ABSTRACT: Within the investigation of deep geological disposal of radioactive waste, the Szecseny schlier was shown as a prospective geological formation. Study of hydrogeological and hydrogeochemical characteristics in this structure was realized in frame of the TC project supported by IAEA in years 2003-2006. New measurements verified very low permeability of the Szecseny schlier formation with hydraulic conductivity ranging from 10-11 to 10-10 m.s-1. Results of experiments and modelling showed that the diffusion seems to be the dominant transport process. Finally, sensitivity of radionuclide migration/fluxes at clay/aquifer interface was studied. The addressed parameters included impacts of effective thickness of host formation, pore-water diffusion coefficient, porosity and retardation factor. The most sensitive parameter seems to be retardation factor for all tested radionuclides and the lowest sensitivity has host rock porosity also for all tested radionuclides.