Steam Oxidation Kinetics and Oxygen Diffusion in UOz at High Temperatures

Results of steam oxidation measurements of UO2 cylinders from 885° to 1835°C may be expressed by the equations: for the parabolic rate of oxidation and for the chemical oxygen diffusion coefficient. Kp and Dc, obtained from thermobalance measurements to 1500° C and from pre- and post-test weights for the higher temperatures, were independent of sample weight from 10 to 149 g and of surfaceto-volume ratios from 2.34 to 18.74 cm-1. Dc varied as the 0.65 power of the final average excess oxygen (x in UO2+x). The oxidation was accompanied by considerable grain growth. A bulk diffusion mechanism was verified by analyses of partially oxidized samples using both X-ray diffraction and analytical chemistry; an oxygen gradient was demonstrated by each technique.