Kalpakkam Fast Breeder Reactor attains first criticality, India enters Stage II of nuclear programme

India's 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam in Tamil Nadu attained first criticality on 6 April 2026 at 8:25 pm. The Department of Atomic Energy described it as a historic step in providing long-term energy security and advancing indigenous nuclear technology.

A "fast breeder" reactor is one that uses fast (un-moderated) neutrons to produce more fissile material than it consumes. The PFBR uses Uranium-Plutonium Mixed Oxide (MOX) fuel. Fast neutrons convert fertile Uranium-238 into fissile Plutonium-239, which can later be reprocessed into fresh fuel. The coolant is liquid sodium, not water, because sodium does not slow down neutrons.

The reactor is a centrepiece of India's three-stage nuclear power programme designed by physicist Homi Bhabha in the 1950s. Stage I uses Pressurised Heavy Water Reactors with natural uranium. Stage II uses fast breeder reactors fuelled by plutonium produced in Stage I. Stage III is a thorium-based cycle using India's vast monazite sand reserves. With first criticality at the PFBR, the country has formally moved from Stage I to Stage II, bringing thorium energy measurably closer.

The reactor is operated by Bharatiya Nabhikiya Vidyut Nigam Ltd (BHAVINI), a Government of India enterprise under the Department of Atomic Energy. Construction began in 2004; the original commissioning target was 2010, but the project saw multiple delays. The final cost is estimated at about Rs 8,181 crore against the original Rs 3,492 crore. India will now be the second country, after Russia, to operate a commercial-scale fast breeder. The PFBR will undergo phased power ascension and is expected to start commercial electricity generation by September 2026, subject to regulatory clearance at each step.

Exam angle: Direct UPSC / State PCS / SSC question types - Stage II of the three-stage programme uses fast breeder reactors and MOX fuel. Operating agency: BHAVINI. Coolant: liquid sodium. Fertile to fissile conversion: U-238 to Pu-239. Location: Kalpakkam (Tamil Nadu).