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Statistical Model for Grain Boundary and Grain Volume Oxidation Kinetics in UO2 Spent Fuel

Published online by Cambridge University Press:  21 February 2011

R. B. Stout ,
H. F. Shaw  and
R. E. Einziger
R. B. Stout
Affiliation:
University of California, Lawrence Livermore National Laboratory P 0 Box 808, L-200, Livermore, CA 94550
H. F. Shaw
Affiliation:
University of California, Lawrence Livermore National Laboratory P 0 Box 808, L-200, Livermore, CA 94550
R. E. Einziger
Affiliation:
Battelle - PNL, P 0 Box 999, Richland, WA 99352
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Abstract

The Yucca Mountain Project of the U.S. Department of Energy is investigating the suitability of a site in the unsaturated zone at Yucca Mountain, NV, for a high-level nuclear waste repository. Most of the waste will consist of UO2 spent fuel in Zircaloy-clad rods from nuclear reactors. If failure of both the waste containers and the cladding occurs within the lifetime of the repository, then the UO2 will be exposed to oxygen in the air and higher oxides of uranium may form. The oxidation state of the spent fuel may affect its dissolution behavior if later contacted by water. A model for the kinetics of spent fuel oxidation under repository-relevant conditions is thus necessary to predict the behavior of the waste form for assessing the performance of the repository with respect to the containment of radionuclides. In spent fuel experiments, the UO2 oxidation front initially propagates along grain boundaries followed by propagation into grain volumes. Thus, the oxidation kinetics is controlled by two processes and the oxidation of spent fuel fragments will depend on the density and physical attributes of grain boundaries. With this in mind, concepts from statistical mechanics are used to define a density function for grain boundaries perunit volume per unit species in a spent fuel fragment. Combining the integral forms of mass conservation and this grain boundary density function, a model for the global rate of oxidation for a spent fuel fragment is obtained. For rapid grain boundary oxidation compared to grain volume oxidation, equations of the model are solved and results compared to existing data.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 176: Symposium U – Scientific Basis for Nuclear Waste Management XIII , 1989 , 475
Copyright
Copyright © Materials Research Society 1990

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References

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