Uranium oxidation kinetics monitored by in-situ X-ray diffraction

Abstract The oxidation kinetics of U-0.1 wt%Cr at oxygen pressures of 150 Torr and the temperature range of 90–150 °C was studied by means of in-situ X-ray diffraction (XRD). A “breakaway” in the oxidation kinetics is found at ∼0.25 μm, turning from a parabolic to a linear rate law. At the initial stage of oxidation the growth plane of UO 2 (111) is the prominent one. As the oxide thickens, the growth rate of UO 2 (220) plane increases and both planes grow concurrently. The activation energies obtained for the oxide growth are Q parabolic  = 17.5 kcal/mol and Q linear  = 19 kcal/mol. Enhanced oxidation around uranium carbide (UC) inclusions is clearly observed by scanning electron microscopy (SEM).