[en] Oxidation process of sintered (UO_2+ZrO_2) pellets in order to obtain sintered pellet oxidation data to produce U_3O_8 powder has been carried out as a preliminary study of fuel recycle simulation with AIROX process. The sintered (UO_2+ZrO_2) pellets with variation of ZrO_2 concentration from 0 – 1% were heated at temperature 300 - 500 °C for 0.5 – 2 hours to produce U_3O_8 powder. From the process above, the oxidation efficiency and the powder characterization, i.e. the density, were determined. The results showed that the oxidation process occurred at temperature above 400 °C after 0.5 hour in which grayish black U_3O_8 pellets had changed into brownish black U_3O_8 powder. Oxidation efficiency of 100% was achieved after 2 hours at ZrO_2 concentration of 0.4%, while the highest density was obtained at ZrO_2 concentration of 0.2%. (author)