The Prototype Fast Breeder Reactor (PFBR) is a 500 MWe (MegaWatt electrical) sodium-cooled, fast breeder nuclear reactor located at Kokkilamedu, near Kalpakkam, Tamil Nadu, India. It is a technological concept and a physical institution, designed by the Indira Gandhi Centre for Atomic Research (IGCAR) and constructed by Bharatiya Nabhikiya Vidyut Nigam Ltd (BHAVINI).
The PFBR is the cornerstone of the crucial second stage of India's three-stage nuclear power programme, a vision conceived by Dr. Homi Jehangir Bhabha. The reactor's construction began in 2004 and it was created to solve the problem of India's limited uranium reserves by leveraging its vast thorium reserves.
The mechanism of the PFBR is to "breed" more fissile fuel than it consumes. It uses Uranium-Plutonium Mixed Oxide (MOX) fuel, which is reprocessed from the spent fuel of the first stage's Pressurised Heavy Water Reactors (PHWRs). The reactor uses high-speed, or fast, neutrons and a blanket of fertile material, such as Uranium-238, which undergoes nuclear transmutation to produce new fissile fuel, specifically Plutonium-239. The reactor uses liquid sodium as a coolant.
The PFBR connects directly to the third stage of the nuclear programme, as it is designed to eventually use Thorium-232 in its blanket to produce Uranium-233. This Uranium-233 will then fuel the final stage of thorium-based reactors, paving the way for India's long-term energy security and self-reliance.
The PFBR achieved a major milestone recently, attaining its first criticality on April 6, 2026, marking the initiation of a sustained nuclear chain reaction. This achievement officially moved India into the second stage of its nuclear programme, and once fully operational, India will become only the second country after Russia to operate a commercial fast breeder reactor.