Installation and tensioning of internal containment tendon strands is under way in the reactor building of the first power unit of LNPP under construction. The strands are laid into special openings called tendon sheathing and go around the inner containment in vertical and horizontal directions.
Steel fibers
The tendon strand system is part of an overall safety system of the reactor building. The system is called “unbonded tensioning system”. Should there be an excessive pressure inside the inner containment sealed volume during any potential emergency situation, the pressure will be taken not only by the concrete containment, but also by the system of tendons. This will allow to equalize the pressure inside the inner containment sealed volume.
Diameter of each strand is 15.7 mm. Maximum load it can withstand is 30 tons. Total load for a tendon (a bundle of strands) is 1200 tons. One tendon consists of 55 strands. Average length of horizontal tendon is 1408 meters, whereas the length of the vertical one varies from 140 to 180 meters depending on its trajectory.
All in all the cylindrical part of reactor inner containment contains 63 horizontal ducts, the dome contains 13 ducts. Horizontal ducts go from level +1,000 and then are spaced at intervals of one meter to envelope the cylindrical and dome parts entirely up to level +58, 000.
There are 50 vertical channels. All of them are already tensioned and fastened with lock-off wedges. Now specialists are laying down and tensioning the horizontal strands. They use special jacks for 55 strands.
Tensioning System
The tendon sheathing in which the tendons are laid were manufactured during the construction of the reactor inner containment. They were installed progressively as the grouting of the containment was advanced, the duct form proper being assembled with pipes.
Tendon sheathing are assembled either of steel shaped pipes, or of corrugated steel pipes. The rigid pipe has a diameter of 211 millimeters, the corrugated: 204 mm.
The strands were brought in using different methods. Vertical tendons were brought in one by one from the top point. The horizontal were brought in with the use of a special pushing tool, one strand at a time.
At present vertical strands have been completely laid. Also nearly all horizontal strands have been tensioned. The works at the facility are scheduled to be completed in the end of December.
Note:
The Holding “Titan-2” is the largest in the North-West group of companies, erecting the most important objects of the nuclear industry and energy. The organization performs a full range of construction and installation works from engineering to commissioning.
The Holding “Titan-2” is one of the main contractors for the construction of power units No. 1 and No. 2 of the Leningradskaya NPP-2. Main organizations of the company perform 30% of general construction and 80% of installation works on the site. Specialists of the holding are engaged on the objects of the Leningradskaya NPP-2 first and second power units. The works are being performed in the buildings of the reactor, turbine, electricity, water, heating system and other structures of power units.