Geopolymers are currently studied at CEA as new binders for the conditioning of Mg alloys cladding wastes, generated from the reprocessing of UNGG spent fuels (Uranium Natural Graphite Gas). This alumino-silicate matrix is activated with NaOH solution in the presence of sodium fluoride (Na-Geopolymer/NaF). Galvanic corrosion of Mg wastes may occur in the geopolymer matrix due to the contact with residual graphite materials or steel from the container. The aim of this work was to study the general corrosion of Mg alloys, and their galvanic corrosion when coupled to Steel S235JR. Corrosion rates of Mg-0.5%Zr on synthetic Na-geopolymer/NaF pore solution were obtained from impedance diagrams. The obtained values indicate a decrease of the instantaneous corrosion rates with time. Corrosion rates calculated for the galvanic coupling Mg-0.5%Zr with Steel S235JR were obtained by ZRA measurements. Higher corrosion rates are observed when Mg-0.5%Zr is coupled to Steel S235JR. XPS analysis showed Mg(OH)2, MgF2, Na- ions and silicates to be the main constituents of the surface. It was showed that the thickness and composition of the surface layer evolve with time. After 3 days the surface composition obtained for the sample under general corrosion test was similar to that obtained after galvanic corrosion. Nevertheless, after 28 days there is a decrease on the silicates composition and in the amount MgF2, which completely disappears for the general corrosion.