Long term corrosion behaviour of the WAK-HLW glass in salt solutions

The corrosion behaviour of the HLW glass GP WAK1 containing simulated HLW oxides from the WAK reprocessing plant in Karlsruhe is investigated in long-term corrosion experiments at high S/V ratios in two reference brines at 110 and 190°C. In case of the MgCl2-rich solution the leachate becomes increasingly acid with reaction time up to a final pH of about 3.5 at 190°C. In the NaCl-rich solution the pH rises to about 8.5 after one year of reaction. The release of soluble elements in MgCl2 solution, under Si-saturated conditions, is proportional to the surface area of the sample and the release increases at 190°C according to a t1/2 rate law. This time dependence may be an indication of diffusion controlled matrix dissolution. However, at 110°C the release of the mobile elements cannot be described by a t1/2 rate law as the time exponents are much lower than 0.5. This difference in corrosion behaviour may be explained by the higher pH of about 5 at 110°C. In case of NaCl solution under alkaline conditions, the release of soluble elements is not proportional to the surface area of the sample and it increases with time exponents much lower than 0.5. After one year of reaction at 190°C a sharp increase of the release values of some elements was observed. This increase might be explained by the high pH of the solution attained after one year. The corrosion mechanism in NaCl solution, as well as in MgCl2 solution at 110°C, has not yet been explained. By corrosion experiments in water at constant pH values between 2 and 10, it could be shown that the time exponents of the release of Li and B decrease with increasing pH of the solution. This result can explain qualitatively the differences found in the corrosion behaviour of the glass under the various conditions.