LONG-TERM CORROSION BEHAVIOR 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 investigate d in long-term corrosion experiments at high S/V ratios in two referen ce brines at 110 and 190 degrees C. In case of the MgCl2-rich solution the leachate becomes increasingly acid with reaction time up to a fin al pH of about 3.5 at 190 degrees 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 proporti onal to the surface area of the sample and the release increases at 19 0 degrees C according to a t(1/2) rate law. This time dependence may b e an indication of diffusion controlled matrix dissolution. However, a t 110 degrees C the release of the mobile elements cannot be described by a t(1/2) rate law as the time exponents are much lower than 0.5. T his difference in corrosion behaviour may be explained by the higher p H of about 5 at 110 degrees C. In case of NaCl solution under alkaline conditions, the release of soluble elements is not proportional to th e surface area of the sample and it increases with time exponents much lower than 0.5. After one year of reaction at 190 degrees C a sharp i ncrease of the release values of some elements was observed. This incr ease might be explained by the high pH of the solution attained after one year. The corrosion mechanism in NaCl solution, as well as in MgCl 2 solution at 110 degrees 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 w ith increasing pH of the solution. This result can explain qualitative ly the differences found in the corrosion behaviour of the glass under the various conditions. (C) 1998 Elsevier Science Ltd. All rights res erved.