Kudankulam 1 has received licence approval for initial fuel loading and approach to criticality.
The clearance builds on preliminary and final safety analysis reports, commissioning procedures.
The VVER-1000 reactor has advanced safety features to protect it against external natural events and design-basis and beyond-design-basis accidents.
The Indian regulator, the Atomic Energy Review Board, also reassessed the reactor design to withstand extreme external events and an extended station blackout, it said.
The station will have to obtain clearance from AERB as it gradually increases power, AERB said.