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Journal Articles

Electronic structure of UTe$$_2$$ studied by photoelectron spectroscopy

Fujimori, Shinichi; Kawasaki, Ikuto; Takeda, Yukiharu; Yamagami, Hiroshi; Nakamura, Ai*; Homma, Yoshiya*; Aoki, Dai*

Journal of the Physical Society of Japan, 88(10), p.103701_1 - 103701_5, 2019/10

 Times Cited Count:2 Percentile:14.97(Physics, Multidisciplinary)

Journal Articles

$$^{125}$$Te-NMR study on a single crystal of heavy fermion superconductor UTe$$_2$$

Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Hattori, Taisuke; Higa, Nonoka; Nakamine, Genki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Nakamura, Ai*; Shimizu, Yusei*; et al.

Journal of the Physical Society of Japan, 88(7), p.073701_1 - 073701_4, 2019/07

 Times Cited Count:5 Percentile:4.38(Physics, Multidisciplinary)

We report $$^{125}$$Te-NMR studies on a newly discovered heavy fermion superconductor UTe$$_2$$. Using a single crystal, we have measured the $$^{125}$$Te-NMR Knight shift $$K$$ and spin-lattice relaxation rate $$1/T_1$$ for fields along the three orthorhombic crystal axes. The data confirm a moderate Ising anisotropy for both the static ($$K$$) and dynamical susceptibilities ($$1/T_1$$) in the paramagnetic state above about 20 K. Around 20 K, however, we have observed a sudden loss of NMR spin-echo signal due to sudden enhancement of the NMR spin-spin relaxation rate $$1/T_2$$, when the field is applied along the easy axis of magnetization (=$$a$$ axis). This behavior suggests the development of longitudinal magnetic fluctuations along the $$a$$ axis at very low frequencies below 20 K.

Journal Articles

Time-controlled synthesis of the 3D coordination polymer U(1,2,3-Hbtc)$$_{2}$$ followed by the formation of molecular poly-oxo cluster {$rm U$_{14}$$} containing hemimellitate uranium(IV)

Dufaye, M.*; Martin, N. P.*; Duval, S.*; Volkringer, C.*; Ikeda, Atsushi; Loiseau, T.*

RSC Advances (Internet), 9(40), p.22795 - 22804, 2019/07

 Times Cited Count:0 Percentile:100(Chemistry, Multidisciplinary)

Two coordination compounds bearing tetravalent uranium (UIV)) were synthesized in the presence of tritopic hemimellitic acid in acetonitrile with a controlled amount of water (H$$_{2}$$O/U $${approx}$$ 8) and structurally characterized. The slow hydrolysis reaction together with the partial decomposition of the starting organic reactants into oxalate and acetate molecules induces the generation of such a large poly-oxo cluster with fourteen uranium centers. Structural comparisons with other closely related uranium-containing clusters, such as the {$rm U$_{12}$$}$ cluster based on the association of inner core [U$_{6}$$O$$_{8}$$] with three dinuclear sub-units {$rm U$_{2}$$}, were performed.

Journal Articles

Study on decontamination of steel surface contaminated with uranium hexafluoride by acidic electrolytic water

Nakayama, Takuya; Nomura, Mitsuo; Mita, Yutaka; Yonekawa, Hitoshi*; Bunbai, Misako*; Yaita, Yumi*; Murata, Eiichi*; Hosaka, Katsumi*; Sugitsue, Noritake

Proceedings of 2019 International Congress on Advances in Nuclear Power Plants (ICAPP 2019) (Internet), 8 Pages, 2019/05

Clearance of contaminated metal is important for recycling and volume reduction of radioactive waste. Among applicable decontamination technologies, immersion method with ultrasonic cleaning is considered to be effective for metal materials having various shapes. in this study is to demonstrate decontamination of carbon steel contaminated by uranium hexafluoride to the target level for clearance (less than 0.04 Bq/cm$$^{2}$$), and minimize secondary waste. In this test, acidic electrolytic water, dilute hydrochloric acid, dilute sulfuric acid and ozone water with various pH and redox potential were used as decontamination solutions to be tested. We found that acidic electrolytic water is effective solution for decontamination of carbon steel contaminated by uranium hexafluoride. It could be decontaminate less than target level for clearance, and reduced secondary waste relatively.

