Teollisuuden Voima Oy (TVO) is investigating the feasibility to dispose of spent nuclear fuel in a final repository constructed in a crystalline rock formation several hundred meters underground. This work is a part of the program of the updated preliminary safety assessment TVO-92. According to the plans the spent fuel, sealed in copper-iron canisters, is emplaced in drillholes below the tunnel floor and surrounded by bentonite clay buffer. The tunnels are backfilled with a mixture of quartz sand (90%) and bentonite (10%). Migration of solutes is retarded by sorption in the backfill and on fracture surfaces of the rocks and by diffusion into fissures and micropores of the rock. In migration calculations retardation due to sorption is derived from distribution ratios of solutes between water and solid. Migration by diffusion in rock is described by diffusion coefficients. Proposals are made for distribution ratios and diffusion coefficients in the backfill and in rocks for the radionuclides of spent significant with respect to safety of the final disposal. The proposals include realistic values besides the conservative values, leading with a high probability to overestimation of radiation doses in the biosphere. (orig.).