Mechanical stability of retained austenite and texture evolution in additively manufactured stainless steel

Chae, H.*; Huang, E.-W.*; Jain, J.*; Lee, D.-H.*; Harjo, S.; 川崎 卓郎; Lee, S. Y.*

Metals and Materials International, 30(5), p.1321 - 1330, 2024/05

https://doi.org/10.1007/s12540-023-01575-8

In situ neutron diffraction during tensile deformation was performed for the stainless steels prepared by the additive manufacturing (AM) processes with two strategies: vertically built and horizontally built. The AM steels were further aged without solid solution treatment. As the results, the retained austenite was found to be more stable because the chemical composition became homogeneous by aging, and the onset of deformation induced martensitic transformation was delayed.

The Precipitation and redistribution of alloying element in Zircaloy-4 cladding tube oxidized in high-temperature steam

天谷 政樹

High Temperature Corrosion of Materials, 15 Pages, 2024/00

https://doi.org/10.1007/s11085-023-10216-9

Zirconium (Zr)-based alloys are widely used as fuel cladding material for light water reactors. Under a loss-of-coolant accident (LOCA) condition, the oxidation of fuel cladding by high-temperature steam induces the degradation of mechanical properties of the cladding and would affect the integrity of fuel rods and/or assemblies, etc., during LOCA. In this study, the distribution of the elements (zirconium, oxygen, tin, iron and chromium) in Zircaloy-4 cladding specimens oxidized in the temperature range of 1350- 1700 K in steam was analyzed along the radial direction of the specimens by using SEM/EPMA, and the cause of element distribution in the specimens was discussed in consideration of the morphology of precipitates in the specimens and hypothesized phase diagrams related to the elements contained in the specimens. The form of the particles precipitated and the comparison between SEM/EPMA results and hypothesized phase diagrams of Zr-Sn-O system suggested that the liquefaction of tin-rich material and/or Zr-(Fe,Cr) compounds occurred during the oxidation test. The results obtained indicate that Zircaloy-4 cladding tubes would start melting at the melting point of tin-oxide and the eutectic point of Zr-(Fe,Cr)compounds, which is much lower than the melting point of Zr, -Zr(O), or zirconium oxide (ZrO).

Key role of temperature on delamination in solid-state additive manufacturing via supersonic impact

Wang, Q.*; Ma, N.*; Huang, W.*; Shi, J.*; Luo, X.-T.*; 冨高 宙*; 諸岡 聡; 渡邊 誠*

Materials Research Letters (Internet), 11(9), p.742 - 748, 2023/09

https://doi.org/https://doi.org/10.1080/21663831.2023.2227221

Cold spray (CS) has emerged as a representative of solid-state additive manufacturing (AM) via supersonic impact. It enables a high deposition rate of solid-state microparticles. Delamination, however, tends to occur when depositing too thick; this remains to be conquered. Here, a CS-like process, warm spray (WS), was presented. Interestingly, it was found that the appropriate increase in particle temperature can effectively reduce the residual stress amplitude, relieving the concentrated tensile stress and safeguarding the additively manufactured components from interfacial delamination even when depositing too thick. The key role of temperature on delamination was identified in solid-state AM via supersonic impact.

Investigation of the core neutronics analysis conditions for evaluation of burn-up nuclear characteristics of the next-generation fast reactors

滝野 一夫; 大木 繁夫

JAEA-Data/Code 2023-003, 26 Pages, 2023/05

JAEA-Data-Code-2023-003.pdf:1.66MB

次世代高速炉は、従来炉よりも高い炉心取出燃焼度を目指しているため、炉心核設計の高度化が求められる。そのため、燃焼核特性解析では、計算コストを抑えつつ十分な計算精度が得られる適切な解析条件が必要とされる。そこで、次世代高速炉の燃焼核特性の計算精度に及ぼす解析条件の影響を、中性子エネルギー群、中性子輸送理論、空間メッシュに着目して調査した。本検討では燃焼核特性として、平衡サイクルにおける臨界性、燃焼反応度、制御棒価値、増殖比、集合体単位の出力分布、最大線出力、ナトリウムボイド反応度、ドップラー係数を取り扱った。検討の結果、エネルギー群を18群とし、拡散近似を用いて1集合体あたり6メッシュ分割して、エネルギー群、空間メッシュ、輸送効果の補正係数を適用することが最適であることが分かった。

