A message from Tarapur

The country's largest nuclear power reactor reaches criticality months ahead of schedule, marking another milestone in its march towards technological self-reliance.

T.S. SUBRAMANIAN in Tarapur

IT was a moment of pride for India. On March 6, the country's largest and very own nuclear power reactor with 540 MWe capacity reached criticality without a hitch, seven months ahead of schedule, and in defiance of some developed countries' attempts to block the technological leap with embargoes on the units of the Department of Atomic Energy (DAE).

It was not a coincidence that three top officials - Anil Kakodkar, Chairman, Atomic Energy Commission, S.K. Jain, Chairman and Managing Director, Nuclear Power Corporation of India Limited (NPCIL), and M.K. Narayanan, National Security Adviser - stressed that the fourth reactor of the Tarapur Atomic Power Project (TAPP-4) had been started up despite draconian embargoes and technology denial regimes aimed at throttling the DAE units. The embargoes, especially those imposed by the United States, were in force when the excavation for the units of TAPP-3 and 4 began in October 1998. But the sanctions, imposed soon after India conducted five nuclear tests in May 1998 at Pokhran, did not deter the NPCIL from going ahead with the construction of the two 540 Mwe reactors.

Kakodkar said that TAPP-4 was not only the largest nuclear power reactor in the country but also the largest power unit in India. It was built seven months ahead of schedule, at a cost much lower than the original estimate. "It shows the high calibre of our staff. I want to compliment the NPCIL for making this tremendous achievement possible," Kakodkar said.

Jain pointed out how ineffective the embargoes had been. "TAPP-3 and 4 were built under draconian nuclear and trade embargoes... It was a difficult time, " he said. Narayanan was more sarcastic: "The sanctions have actually hastened the indigenisation programme and we have achieved criticality well before the due date."

The tension in the fourth unit's sophisticated control room was palpable on the day of its start-up. Although the NPCIL had indigenously built 12 other Pressurised Heavy Water Reactors (PHWRs) that are operating now, the engineers were worried about how the new reactor would behave. This was, after all, the first time that a 540 MWe reactor was built in the country, and it had a new fuel core of natural uranium bundles. A battery of computerised panels in the control room monitored the health of the reactor components. Tension peaked when there was a slight delay, all eyes riveted on a panel called "Start-up Instrumentation System". As the graph in the panel remained constant at 12.41 p.m., applause erupted in the control room. "The sustained chain reaction has started," D.K. Goyal, Station Director, declared.

Jain said all the systems behaved smoothly, though the scientists had expected last minute surprises. This, he said, reflected the maturity of the design, the R&D back-up, and the qualification systems of the Bhabha Atomic Research Centre and other units.

Reaching criticality was not easy. The regulatory body, Atomic Energy Regulatory Board (AERB) headed by its Chairman S.K. Sharma, imposed stringent parameters of safety. The AERB's mandate is to ensure the safety of nuclear power installations. Operations such as hot commissioning the systems, filling the reactor with 500 tonnes of heavy water and loading natural uranium fuel bundles need the AERB's approval. It would take no chances whatsoever with the reactor because it was new and had a huge core.

TAPP personnel were required to demonstrate the worthiness of a robotic fuel-handling machine, fabricated with the help of BARC, before an AERB team approved it. The machine clamps fresh fuel bundles into the reactor at one end of the vault, and pulls out the spent bundles from the other end. Fuelling and defuelling can be done simultaneously, without shutting down the reactor.

According to V.C. Agrawal, Project Director, TAPP-3 and 4, about 88 per cent of the work on the third unit is complete. The unit would go critical in 2005-06.

TAPP-3 and 4 have been built on the shores of the Arabian Sea, in Maharashtra's Thane district. The nearest town is Tarapur, about 140 km from Mumbai. The two new reactors have come up adjacent to Tarapur- 1 and 2, which were built by General Electric of the United States in the 1960s. Both were connected to the grid in 1969. Their original capacity was 210 MW each. These Light Water Reactors use enriched uranium as fuel, and light water (ordinary water) as both coolant and moderator. Tarapur-3 and 4 are totally indigenous PHWRs that use natural uranium as fuel, and heavy water as both moderator and coolant.

Excavation began for TAPP-3 and 4 in October 1998. The foundation pit was 20 metres deep and 60 metres in diameter. The first pouring of concrete, called the zero date, was in March 2000, signalling the beginning of construction. Both units had six to seven years from the zero date for completion. The NPCIL introduced the concept of awarding mega packages for civil construction and delivery of equipment, leading to faster construction. A scheme for the supply of 12-million litres of fresh water a day from a reservoir 48 km away, was commissioned two months before the target date, which resulted in a saving of Rs.6 crores (Frontline, February 27, 2004).

Among the major companies that took part in civil construction and installation of equipment were Larsen and Toubro, Gamon India Limited, AFCONs, BHEL, Vijay Industries, UB Engineers and BHP. The DAE units that took part in the project included BARC and the Nuclear Fuel Complex at Hyderabad, which fabricated the fuel bundles.

Besides the safety features in design and engineering, the plant has physical protection as well. Around the two units run two fences, eight metres apart, with metal sweepers, cameras and detectors installed in between to spot intruders. The unit has two additional systems to shut down the reactor safely in case of an emergency. There is a system to cool the fuel core in emergencies. Both the reactor buildings are topped with a double containment - which is a massive dome with two very thick walls - to prevent radiation from reaching the atmosphere in the event of an accident.

According to Ranjay Sharan, Site Planning Engineer, costs went down because the project was completed in five years instead of seven. The capital cost went down further because interests fell, reducing the burden of market borrowing needed to fund the project. Competitive bidding and simplification of design also reduced cost.

Jain said the initial estimate for both units was around Rs.8,000 crores. This dropped to Rs.6.500 crores and then to Rs.6,000 crores. So, the tariff for every unit would go down from Rs.3.50 to Rs 2.65.

According to Goyal, while Maharastra would receive 39 per cent of the electricity generated from the two units, Gujarat's share would be 19 per cent and Madhya Pradesh's 17 per cent. Goa, and the Union Territories of Daman, Diu and Nagar Haveli would share the rest. The Centre would keep some of it to supply deficient states.