The Department of Atomic Energy (DAE) called it a landmark achievement and a historic step towards long-term energy security and a major boost to indigenous nuclear technology capabilities.
This development enhances the utilisation of nuclear fuel resources, enables India to extract more energy from its limited uranium reserves while preparing for large-scale use of thorium in the future.
With the achievement of first criticality, India moves closer to realising the full potential of its three-stage nuclear power programme. The milestone also demonstrates the strength of India’s indigenous design, engineering, and manufacturing ecosystem.
“Fast breeder technology forms the vital bridge between the current fleet of pressurised heavy water reactors and the future deployment of thorium-based reactors, leveraging the country’s abundant thorium resources for long-term clean energy generation,” the DAE said in a statement.
Fast Breeder Reactors are central to India’s long-term nuclear strategy. Unlike conventional thermal reactors, the PFBR uses uranium-plutonium mixed oxide (MOX) fuel, with a core surrounded by a blanket of uranium-238. Fast neutrons convert uranium-238 into fissile plutonium-239, allowing the reactor to produce more fuel than it consumes.
The reactor is also designed to eventually use thorium-232 in its blanket. Through transmutation, thorium-232 can be converted into uranium-233, which will power the third stage of India’s nuclear programme.
The PFBR incorporates advanced safety systems, high-temperature liquid sodium coolant technology, and a closed fuel cycle that enables recycling of nuclear materials, improving sustainability and reducing waste.
Beyond energy production, the fast breeder programme strengthens India’s capabilities in nuclear fuel cycle technologies, advanced materials, reactor physics, and large-scale engineering. As the country expands its clean energy portfolio, fast breeder reactors will play a key role in delivering reliable, low-carbon base-load power with higher thermal efficiency.
Anil Kakodkar, former chairman of the Atomic Energy Commission and ex-director of BARC, called the development “historic”. “We need adequate base-load power in the form of clean energy and, most importantly, we need those resources to be available within our landmass. So nuclear energy, and particularly thorium, is the energy source that really qualifies for this,” he told Business Standard.
He also highlighted the complexity of PFBR technology, noting that India is among the few countries, alongside Russia, to have developed and operated a reactor of this scale. “It is a major development which will help India's energy security and, more importantly, energy independence going forward,” he said.
According to V K Saraswat, member, NITI Aayog, “In other reactors, we use different kinds of heavy water or natural water for cooling. With a sodium-cooled reactor, we can take heat up to about 500 degrees Celsius and remove it. This will enable future reactors to work on less consumption of water," Saraswat said.
Nuclear scientist R K Singh said the milestone signals India’s transition into the replication phase, with additional fast breeder reactors (FBR-1 and FBR-2) already planned at Kalpakkam. “Policy push and commercial deployment can accelerate in the 2030s. By 2040-2050, fast reactors can contribute significantly to base-load clean power and enable a closed fuel cycle, meaning a near-zero waste paradigm.”
The PFBR was indigenously designed by the Indira Gandhi Centre for Atomic Research (IGCAR) under the DAE, and built and commissioned by Bharatiya Nabhikiya Vidyut Nigam Ltd (BHAVINI), a public sector undertaking. First criticality was attained after meeting all safety requirements set by the Atomic Energy Regulatory Board (AERB), which granted clearance following a rigorous review of the plant’s systems.
The criticality was achieved in the presence of Ajit Kumar Mohanty, secretary, DAE and chairman, Atomic Energy Commission (AEC); Sreekumar G Pillai, director, IGCAR; Allu Ananth, CMD-in-charge, BHAVINI; and K V Suresh Kumar, former CMD, BHAVINI and Homi Sethna Chair.
 "Prototype Fast Breeder Reactor (PFBR)| (Photo: PIB)")