[en] The work reported here was initiated with the objective of establishing oxidation rates for unirradiated or irradiated pellets at temperatures of interest to fuel storage. The time to initiate a spalling and the composition of the oxidation products were determined. UO₂ pellets heated at 150⁰C for 12 months in air showed no weight gain. UO₂ pellets heated at 200, 215, 230, and 250⁰C in air all exhibited an induction period in which pellets gained weight before spalling began. At 230 and 250⁰C, pellet spalling was accompanied by the formation of U₃O₈; however, pellet spalling at 200 and 215⁰C produced powders containing U₈O₁₉ and only small amounts of U₃O₈. At temperatures of 250⁰ and below, UO₂ pellet grain expansion resulting from oxidation in air is accommodated by the cracking and parting of the gain surface, thus producing a spalled powder with a particle distribution similar to the grain size distribution of the pellet