Enhanced thermal conductivity of uranium dioxide–silicon carbide composite fuel pellets prepared by Spark Plasma Sintering (SPS) S. Yeo a , E. Mckenna a , R. Baney a , G. Subhash b,⇑ , J. Tulenko a a Materials Science and Engineering Department, University of Florida, Gainesville, FL, USA b Mechanical Engineering Department, University of Florida, Gainesville, FL, USA article info Article history: Received 19 April 2012 Accepted 10 September 2012 Available online 16 September 2012 abstract Uranium dioxide (UO 2 )–10 vol% silicon carbide (SiC) composite fuel pellets were produced by oxidative sintering and Spark Plasma Sintering (SPS) at a range of temperatures from 1400 to 1600 °C. Both SiC whiskers and SiC powder particles were utilized. Oxidative sintering was employed over 4 h and the SPS sintering was employed only for 5 min at the highest hold temperature. It was noted that composite pellets sintered by SPS process revealed smaller grain size, reduced formation of chemical products, higher density, and enhanced interfacial contact compared to the pellets made by oxidative sintering. For given volume of SiC, the pellets with powder particles yielded a smaller grain size than pellets with SiC whiskers. Finally thermal conductivity measurements at 100 °C, 500 °C, and 900 °C revealed that SPS sintered UO 2 –SiC composites exhibited an increase of up to 62% in thermal conductivity compared to UO 2 pellets, while the oxidative sintered composite pellets revealed significantly inferior thermal conductivity values. The current study points to the improved processing capabilities of SPS compared to oxidative sintering of UO 2 –SiC composites. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Despite the availability of numerous types of nuclear fuels (metals, MOX, nitrides, etc.) commercial reactors in the world are fueled by uranium dioxide (UO 2 ). It is the fuel of choice for several reasons such as high melting point (transient accident resistance [1,2]) and enhanced oxidation resistance. Also, UO 2 behavior has been studied in much more depth throughout different power cy- cles than other fuel types. Increasing the thermal conductivity of nuclear fuel would allow for the output of a reactor to be increased and enhance the safety of a reactor during normal operation and short-term accidents. The maximum heat output from the reactor core could be increased by the high thermal conductivity of the fuel pellet enabling the reactor to produce more thermal energy while maintaining the plant safety. Moreover, with a decrease in centerline temperature caused by the increased thermal conductivity of the fuel pellet, the temperature gradient in the fuel is decreased allowing reduced fission gas release and number of cracked or broken pellets due to thermal stresses while maintaining the desired fuel and cladding temperatures. The concept of incorporating high thermal conductivity mate- rial into a UO 2 pellet has been well studied [3], and silicon carbide has been considered a prime candidate to form path ways through which heat would conduct in the fuel matrix. This is due to its low neutron cross section, high thermal conductivity, chemical stability (strong resistance to oxidation in air and air-moisture environ- ments), and high melting temperature (2973 °C) [4]. Silicon car- bide (b-SiC) also has the advantage of being non-toxic and isotropic over alternatives such as beryllium oxide [5]. Hunt et al. [6] stated that incorporation of at least 4 mol% SiC in UO 2 fuel has a benefit of maintaining O to M ratio near two during irradia- tion. Allen et al. [7] however, found that chemical reactions occur between UO 2 and SiC around 1370 °C which may severely degrade the thermal conductivity of the composite. Solomon and associates [8] investigated reaction products and suggested the formation of USi 1.88 ,U 20 Si 16 C 3 , UC, CO, and SiO. Sarma et al. [9] attempted to produce UO 2 –SiC composites at temperatures below 1370 °C to avoid these reactions. Their method involved fabrication of a UO 2 pellets with open porosity followed by polymer infiltration and pyrolysis of a silicon carbide pre-ceramic polymer. The result how- ever, was a pellet with degraded thermal conductivity compared to a pure UO 2 pellet. Originally, it was believed that a continuous phase of SiC throughout the pellet would lead to significantly high- er thermal conductivity. However, simulations performed by Latta et al. [10] revealed that discontinuous SiC fibers produced nearly the same increase in thermal conductivity as that of a continuous phase. This result is in part due to the higher density and 0022-3115/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnucmat.2012.09.015 ⇑ Corresponding author. Address: Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA. Tel.: +1 3523927005; fax: +1 352 392 7303. E-mail address: Subhash@ufl.edu (G. Subhash). Journal of Nuclear Materials 433 (2013) 66–73 Contents lists available at SciVerse ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat