The heart of the new nuclear power plant, the reactor vessel, is being completed

The reactor vessel, often referred to as the heart of the nuclear power plant, where the chain reaction takes place, is manufactured in St. Petersburg, in one of Europe's largest automated forging plants, under the constant supervision of Russian and Hungarian experts. The four 850 mm diameter stubs located at the lower and upper stub zones of the reactor vessel of Unit 5 have been formed, i.e. „pulled out”. The entire operation took five days, and the process was monitored by The entire operation took five days, and the process was supervised on site by experts from Paks II. Zrt. and staff from the Hungarian Atomic Energy Authority.

The plant has a finished weight of 330 tonnes, a height of more than 11 metres, a diameter of 4.5 metres and a maximum wall thickness of 285 millimetres. The VVER-1200 reactor vessel will be tested not only by continuous neutron flux, but also by temperatures of 300 degrees Celsius and pressures of 162 bar, guaranteed to last for 60 years. Thanks to its advanced material composition and manufacturing technology, the reactor vessel will last up to 100 years.

"During the November production surveillance event, the domestic surveillance team was also present during the selection and marking of the so-called test pieces from the reactor steel alloy and supervised the execution of the required destructive material tests. The inspections gave a very positive impression of the quality culture of the plant staff and the high technical standard of the equipment used. The results of the steel testing at various sampling points confidently and consistently meet the expected requirements, raising the quality of the steels used in the Paks II nuclear power plant to a level that is outstanding worldwide" , said Gábor Kolonics, Senior Programme Quality Expert.

He explained that the process of reactor manufacturing starts with the casting of a raw material specially developed for the requirements of the nuclear industry. The right quality of steel is obtained by "mixing" the right and prescribed proportions of alloying elements, including chromium, nickel, vanadium, molybdenum, silicon, manganese, niobium, which are poured in molten form into a special ladle, a cocotte, taking into account the dimensions of the component to be produced. The solidified 'block', the so-called 'buga', undergoes various forging and heat treatment processes, resulting in the approximate ring-like shape of the six main reactor elements.

First, in November 2024, the most complex shaped stub zones of the reactor were completed, followed by the forging of the remaining rings in spring 2025. After quality acceptance of the stub rings and the other main components, each one will be transported to AEM-Technologies' plant in Volgodonsk, where the reactor vessel components will be welded together and subjected to final machining processes, mostly by machine cutting, and numerous quality tests. Many of the main water circuit equipment for nuclear power plant units is also manufactured here.

The most spectacular operation in metallurgy is forging itself, which is carried out at a temperature of around 1050 °C. The billet extraction operation, which was completed in November and involves the formation of the 850 mm cooling water tubes of the reactor, is the most unusual of these. The stub is initially a 260 mm diameter bore formed on a turning machine - on a ring weighing approximately 100 tonnes - which is "expanded" by applying a force of between 4500 and 8000 tonnes using a press mandrel while the steel ring is in the annealed state.

The St Petersburg plant, which is responsible for the processing of metallurgical raw materials, carries out not only spectacular hot forming technologies, but also very important quality checks of raw materials and semi-finished products, using so-called destructive and non-destructive material tests. The purpose of these tests is to verify the quality of the steel alloy selected by the equipment designer for the application in terms of chemical composition, strength and other specific requirements. The conformity of the tests and measured values are summarised in a quality certificate, which can be considered as a "document of record" throughout the operational life cycle of any industrial equipment. In the case of a nuclear power reactor, where steel is exposed to ionising radiation, all the information available on the raw materials during the long operating cycle (60 years) is of particular importance as it will serve as a basis for subsequent regular health checks.

The manufacturing and inspection processes of the equipment of the nuclear power plant are supervised on site by the plant itself; by the Russian prime contractor Atomsztrojexport, which is ordering the equipment and is also responsible for the overall implementation of the Paks II project; by Paks II. Zrt. as the licensee of the nuclear power plant project; and by the Hungarian nuclear authority, the National Nuclear Energy Office, which also signs the Quality Plan, a quality control document developed for this purpose, to verify the compliance of the manufacturing processes with the specifications.