Engineers at Chernobyl nuclear power station pressed the stop button for the last time yesterday, officially closing the plant.
President Leonid Kuchma relayed an order to the control room of the Number Three reactor, where a worker pressed the button marked BAZ, for "rapid emergency defence".
That slowly lowered control rods into Chernobyl's last functioning reactor to begin the long process of decommissioning a plant, which, in 1986, caused the world's worst nuclear accident.
It was only after years of Western pressure and promises of financial aid to complete replacement reactors elsewhere that Mr Kuchma agreed to the closure.
But in his speech in Kiev, he said the country also saw it as a moral obligation, likening it to Ukraine's voluntary dismantling in the mid-1990s of its inherited nuclear arms, the world's third-largest arsenal.
Environmentalists welcomed the closure, as did the German government, which this year began a long-term phasing out of nuclear power. But Greenpeace called for closures of other Soviet-designed nuclear plants, especially those built around the same notorious RBMK-1000 reactors used at Chernobyl.
Thousands are thought to have died as a result of radiation which spewed from the reactor's burning shell. One in 16 Ukrainians and millions of Russians and Belarussians suffer health disorders attributable to the disaster, including thyroid cancer and respiratory problems, according to authorities.
Chernobyl is encircled by a poisoned 30 km no-go zone, which, scientists say, will be uninhabitable for centuries.
Seen from a ramshackle assembly hall at the Chernobyl complex, where around 100 workers watched the television broadcast, the event in Kiev seemed a pompous affair. The station's 6,000 workers now face an uncertain future and one worker cried out: "We despise Leonid Kuchma."