THERMAL-CONDUCTIVITY OF HYPERSTOICHIOMETRIC SIMFUEL

The thermal conductivity of hyperstoichiometric SIMFUEL and UO2+x was obtained from thermal diffusivity, specific heat and density measurements. The thermal conductivity of UO2+x (no fission products present) decreases with increasing O/U ratio; a reduction of 15%, 37% and 56% at 600 degrees C, and 11%, 23% and 33% at 1500 degrees 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 (Delta G(O2)) of -540 kJ/mol (corresponding to UO2.000) and -245 kJ/mol (corresponding to UO2.007). For SIMFUEL, annealed in reducing conditions, the fission products lowered the thermal conductivity significantly. However, for high oxygen potentials (Delta G(O2) greater than or equal to -205 kJ/mol), the thermal conductivities of UO2+x and SIMFUEL were found to be approximately equal in the temperature range of 600 to 1500 degrees C. Consequently, excess oxygen is the dominant factor contributing to thermal conductivity degradation at high oxygen potentials.