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Journal Articles

An In-situ X-ray absorption spectroelectrochemical study of the electroreduction of uranium ions in HCl, HNO$$_3$$, and NaCO$$_3$$ solutions

Uehara, Akihiro*; Fujii, Toshiyuki*; Yamana, Hajimu*; Okamoto, Yoshihiro

Radiochimica Acta, 104(1), p.1 - 9, 2016/01

 Times Cited Count:2 Percentile:57.25(Chemistry, Inorganic & Nuclear)

The spectroelectrochemical cell was fabricated for in-situ X-ray absorption fine structure (XAFS) measurement. The XAFS spectra of U L$$_3$$-edge were monitored in electrolyte solutions during the electrochemical reduction. Tetravalent uranium was electrochemically prepared from hexavalent uranium and the extended X-ray absorption fine structure (EXAFS) was analyzed. The U$$^{4+}$$ formed in 0.1M HNO$$_3$$ was partially re-oxidized to UO$$_2$$$$^{2+}$$ by NO$$_3$$$$^-$$ in the solution. The UO$$_2$$$$^+$$ carbonates were prepared during electrolysis.

Journal Articles

Theoretical and experimental study of the vibrational frequencies of UO$$_{2}$$$$^{2+}$$ and NpO$$_{2}$$$$^{2+}$$ in highly concentrated chloride solutions

Fujii, Toshiyuki*; Uehara, Akihiro*; Kitatsuji, Yoshihiro; Yamana, Hajimu*

Journal of Radioanalytical and Nuclear Chemistry, 303(1), p.1015 - 1020, 2015/01

 Times Cited Count:3 Percentile:53.75(Chemistry, Analytical)

The $$nu$$$$_{1}$$ symmetric vibrational frequency of UO$$_{2}$$$$^{2+}$$ in chloride solutions was studied by Raman spectrometry and ab initio calculations. The $$nu$$$$_{1}$$ frequency experimentally obtained decreased with the increase of concentration of Cl in solvent chlorides. This is attributable to that hydration water molecules in the equatorial plane of UO$$_{2}$$$$^{2+}$$ are substituted by Cl$$^{-}$$ ions, which was consistent with the calculation results. The theoretical part was expanded to aqua- and chloro- Np(VI) complexes. The $$nu$$$$_{1}$$ frequencies of neptunyl species computed were acceptable compared with the reported Raman shifts.

Journal Articles

Redox equilibrium of the UO$$_2^{2+}$$/UO$$_2^{+}$$ couple in Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic melt at 550$$^{circ}$$C

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Sato, Nobuaki*; Kofuji, Hirohide; Myochin, Munetaka; Yamana, Hajimu*

Journal of Nuclear Materials, 454(1-3), p.159 - 163, 2014/11

 Percentile:100(Materials Science, Multidisciplinary)

The redox equilibrium of UO$$_2^{2+}$$/UO$$_2^{+}$$ couple was measured in Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic melt at 550$$^{circ}$$C by cyclic voltammetry and absorption spectrophotometry. The standard redox potential of UO$$_2^{2+}$$/UO$$_2^{+}$$ couple was approximately evaluated by cyclic voltammetry. Further, the absorption spectrum and equilibrium potential were measured, repeatedly adding UO$$_2^{2+}$$ source material into the melt containing UO$$_2^{+}$$. From the correlation between the equilibrium potential of the melt and the concentration ratio [UO$$_2^{2+}$$]/[UO$$_2^{+}$$] spectrophotometrically evaluated, the standard redox potential of UO$$_2^{2+}$$/UO$$_2^{+}$$ couple was determined to be -0.847$$pm$$0.010 V vs. O$$_{2}$$/O$$^{2-}$$.

Journal Articles

Raman spectroscopic study on NpO$$_{2}$$$$^{+}$$-Ca$$^{2+}$$ interaction in highly concentrated calcium chloride

Fujii, Toshiyuki*; Uehara, Akihiro*; Kitatsuji, Yoshihiro; Yamana, Hajimu*

Journal of Radioanalytical and Nuclear Chemistry, 301(1), p.293 - 296, 2014/07

 Times Cited Count:3 Percentile:61.51(Chemistry, Analytical)

Coordination circumstance of neptunyl ion in concentrated CaCl$$_{2}$$ solutions was analyzed by Raman spectrometry. Besides the symmetric stretch ($$nu$$$$_{1}$$) mode of NpO$$_{2}$$$$^{+}$$ and NpO$$_{2}$$$$^{2+}$$, the asymmetric stretch ($$nu$$$$_{3}$$) mode of NpO$$_{2}$$$$^{+}$$ was found. The Raman intensity of the $$nu$$$$_{3}$$ mode increased with the concentration of CaCl$$_{2}$$ in the system. This would be attributable to the cation-cation interaction between Np(V) and Ca(II).

