Role of retained austenite and deformation-induced martensite in 0.15C-5Mn steel monitored by neutron diffraction measurement during tensile deformation

山下 享介*; 諸岡 聡; Gong, W.; 川崎 卓郎; Harjo, S.; 北條 智彦*; 興津 貴隆*; 藤井 英俊*

ISIJ International, 64(14), p.2051 - 2060, 2024/12

https://doi.org/10.2355/isijinternational.ISIJINT-2024-196

An Fe-0.15C-5Mn-0.5Si-0.05Nb steel annealed at 660C and 685C showed Lders deformation followed by high work hardening, with variations in Lders strain and hardening behavior. neutron diffraction during tensile tests analyzed phase stresses, strength contributions, and austenite orientation. Deformation-induced martensite contributed 1000 MPa to strength near tensile failure, while austenite mainly enhanced ductility via transformation-induced plasticity. Austenite transformed to martensite during Lders deformation regardless of orientation, though 311-oriented grains tended to remain along the tensile direction.

Martensitic transformation behavior of Fe-Ni-C alloys monitored by neutron diffraction during cryogenic cooling

山下 享介*; Harjo, S.; 川崎 卓郎; 諸岡 聡; Gong, W.; 藤井 英俊*; 友田 陽*

ISIJ International, 64(2), p.192 - 201, 2024/01

https://doi.org/10.2355/isijinternational.ISIJINT-2023-208

neutron diffraction measurements were performed on Fe-33Ni-0.004C alloy (33Ni alloy) and Fe-27Ni-0.5C alloy (27Ni-0.5C alloy) during cooling from room temperature to the cryogenic temperature (4 K) to evaluate changes in the lattice constants of austenite and martensite, and changes in the tetragonality of martensite due to thermally induced martensitic transformation. As the martensitic transformation progressed, the lattice constants of austenite in both alloys deviated to smaller values than those predicted considering the thermal shrinkage, accompanied by an increase in the full width at half maximum of austenite. The fresh martensite formed in both alloys had a body-centered tetragonal (BCT) structure, regardless of the carbon content. The tetragonality of martensite decreased with progressive martensitic transformation during cooling in the 33Ni alloy, but was almost constant in the 27Ni-0.5C alloy. This suggests that carbon is necessary to maintain the tetragonality of martensite during cooling. The tetragonality of martensite in the 27Ni-0.5C alloy decreased during room temperature aging because of carbon mobility.

Iterative methods with mixed-precision preconditioning for ill-conditioned linear systems in multiphase CFD simulations

伊奈 拓也*; 井戸村 泰宏; 今村 俊幸*; 山下 晋; 小野寺 直幸

Proceedings of 12th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems ScalA21) (Internet), 8 Pages, 2021/11

https://doi.org/10.1109/ScalA54577.2021.00006

多相熱流動解析コードJUPITERにおける前処理付き共役勾配法(P-CG)ソルバおよびマルチグリッド前処理付き共役勾配法(MGCG)ソルバに対して反復改良(IR)法に基づく新しい混合精度前処理を開発した。このIR前処理では全てのデータを半精度で格納してメモリアクセスを削減するが、全ての演算処理を単精度で行う。このハイブリッド半精度/単精度実装は単精度処理と同様の収束特性を維持しつつ、計算性能は半精度処理に近くなる。開発ソルバを富岳(A64FX)で最適化し、JUPITERの悪条件行列に適用した。新しいIR前処理を用いたP-CGソルバとMGCGソルバは8,000ノードまで良好な強スケーリングを示し、8,000ノードにおいて、これらのソルバはOakforest-PACS(KNL)における従来ソルバに比べてそれぞれ4.86倍および2.39倍に高速化された。

MA分離抽出剤の放射線分解メカニズムの研究

樋川 智洋; 村山 琳*; 熊谷 友多; 山下 真一*; 鈴木 英哉; 伴 康俊; 松村 達郎

UTNL-R-0501, p.24 - 25, 2020/12

東京大学大学院工学系研究科が有するライナック研究施設を利用して平成31年度に得られた成果をまとめたものである。マイナーアクチノイド(MA)の分離プロセスで利用が見込まれるジグリコールアミド抽出剤について、ドデカン及びオクタノール溶液中における放射線分解過程をパルスラジオリシスにより調べた。その結果、アルコールを添加することにより、ジグリコールアミド抽出剤の放射線分解過程は、これまで考えられてきたラジカルカチオンを経由するドデカン単一溶媒中での分解過程とは異なることが示唆された。

