Effect of Sintering Temperature on Microstructure and Phase Composition of U-Hf Burnable Absorber Fuel

The effect of sintering temperature on physical properties, microstructure and phase composition of U-Hf (containing 25wt%HfO2) burnable absorber fuels was studied by SEM, EDS and XRD, etc. The results suggest that:(1) The dried and calcined U-Hf fuel possessed good sintering activity, the densifying of U-Hf fuel was effectively promoted, and the density of fuel increased slightly when the sintering temperature was higher than 1550℃. (2)The sintered U-Hf crystal appeared in the form of UO2 solid solution matrix grains and the small second phase grains which dispersed in matrix grains. The small second phase grains were solid solution which Hf content was higher than stoichiometric, and as the sintering temperature increased, the small grains grew bigger and fewer. (3)The HfO2 crystal underwent a phase transition when the sintering temperature was higher than 1550℃. At about 1750℃, the monoclinic phase HfO2 transformed to the tetragonal phase incompletely, and dissolved into matrix UO2 incompletely.