[en] In order to assess the security of a long-term disposal of nuclear spent fuel, the prediction of radionuclide migration is needed. This paper presents the interaction between uranium(VI) and siderite surfaces, an iron carbonate present both in the near- and far-field of the storage, in carbonate solutions. The amount of uranium on the surface was determined after the interaction by alpha spectrometry. It appeared that the amount of uranium(VI) dropped with high pH and carbonate concentration, likely because of the predominance of UO₂(CO₃)₂^2- and UO₂(CO₃)₃^4- complexes in solution. The U4f X-ray photoelectron spectrum clearly highlighted that uranium present on the film has two different oxidation states and thus that uranium(VI) has been partially reduced by siderite. (orig.)