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The Influence of Near Field Redox Conditions on Spent Fuel Leaching

Published online by Cambridge University Press:  21 March 2011

Kastriot Spahiu ,
Ulla-Britt Eklund ,
Daqing Cui  and
Max Lundström
Kastriot Spahiu
Affiliation:
SKB, P.O. Box 5864, SE-102 40 Stockholm, Sweden, skbks@skb.se
Ulla-Britt Eklund
Affiliation:
Hot Cell Laboratories, Studsvik Nuclear AB, SE-611 82 Nyköping, Sweden
Daqing Cui
Affiliation:
Hot Cell Laboratories, Studsvik Nuclear AB, SE-611 82 Nyköping, Sweden
Max Lundström
Affiliation:
Hot Cell Laboratories, Studsvik Nuclear AB, SE-611 82 Nyköping, Sweden
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Abstract

In a repository, the spent fuel could come in contact with groundwater if the canister or container has breached. The system may be quite complex with oxygen-free water, uranium dioxide, a corroding metal, such as iron, and a radiation field present at the same time. In an anaerobic environment iron and mild steel will corrode and hydrogen will be evolved. The equilibrium hydrogen pressure for this reaction is very high. At some time after water intrusion, there will be large amounts of dissolved hydrogen in the near field, corresponding to a partial pressure at least equivalent to the hydrostatic pressure at the repository depth. For this reason, we investigated the leaching behavior of 0.25-0.5 mm sized fragments of PWR spent fuel (43 MWd / Kg U) in simulated groundwater solution (10 mM NaCl and 2 mM HCO3-) under 5 MPa hydrogen and argon pressure. In a leaching experiment under 5 MPa hydrogen at 25 °C, the total U concentration was found to be <10−8 M. After refilling of the autoclave with new solution at 70°C, the total U concentration first increased to 10−6.3M, and then quickly decreased to 10−8 M. The leaching behavior of uranium and other fuel components indicates that under pressurized hydrogen, the spent fuel dissolution is substantially hindered. Leaching results obtained after the substitution of hydrogen by argon at the same pressure and temperature are also presented. Finally, some results on spent fuel leaching under pressurized argon are presented and comparatively discussed.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 713: Symposium JJ – Scientific Basis for Nuclear Waste Management XXV , 2002 , JJ14.5
Copyright
Copyright © Materials Research Society 2002

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References

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