Journal Articles

Effect of H$$_{2}$$O$$_{2}$$ concentration on oxidative dissolution of U$$_{2}$$O

Kumagai, Yuta

Hoshasen Kagaku (Internet), (107), p.77 - 78, 2019/04

Reaction of hydrogen peroxide (H$$_{2}$$O$$_{2}$$) with uranium dioxide (UO$$_{2}$$) oxidizes U(IV) to water-soluble U(VI). In the concept of direct geological disposal of spent nuclear fuel, this reaction is expected to induce dissolution of UO$$_{2}$$ matrix of the spent fuel. This study investigate effect of H$$_{2}$$O$$_{2}$$ concentration on the kinetics and the yield of U(VI) dissolution of this reaction. A series of experiments of the reaction of H$$_{2}$$O$$_{2}$$ with UO$$_{2}$$ powder dispersed in water has been carried out. The experimental results reveal that increase in the H$$_{2}$$O$$_{2}$$ concentration slows down the reaction and decreases the yield of U(VI) dissolution. This observation suggests that a reaction intermediate is generated in the course of the H$$_{2}$$O$$_{2}$$ reaction on the surface of UO$$_{2}$$.

Journal Articles

Impact of stoichiometry on the mechanism and kinetics of oxidative dissolution of UO$$_{2}$$ induced by H$$_{2}$$O$$_{2}$$ and $$gamma$$-irradiation

Kumagai, Yuta; Fidalgo, A. B.*; Jonsson, M.*

Journal of Physical Chemistry C, 123(15), p.9919 - 9925, 2019/04

 Times Cited Count:0 Percentile:100(Chemistry, Physical)

Radiation-induced oxidative dissolution of uranium dioxide (UO$$_{2}$$) is one of the most important chemical processes of U driven by redox reactions. We have examined the effect of UO$$_{2}$$ stoichiometry on the oxidative dissolution of UO$$_{2}$$ induced by hydrogen peroxide (H$$_{2}$$O$$_{2}$$) and $$gamma$$-ray irradiation. By comparing the reaction kinetics of H$$_{2}$$O$$_{2}$$ between stoichiometric UO$$_{2.0}$$ and hyper-stoichiometric UO$$_{2.3}$$, we observed a significant difference in reaction speed and U dissolution kinetics. The stoichiometric UO$$_{2.0}$$ reacted with H$$_{2}$$O$$_{2}$$ much faster than the hyper-stoichiometric UO$$_{2.3}$$. The U dissolution from UO$$_{2.0}$$ was initially much lower than that from UO$$_{2.3}$$, but gradually increased as the oxidation by H$$_{2}$$O$$_{2}$$ proceeded. The $$gamma$$-ray irradiation induced the U dissolution that is analogous to the kinetics by the exposure to a low concentration (0.2 mM) of H$$_{2}$$O$$_{2}$$. The exposure to higher H$$_{2}$$O$$_{2}$$ concentrations caused lower U dissolution and resulted in deviation from the U dissolution behavior by $$gamma$$-ray irradiation.

Journal Articles

Application of M$$_{V}$$-edge XANES to determination of U oxidation state in zircon

Tanaka, Kazuya; Takahashi, Yoshio*

Geochemical Journal, 53(5), p.329 - 331, 2019/00

We examined three natural zircon samples with different amounts of radiation doses using M$$_{V}$$-edge and L$$_{III}$$-edge U X-ray absorption near-edge structure (XANES). Analysis of XANES spectra at both M$$_{V}$$-edge and L$$_{III}$$-edge suggested that the oxidation state of U in the zircon sample with the highest radiation dose is tetravalent. The XANES spectra of the two other samples with lower radiation doses suggested a mixture of U(IV) and U(VI), while the possibility of U(V) was not excluded. This is the first work on the application of M$$_{V}$$-edge U XANES to the oxidation state of U in natural zircon.

