AVS 60th International Symposium and Exhibition
    Actinides and Rare Earths Focus Topic Tuesday Sessions
       Session AC+AS+SS-TuM

Invited Paper AC+AS+SS-TuM1
From Berkeley to Bristol: Defect Structures in Actinide Oxides

Tuesday, October 29, 2013, 8:00 am, Room 102 C

Session: The Surface Science of Actinides and Rare Earths
Presenter: G.C. Allen, University of Bristol, UK
Correspondent: Click to Email
The first generation of British gas-cooled reactors used natural uranium metal as fuel but UO2 is far and away the most important fuel in use today. It is in fact the first in a complex family of oxides, initially based on the fluorite UO2 unit cell (U4O9 and U3O7) but giving way to layered-type oxides as the O/U ratio increases (U3O8 and UO3). Oxidation in UO2 is known to occur via accumulation of point oxygen interstitials and defect aggregates such as Willis, cuboctahedral and split-interstitial clusters. Spectroscopic evidence is used to demonstrate that the link between defect clusters and the U4O9 and U3O7 structures can be rationalised in terms of multiple Willis, cuboctahedral and split-interstitial clusters. DFT models have been used to examine the stability of different defect clusters in UO2 supercells. The formation energy of each cluster is calculated along with the variation of their concentrations with increasing the temperature. All interstitial clusters are found to be charge compensated by U5+ ions, suggesting this is the highest uranium oxidation state reached amongst the fluorite based structure.