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Journal Articles

Effect of O/M ratio on sintering behavior of (Pu$$_{0.3}$$U$$_{0.7}$$)O$$_{2-x}$$

Nakamichi, Shinya; Hiroka, Shun; Kato, Masato; Sunaoshi, Takeo*; Nelson, A. T.*; McClellan, K. J.*

Journal of Nuclear Materials, 535, p.152188_1 - 152188_8, 2020/07

 Times Cited Count:3 Percentile:76.41(Materials Science, Multidisciplinary)

Oxygen-to-metal ratio (O/M) of uranium and plutonium mixed oxide depends on its oxygen partial pressure. To attain the desirable microstructure and O/M ratio of sintered pellets, it is important to investigate the relation between the sintering behavior and the atmosphere of sintering process. In this study, sintering behavior of (Pu$$_{0.3}$$U$$_{0.7}$$)O$$_{2}$$ and (Pu$$_{0.3}$$U$$_{0.7}$$)O$$_{1.99}$$ in controlled po$$_{2}$$ atmosphere were investigated. It was found activation energy of (Pu$$_{0.3}$$U$$_{0.7}$$)O$$_{1.99}$$ was higher than that of (Pu$$_{0.3}$$U$$_{0.7}$$)O$$_{2}$$. On the other hand, it was observed grain growth during sintering was suppressed in hypo-stoichiometric composition.

Journal Articles

Clades of huge phages from across Earth's ecosystems

Al-Shayeb, B.*; Sachdeva, R.*; Chen, L.-X.*; Ward, F.*; Munk, P.*; Devoto, A.*; Castelle, C. J.*; Olm, M. R.*; Bouma-Gregson, K.*; Amano, Yuki; et al.

Nature, 578(7795), p.425 - 431, 2020/02

 Times Cited Count:83 Percentile:99.63(Multidisciplinary Sciences)

Journal Articles

Thermal and mechanical properties of CeO$$_{2}$$

Suzuki, Kiichi; Kato, Masato; Sunaoshi, Takeo*; Uno, Hiroki*; Carvajal-Nunez, U.*; Nelson, A. T.*; McClellan, K. J.*

Journal of the American Ceramic Society, 102(4), p.1994 - 2008, 2019/04

The fundamental properties of CeO$$_{2}$$ were assessed using a range of experimental techniques. The oxygen potential of CeO$$_{2}$$ was measured by the thermogravimetric technique, and a numerical fit for the oxygen potential of CeO$$_{2}$$ is derived based on defect chemistry. Mechanical properties of CeO$$_{2}$$ were obtained using sound velocity measurement, resonant ultrasound spectroscopy and nanoindentation. The obtained mechanical properties of CeO$$_{2}$$ are then used to evaluate the Debye temperature and Gruneisen constant. The heat capacity and thermal conductivity of CeO$$_{2}$$ were also calculated using the Debye temperature and the Gruneisen constant. Finally, the thermal conductivity was calculated based upon laser flash analysis measurements. This result demonstrates that the thermal conductivity has strong dependence upon material purity.

Journal Articles

Thermal expansion measurement of (U,Pu)O$$_{2-x}$$ in oxygen partial pressure-controlled atmosphere

Kato, Masato; Ikusawa, Yoshihisa; Sunaoshi, Takeo*; Nelson, A. T.*; McClellan, K. J.*

Journal of Nuclear Materials, 469, p.223 - 227, 2016/02

 Times Cited Count:7 Percentile:66.89(Materials Science, Multidisciplinary)

Thermal expansion of (U$$_{0.7}$$Pu$$_{0.3}$$)O$$_{2-x}$$ (x = 0, 0.01, 0.02, 0.03) and (U$$_{0.52}$$Pu$$_{0.48}$$)O$$_{2.00}$$ was measured with a dilatometer in an oxygen partial pressure-controlled atmosphere. The oxygen partial pressure was controlled to hold a constant oxygen-to-metal ratio in the (U,Pu)O$$_{2-x}$$ during the measurement. Thermal expansion slightly increased with the decrease in oxygen-to-metal ratio. The relationship was derived to describe thermal expansion.

Journal Articles

An Evaluation of the thermophysical properties of stoichiometric CeO$$_{2}$$ in comparison to UO$$_{2}$$ and PuO$$_{2}$$

Nelson, A. T.*; Rittman, D. R.*; White, J. T.*; Dunwoody, J. T.*; Kato, Masato; McClellan, K. J.*

Journal of the American Ceramic Society, 97(11), p.3652 - 3659, 2014/11

 Times Cited Count:33 Percentile:87.61(Materials Science, Ceramics)