連続エネルギーモンテカルロコードMVPとJENDL-5によるTRIGA型原子炉体系の臨界ベンチマーク解析

柳澤 宏司; 梅田 幹; 求 惟子; 村尾 裕之

JAEA-Technology 2022-030, 80 Pages, 2023/02

JAEA-Technology-2022-030.pdf:2.57MB
JAEA-Technology-2022-030(errata).pdf:0.11MB

連続エネルギーモンテカルロコードMVPと評価済み核データライブラリJENDL-5によって、ウラン水素化ジルコニウム燃料棒を用いるTRIGA型原子炉体系の臨界ベンチマーク解析を行った。解析対象は、国際臨界安全ベンチマークプロジェクト(ICSBEP)のハンドブックに掲載されているIEU-COMP-THERM-003とIEU-COMP-THERM-013の二種類のデータであり、中性子実効増倍率、制御棒等の反応度価値について旧バーションのJENDLを使用した結果と比較した。その結果、JENDL-5による中性子実効増倍率はJENDL-4.0よりも0.4から0.6%大きく、制御棒等の反応度価値は、JENDL-5とJENDL-4.0との有意な差は無いことが分かった。これらの解析結果は今後予定しているNSRRの制御棒反応度価値等の解析において、計算精度の確認の参考になるものと考えられる。

Emulsification of low viscosity oil in alkali-activated materials

Reeb, C.*; Davy, C. A.*; Pierlot, C.*; Bertin, M.*; Cantarel, V.; Lambertin, D.*

Cement and Concrete Research, 162, p.106963_1 - 106963_16, 2022/12

https://doi.org/10.1016/j.cemconres.2022.106963

Significant amounts of low viscosity mineral oil (20 %vol) are successfully immobilized in alkali-activated materials (AAM), either based on metakaolin or blast furnace slag. Surfactants are required to stabilize of the oil emulsion. Visual observation, torque measurement and rheology evidence two distinct groups of surfactants. One group contributes to structuring the oil/AAM fresh mix, with greater torque and viscosity than without surfactant; the other includes non-structuring surfactants, without change in torque or viscosity. Each group depends on the AAM considered. Whatever the AAM and the surfactant, the interfacial tension between oil/activating solution and the oil droplet size decrease significantly. Therefore, although contributing to stabilize the emulsion, interfacial tension alone does not explain the two distinct behaviors. Characterization of diluted ternary suspensions (solid particles-oil-AS) relates the structuring effect to interactions between oil and solid particles, through the surfactant polar head groups and non-polar hydrocarbon tails. An original mechanism explaining structuration is discussed.

Laser beam direct energy deposition of graded austenitic-to-martensitic steel junctions compared to dissimilar electron beam welding

Villaret, F.*; Boulnat, X.*; Aubry, P.*; 矢野 康英; 大塚 智史; Fabregue, D.*; de Carlan, Y.*

Materials Science & Engineering A, 824, p.141794_1 - 141794_10, 2021/09

https://doi.org/10.1016/j.msea.2021.141794

This article presents the Laser Beam Direct Energy Deposition (DED-LBD) process as a method to build a graded austenitic-to-martensitic steel junction. Builds were obtained by varying the ratio of the two powders during DED-LB processing. Samples with gradual transitions were successfully obtained using a high dilution rate from one layer to the next. Long austenitic grains are observed on 316L side while martensitic grains are observed on Fe-9Cr-1Mo side. In the transition zone, the microstructure is mainly martensitic. Characterizations were performed after building and after a tempering heat treatment at630C during 8h and compared to dissimilar Electron Beam (EB) welds. Before heat treatment, the DBD-LB graded area has high hardness due to fresh martensite formed during building. Tempering heat treatment reduces this hardness to 300 Hv. EDS measurements indicate that the chemical gradient between 316L and Fe-9Cr-1Mo obtained by DED-LB is smoother than the chemical change obtained in EB welds. Microstructures in DED-LB samples are quite different from those obtained by EB welding. Hardness values in DMD-LB samples and in welds are similar; the weld metal and the Fe-9Cr-1Mo HAZ are relatively hard after welding because of fresh martensite, as found in the DED-LB transition zone; both are softened by the tempering heat treatment. Both welds were overmatched at 20, 400 and 550C.

