India’s first prototype fast-breeder reactor (PFBR) in Tamil Nadu‘s Kalpakkam on Monday (April 6, 2026) came another step forward in its civil nuclear journey as it attained criticality.
First criticality in a fast breeder reactor is the moment when the nuclear chain reaction becomes self-sustaining. A breeder reactor is a nuclear reactor that produces more fissile material than it consumes. In a ‘fast’ breeder reactor, the neutrons aren’t slowed, allowing them to trigger specific fission reactions.
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The PFBR is a machine that produces more nuclear fuel than it consumes. Its core-loading event is being hailed as a “milestone” because the operationalisation of the PFBR will mark the start of stage II of India’s three-stage nuclear power programme.
The PFBR in Kalpakkam is the first-of-its-kind nuclear reactor to use plutonium-based mixed oxide as fuel and liquid sodium as coolant. It will also utilise the spent fuel of Pressurised Heavy Water Reactors, which form the mainstay of nuclear power in India at present.
