Determination of the corrosion mechanisms of high level waste containing glass

In the present report, the inactive HLW glass SM 58 LW 11, doped with simulated 'radioactive' waste, was investigated under the following corrosion conditions: temperatures up to 2000C; pressure of 130 bar; corrosion in Q-solution, a highly concentrated salt brine. The aim of the investigations was to identify the rate controlling step of the corrosion process and to determine the correct type of time dependence of the whole process for long times. In particular, the effects of layers formed on the corroding glass and of reaction products accumulated in the leachant, had to be examined for this purpose. The basic mechanism is a network dissolution process proceeding proportional to the corrosion time. The initial period is followed by an intermediate one during which the process proceeds slower than linearly with time. The duration of this period depends on the amount of leachant per glass surface area. Finally, a linear time law is observed again, proceeding at a rate smaller than the initial one. By no means, a permanent stop of the whole process must be expected. The intermediate deviations from a linear time law are due to the accumulation of reaction products in the leachant. Any layers formed during the corrosion process are unprotective against the further corrosion attack. (orig.) With 11 refs., 16 tabs., 8 figs