INTERVIEW – Karine Herviou, Deputy Director General at the Institute for Radiation Protection and Nuclear Safety (IRSN), provides an update on the safety of the former nuclear power plant, cut off from the electricity grid.
The Chernobyl power plant, taken by the Russians at the start of the offensive, “has been completely disconnected from the electricity grid due to the military actions of the Russian occupier”, the Ukrainian operator Ukrenergo announced on Wednesday. The site “no longer has a power supply” and “there is no possibility of restoring the lines” due to the ongoing conflict, he said.
Karine Herviou, Deputy Director General in charge of the safety of installations at the Institute for Radiation Protection and Nuclear Safety (IRSN), explains the consequences that this may or may not have on the installations.
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LE FIGARO.- What is the current situation in Chernobyl?
Karine HERVIOU.- According to the information given to us, there would no longer be any electricity supply to the site via the traditional network. Generators took over but the Ukrainian nuclear safety authorities specified that there was only 48 hours of fuel autonomy. After this time, if the power is not restored, the site will be totally deprived of electricity.
What consequences could this have?
The Chernobyl nuclear power plant is no longer in operation. There were historically four RBMK reactors. After the explosion of reactor n°4 in 1986, the three other reactors were restarted before being definitively shut down, respectively in 1991, 1996 and 2000. There is therefore no longer any active nuclear core or “hot” fuel. requiring active cooling. In other words, there is no significant risk of radioactive release that would be directly attributable to a power outage.
What are the most critical facilities?
There are still 20,000 fuel assemblies with residual activity on the site. Each of these sets of pencils is almost 4m long and 20 to 30 cm in diameter. They are mostly stored in four cooling pools. Normally, heat exchangers keep the water at a given temperature. In the absence of current, the temperature will necessarily rise a little, but it should not exceed 60°C. In other words, the water is not going to boil. There is therefore no risk of “dewatering” of the fuels (that is to say that they end up in the open air, editor’s note), which could generate radioactive leaks. This therefore does not jeopardize the safety of the installation.
What about the damaged reactor?
The melted heart is under a double sarcophagus. The first, made of concrete and lead, was made in a hurry after the disaster. It has since been covered by a gigantic metal containment arch which should allow the old sarcophagus to be dismantled in complete safety. It seems that this operation has not started yet. A power outage does not represent any immediate risk for these installations. However, the monitoring sensors will no longer be powered.
How does the site monitoring network work?
There are temperature and radioactivity sensors in the cooling pools, and neutron sensors that measure the residual activity of the damaged nuclear core in the sarcophagus. Finally, there are beacons in the open air throughout the site and its surroundings to measure any possible discharge from the installations. It was the latter which had recorded a sharp increase at the start of the conflict, probably linked to the passage of Russian tanks which had raised residual radioactive dust buried in the ground, unless it was a question of malfunctions.
Is this loss of surveillance problematic?
It’s not ideal. If something serious is happening at the site, it will probably take them longer to figure out what is happening and to assess the radiological impact on the site. The only possibility is to carry out rounds, visual inspections. Without heating or lighting, the situation will undoubtedly be very uncomfortable for the staff on site.
Is the Chernobyl situation worrying for the power plants in operation?
This confirms what we already thought: rather than a direct attack, of which the Russians would also suffer the consequences, the main risk for the Ukrainian nuclear installations is an accidental loss of electrical power which could induce after 7 to 10 days loss of the fuel cooling systems present in the reactor cores and in the adjacent pools (if the site could not be refueled and the power supply could not be restored).
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