Release of volatile fission products from ThO 2 with a simulated burnup of 4 at%

Abstract

To determine the mechanical properties varying with burnup, the simulated 10 wt% ZrO2-doped UO2 ceramic pellets with burnups ranging from 0 to 250 GW d/tU were prepared by pressureless sintering in a hydrogen reducing environment. Mechanical properties such as hardness, elastic modulus and fracture toughness, as well as microstructures of the simulated pellet samples with different burnups (0, 75, 150 and 250 GW d/tU, respectively) were characterized by Vickers micro-indentation technique, X-ray diffraction, scanning electron microscopy and electron probe X-ray microanalysis, respectively. Results show that the relative densities of the simulated pellet pellets are between 93.5% and 95% and the measured elemental compositions are similar to the expected values. There are three distinct phases in the simulated 10 wt% ZrO2-doped UO2 fuel pellet samples, i.e., the matrix phase with the fluorite type structure, the oxide phase with perovskite type structure, and the metallic ε-phase. The lattice parameter of the simulated 10 wt% ZrO2-doped UO2 fuels gradually decreases with the increase of burnup. The hardness, elastic modulus and fracture toughness of simulated 10 wt% ZrO2-doped UO2 ceramic fuel pellets are significantly decreased by approximately 38.7%, 29.5% and 13.5% when the burnup increases from 0 to 250 GW d/tU, respectively.