Sorption aspects for in situ matrix diffusion modelling at Palmottu natural analogue site

Concentration profiles in rock matrix around water-carrying fissures were measured at Palmottu U deposit. The profiles were interpreted by the classical matrix diffusion concept. Site-specific sorption studies were performed for U using standard batch experiments and surface complexation modelling; the response of sorption isotherms was also tested. Sitespecific matrix properties as well as initial and boundary conditions were used in simulations. Our results indicate that matrix diffusion alone cannot explain the observed enrichment of U and its daughters in the rock matrix.