[en] Takina into consideration insufficiency of experimental data on parameters of fast neutron initial interaction with nuclear reactor materials a tuchnique of their acquisition using mathematical modelling, which is based on the application of various nuclear models, is suggested. For a number of elements used in reactor engineering diagrams of initial defect formation, helium and hydrogen accumulation during 26-group presentation of neutron spectra are presented permitting to operatively obtain the corresponding damaging factor for a certain reactor in pure elements of natural composition and in their alloys