Atomistic simulation methods were used to study the behavior of fission gas atoms in UO2 and α-U3O8. The solution energies were shown to decrease from UO2-x to UO2+x, but increased again during further oxidation to U3O8. It was concluded that the migration of Xe and Kr in UO2+x occurred via a tetra-vacancy trap cluster. In the case of U3O8, the movement of Xe and Kr was assisted by O vacancies. Especially low activation energies for migration were predicted to exist in the case of radiation-assisted vacancy formation.

R.G.J.Ball, R.W.Grimes: Journal of Nuclear Materials, 1992, 188, 216-21