Many nuclear reactors
Ukraine has fifteen reactors currently in working order, relatively recent.
It is the seventh largest producer of nuclear electricity in the world, according to data from the International Atomic Energy Agency (IAEA) for the year 2020.
It is also one of the countries most dependent on nuclear energy, with more than 50% of its electricity coming from this energy.
These are Soviet-designed and then Russian-designed VVER-type reactors using two different technologies, respectively 440 and 1,000 MW.
VVERs are pressurized water reactors, like those installed in France.
Six reactors are grouped together in the largest nuclear power plant in Europe in Zaporozhye, in southern Ukraine, hit overnight by bombardments which caused a fire.
They were put into service between 1984 and 1995.
The plant is of "relatively modern" design, says Mark Wenman of Imperial College London.
"The design is very different from the Chernobyl reactor, which had no containment enclosure" to protect the reactor, he notes.
The Ukrainian electrician Energoatom also recently turned to the American Westinghouse to build new power stations in the country.
The choice of nuclear power notably reflects the fact that the country has significant uranium reserves.
It also had significant energy needs at the time of the USSR, including large industries in the Donbass region.
The Chernobyl disaster
In addition, the country also has the reactors at the Chernobyl site, which were shut down after the 1986 disaster, the most serious in the history of civil nuclear power.
Reactor No. 4, damaged, was first covered in an emergency by a temporary sarcophagus then by a containment arch completed in 2017. But the current reactors are of a different technology deemed safer.
The Ukrainian authorities recently noted an increase in radiation at Chernobyl, but the IAEA considered that the measured values presented "no danger to the public".
Experts have speculated that a rise in radioactivity caused by the military bustle may have turned the earth and stirred up contaminated dust.
The development of nuclear power in the country began in the 1970s with the construction of Chernobyl.
"Even though the Ukrainian nuclear industry had close ties with Russia for many years, it remained relatively stable during the changes that took place when the country became independent from the former Soviet Union", underlines the Association World Nuclear Power (WNA).
She believes that the country has experienced "during this period and since, continuous improvements in operational safety".
Risks associated with war
The NGO Greenpeace estimates that potential damage to Zaporozhye “could result in the radioactive contamination of large European territories for decades, including in Russia”.
But so far Friday's fire has not resulted in any radioactive leaks, according to Ukraine's nuclear regulator.
"The main risk in the current situation is a loss of the electricity network, of the power supply to the plant. Because water and electricity supply are needed to operate the safety systems and cool the reactor core", emphasizes Karine Herviou, Deputy Director General of the French Institute for Radiation Protection and Nuclear Safety (IRSN).
The challenge is to avoid an accident like that of Fukushima (2011) when the means of cooling had been lost following a tsunami.
The Ukrainian reactors have emergency systems, with four emergency generators which normally have fuel to operate for 7 to 10 days.
"They also have mobile equipment on the site, water reserves, to manage the situation and normally avoid a degradation of the heart", adds Ms. Herviou.
The other risk is direct aggression.
The containment building - the large sealed concrete enclosure around the reactor - is designed to withstand the accidental fall of an aircraft.
"They offer a certain resistance but it all depends on what we are talking about. An attack can also affect a part other than the containment enclosure and create an accident if it falls on safety systems", notes Karine Herviou.
© 2022 AFP