Media says nuclear reactions at Chornobyl still smoldering. Is there any danger?

In May 2021, media outlets reported that nuclear reactions at the Chornobyl nuclear power plant were still smoldering. Such articles appeared in both Ukrainian and foreign media; most of them referring to a Science article. It says that fission reactions in uranium fuel are “smoldering like coals in a barbecue” and scientists are recording a rising number of neutrons.

The tone of these reports varies from restrained, “Nuclear processes at Chornobyl have resumed, but there is no danger,” to alarming, “Scientists are talking about a new disaster at Chornobyl.” Headlines of foreign articles also look a little scary. All this began against the backdrop of a recent surge of interest in the Chornobyl disaster due to it being 35 years since the accident happened this past April.

Specialists at the Institute for Safety Problems of Nuclear Power Plants of the National Academy of Sciences responded with a detailed explanation of what is happening and why in the restricted areas of the ChNPP now and how dangerous it is. The Institute is a scientific institution that has been studying the condition of nuclear materials inside the Chornobyl nuclear power plant since the first years after the accident. Here are the main theses from this commentary:

• After the installation of the Arka confinement (NSC) (an isolation structure over the destroyed fourth power unit – Ed.), for about four years, an increase in the neutron flux density at the periphery of the accumulation of fuel-containing materials (FCM) has indeed been observed. It is located in one of the sub-reactor rooms of the Shelter (room 305/2).
• But today, this growth does not exceed the established safety boundaries. A nuclear safety monitoring system monitors these boundaries.
• The experts of the Institute predicted an increase in the neutron flux density back in 2015 because precipitation will no longer fall into the middle of the Shelter after the installation of the Arka NSC. So the current data confirm the scientific hypothesis of the institute, formulated even before the construction of the NSC.
• This hypothesis assumes that room 305/2 has two waterlogged FCM with an increased concentration of material that is being split. Potentially dangerous can be the southern accumulation of FCM, with a two-layer porous structure: the upper layer, consisting of black lava-like FCM and the lower one, with a high concentration of hazardous nuclear materials.
• Before installing the NSC, the dynamics of the neutron flux were kept within the range of seasonal trends: water from precipitation and condensate was getting into the room. After the installation of the NSC, the FCM began to evaporate and lose moisture, which led to an increase in the neutron flux density.

• The experts of the Institute predict that the increase in the neutron flux density will continue to be observed. They emphasize that the FCM condition needs to be studied thoroughly. For this, they have already developed an FCM monitoring program for the Shelter. But today, no resources are allocated for this program (i.e., there is no financing).