Is it producing full power yet?

Not stated. First criticality is the start, followed by low-power tests and gradual power raising.

Is it the same as a bomb reaction?

No. Criticality here means a controlled chain reaction under regulator oversight.

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What is India's Fast Breeder Reactor at Kalpakkam? A simple explainer

The PFBR "makes more fuel than it uses". Here's what that means, and why thorium matters.

Last checked: 28 Oct 2026

Why now: on 27 Oct 2026 at ESTIC 2026, the PFBR's first criticality was highlighted again in public discussion. This page is a plain explainer only.

In short

The 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, Tamil Nadu attained first criticality on 6 April 2026 at about 8:25 PM (DAE / PIB, 7 Apr 2026; PIB, 7 Apr 2026). Criticality means a controlled, self-sustaining fission chain reaction has started — not that the plant is already at full power. The reactor is designed to breed more fuel than it consumes, using a uranium-plutonium MOX core and a uranium-238 blanket, as part of India's three-stage nuclear programme that aims toward thorium.

1. What happened

The 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, Tamil Nadu attained first criticality on 6 April 2026 at about 8:25 PM (DAE, 7 Apr 2026; PIB Delhi, 7 Apr 2026). It came up again on 27 Oct 2026 at ESTIC 2026 (Emerging Science, Technology and Innovation Conclave, New Delhi) (PIB India on X, 27 Oct 2026).

2. What does "criticality" mean?

Criticality is the start of a controlled, self-sustaining nuclear fission chain reaction. It is not the same as producing full power: after criticality, low-power physics experiments are run to study how the reactor behaves. AERB permission covered fuel loading, First Approach to Criticality and Low Power Physics Experiments (PIB/AERB, 2024).

3. Who built it

Designed indigenously by IGCAR (Indira Gandhi Centre for Atomic Research, a DAE R&D centre).
Built and commissioned by BHAVINI (Bharatiya Nabhikiya Vidyut Nigam Ltd, a DAE PSU).
The safety regulator AERB cleared it after a multi-tier safety review with a resident site observer team.

(DAE, 7 Apr 2026; PIB factsheet, 7 Apr 2026; PIB/AERB, 2024)

4. How it "breeds" fuel

It uses uranium-plutonium mixed oxide (MOX) fuel.
The core is surrounded by a blanket of uranium-238.
Fast neutrons turn U-238 into plutonium-239, which is itself fuel, so it can produce more fuel than it consumes.
It is cooled by liquid sodium (not water) and is a pool-type design.
The plutonium comes from reprocessed spent fuel of India's pressurised heavy water reactors.

(PIB factsheet, 7 Apr 2026; DAE, 7 Apr 2026)

5. India's three-stage plan (Homi Bhabha's vision)

Stage 1: PHWRs on natural uranium.
Stage 2: fast breeder reactors using plutonium from Stage 1 — PFBR is India's entry into this stage.
Stage 3: thorium-based reactors using U-233 bred from thorium-232.

India has limited uranium but one of the world's largest thorium reserves. The PFBR is designed to later use thorium-232 in its blanket to make U-233.

(PIB on the three-stage programme and FBR 1&2, sourced; PIB factsheet, 7 Apr 2026)

6. Why it matters

Per PIB, once fully operational India would be only the second country after Russia to operate a commercial fast breeder reactor. The government has approved pre-project activities for a twin 2 × 500 MWe FBR 1&2 project at Kalpakkam (PIB; PIB factsheet, 7 Apr 2026).

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FAQ

Is it producing full power yet?: Not stated. First criticality is the start, followed by low-power tests and gradual power raising.
Is it the same as a bomb reaction?: No. Criticality here means a controlled chain reaction under regulator oversight.
When is Homi Bhabha's birth anniversary?: 30 October.

Sources

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