"When that material then started to smolder downwards out through the floor of the chamber, it threatened to come into contact with a large amount of water that had pooled there as a result of early firefighter attempts to put it out with hoses. This would have ignited a second reaction that would have been the equivalent of a 5 megaton explosion. It would have leveled Kiev and Minsk, and would have ejected the nuclear material from the other 3 Chernobyl reactors with a force that would have rendered much of Europe uninhabitable for hundreds of years. With only days to stop it, Alexei Ananenko, Valeri Bezpalov, and Boris Baranov went into the ruins of the plant, knowingly facing almost certain death from that level of radiation exposure, to release valves that would drain 5 million gallons of water."

Is this really true? Are there better sources than this blog post?