[en] A numerical method for the calculation of diffusion coefficients for GCFR and HTR lattices considering the exact geometry is developed. For infinite regular GCFR lattices results for the axial buckling dependent streaming correction are given. For irregular GCFR lattices whose coolant channels can extend only within one fuel element the dependence of both radial and axial streaming corrections on the fuel element size is studied. For hexagonal HTR lattices a comparison of the numerically calculated diffusion coefficients with the analytical formulae of Benoist is made. (author)