Spent Fuel Waste Form Charactristics: Grain and Fragment Size Statistical Dependence for Oxidation Response

Stout, Ray B.; Kansa, E.; Buchanan, H. C.; Einziger, R. E.; Thomas, L. E.; ,

Spent Fuel Waste Form Charactristics: Grain and Fragment Size Statistical Dependence for Oxidation Response

by Ray B. Stout, Lawrence Livermore Natl Lab, Livermore, United States,
E. Kansa, Lawrence Livermore Natl Lab, Livermore, United States,
H. C. Buchanan, Lawrence Livermore Natl Lab, Livermore, United States,
R. E. Einziger, Lawrence Livermore Natl Lab, Livermore, United States,
L. E. Thomas, Lawrence Livermore Natl Lab, Livermore, United States,

Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1991

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. All of the nuclear waste will be enclosed in a container package. Most of the waste form will consist of fragmented UO₂ spent fuel pellets in Zircaloy-clad rods from nuclear reactors. If failure of both the waste containers and the cladding occurs, then the UO₂ fragments will be exposed to oxygen in the air and higher oxides of uranium may form. Some existing microscopic data from low temperature testing indicate that UO₂ oxidizes to U₄O₉ by a phase transformation front that propagates into the fragments. The oxidation state and its extend into the spent fuel fragments may affect the dissolution behavior of spent fuel if it is contacted by water. Thus, a model for this oxidation response of UO₂ spent fuel fragments is necessary to predict the behavior of the exposed waste form in order to assess the performance of any repository with respect to containment of radionuclides. A preliminary model of phase transformation oxidation response of spent fuel is developed that incorporates a statistical dependence on the size distribution of pellet fragments.

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