Twenty years ago on April 26, 1986, a massive blast at the Chernobyl Nuclear Plant sent a cloud of radioactivity across Europe, affecting millions of people. The Soviet government waited for nearly three days before admitting that the catastrophe took place and only after radiation alarms went off at a nuclear plant in Sweden.

The destroyed reactor is still extremely radioactive, covered by the so-called sarcophagus, built to protect the environment from radiation, but it was only designed to last 15 years and now scientists and environmentalist say it is falling apart. Anya Ardayeva produced this report in Chernobyl. It is narrated by Ernest Leong.

This was the worst nuclear accident the world has ever seen.

A glimpse into Reactor Number Four

A massive explosion blew off the lid of the Reactor Number Four at the Chernobyl Nuclear Plant.  One hundred and ten tons of uranium and nine hundred tons of radioactive graphite blasted into the atmosphere. For about ten days, the reactor kept releasing radioactive materials into the air , as the Soviets did not know how to put out the deadly fire.

The cleanup operation involved some 350,000 people, many of whom received extremely high doses of radiation: The Soviet Union's one proven resource for that kind of job was human labor.

Five months later, a 150-meter steel-and-concrete sarcophagus was built to contain the ruins of the Reactor Number Four.

Yulia Marusich

Twenty years on, radiation levels are still extreme, says Yulia Marusich, Chernobyl's information officer. She says the sarcophagus does not completely seal off the radiation and it is not structurally sound. "The existing shelter is not stable, it is not reliable. It [sarcophagus] was constructed remotely.  On one hand, it reduced the personnel exposure. On the other hand, it didn't provide the accuracy of a shelter structures installation.”   

Outside experts confirm the sarcophagus is falling apart and could collapse.

Francis O'Donnell

Francis O'Donnell, head of the United Nations Development Program in Ukraine, says there is also a problem with what's inside. “They still haven't figured the way to deal with 180 tons of nuclear fuel-containing mass which is at the core of the reactor, there's no nuclear waste disposal strategy, and 20 years on we can do better than this.”

The sarcophagus -- and the tons of nuclear fuel inside of it -- are not the only problem.

There are three other reactors, which were put back on line shortly after the sarcophagus was built. The reactor was not turned off until 2000 and only following international pressure.

And Chernobyl has not been decommissioned completely: Ukraine does not have the facilities for the long-term storage of the plants' nuclear fuel.

Oleg Ryazanov is an engineer at the Chernobyl Plants reactor Number One, who monitors the condition of the disabled reactor. He says money is the real issue.

Oleg Ryazanov

"We have the technology, the people, the knowledge, the desire but we don't have the money.

If the sarcophagus covering the Fourth Reactor collapses, another explosion, though less powerful, is likely to occur. To prevent that, some 28 countries pledged to chip in more than $800 million for the construction of a new steel coffin.

The project is scheduled to be finished by the year 2010. 

But even with the new shelter in place, it is estimated it will take from 30 to 100 years to safely get rid of the fuel and debris inside the plant.