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Journal Articles

Oxygen chemical diffusion in hypo-stoichiometric MOX

Kato, Masato; Morimoto, Kyoichi; Tamura, Tetsuya*; Sunaoshi, Takeo*; Konashi, Kenji*; Aono, Shigenori; Kashimura, Motoaki

Journal of Nuclear Materials, 389(3), p.416 - 419, 2009/06

https://doi.org/10.1016/j.jnucmat.2009.02.018
 Times Cited Count：11 Percentile：59.85(Materials Science, Multidisciplinary)

Plutonium and uranium mixed oxide (MOX) has been developed to use as a core fuel of the fast reactor. The oxygen to metal ratio (O/M) of the MOX fuel is an important parameter to control the FCCI. The oxygen potential and the oxygen diffusion coefficient of the MOX are essential data to understand the oxygen behaviour in MOX. The oxygen potentials of the MOX were measured with accuracy as a function of O/M and temperatures in the previous work. In this work the oxygen chemical diffusion coefficient in (Pu$$_{0.2}$$U$$_{0.8}$$)O$$_{2-x}$$ and (Pu$$_{0.3}$$U$$_{0.7}$$)O$$_{2-x}$$ were investigated using thermo gravimetric technique. The kinetics of the reduction processes of (Pu$$_{0.2}$$U$$_{0.8}$$)O$$_{2-x}$$ and (Pu$$_{0.3}$$U$$_{0.7}$$)O$$_{2-x}$$ were measured by TG-DTA method. The oxygen chemical diffusion coefficients have been estimated from the reduction curves. It was concluded that the oxygen chemical diffusion coefficient in (Pu$$_{0.3}$$U$$_{0.7}$$)O$$_{2-x}$$ is a smaller than that of (Pu$$_{0.2}$$U$$_{0.8}$$)O$$_{2-x}$$.

Journal Articles

Calculations of thermodynamic properties of PuO$$_{2}$$ by the first-principles and lattice vibration

Minamoto, Satoshi*; Kato, Masato; Konashi, Kenji*; Kawazoe, Yoshiyuki*

Journal of Nuclear Materials, 385(1), p.18 - 20, 2009/03

https://doi.org/10.1016/j.jnucmat.2008.10.024
 Times Cited Count：32 Percentile：88.55(Materials Science, Multidisciplinary)

Plutonium dioxide (PuO$$_{2}$$) is the key compounds which will take effect the thermal properties for MOX fuels. But due to the lack of experimental data on plutonium dioxide, computational thermodynamics data were not established. In recently, the coupling of first-principle calculation and lattice dynamics theory, computational thermodynamics data could be obtained numerically. We applied first principle plane-wave calculation and lattice dynamics theory to estimate thermal properties of plutonium oxide for perfect crystal. Total energy calculation for perfect crystal reproduced experimental lattice parameter well. And after phonon dispersion calculation for plutonium dioxide, contribution of lattice vibration to thermal properties was investigated.

Journal Articles

High temperature behavior of irradiated mixed nitride fuel during heating tests

Sato, Isamu; Tanaka, Kosuke; Hirosawa, Takashi; Miwa, Shuhei; Tanaka, Kenya

Journal of Alloys and Compounds, 444-445, p.580 - 583, 2007/10

https://doi.org/10.1016/j.jallcom.2007.02.157
 Times Cited Count：1 Percentile：13.09(Chemistry, Physical)

JAEA performs the study on the applicability of the mixed nitride fuel for the fast reactor by the irradiation test in the experimental fast reactor, "JOYO." In this work, heating tests for the mixed nitride fuel irradiated in JOYO have been performed and the fission gas release and the decomposition behaviours are evaluated for the safety study of Pb-Bi cooled fast reactor. As to the gas release aspects, the behaviour is independent on decomposition of the Nitride fuel. The density change was observed in the fuel after the heating test by slow heating rate. Over the temperature of 2400$$^{circ}$$C, the nitride fuel had decomposed to make some Pu-Rh alloy inclusions.

Journal Articles

The Oxidation rate of (U$$_{0.7}$$Pu$$_{0.3}$$)O$$_{2-x}$$ with two fcc phases

Suzuki, Kiichi; Kato, Masato; Tamura, Tetsuya*; Aono, Shigenori; Kashimura, Motoaki

Journal of Alloys and Compounds, 444-445, p.590 - 593, 2007/10

https://doi.org/10.1016/j.jallcom.2007.02.062
 Times Cited Count：5 Percentile：37.98(Chemistry, Physical)

