It resumed power generation at 1325 hrs, Site Director (Additional Charge) S V Jinna said in a release.
The unit was shut to take up annual generator maintenance on August 4.
Unit-2, a 1000 MWe VVER (water-cooled water-moderated reactor), belongs to the Pressurised Water Reactor category.
After successfully undergoing maintenance, Unit-2 was made critical on November 16 and the mandated "pre and post" criticality tests were carried out, he said.
It was synchronised with the Southern grid at 1325 hrs and scientists would gradually increase the power generation, he said.
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It was "taken offline" for refuelling and maintenance in April and resumed power generation on August 29.
"With two 1000 MWe power units, the KKNPP site has so far generated 20,329.51 million units of electricity," the release said.
The KKNPP, an Indo-Russian joint venture, is located at Tirunelveli district in Tamil Nadu.