New Delhi, April 19: Routine tests before the commissioning of the first of two Russian-designed nuclear reactors at Kudankulam have revealed faults in four valves designed to cool the reactor in extreme emergency situations, India’s nuclear safety regulator has said.

The Atomic Energy Regulatory Board (AERB) said that thorough performance checks on the reactor, after nuclear fuel had been loaded into it, had found that among the thousands of valves installed, four Russian-supplied ones were deficient.

The process of replacing the valves appears to have delayed the commissioning of the first reactor at the proposed nuclear power station in Tamil Nadu, where anti-nuclear protests had earlier stalled activities for several months.

Atomic energy officials had indicated earlier this year that the first reactor would be commissioned by April.

The two 1,000MW reactors are the first set of foreign reactors in India since two US-made reactors were commissioned in Tarapur, Maharashtra, in the 1960s. They are to add significant capacity to the National Power Corporation’s (NPC) existing 4,780MW of installed nuclear power.

The four faulty valves were part of a safety system that is required to function during “extreme accident situations”, AERB chairman Satinder Singh Bajaj told The Telegraph.

Linked to a system called the “second-stage hydro accumulator”, the valves are expected to facilitate the flow of water to cool the reactor under emergency conditions.

“They’re part of a back-up system,” Bajaj said, adding that the deficiencies in the valves had been discovered “a couple of months ago”.

The NPC, the public-sector organisation that runs India’s commercial power reactors, is now replacing the valve components, the AERB said without specifying how long the process might take.

AERB secretary Ramdas Bhattacharya said the reactor’s performance would be reviewed after the valves are replaced.

Both Bajaj and Bhattacharya said such deficiencies had emerged in the past, too, when large and complex systems such as nuclear reactors were evaluated before commissioning. “This is not an unprecedented event,” Bhattacharya said.

The tests during the commissioning process are designed to provide data on the performance of various components and systems under the actual conditions of pressure, temperature and flows that the reactor would encounter during real operations.

The AERB had cleared the fuel-loading process for the first of the two reactors in September 2012. In January this year, atomic energy department chairman Ratan Kumar Sinha had indicated that “certain measurements” observed during the performance evaluation of the first reactor were not within the “ideal or optimal” range, although they were not extraordinary, either.

Sinha had said that engineers were trying to determine why the measurements did not fall in the ideal range. But it is not clear whether the measurements Sinha had referred to in January had any connection with the four faulty valves.

News reports had said in March that Prime Minister Manmohan Singh had told Russian President Vladimir Putin at a meeting in South Africa that the first reactor at Kudankulam would start operating in April this year.

NPC officials were unavailable for comments. A senior NPC engineer in Kudankulam declined to respond to queries.