Laboratory and field tests for radionuclide migration and high flow paths in clay

Two investigations have been undertaken in this programme. Their objectives were to investigate mass transfer in clay-rich geological materials. The principal investigation was at Culham Laboratory, Oxfordshire, England where water flow within the Kimmeridge Clay was measured. The objective was to establish if silt-rich or carbonate-rich horizons within the Kimmeridge Clay act to provide fast transport paths for water flow through the succession. A subsidiary investigation was undertaken in the Underground Research Laboratory at SCK/CEN Mol, Belgium where an in-situ measurement of solute transport by diffusion was attempted. The in-situ migration experiment at the underground Research Laboratory at SCK/CEN Mol, Belgium was unsuccessful, due to problems with the engineering installation. A laboratory test of the equipment using a sample of Boom Clay yielded a value of Di of 5 x 10-11 m2s-1 and an alpha value of 0.2 using an 131I tracer. The work has therefore demonstrated the feasibility of the experiment on a laboratory scale and has identified the modifications needed to allow a successful installation of the engineered assembly. The field measurements at Culham Laboratory, Oxfordshire were completed with the flow testing of a very silty clay layer in the Kimmeridge Clay succession. Flow tests yielded a hydraulic conductivity for the very silty clay layer. Comparative tests in the clay showed its conductivity to be at least fifty times less. (author)