Swedish scientists found that during the Chernobyl accident a nuclear explosion with a capacity of about 75 tons of TNT equivalent occurred. To do this, they analyzed the concentrations of 133Xe and 133mXe isotopes in samples of the Cherepovets air-conditioning plant, and also simulated the weather conditions after the disaster, using the recently published detailed data for 1986.
The accident at the Chernobyl nuclear power plant occurred at night on April 26, 1986. As a result of the production experiment, the station personnel lost control over the reaction, the emergency protection did not work, and the reactor power increased sharply from 0.2 to 320 gigawatts (thermal). Most witnesses point to two powerful explosions, although some speak of more.
According to the generally accepted version, the first of the two explosions is explained by the fact that the water that filled the cooling system instantly evaporated, the pressure in the pipes increased sharply and tore them apart. Then the heated steam began to interact with the zirconium shell of the fuel cells, which led to the active formation of hydrogen (polyrirconium reaction), which burned explosively in the oxygen of the air. In this paper, scientists question the nature of the first explosion and state that in reality it was a small nuclear explosion.
In favor of this hypothesis, the authors of the article give two main arguments. First, a few days after the disaster, scientists from the Radium Institute named after him. Chlopin registered the activity of 133Xe / 133mXe isotopes in liquid xenon obtained at the Cherepovets air-cooling plant.
Generally speaking, the factory mainly produced liquid nitrogen and oxygen to meet the needs of the Cherepovets metallurgical plant, but a side effect of its work was also the liberation of noble gases from the air. Radioactive isotopes scientists searched using high resolution gamma spectroscopy. As a result, the ratio of the activity of the 133Xe / 133mXe isotopes was approximately 44.5 ± 5.5 by the hour of April 29 (approximately 83 hours after the accident).
The change in the ratio of activity of xenon isotopes over time for three different scenarios of their formation. A short vertical line corresponds to data from the Cherepovets factory (Lars-Erik De Geer et al. / Nuclear Technology)
To explain this attitude, physicists simulated the processes taking place in the reactor with the help of the previously developed program Xebate. It took into account that in addition to the standard xenon isotope formation chain, as a result of a change in reactor power in preparation for the experiment (so-called xenon poisoning), isotopes were also produced as a result of a subsequent nuclear explosion of about 75 tons in TNT equivalent. At the zero moment, the ratio of the activity of the 133Xe / 133mXe nuclei formed in these two scenarios was 34.6 and 0.17, respectively.
Then, due to the difference in the half-life of the elements, this ratio changed, so that by the time of their registration, the activity ratio in the samples from the Cherepovets factory was equal. Scientists note that because of the uncertainty in this respect, the explosion power can only be determined approximately, and in fact it lies in the range from 25 to 160 tons with a probability of 68 percent (that is, in the confidence interval 1σ).
Secondly, scientists modeled meteorological conditions over the European part of the USSR after the accident, using the recently published detailed three-dimensional weather data and modern algorithms for calculating the motion of the air fronts. Modeling of the distribution of xenon isotopes scientists carried out for seventeen possible heights of its emission into the atmosphere, lying in the interval from zero to eight thousand meters.
As a result, scientists found that the observed activity of xenon isotopes in samples from the Cherepovets factory (which, incidentally, is located a thousand kilometers from the Chernobyl nuclear power plant) can be explained only on the assumption that the isotopes emitted during the explosion rose to a height of about three kilometers – at other heights would have fallen into the vicinity of Cherepovets either earlier, or later. The required height could just provide the proposed 75-ton nuclear explosion.
Results of modeling the distribution of xenon isotopes over the European part of the USSR at the time of 9:00 UTC on April 29. Black circle marked Chernobyl, white – Cherepovets. (Lars-Erik De Geer et al. / Nuclear Technology)
In addition, physicists give three more indirect evidence in support of their hypothesis. First, after the explosion, it was discovered that in the southeastern quadrant of the reactor core a two-meter serpentine plate disappeared, encased in an iron shell about four centimeters thick.
Further observations showed that it was melted by thin directional flows of high-temperature plasma, which could have formed as a result of a nuclear explosion.
Secondly, immediately after the accident, seismologists recorded two signals with amplitudes corresponding to two bursts of power of about two hundred kilotons and separated by a two-second interval.
In this case, the second of the explosions can be explained by the release of hydrogen, and the conventional theory of the first explosion gives a much smaller estimate for the power (whereas the nuclear explosion hypothesis seems to fit into this framework). Thirdly, several eyewitnesses claimed that they saw a bright blue flash above the reactor. On the other hand, it is known that in the case of uncontrolled nuclear reactions, due to the excitation of oxygen and nitrogen molecules in the air, a bluish glow appears.