Solution of trivalent cations into uranium dioxide

The accommodation of trivalent oxides (M2O3) in uranium dioxide has been investigated using atomic scale simulation. Calculations suggest that all trivalent oxides studied preferentially enter UO2 by associating the substitutional ion with an oxygen vacancy, larger cations forming the cluster {2MU′:VO}×. Solution into hyper-stoichiometric UO2+x was accompanied by the formation of the {MU′:UU}× cluster and smaller solution energies than into stoichiometric UO2. Solubility is a particularly strong function of hyper-stoichiometry for smaller cations such as Cr3+, which has implications for the use of Cr2O3 as a grain enlarger but not so for larger cations such s Gd3+.

► Change in solubility limit of sesquioxides in uranium dioxide with excess oxygen.
► Larger trivalent cations found to be soluble regardless of stoichiometry and limit mainly temperature dependent.
► Iron and chromium cation solution limit strongly dependent on stoichiometry, only soluble with excess oxygen.
► Addition of trivalent cations removes oxygen excess.