Chernobyl: How Human Error, Not Quake, Led To Meltdown

KIEV, Ukraine -- The unfolding disaster at a Japanese nuclear power plant comes on the eve of the 25th anniversary of the worst nuclear accident in history: the explosion of a reactor at the Chernobyl power plant in what is now an independent Ukraine.

Workers wearing plastic suits and respirators for protection pause briefly on their way to drill holes for support rods inside the shaky concrete sarcophagus, a structure hastily built after the explosion to isolate the radioactive rubble of Reactor #4. Their job is to keep the deteriorating enclosure standing until a planned replacement can be built. It is hazardous work: radiation inside is so high that they constantly need to monitor their Geiger counters - and are allowed to work only one shift of 15 minutes per day.

That accident, caused by operator error, resulted in a massive release of radiation that spread across the western Soviet Union and parts of western Europe.

Some 30 workers died in the immediate aftermath, according to the UN Scientific Committee on the Effects of Atomic Radiation.

The number of subsequent deaths attributable to radiation from the accident is subject to dispute. One researcher claims the figure could be as high as a million.

April 26, 1986, 1:00 am - Workers at the Chernobyl nuclear power station begin testing backup power for reactor 4's cooling system. The test requires most safety equipment to be switched off and the speed of the reaction inside the reactor to be reduced to very low and unstable levels.

April 26 1986, 1:23 am - Workers lose control over the reaction process. Two explosions, one from superheated steam and a second from what may have been a very low-grade nuclear blast, destroy the reactor building.

April 26 1986, 1:31 am - Firefighters begin attempts to extinguish fires fed by the still-hot reactor core, which is now exposed to the sky.

April 28 1986 - Mass evacuation begins of villages and towns within 30 kilometres of the reactor. More than 300,000 eventually leave their homes forever.

April 28 1986 - A radioactive cloud containing traces of strontium, cesium and plutonium reaches Sweden and Finland. It is detected and reported in western media. Soviet denials follow.

April 30 1986 - Soviet state-controlled media report 'problems' at the power station in the first official Kremlin acknowledgment of the disaster.

May 3 1986 - Helicopters dropping concrete and sand on the remains of reactor 4 cover the nuclear core sufficiently to stop the release of radioactive smoke and debris.

May 7 1986 - First Soviet news conference on Chernobyl. Officials assert the problem is limited in scale and well under control.

May 9 1986 - The Soviet Politburo holds its first emergency meeting on the disaster.

May 14 1986 - Soviet leader Mikhail Gorbachev appears on television and admits the massive scale of the catastrophe, ending weeks of official denials.

July 19 1986 - Chernobyl plant manager and chief engineer are sacked for 'gross mismanagement.' Most workers involved in the failed reactor test are long dead from radiation poisoning.

August 25 1986 - The Soviets admit several critical design flaws but nonetheless say the main cause of the accident was poorly enforced safety procedures and human error.

November 1986 - Construction is completed of a concrete and steel shelter, or sarcophagus, covering the remains of reactor number 4.

November 1996 - Ukraine, now an independent country, shuts down reactor number 1.

December 2000 - Ukraine shuts reactor number 3, ending electricity production at Chernobyl. G7 nations promise Ukraine more than 1 billion dollars to make repairs to the sarcophagus and to help develop alternate sources of nuclear power.

August - October 2004 - International Chernobyl-related assistance to Ukraine is stalled. Ukraine brings on line two new nuclear power plants - in Rivne and Khmelnitsky - using technology slightly more advanced than that at Chernobyl.

G7 nations criticize the two reactors as much less safe than those used in developed countries.

Source: DPA

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