Par Maxim T’sjoen
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On the banks of the Dnieper, the situation is untenable“. Zaporizhia, Europe’s largest nuclear power plant, has been under near-daily bombardment since the beginning of August. And with the bombs, the fear of a nuclear catastrophe.
The report of the International Atomic Energy Agency paints an extremely worrying picture: it has come out in favor of the establishment of a “ safe area » pour prevent a nuclear accident at the Ukrainian power plant.
Shelling on the site and in the surrounding area must cease immediately to avoid causing further damage to the installations.
kyiv also came out in favor of sending peacekeepers to the site.
While the plant has been occupied by Russian forces since the beginning of March, the situation there is critical.
A power plant that operates in autarky
« The control unit is completely disconnected from the network“, says Karine Herviou, Deputy Director General of the Institute for Radiation Protection and Nuclear Safety (IRSN).
Contacted by actu.fr, she explains that a bombardment on Monday September 5 led to the disconnection of the last supply linedamaged, connecting the plant to the Ukrainian power grid.
The plant operates in autarky. Reactor n°6 works, but only to meet its needs and those of the other reactors.
Indeed, although five of the plant’s six reactors are shut down, they need electricity to run the cooling pumps and cool the reactor core.
“The situation is quite fragile,” notes Karine Herviou. “Because if reactor No. 6 stops, emergency generators will have to take over to cool the reactors. »
They are 20 in number in Zaporijia, and the IAEA has communicated on fuel reserves to last ten days. ” In 10 days, it is therefore necessary to restart a reactor if possible or restore a power line. All in a difficult atmosphere“, recalls Karine Herviou.
Indeed, since the beginning of August, the bombardments around the area are almost daily while Ukrainians and Russians accuse each other.
The risk of a reactor meltdown
This is the main risk currently in Zaporizhia: a core meltdown scenario like in Fukushima.
“As in Fukushima, it is an attack external to the plant that would cut off the electricity”, analyzes David Boilley, President of the Association for the Control of Radioactivity in the West (ACRO), with actu.fr . In Japan, it was a tsunami, in Ukraine, a war.
If the power supply is cut, the reactor core could no longer be cooled and “the fuel could melt”, adds Karine Herviou. Thus, a meltdown of the core of one or more reactors would occur.
In this case, it is the water that evaporates first. The heat, which rises to 2500 degrees, melts the fuel sheath. With the water evaporating, the building is put under pressure: it must be depressurized. Then release gases (which are radioactive) via the chimneys. Otherwise the building does not hold.
“There will be significant releases of radioactivity in the building”, abounds Karine Herviou. “After all, it depends on the tightness of the building, if the heat cannot be evacuated, this will lead to significant emissions into the atmosphere. »
In such scenarios, it must also be taken into account that “the fuel sheath is made of zirconium, and that this material is a catalyst for water vapour: it makes hydrogen. If there are too many of them, there is a risk hydrogen explosion in the building, like in Fukushima”, warns David Boilley.
If the meltdown of the reactor core were to become a reality, the fallout would depend in part on weather conditions and also on the amount of radioactive releases.
In the event of a meltdown, if the building is intact, the impact of radioactivity will essentially occur over a few kilometres. On the other hand, if the building is no longer intact, then there are repercussions over tens of kilometres.
A cloud of radioactivity could indeed pass through Europe and France with this scenario, as during Fukushima. ” There were not little or no health impact“, reassures David Boilley, president of the ACRO. “There would still be radioactive fallout. »
Nevertheless, ” it is very worrying for the nearby areas« .
“For Fukushima, 150,000 people had been displaced due to radioactivity. If that happened in Zaporijia, would it be necessary to evacuate areas over tens of kilometers, in the midst of the conflict? It’s unmanageable, ”said David Boilley.
Oleg Korikov, head of Ukraine’s nuclear safety agency, warned that a nuclear accident would have “consequences not only for Ukraine, but also, clearly, consequences beyond borders”.
In addition to the risks of melting, other dangers threaten the Zaporizhia power plant.
Other buildings are bombed, some of which contain containers, which themselves contain spent fuel assemblies which are radioactive. For now, the containers have, luckily, not been damaged.
“The tank of radioactive effluents, if it were bombarded, would release radioactivity”, also quotes Karine Herviou.
She also notes that the situation of war and occupation “disturbs the operating team”. “Fatigue and stress can trigger poor handling, and the decision-making process is more difficult. »
More reassuring, the cylindrical buildings that can be seen in the photos of the plant “give the installations a certain robustness”.
Exit also the remake of a Chernobyl-style explosion. “It’s not possible,” tempers Karine Herviou. “These are completely different reactors. »
David Boilley recalls, however, that this is “the first time that there has been a high-intensity armed conflict in an area where civilian nuclear power is installed. We are not immune to a scenario that we had not imagined. »
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