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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; Hirooka, 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:7 Percentile:72.51(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

Post-irradiation examinations of annular mixed oxide fuels with average burnup 4 and 5% FIMA

Cappia, F.*; Tanaka, Kosuke; Kato, Masato; McClellan, K.*; Harp, J.*

Journal of Nuclear Materials, 533, p.152076_1 - 152076_14, 2020/05

 Times Cited Count:6 Percentile:61.45(Materials Science, Multidisciplinary)

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

 Times Cited Count:30 Percentile:90.26(Materials Science, Ceramics)

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:9 Percentile:68.73(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:51 Percentile:93.07(Materials Science, Ceramics)

Journal Articles

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

Hirooka, 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

Oxidation and reduction behaviors of plutonium and uranium mixed oxide powders

Hirooka, 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$$_{2}$$ pellet at 673 - 1923 K

Suzuki, Kiichi; Sunaoshi, Takeo*; McClellan, K. J.*; Kato, Masato

no journal, , 

Oral presentation

Thermal properties of (U,Ce)O$$_{2pm x}$$

Hirooka, Shun; Murakami, Tatsutoshi; Kato, Masato; Suzuki, Kiichi; Nelson, A.*; White, J.*; McClellan, K.*

no journal, , 

no abstracts in English

Oral presentation

Evaluation of (U,Ce)O$$_{2}$$ thermal conductivity

Hirooka, Shun; Kato, Masato; Nelson, A.*; McClellan, K.*; White, J.*

no journal, , 

Thermal diffusivity of (U,Ce)O$$_{2}$$ was measured as a function of O/M, and the thermal conductivity was calculated. Thermal conductivity of (U,Ce)O$$_{2}$$ decreased more sharply with increasing temperature compared with that of (U,Pu)O$$_{2}$$. Also, thermal conductivity of (U,Ce)O$$_{2}$$ showed the highest peak at O/M of 2 and decreased as the O/M is apart from 2 on both hypo-stoichiometric and hyper-stoichimetric regions.

Oral presentation

Thermophyisical properties of (U,Ce)O$$_{2pm x}$$

White, J.*; Hirooka, Shun; Murakami, Tatsutoshi; Nelson, A.*; McClellan, K.*; Kato, Masato

no journal, , 

Use of CeO$$_{2}$$ as a surrogate to better understand the behavior of MOX fuels requires a fundamental investigation of the thermophysical properties to assess the appropriate use. The challenge in performing thermophysical property measurements on oxygen non-toichiometric MOX is in handling the kinetics at elevated temperatures and also in determining a reference state from which to measure the oxygen:metal ratio (O:M). This study integrated the use of identical gas handling systems installed on a thermogravimetric analyzer and the property measurement system (differential scanning calorimeter and laser flash analyzer) to control the partial pressure of oxygen, PO$$_{2}$$, between the system and maintain stoichiometry from ambient temperature to 1200$$^{circ}$$C.

Oral presentation

Thermal conductivity of uranium-cerium mixed oxide

Hirooka, Shun; Nelson, A.*; White, J.*; Kato, Masato; McClellan, K.*

no journal, , 

Thermal diffusivity of (U$$_{0.7}$$Ce$$_{0.3}$$)O$$_{2}$$ and (U$$_{0.8}$$Ce$$_{0.2}$$)O$$_{2}$$ was measured by laser flash method as a function of oxygen-to-metal ratio over the temperature range of 373 K to 1473 K and the thermal conductivity was evaluated. Only stoichiometric data of thermal conductivity of (U,Ce)O$$_{2}$$ was reported and that was comparable with thermal conductivity obtained in this work. Thermal conductivity was highest at stoichiometry, and was not perfectly symmetric with respect to the stoichiometry but slightly lower for hyper-stoichiometric compositions. The thermal conductivity of (U,Ce)O$$_{2}$$ showed the trend with temperature to be comparable to that of (U,Pu)O$$_{2}$$. However, the thermal resistivity did not follow the linear function of temperature, A+BT, which is an unique characteristics in (U,Ce)O$$_{2}$$.

Oral presentation

Property measurement of CaF$$_{2}$$

Tsuchimochi, Ryota; Kato, Masato; Hirooka, Shun; Matsumoto, Taku; White, J.*; McClellan, K.*

no journal, , 

High temperature XRD, Thermal expansion measurement, sound speeds measurement and DSC measurement of CaF$$_{2}$$ were carried out. We confirmed that the specific heat of CaF$$_{2}$$ explicity shows the effect of Frenkel defect formation on top of the heat capacity at constant volume and dilatational term. The analysis of the specific heat will be discussed together with the measured data.

Oral presentation

Evaluation of fundamental properties of CaF$$_{2}$$, 1; Experimental approach

Kato, Masato; Tsuchimochi, Ryota; Matsumoto, Taku; White, J.*; McClellan, K.*

no journal, , 

no abstracts in English

Oral presentation

The Bredig transition effect on the thermal conductivity of CaF$$_{2}$$

Matsumoto, Taku; Tsuchimochi, Ryota; Hirooka, Shun; Kato, Masato; White, J.*; McClellan, K.*

no journal, , 

The thermal diffusivity, thermal expansion and heat capacity of CaF$$_{2}$$ was measured with LFA, DIL and DSC up to 1250$$^{circ}$$C, then the thermal conductivity was evaluated. We evaluated how the Bredig transition which is one of the unique features of fluorite structure affect on the thermal conductivity.

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