New finding: nuke blast crippled Chernobyl
A new analysis of the Chernobyl disaster finds a nuclear explosion started the catastrophe. Andrew Masterson reports.
The Chernobyl 4 reactor was destroyed by a nuclear explosion, not a steam one, according to research published in the journal Nuclear Technology.
The reactor, 130 kilometres of Kiev, Ukraine, exploded in on April 25, 1986, killing 30 people, and inducing acute radiation poisoning in 134. Today, encased in thick concrete, it stands at the centre of a 2600 square-kilometre exclusion zone.
Investigations into the causes of the reactor failure concluded that the cause was a steam explosion. This remains the accepted explanation, and is sometimes deployed to bolster the case put by the power industry that no reactor has ever experienced a nuclear explosion.
Now, analysis by researchers from the Swedish Defence Research Agency, Swedish Meteorological and Hydrological Institute, and Stockholm University contradicts the standard explanation.
The team, led by Lars-Erik De Geer, concludes that the first of two explosions reported by eyewitnesses was in fact a nuclear one – or rather, a very rapid series of nuclear ones – followed three seconds later by a secondary steam explosion.
The nuclear explosions, the researchers conclude, sent a jet of debris very high into the sky. The steam explosion immediately afterwards ruptured the reactor and sent still more debris into the atmosphere, but at lower altitudes.
The findings are based on a new analysis of xenon isotopes made four days after the event.
The original study – carried out by scientists from the Leningrad-based VG Khoplin Radium Institute – detected xenon isotopes present in the city of Cherepovets, north of Moscow, and a long way distant from where Chernobyl detritus was predicted to spread.
Re-analysis of these isotopes reveals them to be the products of nuclear fission, implying they could have been created in a nuclear explosion. Xenon isotopes detected within the main Chernobyl detritus track over Scandinavia are slightly different and conform to material simply propelled from the reactor core by a non-nuclear blast.
Looking back at weather patterns in the days after the explosion, De Geer’s team concluded that the Cherepovets isotopes could only have reached the city if they had been sent significantly higher into the air than the bulk of the Chernobyl outpour.
Investigators looking at damage to the reactor as soon as it was practical to do so after the explosion noted that the first blast had generated temperatures hot enough to melt through a two-metre-thick plate beneath the core – an outcome, say the Swedish team, compatible with a nuclear blast. A steam explosion, they say, would not have contained sufficient energy to cause the plate to melt.
"We believe that thermal neutron mediated nuclear explosions at the bottom of a number of fuel channels in the reactor caused a jet of debris to shoot upwards through the refuelling tubes,” says De Greer.
“The steam explosion which ruptured the reactor vessel occurred some 2.7 seconds later.”