Completion of this task significantly improves fire safety of the New Safe Confinement.

The sections of potentially inflammable roof of Turbine Hall located in the area of Arch End Walls within axes 60-62 and 38-40 were dismantled under the project of NSC enclosing perimeter which was completed by construction at the end of 2017.

In the first half of February 2018, three sections within axes 52-54, 56-58 and 60-62 were dismantled. Consequently, the whole area of the roof defined by the design was dismantled.

The work was carried out with two cranes whose lifting power makes 300 and 270 tons. One of them was positioned on the pioneer wall and the other one - to the north of Shelter Deaerator Stack within the NSC temporary storage area.

Currently, the activities associated with cutting the dismantled structures and their removal to specially equipped area for their storage are underway. The dismantled slabs are decontaminated if necessary.

As of February 15, 2018, about 15 % of the dismantled slabs have been removed.

During the work period, the reference levels of external exposure (13 mSv) established for the NOVARKA (Contracting organization) personnel were not exceeded. No emergencies or incidents were recorded.

For information. The necessity to dismantle the light roof was determined by the safety document within the Concept Design of NSC first Commissioning Stage.

It was established that the major fire that can occur within the under-the-arch space is the combustion of the Turbine Hall and Deaerator Stack roof.

To ensure the fire safety and to prevent fires, the design provides for the covering the deaerator stack roof with light concrete mix layer of 50…150 mm thick.

It is decided to equip the Turbine Hall roof with a special system for fire detection and extinguishing. Technical solution for establishing this system has been approved within NSC design. The system includes the tanks for keeping foam-forming mixture, pumping equipment, pipelines and three foam extinguishing towers of about 30 m high. There are foam-generators and thermal imaging camera for detection of potential ignition at the early stages on these towers.

The Turbine Hall roof due to 1986 accident has two layers: potentially inflammable pre-accident layer and protective steel post-accident one. To ensure the access of foam mixture to the ignition source it was necessary to dismantle the steel panels of post-accident layer.

In order to reduce the radiation exposure of the personnel as well as the volume of the radioactive waste it was decided to dismantle not the whole roof but its separate sections at 12 m intervals (every other span).