The diffusion of iodine and caesium in the UO2±x lattice

The migration activation enthalpies of caesium and iodine in UO2+/-x predicted using atomistic simulation methodology, depend greatly on fuel stoichiometry. The mechanisms for stoichiometric and non-stoichiometric fuel require uranium self-diffusion, with the exception of iodine in UO2-x which employs an anion vacancy mechanism. The iodine post-irradiation results compare very well with the predicted activation enthalpy. In-pile iodine release experiments suggest a reduced activation enthalpy for iodine migration. The diffusion model presented allows for this result if uranium diffusion were greatly affected by the irradiation conditions. (C) 2000 Elsevier Science B.V. All rights reserved.