Impact of fission product (Ce, Sn, Sr, Se) oxides on UO2 oxidation to U3O8

Abstract

In order to investigate the impact of fission products on the oxidation of spent fuel in the cladding separation process, the oxidation behavior and kinetic mechanism of UO2 and impact of M (M = Ce, Sn, Sr, Se) oxides on the oxidation of UO2 to U3O8 were investigated by TG/DSC, XRD, FT-IR and Raman. It was found that the oxidation of UO2 to U3O8 went through two stages: UO2→U3O7; U3O7→U3O8. Doping M oxide in UO2 could not change the two-step mechanism, and significantly inhibited the formation of U3O8. The final products of CeO2 and SrO-doped UO2 oxidation contained 20% U3O7 and 47% U3O7, respectively. The doping of M oxide increased the onset oxidation temperature of the two oxidation stages of UO2 by 5–65 °C. In addition, the kinetic mechanism of UO2 oxidation was investigated and found that the first and second oxidation stages were controlled by 1st order reaction or nucleation and growth, and 2nd order reaction, respectively. The doping of M oxide significantly affected the kinetic mechanism of the first stage.