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Heavy fermion state of YbNi$$_2$$Si$$_3$$ without local inversion symmetry

中村 翔太*; 兵頭 一志*; 松本 裕司*; 芳賀 芳範; 佐藤 仁*; 上田 茂典*; 三村 功次郎*; 斉木 克祥*; 磯 孝斉*; 山下 穣*; et al.

Journal of the Physical Society of Japan, 89(2), p.024705_1 - 024705_5, 2020/02

 被引用回数:1 パーセンタイル:32.18(Physics, Multidisciplinary)

We have succeeded in growing a new heavy fermion compound YbNi$$_2$$Si$$_3$$ by the flux method. From electrical resistivity, magnetization, specific heat, magnetic torque and X-ray photoemission measurements concluded that this compound is a heavy fermion compound exhibiting an antiferromagnetic order at 0.35 K.


Oxidation of silicon carbide in steam studied by laser heating

Pham, V. H.; 永江 勇二; 倉田 正輝; 古本 健一郎*; 佐藤 寿樹*; 石橋 良*; 山下 真一郎

Proceedings of International Nuclear Fuel Cycle Conference / Light Water Reactor Fuel Performance Conference (Global/Top Fuel 2019) (USB Flash Drive), p.670 - 674, 2019/09

Silicon carbide (SiC) has recently attracted much attention as a potential material for accident tolerant fuel cladding. To investigate the performance of SiC in severe accident conditions, study of steam oxidation at high temperatures is necessary. However, the study focusing on steam oxidation of SiC at temperatures above 1600$$^{circ}$$C is still certainly limited due to lack of test facilities. With the extreme oxidation/corrosion environment in steam at high temperatures, current refractory materials such as alumina and zirconia would not survive during the tests. Application of laser heating technique could be a great solution for this problem. Using laser heating technique, we can localize the heat and focus them on the test sample only. In this study, we developed a laser heating facility to investigate high-temperature oxidation of SiC in steam at temperature range of 1400-1800$$^{circ}$$C for 1-7 h. The oxidation kinetics is then being studied based on the weight gain and observation on cross-sectioned surface of tested sample using field emission scanning electron microscope. Off-gas measurement of hydrogen (H$$_{2}$$) and carbon monoxide (CO) generated during the test is also being conducted via a sensor gas chromatography. Current results showed that the SiC sample experienced a mass loss process which obeyed paralinear laws. Parabolic oxidation rate constant and linear volatilization rate constant of the process were calculated from the mass change of the samples. The apparent activation energy of the parabolic oxidation process was calculated to be 85 kJ.mol$$^{-1}$$. The data of the study also indicated that the mass change of SiC under the investigated conditions reached to its steady stage where hydrogen generation became stable. Above 1800$$^{circ}$$C, a unique bubble formation on sample surface was recorded.


Validation and verification for the melting and eutectic models in JUPITER code

Chai, P.; 山下 晋; 永江 勇二; 倉田 正輝

Proceedings of 9th Conference on Severe Accident Research (ERMSAR 2019) (Internet), 14 Pages, 2019/03




山下 拓哉; 山下 勇人; 永江 勇二

鉄と鋼, 105(1), p.96 - 104, 2019/01

 被引用回数:1 パーセンタイル:13.55(Metallurgy & Metallurgical Engineering)

火力・原子力発電プラントの使用温度条件である550度では、フェライト鋼と溶接材の界面で破断が生じる研究結果が報告されている。本研究では、フェライト鋼への溶接時の入熱量が異なる2種類の異材継手を製作した。溶接には高入熱であるプラズマ溶接および低入熱であるティグ溶接をそれぞれ使用した。改良9Cr-1Mo鋼に形成された熱影響部の組織はプラズマ溶接とティグ溶接とで異なっていた。改良9Cr-1Mo鋼/Alloy 600部を用いて試験片を製作し、550度のクリープ試験を実施した。試験より、ティグ溶接を使用した試験片は界面破断し、プラズマ溶接を使用した試験片は界面破断しない結果が得られた。そのため、熱影響部のひずみ分布計測および有限要素解析を実施し、フェライト鋼に形成される熱影響部の変形挙動に着目し界面破断メカニズムを力学的観点で分析した。各溶接法により製作した異材接手のフェライト鋼の界面近傍に形成する熱影響部の特性の違いにより、界面近傍でのひずみ分布に違いが生じることが分かった。界面破断を回避するためには、フェライト鋼界面近傍にクリープひずみ速度が遅い熱影響部を形成させる必要がある。


The CMMR program; BWR core degradation in the CMMR-3 test

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

Proceedings of International Conference on Dismantling Challenges; Industrial Reality, Prospects and Feedback Experience (DEM 2018) (Internet), 11 Pages, 2018/10



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

Authors are developing an experimental technology to realize experiments simulating Severe Accident (SA) conditions using simulant fuel material (ZrO$$_{2}$$ 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 $$times$$ 0.3 m $$phi$$) 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.


