Silicon carbide as an inert-matrix for a thermal reactor fuel

This paper reports progress on work to develop methods of fabricating silicon carbide with cerium, as a substitute for plutonium, to achieve high densities at low sintering temperatures. Densities of 97–99% of TD were achieved at 1943 K for cerium oxide concentrations in the starting powders from 5 to 20 wt%. Also reported are: specific heat and thermal conductivity measurements of as-fabricated SiC; compatibility of SiC with coolant and Zircaloy-4; and accelerator simulations of in-reactor fission-fragment damage. The thermal conductivity for as-fabricated SiC with additives was 48 W m −1 K −1 at 298 K decreasing to about 18 W m −1 K −1 at 1773 K. Calculations, based on the measured thermal conductivity, show that the inert-matrix fuel could operate at 55 kW m −1 linear power at a centre-line temperature of only 673 K, i.e., only 100 K above coolant temperature, although it is expected that irradiation-induced degradation of thermal conductivity will lead to higher operating temperatures as burnup accumulates. The increase in central temperatures due to a possible decrease in thermal conductivity caused by fast-neutrons are calculated in the text. SiC appears to be a very promising candidate as an inert-matrix fuel for water-cooled reactors.