This report presents the results of the dynamic leaching tests realised with four different inactive nuclear glasses (SON68, SM513, SM539 and ISG). Dynamic tests provide forward and initial rates of glass dissolution, which are the maximum glass dissolution rates for a certain medium and temperature. Because ONDRAF/NIRAS considers the use of a high pH concrete in the near field of the HLW repository, measurements at different alkaline pH values (between pH 9 and pH 14) were conducted. The tests were done in KOH solution to determine the ‘forward dissolution rate’ and in young cement water (YCWCa) to determine the ‘initial dissolution rate’.
For each glass, the forward rate of dissolution, obtained in KOH solutions, increased as a function of the pH. This increase was faster for SM539 glass than for SON68, SM513 and ISG. This is maybe due to a higher Al/Si ratio for SM539. For SON68, the glass dissolution rates determined in this report are in good agreement with the ones previously reported. However, for SM513 and SM539, more experiments would be necessary to decrease the uncertainty on the results.
The initial rates of dissolution measured in YCWCa were always lower than the forward rates of dissolution in KOH solution at equivalent pH (pH = 13.5). This is caused by the presence of calcium in the cement water, leading to the formation of a (slightly) protective layer at the surface of the glasses. However, the values obtained for SON68 and SM513 in this study are two to four times lower than the ones reported previously. This leads also to the necessity of new experiments to decrease uncertainties.
ICP-AES analysis of the leaching solutions was also realised to check if the glass constituents such as Si, B, Al, Li, Mo,… are released congruently. For all studied glasses, the glass constituents seem to be released rather congruently in comparison with the Si concentration, except for SM513 and ISG in KOH solution at pH 9 where the Si release rate was slower than the Ca and Mo (for SM513) and B (for ISG) release rate.
|Number of pages
|Published - 15 Oct 2020
|Belgian Nuclear Research Center