Chemical durability studies of waste-simulant doped borosilicate glasses

A mixed-alkali modified borosilicate base glass used in the vitrification of high-level nuclear waste (HLW) has been doped with a number of waste simulants to between 2 and 12 mol%. The simulants have been chosen to give two distinct series of glasses: one consisting of trivalent ions having the form M2O3 (where M is La, Bi, Al or Fe) and the other consisting of divalent simulants of the form MO (where M is Pb, Zn or Ba). An international standard Soxhlet leach test procedure was performed on each glass to study the effect of prolonged, moderate-temperature, dynamic water corrosion. Results of these studies show that, except for BaO, as the amount of simulant is increased, the amount of Na and Li leached decreases showing them to become more chemically resistant. These corrosion tests have been correlated to ionic (D.C.) conductivity measurements, which show a decrease in the conductivity of the glass as the amount of waste simulant is increased, and B-11 magic-angle spinning nuclear magnetic resonance (MAS-NMR) studies, which have shown that, as more waste-simulant is loaded into the glasses the rate of conversion of [BO4] to [BO3] units increases. All of the data from these studies reflect the different network forming abilities of the divalent and trivalent cations