Pursuant to the findings of the Commissions, which were investigating the occurrence causes, this incident “did not create the hazard to health and life, did not create the hazard to the environment, did not result in stoppage of production work and is not considered as an accident”.
The Commissions consider that the possible cause of the collapse of Turbine Hall roof fragment and eight wall panels became the collapse of a truss due to combination of negative factors, namely: lack of data on actual damages of the truss and roof decking during the accident of 1986, as well as because of the fact that structures of the additional roof are rested upon the deaerator stack’s columns, which undergone the heavy destructions during the 1986 accident.
Some other negative factors are also given in the findings. At that the experts emphasize that the snow load on the Turbine Hall roof as of the date of the collapse did not exceed the values established by the ChNPP design and operational documentation. “The main cause that made it impossible to prevent the collapse of the specified structures was absence of the possibility to carry out visual inspection of technical state of the structures due to the absence of safe accesses and very hazardous radiation situation” – emphasized in the Commissions’ findings.
In general the experts draw a conclusion on relative stability of the bearing structures adjacent to the collapsed one, and the possibility of their further use provided that the roof is reconstructed.
It is recommended to carry out a survey of Unit 4 Turbine Hall structures involving specialized organizations with the purpose to obtain reliable data on technical state of the structures similar to the collapsed one with the subsequent implementation of technical solutions on reduction of the probability of the collapse of the Turbine Hall bearing structures.
The experts also recommend dismantling the collapsed wall panels in two stages with the purpose to exclude overload of the structures, and reconstructing the collapsed roof section with the purpose to close the containment facility ambit, exclude spread of radioactive substances into the environment and prevent penetration of atmospheric precipitations into the Turbine Hall premises.
