INFLUENCE OF THE ALTERATION LAYER MORPHOLOGY ON THE SILICATE GLASS CORROSION MECHANISMS: ROLE OF CA AND ZR

This study investigates the long term behavior of glasses used for confinement of nuclear wastes. The results have been obtained from a fruitful collaboration between different CEA laboratories (LLB, LIONS, CEA Marcoule) and the Ecole Polytechnique. The corrosion process of the glasses by water creates at the glass surfaces, an alteration porous layer, hydrated and amorphous, called “gel”. This gel, which is the result of the release of soluble elements, of hydrolyses and of silica network recondensation can in specific conditions strongly limit the exchange process between the glass and the solution. Our hypothesis to describe this phenomenon is the closure of the gel porosity. Fig. 1: Scattered intensity (SANS) for different isotopic mixtures for the sample without Zircon (0Zr) after 8 hours of alteration (a), after two months; Fig. 1: Scattered intensity (SANS) for different isotopic mixtures for the sample without Zircon (0Zr) after 8 hours of alteration for the sample containing 4 % of Zircon (4Zr) after leaching 2 months; Fig. 1: Scattered intensity (SANS) for different isotopic mixtures for the sample without Zircon (0Zr) after 8 hours of alteration (a), after two months (b), for the sample containing 4 % of Zircon (4Zr) after leaching 2 months (c). The residual signal observed on figure (b) for the « matching » composition (70%D2O) illustrates the existence of the closed porosity