Formation of columnar and equiaxed grains by the reduction of U3O8 pellets to UO2+x

Yang, Jihoon; Rhee, Young Woo; Kang, Ki Won; Kim, Keon Sik; Song, Kee-Nam; Lee, Seung-Jae

doi:10.1016/j.jnucmat.2006.10.006

Cited by 12 publications

(11 citation statements)

References 22 publications

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“…Indeed, the pellet obtained from the powder converted at 500 • C presented the lowest amount of open porosity of the three samples studied, which agreed well with the J. Martinez et al / Journal of the European Ceramic Society xxx (2015) xxx-xxx high value of relative density determined (i.e., 94% of the calculated value). Also, even if the sintering process started in this case from a mixture of U 3 O 8 and UO 2 , no particular morphology, such as columnar or equiaxed grains [57], was observed. For the samples sintered from powders converted at 800 • C and 1000 • C, a large amount of open porosity was then observed, again in good agreement with the density measurements.…”

Section: Microstructural Evaluationmentioning

confidence: 75%

From uranium(IV) oxalate to sintered UO 2 : Consequences of the powders' thermal history on the microstructure

Martinez

Clavier

Ducasse

et al. 2015

Journal of the European Ceramic Society

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Section: Microstructural Evaluationmentioning

confidence: 75%

From uranium(IV) oxalate to sintered UO 2 : Consequences of the powders' thermal history on the microstructure

Martinez

Clavier

Ducasse

et al. 2015

Journal of the European Ceramic Society

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“…The specific surface area of the UO 2 pellets was determined using TriStar 3000 V6.05 A BET equipment. The equilibrium oxygen potential of the Ar gas, À 149.2 kJ/mol [12], is lower than that of the UO 2.2 (À 111.9 kJ/mol [11]), and thus the U 3 O 8 has a tendency to be reduced during sintering in Ar. It was previously reported that the U 3 O 8 converts into a mixed phase of U 3 O 8 À w and then UO 2 þ x during sintering in Ar [13].…”

Section: Methodsmentioning

confidence: 99%

“…Considering that the removal of fission products is one of the main purposes of the head-end process, the pelletized U 3 O 8 material, therefore, needs to be reduced to UO 2 by thermal treatment in a reducing atmosphere. The reduction behavior of the U 3 O 8 has been extensively studied in many investigations thus far [5][6][7][8][9][10][11]. Among these, many of the previous researches have been made in the hydrogen or hydrogen-containing gas atmospheres [6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Temperature dependences of the reduction kinetics and densification behavior of U3O8 pellets in Ar atmosphere

Jeon

Lee

Kang

et al. 2015

Ceramics International

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“…The diffraction peaks in the pyrolyzed slurry pattern were mostly dominated by the presence of UO 2 providing evidence of the conversion of U 3 O 8 to UO 2 during the first pyrolysis cycle. This conversion has been widely studied [72][73][74]. Since the pyrolysis was carried out in an inert environment, it is highly likely that the reduction took place due to the presence of hydrogen gas that evolves during the pyrolysis of the precursor.…”

Section: Mixed-metal Carbide and Silicocarbide Compositesmentioning

confidence: 99%

“…Since the pyrolysis was carried out in an inert environment, it is highly likely that the reduction took place due to the presence of hydrogen gas that evolves during the pyrolysis of the precursor. In the presence of hydrogen this reduction can take place in the temperature range of 400-600 • C [73,74]. However, this process is highly affected by the powder properties such as BET surface area and size.…”

Section: Mixed-metal Carbide and Silicocarbide Compositesmentioning

confidence: 99%

Novel Processing of Unique Ceramic-Based Nuclear Materials and Fuels

Zhang¹,

Singh²

2008

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Advances in nuclear reactor technology and the use of gas-cooled fast reactors require the development of new materials that can operate at the higher temperatures expected in these systems. These include refractory alloys based on Nb, Zr, Ta, Mo, W, and Re; ceramics and composites such as those based on silicon carbide (SiC f -SiC); carbon-carbon composites; and advanced coatings. Besides the ability to handle higher expected temperatures, effective heat transfer between reactor components is necessary for improved efficiency. Improving thermal conductivity of the materials used in nuclear fuels and other temperature critical components can lower the center-line fuel temperature and thereby enhance durability and reduce the risk of premature failure.Silicon carbide (SiC) is an important ceramic, most commonly used because of its excellent properties such as high strength, high modulus, excellent creep resistance and its high temperature stability. Moreover, crystalline silicon carbide is attracting wide attention as a promising candidate for several applications in nuclear reactors owing to its high thermal conductivity, high melting temperature, good chemical stability, and resistance to swelling under heavy ion bombardment. There have been many efforts to develop SiC based composites in various forms for use in advanced energy systems. However, fabricating SiC based composites by traditional powder processing route generally requires very high temperatures for pressureless sintering. In recent years, with the development of high yield preceramic precursors, the polymer infiltration and pyrolysis (PIP) method has aroused interest for the fabrication of ceramic based materials. Polymer derived ceramic materials offer unique advantages such as ability to fabricate net shaped components, incorporate reinforcements, along with lower processing temperatures, and perhaps most importantly relatively easy control over the microstructure. The raw materials are element-organic polymers whose composition and architecture can be tailored and varied.The primary focus of this work is to use a pyrolysis-based process to fabricate a host of novel silicon carbide-metal carbide/oxide composites, and to synthesize new materials based on mixed-metal (metal/silicon) carbides that cannot be processed using conventional techniques. These mixedcarbide material systems are expected to offer improved material properties for higher-temperature applications. Our fabrication technique resulted in both amorphous and nano-grained SiC matrix composites by controlled pyrolysis of allylhydridopolycarbosilane (AHPCS), the precursor for SiC for our study, under inert argon atmosphere.Cylindrical pellets, φ25 × 25 mm, were fabricated for bulk scale characterization. These samples were analyzed in terms of density and porosity, thermal conductivity, and flexural strength under multiaxial loading conditions. The final composition in the fabricated composite was studied use Xray diffraction (XRD). This was useful in understanding the relative stabil...

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Formation of columnar and equiaxed grains by the reduction of U3O8 pellets to UO2+x

Cited by 12 publications

References 22 publications

From uranium(IV) oxalate to sintered UO 2 : Consequences of the powders' thermal history on the microstructure

From uranium(IV) oxalate to sintered UO 2 : Consequences of the powders' thermal history on the microstructure

Temperature dependences of the reduction kinetics and densification behavior of U3O8 pellets in Ar atmosphere

Novel Processing of Unique Ceramic-Based Nuclear Materials and Fuels

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