Molecular dynamics simulation of intragranular Xe bubble re-solution in UO₂

The homogeneous re-solution of Xe fission gas bubbles in UO₂ is investigated by combined Monte Carlo and molecular dynamics simulations. Using a binary collision model, based on the Ziegler-Littmark-Biersack potential [J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Stopping and Ranges of Ions in Matter, vol. 1, Pergamon Press, New York, 1984], the recoil energy distribution of fission gas atoms is obtained. An extensive library of fission gas atom displacement cascades is then compiled using molecular dynamic simulations. It used for calculating recoil spectrum averaged quantities. The calculations yield a re-solution parameter for homogeneous re-solution and a displacement distribution of fission gas atoms around the fission gas bubbles. The results disagree considerably from past estimates. The importance of channeling and threshold energy for fission gas escape are discussed.