It was reported that sintered MOX pellet of hypostoichiometric composition was oxidized at room temperature in an atmosphere of inert gas and air. The region of two fcc phases exist at room temperature in the (U,Pu)O$$_{2-X}$$ with Pu content of greater than 20%. In this study, the oxidation rate of (U$$_{0.7}$$Pu$$_{0.3}$$)O$$_{2-X}$$ with two fcc phases was investigated to contribute to understanding of the oxidation behavior using thermogravimetric technique. The sintered pellets of (U$$_{0.7}$$Pu$$_{0.3}$$)O$$_{2-X}$$ were prepared by mechanical blending method and were sliced into disc-like sample with about 1 mm thick and 85-93% theoretical density. The oxidation rate of the samples were measured at 60, 125 and 150$$^{circ}$$C in an atmosphere of Air, N$$_{2}$$ and Air/N$$_{2}$$ gas mixture containing moisture of 1 - 700ppm using thermal gravity and differential thermal analysis. The curve of the isothermal oxidation was analyzed by the model of diffusion in a system consisting of two phases. The diffusion model can represent the oxidation curve as a function of time and temperature. In the results of X-ray diffraction measurement, fcc phase with O/M $$approx$$ 2.00 was observed to increase by oxidation of sample. These results indicate that the oxidation of the (U$$_{0.7}$$Pu$$_{0.3}$$)O$$_{2-X}$$ with two fcc phases proceeds by diffusion of the phase with O/M $$approx$$ 2.00 which is formed on the sample surface.

Journal Articles

Study on valence of Pu, Np and Tc in nitric acid after electrolytic reduction

Hoshi, Harutaka*; Wei, Y.-Z.*; Kumagai, Mikio*; Asakura, Toshihide; Morita, Yasuji

Journal of Alloys and Compounds, 444-445, p.663 - 667, 2007/10

https://doi.org/10.1016/j.jallcom.2007.02.060
 Times Cited Count：4 Percentile：33.26(Chemistry, Physical)

no abstracts in English

Journal Articles

Phase behavior of PuO$$_{2-x}$$ with addition of 9% Am

Miwa, Shuhei; Osaka, Masahiko; Yoshimochi, Hiroshi; Tanaka, Kenya; Kurosaki, Ken*; Uno, Masayoshi*; Yamanaka, Shinsuke*

Journal of Alloys and Compounds, 444-445, p.610 - 613, 2007/10

https://doi.org/10.1016/j.jallcom.2006.10.059
 Times Cited Count：14 Percentile：61.53(Chemistry, Physical)

no abstracts in English

Journal Articles

NMR studies of actinide dioxides

Tokunaga, Yo; Sakai, Hironori; Fujimoto, Tatsuya; Kambe, Shinsaku; Walstedt, R. E.*; Ikushima, Kenji*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Haga, Yoshinori; et al.

Journal of Alloys and Compounds, 444-445, p.241 - 245, 2007/10

https://doi.org/10.1016/j.jallcom.2007.03.082
 Times Cited Count：19 Percentile：68.81(Chemistry, Physical)

In this paper, we present our recent NMR works on Neptunium and Plutonium compounds. In order to elucidate the nature of the exotic multipolar ordered phase of NpO$$_2$$, we have initiated the first NMR measurements on this system. We have shown that direct observation of multipole order parameters is possible by means of NMR. Our NMR results provide further insight into the microscopic nature of multipole phase transitions in f-electron systems. We have also performed $$^{69,71}$$Ga NMR/NQR studies on a single crystal of PuRhGa$$_5$$. From the temperature dependence of the spin-lattice relaxation rate ($$1/T_1$$), we have found that PuRhGa$$_5$$ is an unconventional superconductor having an anisotropic superconducting (SC) gap 2$$Delta(0)$$=5$$K_BT_c$$. Furthermore, we have confirmed the Knight shift to be decreased below $$T_c$$. This gives strong evidence for spin singlet SC pairing.

Journal Articles

Multipoles in $$delta$$-Pu

Hotta, Takashi

Journal of Alloys and Compounds, 444-445, p.162 - 167, 2007/10

https://doi.org/10.1016/j.jallcom.2006.11.028
 Times Cited Count：3 Percentile：28.09(Chemistry, Physical)

In order to develop microscopic theories of magnetism and superconductivity in $$f$$-electron compounds, we have proposed the construction of an $$f$$-electron model on the basis of a $$j$$-$$j$$ coupling scheme. Using this model, we have explained spin and orbital structure of UMGa$$_5$$ and NpMGa$$_5$$. Recently, octupole ordering in NpO$$_2$$ has been also understood from the microscopic viewpoint. Encouraged by such successes of the j-j coupling model in actinide materials, we attempt to understand magnetism and superconductivity of Pu and PuMGa$$_5$$. We focus on a key role of 5f orbital state for the appearance of superconductivity in PuMGa$$_5$$ and the absence of magnetism in $$delta$$-Pu. We discuss multipoles as spin-orbital complex degrees of freedom.

Journal Articles

The Search for magnetic order in $$delta$$-Pu metal using muon spin relaxation

Heffner, R. H.; Oishi, Kazuki; Fluss, M. J.*; Morris, G. D.*; MacLaughlin, D. E.*; Shu, L.*; Chung, B. W.*; McCall, S. K.*; Bauer, E. D.*; Sarrao, J. L.*; et al.

