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

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

doi:10.1016/j.jnucmat.2011.09.003

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

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Abstract

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.

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

Publication Date:: Sun Mar 03 00:00:00 EST 2013

Research Org.:: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Sponsoring Org.:: USDOE

OSTI Identifier:: 1073572

Report Number(s):: PNNL-SA-75956
KP1504010

DOE Contract Number:: AC05-76RL01830

Resource Type:: Journal Article

Journal Name:: Journal of Nuclear Materials, 434(1-3):422-433

Additional Journal Information:: Journal Name: Journal of Nuclear Materials, 434(1-3):422-433

Country of Publication:: United States

Language:: English

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

Citation Formats


                    Skomurski, Frances N, Wang, Jianwei, Ewing, Rodney C, and Becker, U. Charge distribution and oxygen diffusion in hyperstoichiometric uranium dioxide UO2+x (x≤0.25).  United States: N. p., 2013. 
        Web.  doi:10.1016/j.jnucmat.2011.09.003.

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                    Skomurski, Frances N, Wang, Jianwei, Ewing, Rodney C, & Becker, U. Charge distribution and oxygen diffusion in hyperstoichiometric uranium dioxide UO2+x (x≤0.25).  United States.  https://doi.org/10.1016/j.jnucmat.2011.09.003

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                    Skomurski, Frances N, Wang, Jianwei, Ewing, Rodney C, and Becker, U. 2013.  
        "Charge distribution and oxygen diffusion in hyperstoichiometric uranium dioxide UO2+x (x≤0.25)".  United States.  https://doi.org/10.1016/j.jnucmat.2011.09.003.

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@article{osti_1073572,

  title        = {Charge distribution and oxygen diffusion in hyperstoichiometric uranium dioxide UO2+x (x≤0.25)},

  author       = {Skomurski, Frances N and Wang, Jianwei and Ewing, Rodney C and Becker, U},

  abstractNote = {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.},

  doi          = {10.1016/j.jnucmat.2011.09.003},

  url          = {https://www.osti.gov/biblio/1073572},
  journal      = {Journal of Nuclear Materials, 434(1-3):422-433},
number       = ,

  volume       = ,

  place        = {United States},

  year         = {Sun Mar 03 00:00:00 EST 2013},

  month        = {Sun Mar 03 00:00:00 EST 2013}

}

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