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Neutron Diffraction Study of the Structural Changes Occurring During the Low Temperature Oxidation of UO2

Published online by Cambridge University Press:  31 January 2011

Gianguido Baldinozzi ,
Lionel Desgranges  and
Gurvan Rousseau
Gianguido Baldinozzi
Affiliation:
[email protected], None Provided, Paris, France
Lionel Desgranges
Affiliation:
[email protected], CEA, DEN DEC LLCC, St Paul-lez-Durance, France
Gurvan Rousseau
Affiliation:
[email protected], CEA, DEN DEC LLCC, St Paul-lez-Durance, France
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Abstract

The oxidation of uranium dioxide has been studied for more than 50 years. It was first studied for fuel fabrication purposes and then later on for safety reasons to design a dry storage facility for spent nuclear fuel that could last several hundred years. Therefore, understanding the changes occurring during the oxidation process is essential, and a sound prediction of the behavior of uranium oxides requires the accurate description of the elementary mechanisms on an atomic scale. Only the models based on elementary mechanisms should provide a reliable extrapolation of laboratory results over timeframes spanning several centuries. The oxidation mechanism of uranium oxides requires understanding the structural parameters of all the phases observed during the process. Uranium dioxide crystal structure undergoes several modifications during the low temperature oxidation that transforms UO2 into U3O8. The symmetries and the structural parameters of UO2, β-U4O9, β-U3O7 and U3O8 were determined by refining neutron diffraction patterns on pure single-phase samples. Neutron diffraction patterns, collected during the in situ oxidation of powder samples at 483 K were also analyzed performing Rietveld refinements. The lattice parameters and relative ratios of the four pure phases were measured during the progression of the isothermal oxidation. The transformation of UO2 into U3O8 involves a complex modification of the oxygen sublattice and the onset of complex superstructures for U4O9 and U3O7, associated with regular stacks of complex defects known as cuboctahedra which consist of 13 oxygen interstitial atoms. The structural modifications during the oxidation process are discussed.

Keywords

crystallographic structurephase transformationoxidation
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1215: Symposium V – Materials Research Needs to Advance Nuclear Energy , 2009 , 1215-V10-05
Copyright
Copyright © Materials Research Society 2010

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