23.11.2017_No234 / News in Brief

Paper Puts Forward New Hypothesis On Chernobyl Explosions

The ill-fated Unit 4 at the Chernobyl nuclear power station. Photo courtesy: Petr Pavlicek/IAEA

23 Nov (NucNet): The two explosions that occurred in the Chernobyl-4 reactor were a thermal neutron mediated nuclear explosion at the bottom of a few fuel channels and then, some 2.7 seconds later, a steam explosion that ruptured the reactor tank, a paper says. The nuclear explosion formed a plasma jet that shot upwards through the still intact refuelling tubes, rammed the 350-kg plugs, and continued through the quite thin roof and then some 2.5 km to 3 km into the atmosphere. The paper, published in Nuclear Technology Journal, says the nature of two explosions, which took place at the Chernobyl-4 reactor less than a minute after 01:23 local time on 26 April 1986, have been the subject of various interpretations. The paper’s conclusions about the nature of the explosions suggest that the first explosion consisted of thermal neutron mediated nuclear explosions in one or rather a few fuel channels, which caused a jet of debris that reached an altitude of some 2,500 to 3,000 metres. The second explosion would then have been the steam explosion most experts believe was the first one. The paper says it appears clear from several witnesses that there were two major explosions, the second, and largest, occurring a couple of seconds after the first. The first one is widely believed to have been a steam or vapour explosion where the energy in the hot cooling water together with the energy generated by a nuclear surge across the reactor core pressurised the steam so much that the reactor ruptured in an explosive way. The next explosion has been described as a hydrogen explosion where hydrogen, produced by exothermic reactions between zirconium in the fuel cladding and water/steam, soon burned explosively with oxygen in the air. Others have argued that the second explosion was also a steam explosion, the paper says. “There is, however, a plethora of hypotheses and interpretations of what exactly happened during that dramatic minute, and they are often quite contradictory,” it adds. The paper was written by 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. The paper is online: http://bit.ly/2z8PFs9

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