"HOOK up, hook up", the man in blue overalls shouted into his walkie-talkie the instruction for the tower-crane operator. As six of us stood crammed in a small cage, the tower crane swung around and winched us up slowly. Gusts of wind swayed the cage now and then. At a height of 70 metres came another instruction: "Level out." And then there was a spectacular view of the structures that were coming up to house the third and fourth reactors of the Tarapur Atomic Power Project (TAPP-3 and 4). Besides the massive reactor buildings, the complex has buildings to locate the turbines, the control room and the administrative offices. Scores of workers in green, blue, white or brown-coloured helmets were busy at the containment dome of TAPP-3 even as twilight descended on the town in Maharashtra's Thane district, 130 km from Mumbai. TAPP-4 stood nearly complete. Beyond the reactors lay the blue-black waters of the Arabian Sea. On one side stood the first two reactors of the Tarapur Atomic Power Station (TAPS-1 and 2), 35 years and going strong.
TAPP-3 and 4 are Pressurised Heavy Water Reactors (PHWR) and will, for the first time, generate 540 MWe each. The 12 operational PHWRs of Nuclear Power Corporation of India Limited (NPCIL) have a capacity of 220 MWe each. All the PHWRs, including those under construction, use natural uranium as fuel and heavy water as both moderator and coolant.
Work on TAPP-4 is more than a year ahead of schedule and the reactor is all set to reach criticality in August/September . It will be connected to the grid before the close of 2004. TAPP-3 will follow six to nine months later. Both will be breaking the six-year barrier, which was the target set. Both units will start generating electricity in less than five years from the first pour of concrete. Work on TAPP-4 began in March 2000 and it expected to generate power from October 2005.
R.C. Rawal, Principal Project Director, TAPP-3 and 4, said on January 15: "All the civil works of TAPP-4 have been completed. The calandria - the heart of the reactor - is ready. The turbine is in position and the final testing is going on. Instrumentation in the control room is in progress. The electrical job is complete. Commissioning activities are going on."
He attributes the speed of the project to the introduction of mega-packages in engineering and construction and the farming out of the mega-packages to big contractors. "This mega-package concept is a 100 per cent success," Rawal said. A 100-metre-high ventilation stack was raised in 60 days against the target of 150 days. A 12-million-litres a day fresh water supply scheme, from a reservoir situated 48 km away, was commissioned two months ahead of schedule, which resulted in a saving of Rs.6 crores. "We have a team of motivated engineers and workers who are pushing themselves hard," Rawal said.
TAPP-3 and 4 are the first of their kind in the country, with many new systems and new equipment, according to S.A. Bohra, Senior Executive Director (Technical), NPCIL. Modern management techniques were introduced to cut down construction time of the TAPP to less than five years. "We knew that otherwise we cannot compete in the electricity market," he said.
An example of the sophistication of the project is the state-of-the-art switchyard, which measures 60 metres by 30 metres and is situated indoors, preventing saline attack and corrosion. The cables are insulated with sulphur hexafluoride gas, which makes the yard virtually maintenance-free. The switchyard was completed a year ahead of schedule. Being indoor, it will not suffer saline attack on this beachhead site. Compare this with the sprawling, open-air switchyard at the Madras Atomic Power Station (MAPS) at Kalpakkam, which is 700 metres long and 300 metres broad.
The construction could be speeded up because of the fast pumping of concrete and the big size of the pour, said V.C. Agrawal, Project Director, TAPP- 3 and 4. A high-performance concrete called M 60 was used in the double containment structure to improve leak-tightness. "In civil construction, we speeded up mechanical works by, among other things, using heavy-duty cranes. Wherever a crane was available in-house, it was erected immediately so that material handling was not delayed," he said. About 600 engineers, 85 per cent of them new recruits, of the operations and maintenance division are in position, waiting for TAPP-4 to start generating power.
According to D.K. Goyal, Station Director, TAPP-3 and 4, the next six months will be "a critical and tough period because many systems have to be commissioned". The commissioning has started and constitutes Phase A of the project. Phase B would be the unit reaching criticality. Phase 3 would involve raising the reactor from low power to its full power of 540 MWe. The hot commissioning of the fourth unit will take place by the end of the second quarter of 2004. "Before the end of the third quarter (September), the unit will go critical," Goyal said.
Work is apace on TAPP-3 too. Although it is scheduled to go critical nine months after TAPP-4, present indications are that it may do so six months later.
The reactors have been designed to meet international safety standards and the site planning involves more than 8,000 drawings, which are available on LAN (local area network), according to Ranjay Sharan, site planning engineer. Eighty per cent of all procedures and documentation were available on LAN. He estimated that about 2,000 km of wiring had been done in the instrumentation of both the units
Safety had been accorded paramount importance in both the units, asserted Rawal. There was a high degree of automation to eliminate human error. Principles of redundancy, diversity and fail-safe methods had been employed. There was double containment to prevent radioactivity from reaching the atmosphere in the unlikely event of an incident or accident.
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