Chennai: The second unit of Kudankulam atomic power project in Tamil Nadu went critical or started nuclear fission on Sunday at 8.56 p.m., said officials of Nuclear Power Corporation of India Ltd (NPCIL). "Criticality achieved at 8.56 p.m.," H.N. Sahu, Station Director of first and second units, said on Sunday. This is the second 1,000 MW pressurised water reactor to go critical in the country. The first unit at Kudankulam went critical in July 2013. The unit will start commercial generation in four to six months time. Prior to that tests have to be conducted and then the unit will be connected to the Southern power grid. The approach towards criticality started on Friday with the gradual removal of the control rods. Asked about the conduct of off-site emergency safety drill prior to the commissioning of the reactor, NPCIL Chairman and Managing Director S.K.Sharma said: "The second unit is part of an operating station (site where a nuclear power plant is already functioning). In such cases off-site emergency drills are conducted once in two years." The first 1,000 MW unit of Kudankulam atomic power project, which is located in Tirunelvelli district, is already functional. Sharma said there are three types of emergency drills that are done at Indian nuclear power plants: plant, site and off-site. "The emergency drills at the plant are done every quarter and the site emergency drill every year," he had said. According to Sahu, the last off-site drill was conducted in January 2015. For NPCIL, the two units of Kudankulam project are expected to contribute handsomely to its topline and bottom line. The first unit experienced several hiccups since starting commercial production in December 2014 but seems to have stabilised now, generating about 940 MW daily on an average. The first unit supplies power to Tamil Nadu (562.5 MW), Puducherry (33.5 MW), Kerala (133 MW), Karnataka (221 MW) and Andhra Pradesh (50 MW). The total outlay on the two units of Kudankulam project has been over Rs 17,000 crore. Once the second unit at Kudankulam starts power generation to its full capacity, the total atomic power capacity in Tamil Nadu would go up to 2,440 MW. Already, the NPCIL has two 220 MW units at Kalkpakkam near here under its Madras Atomic Power Station.