Thermal conductivity of hyperstoichiometric SIMFUEL

Abstract

The thermal conductivity of hyperstoichiometric SIMFUEL and UO 2+ x was obtained from thermal diffusivity, specific heat and density measurements. The thermal conductivity of UO 2+ x (no fission products present) decreases with increasing O/U ratio; a reduction of 15%, 37% and 56% at 600°C, and 11%, 23% and 33% at 1500°C, was found for O/U ratios of 2.007, 2.035 and 2.084, respectively. For 3 at% SIMFUEL there was little difference in the thermal conductivity of specimens annealed at oxygen potentials ( ΔG O 2 of -540 kJ/mol (corresponding to UO 2.000) and -245 kJ/mol (corresponding to UO 2.007). For SIMFUEL, annealed in reducing conditions, the fission products lowered the thermal conductivity significantly. However, for high oxygen potentials ( ΔG O 2 ≥ −205 kJ/mol), the thermal conductivities of UO 2+ x and SIMFUEL were found to be approximately equal in the temperature range of 600 to 1500°C. Consequently, excess oxygen is the dominant factor contributing to thermal conductivity degradation at high oxygen potentials.