The Ukrainian Nuclear Society held a roundtable with the European Nuclear Society on radiation and nuclear safety of the Shelter at the 6th International Conference INUDECO 2021. More than 200 foreign scientists joined the discussions. The information on nuclear safety discussed during the scientific disputes was published in the Science Article https://www.sciencemag.org/news/2021/05/nuclear-reactions-reawaken-chernobyl-reactor and received wide media coverage.
In this regard, the Ukrainian Nuclear Society received numerous questions concerning the risks posed by the changed nuclear safety conditions of the Shelter. The questions concerned both the recorded changes in the neutron flux in one of the least examined premises of the Shelter (room 305/2), as well as availability and reliability of nuclear safety monitoring system of the Shelter.
According to the experts’ communication from the Institute for Safety Problems of NPPs of the NAC of Ukraine a gradual increase in neutron flux density could be observed during the last four years at the periphery of the accumulations of fuel containing materials in room 305/2. The increased neutron flux density confirms the hypothesis of the ISPNPP experts that the neutron flux density would change under the different moisture conditions in the fuel containing materials accumulations and the resulting change of the multiplying medium properties.
In 2016, the New Safe Confinement (NFC) was installed over the Shelter that prevented penetration of atmospheric precipitations inside the Shelter. As a result, the process of evaporation and loss of moisture from the porous structure of lava-like fuel containing materials started, which led to the recorded increase in the neutron flux density.
Thus, the present experimental data obtained over the last years only substantiate the conservative scientific hypothesis developed by the experts of the IPSNPP even before the completion of the NSC.
The hypothesis of the ISPNPP experts have been publicly discussed starting from 2016 and were published several times in the national and foreign scientific magazines (e.g., “The Shelter under the conditions of the new safe confinement” V. О. Krasnov, А. V. Nosovskyi, S. А. Paskevych, V. М. Rudko; under general editorship of А. V. Nosovskyi. ISPNPP NASU. Chornobyl. 2021 – 344 p) and reported at international scientific conferences.
Today, the increase in the neutron flux density does not exceed the established safety limits controlled by the standard nuclear safety monitoring system (NSMS IAMS) and is of multiannual nature according to the conservative model.