Mumbai, Sep 17 (IANS): Two years after the shut down of the Kakrapur Atomic Power Station (KAPS-1&2) due to a leak at Surat in south Gujarat, it's Unit 2 attained 'criticality' early on Monday after undergoing a renovation and modernization programme, a top official said here.

The 220MW KAPS-2 went critical - or initiation of self-sustaining nuclear fission chain reaction in the reactor - at 2.22 a.m today (Monday), said Nuclear Power Corporation of India Ltd (NPCIL)'s Associate Director (CP&CC) A. K. Nema.

The refurbishing work included En-Masse Collant Channel Replacement, En Masse Feeder Replacement and other safety upgrades at the KAPS, around three and a half months before schedule.

The approach to criticality was undertaken after adhering to all the stipulated regulatory requirements and will be followed by various tests, connection to the grid, increase in power level to full power as per laid down procedures and regulatory clearances.

KAPS comprises two units of indigenous 220MW (KAPS-1&2) Pressurised Heavy Water Reactors (PHWR), which commenced commercial operations in 1993 and 1995 respectively.

In March 2016, KAPS-1 had automatically shut down due to a leak of heavy coolant water, leaving both the reactors non-functional.

The leak was plugged some 10 days later after which the refurbishing work was taken up.

While KAPS-2 has resumed operations, KAPS-1 is expected to follow suit soon, said an official.

Besides, two more PHWR units KAPS-3&4 of 700MW are being constructed at the same site in Vyara town near Surat.

NCPIL currently operates 22 nuclear power reactors, including the 100MW RAPS-1, owned by the Department of Atomic Energy, with a capacity of 6780MW.

An additional eight reactors with a capacity of 6200MW are currently under construction in different parts of India, while work is underway for 12 more nuclear reactors with a capacity of 9000MW for which all administrative and financial sanctions have been received from the government, Nema said.