The Director General of the International Atomic Energy Agency (IAEA), Rafael Mariano Grossi, denounced a « violation » of one of the fundamental pillars of nuclear safety but affirmed that this cut had not, at this stage, “of major impact”.
Currently, 20,000 spent fuel assemblies are stored in the site’s storage pool. After being used in a reactor, the spent fuel is still radioactive and releases heat: it is then stored in a “pool” – a basin filled with water – to be cooled. Once its radioactivity and thermal power have decreased sufficiently, after a few years, it can be transported and transferred, in general, to dry storage sites.
The power supply is needed for the pool water, which may contain small amounts of radioactive isotopes, to be pumped and cleaned, and for reintroducing cold water. Without power, the water will heat up and could, in theory, start to evaporate, as well as certain radioactive isotopes present in the water.
At Chernobyl, however, spent fuel, which was being transferred to dry storage, had decades to cool. Due to the time that has elapsed since the 1986 nuclear accident at Chernobyl, “the heat load of the swimming pool and the volume of the cooling water are sufficient to ensure efficient heat removal without electricity”, assured the IAEA. The assessment of the UN nuclear “gendarme” is “understandable given the age of nuclear fuel”and that “significantly reduces the risk of contamination inside the building”reacted on Twitter Claire Corkhill, professor at the University of Sheffield (United Kingdom), specialist in the degradation of nuclear materials.
In a note on the situation in Ukraine published on February 25, the Institute for Radiation Protection and Nuclear Safety (IRSN) also explains that the studies carried out after the accident at the Fukushima power plant in Japan on the consequences of a total loss of cooling of the pool, show a slow rise in pool water temperature (up to a temperature of around 60°C) but no uncovering of the assemblies – i.e. the fuels would still be kept under the ‘water.
If the risk of radioactive leakage therefore seems limited in the current state, the situation of the plant is no less worrying. The remote transmission of data from the radioactivity level monitoring systems is also interrupted and it is therefore impossible to follow what is happening on the spot. The IAEA also reaffirmed, on Tuesday, its concern about the situation “stressful and particularly difficult” of the approximately 200 people who work on the site, and who have not been able to leave the premises since the takeover of the area by the Russian armed forces on February 24.