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Title: Determination of krypton diffusion coefficients in uranium dioxide using atomic scale calculations

We present a study of the diffusion of krypton in UO 2 using atomic scale calculations combined with diffusion models adapted to the system studied. The migration barriers of the elementary mechanisms for interstitial or vacancy assisted migration are calculated in the DFT + U framework using the nudged elastic band method. The attempt frequencies are obtained from the phonon modes of the defect at the initial and saddle points using empirical potential methods. The diffusion coefficients of Kr in UO 2 are then calculated by combining this data with diffusion models accounting for the concentration of vacancies and the interaction of vacancies with Kr atoms. We determined the preferred mechanism for Kr migration and the corresponding diffusion coefficient as a function of the oxygen chemical potential μ O or nonstoichiometry. For very hypostoichiometric (or U-rich) conditions, the most favorable mechanism is interstitial migration. For hypostoichiometric UO 2, migration is assisted by the bound Schottky defect and the charged uranium vacancy, V U 4–. Around stoichiometry, migration assisted by the charged uranium–oxygen divacancy (V UO 2–) and V U 4– is the favored mechanism. Finally, for hyperstoichiometric or O-rich conditions, the migration assisted by two V U 4– dominates. Krmore » migration is enhanced at higher μ O, and in this regime, the activation energy will be between 4.09 and 0.73 eV depending on nonstoichiometry. The experimental values available are in the latter interval. Since it is very probable that these values were obtained for at least slightly hyperstoichiometric samples, our activation energies are consistent with the experimental data, even if further experiments with precisely controlled stoichiometry are needed to confirm these results. Finally, the mechanisms and trends with nonstoichiometry established for Kr are similar to those found in previous studies of Xe.« less
Authors:
 [1] ; ORCiD logo [2] ;  [1] ; ORCiD logo [2] ;  [2] ; ORCiD logo [2] ; ORCiD logo [1]
  1. CEA, DEN, DEC Saint-Paul-lez-Durance (France)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
LA-UR-16-23479
Journal ID: ISSN 0020-1669
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 56; Journal Issue: 1; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Nuclear Energy (NE)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1351192

Vathonne, Emerson, Andersson, David Ragnar Anders, Freyss, Michel, Perriot, Romain Thibault, Cooper, Michael William Donald, Stanek, Christopher Richard, and Bertolus, Marjorie. Determination of krypton diffusion coefficients in uranium dioxide using atomic scale calculations. United States: N. p., Web. doi:10.1021/acs.inorgchem.6b01560.
Vathonne, Emerson, Andersson, David Ragnar Anders, Freyss, Michel, Perriot, Romain Thibault, Cooper, Michael William Donald, Stanek, Christopher Richard, & Bertolus, Marjorie. Determination of krypton diffusion coefficients in uranium dioxide using atomic scale calculations. United States. doi:10.1021/acs.inorgchem.6b01560.
Vathonne, Emerson, Andersson, David Ragnar Anders, Freyss, Michel, Perriot, Romain Thibault, Cooper, Michael William Donald, Stanek, Christopher Richard, and Bertolus, Marjorie. 2016. "Determination of krypton diffusion coefficients in uranium dioxide using atomic scale calculations". United States. doi:10.1021/acs.inorgchem.6b01560. https://www.osti.gov/servlets/purl/1351192.
@article{osti_1351192,
title = {Determination of krypton diffusion coefficients in uranium dioxide using atomic scale calculations},
author = {Vathonne, Emerson and Andersson, David Ragnar Anders and Freyss, Michel and Perriot, Romain Thibault and Cooper, Michael William Donald and Stanek, Christopher Richard and Bertolus, Marjorie},
abstractNote = {We present a study of the diffusion of krypton in UO2 using atomic scale calculations combined with diffusion models adapted to the system studied. The migration barriers of the elementary mechanisms for interstitial or vacancy assisted migration are calculated in the DFT + U framework using the nudged elastic band method. The attempt frequencies are obtained from the phonon modes of the defect at the initial and saddle points using empirical potential methods. The diffusion coefficients of Kr in UO2 are then calculated by combining this data with diffusion models accounting for the concentration of vacancies and the interaction of vacancies with Kr atoms. We determined the preferred mechanism for Kr migration and the corresponding diffusion coefficient as a function of the oxygen chemical potential μO or nonstoichiometry. For very hypostoichiometric (or U-rich) conditions, the most favorable mechanism is interstitial migration. For hypostoichiometric UO2, migration is assisted by the bound Schottky defect and the charged uranium vacancy, VU4–. Around stoichiometry, migration assisted by the charged uranium–oxygen divacancy (VUO2–) and VU4– is the favored mechanism. Finally, for hyperstoichiometric or O-rich conditions, the migration assisted by two VU4– dominates. Kr migration is enhanced at higher μO, and in this regime, the activation energy will be between 4.09 and 0.73 eV depending on nonstoichiometry. The experimental values available are in the latter interval. Since it is very probable that these values were obtained for at least slightly hyperstoichiometric samples, our activation energies are consistent with the experimental data, even if further experiments with precisely controlled stoichiometry are needed to confirm these results. Finally, the mechanisms and trends with nonstoichiometry established for Kr are similar to those found in previous studies of Xe.},
doi = {10.1021/acs.inorgchem.6b01560},
journal = {Inorganic Chemistry},
number = 1,
volume = 56,
place = {United States},
year = {2016},
month = {12}
}