New Delhi/Chennai: The construction work for units 5 and 6 of the Kudankulam Nuclear Power Plant (KKNPP) commenced Tuesday with the first concrete pouring into the foundation plate of the reactor building, the NPCIL said, marking an important milestone in ramping up the country's nuclear power capacity.

Russia''s ROASTOM and the Nuclear Power Corporation of India Ltd (NPCIL), a public sector undertaking of the Department of Atomic Energy (DAE), are building six power reactors of 1,000-MW each at Kudankulam, about 625 kilometres from Chennai.

On completion, the KKNPP will be the highest nuclear power generation park in the country.

Its unit 1 and unit 2 are in operation while units 3 and 4 are under construction and currently have reached about 50 per cent progress. The NPCIL said in a statement the construction of units 5 and 6 is scheduled to be completed by 2026-2027.

"The construction of Units 5 and 6 at Kudankulam commenced today with the placement of First Pour of Concrete (FPC). The First Pour of Concrete is an important milestone in a nuclear power project that is reckoned as the start date of the project," it added.

ROASTOM, the State-run Russian company tasked with building the reactor, said in a separate statement, "On June 29, an official ceremony was held that was dedicated to the first concrete pouring into the foundation plate of the reactor building for Kudankulam NPP Unit 5 (Republic of India).

"Due to anti-epidemiological restrictions, the ceremony was held via video conference," it added.

The ceremony was attended by senior officials of the DAE, including Atomic Energy Commission Chairman V N Vyas, the NPCIL and ROASTOM.

The first concrete pouring was preceded by continuous preliminary work -- concrete bedding for foundations of the reactor building, auxiliary reactor building with the main control room, turbine building and power supply building for normal operation, emergency power supply and safety control systems, the company said.

The General Framework Agreement (GFA) between India and Russia was signed on April 10, 2014 for the construction of units 3 and 4.

Negotiations between the two countries over the construction of unit 5 and 6 arrived at the agreement that these units would be constructed in compliance with the same design stipulated for units 3, 4.

On June 1, 2017, the credit protocol to the Intergovernmental Agreement of December 5, 2008 and the GFA for Kudankulam NPP Units 5, 6 were signed.

"or many years, the Kudankulam NPP construction project has been a symbol of close cooperation between Russia and India. However, we do not want to stop at what had already been achieved.

"ROASTOM has all the most advanced nuclear power technologies. Together with our Indian colleagues we are ready to launch the serial construction of the state-of-the-art Generation III+ Russian-designed nuclear power units at a new site in India. It is stipulated by the existing agreements," ROASTOM Director General Alexey Likhachev said during the event.

Russian enterprises are already manufacturing equipment required for the first priority installation, the equipment for the reactor facilities and turbine hall for Unit 5, the company added.

According to NPCIL, unit 1 at KKNPP commenced commercial operation on December 31, 2014, while Unit II on March 31, 2017.

India’s present installed nuclear power capacity is 6,780 MW through 22 reactors.