PFBR at Kalpakkam Achieves First Criticality: India Enters Stage II of Nuclear Programme
The 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, Tamil Nadu attained first criticality on April 6, 2026, at 8:25 PM IST.
"Criticality" is the precise condition where a nuclear chain reaction becomes self-sustaining — each fission event produces exactly enough neutrons to trigger the next reaction at a steady rate.
The reactor is built and operated by Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI), a Government of India enterprise under the Department of Atomic Energy.
Achieving criticality does not mean the reactor is generating electricity — it marks the beginning of low-power physics experiments before a staged increase in power output.
Commercial operations are expected to begin by September 2026, after grid synchronisation.
With this milestone, India formally advances into Stage II of its three-stage nuclear power programme.
Upon full commercial operation, India will become only the second country after Russia to operate a commercial-scale fast breeder reactor.
India's Three-Stage Nuclear Power Programme
Conceived in the 1950s by physicist Homi Bhabha, India's three-stage nuclear programme is designed to work around the country's limited uranium reserves (only 1–2% of global deposits) while leveraging its enormous thorium reserves (approximately 25% of global known thorium). The programme creates a fuel cycle where each stage produces fuel for the next.
The PFBR achieving criticality is the first major operational step of Stage II, the lynchpin of the entire programme. Without a functioning FBR, India cannot produce enough uranium-233 to fuel Stage III and realise its thorium-based energy independence vision.
Fast Breeder Reactor Technology
Unlike conventional thermal reactors that use slow (thermal) neutrons, fast breeder reactors use high-energy (fast) neutrons to sustain fission. The PFBR uses Uranium-Plutonium Mixed Oxide (MOX) fuel in its core, surrounded by a blanket of uranium-238. Fast neutrons striking the blanket convert U-238 into fissile Pu-239 — producing more fuel than the reactor consumes.
The PFBR's successful criticality validates India's indigenous mastery of fast breeder technology, a capability held by only a handful of nations globally.
Nuclear Energy and India's Energy Security
India currently generates about 7,000 MW from nuclear power, which is roughly 3% of total electricity generation. The government has set a target of 100 GW of nuclear power by 2047 under the Viksit Bharat framework. The PFBR is pivotal to scaling this capacity, as the breeder cycle can multiply the effective fuel supply many times over.
The PFBR milestone strengthens the case for nuclear energy in India's clean energy mix and is a demonstration of successful self-reliance (Atmanirbhar Bharat) in a high-stakes strategic technology.
- Reactor name: Prototype Fast Breeder Reactor (PFBR)
- Location: Kalpakkam, Tamil Nadu (Indira Gandhi Centre for Atomic Research campus)
- Capacity: 500 MWe
- Operator: BHAVINI (Bharatiya Nabhikiya Vidyut Nigam Limited), under DAE
- Date of criticality: April 6, 2026
- Fuel: Uranium-Plutonium Mixed Oxide (MOX), with U-238 and Th-232 blankets
- Coolant: Liquid sodium
- Stage in India's nuclear programme: Stage II (Fast Breeder stage)
- India's thorium reserves: ~25% of global known reserves, the largest in the world
- India's uranium reserves: Only ~1–2% of global deposits
- Countries operating commercial-scale FBRs: Russia (BN-800, BN-1200); India (PFBR) will be second
- Target for commercial operation: September 2026
- India's nuclear power target: 100 GW by 2047