Colloid Retention in Aespoe Crystalline Rock: A Generic Computational Assessment

摘要

1. Colloids are subject to comparatively weak retention, relative to tracers; nevertheless the retention is a mechanism that may be important, in particular for shorter lived radionuclides. 2. This analysis is based on the combination of "first principles" with data from Knapp et al. for tuff. No site-specific experimental data on colloidal transport at Aespoe are available. The in situ retention of colloids may be larger than assumed here. 3. One potentially important neglected mechanism is irreversible removal of colloids. The "sorption" (attachment/detachment) coefficient for crystalline rocks could be significantly larger than for tuff (assumed here). Site-specific data are required for a more accurate assessment of colloidal transport. For a full assessment of potential impact of colloid-facilitated RN transport, we need field parameters. But even more importantly, we need to characterise the source term, i.e., how colloids can be generated from bentonite and to which colloid concentrations this could lead in a field situation. Research is going in this field.