In the first power unit of Akkuyu Nuclear Power Plant (NGS), welding works for the main circulation pipeline (ASBH) of the reactor building, which is the most important phase of 2022, have started. ASBH forms the first cycle of the NPP by connecting the reactor, steam generators and main circulation pumps, which are the main equipment of the unit.
Akkuyu Nuclear Inc. Anastasia Zoteeva, Managing Director, said: “Welding in the main circulation pipeline is one of the key stages in the construction of a power unit. If the reactor of a nuclear power plant is likened to the human heart, the main circulation pipeline is the aortic main vein emerging from this heart. During the operation of the nuclear power plant, the water contained in it constantly circulates at a temperature of 330 degrees. Only special pipes with a thickness of 70 millimeters can withstand such loads. Therefore, the welding of the pipeline is a complex and high-tech operation that is subject to the most stringent controls. The completion of the welding process will be the starting point for the transition from the pipes to the open reactor. “At this stage, we will check the transit capability of the pipelines, perform post-installation cleanups, and make sure the equipment is ready for the commissioning phase.”
The assembly of the main circulation pipeline includes not only the assembly and welding of the pipes, but also the high-temperature processing of the joints. Then, a special surface coating is applied to this part from inside the pipeline. This practice prevents the pipeline from oxidizing, increases the strength of the welded joints, and ensures the pipeline's lifespan is at least sixty years. During the installation process, specialists need to weld 28 pipeline joints, assemble about 260 tons of pipes and metal structures, as well as provide quality control of the welding joints.
TITAN2 IC IÇTAŞ A.Ş., the main contractor of Akkuyu NPP. Aleksey Mezhiritsky, program director of the joint venture, made the following assessment of the comprehensive control of the quality of welding work:
“ASBH weld joints are strictly controlled and their implementation is done at the maximum level of security. Welding quality control takes place in several stages and includes independent control methods according to accepted norms and standards. The quality control service performs the acceptance of each prepared part to ensure that the parts meet the set standards. During the welding process, experts perform step-by-step control of all processes: visual, measurement, radiographic, impermeability and ultrasonic. Quality control personnel must meet the highest qualification demands. Only professionals are allowed to do this type of work after passing rigorous certification tests.”
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The thickness of the ASBH pipe, which is 160 meters long and made of special steel, reaches 7 centimeters. During the operation of the NGS, coolant can circulate in the ASBH up to 160 degrees Celsius at a pressure of 330 atmospheres.
The thermal energy produced in the reactor is transferred from the first cycle to the second through the heat exchange pipes of the steam generator and saturated steam is obtained here. The saturated steam enters the steam pipeline, activating the generator that produces electricity.
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