Atoms for Peace and Power: Nuclear Energy

Nuclear energy is the energy released from the nucleus of an atom, either by splitting heavy nuclei (fission) or by fusing light ones (fusion). A kilogram of nuclear fuel releases millions of times more energy than a kilogram of coal, which is why nuclear power is a compact, low-carbon source of round-the-clock electricity. For India, nuclear energy is also a seven-decade strategic project: from Homi Bhabha's three-stage vision of 1954 to the fast-breeder milestone of April 2026 and the SHANTI Act of December 2025, it links energy security, climate commitments and technological self-reliance.

Fission, fusion and the reactor family

Nuclear fission is the splitting of a heavy atomic nucleus, such as uranium-235 or plutonium-239, when struck by a neutron; the split releases heat and more neutrons, which sustain a controlled chain reaction. The heat converts water to steam that drives a turbine-generator. Nuclear fusion is the merging of light nuclei, such as the hydrogen isotopes deuterium and tritium, into a heavier nucleus, releasing even greater energy; it is the reaction that powers the sun. Criticality is the point at which a reactor achieves a self-sustaining chain reaction, the essential first step toward generating electricity. Baseload power is the minimum round-the-clock power a grid needs to stay operational, which nuclear supplies reliably, complementing intermittent solar and wind.

Reactors come in families. A Pressurised Heavy Water Reactor (PHWR) uses heavy water as moderator and coolant and burns natural uranium; it is the backbone of India's indigenous programme. A Pressurised Water Reactor (PWR) uses ordinary water under high pressure; Kudankulam's Russian-built VVER units are PWRs. A Boiling Water Reactor (BWR) lets water boil inside the core to make steam directly. A Fast Breeder Reactor (FBR) produces more fissile fuel than it consumes by converting fertile material into fissile material. Small Modular Reactors (SMRs) are nuclear reactors with capacity up to 300 megawatts, approximately one-third of conventional reactors. They are factory-assembled, modular, and designed for flexible deployment; India is developing the 220 MWe Bharat Small Modular Reactor (BSMR-200) and a 55 MWe SMR-55. The Advanced Heavy Water Reactor (AHWR) is a next-generation indigenous design meant to use the thorium-based fuel cycle, a bridge to Stage 3. The 700 MWe Kakrapar-4, an indigenous PHWR, has achieved criticality, the controlled fission chain reaction that precedes power generation, validating the fleet-mode design now being rolled out.

The reactor family at a glance. India's fleet is dominated by one home-grown design, with imported light-water reactors and the Kalpakkam fast breeder marking the newer chapters.

Why Bhabha chose the three-stage path

In 1954, Dr Homi J. Bhabha, the architect of India's nuclear programme, proposed a strategy shaped by geology: India has modest uranium reserves but some of the world's largest thorium reserves, found in the monazite sands of Kerala, Tamil Nadu and Odisha. Thorium itself is not fissile, meaning it cannot directly fuel a reactor, but it is fertile, meaning it can be converted into fissile uranium-233 inside a reactor. The three-stage programme is therefore designed to start with scarce uranium, breed fissile material step by step, and ultimately unlock abundant thorium. A closed fuel cycle completes the logic: spent fuel is reprocessed to recover reusable plutonium and uranium instead of being treated as waste, extracting maximum energy from limited domestic uranium.

The three stages, step by step

Stage 1 uses Pressurised Heavy Water Reactors fuelled by natural uranium. These reactors produce plutonium-239 as a by-product, and their spent fuel is reprocessed to recover that plutonium. Stage 2 uses Fast Breeder Reactors fuelled by the recovered plutonium in mixed-oxide form; with a uranium-238 blanket they breed more plutonium than they consume, and with a thorium-232 blanket they convert thorium into fissile uranium-233 for the final stage. Stage 3 will use advanced reactors fuelled by uranium-233 with thorium-232, finally tapping India's vast thorium reserves for long-term energy independence.

Stage 2 became real on 6 April 2026, when the 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam in Tamil Nadu attained first criticality. Designed by the Indira Gandhi Centre for Atomic Research (IGCAR) and built by Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI), both under the Department of Atomic Energy, the sodium-cooled reactor uses uranium-plutonium mixed-oxide fuel. Once fully operational, India will be only the second country after Russia to operate a commercial-level fast breeder reactor, and the thorium blanket will begin breeding the uranium-233 needed for Stage 3.

