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

The oxidation kinetics of U-0.1 wt%Cr at oxygen pressures of 150 Torr and the temperature range of 90-150 degrees C was studied by means of in-situ X-ray diffraction (XRD). A breakaway in the oxidation kinetics is found at -0.25 gm, turning from a parabolic to a linear rate law. At the initial stage of oxidation the growth plane of UO2(111) is the prominent one. As the oxide thickens, the growth rate of UO2(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). (C) 2017 Elsevier B.V. All rights reserved.