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Title: The defect chemistry of U O 2 ± x from atomistic simulations

Abstract

Control of the defect chemistry in UO2±x is important for manipulating nuclear fuel properties and fuel performance. For example, the uranium vacancy concentration is critical for fission gas release and sintering, while all oxygen and uranium defects are known to strongly influence thermal conductivity. Here the point defect concentrations in thermal equilibrium are predicted using defect energies from density functional theory (DFT) and vibrational entropies calculated using empirical potentials. Electrons and holes have been treated in a similar fashion to other charged defects allowing for structural relaxation around the localized electronic defects. Predictions are made for the defect concentrations and non-stoichiometry of UO2±x as a function of oxygen partial pressure and temperature. If vibrational entropy is omitted, oxygen interstitials are predicted to be the dominant mechanism of excess oxygen accommodation over only a small temperature range (1265 K to 1350 K), in contrast to experimental observation. Conversely, if vibrational entropy is included oxygen interstitials dominate from 1165 K to 1680 K (Busker potential) or from 1275 K to 1630 K (CRG potential). Below these temperature ranges excess oxygen is predicted to be accommodated by uranium vacancies, while above them the system is hypo-stoichiometric with oxygen deficiency accommodated by oxygen vacancies.more » Our results are discussed in the context of oxygen clustering, formation of U4O9, and issues for fuel behavior. In particular, the variation of the uranium vacancy concentrations as a function of temperature and oxygen partial pressure will underpin future studies into fission gas diffusivity and broaden the understanding of UO2±x sintering.« less

Authors:
ORCiD logo [1];  [2]; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Lancaster Univ. (United Kingdom). Dept. of Engineering
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE); USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1524370
Alternate Identifier(s):
OSTI ID: 1550712
Report Number(s):
LA-UR-17-29135
Journal ID: ISSN 0022-3115
Grant/Contract Number:  
89233218CNA000001; AC52-06NA25396
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Nuclear Materials
Additional Journal Information:
Journal Volume: 504; Journal Issue: C; Journal ID: ISSN 0022-3115
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS

Citation Formats

Cooper, Michael William Donald, Murphy, Samuel T, and Andersson, Anders David Ragnar. The defect chemistry of UO2±x from atomistic simulations. United States: N. p., 2018. Web. https://doi.org/10.1016/j.jnucmat.2018.02.034.
Cooper, Michael William Donald, Murphy, Samuel T, & Andersson, Anders David Ragnar. The defect chemistry of UO2±x from atomistic simulations. United States. https://doi.org/10.1016/j.jnucmat.2018.02.034
Cooper, Michael William Donald, Murphy, Samuel T, and Andersson, Anders David Ragnar. Fri . "The defect chemistry of UO2±x from atomistic simulations". United States. https://doi.org/10.1016/j.jnucmat.2018.02.034. https://www.osti.gov/servlets/purl/1524370.
@article{osti_1524370,
title = {The defect chemistry of UO2±x from atomistic simulations},
author = {Cooper, Michael William Donald and Murphy, Samuel T and Andersson, Anders David Ragnar},
abstractNote = {Control of the defect chemistry in UO2±x is important for manipulating nuclear fuel properties and fuel performance. For example, the uranium vacancy concentration is critical for fission gas release and sintering, while all oxygen and uranium defects are known to strongly influence thermal conductivity. Here the point defect concentrations in thermal equilibrium are predicted using defect energies from density functional theory (DFT) and vibrational entropies calculated using empirical potentials. Electrons and holes have been treated in a similar fashion to other charged defects allowing for structural relaxation around the localized electronic defects. Predictions are made for the defect concentrations and non-stoichiometry of UO2±x as a function of oxygen partial pressure and temperature. If vibrational entropy is omitted, oxygen interstitials are predicted to be the dominant mechanism of excess oxygen accommodation over only a small temperature range (1265 K to 1350 K), in contrast to experimental observation. Conversely, if vibrational entropy is included oxygen interstitials dominate from 1165 K to 1680 K (Busker potential) or from 1275 K to 1630 K (CRG potential). Below these temperature ranges excess oxygen is predicted to be accommodated by uranium vacancies, while above them the system is hypo-stoichiometric with oxygen deficiency accommodated by oxygen vacancies. Our results are discussed in the context of oxygen clustering, formation of U4O9, and issues for fuel behavior. In particular, the variation of the uranium vacancy concentrations as a function of temperature and oxygen partial pressure will underpin future studies into fission gas diffusivity and broaden the understanding of UO2±x sintering.},
doi = {10.1016/j.jnucmat.2018.02.034},
journal = {Journal of Nuclear Materials},
number = C,
volume = 504,
place = {United States},
year = {2018},
month = {6}
}

Journal Article:

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Cited by: 11 works
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Figures / Tables:

Figure 1 Figure 1: U-O phase diagram taken from Ref. [75] with experimental data [7, 15, 17, 18, 21, 23, 76–81] shown by points.

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Works referencing / citing this record:

Nanoscale oxygen defect gradients in UO 2+ x surfaces
journal, August 2019

  • Spurgeon, Steven R.; Sassi, Michel; Ophus, Colin
  • Proceedings of the National Academy of Sciences, Vol. 116, Issue 35
  • DOI: 10.1073/pnas.1905056116

Atomistic description of self-diffusion in molybdenum: A comparative theoretical study of non-Arrhenius behavior
journal, January 2020