Molecular dynamics simulations of Gd and Cr doped UO2

Doping uranium dioxide is now used at industrial scale in order to optimise the behaviour of nuclear fuel. Gadolinia has been used for a long time for its neutronic properties as burnable poison. Chromia has only recently been introduce in order to promote for larger grains. The main objective is to increase the diffusion length for gaseous fission products, but the improved creep/plasticity of the fuel is an additional benefit bearing in mind the PCMI issues. Although both Cr and Gd are trivalent ions, their behaviour is radically different in the fuel: Cr shows a limited solubility while Gd is almost perfectly soluble up to 50%. At the same time, lattice contraction due to the presence of Cr is far more important than with Gd. This work aims at investigating for the behaviour of these elements using atomic scale simulation techniques, both in order to provide an explanation for the dissimilarities in the behaviour of Cr and Gd and to assess the capabilities of such techniques to model this.