Final-stage densification of mixed oxide fuels

The final-stage densification of hypostoichiometric (U, Pu)O2−x has been studied using a double-action punch and die, in the temperature range of 1325 to 1550°C between stresses of 7.6 and 76 MPa. At low stresses the densification rate is nearly proportional to stress and has an activation energy comparable to that measured for steady-state creep. The stress exponent increases as stress is increased. The data compare tolerably well with the predictions of theoretical pressures-intering maps once grain growth (which was found to occur at the higher temperatures) is accounted for. The controlling mechanism throughout the experiments is shown to be lattice diffusion.