The dismantling of UNGG (Uranium Natural Graphite Gas) nuclear reactors generates cladding wastes mainly made of Mg alloys. The storage strategy could be to encapsulate these long-lived wastes into a mineral binder, for example geopolymer matrix. Thus, the durability of the geopolymer/Mg with respect to the storage requirements has to be studied. Indeed, the aqueous reactivity of the magnesium wastes in repository and disposal implies that the metal can corrode resulting in a H2 gas release that is detrimental to the safe storage of conditioned waste packages.
In order to understand the corrosion mechanisms related to each constituent of the geopolymer, the influence of different additives on Mg corrosion performance should be studied. In this work, we studied corrosion products growth kinetics on MgZr (0.5%) alloy in aqueous environment, which mimics poral solution of geopolymer containing F-, SiO32- as major additives.
We proposed a multiscale analytical approach which includes in-situ Raman spectroscopy and ex-situ Auger Electron Spectroscopy (AES). Elemental depth profiling provided by AES was shown to be a suitable method to estimate corrosion products thickness as well as growth kinetics at the very beginning of corrosion (order of several days, thickness less then ~100 nm). In-situ Raman spectroscopy was used for corrosion products identification and kinetics measurement for further corrosion process (order of several months) when the layer thickness exceeds ~100 nm.
MgO/Mg(OH)2 bilayered structure with the thickness about 100 nm was detected on MgZr samples immersed in simplified solution (NaOH, pH 12.5) during 3 days. Addition of SiO32- and F- limited formation of Mg(OH)2 whereas layer of Mg-silicates and fluoro-silicates was formed generally. Growth kinetics slows down in presence of SiO32- and F- (20 nm vs 100 nm for 3 days for simplified high alkaline solution).
This work is performed within the Investments for the future program of the French Government and operated by the French National Radioactive Waste Management Agency (Andra).
Souhaitez-vous présenter une affiche ?Mg, corrosion, poral solution of geopolymer, Auger electron spectroscopy, Raman spectroscopy