Charge distribution and oxygen diffusion in hyperstoichiometric uranium dioxide UO2+x (x≤0.25)
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 Lab. (PNNL), Richland, WA (United States)
- 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
Similar Records
Pauling’s rules for oxide-based minerals: A re-examination based on quantum mechanical constraints and modern applications of bond-valence theory to Earth materials
Average structure and local configuration of excess oxygen in UO2+x