Creep of Mixed-Oxide Fuel Pellets at High Stress

The rate of steady‐state compressive creep in (U,Pu)O2‐ε was investigated in the power‐law creep region (at a constant stress of 69 MN/m2 between 1600° and 1500°C) as a function of the oxygen‐to‐metal (O/M) ratio (1.88 to 1.995). The creep rate over this range is independent of the starting material and decreases with increasing O/M ratio. The apparent activation energy for creep and the preexponential structure factor are sensitive functions of the O/M ratio, with approximately the same dependence on this ratio as these parameters measured at low stresses. These results imply that diffusion of the same defect species controls creep deformation in both the stress‐assisted diffusion region (ε∞σ) and the dislocation‐motion region (ε∞σ4.4).