C Shivakumar @ Chennai:
It has been a 16-year wait since I first began covering nuclear energy and asking when the Prototype Fast Breeder Reactor (PFBR) would attain criticality. The answer finally came on Monday, when Prime Minister Narendra Modi announced that the reactor had achieved the milestone.
I recall a visit to Kalpakkam on September 29, 2010, when journalists were taken to the site shortly after the inner vessel had been lowered earlier that month, during the tenure of Dr Baldev Raj, then Director of the Indira Gandhi Centre for Atomic Research (IGCAR).
The inner vessel is a critical component of the PFBR. It separates the hot and cold pools of liquid sodium and provides structural support and positional accuracy to the heat exchangers operating in the hot sodium pool.
The 500 MW PFBR — the first of its kind in India — has been designed by IGCAR and comprises three primary vessels: the safety vessel, the main vessel and the inner vessel. Together with other core systems, these form the backbone of the reactor, which marks the beginning of the second stage of India’s nuclear power programme.
Construction milestones were staggered over several years. The stainless steel safety vessel was installed in June 2008, followed by the lowering of the main vessel in December 2009. The thermal baffle — a 70-tonne component designed to extend the reactor’s operational life — was erected in May 2010, ahead of the installation of the inner vessel.
Designed by IGCAR scientists, the thermal baffle creates an annular passage for cold sodium to circulate and cool the main vessel. This is crucial because the reactor contains about 1,100 tonnes of liquid sodium at temperatures of around 550°C. The cooling system ensures that the main vessel temperature remains below 450°C during normal operations, thereby reducing the risks of creep, thermal fatigue and material embrittlement.
The PFBR is intended as a technological stepping stone, offering operational and engineering lessons as India plans a fleet of fast breeder reactors.
The technology places India among a small group of nations with fast breeder capability, building on early experimental success achieved in 1985. The Kalpakkam reactor operates on a closed fuel cycle, where spent fuel is reprocessed to extract fissile material and refabricated into plutonium-rich mixed carbide fuel. This approach is central to maximising energy output from limited uranium reserves while enabling the long-term use of India’s abundant thorium resources.
India’s three-stage nuclear programme, conceived by Homi Jehangir Bhabha, envisages a phased expansion of nuclear capacity. The first stage is based on natural uranium-fuelled pressurised heavy water reactors, which currently dominate the country’s nuclear fleet. The second stage — now entering a decisive phase with the PFBR — focuses on fast breeder reactors that can convert uranium-238 into plutonium and thorium into uranium-233, potentially scaling capacity to around 300 GW over time. The final stage aims to fully deploy thorium-based reactors, with projections of sustaining up to 1,000 GW for centuries.
Despite concerns among critics over the use of sodium coolant — which reacts vigorously with air and water — proponents argue that fast breeder reactors offer a pathway to more efficient fuel utilisation and a reduction in long-term radioactive waste.
https://www.newindianexpress.com/states/tamil-nadu/2014/Jun/28/500-mw-kalpakkam-reactor-to-reach-criticality-629561.html
https://www.newindianexpress.com/states/tamil-nadu/2010/Sep/21/lowering-of-inner-vessel-marks-another-milestone-188739.html
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