Computer simulation of defects formation and equilibrium in non-stoichiometric uranium dioxide

Formation and stability of different types of clusters in hyperstoichiometric UO2+x, including Willis’s 2:2:2 interstitial dimers as well as cuboctahedral tetra- and pentamers are investigated under static and dynamic conditions based on a partly-ionic model. A ‘Free Hopping Approximation’ for small polarons is proposed and implemented in a molecular dynamic simulation computer code. Lattice parameter and other equilibrium properties of UO2+x are calculated and compared with existing experimental data in a wide range of temperature and stoichiometry.