First Principles Modelling of Oxygen Impurities in UN Nuclear Fuels

We report results of first principles VASP supercell calculations of O impurity in UN fuels placed either at an interstitial tetrahedral position or as a substitution for a host N ion. In the latter case O perfectly fits into N site producing no lattice distortion. Such the O substitutional impurity only slightly affects the formation energies of U and N vacancies nearby. In both interstitial and substitutional positions O atom attracts the additional electron density and transforms into the negatively charged ion. Oxygen incorporation into pre-existing N vacancy is energetically more favourable than into the interstitial position. The O impurities produce an additional peak at the low energy side of N contribution to the DOS calculated for uranium mononitride which could be used for the O identification by means of the UPS spectroscopy. We compare also the DOS calculated for UN and hypothetical isostructural UO. Both O solution and incorporation energies are negative, indicating that O penetration into UN fuel is the energetically favourable. The migration energy of the interstitial O ion is estimated as 2.8 eV.

MASTRIKOV Y.;  KOTOMIN E. A.; 

2008-08-07

ELSEVIER SCIENCE BV

JRC47066

0022-3115,   

www.elsevier.com/locate/jnucmat,    https://publications.jrc.ec.europa.eu/repository/handle/JRC47066,   

10.1016/j.jnucmat.2008.04.015,