A one-step, continuous, fluid-bed process for the conversion of uranium hexafluoride to uranium dioxide was successfully carried out in preliminary experiments in a 1 1/2-inch-diameter Monel reactor. Hydrogen and steam were used for simultaneous reduction and pyrohydrolysis reactions carried out at 600 deg C, resulting in the formation of a dense coating of dioxide on the starting bed of uranium dioxide. The effects of uranium hexafluoride feed rate and reactant excesses on conversion were investigated. Results of fluid-bed steam pyrohydrolysis runs on uranium tetrafluoride are also presented.