Journal Articles

Mechanism of phase transfer of uranyl ions; A Vibrational sum frequency generation spectroscopy study on solvent extraction in nuclear reprocessing

Kusaka, Ryoji; Watanabe, Masayuki

Physical Chemistry Chemical Physics, 20(47), p.29588 - 29590, 2018/12

 Times Cited Count:3 Percentile:61.57(Chemistry, Physical)

Mechanistic understanding of solvent extraction of uranyl ions (UO$$_{2}$$$$^{2+}$$) by tributyl phosphate (TBP) will help improve the technology for the treatment and disposal of spent nuclear fuels. So far, it has been believed that uranyl ions in the aqueous phase are adsorbed to a TBP-enriched organic/aqueous interface, form complexes with TBP at the interface, and are extracted into the organic phase. Here we show that uranyl-TBP complex formation does not take place at the interface using vibrational sum frequency generation (VSFG) spectroscopy and propose an alternative extraction mechanism that uranyl nitrate, UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$, passes through the interface and forms the uranyl-TBP complex, UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(TBP)$$_{2}$$, in the organic phase.

Journal Articles

Effect of surface conditions of the filament used in thermal ionization mass spectrometry on an uranium isotopic measurement

Taguchi, Shigeo; Miyauchi, Hironari*; Horigome, Kazushi; Yamamoto, Masahiko; Kuno, Takehiko

Bunseki Kagaku, 67(11), p.681 - 686, 2018/11

In thermal ionization mass spectrometry, de-gassing is one of the important treatments to release impurities of filaments and to minimize the influence of background. In this work, the effect of the surface change in the tungsten filament induced by the conductively heating treatment on uranium isotopic ($$^{235}$$U/$$^{238}$$U) measurement has been investigated. It was found that the conductively heating treatment of the filament has the effect of smoothing the surface of the filament and also has the effect of improving the deposition of the sample on the filament surface. As a result of either these effects, the precision of uranium isotopic ($$^{235}$$U/$$^{238}$$U) measurement was improved.

Journal Articles

Separation technique using column chromatography for safeguards verification analysis of uranium and plutonium in highly-active liquid waste by isotope dilution mass spectrometry

Yamamoto, Masahiko; Taguchi, Shigeo; Horigome, Kazushi; Kuno, Takehiko

Proceeding IAEA Symposium on International Safeguards; Building Future Safeguards Capabilities (Internet), 8 Pages, 2018/11

In this study, the single-column extraction chromatographic separation has been developed for analysis of U and Pu in highly active liquid waste by isotope dilution mass spectrometry (IDMS). The commercially available TEVA$$^{textregistered}$$ resin is selected as an extraction chromatography resin. The U is chromatographically separated from fission products (FP) elements by nitric acid while Pu(IV) is adsorbed on the resin. After that, Pu is eluted by reducing to Pu(III). The method has been successfully achieved the separation with yielding the enough recovery and sufficient decontamination factors for subsequent IDMS analysis. The column dose rate after the FP removal is decreased to the background. The analytical results obtained by the developed method are in a good agreement with those of the conventional method. It provides simple and rapid separation and expected that the method can be applied to join IAEA/Japan on-site analytical laboratory.

Journal Articles

Trace analysis for nuclear non-proliferation and security

Esaka, Fumitaka

Bunseki, 2018(10), p.408 - 411, 2018/10

Recent development of analytical techniques for identification of particles containing nuclear materials, isotope ratio analysis of uranium and plutonium using mass spectrometry, and age determination is described in this paper. These techniques are successfully applied to the trace analysis for nuclear non-proliferation.

Journal Articles

The Role of surface-bound hydroxyl radicals in the reaction between H$$_{2}$$O$$_{2}$$ and UO$$_{2}$$

Fidalgo, A. B.*; Kumagai, Yuta; Jonsson, M.*

Journal of Coordination Chemistry, 71(11-13), p.1799 - 1807, 2018/07

 Times Cited Count:6 Percentile:17.54(Chemistry, Inorganic & Nuclear)

