Based on the model of the nuclear shells, a computer model of the spatial structure of the atomic nucleus was constructed. The application of the new approach, by analogy with the modeling of the atom electron shell, allowed us to visualize the structure of the atomic nucleus. In the presented spatial model, the concept of nucleon is also extended to include, besides protons and neutrons, deuterons in the nuclear shell. The nature of quantum and magic numbers is clarified, and the structure of the nuclear shell is shown. The resulting spatial arrangement of nucleons clearly shows the presence of a fine structure in the nucleus. Adequacy of the model is confirmed by correlations of the dependences of the nucleus radius on the charge number, as well as by the curve of the asymmetric nucleus shape dependence on the charge number which almost entirely coincides with a similar dependence of the electric quadrupole moment. The reasons for limiting the number of isotopes existing in nature have been considered. Based on the results obtained, equations for estimating the limiting number of isotopes in atoms for the NP-diagram have been determined.