The Role of Gd₂O₃ Phase Transition on UO₂-Gd₂O₃ Fuel Sintering

Gadolinium has been added to nuclear fuel to enable longer fuel cycles. UO₂-Gd₂O₃ mixed fuel shows bad sintering behavior, which is hindered at temperatures of [approximately]1200°C. The mechanism that explains this unusual sintering behavior is not yet fully understood. The formation of Gd-rich phases with low diffusivity or pore formation during sintering have both been suggested as possible causes. Experimental data published in the literature appear not to support phase formation; however, the formation of large closed pores in Gd₂O₃-rich regions of the fuel has been reported. Pore formation could be developed during the Gd₂O₃ C[right arrow]B phase transition, which is followed by volume reduction. Our study investigated this hypothesis. The results showed that the mechanism proposed does not explain the UO₂-Gd₂O₃ sintering behavior.