I don’t know what I would have done without Red Atom: Russia’s Nuclear Power from Stalin to Today (2000, W. H. Freeman, New York; I quote from p. 61). American historian Paul Josephson gained remarkable access to the nuclear centers of Russia during the 90s and Red Atom is one of only three book-length English language histories available to us Westerners. But Josephson’s writings, while indispensable, require work to untangle, and his coverage of BR-2, the second Soviet breeder reactor, a tiny 100 kWt experimental machine, had me baffled for a while. It ran for a couple of years from 1955. Its distinguishing feature is that it was the only reactor ever to have employed liquid mercury as the coolant. Josephson writes:

However, mercury would not work in industrial reactors. It had a very high cross section of neutron capture, which lowered the breeding coefficient, and it had a noticeable corrosive effect.

Surely, I wondered, the Soviet physicists would have known of these crippling disadvantages? Other nations’ scientists knew and never tried this liquid metal. It took me a while to notice a minor aside by Josephson: “It did not require any special pumps or heat transfer devices, as sodium would.” Aha! I recalled how much American technical innovation was required to come up with pumps that work with liquid sodium, for example. The Soviets were in a hurry and wanted to use ordinary industrial pumps. And an earlier sentence from Josephson reinforces that conclusion: “The physicists did everything associated with the BR-2 themselves, because engineers were not yet prepared to assist them.” In the hierarchical Soviet Union, a handful of scientists simply had no idea how to make different pumps, and no one would assist them.