India's Prototype Fast Breeder Reactor In Tamil Nadu Achieves Criticality In Historic Nuclear Milestone: Why This Is Important
· Free Press Journal
India has taken a landmark step in its long-running nuclear programme, with the Prototype Fast Breeder Reactor (PFBR) at Kalpakkam in Tamil Nadu achieving criticality, meaning the reactor has successfully initiated and sustained a self-sustaining nuclear chain reaction for the first time.
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Prime Minister Narendra Modi hailed the achievement, calling it 'a defining step forward in India's civil nuclear journey, marking significant progress in the second stage of its nuclear programme.'
What does 'achieving criticality' actually mean?
In terms of nuclear energy, criticality means the reactor has reached the point where it can sustain a nuclear fission reaction, with the number of neutrons produced in the reactor sufficient to keep the chain reaction going without external intervention. It does not mean the reactor has begun supplying electricity at full capacity - that will follow a staged commissioning process - but it is one of the most critical milestones in bringing any nuclear reactor online.
Today, India takes a defining step in its civil nuclear journey, advancing the second stage of its nuclear programme.
— Narendra Modi (@narendramodi) April 6, 2026
The indigenously designed and built Prototype Fast Breeder Reactor at Kalpakkam has attained criticality.
This advanced reactor, capable of producing more fuel…
India's three-stage nuclear vision
With this milestone, India has entered Stage II of the nuclear programme that Dr. Homi Bhabha had envisioned. The PFBR uses Uranium-Plutonium Mixed Oxide fuel, while a surrounding blanket of Uranium-238 undergoes transmutation to produce additional fuel. In later stages, Thorium-232 will be used to produce Uranium-233, paving the way for the third stage of India's nuclear programme and enabling the utilisation of the country's vast thorium reserves.
Why this is a game-changer for India
The significance of this milestone extends well beyond the reactor itself. India has limited uranium resources but holds about 25 percent of the world's thorium deposits, offering a path to energy independence for centuries. This will reduce reliance on imported uranium, which currently makes up over 70 percent of India's needs.
Once fully operational, India will become only the second country after Russia to have a commercial fast breeder reactor. The reactor was built indigenously with contributions from over 200 Indian industries, including several MSMEs, aligning with the government's push for self-reliance under the Aatmanirbhar Bharat initiative.
The government has set out plans to expand nuclear capacity to around 22 GW by 2031-32 and a much larger 100 GW ambition by 2047 under the Nuclear Energy Mission. In a March 2026 parliamentary reply, the government said that once the PFBR achieved first criticality, it would approach the financial sanction of the twin FBR 1 and FBR 2 projects at Kalpakkam, signalling that this milestone is set to unlock the next wave of breeder reactor investment across the country.