by Anatoly ZRODNIKOV, Dr. Sc. (Tech.), General Director, RF Research Center - Leipunsky Institute of Physics and Power Engineering; Alexander YEFANOV, Dr. Sc. (Tech.), Director of Heat Physics Department of the same Institute; F. KOZLOV, Dr. Sc. (Tech.), Deputy Director of the Department; Valery YUGAI, Cand. Sc. (Tech.), Assistant Director of the Department Most, if not all, expectations for the progress of atomic power engineering in the 21st century are associated with fast, or fast-neutron, reactors. These units process their uranium fuel practically completly and not just a small fraction as is the case with their thermal-neutron analogues, something which broadens the scale of raws utilization in a closed cycle. When scientists were just starting working on fast reactors they knew already that the high density of energy release in the fuel core (10 to 100 times greater than in thermal reactors) and the possibility of using within it materials with low neutron capture- these are the main criteria for the selection of the coolant, or heat- transfer agent. But coolants like water, or organic and silico- organic compounds with appropriate heat-transfer parameters were rejected as inappropriate because of their high rates of neutron capture. This being so, a whole range of substances were tested until in the late 1940s and early 1950s. Academician A. Leipunsky came up with the original idea of using liquid metals as heat-transfer agents, or coolants. The idea was confirmed by the subsequent experiments because fast neutron capture by potassium, sodium, lead, bismuth, iron, chromium and nickel proved to be quite insignificant. Later on scientists of the Institute of Physics and Power Engineering carried out a program of studies into the properties of liquid metals, like sodium, eutectic sodium-potassium alloys and lead-bismuth and lithium, which laid the foundation of heat hydraulics, physical chemistry and of the technologies of their application as coolants ... Read more