented by a nonyl hydrophobic core and polar [(N,N-dimethylammonio)-propylsulfate] headgroup shell. Results revealed that the CAPSO micelle aggregates are spherical in shape with a core diameter of 2.56 nm and shell thickness of 2.28 nm and an aggregation number of 30 at 40C. The data at 70C indicated that the aggregates were slightly larger in size, i.e., core diameter of 2.70 nm and shell thickness of 2.52 nm with an aggregation number of 35. At a fixed surfactant concentration, the aggregation number and size slightly decreased with a decrease in temperature from 70 to 40C.

Uncertainty analysis of the inverse LASSO estimation scheme on radioactive source distributions inside reactor building rooms from air does rate measurements

Shi, W.*; 町田 昌彦; 山田 進; 岡本 孝司

Progress in Nuclear Energy, 184, p.105710_1 - 105710_10, 2025/06

https://doi.org/10.1016/j.pnucene.2025.105710

最近、原子炉建屋内の少ない観測点で測定された空間線量値から放射線源分布を逆推定する方法としてLASSO(Least Absolute Shrinkage and Selection Operator)が提案された。しかし、空間線量値を測定する際には誤差が含まれるが、この誤差が逆推定結果の精度にどのように影響するかは解析されていなかった。そこで本論文では、LASSOに対する不確実性解析を行い、Candesの理論に基づく不確実性推定関数を提案した。実際に、モンテカルロ法の1つであるParticle and Heavy Ion Transport code System (PHITS)を使用して得られた不確実性を持つ数値を入力値として用いたテスト計算を実施し、計算結果の誤差が提案された推定関数に従うことを示した。これにより、LASSOは推定された不確実性の範囲内で放射線源分布を求めることができる方法であることが確認できた。

加速器駆動システムの通常運転時の燃焼反応度測定精度に関する検討

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。