PROTOTYPE FAST BREEDER REACTOR (PFBR)

Why in News?

The indigenously designed and built Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, Tamil Nadu, successfully achieved its first criticality on 6 April 2026. The milestone marks a major step towards the implementation of Dr. Homi J. Bhabha’s Three-Stage Nuclear Power Programme and India’s long-term nuclear energy security.

What is the First Criticality?

• Criticality is achieved when a nuclear reactor sustains a self-sustaining nuclear fission chain reaction.
• First criticality is an important milestone before the reactor progresses towards subsequent stages of power generation and commercial operation.

About Prototype Fast Breeder Reactor (PFBR)

• Location: Kalpakkam, Tamil Nadu
• Type: Fast Breeder Reactor (FBR)
• Fuel: Uranium-Plutonium Mixed Oxide (MOX) fuel
• Coolant: Liquid sodium
• Role: Forerunner of India’s second stage of the three-stage nuclear programme.
• It is India’s first commercial fast reactor.

How Does a Fast Breeder Reactor Work?

The PFBR uses fast neutrons to convert fertile material into fissile material.

• The reactor core uses MOX fuel containing uranium and plutonium.
• It is surrounded by a Uranium-238 (U-238) blanket.
• Fast neutrons convert U-238 into Plutonium-239 (Pu-239).
• Pu-239 can subsequently be used as nuclear fuel.
• Thus, a breeder reactor can produce more fissile fuel than it consumes.

The PFBR is also important for India’s eventual transition towards thorium-based nuclear energy.

• Thorium-232 (Th-232) can be placed in the reactor blanket.
• Through nuclear transmutation, Th-232 can be converted into Uranium-233 (U-233).
• U-233 is a fissile material that can serve as fuel for India’s third-stage nuclear programme.

India’s Three-Stage Nuclear Power Programme

The programme was conceived under the vision of Dr. Homi J. Bhabha to maximise India’s limited uranium resources and utilise its abundant thorium reserves.

Stage I – Pressurised Heavy Water Reactors (PHWRs)

• Uses natural uranium as fuel.
• Natural uranium primarily contains U-238 and a small proportion of U-235.
• PHWRs generate electricity and produce spent nuclear fuel containing plutonium.
• The spent fuel is reprocessed to recover Pu-239.

Natural Uranium → PHWRs → Plutonium recovery

Stage II – Fast Breeder Reactors (FBRs)

• Uses plutonium recovered from Stage I as fuel, generally in the form of MOX.
• FBRs use fast neutrons to convert U-238 into Pu-239.
• This allows India to expand its fissile-material inventory while generating electricity.

Pu-239 + U-238 → FBRs → More Pu-239

The PFBR is the forerunner of this second stage.

Stage III – Thorium-Based Nuclear Power

• Once sufficient FBR capacity is established, India plans to utilise its large thorium reserves on a large scale.
• Th-232 will be converted into U-233.
• U-233 will then serve as the principal fissile fuel for the third-stage reactors.

Th-232 → U-233 → Third-stage nuclear reactors.

Source: PIB

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