The second layer of the inner protection shell (IKK) was installed in the reactor building of the second power unit of the Akkuyu Nuclear Power Plant (NGS). IKK, which is one of the main elements of the safety system of the nuclear power plant and ensures the protection of the reactor building, acts as a support for the pipe and polar crane entrances. In this way, the maintenance operations of the nuclear reactor are carried out during the operation phase of the NPP.
The IKK consists of a steel layer and special concrete that seals the reactor building. The second layer of the IKK has the distinction of being a welded metal construction consisting of 12 sections, two layers of 24 sections each. The 5-meter-high sections weighing between 7-6 tons are welded together and assembled into a single cylindrical construction equipped with fittings and embedded parts. The total weight of the construction is 321,9 tons, its height is 12 meters and its perimeter is 138 meters.
As the installation of the IKK layer is a complex and time-consuming technological operation, it took 13000 hours to assemble the second layer in the design location with a Liebherr LR 12 heavy-duty crawler crane.
After the installation of the second layer, the height of the reactor building of the second unit increased by 12 meters, reaching 16,95 meters. After the builders weld the first and second layers together, strengthen the shell and pour concrete, the concrete walls of the cylindrical section of the IKK will be 1,2 meters thick. After the assembly of all parts and the concreting of the protective shell are completed, a leak test will be carried out.
AKKUYU NUCLEAR INC. Sergey Butckikh, First Deputy General Manager – Director of Construction Affairs, stated: “Another important event of 2021 has been completed and the second ECC layer of the reactor building of the second unit has been installed at the design location. Specialists carried out the installation of sections into a single construction for several months, and before starting its installation, all welded joints were checked for defects by ultrasonic method. The technology of enlarged assembly of the layers of the inner protection shell has proven itself in the construction of the Leningrad NGS-2. We set up the second and third IKK layers of the first unit with this method. The technology allows to increase the installation precision of the constructions and optimize the construction time of the power units, it is also suitable for work safety as it reduces the number of installation operations at height. In the reactor building of the second unit, the construction of the reactor wall continues. The floors of the turbine building are being strengthened.”
Parts of the inner protection shell were produced at a factory located in the Leningrad Region (Russia). Independent divisions, by sea St. Petersburg, Akkuyu NPP was delivered to the construction site, where it was assembled in a single layer. The enlarged assembly of sections of the second layer of the IKK for the second unit began in mid-April 2021.
The reactor buildings of Akkuyu NPP power units are equipped with double protection shells. The reinforced concrete outer protection shell is designed to withstand earthquakes up to magnitude 9, tsunamis, hurricanes and their combinations.