Computational Investigation of the Formation of Hyper-stoichiometric Uranium Dioxide (UO{sub 2+x})

Conference · Sun Jul 01 04:00:00 EDT 2007

OSTI ID:21062387

Skomurski, Frances; Becker, Udo; Ewing, Rodney ^[1]

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1. Geological Sciences, University of Michigan, 2534 C.C. Little Building, 1100 North University Ave., Ann Arbor, MI, 48109 (United States)

Understanding the mechanisms behind the formation of hyper-stoichiometric UO{sub 2} phases is important because oxidation of uranium atoms upon the addition of excess oxygen to the UO{sub 2} structure leads to volume changes that increase the susceptibility of spent fuel to corrosion. While a variety of diffraction and spectroscopic studies have been used to investigate structural changes as UO{sub 2} oxidizes to U{sub 4}O{sub 9}, the effect of interstitial oxygen on the charge distribution of uranium in hyper-stoichiometric UO{sub 2} remains inconclusive. In this study, quantum mechanical techniques were used to model the effects of interstitial oxygen on the structure and charge distribution of atoms in a simplified U{sub 4}O{sub 9} unit cell. A density functional theory-based approach was used to optimize the geometry and charge distribution of a variety of U{sub 4}O{sub 9} starting models with different U{sup 4+}, U{sup 5+} and U{sup 6+} charge configurations. Results from our calculations suggest that the formation of one U{sup 5+} per addition of interstitial oxygen at a perpendicular bisector site is favorable; this oxidation event is accompanied by partial reduction of the interstitial oxygen atom. Deflection of two lattice oxygen atoms along the body diagonal of the cubic site surrounding the U{sup 5+} is also observed upon the addition of one interstitial oxygen atom. Structural and bond length data are compared with experimental data whenever possible. (authors)

• Research Organization: Materials Research Society, 506 Keystone Drive, Warrendale, PA, 15086-7573 (United States)
• OSTI ID: 21062387
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COMPUTERIZED SIMULATION
CORROSION
DENSITY FUNCTIONAL METHOD
DIFFRACTION
INTERSTITIALS
OXIDATION
SPENT FUELS
STOICHIOMETRY
URANIUM DIOXIDE
URANIUM IONS