Sintering behaviour of niobia-doped large grain UO2 pellet

Abstract

The densification and grain growth of niobia-doped UO2 pellets have been studied with the purpose of obtaining a large grain size. The solid solution limit of niobium oxides in UO2 was about 0.5 wt% Nb2O5 as measured by the variation of the lattice parameter. The addition of 0.3 wt% Nb2O5 or NbO2 increased the grain size more when the oxygen partial pressure in the sintering atmosphere was above the equilibrium value for Mb5+ than when it was above that of Nb4+. This effect of the oxygen partial pressure made it possible to manufacture a large grain UO2 pellet doped with a small amount of niobia below the solid solution limit and sintered at a low temperature in a sintering atmosphere in which the oxygen partial pressure was controlled.