Measurement of the average neutron generation lifetime in IBR-2

Abstract

The purpose of this work was to measure the lifetime of a neutron generation in an IBR-2 core as a function of its state and the core environment. The main problem was to study the possibility of decreasing the duration of a neutron pulse. Different measurement methods were used. The main one was the α-Rossi method. For comparing with experiment, the lifetime was estimated by a computational method. It was shown that the results obtained by all measuring methods used agree with one another. For the standard state of a reactor, the lifetime of neutrons in the IBR-2 core is 62 ± 2 nsec. The contribution of individual elements of the core and its surroundings to the total lifetime of a neutron generation is presented. It is noted that in experiments with part of the radiation shielding moved away there are discrepancies in the estimate of the effective fraction of the delayed neutrons of a factor of 1.5 as compared with the standard state of the reactor. No explanation has been found for such a discrepancy.