Technique for reactivity modulation in a pulsed nuclear reactor with fast or intermediate spectrum

A method of reactivity modulation in a pulsed nuclear reactor with fast or intermediate spectrum of neutrons is described. The invention is aimed at out-of-reactor attaining high pulse parameters of slow neutrons with a low-background level between pulses and the expansion of experimental zone around the reactor. The method consists in the streaming of hydrogen-containing material, decelerating neutrons, through the reactor over the core perimeter. The thickness of the hydrogen-containing material is similar to the length of neutron migration in it