The experience and know-how needed to carry out radiotracer experiments at the Grimsel Test Site (GTS) was initially gained in the Radionuclide Migration Programme (RMP).

This experiment was a 10 year project carried out in shear zone AU 96 in the GTS along with parallel experiments at JNC's former URL at Kamaishi, north east Japan. The overall aim of the project was to examine the retardation of radionuclides in this shear zone. The first phase of the project involved extensive characterisation of the chemical and physical properties of this shear zone (Geology / Hydrogeology / Hydrology / etc).

The data from the extensive characterisation was used to create models that would predict the behaviour of radionuclides in a repository host rock. These models were then tested by carefully adding safety-relevant radionuclides to the shear zone and observing their in situ retardation behaviour.

The two most important factors affecting radionuclide migration through the shear zone are diffusion and sorption.

Diffusion of radionuclides occurs when the radionuclides move from the main flow path into the pore spaces in the granodiorite around the flow path (the flow path being the open area of the shear zone - see above).

Effect of Diffusion on breakthrough curve

Sorption occurs when the radionuclides bind onto material with the shear zone.

Effect of Sorption on breakthrough curve