Partition of soluble fission products between the grey phase, ZrO2 and uranium dioxide

Abstract The energies to remove fission products from UO 2 or UO 2+ x and incorporate them into BaZrO 3 , SrZrO 3 (grey phase constituent phases) and ZrO 2 have been calculated using atomistic scale simulation. These energies provide the thermodynamic drive for partition of soluble fission products between UO 2 or UO 2+ x and these secondary oxide constituents of the fuel system. Tetravalent cation partition into BaZrO 3 , SrZrO 3 and ZrO 2 was only preferable for species with smaller radii than Zr 4+ , regardless of uranium dioxide stoichiometry. Under stoichiometric conditions both the larger and the smaller trivalent cations were found to segregate to BaZrO 3 but only the smaller fuel additive elements Cr 3+ and Fe 3+ segregate to SrZrO 3 . Partition from UO 2+ x was always unfavourable for trivalent cations. Additions of excess Cr 3+ (as a fuel additive) are predicted make the partition into BaZrO 3 and SrZrO 3 more favourable from UO 2 for the larger trivalent cations. Trivalent fission products with radii smaller than or equal to that of Sm 3+ were identified to segregate into ZrO 2 only from UO 2 . No segregation to SrO or BaO is predicted.