Chernobyl Designers Failed to Allow for Possible Errors, Expert Says
VIENNA, Austria (AP) _ Designers of the Chernobyl nuclear reactors erred in failing to make allowances for operator mistakes, a British atomic power expert said today.
″The whole sequence of operator errors have not been foreseen and appreciated by the designers,″ said Bryan Edmondson, director of the Nuclear Operations Support Group of the British Central Electricity Generating Board.
A Soviet report on the April 26 disaster placed blame on the plant’s operators and abstained from criticizing reactor design. But Valery A. Legasov, a top Soviet nuclear power official, acknowledged here Monday that half the country’s Chernobyl-type reactors have been shut down for technical modifications.
Legasov did not disclose how many reactors were involved, but documents submitted at the international conference under way here on the accident indicated the Soviet Union has 18 reactors like those at Chernobyl.
Legasov is the chief Soviet delegate at a conference of 500 nuclear power experts from 50 countries meeting under the auspices of the International Atomic Energy Agency to draw conclusions from the Chernobyl accident. The disaster killed 31 people and sent radioactive debris worldwide.
The Chernobyl design is used almost exclusively in the Soviet Union.
Edmondson, chairman of a technical working group, met privately with other experts today to consider aspects of plant design, safety and other technical aspects.
″We are coming to the crux of the matter - the interaction between the design and operation,″ he told reporters at a briefing.
British engineers examined the first 1,000 megawatt reactor of the Chernobyl type at Leningrad in 1976 and found seven design deficiencies, including one which allows an uncontrollable power buildup, said Peter Vey, spokesman for the British organization.
Vey said Soviet engineers were told of the failures at the time and that they had attempted to overcome some of them.
The Soviets have reported that a power surge and a buildup of steam in the reactor core were main factors in causing the Chernobyl explosion.
Another working group also met behind closed doors today to study emergency measures taken by the Soviets after the explosion of the No. 4 reactor.
Armen Abagyan, another Soviet delegate, said a protective shell around the wrecked reactor would be completed by this coming fall. Workers have been burying the reactor in concrete, dirt and chemical mixtures to prevent further leaks of radioactivity.
Legasov on Monday, the first day of the conference, made a five-hour presentation to the experts.
″Our experts have proposed a number of technical solutions which fit fully into the actual construction of our RBMK (Chernobyl-type) reactors,″ he said.
″Our specialists believe these should make it possible to continue their operation with a very high level of reliability.″
RBMK is the Soviet abbreviation for light-water cooled, graphite-moderated reactors.
The 382-page Soviet report put heavy blame on human error rather than faulty equipment for the explosion and fire. Pressed by reporters, Legasov said:
″The defect of the system was that the designers did not foresee the awkward and silly actions by the operators.″
The disaster forced the evacuation of 135,000 people and caused $2.8 billion in damage.
The report presented on Monday catalogued a string of procedural errors by workers at Chernobyl.
It said the reactor was brought down to low power on April 25 during a routine shutdown and a planned test of how long one of the generators it supplied would keep going if its steam supply were cut off.
The report said a key mistake was made when reactor personnel allowed the reactor to keep running even though the emergency cooling system had been shut down.
Emergency warning systems were also shut down, it said.
By 1:23 a.m. on April 26, steam had built up inside the reactor core, the report said, creating conditions for high-pressure, hot chemical explosions.