Journal of Alloys and Compounds, 444-445, p.80 - 83, 2007/10

https://doi.org/10.1016/j.jallcom.2006.12.026
 Times Cited Count：8 Percentile：48.54(Chemistry, Physical)

We summarize the results of muon spin relaxation ($$mu$$SR) measurements carried out in$$alpha$$- and $$delta$$-Pu and in the superconducting state ofPuCoGa$$_5$$. In Pu metal, interest has centered on whether or not magnetic order exists in the hightemperature fcc $$delta$$ phase,The Pu metal studies were designed to search for evidence of magnetic ordering, andhave set the most stringent limits to date for the ordered moment. In PuCoGa$$_5$$ the temperature dependence of themagnetic penetration depth $$lambda$$(T) was investigated in a fresh sample and again in the same sampleafter 400 days of aging. We find $$lambda$$(T)$$propto$$ T for T $$<$$ Tc/2, indicating a line of nodes in thesuperconducting order parameter. Remarkably, the temperature dependence of $$lambda$$(T) is littlechanged even after significant radiation damage.

Journal Articles

Single crystal growth, superconductivity and Fermi surface study of plutonium compounds

Haga, Yoshinori; Aoki, Dai*; Yamagami, Hiroshi*; Matsuda, Tatsuma; Nakajima, Kunihisa; Arai, Yasuo; Yamamoto, Etsuji; Nakamura, Akio; Homma, Yoshiya*; Shiokawa, Yoshinobu*; et al.

Journal of Alloys and Compounds, 444-445, p.114 - 118, 2007/10

https://doi.org/10.1016/j.jallcom.2006.11.206
 Times Cited Count：3 Percentile：28.09(Chemistry, Physical)

We report the first dHvA study in plutonium compound PuIn$$_3$$ with the cubic AuCu$$_3$$ type structure, which can be regarded as a reference compound of PuCoGa$$_5$$. The result of the angular dependence of the dHvA frequency, which corresponds to the extremal cross section of the Fermi surface perpendicular to the field direction, was analyzed by the band calculations. The experimental data agree well with the theory, indicating that the 5f electrons can be treated as itinerant ones. The experimental dHvA study for plutonium-based superconductors such as PuCoGa$$_5$$ are also desired but more challenging because the superconducting mixed state extremely weaken the dHvA amplitude.

Journal Articles

Molecular magnetism in neptunyl(+1,+2) complexes; $$^{237}$$Np-M$"o$ssbauer and magnetic study

Nakamura, Akio; Nakada, Masami; Nakamoto, Tadahiro*; Kitazawa, Takafumi*; Takeda, Masuo*

Journal of Alloys and Compounds, 444-445, p.621 - 633, 2007/10

https://doi.org/10.1016/j.jallcom.2006.12.062
 Times Cited Count：3 Percentile：28.09(Chemistry, Physical)

no abstracts in English

Journal Articles

Probing the Coulomb interaction of PuCoGa$$_5$$ by phonon spectroscopy

Raymond, S.*; Piekarz, P.*; Sanchez, J. P.*; Serrano, J.*; Kirsch, M.*; Detlefs, B.*; Rebizant, J.*; Metoki, Naoto; Kaneko, Koji; Jochym, P. T.*; et al.

Journal of Alloys and Compounds, 444-445, p.104 - 108, 2007/10

https://doi.org/10.1016/j.jallcom.2006.09.053
 Times Cited Count：2 Percentile：21.49(Chemistry, Physical)

The phonon dispersion curves of the unconventional superconductor PuCoGa$$_5$$ were studied by inelastic X-ray scattering at room temperature. The experimental data agree well with ab initio lattice dynamics calculations. An accurate theoretical description of the phonon spectrum is obtained only when a local Coulomb repulsion $$U{approx}$$3 eV among 5f electrons is taken into account. This implies partial localization of the 5f electrons in this compound. A comparison made with the phonon spectrum of UCoGa$$_5$$ suggests that the latter compound is better described with a fully itinerant f electrons model.

Oral presentation

Plutonium and other actinides behaviour in NEXT process

Miura, Sachiko; Nakahara, Masaumi; Sano, Yuichi; Kamiya, Masayoshi; Nomura, Kazunori; Komaki, Jun

no journal, , 

The behaviour of Pu and other actinides in the crystallization process and U-Pu-Np co-recovery process was discussed. Pu showed the different behaviour in the crystallization process according to its valence in the dissolver solution. Low DF of Cs in some crystallization conditions might be related with the formation of some kinds of Cs compounds with Pu in the dissolver solution. In the U-Pu-Np co-recovery process, Although there are some considerable points, e.g. temperature control in the stripping section, suitable condition for Np extraction, etc., we confirmed that it was possible to co-recover U-Pu-Np under the appropriate condition.

Oral presentation

Interactions of heavy elements with microorganisms

Yoshida, Takahiro*; Ozaki, Takuo; Sakamoto, Fuminori; Kozai, Naofumi; Nankawa, Takuya; Suzuki, Yoshinori; Francis, A. J.*; Onuki, Toshihiko

no journal, , 

no abstracts in English

14 (Records 1-14 displayed on this page)
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