Fusion: the ITER gamble

While fission powers today's reactors, fusion is the long-term prize. ITER, the International Thermonuclear Experimental Reactor, is the world's largest tokamak, a doughnut-shaped device that uses powerful magnetic fields to confine super-hot plasma for magnetic confinement fusion. Being built at Cadarache in France by 35 partners including India, the European Union, the US, Russia, China, Japan and South Korea, ITER aims to demonstrate self-burning plasma and a fusion gain of more than ten, meaning ten times more energy out than heating energy in. Its giant cryostat keeps the magnets at ultra-cold temperatures in a vacuum.

India joined ITER in 2005 and has made significant contributions, including fabrication of the world's largest cryostat, cooling systems and high-precision components. ITER-India, supervised by the Institute for Plasma Research (IPR) under the Department of Atomic Energy, also runs India's own tokamaks, ADITYA-U and SST-1, building domestic fusion expertise. The cryostat, the world's largest, was fabricated in India by Larsen & Toubro in collaboration with ITER-India.

Fusion's promise and its problems. The physics is seductive and the engineering is brutal, which is why commercial timelines keep slipping.

The 2025-26 policy turn

The Union Budget 2025-26 announced the Nuclear Energy Mission with an outlay of ₹20,000 crore, targeting 100 GW of nuclear capacity by 2047 against about 8.7 GW today. Its centrepiece is at least five indigenously designed SMRs operational by 2033, including the BSMR-200 developed jointly by BARC and the Nuclear Power Corporation of India (NPCIL), 220 MWe Bharat Small Reactors for captive industrial use and retiring coal sites. Separately, ten indigenous 700 MWe PHWRs sanctioned in fleet mode in 2017, now being taken up at Kaiga, Gorakhpur, Chutka and Mahi Banswara for faster rollout. A 5 MWth high-temperature gas-cooled reactor meant for hydrogen generation is also under development, linking nuclear heat to the green-hydrogen mission. Project execution is monitored through the PRAGATI platform, and the Global Centre for Nuclear Energy Partnership provides training and capacity building in nuclear safety and security.

The legal enabler is the SHANTI Act, the Sustainable Harnessing and Advancement of Nuclear Energy for Transforming India Act, adopted in December 2025. It consolidates and modifies the Atomic Energy Act, 1962 and the Civil Liability for Nuclear Damage Act, 2010, opening the tightly controlled civil nuclear sector to private companies and joint ventures for the first time in decades, and replaces the old supplier-liability regime with a graded liability framework capped at the rupee equivalent of 300 million Special Drawing Rights, without diluting victim compensation.

Internationally, the 2008 India-US civil nuclear agreement and the Nuclear Suppliers Group waiver of 2008 ended decades of nuclear isolation, letting India trade nuclear fuel despite not signing the Non-Proliferation Treaty, while civilian reactors were placed under International Atomic Energy Agency (IAEA) safeguards. Russia's Rosatom built the Kudankulam VVER units, India's largest station at 2,000 MWe operating; France's EDF is slated to supply EPR reactors for the proposed Jaitapur plant. In 2025, Washington delisted BARC, IGCAR and the Indian Rare Earths Limited and cleared Holtec to license SMR technology to three Indian firms (Holtec Asia, Larsen & Toubro, and Tata Consulting Engineers), while uranium-supply agreements with Russia, Kazakhstan, Canada and Australia secure imported fuel.

The Civil Liability for Nuclear Damage Act, 2010

Every foreign nuclear deal India has pursued since 2008 has run into the same wall: a 2010 law that makes India an outlier in global nuclear liability. The Civil Liability for Nuclear Damage Act, 2010, passed by Parliament in September 2010, is India's domestic law on who pays if a civil nuclear accident occurs. It places strict, no-fault liability on the operator, meaning the plant operator must compensate victims without anyone having to prove negligence, and caps the operator's liability at Rs 1,500 crore per nuclear incident. Claims beyond that are met by the government, up to the rupee equivalent of 300 million Special Drawing Rights, the International Monetary Fund's reserve asset used as an international unit of account.

