Colloid Formation and Migration (CFM) Concept

A potential source of heterogeneous radiocolloids is 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 over relevant distances.

The stability of the bentonite-derived colloids and possible reversibility of radionuclide uptake onto these colloids can be investigated in time scales which minimise kinetic effects. The basic concept behind this experiment is shown below:

• A bentonite emplacement borehole (shown below in grey) supplies the access for the colloid source (shown below in blue) to a water conducting feature in the host rock, outside the influence of the GTS tunnel system
  
• Sealing of the shear zone at the tunnel surface with a tunnel mega-packer (the yellow submarine) to create a no flow boundary and to reduce the gradient in the groundwater heads from the rock towards the tunnel(shown below in brown)
  
• Seal the upper and lower boundaries of the flow field with two resin impregnated boreholes in order to cut off the natural groundwater flow (shown below in green)
  
• Drilling of a small diameter borehole close to the tunnel surface in order to apply a monopole flow field (shown below in red)
  

Conceptual layout