Forest fires near Chernobyl: should we worry about an increase in radioactivity?

After the power cuts, the fires? According to New York Times, several small fires were spotted earlier this week in the forest near the Chernobyl nuclear power plant. Even if according to the Ukrainian authorities, the latter now seem extinct, the incident revives fears of the suspension of radioactive particles. Especially since the firefighters cannot intervene normally because of the presence of the Russian military. L’Express takes stock of the risks with Marc Gleizes, deputy director of the environment at IRSN (Institute for Radiation Protection and Nuclear Safety).

L’Express: This is not the first time that forest fires have affected the exclusion zone. What do studies say about the risk of resuspension of radioactive particles?

Marc Gleizes : Indeed, the Chernobyl exclusion zone is regularly the prey of flames. We remember, for example, the very important fire of April 2020 which lasted one month. However, we also recorded fires in 1992, 1999, 2000, 2002, 2004, 2006, 2015, 2016 and 2018! Each time this type of event occurs, the heat and smoke lead to the resuspension of radioactive particles due to the contamination of the ground near the plant. Fortunately, the consequences for France remain minimal, and weak for the firefighters intervening on the spot.

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After the fire of 2020, we noted in France, 2 microBecquerels per cubic meter. This is four million times less than the levels measured in 1986 after the nuclear accident in Ukraine. This result is explained above all by the fact that the explosion of a reactor releases much more energy – and therefore particles – than a forest fire. The dispersion of radioactivity in the atmosphere also protects us: air masses rarely move in a straight line over long distances. Then, several thousand kilometers separate the two countries. Finally, some particles fall to the ground depending on weather conditions. So only a part continues on its way and crosses the borders.

Is there a health risk for the local population?

Not if we refer to our calculations, carried out during the fire of 2020. At the time, the risk of exposure of firefighters, in particular by the inhalation of radioactive particles, was not negligible but it did not exceed regulatory thresholds. However, the situation seemed much more serious: 800 square kilometers of forest went up in smoke, including about 65 in the Chernobyl exclusion zone. Today, if we are to believe the news from Ukraine, only a few square kilometers seem concerned. The exposure levels involved are therefore much lower.

Has the radioactivity of the waste stored at Chernobyl decreased significantly since 1986?

Not really. Some elements, such as cesium 137 or strontium 90, see their radioactivity halve every thirty years. But others, like plutonium, have much longer lifespans. This is also the reason why a network of sensors monitors the situation on site. Certainly, since the Russian forces control the plant, the data no longer reaches us. We therefore remain on the alert, checking the filters of our own installations, and analyzing the information that comes to us from other countries. Switzerland and the Czech Republic, for example, do not report any abnormal increase in radioactivity. However, these two territories are located a priori on the trajectory of the discharges caused by the fire in Ukraine. The latter therefore seems to have an infinitesimal effect.

So the highest risk in Chernobyl remains that of another power cut at the plant?

During the recent outages, we asked ourselves the following question: can the loss of the electricity supply lead to a significant increase in the temperature of the water in the basin used to cool the spent fuels? If this is the case, there could be an evaporation of the liquid and the combustibles would end up in the open air.

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However, simulations carried out after the Fukushima incident – including at Chernobyl – show that the temperature of the swimming pool would probably not exceed 60°C, even in the event of a prolonged “blackout”. In addition, there are emergency diesels that can supply energy to the cooling system. We can therefore consider that the situation on the spot remains under control.