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Oxidative Corrosion of Spent uo2 Fuel in Vapor and Dripping Groundwater at 90°C

Published online by Cambridge University Press:  10 February 2011

Robert J. Finch ,
Edgar C. Buck ,
Patricia A. Finn  and
John K. Bates
Robert J. Finch
Affiliation:
Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
Edgar C. Buck
Affiliation:
Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
Patricia A. Finn
Affiliation:
Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
John K. Bates
Affiliation:
Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
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Abstract

Oxidative dissolution of spent UO2 fuel in vapor and dripping groundwater at 90°C occurs via general corrosion at fragment surfaces. Dissolution along fuel-grain boundaries is also evident in samples contacted by the largest volumes of groundwater, and corroded grain boundaries extend at least 20 or 30 grains deep (> 200 μm), possibly throughout mm-sized fragments. Apparent dissolution of fuel along defects that intersect grain boundaries has produced 50 to 200 nm-diameter dissolution pits that penetrate 1–2 μm into each grain, giving rise to a “worm-like” texture along fuel-grain boundaries. Sub-micrometer-sized fuel shards are common between fuel grains and may contribute to the reactive surface area of fuel exposed to groundwater. Outer surfaces of reacted fuel fragments develop a fmne-grained layer of corrosion products adjacent to the fuel (5–15 μm thick). A more coarsely crystalline layer of corrosion products commonly covers the fine-grained layer, the thickness of which varies considerably among samples (from less than 5 μm to greater than 40 μm). The thickest and most porous corrosion layers develop on fuel fragments exposed to the largest volumes of groundwater. Corrosion-layer compositions depend strongly on water flux, with uranyl oxy-hydroxides predominating in vapor experiments, and alkali and alkaline earth uranyl silicates predominating in high drip-rate experiments. Low drip-rate experiments exhibit a complex assemblage of corrosion products, including phases identified in vapor and high drip-rate experiments.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 556: Symposium QQ – Scientific Basis for Nuclear Waste Management XXII , 1999 , 431
Copyright
Copyright © Materials Research Society 1999

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References

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