Multipulse operation of the IGRIK reactor

Abstract

The operation of the IGRIK pulsed homogeneous solution research complex in a multipulse regime followed by a reactivity increase is examined. The experimental data give an idea of the processes occurring in the reactor core when the multipulse regime is implemented. These data showed that the IGRIK reactor can be operated in this regime, and they made it possible to determine the range of the pulse parameters and the limitations which the physical processes and the special design features of the system impose. It is shown that there are several possible variants for the generation of a series of successive pulses. The dependences of the fission-pulse characteristics in this regime on the initial conditions and the pulse implementation methods are investigated.The IGRIK pulsed reactor, which is a solution reactor, was put into operation in1976 [1,2]. The core of the reactor consists of a solution of uranyl sulfate in light water. A feed pump dispenses the solution from a storage tank into the core vessel immediately before a pulse is obtained. IGRIK operates in three basic operating regimes -pulsed, quasipulsed, and static.The pulsed regime is obtained by fission of uranium nuclei by prompt neutrons with four pulse rods extracted from the core at the same time. The total reactivity excess of the rods is 6β eff . The initial level of the fuel solution in the core vessel is changed to obtain the required energy release. The energy released over a single pulse is 5-60 MJ. The pulse width at half-height ranges from 2 to 20 msec.The quasipulse regime is a modification of the pulse regime where the pulse is due to delayed neutrons. The reactivity which is introduced varies in the range (0.5-1.2)β eff above the critical state on delayed neutrons. When the system is transferred above the prompt criticality state, a wide fission pulse on prompt neutrons actually obtains in the range (0.07-0.2)β eff and the "tail" of this pulse, which is formed by the delayed neutrons, contains up to 50% of the total energy released. The pulse duration in this regime varies from 0.02 sec to several tens of seconds.The reactor can operate in the static regime at power levels up to 30 kW for along time (several hours). The prescribed power is reached by adding the required amount of the fuel solution into the core vessel. A decrease of the power is compensated by periodically adding fuel solution from the storage tank.The reactor is used mainly to obtain single fission pulses. Each successive pulse is generated, as a rule, several hours after the preceding pulse. However, a series of successive pulsed separated by a short time interval is needed for some experiments in nuclear physics. The present article examines variants of successive extraction of all four rods one at a time from the core in order to obtain four or more fission pulses. When pulses are produced in this manner, ordinary pulses and quasipulses can be obtained. Consequently, for this operating regime it is especially important to take account of the factors influencing the rea...