The broad objectives of the LTD project are to provide quantitative information on matrix diffusion in fractured rock under in situ conditions.

The specific aims of LTD are:

  • Clearly defining the degree of realism of the matrix diffusion and flow-wetted surface parameters employed in current PA calculations
  • Demonstration of in situ radionuclide retardation in the rock matrix, especially for the suite of weakly- and non-sorbing elements (so minimising the over-conservatism in current PA calculations)
  • In situ verification of long-term and large-scale diffusion concepts for radionuclides transported from a water-conducting system into a rock matrix under well-defined boundary conditions
  • Verification of the conceptualisation in existing transport codes (via predictive and post mortem testing) of the transport of radionuclides across the flow-wetted surface and subsequent diffusion in the rock matrix
  • Comparison of field and laboratory data
  • The full characterisation of spatial distribution of porosity in the matrix, and its link with the mineralogy, in order to better identify microstructure-derived residence time distributions in the matrix
  • The identification of flow-wetted surfaces in order to better define the spatial distribution of mass transfer coefficients controlling transport from fracture to matrix


Long Term Diffusion project (LTD) Experiment Diffusion - Long Term Diffusion project (LTD)