PNNL

Abstract

This report presents the results of classical molecular dynamics simulations of the diffuse pre-melting transition, melting, and defect production by 1 keV U recoils in UO2 using five different rigid-ion potentials. The experimentally-observed pre-melting transition occurred for all five cases. For all the potentials studied, dynamic defect annealing is highly effective and is accompanied by replacement events on the anion sublattice. The primary damage state after ~15 ps consists of isolated Frenkel pairs and interstitial and vacancy clusters of various sizes. The average displacement energy varies from ~28 to ~83 eV and the number of Frenkel pairs is different by a factor of three depending on the choice of potential. The size and spatial distribution of vacancy and interstitial clusters is drastically different for the potentials studied. The results provide statistics of defect production. They point to a pressing need to determine defect formation, migration and binding energies in UO2 from first principles and to develop reliable potentials based on this data for simulating microstructural evolution in nuclear fuel under operating conditions.