Between 15,000 and 30,000 people died when the plant's reactor number four exploded on April 26, 1986, spewing a cloud of radioactive matter across much of Europe.

The name of the small town of Chernobyl has become a symbol for the dangers of nuclear power, and the world breathed a collective sigh of relief when the last of the plant's reactors was shut down last December.

However experts have warned that the crippled site will remain a radioactive time bomb for decades to come, with 160 tonnes of radioactive material locked inside a hastily-erected stone casing that is already crumbling.

The explosion, which released radiation into the atmosphere equivalent to 500 times that of the atomic bomb dropped on Hiroshima in 1945, remains the world's worst civilian nuclear disaster.

Religious services will be held during the night of Wednesday to coincide with the exact time of the explosion, at Kiev and at Slavutich, the small town near Chernobyl inhabited mainly by former employees at the power plant and their families.

It was at 1:23 am on the fateful day in 1986 that the two explosions in reactor number four erupted, shattering the world's complacency over nuclear power and setting off a 10-day meltdown that threatened an ecological catastrophe.

The blast had political fallout too, coming little more than a year after Mikhail Gorbachev had moved into the Kremlin and contributing to his decision to launch the twin programmes of perestroika and glasnost, setting in train a process that led ultimately to the collapse of the Soviet Union.

Chernobyl was seen at the time as one of the proudest achievements of the Soviet nuclear industry, launched during the 1970s as part of an ambitious programme of power production.

It had been intended to build six reactors, but the fifth and sixth, which had gone into construction in 1981, were rapidly discontinued.

Russia and Lithuania are still operating 13 RBMK reactors of the type that exploded at Chernobyl. Although the most powerful in terms of capacity, they are considered unreliable and badly designed by western experts.

Under a 1995 protocol, the West promised 2.3 billion dollars (2.6 billion euros), comprising 500 million in grants and 1.8 billion in loans, to help provide substitute power for Ukraine, which was still obtaining about five percent of its electricity from Chernobyl until last December.

In addition to making the site safe -- or, at any rate, less dangerous -- the funds have been devoted to social programmes to help reduce the economic fallout of closure and on boosting safety at Ukraine's four other nuclear centres (Rivne, Khmelnitsky, Pivdenno Ukrainska and Zaporizhiya).

Meanwhile Chernobyl will continue to prey on the world's nuclear anxieties as its stone casing, or sarcophagus, continues to decay.

A Russian nuclear expert said Monday that a new casing around the entombed nuclear reactor would cost between 1.5 billion and 2.5 billion dollars.

And earlier this month a former nuclear security chief at Chernobyl painted an alarmist picture of the situation, telling a German magazine that the sarcophagus was in danger of imminent collapse.

"The sarcophagus is so porous that radioactivity escapes each day," he said. "We don't even have the ability to measure the amount. If we could see the radioactivity there would be a cloud of smoke above the sarcophagus."

Another official, Vladimir Asmolov of the Kurchatov Nuclear Institute in Moscow, dismissed fears of another disaster, but western governments are already collecting the sums needed to finance the building of a new casing as soon as possible.

Copyright © 2001 AFP

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