Homogenisation in mixed UO2-PuO2 compacts was studied using X-ray diffraction. It was observed that the homogenisation proceeded mainly by the assimilation of UO2 into PuO2. The nearly one-way flow of material, from UO2 to PuO2, was shown to be due to the high activity of the PuO2 powder as compared to that of the UO2 powder. A concentric core-shell diffusion model, in which the UO2 formed a solute core and PuO2 formed a solvent shell, was used to deduce cation interdiffusion coefficients from the homogenisation data. The temperature dependence of cation diffusivity at 1573 to 1873K was described by:

D (m2/s) = 2.55 x 10-11 exp[−2.22(kJ/mol)/RT]

The diffusivity values at 1573 and 1673K indicated an activation energy of 126kJ/mol. This suggested that grain-boundary diffusion was the main homogenisation mechanism within this temperature range.

Study of Homogenisation and Cation Interdiffusion in Mixed UO2-PuO2 Compacts by X-Ray Diffraction. R.Verma: Journal of Nuclear Materials, 1984, 120[1], 65-73