Aspects of experimental investigations of the physical characteristics of reactor cores, performed at Aleksandrov NITI as part of tests conducted on prototype test bases for nuclear propulsion reactors, are analyzed. Aside from conventional methods, new or improved methods of measurement were used to determine the neutronics characteristics. One of the basic problems solved by the Institute’s experimental physicists for the purpose of increasing the quality of neutronics measurements is the development of wide-ranging apparatus, based on modern hardware components, for monitoring the neutron flux density and for performing reactivity calculations.