In order to provide basic data for the calculation of the dose burden from a repository for spent LWR fuel in a salt dome, a formula is given for determining activity release into the surrounding salt brine under accident conditions. The main characteristic of this source term is a time-independent, instantaneous release of part of the activity and mobilization of another part at a continuous and temperature dependant rate, using nuclide-specific leach rates. Changes in leach rates resulting from reduction of the waste surface during mobilization and precipitation are taken into account. The model also takes into account axial and radial activity distribution in the fuel rods.