Key Terms & Concepts — UPSC Mains
Fast Breeder Reactor (FBR)
"A nuclear reactor that uses fast (unmoderated) neutrons to both sustain a chain reaction and 'breed' new fissile material (plutonium-239) from fertile uranium-238, producing more fuel than it consumes."
A Fast Breeder Reactor (FBR) is a nuclear fission reactor that uses high-energy (fast) neutrons — as opposed to the slow, thermalised neutrons used in conventional reactors — to sustain the chain reaction. The distinguishing feature is its ability to 'breed' fissile plutonium-239 from non-fissile uranium-238 (which comprises 99.3% of natural uranium) through neutron capture and beta decay. A breeder reactor with a 'breeding ratio' greater than 1 produces more fissile fuel than it consumes. India's Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, Tamil Nadu — developed by Bhavini (Bharatiya Nabhikiya Vidyut Nigam Limited) — is a 500 MWe sodium-cooled FBR. Liquid sodium is used as coolant (rather than water) because sodium does not moderate neutrons. The reactor uses mixed oxide (MOX) fuel — a combination of uranium-238 and plutonium-239 — with uranium-238 and thorium-232 blankets that breed new Pu-239 and U-233 respectively. The PFBR was originally scheduled for completion in 2010 but faced successive delays due to technical and governance challenges. It achieved first criticality in 2024.
The FBR is the pivotal technology of India's three-stage nuclear programme — Stage 2 depends entirely on FBR technology to breed plutonium and produce the fissile material needed for Stage 3 (thorium-based reactors). Without successful FBRs, India cannot transition to Stage 3 or achieve nuclear energy self-sufficiency.
- 1 Core principle: breeds more fissile Pu-239 from fertile U-238 than it consumes — net gain in fissile material
- 2 Coolant: liquid sodium (not water) — sodium does not slow neutrons; sodium fire risk is a key safety challenge
- 3 Fuel: Mixed Oxide (MOX) — plutonium-239 + uranium-238
- 4 Blanket material: U-238 breeds Pu-239; Th-232 breeds U-233 (linking to Stage 3)
- 5 PFBR location: Kalpakkam, Tamil Nadu — operated by BHAVINI under DAE
- 6 Design capacity: 500 MWe; first criticality: 2024 (16 years behind original 2010 schedule)
- 7 Cost escalation: ₹3,500 crore (2004 estimate) to ₹8,000+ crore (2024 actual)
- 8 AERB (Atomic Energy Regulatory Board) oversees nuclear safety — independence from DAE is a structural concern
The PFBR at Kalpakkam achieved first criticality in 2024 — a milestone that activates Stage 2 of India's nuclear programme. Once commercially operational, the PFBR will breed plutonium to fuel the next generation of FBRs, which will in turn breed uranium-233 from thorium to power Stage 3 reactors — the end-state of India's self-sufficient thorium-based nuclear future.