Development of experimental technology for simulated fuel-assembly heating to address core-material-relocation behavior during severe accident

阿部 雄太; 山下 拓哉; 佐藤 一憲; 中桐 俊男; 石見 明洋

Journal of Nuclear Engineering and Radiation Science, 6(2), p.021113_1 - 021113_9, 2020/04

https://doi.org/10.1115/1.4045450

The authors are developing an experimental technology for simulating severe accident (SA) conditions using simulate fuel material (ZrO) that would contribute, not only to Fukushima Daiichi (1F) decommissioning, but also to enhance the safety of worldwide existing and future nuclear power plants through clarification of accident progression behavior. Nontransfer (NTR) type plasma, which has been in practical use with a large torch capacity as high as 2 MW, has the potential to heat subject materials to very high temperatures without selecting the target to be heated. When simulating 1F with SA code, the target of this core-material-melting and relocation (CMMR) experiment was to confirm that NTR plasma has a sufficient heating performance realizing large temperature gradients ( 2000 K/m) expected under 1F conditions. The authors selected NTR-type plasma-heating technology that has the advantage of continuous heating in addition to its high-temperature level. The CMMR-2 experiments were carried out in 2017 applying the improved technology (higher heating power and controlled oxygen concentration). The CMMR-2 experiment adopted a 30-min heating period, wherein the power was increased to a level where a large temperature gradient was expected at the lower part of the core under actual 1F accident conditions. Most of the control blade and channel box migrated from the original position. After heating, the simulated fuel assembly was measured by X-ray computed tomography (CT) technology and by electron probe micro-analyzer (EPMA). CT pictures and elemental mapping demonstrated its excellent performance with rather good precision. Based on these results, an excellent perspective, in terms of applicability of the NTR-type plasma-heating technology to the SA experimental study, was obtained.

Communication avoiding multigrid preconditioned conjugate gradient method for extreme scale multiphase CFD simulations

井戸村 泰宏; 伊奈 拓也*; 山下 晋; 小野寺 直幸; 山田 進; 今村 俊幸*

Proceedings of 9th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems (ScalA 2018) (Internet), p.17 - 24, 2018/11

https://doi.org/10.1109/ScalA.2018.00006

多相流体CFDコードJUPITERの圧力ポアソン方程式に省通信マルチグリッド前処理付共役勾配(CAMGCG)法を適用し、省通信クリロフ部分空間法と計算性能と収束特性を比較した。JUPITERコードにおいてCAMGCGソルバ問題サイズによらずロバーストな収束特性を有し、通信削減と収束特性向上を両立することから、通信削減のみを実現する省通信クリロフ部分空間法に対する優位性が高い。CAMGCGソルバを億自由度の大規模多相流体CFDシミュレーションに適用して反復回数を前処理付CG法のに削減し、Oakforest-PACSにおける8,000ノードまでの良好な強スケーリングとCG法の倍の性能向上を達成した。

Development of experimental technology for simulated fuel-assembly heating to address core-material-relocation behavior during severe accident

阿部 雄太; 山下 拓哉; 佐藤 一憲; 中桐 俊男; 石見 明洋; 永江 勇二

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 9 Pages, 2018/07

https://asme.pinetec.com/icone26/

Authors are developing an experimental technology to realize experiments simulating Severe Accident (SA) conditions using simulant fuel material (ZrO with slight addition of MgO for stabilization) that would contribute not only to Fukushima Daiichi (1F) decommissioning but also to enhance the safety of worldwide existing and future nuclear power plants through clarification of the accident progression behavior. Based on the results of the prototype test, improvement of plasma heating technology was conducted. The Core Material Melting and Relocation (CMMR)-1/-2 experiments were carried out in 2017 with the large-scale simulated fuel assembly (1 m 0.3 m ) applying the improved technology (higher heating power and controlled oxygen concentration). In these two tests, heating history was different resulting basically in similar physical responses with more pronounced material melting and relocation in the CMMR-2 experiment. The CMMR-2 experiment is selected here from the viewpoint of establishing an experimental technology. The CMMR-2 experiment adopted 30-min heating period, the power was increased up to a level so that a large temperature gradient ( 2,000 K/m) expected at the lower part of the core in the actual 1F accident conditions. Most of the control blade and the channel box migrated from the original position. After the heating, the simulated fuel assembly was measured by the X-ray Computed Tomography (CT) technology and by Electron Probe Micro Analyzer (EPMA). CT pictures and elemental mapping demonstrated its excellent performance with rather good precision. Based on these results, an excellent perspective in terms of applicability of the non-transfer type plasma heating technology to the SA experimental study was obtained.

