Fluorination of uranium and plutonium oxides to the volatile hexafluorides, UF6 and PuF6, is a major step for the fluidized-bed volatility processing of spent Zircaloy-clad UO2-PuO2 power reactor fuel. This step was studied in a 2-in.-diam reactor using 0.3- to 1.2-kg charges of simulated spent fuel pellets containing UO2, PuO2, and nonradioactive oxides of elements that would be formed in fission. Retention of uranium and plutonium by the fluidized bed of inert alumina, which is discarded after serving as a heat-transfer medium, was minimized and amounted to only 0.02% of the uranium and 3.5% of the plutonium in a 0.65-kg pellet charge. The total plutonium retention was reduced to ∼ 1% of the plutonium charge by using a single 1.2-kg bed of alumina to process three charges (1.95 kg) of fuel pellets.