Dissolution mechanism of the SON68 reference nuclear waste glass: New data in dynamic system in silica saturation conditions

The alteration of SON68 glass (inactive R7T7 type nuclear waste glass) was studied to measure the long-term residual dissolution rate under different conditions. Experiments were conducted in Flow-through conditions (solution Flow rate 3-5 mL/day) at pH 8.0, 9.5, and 10.5 under various initial Si concentrations, a glass surface-to-volume ratio near 14,000 m(-1) and at a temperature of 90 degrees C. This set of long-term experiments (200 days) showed leaching rates dependent on the initial silica concentration and the initial pH. Interpretation of results at pH 8.0 was difficult due to the use of a synthetic water used to represent waters found at a potential French repository site. Because very small glass powder sizes were used (circle divide = 1 mu m), a complete dissolution of the pristine glass was achieved at low initial silica concentrations where higher leaching rates were produced. In all cases, initial high normalized leaching rates were observed followed by a decrease in leaching rate with rate levels ranging from 9 (+/- 4) to 5 (+/- 3) x 10(-4) g m(-2) d(-1) at 200 days under silica saturated conditions at pH 9.5 and 10.5, respectively. We have compared these results to previous results obtained in similar leaching conditions. Modeling using the GM2004 model program and model output values were shown to be in agreement with experimental results. (C) 2011 Elsevier B.V. All rights reserved.