The globally unusual part is Section 17(b): the operator's right of recourse against the supplier. A right of recourse is the operator's legal right to recover compensation it has paid from another party. Under Section 17(b), the operator can claim against the supplier where the incident resulted from an act of the supplier or its employee, including the supply of equipment or material with patent or latent defects or sub-standard services. Patent defects are flaws visible on inspection; latent defects are hidden flaws that surface later. Most international regimes, including the Convention on Supplementary Compensation (CSC), the International Atomic Energy Agency's 1997 convention setting minimum national compensation standards and a global pooling mechanism for catastrophic accidents, channel liability exclusively to the operator and allow recourse against suppliers only where a written contract expressly provides it or the damage was caused intentionally. India's clause goes further, and it carries the imprint of the Bhopal gas tragedy of 1984, whose lesson, that defective equipment supplied from abroad could escape accountability, the drafters wrote into the law.

India ratified the CSC in 2016, but suppliers, foreign and domestic, read Section 17(b) as open-ended exposure: a reactor vendor could face claims decades after delivery for a latent defect. The Civil Liability for Nuclear Damage Rules, 2011 softened this by tying the recourse period to the initial licence duration or the product liability period, whichever is longer, and India set up a domestic nuclear insurance pool so operators and suppliers could cover their exposure, but vendors remained wary of signing.

The practical cost was diplomatic. Agreements for foreign reactors, the French EPR units planned for Jaitapur in Maharashtra and the reactors proposed for Kovvada in Andhra Pradesh among them, stalled for years, with supplier-side liability concerns widely cited as one of the obstacles alongside pricing and technology transfer. The December 2025 SHANTI Act, which consolidates this Act with the Atomic Energy Act, 1962 and opens civil nuclear power to private companies, is the government's attempt to reopen the chapter. Whether the recourse clause survives in its strong form will decide whether foreign vendors finally sign on the dotted line.

Nuclear energy and the climate math

Nuclear power's climate case rests on two facts: it generates electricity with near-zero carbon emissions during operation, and it does so around the clock. In FY25, nuclear generation in India avoided roughly 49 million tonnes of carbon dioxide. With a 2070 net-zero commitment and rising electricity demand from industry, data centres and electric mobility, firm low-carbon power becomes the binding constraint, which is why the Economic Survey has described nuclear as one of the cleanest forms of energy, capable of overcoming the intermittency concerns of solar and wind.

The scale of the ambition is visible in the numbers: from about 8.7 GW of installed nuclear capacity today to 100 GW by 2047, which needs roughly 4 GW of new nuclear capacity every year for two decades, a build rate India has never attempted. That is the real significance of the 2025-26 policy turn: the Nuclear Energy Mission's financing, the SHANTI Act's private participation and the SMR programme are all attempts to build an industrial pipeline, not just individual reactors.

In FY 2024-25, India's nuclear plants generated about 56,681 GWh (56,681 million units), roughly 3 per cent of the country's electricity, which is the baseline the 100 GW target must grow from.

India's fleet in numbers (2025). As of 2025, India operates 25 nuclear reactors with an installed capacity of 8,880 MW, and 11 more reactors totalling 8,700 MW are under construction. The Nuclear Energy Mission announced in the Union Budget 2025-26 targets 100 GW of capacity by 2047, an eleven-fold climb from today's base.

Challenges and the way forward

Nuclear power still supplies only about 3 per cent of India's electricity despite decades of effort. Capital costs are high: the Mahi Banswara project alone entails an investment of about ₹42,000 crore for 2,800 MW, being built by the NPCIL-NTPC joint venture ASHVINI whose foundation stone was laid in September 2025. The 2010 supplier-liability law long deterred foreign vendors, a legacy the SHANTI Act now addresses. Scarce domestic uranium constrains the first-stage fleet, land acquisition and clearances stretch projects over a decade, and safety fears after Fukushima fuel local opposition, as seen at Kudankulam and Jaitapur. Safe long-term storage of radioactive waste remains an unresolved global challenge, and thorium and fast-reactor technologies are still maturing toward commercial scale.

The way forward is to mobilise private capital, green bonds and joint ventures for the 100 GW target; quickly operationalise the SHANTI Act with rules and licences; commercialise Bharat Small Modular Reactors to decarbonise industry and replace coal plants; accelerate fast-reactor and thorium research for the third stage; expand domestic uranium mining and diversify imports; build public trust through transparent safety communication; keep the Atomic Energy Regulatory Board (AERB) independent; and expand nuclear-engineering education for a growing fleet.

