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

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 (UO{sub 2}) in which the kinetics is mediated by defect clustering dynamics. In particular, the kinetic Monte Carlo method has been used to investigate the kinetics of oxygen transport in UO{sub 2} under the condition of creation and annihilation of oxygen vacancies and interstitials as well as oxygen interstitial clustering, with variable off-stoichiometry and temperature conditions. It is found that in hypo-stoichiometric UO{sub 2−x}, oxygen transport is well described by the vacancy diffusion mechanism while in hyper-stoichiometric UO{sub 2+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 di-interstitial 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 an explanation of the experimental observation of saturation or even drop of oxygen diffusivity at high off-stoichiometry.
Authors:
;  [1] ;  [2] ;  [1] ;  [3]
  1. Idaho National Laboratory, Idaho Falls, Idaho 83415 (United States)
  2. School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)
  3. (United States)
Publication Date:
OSTI Identifier:
22416229
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 142; Journal Issue: 9; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANNIHILATION; COALESCENCE; DIFFUSION; DISSOCIATION; INTERSTITIALS; IONIC CONDUCTIVITY; KINETICS; MONTE CARLO METHOD; OXYGEN; PHASE TRANSFORMATIONS; STOICHIOMETRY; TEMPERATURE RANGE 0400-1000 K; URANIUM DIOXIDE; VACANCIES