A new approach for solving the important problem of choosing the optimal delayed-neutron data (number of groups, fractions β j , energy spectra χ j , decay constants λ j of precursors) for a particular reactor is proposed [1][2][3][4][5][6][7][8][9][10][11].The evolution of the neutron flux in a reactor is described by the direct kinetic equation [5][6][7][8]