Radiation effects on the structure and alteration behavior of a SiO$_2$ ‐Al$_2$ O$_3$ ‐B$_2$ O$_3$ ‐Na$_2$ O glass
Résumé
As borosilicate glasses are used in many countries to immobilize fission products and minor actinides after spent fuel reprocessing before storage in a deep geological repository, assessing their chemical durability is of paramount importance. Here pristine and pre-irradiated (952MeV, 136Xe) SiO2-B2O3-Al2O3-Na2O glasses with the same molar ratios as in the French SON68 and ISG glasses have been subjected to aqueous corrosion in deionized water and in silica saturated solution to measure the initial and longer-term alteration rates. Pristine and pre-irradiated glasses corrode following the same mechanisms but the pre-irradiation has a strong impact on the initial dissolution rate (increase by a factor of 5.6), and on the alteration layer depth in silica saturated conditions (by 2–3 folds). The later result is related to the formation of a more porous, less passivating gel on the pre-irradiated glass specimen. Using both experimental spectroscopies (NMR, IR, SFG) and classical molecular dynamics, the radiation effects on the glass structure and water diffusion have been assessed. After pre-irradiation, the density and the polymerization degree of the glass decrease while the topological disorder increases. In consequence, water diffusion accelerates. These observations allow to correlate the radiation impact on the alteration behavior to the structural changes.