Journal Articles

Reduction behavior of UO$$_{2}$$$$^{2+}$$ in molten LiCl-RbCl and LiCl-KCl eutectics by using tungsten

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Yamana, Hajimu*

Journal of Nuclear Materials, 439(1-3), p.1 - 6, 2013/08

 Times Cited Count:1 Percentile:84.29(Materials Science, Multidisciplinary)JP, 2011-035573   Licensable Patent Information Database   Patent publication (In Japanese)

The reduction of uranium from UO$$_{2}$$$$^{2+}$$ to UO$$_{2}$$$$^{+}$$ or U$$^{4+}$$ in molten LiCl-RbCl and LiCl-KCl eutectics was examined by using tungsten and chlorine gas. Spectrophotometric technique was adopted to determine the concentration of uranium species. When tungsten was immersed into the LiCl-RbCl eutectic melt at 400$$^{circ}$$C without supplying chlorine gas, 36% of the total weight of the hexavalent of UO$$_{2}$$$$^{2+}$$ was reduced to the pentavalent of UO$$_{2}$$$$^{+}$$. Under purging chlorine gas into the melt, 96% of UO$$_{2}$$$$^{2+}$$ was reduced to the tetravalent of U$$^{4+}$$. Tungsten oxy-chloride of WOCl$$_{4}$$ was produced via the reductions of UO$$_{2}$$$$^{2+}$$, which was volatized from the melt and adsorbed on the upper part of experimental cell. On the other hand, 84% of UO$$_{2}$$$$^{2+}$$ in the LiCl-KCl eutectic melt at 500$$^{circ}$$C was reduced to U$$^{4+}$$ by using tungsten and chlorine gas.

Journal Articles

Quantitative analysis of neodymium, uranium, and palladium in nitric acid solution by reflection absorption spectrophotometry

Fujii, Toshiyuki*; Egusa, Soichiro*; Uehara, Akihiro*; Yamana, Hajimu*; Morita, Yasuji

Journal of Radioanalytical and Nuclear Chemistry, 295(3), p.2059 - 2062, 2013/03

 Times Cited Count:1 Percentile:84.29(Chemistry, Analytical)

Quantitative analysis of Nd, U, or Pd in 3 mol dm$$^{-3}$$ (M) HNO$$_{3}$$ was performed by reflection absorption spectrophotometry at ultraviolet-visible-near-infrared (UV/Vis/NIR) region. A sample chamber with optics for reflection measurement was designed and attached to a UV/Vis/NIR spectrophotometer by optical fibers. The reflection absorbance showed linear relations with concentrations of Nd, U, and Pd at the absorbance region less than 0.1. The quantitative analysis was found to be possible for 3 M HNO$$_{3}$$ solutions containing [Nd] ca. 0.2 M, [U] ca. 0.04 M, or [Pd] ca. 0.01 M at maximum.

Journal Articles

Synthesis and investigation of uranyl molybdate UO$$_{2}$$MoO$$_{4}$$

Nagai, Takayuki; Sato, Nobuaki*; Kitawaki, Shinichi; Uehara, Akihiro*; Fujii, Toshiyuki*; Yamana, Hajimu*; Myochin, Munetaka

Journal of Nuclear Materials, 433(1-3), p.397 - 403, 2013/02

 Times Cited Count:7 Percentile:34.56(Materials Science, Multidisciplinary)

In order to examine easily synthetic conditions of uranyl molybdate, UO$$_{2}$$MoO$$_{4}$$, used for the reprocessing process study of spent nuclear oxide fuels in alkaline molybdate melts, the uranium molybdate compounds were produced from U$$_{3}$$O$$_{8}$$ powder and anhydrous MoO$$_{3}$$ reagent. The results of having investigated them in solid state by using X-ray diffractometry and Raman spectrometry, it was confirmed that UO$$_{2}$$MoO$$_{4}$$ could be synthesized by heating mixed powder of U$$_{3}$$O$$_{8}$$ and MoO$$_{3}$$ with stoichiometric mole ratio at 770$$^{circ}$$C for 4 h under air atmosphere. Moreover, adding this UO$$_{2}$$MoO$$_{4}$$ into Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic melt, most of the dissolved uranium species in the melt were observed as hexa-valent uranyl ions by absorption spectrophotometry.

