Nuclear Energy in India: Fission Basics, Three-Stage Programme, Reactor Types, PFBR, SMRs and Policy (UPSC Notes + PYQs)

Background: why nuclear power matters for India

India needs large amounts of reliable electricity to grow, while it has committed to cutting the carbon intensity of its economy and reaching net zero by 2070. Coal still provides most power, and solar and wind vary with the weather and season. Nuclear power offers steady, round-the-clock electricity with very low carbon emissions over its life cycle. India’s nuclear story began with the Atomic Energy Act, 1948 and the Department of Atomic Energy (1954), under Homi J. Bhabha. The first power reactors at Tarapur started in 1969. After the 1974 and 1998 tests, India faced international restrictions on fuel and technology, which shaped its reliance on indigenous Pressurised Heavy Water Reactors. The 2008 civil nuclear agreement with the US and the NSG waiver opened access to imported uranium and reactors.

Fission and fusion

In fission, a heavy nucleus such as U-235 splits when hit by a neutron, releasing energy and more neutrons that sustain a chain reaction. Moderators (heavy water, light water, graphite) slow neutrons; control rods (boron, cadmium) absorb them. Fusion joins light nuclei (hydrogen isotopes) and powers the sun; ITER in France, where India is a partner, aims to show it at scale.

Three-stage programme

India has modest uranium but some of the world’s largest thorium reserves, mostly in monazite sands of Kerala and Odisha coasts.

Where India stands

About two dozen operating reactors, run mainly by NPCIL, with installed capacity of around 8.8 GW. Indigenous 700 MWe PHWRs (Kakrapar 3 and 4, Rajasthan 7) are now operating. Kudankulam uses Russian VVER light-water reactors. The PFBR, built by BHAVINI, began core loading in 2024.

New directions

The 2025 Union Budget announced a Nuclear Energy Mission with ₹20,000 crore for small modular reactors, aiming for at least five indigenous SMRs by 2033, and amendments to the Atomic Energy Act and the Civil Liability for Nuclear Damage Act to allow private participation. Bharat Small Reactors (220 MWe PHWR design) are planned for captive industrial use.

Types of reactors

The type matters because each stage of India’s programme depends on a different reactor: PHWRs in stage one, fast breeders in stage two and thorium-based reactors in stage three.

Debates

For: low-carbon baseload power, energy security, net zero by 2070. Against: high capital cost, long delays, waste management, safety fears after Fukushima (2011), and land and protest issues (Kudankulam, Jaitapur).

Fast breeder vs thermal reactor

A thermal reactor uses slow neutrons. A moderator such as heavy water or graphite slows the neutrons so that they can split uranium-235 atoms efficiently. Most of the uranium, uranium-238, is not used. A fast breeder reactor uses fast neutrons and no moderator. Its core contains plutonium-239, surrounded by a blanket of uranium-238 or thorium-232. The fast neutrons convert the blanket material into new fissile fuel: plutonium-239 from uranium-238, or uranium-233 from thorium. So it ‘breeds’ more fuel than it consumes. Because heat in the core is very intense, liquid sodium is used as the coolant. The Prototype Fast Breeder Reactor at Kalpakkam, built by BHAVINI with a design capacity of 500 MWe, is the key step to stage two.

Fission vs fusion and ITER

India is one of seven members of ITER, the international fusion project being built in France, along with the EU, China, Japan, Korea, Russia and the US. India joined in 2005 and contributes in kind: the cryostat (the large steel vessel around the machine), in-wall shielding, cooling water systems, cryolines, and heating and power systems, built largely by Indian industry. At home, the Institute for Plasma Research, Gandhinagar, runs the tokamaks Aditya and SST-1.

Safety, liability and waste

Public concern about nuclear power centres on accidents, waste and the cost of liability. Chernobyl (1986) and Fukushima (2011) showed what can go wrong, and protests at Kudankulam and Jaitapur followed. India’s regulator is the Atomic Energy Regulatory Board (1983). The Civil Liability for Nuclear Damage Act, 2010 channels liability to the operator and gives the operator a right of recourse against suppliers, which foreign vendors said discouraged them. India follows a closed fuel cycle: spent fuel is reprocessed to recover plutonium and uranium, which reduces the volume of high-level waste that must be vitrified and stored. A balanced Mains answer acknowledges these concerns and points to strong regulation, transparency and local benefit sharing as the way to build trust.

Writing a Mains answer

For questions on India’s nuclear programme, begin with the three-stage plan and the thorium logic, then use a table of reactor types. Explain the PFBR as the bridge to stage two. Add India’s role in ITER for fusion. Close with challenges: cost and delays, fuel supply, liability, public acceptance, and the need for private and state participation to scale up.

Nuclear Energy: UPSC angle

Nuclear Energy UPSC PYQs (Prelims)

Questions UPSC has actually asked, from the official papers. Pick an option to check yourself.

Mains PYQs on this topic

Questions from the official UPSC Mains papers (2023-2026 in the Battle IAS Mains bank), newest first. Each links to a model answer.

1. UPSC Mains 2026 · GS Paper III · Q6 · 10 marks

   Distinguish between a Fast Breeder Reactor (FBR) and a thermal nuclear reactor. In the context of first indigenously developed prototype FBR at Kalpakkam, explain the term 'criticality'. What are its implications for clean energy future of our country?

   Model answer and approach

2. UPSC Mains 2025 · GS Paper III · Q5 · 10 marks

   The fusion energy programme in India has steadily evolved over the past few decades. Mention India’s contributions to the international fusion energy project — International Thermonuclear Experimental Reactor (ITER). What will be the implications of the success of this project for the future of global energy ?

   Model answer and approach

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Image: Petr Pavlicek/IAEA, Wikimedia Commons, Attribution