Effects of Water Composition on the Dissolution Rate of UO₂ Under Oxidizing Conditions

by C. N. Wilson, Pacific Northwest Lab, United States,
W. J. Gray, Pacific Northwest Lab, United States,



Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1990

Abstract:

Dissolution rates were measured on crushed unirradiated UO₂ fuel pellet samples under oxidizing conditions using a flow-through testing method. Water compositions included Nevada Test Site J-13 well water, deionized distilled water (DIW), and variations on the J-13 water composition selected to measure the effects of various J-13 water components on UO₂ dissolution rates. Lower apparent UO₂ dissolution rates were measured in waters containing Si and Ca than in DIW or in dilute NaHCO₃ solution. A thin (approx. 5 nm) U-Si-O surface alteration layer was identified by Auger microprobe examination of UO₂ particles tested at 25?C in Ca-Si containing waters, and a thin layer containing Ca + Si was identified on the surface of particles tested at 85?C. Limited data suggest that the alteration layers act as kinetic barriers to UO₂ dissolution rather than as solubility limiting phases. These experiments and their preliminary results are discussed as they apply to the potential disposal of spent nuclear fuel at the candidate Yucca Mountain repository site.

Subject Headings: Fuels | Uranium | Radioactive wastes | Chemical properties | Site investigation | Nuclear power | Chemical wastes | Nevada | United States

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