Low Temperature Synthesis of Silicon Carbide Inert Matrix Fuel (IMF)
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1215-V11-05
Low Temperature Synthesis of Silicon Carbide Inert Matrix Fuel (IMF) Chunghao Shih1, James Tulenko2 and Ronald Baney1 1 Department of Materials Science and Engineering, University of Florida, Gainesville FL 32611, U.S.A. 2
Department of Nuclear and Radiological Engineering, University of Florida, Gainesville FL 32611, U.S.A. ABSTRACT A process for the synthesis of silicon carbide (SiC) inert matrix fuels at a low temperature (1050 ˚C) is reported which utilized a liquid polymer precursor. As the polymer content increased, the theoretical density of the pellet at first increased and then reached a plateau. From the onset of the plateau, the packing of the one micron SiC particles in the green body was determined to be 64-68% at 600 MPa pressing pressure. As expected, mixing coarse and fine SiC particles gave a higher pellet density. The maximum density achieved was 80% of the theoretical density. Mercury porosimetry showed that the largest pore size was around 10% of the largest particle sizes present in the green body. SEM images showed that ceria, which was selected as a surrogate for PuO2 in the present study, was well distributed. INTRODUCTION More than 1400 metric tones of plutonium have been created around the world during the past 50 years [1]. In addition to Pu, minor actinides such as Np, Am and Cm with very long half-lives are generated in reactors. A strategy for reducing the amount of both Pu and the minor actinides is to transmute the actinides in a reactor. Mixed oxide fuel (MOX) is the current fuel for plutonium disposition. MOX is a mixture of UO2 and PuO2. It contains 238U which is a fertile material that absorbs neutrons and transmute into fissionable 239Pu. A more efficient way would be to replace the MOX by a neutron transparent matrix which contains less or no fertile materials. Thus, the concept of an inert matrix fuel (IMF) has been proposed. Inert matrix materials are selected for optimum neutronic performance based on the following criteria: low neutron absorption cross section, high melting point, high thermal conductivity, good irradiation stability, and good chemical stability with cladding material and coolant. The properties of silicon carbide (SiC) make it a very promising candidate as an inert matrix material. The thermal conductivity of SiC is 30 W/m-K at 1000 ˚C [2], which is about 10
times higher than MOX. SiC also has good irradiation stability and good chemical stability to air and hot water [2]. Good mechanical properties normally associated with SiC monolithic parts are not required in SiC IMF’s because only sufficient mechanical properties to assemble the fuel are required. Pre-ceramic polymer precursors have been used as sintering aids to produce SiC [3]. This process offers a route to synthesize SiC at lower temperatures which is desirable for SiC IMF’s to avoid reactions between SiC and PuO2 [4,5] and to avoid the loss of some minor actinides due to their high vapor pressures at higher temperatures. In this paper, we report on a low temperature (1050 ˚C) synt
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