ABSTRACT
In all operations with fissile materials destined for nuclear weapons the amounts of these materials loaded in particular equipment used in various technological processes usually did not exceed a minimum critical mass (M^¡.n). On the contrary, in nuclear reactors (especially in high-power NPP reactors) the total mass of fissile materials loaded in the reactor core sometimes exceeded the critical mass M^J n by a factor of 10. So the control of a nuclear reactor has became one of the most important problems along with the problems of heat removal and the efficient utilization of nuclear fuel, i.e., an optimized fuel burnup. A specific character of a nuclear reactor exploitation is related to the presence of large amounts of radioactive substances in it. Even in low-power research reactors the amount of fission products is as high as millions of curies.
