Inspectors from the International Atomic Energy Agency (IAEA) arrived on Wednesday, August 31, at the site of the Zaporizhia power plant in Ukraine to check its operating condition, while it is the target of bombardments. since weeks. A situation that fuels the fears of the international community and has revived the specter of a nuclear disaster.
Emmanuelle Galichetteacher-researcher in nuclear physics at the National Conservatory of Arts and Crafts (CNAM), answered your questions about nuclear site safety and the role of IAEA experts.
Rico: What is the purpose of the mission of the IAEA experts? Why are they going there?
The purpose of the mission of the experts of the International Atomic Energy Agency (IAEA) is technical. It will carry out a general inventory of the facility (safety systems, radioactive waste storage site, etc.) and also check the operator’s working conditions. It is important that they go on site, because it will be the first time that we will have an independent assessment of the state of the installation. Finally, we will have an objective technical inventory.
Saxifrage: I was wondering about the security safeguards for IAEA agents: are they well defined? Because these agents, who are only civilians, still take great risks by going to a conflict zone.
You’re right, they take great risks. We must underline their immense courage. However, I think that the two belligerents have no interest in putting the experts in a perilous situation. They are totally neutral and pursue a technical and support mission. If they left, it was because the security conditions were met.
Jacques68: Wouldn’t it be possible to determine the perimeters of no man’s land around all the nuclear power plants on the planet?
If I understand your question correctly: would you like to have a security perimeter around the plants? It already exists. In addition, the international legal framework (Geneva Convention and its additional protocol) stipulates that nuclear installations must not be targeted in war. I think that international bodies will reflect on more important obligations in the future.
Pierre: What information do we have on the state of the plant? How to be sure that there are not already radioactive leaks?
There is a European watch on the release of radioactivity into the atmosphere. In France, the Institute for Radiation Protection and Nuclear Safety (IRSN) is responsible for this. The Zaporizhia power plant is part of the monitoring zone. So there are radioactivity measurement captures all around the Zaporizhia power plant and in Ukraine. Therefore, if there is even an infinitesimal increase in radioactivity, IRSN will see it and inform the authorities. For the moment, the information we have on the state of the plant allows us to say that there has been no abnormal release of radioactivity.
Cam: Concretely, what happens if there is an accident? How real/significant is the risk?
The risk of a major accident at the Zaporijia power plant is a core meltdown accident if it loses all of its electrical power supplies. This is the most important risk that exists in terms of dangerousness. However, it is very unlikely, because the plant has twenty generators with approximately one week to ten days of fuel autonomy and five external power lines. There is therefore time to react on this point.
In the case of the core meltdown accident, it seems to me very unlikely to have the creation of a radioactive cloud. The corium (mixture of molten fuel and metallic fuel support structures in the core) is very highly radioactive and toxic. It can pierce the civil engineering under the heart, if nothing is done. At the time of the Fukushima accident (the closest one could imagine here), the explosion was due to hydrogen which in contact with air can ignite and explode. From the REX [retour d’expérience] made it possible to add hydrogen recombiners in the containment building. So the risk of explosion seems totally improbable to me.
The other risks, it seems to me, are on open-air radioactive waste storage areas. Their radioactivity has greatly diminished. It is for this reason that they are in the open air. If the very robust containers in which they are stored were to give way, there will be a dissemination of radioactivity around the storage area. Again, no radioactive clouds in the upper atmosphere.
Guigui38: In the event of a nuclear accident at the Zaporijia plant, what would be the impact on the populations around the plant, as well as on the French population? Can we prepare for such an accident? And how ?
I think that the French population has nothing to fear. We are far from Zaporizhia. For the populations around the plant, if it happens that, despite all the defense barriers of the plant, there is a release of radioactivity, it will be necessary to shelter the population and take iodine tablets. But again, it seems to me highly unlikely. The two belligerents know the plant perfectly and have no interest in there being an accident. It is a young plant that produces a lot of vital electricity for everyone.
CR: The concordance between the mission of the IAEA and the Ukrainian counter-offensive is troubling. How to ensure that it is independent and not instrumentalized? What nationalities are these members?
I am not an expert in geopolitics. The nationalities of the members of the mission are public. I know there is no American or English. A Frenchwoman is part of the mission. All of them are IAEA employees and in no way represent their country. The IAEA is completely neutral.
Terry: For whom is the report that will be made by the IAEA following their inspection intended?
The report will be public. It is extremely important. This gives confidence in the neutrality of the Agency. Its director, Rafael Grossi, is very keen on it. He repeated several times the quality of independence of the IAEA.
Claire: Can the IAEA’s mission impose changes in the governance of the plant? Can it request or impose a withdrawal of Russian soldiers and all their equipment stored in the plant?
The mission of the IAEA is technical. Its purpose is to avoid a nuclear accident. I don’t think she can demand such things. However, I think that the moral and charismatic weight of its director will calm the two belligerents.
Julien: If one day such a conflict were to occur in France, are our power stations designed to withstand bombardments?
No demonstration of safety in the world has taken into account a situation of war. However, the containment enclosures of the French and Ukrainian power plants are sized to withstand aircraft crashes, earthquakes, falling lightning, etc. Those of Zaporijia are made of pre-stressed reinforced concrete one meter thick and have a metal sealing skin. Experts believe they must withstand a certain number of missile strikes.
I think that the protections of the French power stations (like those of the Ukrainian power stations) make it possible to rule out possible degradation of the reactor building and a disaster scenario with the release of radioactivity outside the building in the event of firing.
Filou: What differentiates Zaporizhia from Chernobyl from the point of view of nuclear safety?
There are a lot of differences between the two plants. It is not the same sector since Chernobyl is a graphite sector and Zaporijia a light water sector. In terms of safety, and without going too much into the details of core physics:
- no containment at Chernobyl;
- the insertion time of the control rods (which make it possible to stop the fission reactions by absorbing the neutrons, particles essential to the chain reaction) too long at Chernobyl;
- no graphite that can ignite in Zaporizhia;
- in Chernobyl, the reactor dated from the 1970s, and that of Zaporizhia dates from the mid-1980s. So all nuclear safety is better considered as experience feedback is taken into account;
- Zaporijia also benefited from the feedback from Fukushima and, in particular, the addition of redundancies on safety systems, hydrogen recombiners, modifications for earthquake resistance, etc. ;
- a more technical argument: the positive temperature coefficient at Chernobyl, whereas it is negative in the light water power plants. This allows the fission chain reaction to be stifled in a natural way in the event that it is negative. A positive coefficient means that as the core temperature increases, the power increases and so on. This is not an interesting feature from a safety point of view.
Xji: You seem very optimistic… Shouldn’t we precisely work on highly improbable scenarios? And therefore the most catastrophic.
You are right ! I think that the world’s safety authorities will quickly take into account the feedback from this unprecedented situation. I will not be surprised if future safety demonstrations will take into account the risk of war. Anyway, I think it’s necessary.
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