Summary of the Congress

4 October 1986

Why a kind of hush fell over the Chernobyl conference / Western atomic agencies’ attitude to the Soviet nuclear accident.

What is the half-life of Chernobyl? Upwards of 95 percent of the radioactive fuel is still inside the ruined reactor. Some of its radioactive constituents will remain dangerous for centuries. In late August, at the Vienna conference on the accident, the Soviet authorities displayed a model of the impromptu mausoleum now rising to entomb the ruin. The longevity of this structure will be crucial for the future of South Ukraine. It must be built to last; once it is in place there will be no opportunity to remove it and rebuild it.

No steel-and-concrete structure ever erected hitherto has had to meet such stringent criteria for durability. The entire history of the use of concrete as a building material has been much shorter than the anticipated service life of the Chernobyl mausoleum. No one can guarantee the condition of the concrete more than a century hence.

The long-term health effects of the radioactivity released during the accident will also extend for decades, if not centuries. Be that as it may, at the Vienna conference, nuclear industry delegates appeared to be concerned with the timescale not so much of the physical and pathological consequences of the accident as of its psychological effects. What would be the half-life of Chernobyl in the public mind? How long would Chernobyl influence public attitudes to nuclear power?

At the Vienna conference, government and industry delegates had to face up to the accident and come to terms with it. They took only the length of the conference. Within five days, August 25-29, the mood of the delegates underwent a remarkable metamorphosis. On the Monday they were grim, gloomy and tense. By Friday they exuded bonhomie and esprit de corps, a global nuclear community that had pulled itself together and convinced itself that It had little to worry about after all.

On the technical level, the trend of the argument was evident long before the Vienna convocation. The RBMK-1000 reactor was a design unique to the Soviet Union. Early suggestions that it was also somehow primitive, Neanderthal technology, were long since discredited, and the Soviet report erased any lingering doubts on this score. As Academician Valery Legasov, leader of the Soviet delegation pointed out, each type of reactor had advantages and disadvantages. Soviet designers were fully aware of the potential drawbacks of the RBMK concept, and believed that they had engineered control and safety features amply adequate to compensate for them.

Legasov had barely finished delivering this part of his presentation, however, when Lord Marshall, chairman of Britain’s Central Electricity Generating Board, gave an audience for journalists in an adjoining corridor, asserting that Legasov had admitted “defects” in the RBMK design. No official translation appeared to support Marshall’s attribution of the word “defects” – a much more serious shortcoming than “disadvantage” or “drawback”. The semantic difference nevertheless allowed Marshall to claim that even the Soviets conceded that the RBMK design was inherently inadequately safe – unlike Western designs; and that the Chernobyl accident therefore had little to teach Western nuclear engineers.

Marshall laid great stress on the RBMK’s so-called “positive void coefficient”: a power-surge that increases the volume of bubbles as the cooling water reinforces itself. The “void coefficient” undoubtedly contributed to the severity of the Chernobyl accident. But the Soviet report also identified other factors of major significance. Dispassionate observers noted how Western delegates assigned different relative importance to these other factors. US participants referred repeatedly to the role of the graphite in the RBMK, and stressed that US reactors did not use graphite. Marshall and the British delegation said little about graphite: all British commercial nuclear stations have a graphite moderator like the RBMK. The Soviet report revealed for the first time that the primary destructive event during the accident was a “stream explosion”: the water coolant flashed to steam so violently that the pressure shock shattered the top of the reactor, containment and all. A hydrogen explosion followed within two or three seconds, showering the site with blazing chunks of core and starting about 30 fires. Neither the steam explosion nor the hydrogen explosion could have occurred had the reactor not been cooled by water.

US delegates, however,, played down the importance of water in the accident; all US commercial nuclear stations are water-cooled. Canadian delegates, for their part, alluded only to “design differences” between the RBMK and the Canadian CANDU design; CANDUs are not only water-cooled, but also have a positive void coefficient. British delegates refrained from mentioning the advantages of gas-cooling in this respect; although all Britain’s operating commercial reactors are gas-cooled, the CEGB is eager to switch to the pressurised-water reactor for Sizewell B and subsequent plants.

As the conference progressed, Western criticism of Soviet nuclear technology became suddenly muted. The last thing in the world the nuclear industry needed was open civil war between proponents of different nuclear technologies: better to lay the blame on the handful of staff that had switched off the safety systems at Chernobyl 4 – and paid for their folly with their lives.

What, however, of the wider human cost of the accident? Legasov’s opening presentation left no doubt about the horror of April 26. Even so, only 31 people had thus far died. Press conference panellists compared this toll with that in car accidents, air crashes, and other mishaps, and insisted that matters must be kept in proportion.

In the course of the Vienna conference, the controversial question of long-term health effects gradually assumed an aspect not hitherto manifest. True the Soviet figures indicated that radiation exposure from Chernobyl might lead to 24,000 fatal cancers, not to mention many more not directly fatal, but these cancers would show up only over 70 years, in a population of many millions. Compared to all the other deaths in the same population over the same period, the number was insignificant. In any case, there would be no “extra deaths”: everyone dies exactly once. By implication, if Chernobyl didn’t get you, something else will; so why worry about a nuclear accident?

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