[en] The large grain pellet is a candidate for a high burnup fuel pellet. We have investigated the large grain pellet in which Al and Si are added within the impurity limits. These additives promote the grain growth of uranium dioxide during sintering and modify the characteristics of the grain boundary. It is expected to reduce fission gas release and pellet cladding mechanical interaction. We have already confirmed that there is a slight difference in the out of pile properties of the UO₂ pellet except for creep behavior. The additive enhances the creep rate over a wide range of creep conditions. To precisely understand the effect of additives on the fabrication conditions and properties of the pellet, we investigated a UO₂ pellet in which an excess of Al and Si is added. As for grain growth only small amount of additives is needed to cover the grain boundary of UO₂. An excess of additive does not promote further grain growth but leads to suppression of pellet densification by volatilization of the additives. So, an excess of Al and Si is not necessary to improve the microstructure of the pellet and creep behavior, while thermal expansion and diffusivity are not significantly affected by the amount of additive. (author)