The Kalpakkam prototype of the nuclear plant that powers the submarine Arihant

Kalpakkam, Aug. 2: Inside a cavernous, 20-metre-tall, light greenish building at the nuclear complex in Kalpakkam lies the elder sibling of India’s “secret weapon”.

Here, 75km from Chennai, is located the prototype of the nuclear plant that powers the Indian Navy’s first indigenously built nuclear-powered submarine, the Arihant.

While the sleek, 112-metre submarine was revealed to the world last week amid fanfare, the media today got their first glimpse of the top-secret project code-named — deliberately and misleadingly — Plutonium Recyling Project (PRP) since no plutonium is involved in the process.

This is where the first step towards building the nuclear plant for an Indian Navy submarine began in the late 1990s. Inside the hall, the land-based template of the Airhant’s nuclear reactor had been running smoothly since September 2006, churning out crucial readings that helped refine, design and fabricate the Arihant’s enriched uranium power plant at distant Visakhapatnam.

“In PRP we have what we call the ‘half boat’ in which the inner chamber of the rear half of a nuclear submarine is anchored to the ground. From its pressurised belly the 80MW nuclear plant operates,” explained PRP director S. Basu.

“The entire propulsion plant with primary, secondary, electrical and propulsion systems is packed into the half boat — measuring 42 metres in length and eight metres in diameter — and forms the heart of the nuclear submarine that powers its journey.

The navy sent its personnel here to be trained to operate the nuclear plant.

“This project saw India indigenously develop its first ever compact pressurised water reactor,” said Bhabha Atomic Research Centre director S. Banerjee.

“Although smaller and lighter, the plant generates power quickly, so essential for a submarine’s fast pick-up and quick manoeuvrability. For this the plant uses light water and enriched uranium unlike our land-based reactors that use heavy water and non-enriched uranium.”

Anil Kakodkar, chairman of the Atomic Energy Commission, said the light-water reactor had proved to be a technology demonstrator and given India a new capability, the marine propulsion reactor technology, to produce nuclear-powered submarines.

“This will help us explore (the possibility of) using these compact reactors for generating power in remote areas,” he said.

Asked when the nuclear reactor would achieve its first criticality (operational capability), Kakodkar said that before that the vessel had to go through the sequence of harbour and sea acceptance tests that would test the plant’s stability during a submarine’s journey.

Rear Admiral Michael Moraes, Flag Officer Commanding of submarines, said that ideally, the navy required another 13 nuclear-powered submarines.

“Even for us, the Arihant is a novel experience and in spite of the slightly higher noise levels of nuclear submarines, (acoustic) dampening features continue to give these submarines the much needed stealth advantage that makes them an ultimate secret weapon,” he said.

Asked if he was waiting to take the first dive once the Arihant was commissioned, Moraes quipped: “I am dying to, and I hope it happens soon.”