Densification Enhancement in AUC UO2 Pellet with High Lubricant Content

In a fabrication process of a UO2 annular pellet, the accuracy and the precision of the pellet dimension is very important. For an improvement of the dimension deviation, the addition of 1.0 wt% zinc stearate was performed in the process. The improvement is to decrease an axial deviation of the diameter in an annular pellet. Lubrication with a suitable lubricant (zinc stearate) reduces a friction between the die wall and the compact. As a result, the in-homogeneity of the density distribution in the compact can be reduced. However, the sintered density of UO2 pellets is decreased. The addition of various dopants in UO2 has been tried as a way to increase the density of UO2 pellets, without having a higher sintering temperature or a longer sintering time. The effects of some additives on the grain growth and densification have been widely studied. Some researchers have studied the effects of sintering additives such as Al2O3, TiO2 and Cr2O3-SiO2. Assmann et al. showed that a simply mixed UO2- Gd2O3 powder was able to be sintered up to 95%TD by adding Al2O3. It is reported that Al(OH)3 and TiO2 have a beneficial effect on the densification of the UO2- Gd2O3 pellets. Kim et al. have investigated the role of a composite additive, Cr2O3-SiO2, and they also observed an enhanced densification of the UO2-Gd2O3 pellets. All the above additives increased the sintered density after a final-stage sintering. In order to improve the sintered density drop due to the addition of 1.0 wt% zinc stearate, in this paper, it was described that the effect of TiO2 as an additive on the sintered density of a UO2 solid pellet