Reinterpreting Chernobyl

A new explanation of the Chernobyl accident has been put forward in a paper published by the Nuclear Technology journal on 16 November. Lars-Erik De Geer, a nuclear physicist retired from the Swedish Defence Research Agency and the Comprehensive Nuclear-Test-Ban Treaty Organisation in Vienna, Christer Persson and Henning Rodhe suggest the initial explosions at unit 4 of the Chernobyl NPP in 1986 were nuclear in nature – something previously rejected by all the official reports.

They argue that a series of initial nuclear explosions sent a plume of debris up to 3 km into the air around the site, which then triggered a steam explosion 2.7 seconds later, rupturing the reactor building and sending more debris into the sky at lower altitudes. They say the two explosions that occurred in the reactor were a thermal neutron mediated nuclear explosion at the bottom of a few fuel followed by a steam explosion. The nuclear explosion formed a plasma jet that shot upwards through the still intact refuelling tubes, rammed the 350kg plugs, and continued through the quite thin roof and up to 2.5-3km into the atmosphere. The paper cites several witnesses confirming two explosions.  

In the official version, the first a steam or vapour explosion was caused by hot cooling water together with the energy generated by a nuclear surge across the reactor core pressurising the steam which  ruptured the reactor. The next   explosion occurred when hydrogen, produced by exothermic reactions between zirconium in the fuel cladding and water/steam, burned explosively with oxygen in the air. Some scientists have argued that the second explosion was also a steam explosion. “There is, however, a plethora of hypotheses and interpretations of what exactly happened during that dramatic minute, and they are often quite contradictory,” the paper says.

The new theory rests on three pieces of evidence. Firstly, it was reported by Russia’s VG Khlopin Radium Institute in St Petersburg that in late April 1986 they had measured radioactive noble gas nuclides in air at Cherepovets 370km north of Moscow and 1000km north-northeast of Chernobyl. They  detected xenon fission products – something found in nuclear reactor fuel – with an isotopic mix which was characteristic of very recent production by nuclear fission.  

Secondly, modern dispersion technology calculates that these xenon isotopes found north of Moscow could only have got there if they were blasted to a far higher altitude than the debris that turned towards western Europe as a result of the steam blast. Thirdly, the destroyed reactor tank suggested that the initial explosion caused temperatures hot enough to melt a two-metre bottom plate – something more consistent with a nuclear explosion. The researchers note that the nuclear theory is supported by witnesses who saw a “bright blue flash” moments after the first explosion.

Back in January 1999 Nuclear Engineering International magazine published 'A different view on Chernobyl' in which Russian physicist Konstantin Checherov, who worked at the Kurchatov Institute in Moscow, also suggested a nuclear explosion had occurred, but said this was because the cooling pumps had failed. "The reactor itself was not to blame for the accident," said Checherov. "Nor was the control and protection system. It was a loss of coolant accident due to failure of the pumps." 

Checherov was one of the first scientists to visit the crippled reactor within weeks of the accident, risking massive radiation exposure to take temperature measurements. Over the next 20 years he visited the site more than 1000 times to take measurements inside the reactor. He concluded that the reactor shaft was virtually empty, because approximately 90% of the nuclear fuel had been ejected into the Earth's biosphere during that nuclear explosion to an altitude of 1-15km and was carried by winds around the globe.

He said the explosion occurred within the reactor shaft - partially melting the bottom of the shaft resulting in a fuel melt mixture with metal and concrete structures – lava fuel-containing materials – which was spread over the under-reactor areas. His measurements of the lava indicated that the fuel remaining in the ruins of the former reactor and under it barely totalled 10% of the original amount. This was also fiercely rejected by the official version which insists that 95% of the fuel still remains inside the reactor.

In an interview with Nezavisimaya Gazeta in 2011, Checherov said it could only have been a nuclear explosion because of the amount of graphite scrap left at the station and around it. “According to our  estimates and those of others, less than 10% of the graphite masonry has been found. It would be strange if almost all the graphite dispersed, but the fuel remained. We measured the amount of fuel left at the station using simple, basic methods. We measured the volumes of fuel-containing material took samples, measured the uranium content of in them, and did the calculations. As we expected we found that 90% of the fuel was no longer inside the reactor."

Checherov, known as the most irradiated person in the world, died in Moscow in November 2012, at the age of 65, after a long and severe illness caused by the huge radiation doses he had received. His nuclear explosion theory now seems to have been vindicated. It remains to be seen whether similar vindication will follow with respect to his views on the amount of fuel remaining inside the reactor.