The Monte Carlo simulations show the experimentally observed silica condensation, resulting in a protective effect of the alteration layer and an initial silica dissolution rate decreasing as a function of time. The simulations explain the temporary silica oversaturation sometimes observed in experiments. They show that the silica solubility in solution is not that of the highest energy state (the glass). Instead, it is close to, that of the lowest energy state (the gel). This is consistent with the fact that most silica bearing sites at the surface with the solution are in that lowest energy state. The silica solubility depends on the amount of silica particles in contact with the solution (the surface), implying that replacing part of the silica by another poorly soluble glass network former lowers the silica solubility. Defects in the structure tend to cause higher Si concentrations in solution.
The sodium leaching at silica saturation mainly looks caused by the temporarily opening and closing of pathways out of the glass. Due to the random character of this process, the reproduction of such rates in severals runs of the code is very poor, which is similar to experimentally observed behaviour.
|Number of pages
|Published - Nov 2009
|Studiecentrum voor Kernenergie