Hydrogen suppresses UO2 corrosion
Artikel i vetenskaplig tidskrift, 2009

Release of long-lived radionuclides such as plutonium and caesium from spent nuclear fuel in deep geological repositories will depend mainly on the dissolution rate of the UO2 fuel matrix. This dissolution rate will, in turn, depend on the redox conditions at the fuel surface. Under oxidative conditions UO2 will be oxidised to the 1000 times more soluble UO2.67. This may occur in a repository as the reducing deep groundwater becomes locally oxidative at the fuel surface under the effect of alpha-radiolysis, the process by which alpha-particles emitted from the fuel split water molecules. On the other hand, the groundwater corrodes canister iron generating large amounts of hydrogen. The role of molecular hydrogen as reductant in a deep bedrock repository is questioned. Here we show evidence of a surface-catalysed reaction, taking place in the H-2-UO2-H2O system where molecular hydrogen is able to reduce oxidants originating from alpha-radiolysis. In our experiment the UO2 surface remained stoichiometric proving that the expected oxidation of UO2.00 to UO2.67 due to radiolytic oxidants was absent. As a consequence, the dissolution of UO2 stopped when equilibrium was reached between the solid phase and U4+ species in the aqueous phase. The steady-state concentration of uranium in solution was determined to be 9 x 10(-12) M, about 30 times lower than previously reported for reducing conditions. Our findings show that fuel dissolution is suppressed by H-2. Consequently, radiotoxic nuclides in spent nuclear fuel will remain immobilised in the UO2 matrix. A mechanism for the surface-catalysed reaction between molecular hydrogen and radiolytic oxidants is proposed. (C) 2009 Elsevier Ltd. All rights reserved.

uranium-dioxide

spent fuel

solubility

behavior

nuclear-waste

uraninite

water

waste-disposal conditions

Författare

P. Carbol

European Commission Joint Research Centre, Institute for Transuranium Elements Karlsruhe

Patrik Fors

European Commission Joint Research Centre, Institute for Transuranium Elements Karlsruhe

T. Gouder

European Commission Joint Research Centre, Institute for Transuranium Elements Karlsruhe

Kastriot Spahiu

Chalmers, Kemi- och bioteknik, Kärnkemi

Geochimica et Cosmochimica Acta

0016-7037 (ISSN) 0046-564X (eISSN)

Vol. 73 15 4366-4375

DOI

10.1016/j.gca.2009.04.041

Mer information

Skapat

2017-10-07