EFFECT OF MICROSTRUCTURE AND MICROCRACKING ON THE THERMAL-CONDUCTIVITY OF UO2-U4O9

Several microstructures were produced in dense polycrystalline UO2‐U4O9 specimens by cooling UO2+x, solid solutions at different rates. Void formation (intragranular pores, grain‐boundary microcracks) was observed in specimens which had a nonuniform distribution of the U4O9 precipitate; such formation was probably caused by the relief of stresses generated by differential thermal contraction. The microstructures were assessed quantitatively and used to calculate thermal conductivities from theoretical models. The effect of microcracking was calculated. Thermal conductivities were also determined from thermal diffusivity values measured by the laser‐flash method. The thermal conductivity was primarily influenced by the amount of U4O9, present and the occurrence of voids, whereas the effect of U4O9, distribution was minor. Good agreement was obtained between theoretical predictions of thermal conductivity based on microstructure and experimental values. Copyright © 1979, Wiley Blackwell. All rights reserved