Model Calculations and Assessment of the Importance of the Colloidal based Radionuclide Transport in a Waste Repository in Granite

Highly compacted bentonite buffers are planned to be used as engineered barriers in the near-field of nuclear waste repositories in crystalline formations. The erosion of these bentonite buffers at the boundary to the surrounding Excavation Disturbed Zone (EDZ) can be a source of colloids leading to a notable concentration of colloids in the EDZ water, which is high above the natural colloid concentration in granitic groundwater. The colloids are transported with the fracture water through the far-field of the repository. In this work the influence of the bentonite colloids on the radionuclide transport in the far-field and on the resulting dose is studied for the Finnish safety assessment TILA-99 [7]. This work was carried out as part of the Benipa project [1]. The release of radionuclides from the far-field is calculated without the presence of colloids in the reference case and is compared to the release rate with the presence of colloids at different concentrations. This study shows, that the colloids can have an impact on the release rate of some special radionuclides, however these nuclides have shown not to be dose-relevant in this calculations.