Charge distribution and oxygen diffusion in hyperstoichiometric uranium dioxide UO2+x (x≤0.25)

Journal Article · Sun Mar 03 04:00:00 EST 2013 · Journal of Nuclear Materials, 434(1-3):422-433

DOI:https://doi.org/10.1016/j.jnucmat.2011.09.003· OSTI ID:1073572

Skomurski, Frances N; Wang, Jianwei; Ewing, Rodney C; Becker, U

Quantum-mechanical techniques were used to determine the charge distribution of uranium atoms in UO2+x (x ≤ 0.25) and to calculate activation-energy barriers to oxygen diffusion. Upon optimization, the reduction in unit-cell volume relative to UO2, and the shortest and bond-lengths (0.22 and 0.24 nm, respectively) are in good agreement with experimental data. The addition of interstitial oxygen to the unoccupied cubic sites in the UO2 structure deflects two nearest-neighbor oxygen atoms along the body diagonal of uranium-occupied cubic sites, creating lattice oxygen defects. In (1×1×2) supercells, the partial oxidation of two U4+ atoms is observed for every interstitial oxygen added to the structure, consistent with previous quantum-mechanical studies. Results favor the stabilization of two U5+ over one U6+ in UO2+x. Calculated activation energies (2.06-2.73 eV) and diffusion rates for oxygen in UO2+x support the idea that defect clusters likely play an increasingly important role as oxidation proceeds.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1073572
• Report Number(s): PNNL-SA-75956; KP1504010
• Journal Information: Journal of Nuclear Materials, 434(1-3):422-433, Journal Name: Journal of Nuclear Materials, 434(1-3):422-433
• Country of Publication: United States
• Language: English

Related Subjects

U4O9
UO2+x
charge distribution
diffusion
nuclear fuel
oxidation
uranium dioxide