The sintering blocking mechanism on the UO2-GD2O3 system. Part 2: the occurrence of the Kirkendall effect

In this part of the work it has been shown that the sintering blocking mechanism is based on pore formation b Kirkendall effect, instead of the formation of low diffusivity phases. Gadolinium from Gd2O3 agglomerates diffuses preferentially into the UO2 phase. The UO2 matrix the n expands for receiving extra gadolinium cations and a void is generated at the place of the original Gd2O3 agglomerate. The formation of a solid solution during the intermediate stage of sintering causes pore formation, which is difficult to remove in the final stage of sintering. Based on this mechanism, possible technological solutions were proposed to prevent densification problems in sintering UO2-Gd2O3 fuel when dry mechanical blending of powders is chosen as process route. (author)