A one-dimensional radionuclide chain transport model is developed, taking into account sorption, longitudinal dispersion, and arbitrary repository concentrations. For piecewise constant geologic parameters, a semianalytic solution can be written down, when, at the layer boundaries, mass conservation is considered rigorously and flux conservation to a good approximation. The solution consists of a superposition of terms that are easily interpreted and is invariant under layer permutation and parameter scaling. A corresponding computer code RANCH has been developed. The 245Cm chain has been investigated for a broad variation of parameters of a three-layer geology. For very small retention factors only, 245Cm and 241 Am can survive migration in  the geologic medium, while 237Np is reduced by at most three orders of magnitude.