"Sustained fission reaction and a series of steps will be going on in the second unit. Every step will be monitored and clearance will be obtained from The Atomic Energy Regulatory Board for going on to the next process," he told reporters here.
The second unit of KKNPP attained criticality at 8.56 pm, Sharma said.
The first approach to attain criticality at the second unit began on July 8.
The second unit would attain the maximum capacity of 100 per cent power generation within three months and its synchronisation would be achieved within a month, he said.
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Tamil Nadu's share of power generated by Unit-II would be 562 MW, he said.
The first unit, which began generating power in October 2013, has so far produced 1006 crore MW.
Excavation works on the third and fourth units are going on at the site, he said, adding, in 2023-24, the NPCIL's total power production would be 30,000 MW.
The second reactor is the NPCIL's 22nd unit.
Unit 1 and 2 of the KKNPP VVER reactors are being built with Russian collaboration. Each reactor has the capacity to generate 1000 MW of electricity.
reactors based on enriched uranium and its second unit was expected to start operations later this year.
The completion of the first unit was delayed in view of strident protests by local people, who raised safety concerns, before it became operational.
The Pressurised Water Reactor (PWR) VVER-1000 had gone critical in July 2014 and the commercial operations started from December 31 the same year, with the unit coming to the aid of the then power starved Tamil Nadu.
The Cumulative Generation of Unit I since the date of commercial operation is 6,498 million units (MU) with its capacity factor peaking to 100 per cent in June this year.
"In successful completion, it is not only another fine example of the strength of our special and privileged strategic partnership, it is also a celebration of our binding friendship. It is only a start of our cooperation in this field," he said.
Modi said five more units of 1,000 MW each would be built at the KNPP.
"Today's event is also a joyful occasion for the team of Indian and Russian scientists and technicians. We salute their dedication and hard work and congratulate them for the fruits of their labour," he said.
"The dedication of the KNPP is a major milestone in Indo-Russian cooperation. Throughout my 10 years in office as the Chief Minister of Tamil Nadu I have always extended support to the implementation of the Kudankulam project while at the same time laying focus on allaying the fears of the local people by convincing them about its safety," she said.
Noting that a nuclear power plant takes long time to be built and commissioned than conventional units, she said very high safety standards were needed to be observed.
Successful commissioning of the project was an object lesson on how the fears and apprehensions of the local population could be and should be allayed through a process of engagement and reassurance and by building community assets and infrastructure, she said.
Modi said he always valued the Indo-Russian friendship.
"I am grateful to you Mr President (Putin), the people of India are associated with your great country and personally I have always deeply valued our friendship.
The Prime Minister said he looked forward to meeting Putin during the coming G20 conclave in China.
Putin said making operational the "designed capacity of the first unit and in the near future the second unit will significantly enhance India's energy supply and strengthen its economic positions."
The Russian President stressed that the unit was built based on the most modern Russian technologies and that the construction was carried out by specialists of both countries.
Putin noted that 85 per cent of the funding for this project was being done by the Russian Federation.
Tracing the measures taken by her governments to allay the apprehensions of local people, Jayalalithaa said she was confident that the Nuclear Power Corporation of India would maintain the highest safety standards.
She hoped NPCIL would also ensure continuous power generation in the two units so that Tamil Nadu and neighbouring states can rely on it as a reliable base load power station.
"I thank the Prime Minister for dedicating the plant along with Putin. I also request the commissioning of the second unit may be expedited," she said.
Jayalalithaa was seen visibly happy when Modi spoke a sentence in Tamil welcoming her to the event. She acknowledged Modi's gesture with a 'namaskar' and clap.
Modi also mentioned a few lines in Russian in his inaugural and concluding remarks while addressing Putin.