Chernobyl twenty years on

She is known as "Maria of Chernobyl" and - though she is not a saint - many view her birth in the shadow of the infamous reactor as little short of miraculous.

Now aged six, Maria Vedernikova is the first and only child to be born in Chernobyl's post-catastrophe dead zone, a bleak and frightening area 18 miles in radius, now in Ukraine.

Indeed, if you ask a guide at Chernobyl whether anyone has been born in the zone since 20 years ago this Wednesday, when the reactor exploded, you will get an emphatic "net".

Officially nobody is allowed to live here and the several hundred masochistic souls who insist on doing so are here illegally.

The soil is poisoned with caesium and strontium. Only temporary workers and catastrophe tourists are allowed to enter for short periods at their own risk. And "the zone" is associated in most people's minds with only one thing: death.

Yet Maria's parents - canteen worker Lida Savenko and clean-up worker Mikhail Vedernikov - insist that she did indeed take her first breaths here, in a ramshackle peasant's cottage in Chernobyl village.

Maria's upbringing has been unconventional; her food is checked with a Geiger counter and her home is regularly tested for radiation. She swims in a "nuclear" river and has no other children to play with.

Since she has started going to school outside the zone, she has begun to lead a more normal life. So far she has shown no signs of being affected by radiation and appears healthy.

Long may she continue to be so. For the toll of the catastrophe that erupted at four seconds past 1.23am on 26 April 1986 has spread all over the surrounding area - and nearly half of Europe.

More than 200 times as much radioactivity was released as by the Hiroshima and Nagasaki bombs. The reactor's operators switched off all its safety systems while trying to carry out an officially authorised, but dangerous, experiment.

Suddenly, as the official investigator of the accident put it, the reactor "was free to do as it wished". Its power surged to several hundred times its normal level in the very last second of its life, and a massive explosion blew its 1,000-ton lid clean off, blasting highly radioactive material more than 7km up into the atmosphere. Its core then caught fire, pouring out yet more radioactivity.

The toll on health and lives was determined by a mixture of happenstance and freak weather conditions, which spared the immediate area an even greater catastrophe - but spread its effects out over the continent.

First, the accident took place at night so there were just hundreds, not the usual thousands, of people on duty at the plant. More important, the people of the area were asleep indoors: their homes shielded them from 90 per cent of the radiation.

Then, the very fierceness of the fire sent the radioactive emissions high into the air, as if contained in an invisible chimney. It was a still night, and so the radioactive plume was able to rise steadily until it reached about 1km up where a high, gentle south-easterly breeze wafted it over some relatively uninhabited marshes. Most fortunate of all, it did not rain for days afterwards. This would have brought down radioactive materials with it. Instead, the longer they stayed up in the air the more the most virulent, short-lived ones decayed.

The first result of this was that only 28 people died in the accident and its immediate aftermath- and they were all people at the reactor site at the time, or when fighting the blaze (another 19 of them have died from their exposures since). This is extraordinarily few: studies suggest that thousands would have died if conditions had been different.

The second result is that the radioactivity spread far and wide. Indeed the accident first became known the following afternoon when radiation monitors in Sweden - set up to check compliance with the 1963 test ban treaty - detected high levels of radioactivity crossing its borders.

For days the Chernobyl cloud wandered over Europe, blown by varying winds, and shedding some of its radioactive cargo whenever it rained. It reached Britain on 2 May.

European Union measurements show that, in all, 40 per cent of the continent was contaminated. Areas with particularly high fallout - apart from Russia, Belarus and Ukraine, all near the plant in what was then the Soviet Union - include Austria, Slovenia, northern Greece, southern Finland, parts of Norway and Sweden, Cumbria, north Wales and parts of Scotland. Even now some 375 sheep farms in Cumbria and Wales suffer restrictions on marketing their meat because their pastures are so radioactive. There are similar restrictions on reindeer in Sweden and Finland and on wild boar and mushrooms, berries and some fish across much of Europe.

Unexpectedly high levels of thyroid cancer, in people who were children at the time of the accident, have emerged in Russia, Belarus and Ukraine. And as we report today, rates of the same rare cancer in children have risen twelvefold in Cumbria.

Nobody knows what the final toll from Chernobyl will be - not least because the solid cancers that will be some of its main effects take decades to develop, while genetic damage will take generations to show.

Last year the International Atomic Energy Agency predicted 4,000 deaths, but this has been widely discredited as too low. Equally, a Greenpeace estimate of 100,000 deaths published last week seems overblown. The best estimates range between 16,000 deaths (the International Agency for Research on Cancer, on Thursday) and 60,000, most outside the old USSR.

The effect on nuclear power was more immediate - applying the coup de grace to an already failing industry across much of the world - but may now be fading as Tony Blair, George Bush and other leaders try to revive the technology. But it still carries a warning, At the time Dr Pierre Tanguy, a leader of the aggressive French nuclear industry, confessed that the catastrophe was caused by "the kind of operator error that we all experience in our plants, and is hard to eliminate".

Back in Chernobyl another disaster may be brewing. For the vast concrete "sarcophagus" shielding the shattered reactor is listing to one side, cracking and in danger of collapsing.

But Maria of Chernobyl is, illegally, staying put. "This child will regenerate our land", insists her mother. "We won't let her be taken away from here."

Additional reporting by Severin Carrell

Eyewitness: Natalia Manzurova

Natalia Manzurova, a radiation expert ,spent four and a half years clearing up Chernobyl and the nearby town of Pripiat. She has written a vivid memoir of her experiences. Here extracts are published for the first time

When I arrived, Pripiat was a city of abandoned, sometimes looted, multi-storeyed apartment houses, public squares, buildings, athletic complexes and stores, greeting us with a stench leaking from refrigerators that had not been turned on for over a year. Mice were everywhere. Sometimes I wept at the things I saw: children's beds and their toys and living room floors covered with photographs of people's smiling faces which I could never ignore, or bring myself to walk on.

Photos in the kindergarten saddened me immensely and I hoped some miracle had spared their young owners. In one of its rooms I found a cage with the prickly skin of a hedgehog as wrinkled as an empty plastic bag. A second cage held bird feathers, the bodies likely eaten by mice.

A sick dog lay in a child's bed in one of the napping rooms. It was the only bed that looked used so perhaps the child that slept there had befriended her. She crawled towards me with difficulty. She had no hair on her paws and lower legs, her flesh was bleeding, her eyes clouded and saliva streamed from her mouth. She had external beta radiation burns from hunting in contaminated grass .

I went to an abandoned hospital to find a container we could use for water samples. I found a suitable large farm milk can, but inside it was the saddest thing imaginable - four, six or eight months old chocolate-coloured 'mummified' newborns with closed eyes and bowed arms and legs.