The outer containment (OC) is one of the physical barriers that protect the reactor plant from extreme external influences, which is a reinforced concrete structure. In addition to the outer, there is an internal protective shell that provides reliable protection for personnel, the public and the environment. Its construction was completed in October 2022. Double containment is a distinctive feature of the Russian design of power units with PWR-1200 and PWR-TOI reactors, which provides the maximum level of nuclear power plant safety.

The process of erecting the dome of the NZO takes place in several stages: the manufacture of the constituent elements of each of the six tiers, then their installation and phased concreting. The protective shell has a height of 65.4 meters, a diameter of 26.9 meters, and a wall thickness of 1500 millimeters. The full cycle of construction work was completed in 206 days. In total, about 4,000 cubic meters of concrete were placed in the dome.

“Concreting of the OC dome is the final stage in the construction of one of the physical barriers of the nuclear power plant's defense in depth. We used self-compacting concrete, capable of spreading under gravity, filling the mold and achieving full compaction even in heavily reinforced structures. The mixture ensures fast laying, speeds up construction time and is evenly distributed in the reinforced concrete structure,” explained Andrey Osharin, first deputy director for the construction of new blocks. — Concrete's fluidity and resistance to delamination provide a high degree of uniformity, and minimal voiding, as well as the possibility of obtaining high-quality surfaces and durability of the structure. The concrete used has a low water-cement ratio, which contributes to the acceleration of strength development and the dismantling of the formwork at an earlier time.”

Taking into account the high safety requirements for the main building of the replacement station, the specialists of Trest RosSEM LLC controlled the quality of the concrete mixture throughout the entire period of concreting. Completion of the concreting of the OC allows us to say that today the reactor building has almost reached its design dimensions. Next, the contractors will proceed with the installation of the deflector and air ducts of the passive heat removal system (PHRS).