[en] The method of fast reactor characteristics simulation based on interpolation by means of N-dimensional piece-polinomial functions (spline functions) is described. For the BOR-60 reactor taken as an example, the simulation of distribution of six neutron groups is carried out. A new approach to optimization is proposed and substantiated. This approach includessimulation of the efficient multiplication factor group fluxes and burn up by the method of spline-functions. The comparison with other simulation met-- hods is made. The conclusion is drawn that the proposed method may be effectively used in the problems of reactor fueling and fuel burnup optimization