For the in-situ CFM experiment, a potential source of radionuclides and colloides (with radionuclides pre-spiked bentonite rings) will be emplaced in an advective flow system in the host rock.
The formation and transport of colloids and colloid-associated radionuclides is monitored under repository relevant flow conditions and over relevant distances.
The stability of the bentonite-derived colloids and possible reversibility of radionuclide uptake onto these colloids is investigated in time scales which minimise kinetic effects.
CFM in-situ experiment – situation at the AU tunnel
The overall concept has been defined, its implementation in terms of the in-situ set-up for the CFM experiment has not yet been finalised in detail. The principle elements are:
- Sealing the shear zone at the tunnel surface with a megapacker to create a no(or low) flow boundary and to reduce the gradient in the groundwater heads from the rock towards the tunnel
- Generating a monopole flow field via a short, small-diameter borehole reaching into the shear zone near the tunnel surface
- Placing a colloid source (bentonite) into the water conducting shear zone (beyond the radius of influence of the GTS tunnel system) via a bentonite emplacement borehole
An essential requirement for the success of the experiment is the perfect seal of the tunnel surface where it is intersected by the shear zone. This requirement has been fulfilled with the megapacker.
The video above shows the concept of the transport of colloids through the shear zone.
Colloid Formation and Migration Experiment
