India's Three-Stage Nuclear Power Programme

India's Three-Stage Nuclear Power Programme is a long-term plan to make India self-reliant in nuclear power. India has very little uranium, the usual nuclear fuel, but it has some of the largest thorium reserves in the world. Thorium cannot be used as fuel directly. So the plan uses three kinds of reactors, one after another, to slowly turn India's small uranium stock and huge thorium stock into usable fuel.

Why does India need a special plan?

Most countries simply run their reactors on uranium. India cannot rely on that path for long. NPCIL has estimated that India's own uranium can support only about 10 GWe of power from its main reactor type for about 40 years. That is tiny compared to India's needs. But India has large deposits of thorium, mostly in the beach sands of its coasts.

If India can use thorium, it would have fuel for centuries. The three-stage plan is the bridge from "little uranium" to "plenty of thorium".

Where did it come from?

The plan was drawn up by Dr Homi J. Bhabha, often called the father of India's nuclear programme. India set up the Atomic Energy Commission (AEC) in August 1948, with Bhabha as its first chairman. The Department of Atomic Energy (DAE) came into being on 3 August 1954, directly under the Prime Minister. Bhabha presented the three-stage plan in 1954, and the government formally adopted it in 1958. This choice to build around thorium was unusual. Almost no other country took this path.

First, a little nuclear science

To understand the stages, you need two ideas:

• Fissile material can split (undergo fission) and keep a chain reaction going. Examples: uranium-235, plutonium-239 and uranium-233.
• Fertile material cannot keep a chain reaction going by itself. But when it absorbs a neutron inside a reactor, it turns into fissile material. Examples: uranium-238 turns into plutonium-239; thorium-232 turns into uranium-233.

Think of fertile material as raw wheat and fissile material as flour. You cannot eat raw wheat, but once it is milled, it becomes useful. The reactors in Stages 1 and 2 are the "mills" that turn fertile material into fuel.

Stage 1: Pressurised Heavy Water Reactors (PHWRs)

These reactors burn natural uranium (uranium as dug from the ground, without enrichment). They use heavy water both to cool the reactor and to slow down neutrons (as a moderator). Natural uranium is about 99.3% uranium-238 and only about 0.7% uranium-235. While the uranium-235 burns and makes electricity, some of the uranium-238 absorbs neutrons and becomes plutonium-239.

This plutonium is taken out of the used fuel by reprocessing and saved for Stage 2. India chose heavy-water reactors because building heavy-water plants was easier for it than building uranium enrichment plants. Almost all of India's operating reactors today are PHWRs, including the standard 700 MW design being built in "fleet mode".

Stage 2: Fast Breeder Reactors (FBRs)

These reactors use plutonium-239 from Stage 1, mixed with uranium, as fuel. They use fast neutrons (neutrons that are not slowed down), so there is no moderator, and they are cooled by liquid sodium instead of water. Their special feature is breeding: around the core sits a "blanket" of uranium-238, which absorbs neutrons and becomes new plutonium-239.

A breeder makes more fissile fuel than it burns. Over time, this lets India multiply its fuel stock and build many more reactors. Later, thorium will be placed in the blanket so that it turns into uranium-233, the fuel for Stage 3.

• India's first fast reactor, the Fast Breeder Test Reactor (FBTR) at Kalpakkam, Tamil Nadu, first went critical on 18 October 1985. It uses a special mixed carbide fuel of plutonium and uranium.
• The Prototype Fast Breeder Reactor (PFBR), a 500 MWe sodium-cooled reactor at Kalpakkam, was designed by the Indira Gandhi Centre for Atomic Research (IGCAR) and built by BHAVINI (Bharatiya Nabhikiya Vidyut Nigam Limited), a government company under the DAE. It uses uranium-plutonium mixed oxide (MOX) fuel. The project began in 2003-04 and was planned to run by 2010, but faced long delays. It reached first criticality on 6 April 2026, marking India's real entry into Stage 2.

Stage 3: Thorium-based reactors

In the final stage, reactors will run on thorium-232 together with uranium-233. As they run, the thorium keeps turning into new uranium-233, so the reactor keeps making much of its own fuel. This is how India's vast thorium reserves would finally be used.

• KAMINI (Kalpakkam Mini reactor), a 30 kW research reactor at Kalpakkam built by BARC and IGCAR, went critical on 29 October 1996. It is the world's only operating reactor fuelled by uranium-233.
• The Advanced Heavy Water Reactor (AHWR), a 300 MWe design by the Bhabha Atomic Research Centre (BARC), is meant to show large-scale use of thorium. It is designed to get about two-thirds of its power from thorium. It is still a design; it has not been built yet.

How much thorium does India have?

