The migration of wall material or seeding impurities plays an important role in the formation of mixed materials, the impurity contamination of the plasma and tritium retention. First, this work presents an improved model for the sputtering from mixed material surfaces in WallDYN. Second, we present dynamic SDTrimSP and WallDYN simulations of the nitrogen implantation in Be and the migration of nitrogen in tokamaks with a Be main wall. The simulations with the binary collision code SDTrimSP predict that N accumulates directly at the surface and that the Be erosion decreases with increasing N surface content. A first application of WallDYN to the nitrogen migration with an ITER-like wall indicates that the Be main wall may cause wall pumping of N by co-deposition with Be.