Welding of the main coolant pipeline has been completed in the reactor
compartment of Unit 2 of the Akkuyu NPP (being built by Rosatom State
Corporation). Thus the reactor, steam generators and reactor coolant pumps are connected
in the primary circuit system.
Main coolant pipeline (MCP) welding has been completed for 73 days. Within the period welding works were performed at all 32 pipeline joints. Engineers, welders, fitters, pipe cutters, flaw detection and heat treatment specialists, quality control service employees were engaged in the works. All stages of the operation were performed according to the strict process sequence.
Welded joints were subject to thorough control during welding, and the specialists proceeded with a next stage only after the positive results were obtained. All joints have undergone a high temperature treatment necessary for relief of the internal stress in metal and ensuring the design-basis operating characteristics. Special surfacing was applied on the internal surface of joints in order to protect the pipeline against corrosion. Following the completion of process operations, the quality of welded joints was thoroughly checked by using various methods of control, including ultrasonic, penetrant and radiographic testing.
"Welding of the main coolant pipeline is one of the most critical process operations during the Power Unit construction. It has been completed for 73 days at the second Unit, which means a good job that was well-orchestrated within the team of experienced professionals. The quality was the main criterion at every stage. Having completed welding of MCP, we formed the Unit's primary circuit and created conditions for further piping installation on the equipment of the reactor plant and preparation of start-up and adjustment works", noted Akkuyu Nuclear JSC Chief Executive Officer Sergei Butckikh.
The main coolant pipeline is the key component of a reactor plant. Demineralized water with
the temperature of up to 330 Co at the pressure of about 160 atmospheres will
circulate in the pipeline during operation; this is why the quality of
installation and welded joints matters that much. The total length of MCP pipes
exceeds 150 meters; the wall thickness is 70 millimeters. The main coolant
pipeline is intended for the coolant circulation between the reactor, steam
generators and reactor coolant pumps. In the process of power unit operation, the
primary circuit coolant transfers thermal energy through the heat exchanging
surfaces of steam generators to water of the secondary circuit, where steam is
generated for the turbine generator operation.
Akkuyu NPP is the first nuclear power plant being built in the Republic of Türkiye. The Akkuyu NPP project includes four power units equipped with Generation 3+ VVER reactors of Russian design. The capacity of each power unit is 1200 MW. Akkuyu NPP is the first project in the global nuclear industry being implemented according to the Build-Own-Operate business model.
