Molecular modelling of transmutation fuels and targets

The stability of point defects and the behaviour of rare gases in uranium dioxide have been studied using electronic structure calculations. Krypton atoms are found to be insoluble in UO2 whatever the trapping site considered. Their presence induces a swelling of the lattice when they are located in interstitial sites or in oxygen vacancy sites. Due to its smaller atomic size, the predicted helium behaviour is very different. Indeed, helium is found to be soluble in stoichiometric and hyperstoichiometric uranium dioxide in the presence of uranium vacancies or divacancies. Moreover helium atoms induce a lattice contraction except in interstitial sites for which a slight expansion is found. Some preliminary results concerning xenon are also given.