Rosatom specialists have begun assembly of the first tier of the internal containment (VZO – Vnutrennei Zatsitnoi Obolochki) for unit 7 of the Leningrad NPP (also known as Leningrad-II unit 3). In total, they will have to mount and weld 24 steel grades together, as well as supplement the resulting frame with hermetic penetrations and other elements.
Currently Leningrad NPP has four units in operation – units 3&4 with Soviet RBMK-1000 reactors, as well units 5&6 with new VVER-1200 units (also known as Leningrad-II 1&2). Units 5&6 replaced units 1&2 with RBMK-1000 reactors, which were decommissioned in 2018 and 2020. New VVER-1200 units (7&8) will replace units 3&4.
“Today we are developing the first security system for the future power unit. We have almost 2.5 years of hard work ahead of us,” said Leningrad NPP Director Vladimir Pereguda. “During this time, it is necessary to erect a powerful prestressed reinforced concrete structure lined with steel, which will safely cover the reactor installation and maintain the tightness of the internal space of the reactor building during all operating modes. At the same time, we will complement the inner protective shell with the outer one. It will protect the reactor and other important equipment from external influences – natural and man-made. Because of the double protective shell and a number of other active and passive safety systems, the new facility will be absolutely safe for people and the environment.
For assembly of the VZO, builders use a special slipway 12 metres high and 44 metres in diameter. It was installed in advance in the immediate vicinity of the reactor building. It will be used for assembling and welding all cylindrical parts of the shell. Before creating the dome structures of the reactor building, the slipway will be transformed in line with the shape of the building.
Assembly on a slipway is an industrial construction method that proved itself during similar work at the first stage of VVER-1200 construction at the Leningrad NPP. Today it is replicated at other nuclear construction sites in Russia and abroad. The slipway makes it possible to avoid undertaking installation and welding operations at height. This means that the work will be carried out without unnecessary labour costs, with high quality, high productivity and safely.
Installation of VZO structures will be carried out 24/7. Workers pay special attention to the geodetic accuracy of installation as well as the quality of their welded joints. Each joint will undergo double inspection; it will be checked by both specialists from the general contractor’s laboratory and the customer’s quality control officials.
Considering the importance of the VZO during operation of the power unit, highly qualified specialists are involved in their assembly and welding: most have already performed similar operations at the currently operating units 5&6 at the Leningrad NPP and at the units of the Akkuyu NPP under construction in Türkiye.
Installation of the first tier of the unit 7 VZO should be completed in early autumn. A special multi-vector traverse and a heavy crawler crane will be needed. The traverse will be manufactured and tested, and the crane will be assembled and tested by the end of August. The next stages will see the remaining tiers of the cylindrical and dome parts of the VZO manufactured, mounted, installed and concreted.
Read also: Leningrad 7 assembly starts
