The code COREDIV, self-consistent both with respect to the interaction plasma coreplasma edge and main plasma-impurities, is used to simulate nitrogen seeded JET discharges. The model is fully described and comparison of the numerical results is done with experimental data pertaining to two series of discharges different in input power, in confinement, in the level of the power radiated and in the puffing rate of the main gas and of nitrogen. Impurity sources, their transport and densities are considered as a function of the edge and core parameters and the consistency with the power they radiate is discussed. Special emphasis is given to the analysis of the fluxes of carbon and of the recycling fluxes of deuterium.