The CMMR program; BWR core degradation in the CMMR-1 and the CMMR-2 tests

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

Proceedings of 12th International Conference of the Croatian Nuclear Society; Nuclear Option for CO$$_{2}$$ Free Energy Generation (USB Flash Drive), p.109_1 - 109_15, 2018/06



Preheat effect on titanium plate fabricated by sputter-free selective laser melting in vacuum

佐藤 雄二*; 塚本 雅裕*; 菖蒲 敬久; 山下 順広*; 山縣 秀人*; 西 貴哉*; 東野 律子*; 大久保 友政*; 中野 人志*; 阿部 信行*

Applied Physics A, 124(4), p.288_1 - 288_6, 2018/04

 被引用回数:10 パーセンタイル:59.67(Materials Science, Multidisciplinary)



Metallurgical investigations on creep rupture mechanisms of dissimilar welded joints between Gr.91 and 304SS

山下 拓哉; 永江 勇二; 菊地 浩一*; 山本 賢二*

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 8 Pages, 2017/04

A dissimilar welded joint was adopted to achieve higher thermal efficiency and economy levels in nuclear and thermal power plants. 2 types of dissimilar welded joints which were different heat input during welding to the ferrite steels were manufactured. The dissimilar welded joints were made of following materials; the modified 9Cr-1Mo steel (Gr. 91) for the ferritic steels, the 304 stainless steel for the austenitic steels and the Inconel 600 for the filler metals, Welding methods for the modified 9Cr-1Mo steel were used Plasma Arc Welding and Gas Tungsten Arc Welding (GTAW), respectively. Creep tests were conducted. Specimens by GTAW failed in base metal part and interface between the modified 9Cr-1Mo steel and Inconel 600. Interface failure mechanisms were analyzed from a perspective of metallurgy which were precipitation and growth of type I carbide and formation of oxide layer.


Strength of 316FR joints welded by Type 316FR/16-8-2 filler metals

山下 拓哉; 永江 勇二; 佐藤 健一郎*; 山本 賢二*

Journal of Pressure Vessel Technology, 138(2), p.024501_1 - 024501_7, 2016/04

 被引用回数:0 パーセンタイル:0(Engineering, Mechanical)

316FR stainless steel is a candidate structural material of JSFR. Two types of weld metals are candidates for 316FR welded joints; 316FR weld metal and 16-8-2 weld metal. This study evaluated the need to consider the welded joint strength reduction factors in 316FR welded joints. To this end, the tensile and creep strengths of Type 316FR and Type 16-8-2 weld metals were measured, and the effect of delta-ferrite in weld metals was evaluated in creep-strength tests of 316FR welded joints. In tensile and creep strengths of 316FR joints welded by both metal types, the welded joint strength reduction factors were immaterial. The creep strength of 316FR welded joints was negligibly affected by delta-ferrite levels from 4.1 FN to 7.0 FN. Furthermore, the tensile and creep strengths of 316FR joints welded by two methods (Tungsten Inert Gas Welding and Shielded Metal Arc Welding) were the same.


Effects of weak organic acids on the size distribution and size-dependent metal binding of humic substances as studied by flow field-flow fractionation

山下 祐司*; 斉藤 拓巳

Journal of Environmental Chemical Engineering, 3(4), p.3024 - 3029, 2015/12

腐植物質はサイズや官能基組成の点で不均質な天然有機物であり、幅広い金属イオンと結合し、動態を変化させる。本研究では、ナノメートルスケールの連続的なサイズ分画が可能な流動場分画法を用いて、腐植物質のサイズ分布に与える有機酸の影響、および、腐植物質の分子サイズに依存した金属イオンの結合量の比較を行った。通常、pH緩衝剤としてもちいられるTris, MES, MOPSの3種類の有機酸存在下でのAldrichフミン酸(PAHA)のサイズ分布を調べた結果、Tris, MESでは、それぞれ、サイズの増加と減少が見られ、MOPSでは、有機酸無しの場合と同様のサイズが得られた。これらの結果は、TrisおよびMESとの相互作用により、PAHAのサイズが変化したことを示唆する。MOPS存在下で、PAHAに結合したユーロピウムとウランのサイズ分布を調べたところ、これらの金属イオンが特定の5nmのサイズを持つPAHA分子に高い親和性を示すことが分かった。


Decontamination and volume reduction of cesium-contaminated soil by combining soil solidification with interpolyelectrolyte complex and wet classification

山下 祐司*; 柳瀬 信之; 永野 哲志; 三田村 久吉; 長縄 弘親

Journal of Radioanalytical and Nuclear Chemistry, 305(2), p.583 - 587, 2015/08

 被引用回数:4 パーセンタイル:40.75(Chemistry, Analytical)



Colossal thermomagnetic response in the exotic superconductor URu$$_2$$Si$$_2$$

山下 卓也*; 下山 祐介*; 芳賀 芳範; 松田 達磨*; 山本 悦嗣; 大貫 惇睦; 住吉 浩明*; 藤本 聡*; Levchenko, A.*; 芝内 孝禎*; et al.

