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Segregation of Fission Products to Surfaces of UO2

Published online by Cambridge University Press:  21 March 2011

C.R. Stanek
Affiliation:
Dept. of Materials, Imperial College of Science, Technology and Medicine London, SW7 2BP, UNITED KINGDOM
Robin W. Grimes
Affiliation:
Los Alamos National Laboratory MS-K765 Los Alamos, NM 87545
Mark R. Bradford
Affiliation:
British Energy Generation Ltd. Barnwood, Gloucestershire, GL4 3RS, UNITED KINGDOM
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Abstract

In order to predict the release rates of fission products from UO2 nuclear fuel, it is necessary to determine the energetics associated with their segregation from the bulk to surfaces. Here segregation is determined by calculating the total energy of a simulation repeat unit which includes a fission product, as a function of the distance of the fission product from the surface. We have investigated the possibility that specific fission products segregate preferentially to certain surfaces. In particular, Ce4+ and Zr4+ segregate to the (100) surface, while Ba2+ and Sr2+ segregate to the (111) surface. Two issues make these calculations more complex. First, charged defects need to be compensated by oxygen vacancies. For example, divalent Ba2+ and Sr2+ substituting on uranium sites are compensated by a single oxygen vacancy. Second, certain surfaces, such as the (100), are inherently unstable, but can be stabilized by oxygen vacancies. Arrangements of these surface defects lead to complex surface structures that affect segregation energetics.

Type
Research Article
Copyright
Copyright © Materials Research Society 2001

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