Journal Articles

Support system for training and education of future expert at PIE Hot Laboratories in Oarai JAEA; FEETS

Osaka, Masahiko; Donomae, Takako; Ichikawa, Shoichi; Sasaki, Shinji; Ishimi, Akihiro; Inoue, Toshihiko; Sekio, Yoshihiro; Miwa, Shuhei; Onishi, Takashi; Asaka, Takeo; et al.

Proceedings of 1st Asian Nuclear Fuel Conference (ANFC), 2 Pages, 2012/03

Support system for training and education of future expert in hot laboratories of Oarai-JAEA, named FEETS, is presented. The system has been established based on research results on both characterization of Oarai hot laboratory and user-needs. Various programs under FEETS are also introduced.

Journal Articles

Actinide-handling experience for training and education of future expert under J-ACTINET

Osaka, Masahiko; Konashi, Kenji*; Hayashi, Hirokazu; Li, D.*; Homma, Yoshiya*; Yamamura, Tomoo*; Sato, Isamu; Miwa, Shuhei; Sekimoto, Shun*; Kubota, Takumi*; et al.

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 5 Pages, 2011/12

Summer schools for future experts have successfully been completed under Japan Actinide Network (J-ACTINET) for the purpose of development of human resources who are expected to be engaged in every areas of actinide-research/engineering. The first summer school was held in Ibaraki-area in August 2009, followed by the second one in Kansai-area in August 2010. Two summer schools have focused on actual experiences of actinides in actinide-research fields for university students and young researchers/engineers as an introductory course of actinide-researches. Several quasi actinide-handling experiences at the actinide-research fields have attracted attentions of participants at the first school in Ibaraki-area. The actual experiments using actinides-containing solutions have been carried out at the second school in Kansai-area. Future summer schools will be held every year for the sustainable human resource development in various actinide-research fields.

Journal Articles

J-ACTINET activities of training and education for actinide science research

Minato, Kazuo; Konashi, Kenji*; Yamana, Hajimu*; Yamanaka, Shinsuke*; Nagasaki, Shinya*; Ikeda, Yasuhisa*; Sato, Seichi*; Arita, Yuji*; Idemitsu, Kazuya*; Koyama, Tadafumi*

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 5 Pages, 2011/12

Actinide science research is indispensable to maintain sustainable development of innovative nuclear technology. For actinide science research, special facilities with containment and radiation shields are needed to handle actinide materials. The number of facilities for actinide science research has been decreased, especially in universities, due to the high maintenance cost. J-ACTINET was established in 2008 to promote and facilitate actinide science research and to foster many of young scientists and engineers in actinide science. The research program was carried out, through which young researchers were expected to learn how to make experiments with advanced experimental tools and to broaden their horizons. The summer schools and computational science school were held to provide students and young researchers with the opportunities to come into contact with actinide science research. The overseas dispatch program was also carried out.

Journal Articles

Electronic absorption spectra of palladium(II) in concentrated nitric acid solutions

Fujii, Toshiyuki*; Egusa, Soichiro*; Uehara, Akihiro*; Kirishima, Akira*; Yamagishi, Isao; Morita, Yasuji; Yamana, Hajimu*

Journal of Radioanalytical and Nuclear Chemistry, 290(2), p.475 - 478, 2011/11

 Times Cited Count:11 Percentile:24.46(Chemistry, Analytical)

Palladium complexation in concentrated nitric acid solutions was studied by UV/Vis absorption spectrophotometry. The ionic strength of the solutions was fixed to $$I$$ = 1, 3, or 5 M by mixing of HNO$$_{3}$$ and HClO$$_{4}$$. The major palladium species were found to be Pd$$^{2+}$$, PdNO$$_{3}$$$$^{+}$$, and Pd(NO$$_{3}$$)$$_{2}$$. The formation constant of PdNO$$_{3}$$$$^{+}$$ was determined to be $$beta$$$$_{1}$$ = 1.32 ($$I$$ = 1 M), 1.49 ($$I$$ = 3 M), or 1.47 ($$I$$ = 5 M), while that of Pd(NO$$_{3}$$)$$_{2}$$ to be $$beta$$$$_{2}$$ = 0.45 ($$I$$ = 3 M) or 0.14 ($$I$$ = 5 M).

