Using density functional theory, a recently discovered structure for di-interstitial

oxygen clusters in UO2+x was considered, in which three oxygen ions shared one

lattice site. This di-interstitial cluster exhibited fast diffusion; the migration barrier

to these clusters being about half that for mono-interstitials. Using kinetic Monte

Carlo methods, the diffusivity of oxygen with and without the di-interstitial

mechanism was calculated as a function of x and it was found that oxygen transport

was significantly increased for higher values of x when the di-interstitial

mechanism was included; thus agreeing much more closely with experimental data.

These results emphasized the importance of clustering phenomena in UO2+x and

had implications for the evolution of UO2+x.

Role of Di-Interstitial Clusters in Oxygen Transport in UO2+x from First

Principles. D.A.Andersson, T.Watanabe, C.Deo, B.P.Uberuaga: Physical Review

B, 2009, 80[6], 060101