Derek Stoffel covers southern Ontario for CBC National Radio News. Based out of Toronto, Stoffel reports on news stories that affect Canadians and Ontarians, ranging from health, education to political issues. Stoffel spent much time in 2000 and 2001 in Walkerton, Ontario, following the e-coli outbreak in the town, and the public inquiry called to examine it. Stoffel also reported on the SARS outbreak - how it affected the Toronto region, and from Geneva, what the World Health Organization did to try to stop the disease.

Petro Chaliy and his wife Nina, planting potatoes near the town of Novo Ladyzhychi.

The lake was shimmering in the spring sunshine – perfect fishing weather for Petro Chaliy, who was enjoying his Saturday off work. It was the morning of April 27, 1986. A plume of brown smoke rose into the sky, to the north of the lake, in the direction of the Chornobyl Nuclear Power Plant. Chaliy thought nothing of it.

At home, a relative was waiting with some news: There had been an accident at the plant. "I wasn't scared of it," Chaliy says. "We just didn't know what had happened. How serious it was."

It was the most serious accident in the short history of the nuclear industry. At 1:23 a.m. on April 26, 1986, two explosions ripped through the No. 4 reactor at Chornobyl, in the then Soviet Republic of Ukraine. The plant lies 20 kilometres north of where Chaliy lived with his wife and two sons.

• INDEPTH: The catastrophe of Chornobyl
• PHOTO GALLERY: Chornobyl

The rumours about what happened at the plant spread as quickly as the radiation that contaminated parts of Ukraine, Belarus and Russia. Chaliy says people in his town were given no official word about the scope of the nuclear explosion. It wasn't until four days after the meltdown that they were told to leave the area.

"I was worried about moving. I didn't want to go," Chaliy says as he leans on a spade, taking a break from planting potatoes. "My home was back there. We hoped that we only had to go away for a few days, while they cleaned. Well, now it's been 20 years."

Chaliy and his family are among the 115,000 people who lived in a 30-kilometre radius of the nuclear plant. Forced evacuations spread the residents across many parts of Ukraine and Belarus. As thousands of buses arrived to move people, local officials told them to pack only enough belongings to last three days.

No word from Moscow

The explosion inside the reactor vaporized 50 tonnes of uranium fuel instantly, blasting it high into the atmosphere. Another 70 tonnes of uranium, along with 900 tonnes of radioactive graphite, were scattered throughout the area surrounding the plant, causing some 30 fires. The graphite that remained in the reactor core immediately caught fire and would burn for 10 days, creating a situation where radiation escaped into the air as long as the fire burned.

In Moscow, there was silence. It took the Soviet government three full days to admit there was a problem at Chornobyl. The news was broken only after a cloud of radiation set of alarms at a nuclear plant in Sweden. The contamination travelled around the world, reaching countries as far away as Canada and Japan.

Sergey Volodin in Kiev.

Sergei Volodin's telephone rang, early on that Saturday morning, just hours after the explosion. A captain in the Red Army, he piloted a helicopter that mainly ferried army generals and politicians around. His mission that morning was to take a high-ranking army official from Kiev to the Chornobyl plant. He was not told about the accident.

But as he approached the site, he knew something was wrong. The fire was out by this point, but smoke was still rising from the reactor. "The western part of the plant was completely destroyed," he remembers. "It looked to me like the concrete was burning."

Volodin's mission soon changed. He and his crew were ordered to fly around the plant, and using the helicopter's built-in Dosimeter, measure the level of radiation. In some places, the meters hardly registered anything. But within minutes, he saw droplets forming on the windshield of the helicopter. "I looked up and the sky was blue, so it wasn't rain."

The radiation meter, Volodin recalls, started beeping rapidly. The first officer adjusted the device through the various readings – 10, 100, 250, to 500 roentgen an hour. Humans are not supposed be exposed to levels above 500. Yet the Dosimeter's needle ran off the end of the dial. A senior army officer on board the helicopter burst into the cockpit, yelling: "You are a murderer! You're going to kill all of us!" Volodin landed the craft, but says he'll never forget that moment.

The exposure to high levels of radiation left Volodin hospitalized for nearly a month. Many of the doctors weren't sure how to treat the illnesses, so they turned to what Volodin calls folk medicine. "Red wine! We were drinking vodka – heavily – to try to deal with the radiation," he says. After his release, he spent five weeks flying missions to the Chornobyl plant. The 58-year-old has been awarded several honours, including, just last week, the Ukrainian award for courage and bravery.

The debate over the consequences

The numbers tell of Chornobyl's chilling consequences. It's estimated that about five million people were affected by the nuclear disaster in Ukraine, Belarus and Russia.

Almost 5,000 square kilometres of farmland and 4,300 square kilometres of forest were left unusable in the three countries. More than half a million people, called "liquidators," were brought into the region north of Kiev after the disaster to clean up the aftermath.

There is no agreement, however, on the number of people who were killed and made ill by the meltdown. It remains a source of bitter debate.

Several United Nations' agencies, including the World Health Organization and the International Atomic Energy Agency, produced a scientific study of Chornobyl last year. The report put the number of deaths from the accident at 4,000. WHO has now increased that figure to 9,000.

Protesters demonstrate at an international conference on the effects of Chornobyl, held this week in Kiev.

That number drew the scorn of protesters from around the world, who gathered in Kiev this week, to highlight the effects of Chornobyl. "Tens of thousand have gotten cancer because of Chornobyl and the IAEA is covering that up," says Scott Denman, an anti-nuclear activist from the United States.

Greenpeace puts the death toll at 93,000 and says 270,000 people in the three affected countries could get Chornobyl-related cancers.

The environmental group accuses the United Nations of downplaying the affects of Chornobyl, to appease the nuclear industry.

"WHO has got no axe to grind. We're not promoting nuclear power," says Dr. Michael Repacholi, the co-ordinator of the WHO's radiation and environmental health department. "But we are promoting quality science. And our results are based on the best science that's available."

' I was drawn back home'

There is no debate that living close to Chornobyl has affected the health of Yevdokiya Symoneko. She has been hospitalized three times in 20 years, suffering from bad headaches. The 81-year-old recalls boarding a bus two days after the accident. She looked over her shoulder at the house she and her husband built and she vowed to return.

Yevdokiya Symoneko sitting on the bench in front of her house in Ilintsy.

That's exactly what Symoneko did. A few months after the meltdown, her husband borrowed a friend's truck, and the couple loaded up their belongings and made the journey home to the village of Ilintsy, eight kilometres from the nuclear plant.

The Ukrainian government banned residents from returning to their homes in the exclusion zone, but has turned a blind eye to the 186 who have done so.

"I was drawn back home very strongly," Symoneko says as she sits on the bench in front of her house. "This is our motherland."