Journal Articles

Absorption spectra and cyclic voltammograms of uranium species in molten lithium molybdate-sodium molybdate eutectic at 550 $$^{circ}$$C

Nagai, Takayuki; Uehara, Akihiro*; Fukushima, Mineo; Myochin, Munetaka; Fujii, Toshiyuki*; Sato, Nobuaki*; Yamana, Hajimu*

Proceedings in Radiochemistry, 1(1), p.151 - 155, 2011/09

Absorption spectra of dissolved uranium species in molten Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic at 550 $$^{circ}$$C were measured by spectrophotometry, and their redox reactions were also investigated by cyclic voltammetry. Observed absorption spectra of uranium species were similar to those of UO$$_{2}$$$$^{+}$$ in molten chlorides. After purging oxygen into the melt, the absorption peaks of UO$$_{2}$$$$^{+}$$ decreased and UO$$_{2}$$$$^{+}$$ was thought to be oxidized to UO$$_{2}$$$$^{2+}$$. When the uranium species were not contained in the melt, we confirmed that alkali metals deposited at -0.7 V and a small reduction of this melt was observed at -0.3 V. When UO$$_{2}$$ was dissolved into the melt, the reduction of the uranium species was observed at -0.2 V. It was suggested that the dissolved uranium species are recovered as mixed uranium-molybdenum oxides by electrolysis.

Journal Articles

EXAFS analysis of uranium(IV) and thorium(IV) complexes in concentrated CaCl$$_{2}$$ solutions

Uehara, Akihiro*; Fujii, Toshiyuki*; Matsuura, Haruaki*; Sato, Nobuaki*; Nagai, Takayuki; Minato, Kazuo; Yamana, Hajimu*; Okamoto, Yoshihiro

Proceedings in Radiochemistry, 1(1), p.161 - 165, 2011/09

Journal Articles

Electrochemical behavior and electronic absorption spectra of uranium trivalent ions in molten LiCl-CsCl mixtures

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Sato, Nobuaki*; Yamana, Hajimu*

Journal of Nuclear Materials, 414(2), p.226 - 231, 2011/07

 Times Cited Count:5 Percentile:50.9(Materials Science, Multidisciplinary)

Journal Articles

Coordination characteristics of trivalent lanthanides and actinides in molten hydrate salts of Ca(NO$$_3$$)$$_2$$ and CaCl$$_2$$

Fujii, Toshiyuki*; Okude, Genki*; Uehara, Akihiro*; Sekimoto, Shun*; Hayashi, Hirokazu; Akabori, Mitsuo; Minato, Kazuo; Yamana, Hajimu*

Journal of Radioanalytical and Nuclear Chemistry, 288(1), p.181 - 187, 2011/04

 Times Cited Count:4 Percentile:57.93(Chemistry, Analytical)

Distribution behavior of Ce(III), Am(III), and Cm(III) between tri-n-butyl phosphate solution and molten calcium nitrate hydrate Ca(NO$$_3$$)$$_2cdotmathit{R}$$H$$_2$$O or molten calcium chloride hydrate CaCl$$_2cdotmathit{R}$$H$$_2$$O was studied radiochemically. In Ca(NO$$_3$$)$$_2cdotmathit{R}$$H$$_2$$O systems, maximum separation factors of Ce and Cm to Am were observed to be 12 (Ce/Am) and 1.7 (Cm/Am). The distribution ratios of these elements increased with the decrease of water activity in the hydrates, and the extractabilities at the water deficient region was less sensitive compared to those at the water abundant region. This trend was similar to the coordination circumstance change observed in electronic absorption spectra of Nd(III) in the hydrates.

