Alkali diffusion and radiation effects in the waste glass VG 98/12

Abstract

The German waste glass VG 98/12 was implanted with Rb and Cs, and Rutherford backscattering was used to measure diffusion of the alkalis in the temperature range between 350 and 665° C. Additional measurements were made with radioactive Rb and Na, using the conventional sectioning technique to evaluate diffusion profiles. Radiation enhanced Na-diffusion was observed during implantation. In contrast, radiation damage due to ion implantation retarded thermally activated diffusion: The implanted ions interacted with the damage configuration resulting from ion bombardment. Damage annealing and/or dissociation of Rb from the damage needed annealing temperatures of ∼ 500° C for Rb, and ∼ 600° C for the larger Cs-ions. These results were confirmed with gas release measurements using Kr and Xe. Even following annealing of the damage, Rb and Cs diffusion was much slower than that of Na. The resulting Arrhenius diagrams for Rb and Cs were curved. The implication of these results on the behavior of the glasses under repository conditions are discussed.