We will never be able to put an accurate figure on how many people will eventually die as a result of that cloud. Estimates which started in the low thousands in the immediate aftermath of the disaster had reached more than a million (half in the Soviet Union, the rest elsewhere) by the time the story faded.
But one thing is certain. More than six years later, 25 reactors with design flaws which make them at least as dangerous as the Chernobyl one are still throbbing away generating power in Eastern Europe. Moreover, safety standards at the region's other 32 reactors are little short of appalling.
It may sound short-sighted, but impoverished Eastern governments cannot afford to fix, replace or shut down dangerous reactors. They do not have the hard currency to buy the relevant parts and expertise from the West, nor, since nuclear energy supplies around a quarter of the region's power needs, is simply closing down the affected plants an option for them. Rightly or wrongly, they argue that if they did so, as many people would die of heat and power deprivation as might in another nuclear disaster.
But with a nuclear workforce even more demoralised and underpaid than the one which made such catastrophic decisions in Kiev, the question is not whether there will be an accident, but when.
Given the ease with which radioactive clouds can stroll across national borders, it might have been expected that the West would have acted swiftly to defuse these nuclear time-bombs. Unlike most of the problems of the new world order, all this one requires is money.
Putting a thin sticking-plaster on Eastern Europe's reactors would cost around pounds 300m; a more extensive refitting programme around pounds 3.5bn. Those sums are big, but hardly something a few years of British Gas profits could not comfortably cover.
Yet the West's response has been a quagmire of bureaucratic delay and blind self-interest. It took the European Commission a year to award contracts worth pounds 3m for repairs to what is arguably the most dangerous reactor in the world, Kozloduy in Bulgaria.
Governments have concentrated their efforts on trying to ensure their national nuclear companies will be the ones to benefit from the spending.
At last month's G7 meeting in Munich, fears that their companies would lose out ruined attempts to get Western governments to create a pool of funds to deal with the problem. It was all the EC, the United States and Japan could do to bring themselves to pledge to try to meet the cost of the emergency programme bilaterally.
Industry observers insist the European Commission has developed a new sense of urgency since Munich, though there are few signs work has started in earnest. Until it does, each time it rains, keep an eye on which way the wind is blowing.Reuse content