Journal Articles

Speciation of palladium in nitric acid solutions

Egusa, Soichiro*; Fujii, Toshiyuki*; Uehara, Akihiro*; Yamana, Hajimu*; Yamagishi, Isao; Morita, Yasuji

Kyoto Daigaku Genshiro Jikkenjo Dai-45-Kai Gakujutsu Koenkai Hobunshu, p.123 - 125, 2011/01

Speciation of palladium in nitric acid solutions was studied through spectrophotometric methods to obtain basic data for development of Pd separation process. Stability constants of nitrate complexes of Pd were determined by analysis of absorption spectra of nitric acid solutions of various concentrations with the constant ionic strength.

Journal Articles

Unique extraction behavior of americium and curium in a system of TBP and calcium nitrate hydrate melt

Okude, Genki*; Fujii, Toshiyuki*; Uehara, Akihiro*; Sekimoto, Shun*; Minato, Kazuo; Yamana, Hajimu*

IOP Conference Series; Materials Science and Engineering, 9, p.012067_1 - 012067_7, 2010/05

 Times Cited Count:2 Percentile:21.97

Journal Articles

Redox equilibria of the U$$^{4+}$$/U$$^{3+}$$ and U$$^{3+}$$/U couples in molten LiCl-RbCl eutectic

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Shirai, Osamu*; Sato, Nobuaki*; Yamana, Hajimu*

Denki Kagaku Oyobi Kogyo Butsuri Kagaku, 77(8), p.614 - 616, 2009/08

 Times Cited Count:11 Percentile:68.3(Electrochemistry)

Formal redox potentials of the U$$^{4+}$$/U$$^{3+}$$ and U$$^{3+}$$/U couples in molten LiCl-RbCl eutectic were determined by cyclic voltammetry. These redox potentials were more negative than those in the LiCl-KCl eutectic but positive comparing to those in the NaCl-CsCl eutectic. This relation would be correlated with the averaged alkali cation radius.

Journal Articles

Redox equilibria of Pu$$^{4+}$$/Pu$$^{3+}$$ and PuO$$_{2}$$$$^{2+}$$/Pu$$^{4+}$$ couples in molten NaCl-CsCl eutectic as measured by absorption spectrophotometry

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Shirai, Osamu*; Myochin, Munetaka; Yamana, Hajimu*

Radiochimica Acta, 97(4-5), p.209 - 212, 2009/05

 Times Cited Count:3 Percentile:69.9(Chemistry, Inorganic & Nuclear)

Redox behavior of uranium and plutonium in molten salts is the essential information for establishing an effective reprocessing process with spent MOX fuel. In an oxide electro-winning reprocessing process, the spent nuclear fuel is dissolved into the molten NaCl-CsCl eutectic, and the dissolved U(VI) and Pu(VI) species are reduced to be dioxides by electrolysis. In the present study, formal redox potentials of the Pu$$^{4+}$$/Pu$$^{3+}$$ and PuO$$_{2}$$$$^{2+}$$/Pu$$^{4+}$$ couples in the molten NaCl-CsCl eutectic at 923 K were determined. The fractions of Pu$$^{3+}$$, Pu$$^{4+}$$, and PuO$$_{2}$$$$^{2+}$$ were determined by UV/Vis/NIR absorption spectrophotometry. PuO$$_{2}$$ was dissolved into the molten NaCl-CsCl eutectic by Cl$$_{2}$$$$_{2}$$ gas purging. Valences of plutonium (Pu$$^{0}$$, Pu$$^{3+}$$, Pu$$^{4+}$$, and PuO$$_{2}$$$$^{2+}$$) were controlled by changing the flow rates of Cl$$_{2}$$, O$$_{2}$$, and Ar gases.

Journal Articles

Redox equilibria of the U$$^{4+}$$/U$$^{3+}$$ and U$$^{3+}$$/U couples in molten LiCl-RbCl eutectic

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Shirai, Osamu*; Sato, Nobuaki*; Yamana, Hajimu*

Proceedings of 2008 Joint Symposium on Molten Salts (USB Flash Drive), p.927 - 932, 2008/10

Formal redox potentials of the U$$^{4+}$$/U$$^{3+}$$ and U$$^{3+}$$/U couples in molten LiCl-RbCl eutectic were determined by cyclic voltammetry. These redox potentials were more negative than those in the LiCl-KCl eutectic but approximately similar to those in the NaCl-CsCl eutectic. These redox potentials in molten alkali chlorides would be correlated with the averaged alkali cationic radius of the melt.

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