The Department of Atomic Energy, which reports to the Prime Minister, has been insisting that the nuclear facility in coastal Tamil Nadu is safe and ready to be commissioned in weeks.
Protesters, including local fishermen and villagers who have campaigned long and hard against the nuclear plant, have repeatedly shared their concern that sub-standard equipment has been installed at the facility.
The AERB confirms that "performance of four valves of a particular type were found to be deficient".
Officials added, "As corrective measures, the valve components are being replaced by the Nuclear Power Corporation of India Limited."
15,000 crores have been invested so far on the nuclear power plant which uses Russian technology. Tamil Nadu is meant to get the lion's share of the power that will be generated from the two nuclear reactors.
AERB told NDTV that the defective valves were part of the special passive cooling system installed in these nuclear reactors to avert a Fukushima-type accident.
The AERB said subsequent clearances will be granted only after satisfactory review.
SP Udayakumar, leader of the anti-Kudankulam protesters, said the nuclear watchdog's finding proves that the plant is not safe. "Not just valves, the reactor pressure vessel itself is deficient. The project should be scrapped," he said.