Sensitivities of nuclide importance for neutron economy to one-group neutron cross sections

The calculation method of sensitivity coefficients of nuclide importance is developed by using perturbation method. It is employed for evaluating net neutron surplus for each inserted nucleus to one-group neutron cross sections for a fast reactor spectrum. The signature of important nuclide is opposite to each other for the fission and absorption cross section. The sensitivity of neutron economy to spectrum change can be expected small for the important fissile nuclide