Due to sorption and matrix diffusion radionuclides usually migrate much lower speed than the velocity of the flowing water. Influence of the rock matrix on the retention can be characterised by porosity of the rock matrix and solute diffusivity in the rock matrix. In the performance assessment conditions most of the retention takes place in the vicinity of the deposition holes. In-situ diffusion experiments are able to provide data on the rock matrix retention properties that is relevant for the repository near field conditions.

The present research plan aims to complete other measurements by an extensive series of in-situ measurements. The objective of the experiments is to investigate rock matrix retention properties under in-situ conditions and to demonstrate that assumptions applied in the safety case are in line with the site evidence.

Three different experiment types are applied to investigate rock matrix retention properties: tracer experiments in water phase, diffusive gas transport in rock matrix and electrical method for logging of the rock matrix pore structure. Experiments will be executed along an artificial flow channel along a drill hole sections.

Diffusion is a slow process and the whole experimental program will take years. First results are expected from the electrical logging of the rock matrix pore structure. It can be performed in deep surface drill holes and the measurement can be performed quickly compared to the diffusion experiments. Electrical logging of the rock matrix properties using a focused resistivity tool have also been successfully applied in Sweden in the similar kind of granitic rock as there is in the Olkiluoto,
Gällande start-/slutdatum01/03/2011 → …


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