VVER-TOI: the latest evolution19 November 2021
The first-of-a-kind VVER-TOI reactor, being built at Kursk II in Russia, uses the same engineering approaches as earlier VVERs, but has a few unique features
The Russian-designed VVER-TOI is based on the engineering solutions used for a nuclear power plant with VVER-1200 reactors.
The VVER-TOI design provides for a longer self-sustained emergency operation of a plant, as well as a smaller amount of solid radioactive waste and emissions. It combines active and passive safety systems. In addition, it ensures the transition of the reactor plant to a safe state in the event of various combinations of natural and man-made events causing a complete black-out: the power unit can survive a commercial aircraft crash, an earthquake and a tsunami happening simultaneously. The plant grace period requiring no operator intervention has been extended to 72 hours.
Since the VVER-TOI design uses the same engineering approaches as its predecessor, it requires no changes in the basic conceptual, structural and layout solutions for the power plant, though a new equipment layout is required. The steam generators are arranged in two rows, with two steam generators in a row. Earlier designs required a tangential arrangement around the nuclear reactor.
Steam generator design
The equipment modification includes a new design of the steam generator without a steam header at its top. Steam comes out of one nozzle directly connected to the steam line (the classical design provided for 10 nozzles of earlier design, through which the steam enters a common steam header and then the steam line). The new steam generator is one metre longer at 15m, and its diameter exceeds 4m. The weight of a steam generator is 355t. The steam generator has coolant inlet and outlet headers in its middle part, where the ends (coils) of 11,000 heat exchange tubes are fixed. The tube diameter is 16mm, the wall thickness is 1.5mm, and the length is 11-17m.
The VVER-TOI steam generator has an increased steam generation capacity, which is 1652t/h, compared with the VVER-1200 PGV-type steam generator capacity of 1602t/h. The nominal thermal power of the new steam generator is 828MW, compared with 803MWt for the VVER-1200 PGV steam generator.
Reactor pressure vessel
The reactor vessel design has also been changed. The bottom diameter has been increased by 100mm and is equal to the outer diameter of the core shell (the classical design provides for a structural connection between the bottom and the core shell). The bottom shell of the nozzle area is also the support shell, though the welded joint is excluded (there are four vessel welds, in comparison with five or six welds in the classic designs). The angle between the axes of the even and odd nozzles has changed to 78° (the classic design provides for 55°).
Fewer welded joints mean faster manufacturing of the reactor vessel, and lower labour costs for welding, cleaning and non-destructive testing in proportion to the deposited metal, which also results in better reliability of the reactor vessel design.
Kursk II — leading the way
Kursk II is the first project to use the VVER-TOI and it has four new power units with a capacity of 1300MW each.
AEM-Technology (a subsidiary of AtomEnergoMash, Rosatom’s mechanical engineering division), the only Russian manufacturer capable of making a complete nuclear steam generator, is also the manufacturer for the VVER-TOI.
The company started manufacturing the first VVER-TOI in 2018. The reactor vessel and steam generators for Kursk II-1 were manufactured in 2020 and shipped in April 2021. The manufacturing of equipment for the Kursk II-2 is currently under way. The complete steam generator set for unit 2 will be shipped in the first half of 2022.
According to Igor Kotov, director general of AEM Technology, the Kursk II project is the next stage in the development of Russian VVER technology.
“AEM-technology is the largest manufacturer of this equipment, and VVER-TOI manufacturing is a challenge for us. It is an opportunity to show our ability to quickly adapt manufacturing processes to meet new challenges maintaining high standards. Despite the quarantine restrictions, we succeeded in manufacturing the first set of equipment with a new Russian reactor of VVER-TOI type,” says Kotov.
AEM-technology facilities manufacture up to four sets of equipment per year. The company backlog of orders for the period up to 2025 is worth 193 billion rubles. The company’s manufacturing plan for nuclear plant equipment for the period to 2028 includes 24 reactor vessels with internals and 93 steam generators. The extensive investment programme, providing for the commissioning of 388 new equipment items and associated investment, is around 9.7 billion rubles.
AEM-technology facilities are now manufacturing equipment for nuclear units at Rooppur (Bangladesh), Akkuyu (Turkey), Kudankulam (India), Tianwan (China), Xudapu (China) and Kursk II (Russia).
Photo: Kursk II construction site where the first VVER-TOI reactors will be located (Credit: Rosenergoatom)