The scene of a nuclear disaster in 1986, the Chernobyl plant in Ukraine is still the subject of increased surveillance by scientists.
However, they have recently observed an increase in nuclear fission reactions which questions them.
Europe 1 takes stock of what we know.
DECRYPTION
What is happening at the Chernobyl plant in Ukraine?
35 years after the nuclear accident, researchers recently revealed that nuclear fission reactions under the concrete slab covering the reactor that exploded on April 26, 1986 have increased.
These are sensors, placed above the concrete screed covering the gutted reactor that gave the alert on this abnormal activity.
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An increase of 40% compared to 2016
Concretely, these sensors reveal an abnormal rate of neutrons.
These are emitted by the mixture of debris and radioactive material with an increase of 40% compared to 2016. The situation strongly questions scientists.
At the microphone of Europe 1 Friday, Igor Le Bars, who works at the Institute for Radiation Protection and Nuclear Safety, believes that this increase in activity could come from water infiltration in the reactor.
"The water, on the neutrons, will have the capacity to modify their energy and facilitate all these multiplication phenomena", he explains.
"This is why one of the questions that arises today is whether there are variations in humidity which cause this neutron multiplication capacity to increase or not."
Towards more sensors to better monitor the situation?
The building being condemned under an enormous sarcophagus, it is impossible to really know what is going on there.
A priori, there would be no risk of a nuclear explosion, but experts specify that it is necessary to install new sensors as soon as possible to monitor the situation as closely as possible over the coming months.