Welding of the main circulation pipeline (MCP), which connects the reactor, steam generators and main circulation pumps into a single primary circuit system, has been completed at unit 2 of the Akkuyu NPP under construction in Türkiye. The welding of the 32 pipeline joints involved engineering and technical specialists, welders, installers, pipe cutters, flaw detectors, heat treatment specialists, and quality control service employees. All stages of the operation were carried out in strict technological sequence.
During the work, the welded joints were subjected to careful control, and only after receiving positive results did specialists move on to the next stage. All joints underwent high-temperature heat treatment, necessary to relieve internal stresses of the metal and ensure design performance characteristics. A special surfacing was applied to the inner surface of the joints to protect the pipeline from corrosion. On completion, the quality of the welded joints was carefully checked by various inspection methods, including ultrasonic, capillary and radiographic measures.
“Welding of the main circulation pipeline is one of the most important technological operations during the construction of a power unit,” said Sergei Butskikh, Director General of project company Akkuyu Nukleer. “At the second unit, it was completed in 73 days – this is a worthy result achieved thanks to the precise organisation of work and the coordinated actions of an experienced team of specialists. At the same time, quality remained the main criterion at each stage.”
The MCP ensures the circulation of the coolant and its welding is one of the most important operations during the plant construction, explained Sergey Kizhapkin, head of the production coordination department of the Main Machinery Room and Engine Machinery Room at T2IC (Titan-2 IC İçtaş İnşaat Anonim Şirketi – a joint venture between Russia’s TITAN-2 and the Turkish IC İçtaş construction company). “All connections were carried out according to approved technical processes and underwent strict multi-level control, including non-destructive diagnostics. Thanks to the professionalism and well-coordinated work of specialists, we completed this stage ahead of schedule.”
During operation of the power unit, the primary circuit coolant transfers thermal energy through the heat exchange surfaces of the steam generators to the secondary circuit water, where steam is generated for the operation of the turbogenerator. During operation, the pipeline will circulate desalted water at temperatures up to 330 degrees Celsius under a pressure of about 160 atmospheres, so special requirements are placed on the quality of installation and welded joints. The MCP is more than 150 metres long with a wall thickness of 70 millimetres.
The Akkuyu NPP will eventually host four Russian-designed VVER-1200 reactors. The pouring of first concrete for unit 1 took place in April 2018, for unit 2 in June 2020, for unit 3 in March 2021, and for unit 4 in July 2022. Rosatom is constructing the reactors according to a build-own-operate model. Work continues at the facilities of all four units and auxiliary structures as well as a new town for plant operators. Unit 1 is due to launch by the end of 2026.
