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Modelling Oxidative Dissolution of Spent Fuel

Published online by Cambridge University Press:  03 September 2012

Ivars Neretnieks
Ivars Neretnieks*
Affiliation:
Department of Chemical Engineering and Technology, Royal Institute of TechnologyS-100 44 Stockholm, SWEDEN
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Abstract

Spent nuclear fuel will, by the radiation, split nearby water into oxidizing and reducing compounds. The reducing compounds are mostly hydrogen that will diffuse away. The remaining oxidizing compounds can oxidize the uranium oxide of the fuel and make it more soluble. The oxidised uranium will dissolve and diffuse away. The nuclides previously incorporated in the spent fuel matrix can then be released and also migrate away from the fuel.

A model is proposed where the produced oxidizing species compete for reaction with the fuel and for escaping out of the system. The chemical reaction rate of oxygen and fuel is taken from literature values based on experiments. The escape rate of oxidants to a receding redox front in the backfill is modelled assuming a redox reaction of oxidizing component and reducing component in the surrounding. The rate of movement of the redox front is determined from the rate of production of oxidants. This is estimated using a previously devised model that has been calibrated to in situ observed radiolysis.

Three cases are modelled. In the first case it is assumed that the reducing compound is insoluble and that the reaction between oxygen and reducing mineral is very fast. In the second case it is assumed that the reducing component has a known solubility and that it can migrate to meet the oxygen and quickly react. In a third case a finite reaction rate is modelled between the oxygen and the reducing species.

The sample calculations show that if the reducing mineral has to be supplied from the backfill a large fraction of the spent fuel could be oxidised. If the corrosion products of a degraded steel canister can supply the reducing species and the redox reaction is fast, very small amounts of the fuel could be oxidised. Literature data indicate that the redox reaction rate may not be so fast that it can be considered instantaneous and then a considerable fraction of the fuel could be oxidised. The model gives a means of exploring which mechanisms and data may be of most importance for radiolytic fuel dissolution, but the realism of the data and the model must be tested further. There is a lack of understanding and data on reaction rates, heterogeneous as well as homogeneous. This is crucial to the results.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 465: Symposium II – Scienfific Basis for Nuclear Waste Management XX , 1996 , 573
Copyright
Copyright © Materials Research Society 1997

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References

REFERENCES

1. Cross, J.E., Haworth, A., Neretnieks, I., Sharland, S.M., Tweed, C.J. Modelling of Redox Front and Uranium Movement in a Uranium Mine at Poços de Caldas. Radiochimica Acta 52/53 p 445–451, 1991 Google Scholar
2. Romero, L. The near-field transport in a repository for high-level nuclear waste. Ph. D. Thesis, Dept. Chemical Engineering and Technology, Royal Institute of Technology, Stockholm, Sweden, 1995. TRITA-KET R21, ISSN 1104–3466 Google Scholar
3. Neretnieks, I. Modelling oxidative dissolution of spent fuel. NAGRA internal report 1996.10.1557/PROC-465-573Google Scholar
4. Jinsong, Liu. Development and test of models in the natural analogue studies of the Cigar Lake uranium deposit. Ph.D. Thesis, Dept. Chemical Engineering and Technology, Royal Institute of Technology, Stockholm, Sweden, 1995. TRITA-KET R24, ISSN 1104–3466 Google Scholar
5. Johnson, L.H., Shoesmith, D.W., Tit, J.C. Release of radionuclides from spent LWR U02 and mixed-oxide (MOX) fuel. Nagra Interner Bericht 94–40, AECL research, Whiteshell Laboratories, April 1994.Google Scholar
6. Bruno, J., Cera, E., Duro, L., Eriksen, T.E., Werme, L.O. A kinetic model for the stability of spent fuel under oxic conditions, J. Nucl. Mater., In press 1996 Google Scholar
7. Choppin, G., Rydberg, J., Liljenzin, J.O. Radiochemistry and Nuclear chemistry, 2nd Ed. Butterworth-Heinemann 1995 Google Scholar
8. Gray, W.J., Leider., H.R., Steward, S.A. Parametric study of LWR spent fuel dissolution kinetics, J. Nucl. Mater. 190, p 46–52, 1992 10.1016/0022-3115(92)90074-UGoogle Scholar
9. Grambow, B. Spent fuel dissolution and oxidation. An evaluation of literature data. SKB Technical Report 89–13, 1989 Google Scholar
10. Stumm, W., Morgan, J.J. Aquatic Chemistry, Wiley & Sons, 1981 Google Scholar
11. Morel, M. M., Hering, J. J Principles and applications of aquatic chemistry, Wiley, 1993 Google Scholar