India's thorium is found mainly in monazite, a mineral present in beach and inland sands. The Atomic Minerals Directorate (AMD) earlier estimated about 11.93 million tonnes of monazite, containing roughly 1.07 million tonnes of thorium. More recent estimates put monazite at about 13.15 million tonnes. Indian monazite has about 9 to 10% thorium oxide. Deposits are spread over Kerala, Tamil Nadu, Odisha, Andhra Pradesh, West Bengal, Maharashtra and Gujarat, with inland deposits in Jharkhand and West Bengal. Indian Rare Earths Limited (IREL) processes monazite at Chavara (Kerala), Manavalakurichi (Tamil Nadu) and OSCOM (Odisha).

Where does India stand today?

As of mid-2026, India has 24 reactors in commercial operation with about 8,780 MW of capacity, a little over 3% of India's electricity. Most of these are Stage 1 PHWRs. Since the 2008 NSG waiver, India also imports uranium and runs some foreign-design light water reactors (like the Russian VVERs at Kudankulam) under IAEA safeguards.

These are outside the three-stage plan but add to capacity. The government target is 100 GW of nuclear power by 2047. The 2025-26 Budget announced a Nuclear Energy Mission with ₹20,000 crore for research on Small Modular Reactors (SMRs), aiming for at least five Indian-designed SMRs running by 2033.

The law on who can run reactors has also changed. The SHANTI Act, 2025 (Sustainable Harnessing and Advancement of Nuclear Energy for Transforming India Act) was passed by Parliament in December 2025 and got the President's assent on 20 December 2025. It replaces the Atomic Energy Act, 1962 and the Civil Liability for Nuclear Damage Act, 2010. For the first time, it allows private companies and joint ventures to build, own and run nuclear power plants under a government licence.

The sensitive steps of the fuel chain stay only with the government or its companies. These include mining uranium and thorium, enrichment (raising the share of uranium-235 in uranium), reprocessing of used fuel, managing high-level waste (the most radioactive leftovers) and making heavy water. This matters for the three-stage plan, because reprocessing is the step that takes plutonium out of Stage 1 fuel to feed Stage 2.

As of October 2026, about 17 more reactors (about 13 GW) are at various stages of being built, and the government expects private companies to add about 30 GW of the 100 GW target by 2047.

Commonly confused concepts

• Fissile vs fertile: Fissile material (U-235, Pu-239, U-233) can sustain a chain reaction. Fertile material (U-238, Th-232) cannot, but turns into fissile material after absorbing a neutron.
• PHWR vs PWR: A PHWR uses natural uranium and heavy water. A PWR (Pressurised Water Reactor) uses enriched uranium and ordinary (light) water. India's own reactors are mostly PHWRs.
• Fast reactor vs thermal reactor: A thermal reactor slows neutrons down with a moderator (water, heavy water or graphite). A fast reactor uses fast neutrons and has no moderator.
• FBTR vs PFBR: FBTR (1985) is a small test reactor. PFBR (criticality 2026) is a 500 MWe prototype power reactor. Both are at Kalpakkam.
• AEC vs AERB: The Atomic Energy Commission makes nuclear policy and approves programmes. The Atomic Energy Regulatory Board checks safety and gives licences.

Issues, criticism and the way forward

• Very long delays: The PFBR reached criticality more than 15 years behind its original schedule, and its cost more than doubled. Stage 3 at commercial scale is still decades away.
• Slow growth of Stage 1: Stage 2 needs plutonium from Stage 1. Because Stage 1 grew slowly, there is less plutonium to build many breeders quickly.
• Hard technology: Liquid sodium burns when it touches air or water, so sodium-cooled reactors need very careful engineering. Using uranium-233 is also hard because it comes with uranium-232, which gives off strong radiation and makes fuel handling difficult.
• Way forward: Experts suggest building more PHWRs in fleet mode, starting follow-up fast breeder units after PFBR runs well, building an AHWR demonstrator, and using imported uranium for faster capacity growth while the thorium path matures.

Concepts to Know

• Criticality: The point when a reactor's chain reaction becomes self-sustaining, meaning each fission causes, on average, exactly one more fission. It is the reactor "switching on", not full power.
• Heavy water: Water in which the hydrogen atoms are a heavier form called deuterium. It slows neutrons without absorbing many of them, which lets natural uranium work as fuel.
• Moderator: A material that slows down neutrons so they can split uranium-235 more easily.
• Reprocessing: Chemically treating used reactor fuel to separate the useful plutonium and uranium from waste.
• MWe (megawatt electric): The amount of electricity a power plant sends out, as opposed to the heat it makes (MWt, megawatt thermal).
• Monazite: A reddish-brown mineral found in beach sands, rich in thorium and rare earth elements.