What is criticality in a nuclear reactor?

Criticality is the point at which a nuclear reactor achieves a self-sustaining fission chain reaction: the neutrons produced by fission exactly balance those lost to absorption and leakage. It marks the transition from construction to operation and is the essential first step before a reactor generates heat and electricity.

Why did India bet on thorium?

India has modest uranium reserves but some of the world's largest thorium reserves in its coastal monazite sands. Thorium is fertile rather than fissile: it can be converted into fissile uranium-233 inside a reactor. Bhabha's three-stage programme is designed to breed that conversion step by step, turning a geological constraint into long-term energy security.

What is a tokamak?

A tokamak is a doughnut-shaped device that uses powerful magnetic fields to confine super-hot plasma for fusion. Because no material can withstand fusion temperatures, magnetic confinement holds the fuel away from the walls. ITER, under construction in France, is the world's largest tokamak.

Are Small Modular Reactors cheaper than large reactors?

Not necessarily per unit of power. The case for SMRs is that they are manufactured in factories rather than constructed on site, which can cut construction risk and time, and they fit where a large reactor does not: beside retiring coal plants, industrial clusters or weak grids. India plans at least five indigenous SMRs operational by 2033.

Key Terms

• Nuclear energy: Energy released from atomic nuclei, either by splitting heavy nuclei (fission) or fusing light ones (fusion), which is converted into heat to generate electricity. It is a low-carbon energy source that provides firm, round-the-clock power unlike intermittent renewables, but it raises concerns over radioactive waste disposal, accident risk and high upfront capital cost. Its role in clean-energy transitions is a live debate in climate policy. Example: Nuclear power supplies roughly one-tenth of the world's electricity, with France generating the majority of its electricity from nuclear plants.
• fission: The splitting of a heavy atomic nucleus, such as uranium-235 or plutonium-239, into two lighter nuclei when struck by a neutron, releasing a large amount of energy along with more neutrons that can sustain a chain reaction. Controlled fission in a reactor core is the basis of all commercial nuclear power, while uncontrolled fission drives atomic bombs. About 200 MeV of energy is released per fission event, millions of times more than a chemical reaction. Example: India's Pressurised Heavy Water Reactors (PHWRs) generate electricity from the fission of natural uranium fuel, moderated by heavy water.
• fusion: The process in which two light atomic nuclei combine to form a heavier nucleus, releasing enormous energy because the product weighs slightly less than the inputs, with the difference converted to energy by E=mc2. Fusion powers the sun and stars, where hydrogen fuses into helium at extreme temperature and pressure. Reproducing controlled fusion on Earth, the goal of projects like ITER in France, promises near-limitless clean energy with abundant fuel (deuterium from seawater) and no long-lived radioactive waste. Example: In December 2022, the US National Ignition Facility achieved fusion ignition, releasing more fusion energy than the laser energy delivered to the fuel pellet.
• SHANTI Act: The SHANTI Act (Sustainable Harnessing and Advancement of Nuclear Energy for Transforming India), passed in December 2025, is India's new nuclear law that repeals and consolidates the Atomic Energy Act, 1962 and the Civil Liability for Nuclear Damage Act, 2010. For the first time since Independence it allows private companies and joint ventures to build, own, operate and decommission nuclear power plants, while sensitive activities like fuel production, heavy water manufacture and waste management stay with the state. It gives statutory backing to the Atomic Energy Regulatory Board and replaces the 2010 supplier-liability regime with graded, capacity-linked operator liability. Example: The Act supports India's target of 100 GW of nuclear capacity by 2047.
• Nuclear fission: The process in which the nucleus of a heavy atom, such as uranium-235 or plutonium-239, splits into two or more smaller nuclei when struck by a neutron, releasing a large amount of energy together with additional neutrons that sustain a chain reaction. In reactors the reaction is controlled to produce steady heat for electricity; uncontrolled, it releases the explosive energy of nuclear weapons. Fission of one kilogram of uranium-235 yields energy equivalent to burning about 3,000 tonnes of coal. Example: India's pressurised heavy water reactors burn natural uranium in a controlled fission chain reaction moderated by heavy water.