In this work, we have studied the reaction between H$$_{2}$$O$$_{2}$$ and UO$$_{2}$$ with particular focus on the nature of the hydroxyl radical formed as an intermediate. Experiments were performed to study the kinetics of the reaction at different initial H$$_{2}$$O$$_{2}$$ concentrations. The results show that the consumption rates at a given H$$_{2}$$O$$_{2}$$ concentration are different depending on the initial H$$_{2}$$O$$_{2}$$ concentration. This is attributed to an alteration of the reactive interface, likely caused by blocking of surface sites by oxidized U/surface-bound hydroxyl radicals. The U dissolution yield decreases with increasing initial H$$_{2}$$O$$_{2}$$ concentration. This is expected from the mechanism of catalytic decomposition of H$$_{2}$$O$$_{2}$$ on oxide surfaces. As the experiments were performed in solutions containing 10 mM and a strong concentration dependence was observed in the 0.2 - 2.0 mM H$$_{2}$$O$$_{2}$$ concentration range, we conclude that the intermediate hydroxyl radical is surface bound rather than free.

Journal Articles

Magnetization, specific heat, $$^{17}$$O NMR, and $$^{237}$$Np M$"o$ssbauer study of U$$_{0.15}$$Np$$_{0.85}$$O$$_2$$

Martel, L.*; Hen, A.*; Tokunaga, Yo; Kinnart, F.*; Magnani, N.*; Colineau, E.*; Griveau, J.-C.*; Caciuffo, R.*

Physical Review B, 98(1), p.014410_1 - 014410_8, 2018/07

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

We report a study of the magnetic and electronic properties of the U$$_{0.15}$$Np$$_{0.85}$$O$$_2$$ solid solution, based on dc- and ac- magnetisation, $$^{237}$$Np M$"o$ssbauer spectroscopy, $$^{17}$$O Nuclear Magnetic Resonance (NMR), and specific heat measurements. The compound orders antiferromagnetically at T$$_N$$ = 17 K. The different techniques reveal the complexity of this system with:(1) a spatial distribution of ordered moments, (2) a small Np ordered moment, and (3) an additional specific heat anomaly at 7.4 K, with a residual value at very low temperature and a reduced magnetic entropy. The results are compared to the end-members of the series, UO$$_2$$ and NpO$$_2$$, as well as to the other solid solutions previously reported in this system. We discuss how the properties of U$$_{0.15}$$Np$$_{0.85}$$O$$_2$$ add new input to the trend previously reported for the series, in view of the models that have been previously proposed.

Journal Articles

Odd-parity electronic multipolar ordering in URu$$_2$$Si$$_2$$; Conclusions from Si and Ru NMR measurements

Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori; Hattori, Taisuke; Higa, Nonoka; Matsuda, Tatsuma*; Haga, Yoshinori; Walstedt, R. E.*; Harima, Hisatomo*

Physical Review B, 97(23), p.235142_1 - 235142_10, 2018/06

AA2018-0180.pdf:1.09MB

 Times Cited Count:5 Percentile:28.96(Materials Science, Multidisciplinary)

Journal Articles

Safety and economics of uranium utilization for nuclear power generation

Fukaya, Yuji

Uranium; Safety, Resources, Separation and Thermodynamic Calculation, p.22 - 48, 2018/05

Safety and economics of uranium utilization for nuclear power generation were investigated and discussed. In order to sustain energy supply with nuclear power generation, uranium resources should be abundant. From the viewpoint of depletion of the resources, FBR, which is breeder reactor of plutonium, has been developed, but that has been not diffused as a commercial reactor yet. Instead of obtaining inexhaustible resources by breeding plutonium, it is known that the inherent safety feature becomes weak in the fast neutron spectrum. As the result of the investigation, it is confirmed with concrete FBR designs that the inherent safety feature and breeding ability are related to the transactions. The amount of uranium resources and electricity generation cost with the resources were investigated. It is concluded that the semi-permanently sustainable energy supply can be established with reasonable cost by using seawater uranium. In addition, the significance of P&T, which is one of the advantages of FBR, was also discussed from the viewpoint of environmental burden from radioactive waste.

