The potentially inflammable roof of the turbine hall within the NSC Arch at Chornobyl NPP was dismantled. The need for this work and its scope were specified in the document on safe conceptual project for NSC Startup Stage No. 1.
The turbine hall roof at ChNPP unit 4 has two layers: pre-accident layer and protective post-accident steel one. It was established that a major fire could occur under the arch exactly resulting from ignition of the pre-accident layer in the turbine hall roof. A fire detection and firefighting system with thermal imaging cameras, foam generators and other equipment will be installed there to avoid emergencies.
The post-accident steel layer in the roof must be removed to ensure efficient performance of the system in case of fires. This will provide access of the foam mixture to the potential ignition source.
Considering that personnel had to work under complicated radioactive contamination conditions, it was decided to dismantle not the entire roof but its separate sections at 12 m intervals.
The post-accident layer specified in the design has been completely dismantled. The dismantled structures are currently being cut into fragments, decontaminated and transferred to a specially equipped storage site.
According to Chornobyl NPP website