Russians and Ukrainians are passing the buck to each other to find out who is responsible for the partial destruction of the large Kakhovka hydroelectric dam, located in southern Ukraine and fed by the Dnieper. Ukrainian authorities announced the disaster on Tuesday and, among other concerns, include the safety of the Zaporizhzha nuclear power plant. However, the situation seems reassuring on this side. "There is no risk of flooding of the plant by the dam, which is located 150 kilometers to the south," says Karine Herviou, Deputy Director General of IRSN (Institute for Radiological Protection and Nuclear Safety). The French expert confirms the information given on the ground by inspectors from the International Atomic Energy Agency, who monitor the largest nuclear power site in Europe.
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Even if this flood risk is eliminated, what about the cooling of the plant? There will probably be a decrease in the flow of the Dnieper, because of the removal of the reservoir. However, "there is no immediate risk to the cooling of the six nuclear reactors that are all shut down," continues the Deputy Director General. Of these, five are "hot" and one is "cold" stopped, meaning waste heat is still used to run generators and produce energy. But there is no longer a nuclear fission reaction in any of the reactors.
No risk is therefore "envisaged for several weeks", adds the French expert. This analysis corroborates that of IAEA experts who assured on Twitter that there is no "immediate nuclear danger".
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The level of the cooling basin has not changed "said on Telegram Yuri Chernichuk, director of the Zaporizhzhya nuclear power plant, under the control of the Russian authorities. In addition to the large water retention basin, on the site of the plant there is a second water reserve, called in the jargon "Ultimate Heat Sink", which allows it to be replenished to continue to permanently cool the six reactors. These facilities were reinforced following the Fukushima accident when extreme scenarios were imagined to increase the safety of the plants. "One of them was for the destruction of the Kakhovka dam following an earthquake," said Ludovic Dupin of the French Nuclear Energy Company (SFEN).
The water capacity on the site therefore makes it possible to last several weeks, even with a decrease in the level of the Dnieper. And in case these reserves on the site are too threatened, there could be "alternative resources," said the director of the plant. We can imagine "a supply with tanker trucks if necessary," says Karine Herviou.
It indicates, however, that another risk may arise, "the disruption of the electricity supply". Because even when shut down, the plant needs energy for the pump systems to bring water to permanently cool nuclear fuel assemblies. But even in this case, "there are 20 small emergency generators, including 4 per reactor," recalls the IRSN expert. While at the beginning of the crisis last year these generators could have provided energy for ten days, now "they should be able to operate for at least two weeks, if fuel does not run out on the site"
In this context, IRSN's reassuring analysis, in line with that of the IAEA, must temper the alarmist statements of the presidential adviser, Mykhaïlo Podoliak. "The world is once again on the brink of nuclear disaster because the Zaporizhjia nuclear power plant has lost its cooling source. And this danger is growing rapidly," said the adviser to Ukrainian President Volodymyr Zelensky, in a written message sent to journalists and relayed by AFP. Alarm bells are part of the war.