Nature Physics, 11(1), p.17 - 20, 2015/01

 被引用回数:39 パーセンタイル:89.4(Physics, Multidisciplinary)

Observation of a colossal Nernst signal is reported. URu$$_2$$Si$$_2$$ is known as a heavy fermion superconductor. The superconductivity coexists with the so-called hidden-order phase. The Nernst coefficient is enhanced by as large as million times over the theoretically expected value within the standard framework of superconducting fluctuations. Moreover, contrary to the conventional wisdom, the enhancement is more significant with the reduction of the impurity scattering rate. This anomalous Nernst effect intimately reflects the highly unusual superconducting state in URu$$_2$$Si$$_2$$.



山下 理代; 濱 克宏; 竹内 竜史; 森川 佳太*; 細谷 真一*; 中村 敏明*; 田中 由美子*

JAEA-Technology 2014-029, 118 Pages, 2014/09




Material strength evaluation for 60 years design in Japanese sodium fast reactor

永江 勇二; 鬼澤 高志; 高屋 茂; 山下 拓哉

Proceedings of 2014 ASME Pressure Vessels and Piping Conference (PVP 2014) (DVD-ROM), 9 Pages, 2014/07

316FR and Mod.9Cr-1Mo steels are candidates as structural materials for Japanese Sodium Fast Reactor, JSFR. The design life and operation temperature of JSFR is 60 years and 823K, respectively. Time-dependent allowable stress is essential. The evaluation of allowable stresses to 500,000 h is a considerable item. Long term strength is evaluated from a viewpoint of microstructural evaluation related to fracture mechanism. In addition, degradation after long term operation at elevated temperature is important. Aging is considered as one of the degradation. The effect of aging on short term property is analyzed. Material strength standard is also necessary for very thick tube sheets of forgings and small diameter thin walled seamless pipes, which are made of Mod.9Cr-1Mo steel in steam generators. This paper summarized currently available data and information on the above items, and shows path forward to the development of material strength standard for 60 years design in JSFR.


Continuous liquid-liquid extraction of nickel from simulated electroless nickel plating liquid wastes by using a counter current emulsion flow extractor

永野 哲志; 三田村 久吉; 山下 祐司; 柳瀬 信之; 鈴木 英哉; 長縄 弘親

Solvent Extraction Research and Development, Japan, 21(1), p.111 - 117, 2014/00




山下 祐司; 田邊 洋祐*; 足立 泰久*

農業農村工学会論文集, 81(6), p.33 - 37, 2013/12

分画分子量30,000-100,000g/mol(SHA)、あるいは100,000-300,000g/mol(LHA)のフミン酸をさまざまなNaCl濃度で酸性条件下のガラスビーズ充填カラムへ流し入れ、その流出量の経時変化から破過曲線を得た。すべての条件において、破過曲線の立ち上がり後、相対濃度(流出濃度/流入濃度)は漸近的にある一定値へ収束し、NaCl濃度が増加するとともにその収束値は減少した。破過曲線で得られた相対濃度の収束値から、フミン酸の無次元沈着速度定数を算出し、さらに衝突係数を求めることで、フミン酸のコロイド安定性に対する分画分子量の影響を評価した。NaCl濃度と衝突係数の両対数プロット(安定度曲線)から、両フミン酸において急速沈着領域と緩速沈着領域の境である臨界沈着濃度(CDC)が明確に現れること、分画分子量の大きい方が緩速沈着領域における曲線の傾きは急峻であること、CDC$$_{LHA,pH3}$$=0.73M, CDC$$_{SHA,pH3}$$=1.46Mで分画分子量の小さなフミン酸のCDCが高いことが明らかとなった。



足立 泰久*; 小林 幹桂*; Feng, L.*; 辻本 陽子*; 山下 祐司

オレオサイエンス, 13(7), p.299 - 307, 2013/07



Transport behavior and deposition kinetics of humic acid under acidic conditions in porous media

山下 祐司*; 田中 忠夫; 足立 泰久*

Colloids and Surfaces A; Physicochemical and Engineering Aspects, 417, p.230 - 235, 2013/01

 被引用回数:10 パーセンタイル:30.02(Chemistry, Physical)



Conduction-band electronic states of YbInCu$$_4$$ studied by photoemission and soft X-ray absorption spectroscopies

内海 有希*; 佐藤 仁*; 栗原 秀直*; 間曽 寛之*; 平岡 耕一*; 小島 健一*; 飛松 浩明*; 大河内 拓雄*; 藤森 伸一; 竹田 幸治; et al.

Physical Review B, 84(11), p.115143_1 - 115143_7, 2011/09

 被引用回数:7 パーセンタイル:31.79(Materials Science, Multidisciplinary)

典型的な価数揺動系であるYbInCu$$_4$$の価電子状態を、硬X線内殻光電子分光,軟X線吸収実験、及び軟X線光電子分光の温度依存性の実験から研究した。YbInCu$$_4$$の価数転移について、価電子帯からYb 4$$f$$状態への電荷移動で記述した。

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