Control of R7T7 Nuclear Glass Alteration Kinetics Under Saturation Conditions

Abstract

AbstractThe hypothesis of French nuclear waste glass disposal in a geological repository implies a comprehensive assessment of all the glass elements liable to participate in controlling the material alteration kinetics. The hypothetical existence of kinetically limiting elements other than silica could account for the observed R7T7 glass behavior in the presence of certain clays, and notably the continued high alteration rates observed even after silica saturation occurs. Flowing experiments with solutions near silica saturation but highly subsaturated with respect to aluminum hydroxide were defined to investigate the possible limiting role of aluminum. Experiments were conducted at different flow rates with the same constant steady-state H4 SiO4 activity for all the tests. The glass dissolution rate was observed to depend on the solution flow rate, indicating that under these conditions the kinetics are not controlled by dissolved silica alone. An additional experiment, in which only the Al(OH)4− activity in solution was allowed to vary, demonstrated the critical role of this element. Several interpretations are discussed.