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Title: Oxygen transport in off-stoichiometric uranium dioxide mediated by defect clustering dynamics

In this study, oxygen transport is central to many properties of oxides such as stoichiometric changes, phase transformation and ionic conductivity. In this paper, we report a mechanism for oxygen transport in uranium dioxide (UO2) in which the kinetics is mediated by defect clustering dynamics. In particular, the kinetic Monte Carlo (KMC) method has been used to investigate the kinetics of oxygen transport in UO2 under the condition of creation and annihilation of oxygen vacancies and interstitials as well as oxygen interstitial clustering, with variable offstoichiometry and temperature conditions. It is found that in hypo-stoichiometric UO2-x, oxygen transport is well described by the vacancy diffusion mechanism while in hyper-stoichiometric UO2+x, oxygen interstitial cluster diffusion contributes significantly to oxygen transport kinetics, particularly at high temperatures and high off-stoichiometry levels. It is also found that diinterstitial clusters and single interstitials play dominant roles in oxygen diffusion while other larger clusters have negligible contributions. However, the formation, coalescence and dissociation of these larger clusters indirectly affects the overall oxygen diffusion due to their interactions with mono and di-interstitials, thus providing a explanation of the experimental observation of saturation or even drop of oxygen diffusivity at high off-stoichiometry.
Authors:
 [1] ;  [1] ;  [2] ;  [3]
  1. Idaho National Lab. (INL), Idaho Falls, ID (United States)
  2. Purdue Univ., West Lafayette, IN (United States)
  3. Idaho National Lab. (INL), Idaho Falls, ID (United States); Univ. of Wisconsin-Madison, Madison, WI (United States)
Publication Date:
OSTI Identifier:
1248176
Report Number(s):
INL/JOU--14-33670
Journal ID: ISSN 0021-9606; JCPSA6
Grant/Contract Number:
AC07-05ID14517
Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 142; Journal Issue: 9; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Research Org:
Idaho National Laboratory, Idaho Falls, ID (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS uranium dioxide; oxygen transport; kinetic Monte Carlo; diffusion; interstitial defects; vacancies; Monte Carlo methods; cluster analysis