The fifth and the sixth unit of India's largest nuclear power plant in Tamil Nadu will cost about Rs.50,000 crore to build with half of it being funded by Russia as loan.

The project will take seven years to start generating electricity, Nuclear Power Corporation of India (NPCIL) Chairman and Managing Director S K Sharma said.

India and Russia yesterday signed an agreement for the two new reactors for the Kudankulam Nuclear Power Plant (KNPP) on the sidelines of the annual summit between Prime Minister Narendra Modi and Russian President Vladimir Putin.

"The entire project will cost about Rs 50,000 crore. The first unit will be commissioned in 66 months and the second six months thereafter," Sharma said.

Atomstroyexport, a unit of Russian state nuclear corporation Rosatom, will build the reactors.

"The project will be funded in 70:30 debt-equity ratio (70 per cent debt, 30 per cent equity)," he said.

The Russian government will lend India $4.2 billion to help cover the construction cost.

Sharma said the equity portion of project will either come from NPCIL's own resources or from government.

At the agreement signing ceremony yesterday, Russian President Putin said the first unit of the Kudankulam nuclear power plant was put into operation.

"The most reliable, latest Russian technology was used in its construction. The plant's second unit has also started to generate electricity.

"At a joint teleconference in October 2016 with Narendra Modi we launched the construction of the plant s third and fourth units. And we reaffirmed our intention to build in India at least 12 Russian-designed energy units, which will make a large contribution to the development of India's nuclear industry," he said.

The KKNPP was the outcome of an inter-governmental agreement between the erstwhile Soviet Union and India in 1988. It is the single largest nuclear power station in India.

The power station was envisaged to have six units with total capacity to generate 6,000 MW of electricity (1,000 MW each).

Construction on the plant began on March 31, 2002 and Unit 1 was synchronised with the southern power grid in October 2013. The second unit started generating electricity in August last year. The original cost of the two units was Rs 13,171 crore, but it was later revised to Rs 17,270 crore.

Russia advanced a credit of Rs 6,416 crore for construction of the two units.

Construction of plant's third and fourth units was launched last year and will cost Rs 39,747 crore. While the cost of generating power from first two units is reported at Rs 4.29 per unit, the cost from 3 and 4 is likely to be significantly higher than that.

Units 3 and 4 of the Kudankulam plant are expected to be commissioned by 2022-23.

The Russian built Water-Water Energetic Reactor (VVER) reactor Kudankulam unit 1 and 2 are the largest power generating stations in the country. After all the units (1-6) of the plant are commissioned, the nuclear park will have the power generating capacity of 6,000 MW, boosting significantly the country's nuclear power generation.

The current nuclear power generation capacity of all 22 nuclear power reactors in India is 6780 MW.