Effect of Na2O on aqueous dissolution of nuclear waste glasses

Sodium oxide is present in the majority of commercial and waste glasses as a viscosity-reducing component. In some nuclear waste glasses, its source is the waste itself. As such, it can limit the waste loading because of its deleterious effect on the resistance of the glass to attack by aqueous media. The maximum tolerable content of Na2O in glass depends on the presence and concentration of components that interact with it. To assess the acceptability limits of Na2O in the composition region of nuclear waste glasses, we formulated 11 baseline compositions by varying the content of oxides of Si, B, Al, Ca, Zr, and Li. In each of these compositions, we varied the Na2O fraction from 8-16 mass% to 23-30 mass%. To each of 146 glasses thus formulated, we applied the seven-day Product Consistency Test (PCT) to determine normalized B and Na releases (ri, where i ≡ B or Na). Fitting approximation functions ln(ri/gm−2) = Σbijgj to ri data (gj is the j-th component mass fraction and bij the corresponding component coefficient), we showed that the rB (and, consequently, the initial glass alteration rate) was proportional to the glass component mass fractions in the order Al2O3