Effects of sintering processes on the duplex grain structure of UO 2

Abstract

The grain structure of UO 2 has been investigated under the conditions of three sets of sintering atmospheres and powder properties: (1) CO 2 atmosphere and the powder derived from the AUC process, (2) H 2CO 2 atmosphere and powder from the AUC process, and (3) CO 2 atmosphere and powder from the AU process. Powder compacts have been sintered at 1300°C for 0.1 h or partially sintered. The duplex grain structure which consists of coarse and irregular grains and fine and regular grains develops only under the conditions of both CO 2 atmosphere and powder derived from the AUC process. It is found that the difference in uranium diffusivity between the U 4O 9-z and the UO 2+x phases does not play a dominant role in the development a duplex grain structure. The microstructural features suggest that the coarse and irregular grains develop abnormally. The reason for the development of the duplex grain structure is discussed on the basis of the inhomogeneity of the powder compacts derived from the AUC process.