As a very tall crane ever so slowly winched up the circular contraption weighing 78 tonnes with “a spider” gripping it from top on Thursday, the contraption called thermal baffle sometimes stayed still in midair. At times, it swayed slowly as it rose in the air and hundreds of eyes were riveted on it. “Roger,” “roger” went the commands on walkie-talkies to those manning the crane. As the thermal baffle reached a height of about 80 metres, it was gingerly lowered to a height of 54 metres from the ground and then placed deftly inside the main vessel of the Prototype Fast Breeder Reactor (PFBR) under construction at Kalpakkam, near Chennai.
Applause rang out as the baffle fitted flush inside the main vessel, with just 90 mm of space separating the two contraptions. With that, the tension that had gripped the engineers of Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI), which is building the PFBR, was gone. The entire operation took about an hour.
Prabhat Kumar, Project Director, BHAVINI, who was happy that the PFBR project had flawlessly crossed the milestone, said “the entire world was looking at India” building the 500 MWe PFBR. Its construction signalled the beginning of the second stage of India's nuclear power programme, under which a series of fast breeder reactors would be built.
The PFBR will use plutonium-uranium oxide as fuel and liquid sodium as coolant. It will go critical in March 2012.
All the internals of the reactor including the core and the primary sodium circuit are contained in a single main vessel.
The thermal baffle, with two concentric shells, is about 12.5 metres in diameter and five metres tall. Although the baffle itself weighs 78 tonnes, the total weight handled for its erection was 170 tonnes.
Under the first stage of the Department of Atomic Energy's nuclear power programme, a series of Pressurised Heavy Water Reactors, using natural uranium as fuel and heavy water as both coolant and moderator, has already been built.
Mr. Prabhat Kumar said the baffle would provide passage for the cold sodium to cool the main vessel and bring down the temperature during the normal operation of the reactor from 550 deg. Celsius to 450 deg. Celsius. This was to minimise the effect of creep, thermal fatigue and embrittlement of the structure. The baffle was fabricated at the site by Bharat Heavy Electricals Limited and will be integrated to the main vessel by in situ welding.
P. Chellapandi, Director, Nuclear Group, Indira Gandhi Centre for Atomic Research (IGCAR), said the winching up of the baffle employed a “floating spider concept.”
Requires careful planning
The handling of its two concentric shells required careful planning and development of procedures. Conventional methods would not do. “We adopted an innovative method wherein the shape of the thermal baffle was maintained to a high degree of accuracy and there was no fear of collapsing of the structure due to buckling,” Mr. Chellapandi said. It was the IGCAR which designed the PFBR, he added.
S.C. Chetal, Director, Reactor Engineering Group, IGCAR, said the PFBR would have a life of 40 years.
“We have been able to demonstrate to the country that we can build this reactor with high standards of safety,” he said.