Glass leaching tests were performed at 30°C in cementitious water at pH 13.5 with or without cement. These experiments have allowed to propose a pessimistic range of dissolution rates of 0.025-0.082 g.m-2.d-1 for the SON68 glass and 0.2-0.3 g.m-2.d-1 for the SM539 glass. These rates can be used as preliminary values in performance assessment calculations. Tthe presence of cement maintains the dissolution rate at the high initial rate,because it acts as a sink for Si and Al. The mechanism responsible for the fixation of Si and Al on the cement seems to depend on the glass composition. For SM539, there is ample evidence for secondary phase formation. For SON68, there is no such evidence, and the fixation mechanisms is not clear . Because the pH, and Si, Ca and Al concentrations were stable in the tests with cement, the dissolution rate may remain constant for a long time. So there is no clear evidence for the existence of a lower long term rate, although this can be expected at sufficient reaction progress. The proposed dissolution rates are considerably higher than the long term rate observed in neutral pH conditions, which are expected to be lower than 10-4 g.m-2.d-1.
|Conference||Cementitious Materials in Safety Cases for Geological Repositories for Radioactive Waste: Role, Evolution and Interactions|
|Period||2009-11-17 → 2009-11-20|