Sintering process for large grain UO2 pellets

Small amount of additives doped large grain UO2 pellets are being developed by KAERI to enhance the pellet-cladding interaction (PCI) behavior of fuel rods. The process parameters which could control the grain size have been evaluated and the high temperature deformation property of doped UO2 pellets has been characterized in this study. An introduction of a step-wise variation of oxygen partial pressure during the sintering enhances the grain growth of UO2 pellets Sintering in wet hydrogen and then reasserting in dry hydrogen also increases the grain size of doped pellets. This oxygen partial pressure variation effect during the annealing at high temperature has been explained in terms of a increase of dopants solubility along the grain boundary. The compressive creep tests to estimate the high temperature deformation behavior of doped pellets showed that the deformation strain was increased considerably in the pellets sintered by step-wise process. The enhancement of creep strain is related with the grain size increment of sintered pellets