BY MEANS OF A TWO-PHASE EQUILIBRIUM REACTION

We chose cadmium and its compounds, as well as boron trifluoride gas, as absorbers. Studies of the sorption kinetics involved weight and volume techniques applied to the activated carbon-cadmium system; the studies have shown that the particular pair can be efficiently used to regulate the neutron flux at temperatures above 600~ whereas the pair consisting of activated carbon and boron trifluoride can be employed in the temperature range 20-300~ In order to check the possible neutron flux regulation in the apparatus with the aid of sorption systems, we developed a tube with the activated carbon-cadmium system. The channel was designed in the form of several coaxial cylinders. The inner cylinder 1 contained a calorimeter assembly [2] with two thermal dispersers of radiation which were filled with material capable of undergoing fission (uranium dioxide with 2% =3~U enrichment). Cylinders 2 and 5 formed an autonomous evacuated volume communicating with a cadmium thermostat mounted below the core. The 0.65 cm wide gap between cylinder 5 and the perforated partition was filled with activated carbon; the space between cylinder 2 and the partition served for admitting the cadmium vapor phase through four distributors into the plane of the core center. A jacket formed around the entire assembly a protected cavity which was evacuated by pumping during the entire experiment. The temperature of the individual components was kept constant with four electric heaters and checked with Chromel-Alumel thermocouples. A directly charged sensor was attached to the outer surface of the jacket for measuring the neutron flux in the cell. The experimental tube for regulating the neutron flux density was tested in the VVR-M reactor of the Institute of Nuclear Research of the Academy of Sciences of the Ukrainian SSR. The degree of attenuation of this particular sorption system was measured at various power ratings of the apparatus and for various temperature conditions of the sorbent and the absorber. The results of this research (Fig. 2) have shown that the change in the degree of attenuation is correlated to the change in the temperature of sorbent and absorber, the temperature determining the specific cadmium concentration in the activated carbon. The degree of attenuation of the sorption system was defined as the ratio of neutron flux density required for obtaining the experimentally measured liberation of heat in the calorimeters to the neutron flux density in the experimental cell. The flux density of the thermal neutrons in the cell was determined from the external directly charged sensors (sensitivity of 3.15.10 -~~ A'cm2"sec).