Journal Articles

Oxygen thermochemistry of urania-rare earth system; UO$$_2$$-CeO$$_2$$

Hiroka, Shun; Murakami, Tatsutoshi; Nelson, A. T.*; McClellan, K. J.*

INL/EXT-14-33515, p.34 - 36, 2014/10

Collaborative study has been done on the properties of nuclear materials between the DOE and Japan and the oxygen potential of (U,Ce)O$$_2$$ was measured in this year. Experimental measurements of the oxygen potential were conducted on Ce=20% and 30% composition rates simulating Pu content in advanced MOX fuel in JAEA by gas equilibrium method where oxygen partial pressure in the atmosphere was controlled with mixing dry/wet Ar/H$$_2$$ gas. More than 100 data points were obtained in the O/M range of 1.945 $$sim$$ 2.000 at 1200$$^{circ}$$C, 1400$$^{circ}$$C and 1600$$^{circ}$$C. The experimental results were analyzed by the defect analysis and analytical equations were obtained to calculate O/M as functions of temperature and oxygen potential. From the comparison with that of (U,Pu)O$$_2$$, applicability of the same defect chemistry and S-style curve are common. Also, it is revealed that (U,Ce)O$$_2$$ requires evidently higher oxygen potential for the O/M.

Journal Articles

Property measurements of (U$$_{0.7}$$,Pu$$_{0.3}$$)O$$_{2-x}$$ in $$P$$$$_{O2}$$-controlled atmosphere

Kato, Masato; Murakami, Tatsutoshi; Sunaoshi, Takeo*; Nelson, A. T.*; McClellan, K.*

Proceedings of International Nuclear Fuel Cycle Conference; Nuclear Energy at a Crossroads (GLOBAL 2013) (CD-ROM), p.852 - 856, 2013/09

Uranium and plutonium mixed oxide (U$$_{0.7}$$,Pu$$_{0.3}$$)O$$_{2-x}$$ which has been developed as a fast reactor fuel is nonstoichiometric compound. The stoichiometry significantly affects various properties. The relationship between oxygen potential and oxygen-to-metal (O/M) ratio has been investigated so far. The measurement results showed that it is essential to control oxygen partial pressure ($$P$$$$_{O2}$$) for holding constant O/M ratio in high temperature range. Therefore, properties of (U$$_{0.7}$$,Pu$$_{0.3}$$)O$$_{2-x}$$ were measured in $$P$$$$_{O2}$$-controlled atmosphere in this work. In this work, properties of O/M change, sintering and thermal expansion were investigated in $$P$$$$_{O2}$$-controlled atmosphere.

Journal Articles

Oxidation and reduction behaviors of plutonium and uranium mixed oxide powders

Hiroka, Shun; Kato, Masato; Tamura, Tetsuya*; Nelson, A. T.*; McClellan, K. J.*; Suzuki, Kiichi

Proceedings of International Conference on Fast Reactors and Related Fuel Cycles; Safe Technologies and Sustainable Scenarios (FR-13) (USB Flash Drive), 8 Pages, 2013/03

As research and development activities for MOX fuel pellet production, oxidation and reduction behaviors of MOX powders were investigated by thermogravimetry and X-ray diffraction measurements. It was observed that the oxidation limit decreased with oxidizing temperature and Pu content. The MOX powders showed a two-step oxidation and kinetic stability under non-stoichiometry. The oxidation rates were evaluated from the isothermal oxidation tests. It was found that the reduction temperature of M$$_{4}$$O$$_{9}$$ + M$$_{3}$$O$$_{8}$$ was higher than that of M$$_{4}$$O$$_{9}$$. This indicated that the reduction of M$$_{4}$$O$$_{9}$$ was prevented by the existence of M$$_{3}$$O$$_{8}$$. Activation energy of the reduction was derived from the non-isothermal reduction tests. The data are expected to contribute to establishing a control technique for O/M ratio during MOX powder storage and pellet production.

Oral presentation

Oxidation behavior of UO$$_{2}$$ in air

Suzuki, Kiichi; Nelson, A. T.*; Sunaoshi, Takeo*; McClellan, K.*; Kato, Masato

no journal, , 

In a reactor core or a spent fuel pool loss of coolant accident, fuel cladding may be breached and cause rapid oxidation of UO$$_{2}$$ pellets. Oxidation of UO$$_{2}$$ results in pulverization of the pellet and significant evaporation of UO$$_{3}$$, possibly leading to spread of nuclear material to the environment. Therefore, understanding the oxidation behavior of UO$$_{2}$$ is an important factor. In this study, the oxidation behavior of UO$$_{2}$$ pellets and powders in air was investigated over a wide temperature range. Isothermal oxidations were carried out from 673 to 1923 K. Oxidative pulverization was observed below 1073 K. The weight gain rate at 773 K was larger than that at 873 K, suggesting the oxidation mechanism might change in this regime. Rapid weight loss was observed above 1723 K. The vapor pressure of each phase in the U-O system was calculated, indicating that volatilization of UO$$_{3}$$ was likely responsible for the measured weight loss. The evaporation rate of UO$$_{3}$$ for a urania pellet was then evaluated.

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