Dilatometric Study of U1−xAmxO2±δ Sintering: Determination of Activation Energy



In the framework of minor actinide bearing blanket fuel fabrication, the sintering of uranium/americium (U0.85Am0.15O2 ± δ) homogeneous mixed-oxide pellets was studied. After the characterization of the U0.85Am0.15O2 ± δ starting powder (granulometry, X-ray diffraction, and scanning electron microscopy), its densification under a reducing atmosphere was monitored through dilatometric measurements and compared to a similar experiment with UO2+δ. During the heating phase, up to 2173 K, the U0.85Am0.15O2 ± δ pellet shrinks from 70 to 95%TD (theoretical density). Neck formation and growth initiate the densification of this pellet at 1200 K. Two subsequent mechanisms were also evidenced, and a maximum shrinkage rate was observed between 2000 and 2100 K, suggesting an optimal sintering temperature within this range. The associated activation energy (Q) of sintering process was also determined using three different models which yield values noticeably higher than those reported or measured for UO2.