Theoretical and experimental density of (U, Gd)O2 and (U, Er)O2

An analytical expression is obtained for calculating the theoretical density of a stoichiometric, equilibrium, solid solution of the type U1–yRyO2 for uranium-gadolinium and uranium-erbium oxide fuel with different initial Gd2O3 or Er2O3 content. It is shown that the theoretical density of oxide fuel, containing a rare-earth oxide of the type R2O3, determined on the basis of the x-ray density is 0.03 g/cm3 higher and 0.02 g/cm3 lower than the computed density of (U, Gd)O2 and (U, Er)O2, respectively. It is found that the density of sintered uranium-gadolinium oxide pellets with an equilibrium solid solution of the type (U, Gd)O2 is 96–98% with initial Gd2O3 mass fraction to 3.35% of the theoretical value and 98–99% with 5% and higher.