On the night of April 25,1986, what was later described by Sen. Patrick Leahy (D,Ver.), as "by far the worst nuclear reactor accident known to mankind... beyond even the worst nightmares of nuclear scientists," occurred in the Soviet Union. At first, the Soviets said nothing about it. Only after Moscow officials were pressured by Sweden for an explanation of the sudden increase in radioactivity that Sweden detected, did the Soviet Council of Ministers issue the following statement through the Soviet News Agency Tass: "An accident has occurred at the Chernobyl nuclear power plant as one of the reactors was damaged." Measures are being taken to