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Determination of Criteria for Selecting A UO2 Fuel Dissolution Model for Nuclear Fuel Waste Management Concept Assessment

Published online by Cambridge University Press:  25 February 2011

S. Sunder ,
D.W. Shoesmith ,
N.H. Miller  and
G.J. Wallace
S. Sunder
Affiliation:
AECL Research, Whiteshell Laboratories, Pinava, Manitoba, Canada. ROE ILO
D.W. Shoesmith
Affiliation:
AECL Research, Whiteshell Laboratories, Pinava, Manitoba, Canada. ROE ILO
N.H. Miller
Affiliation:
AECL Research, Whiteshell Laboratories, Pinava, Manitoba, Canada. ROE ILO
G.J. Wallace
Affiliation:
AECL Research, Whiteshell Laboratories, Pinava, Manitoba, Canada. ROE ILO
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Abstract

Assessing the concept of direct disposal of used nuclear fuel in a geological vault requires a model to predict the dissolution rate of UO2 in groundwater. A solubility-limited model can be used to calculate the dissolution rate of UO2 fuel under non-oxidizing conditions. When the oxidative dissolution of UO2 is an irreversible process, a kinetic model is more suitable to describe the dissolution of UO2 under oxidizing conditions. Experimental studies were carried out using electrochemical techniques and X-ray photoelectron spectroscopy, XPS, to determine criteria for selecting the appropriate model for estimating used-fuel dissolution rates as a function of the redox conditions in the vault at the time of container failure. UO2 electrodes were subjected to prolonged (>1000 min) potentiostatic oxidation, and the rate of oxidation and dissolution of UO2 fuel was investigated as a function of the applied potential. UO2 oxidation was also carried out by the products of water radiolysis and studied as a function of dose rate, total dose and solution chemistry.

These studies show that significant oxidative dissolution of UO2 appears possible for potentials more positive than -100 mV vs SCE in solutions with a pH close to that of the deep groundwaters, i.e., from 6 to 10. A kinetic model, which takes into account the mechanism of UO2 oxidation, is more appropriate to estimate dissolution rates of UO2 fuel for redox conditions more oxidizing than -100 mV vs SCE.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 257: Symposium – Scientific Basis for Nuclear Waste Management XV , 1991 , 345
Copyright
Copyright © Materials Research Society 1992

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References

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