Nanoparticles/ colloids are ubiquitous in groundwater systems and can enhance contaminant migration if these nanoparticles are mobile. Bentonite colloids might be generated from the geotechnical barrier (bentonite backfill/buffer) of a multi- barrier system of a nuclear waste repository especially in contact with low ionic strength groundwater as expected in glacial periods. Laboratory studies and field experiments performed in a water-conducting shear zone at the Grimsel Test Site (GTS, Switzerland) indicate that the sorption/ desorption processes of actinides on mobile and immobile colloids are kinetically controlled and that colloid filtration occurs. Furthermore, by the use of accelerator mass spectrometry (AMS) very slow long-term desorption kinetics are accessible. The obtained data were feed in a 1D double- porosity (single fracture integrated into porous rock) advective contaminant transport model named COFRAME. The presentation will show latest results of laboratory and field experiments in comparison with model fitting results and compare the obtained kinetic parameters. These results are compared to fall-out plutonium/ uranium mobility on the formation scale. Finally, model calculations will be presented to evaluate the effect of kinetics for a reference case in a deep geological repository in crystalline host rock.

Influence of kinetics on nanoparticle migration in fractured rocks: Experiences from URL work

251st National Meeting (2016)

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