蒸気種遷移挙動評価手法の開発; FP蒸気種及びエアロゾルの化学形や、エアロゾルの物理的パラメータの評価に適用可能な測定技術の調査及び試計測に基づく適用可能性評価

高井 俊秀; 佐藤 勇*; 山下 真一郎; 古川 智弘

JAEA-Technology 2015-043, 56 Pages, 2016/02

JAEA-Technology-2015-043.pdf:23.14MB

ソースターム評価手法の高度化及び福島第一原子力発電所廃止措置に係る研究開発として、シビアアクシデント時に溶融燃料から放出される核分裂生成物(FP)の移行モデルの改良・高度化への適用に向けて、FPの化学挙動解明に向けた基礎基盤研究が実施されている。本研究では、FP移行モデルの改良に向けて必要となる、(1)放出直後からエアロゾル化するまでのFPの化学的な挙動や、(2)その後の化学挙動に影響を与えうるエアロゾル形状等の物理的パラメータの評価に適用可能な測定技術について調査するとともに、有望と考えられた分析手法については試計測により適用可能性を調べた。その結果、FP蒸気種及びエアロゾルの化学形の評価については、ラマン分光法が有望であり、室温同様、500Cに加熱した状態でも化学形の識別が可能であることが確認された。また、エアロゾルの化学形については、高温X線回折法も活用可能であることが確認された。一方、エアロゾルの物理的パラメータの評価については、カスケードインパクタで採取した試料を、透過型電子顕微鏡、エネルギー分散型X線分光法を用いて、観察・分析することが有望であることが確認された。

Experimental study for the production cross sections of positron emitters induced from C and O nuclei by low-energy proton beams

赤城 卓*; 八木 雅史*; 山下 智弘*; 村上 昌雄*; 山川 善之*; 北村 圭司*; 小倉 浩一; 近藤 公伯; 河西 俊一*

Radiation Measurements, 59, p.262 - 269, 2013/12

https://doi.org/10.1016/j.radmeas.2013.07.005

陽子線癌治療では体内のCあるいはOと陽子線の相互作用によって陽電子放出核が生成される。この陽電子放出核に起因する陽電子の消滅放射線をPET装置でモニタリングすることによって陽子線の到達深さと照射線量を確かめる方法の研究が行われている。我々は、通常の陽子線治療施設で使われている装置を使って、照射線量を評価するために必要な陽電子放出核生成断面積を測定する方法を研究している。高感度PETスキャナー装置を使用し陽電子放出核に起因する消滅放射線の強度の時間変化を測定することによって4つの反応反応(O(p,pn)O, O(p,3p3n)C, O(p,2p2n)N, C(p,pn)C)の断面積を評価した。その結果、O(p,pn)O反応の結果は以前の測定結果とよく一致した。一方、C(p,pn)C反応の結果は以前の測定より低い値であった。

Dose-response measurement in gel dosimeter using various imaging modalities

藤淵 俊王*; 川村 拓*; 山梨 宏一*; 廣木 章博; 山下 真一*; 田口 光正; 佐藤 裕一*; 三村 功一*; 牛場 洋明*; 沖原 徹*

Journal of Physics; Conference Series, 444(1), p.012089_1 - 012089_4, 2013/06

https://doi.org/10.1088/1742-6596/444/1/012089

Measurement methods that accurately measure radiation dose distribution in a three dimensional manner in order to allow comparisons of treatment plans are needed for quality assurance. One such measurement method involves the use of a polymer gel dosimeter to measure the dose distribution in three dimensions. During irradiation, a polymerization reaction makes new chemical bonds and induces changes of the chemical structure of the gel of the gel dosimeter. In the present study, dose-response measurement of an environment-friendly material used in the gel dosimeter was performed by imaging with computed tomography (CT) and R1, R2, and fluid-attenuated inversion-recovery (FLAIR) magnetic resonance imaging (MRI) under various imaging conditions. Dose-response characteristics in the gel dosimeter used in the experiment were observed at doses of 5-20 Gy administered by X-ray CT and MRI. Although the FLAIR signal was a relative value, the dose-response values with FLAIR were excellent compared to those with R1, R2, and CT. Determination of more appropriate imaging conditions could help expand the dose-response parameters of each measurement method.