Journal Articles

Investigation of chemical state of uranium included in glass

Nagai, Takayuki; Akiyama, Daisuke*; Sato, Nobuaki*

Bisshitsu, Debaisu Ryoiki Kyodo Kenkyu Kyoten Kenkyu Seika Hokokusho (Heisei-29-Nendo) (CD-ROM), 1 Pages, 2018/04

no abstracts in English

JAEA Reports

Uranium and environmental research platform; Social gathering of uranium and environmental research

Nakayama, Takuya; Yagi, Naoto; Sato, Kazuhiko; Hinoda, Shingo; Nakagiri, Toshio; Morimoto, Yasuyuki; Umezawa, Katsuhiro; Sugitsue, Noritake

JAEA-Review 2018-005, 163 Pages, 2018/03

JAEA-Review-2018-005.pdf:72.95MB

The Ningyo-toge Environmental Engineering Center of JAEA has been working together with local communities for more than 60 years. Through our R&D projects on from uranium exploration to uranium enrichment as a part of the nuclear fuel cycle (i.e., front-end), we have accumulated experiences in the fields of management of uranium related technology. Taking advantage of such our potential, we will start new R&D program on "Research on Uranium and the Environment." In December 2016 we announced our new concept of the "Uranium and Environmental Research Platform" as a framework aimed at contributing to regional and international society through R&D programs (environmental research and uranium waste engineering research) that are needed to steadily carry out decommissioning of uranium handling facilities.

Journal Articles

IAEA low enriched uranium bank; Towards the realization of international management initiatives

Tamai, Hiroshi; Tazaki, Makiko; Suda, Kazunori

Nippon Genshiryoku Gakkai-Shi, 60(1), p.25 - 29, 2018/01

IAEA Low Enriched Uranium Bank, which is one of international management initiatives of nuclear materials operated by IAEA, will be realized soon. During increasing concern on proliferation risk of sensitive nuclear technologies as well as in this century the potential acquisition by terrorists, the IAEA bank will offer the fuel assurance aiming at decreasing incentive for acquiring those sensitive technologies. Throughout the argument on the criteria for the fuel supply, the bank site and its requirement have been established and will be in operation next year. The background, significance, and development of this initiative are described.

Journal Articles

Evaluation of uranium chemical state in borosilicate glasses by using XAFS measurement

Nagai, Takayuki; Kobayashi, Hidekazu; Okamoto, Yoshihiro; Akiyama, Daisuke*; Sato, Nobuaki*

Photon Factory Activity Report 2017, 2 Pages, 2018/00

no abstracts in English

Journal Articles

Reaction of hydrogen peroxide with uranium zirconium oxide solid solution; Zirconium hinders oxidative uranium dissolution

Kumagai, Yuta; Takano, Masahide; Watanabe, Masayuki

Journal of Nuclear Materials, 497, p.54 - 59, 2017/12

 Times Cited Count:1 Percentile:73.02(Materials Science, Multidisciplinary)

We studied oxidative dissolution of uranium and zirconium oxide [(U,Zr)O$$_{2}$$] in aqueous H$$_{2}$$O$$_{2}$$ solution. The interfacial reaction is essential for anticipating how a (U,Zr)O$$_{2}$$-based molten fuel may chemically degrade after a severe accident under influence of ionizing radiation. We conducted our experiments with (U,Zr)O$$_{2}$$ powder and quantitated the H$$_{2}$$O$$_{2}$$ reaction via dissolved U and H$$_{2}$$O$$_{2}$$ concentrations. The dissolution yield relative to H$$_{2}$$O$$_{2}$$ consumption was far less for (U,Zr)O$$_{2}$$ compared to that of UO$$_{2}$$. The reaction kinetics indicates that most of the H$$_{2}$$O$$_{2}$$ catalytically decomposed to O$$_{2}$$ at the surface of (U,Zr)O$$_{2}$$. We confirmed the H$$_{2}$$O$$_{2}$$ catalytic decomposition via O$$_{2}$$ production (quantitative stoichiometric agreement). In addition, post-reaction Raman scattering spectra of the undissolved (U,Zr)O$$_{2}$$ showed no additional peaks (indicating a lack of secondary phase formation). The (U,Zr)O$$_{2}$$ matrix is much more stable than UO$$_{2}$$ against H$$_{2}$$O$$_{2}$$-induced oxidative dissolution.

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