A response surface design of experiment (DOE) was developed to model crystallographic changes of UO 2 and α-U 3 O 8 after aging at elevated temperatures in controlled oxygen environments. Crystallographic changes to UO 2 and α-U 3 O 8 were quantified using powder X-ray diffractometry ( p -XRD). In total, 108 samples were analyzed to build the DOE model on aging between 2 and 48 h, temperatures from 100 °C to 400 °C, and partial pressures of O 2 from ∼0.0 kPa to 21.3 kPa. Rietveld refinement analysis was performed on all p -XRD patterns to quantify the exact composition of UO 2 , U 4 O 9 , U 3 O 7 , U 3 O 8 , and UO 3 . While no oxidation of the U 3 O 8 was observed for the conditions evaluated in these experiments, the UO 2 readily oxidized to U 4 O 9 and U 3 O 7 over short time periods, with low concentrations of oxygen. As the oxygen content increased, the oxidation of UO 2 to U 3 O 8 occurred rapidly. The response surface model indicates that oxidation of UO 2 occurs within 2 h when any oxygen is present at elevated temperatures. Results from this study are presented relative to the oxidation of UO 2 fuel in nuclear power reactors; as well as a forensics signature for identifying processing history in nuclear forensics. [ABSTRACT FROM AUTHOR]