To support dry storage technology, oxidation tests were conducted with light water reactor spent fuel. The initial rate of weight gain for spent fuel was up to 50 times greater than the initial rate for nonirradiated pellets. Spent fuel formed measurable U4O9+x particulates at weight gains significantly higher than those at which the nonirradiated pellets formed U3O8 powder. Initial test results on three types of pressurized water reactor (PWR) spent fuel indicated that fuel type had a significant influence on weight gain. Additional tests were performed at temperature levels from 135 to 230°C on fuel with burnups from 8 to 34 GWd/ tonne U irradiated in five different reactors. The tests were conducted in static air at controlled moisture levels in a 105 R/h gamma field. In the 230°C tests, weight gains for PWR and boiling water reactor (BWR) fuels exceeded 4 wt% after 4000 h of exposure. Powder formation time on BWR fuels increased with increasing burnup; weight gain magnitudes were independent of fuel burnup.