IGRIK reactor operation in a two-pulse mode

Abstract

The results of investigations of the operation of the IGRIK pulsed homogeneous solution research complex in the unconventional (for pulsed reactors) two-pulse mode with successive reactivity increments with generation of prompt-or delayed-neutron pulses are presented. Experimental data which give an idea of the processes occurring in the reactor core in the two-pulse regime are obtained. These data made it possible to determine whether or not the IGRIK reactor can be operated in this regime and the limitations imposed by the physical processes and special design characteristics of the system. It is shown that are pulses can be generated in several different ways. The dependences of the fission-pulse characteristics in a given regime on the initial conditions and the methods for obtaining the pulses are investigated. Methods are proposed for increasing the operational possibilities of the reactor.Over more than 30 years of operation, the IGRIK reactor has proven itself to be a powerful pulsed source of neutron and γ radiation, making it possible to vary the fission-pulse parameters over a wide range [1,2]. The pulsed regime has been perfected and does not differ in any fundamental way from the operating regime of other research reactors in this class. A rapid increase of reactivity is achieved by using four rods with independent pneumatic drives. In the ordinary pulsed regime, all rods are moved synchronously, which gives a pulse with the nominal parameters. To obtain a regime with paired pulses, each rod can be moved independently using a programmed facility -a block of temporal commands, which ensures that the rods are removed from and inserted into the core according to a prescribed program in an interval from 0 to 99 sec. The shortest interval between commands is 0.1 sec.The radiation characteristics of the IGRIK reactor (the neutron fluence in the experimental channel is ~1.5·10 15 cm -2 , the γ-ray dose is ~1.4·10 6 rad, the radiation acts for 2 to 20 msec) which are realizable in this regime make it possible to solve diverse research problems. However, there remain problems that can be solved only by perfecting regimes which are unconventional for a pulsed reactor:• a two-pulse regime where two successive fission pulses with duration from 4 to 10 msec and separated by 0.7 to 10 sec are generated; • a two-pulse regime with one pulse generated by delayed neutrons, which is characterized by action time from 0.1 to several seconds and a relatively low yield of neutron and γ radiation. Recording the Pulse Parameters. The time dependence of the energy release, the form of this dependence, the ratio of the integrals in the first and second pulses, and the time interval between the pulses were determined in this work. The problem in this case is complicated by the large difference between the pulse parameters -up to several orders of magnitude in amplitude and up to a factor of a thousand in duration. For example, the duration of the quasipulse which develops as a result of supercriticality on delayed neutrons is a...