Temporal change in atmospheric radiocesium during the first seven years after the Fukushima Dai-ich Nuclear Power Plant accident

阿部 智久; 吉村 和也; 眞田 幸尚

Aerosol and Air Quality Research, 21(7), p.200636_1 -  200636_11, 2021/07

https://doi.org/10.4209/aaqr.200636

After the Fukushima Dai-ichi Nuclear Power Plant accident, atmospheric radiocesium concentration has been monitored by the Nuclear Regulation Authority (NRA) as a national project to assess its temporal change from August 2011 to November 2017. During the first two years, the atmospheric radiocesium concentration ranged between 10 - 100 Bq m, while concentrations of 10 - 10 Bq m were detected about seven years after the accident. Moreover, two years after the accident, the resuspension factor (RF) ranged between 10 - 10 m and gradually decreased to 10 - 10 m over time. Thus, the time dependence of RF can be divided into two phases, including a rapid decrease for the first two years, followed by a slow decreasing phase. The annual average RF values were also reduced by about half due to decontamination. Furthermore, to investigate the impact of anthropogenic activities on the RF temporal change, the monitoring data were classified into two groups, namely inside and outside the Fukushima evacuation zone. The RF decreased faster in the second than in the first group, which was consistent with the reported data on the time dependence of the air dose rate, suggesting that anthropogenic activities can promote environmental remediation and thereby reduce atmospheric radiocesium content. In addition, the currently observed RF reduction was faster than that reported for the Chernobyl Nuclear Power Plant accident for the same period, consisting with faster environmental remediation at catchment scale in Fukushima compared to Europe.

高レベル放射性廃液ガラス固化体の表面積の増加に関する調査及び評価; 地層処分性能評価のための割れによる表面積増加比及びその根拠等

五十嵐 寛

JAEA-Review 2020-006, 261 Pages, 2020/09

JAEA-Review-2020-006.pdf:4.42MB

本調査報告では、公開情報を対象に我が国の地層処分研究開発第2次取りまとめ(H12レポート)以降の諸外国の包括的性能評価報告書を中心として、ソースタームとしての核種溶出モデルにおけるガラス固化体の割れによる表面積増加比の設定値及びその根拠・背景の視点から調査した。また、海外の知見を参考に表面積増加に関する試験の日本の報告例に対する評価を試行した。調査文献から得られた知見に基づき、ガラス固化体の直径、ガラス固化体製造時の冷却条件、ガラス固化体への衝撃、地層処分場閉鎖後の水との接触等の環境条件等が、割れによる表面積増加比(又は割れ係数)に及ぼす影響について検討した。多くの国において、ガラス固化体の割れの要因はガラス固化体の製造, 輸送, 保管, 貯蔵など処分前管理の段階及び処分後の現象又は事象に起因するとされている。その影響は地層処分の性能評価における核種溶出モデルでも考慮されている。各国の核種溶出モデルにおける表面積増加比とその根拠等を概観し、各国の間の相違点及び共通点を整理するとともに、これまでに報告された表面積増加比の測定値と測定方法との関係及び測定方法の特性について考察した。また、各国の核種溶出モデルで設定されている表面積増加比の根拠としての表面積増加比の測定に用いられた測定方法を整理した。さらに、廃棄物管理工程の流れの中でのガラス固化体の割れによる表面積増加比に影響する要因、表面積増加比の特徴等の各工程との関わりを検討した。これらの調査及び検討により、性能評価における保守的かつ現実的な表面積増加比の適用に向けた知見を拡充し、我が国の地層処分のシステムのセーフティケースの作成・更新に資することができる。

Investigation on the influence of additional protective measures on sheltering effectiveness for internal exposure

廣内 淳; 高原 省五; 駒ヶ峯 弘志*; 宗像 雅広

Proceedings of Asian Symposium on Risk Assessment and Management 2019 (ASRAM 2019) (USB Flash Drive), 7 Pages, 2019/09

屋内退避による内部被ばくの低減効果を高めるための手段の一つとして空気清浄機の稼動が挙げられる。低減効果を最も効果的に高める空気清浄機の稼動方法を検討するために、本研究では、空気清浄機の除去効率を実験的に調査し、その実験結果を用いて低減効果を計算した。その結果、空気清浄機の風量が大きいほど低減効果がより高まることが示された。