High-pressure glass-ceramics for iodine nuclear waste immobilization: Preliminary experimental results

Several matrix types have been considered for the immobilization of iodine radioisotopes from which glass-ceramics represent a serious candidate; however, I-bearing glass-ceramics are challenging owing to the iodine volatility. We have synthesised glass-ceramics from the partial crystallization of a parental glass enriched with different iodine sources (I2 and I2O5) under high-pressure conditions (up to 1.5 GPa). The samples were characterized using Scanning and Transmission Electron Microscopy and X-ray Diffraction. Using standard synthesis protocol: melting, nucleation and crystal growth, we have obtained glass-ceramics showing the coexistence between I-bearing glass (<0.8 mol.% I), nepheline (NaAlSiO4) and iodosodalite (Na8Al6Si6O24I2 with up to 14 mol.% I). For several samples, we observed also the presence NaPt3O4 witnessing a chemical reaction between the container walls and the inside experimental charge. The structure of iodosodalite is entirely resolved by Rietveld refinement of the XRD pattern for I2 experiments whereas it cannot be solved for I2O5 experiments suggesting a change in the iodosodalite structure probably due to the β cage filling by IO3− clusters instead of I−. Our present work could represent a potential solution to tackle the problem of iodine radioisotopes immobilization