Dilatometric Study of U 1− x Am x O 2±δ Sintering: Determination of Activation Energy

In the framework of minor actinide bearing blanket fuel fabrication, the sintering of uranium/americium ( U 0.85 Am 0.15 O 2 ± δ ) homogeneous mixed‐oxide pellets was studied. After the characterization of the U 0.85 Am 0.15 O 2 ± 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 UO 2+δ . During the heating phase, up to 2173 K, the U 0.85 Am 0.15 O 2 ± 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 UO 2 .