The second tier of the internal containment shell (ICS), which refers to the main components of the nuclear power plant's safety system, was installed in the reactor building of the second power unit of Akkuyu NPP. ICS ensures protection of the reactor compartment and acts as support for pipeline penetrations and the polar crane, which is used to carry out nuclear reactor maintenance operations at the NPP operation stage.
ICS consists of steel liner, which ensures leak-tightness of the reactor compartment, and special concrete. Second tier of the ICS is a welded metal structure consisting of 24 sections, with two tiers each containing 12 sections. 6-metre-high and 5-to-7-ton sections are welded to each other and assembled into a single cylindrical structure equipped with rebars and embedded parts. The total weight of this 12-metre-hight structure is 321.9 tons, while its circumferential length is 138 metres.
Installation of an ICS tier is a complex and time-consuming operation. Installation of the second tier in the design position using Liebherr LR 13000 heavy crawler crane took 12 hours.
Upon installation of the second tier, the height of the Unit 2 reactor building rose 12 metres and reached 16.95-metre elevation. Afterwards the builders will weld the first tier and the second tier to each other and carry out additional reinforcement and concrete pouring of the shell. The thickness of concrete-enveloped walls of ICS cylindrical part will be 1.2 metres. Once installation of all components and concrete pouring of the containment are completed, it will be subjected to leak-tightness tests.
“Another important milestone of 2021 has been completed, with the second ICS tier of Unit 2 reactor compartment having been installed in the design position. Specialists have been assembling sections into single structure for several months, and prior to its installation all welded joints were subjected to ultrasonic testing to conform that there were no any defects. The internal containment shell tier pre-assembly technology proved itself during construction of Leningrad NPP-2. We used this method to install the second tier and the third tier of ICS at Unit 1. The technology allows to improve the precision of structure assembly and to reduce construction periods of power units, as well as complies with the occupational safety assurance principles, since it implies a reduced number of installation operations at height. There are ongoing works to build the reactor shaft in the Unit 2 reactor building. Floors are being reinforced in the turbine building," emphasized first deputy CEO and director of the NPP under construction Sergei Butсkikh.
The internal containment shell sections were manufactured at a steelworks in Leningrad region (Russia). Separate sections were delivered by sea from Saint Petersburg to the Akkuyu NPP construction site where they were assembled into a single tier. Pre-assembly of the ICS second tier sections for Unit 2 started in mid-April 2021.
Rector buildings of Akkuyu NPP Power Units are equipped with two-layer containment shells. The external containment is built of reinforced concrete and designed to withstand any extreme external impacts, such as magnitude 9 earthquakes, tsunami, hurricanes, as well as their combinations.