The international service of Czech Radio 
29-11-2020, 11:15 UTC

Current state of the Object 'Shelter'
In the more than 20 years since the accident no more than 60 percent of the Shelter rooms have been surveyed. The surveying of residuary premises is impossible because of high radiation areas or impenetrable obstructions, which are caused by the structural collapses and the generation of lava-like fuel containing materials. There are also several rooms that were filled with concrete during the Shelter construction.
The lack of knowledge of large portions of the Shelter contributes to some of the most serious risks today. It is estimated that the Shelter still contains about 95% of the fuel. At present, the total activity is about 16 million curies. The main hazard represents the potential dust generation from irradiated fuel and the lava-like fuel containing materials. Dust is generated on the surface of the irradiated fuel and released outside the Shelter by its ventilation system. There can be approximately 4 tons of radioactive dust in the Shelter. Because of impossibility to inspect the damaged structures used as the supporting elements, the precise assessment of their actual bearing capacity and durability is not known. The structures are exposed to atmosphere impacts and there is high humidity in the Shelter. The water corrosion is causing the progressive destruction of the concrete structures.