• chain reaction: A chain reaction is a self-sustaining sequence of nuclear fissions in which neutrons released by one fission trigger further fissions. In nuclear reactors the reaction is controlled with moderators and control rods; in nuclear weapons it is deliberately uncontrolled. Example: India's pressurised heavy water reactors sustain a controlled chain reaction to generate electricity.
• Nuclear fusion: The process in which two light atomic nuclei, typically isotopes of hydrogen such as deuterium and tritium, combine to form a heavier nucleus, releasing energy as a small amount of mass is converted into energy. It is the reaction that powers the Sun and stars, and it produces no long-lived high-level radioactive waste, but sustaining controlled fusion on Earth requires temperatures above 100 million degrees Celsius and extraordinary confinement. Achieving net energy gain from fusion remains an unsolved engineering challenge. Example: The ITER project in France is the world's largest experimental effort to demonstrate net fusion energy using a tokamak device.
• Criticality: Criticality is the state of a nuclear fission chain reaction in which each fission event produces, on average, exactly one further fission, so the reaction sustains itself at a constant power level. In reactor physics this is expressed by the effective multiplication factor k equal to one; below one the reactor is subcritical and the reaction dies out, above one it is supercritical and power rises. Achieving first criticality is the commissioning milestone at which a new reactor is shown to sustain a controlled chain reaction. Example: Unit 1 of the Kudankulam Nuclear Power Plant attained first criticality in July 2013, the first step toward its commercial operation.
• Baseload power: Baseload power is the minimum level of electricity demand on a grid over a given period, the continuous load that must be supplied around the clock regardless of the time of day. Baseload power plants, such as nuclear and coal plants, run continuously at high capacity factors to meet this constant demand, in contrast to peaking plants that ramp up only during high-demand hours. The concept is central to debates on integrating intermittent renewables, since solar and wind cannot by themselves guarantee round-the-clock baseload without storage or backup. Example: A nuclear reactor operating at over 90 percent capacity factor provides steady baseload power, complementing solar and wind generation which varies with weather.
• Dr Homi J. Bhabha: Dr Homi Jehangir Bhabha is regarded as the father of India's nuclear programme. He founded the Tata Institute of Fundamental Research in 1945 and the Atomic Energy Establishment at Trombay, later renamed the Bhabha Atomic Research Centre, and as the first chairman of the Atomic Energy Commission he conceived the three-stage nuclear power programme that still guides India. He died in the crash of Air India Flight 101 over Mont Blanc on 24 January 1966. Example: India's three-stage programme, using uranium-fuelled reactors first, then plutonium, then thorium, was Bhabha's long-term design for energy independence.
• thorium: Thorium is a naturally occurring radioactive element, abundant in India's monazite sands, that can be converted into fissile uranium-233 for nuclear fuel. India holds one of the world's largest thorium reserves, and thorium powers the third stage of Homi Bhabha's three-stage nuclear programme. It serves GS3 science and technology: energy security and nuclear policy. Example: The monazite-rich beach sands of Chavara, Kerala, mined by Indian Rare Earths.
• fertile: In nuclear science, fertile material refers to isotopes that are not themselves fissile but can be converted into fissile fuel by neutron capture followed by radioactive decay. The main fertile isotopes are uranium-238, which breeds plutonium-239, and thorium-232, which breeds uranium-233. Fertile materials are the backbone of breeder reactors, which produce more fissile fuel than they consume. Example: India's abundant thorium-232 reserves are fertile material for the third stage of its three-stage nuclear programme, where fast breeder reactors convert thorium into fissile uranium-233.
• closed fuel cycle: A closed fuel cycle is a nuclear fuel management strategy in which spent fuel is reprocessed to recover usable plutonium and uranium for reuse in reactors, instead of being treated as waste. It extracts maximum energy from limited fuel and underpins India's three-stage nuclear programme, which is designed to unlock abundant domestic thorium. Example: India reprocesses spent fuel from its pressurised heavy water reactors to recover plutonium for use in fast breeder reactors.
• Stage 1: Stage 1 of India's three-stage nuclear power programme uses Pressurised Heavy Water Reactors (PHWRs) fuelled by natural uranium. These reactors generate power and produce plutonium-239 as a by-product; their spent fuel is reprocessed to recover that plutonium, which becomes the fuel for Stage 2. Conceived by Homi Bhabha to suit India's limited uranium and abundant thorium reserves, Stage 1 is the operational backbone of Indian nuclear power today. Example: The 700 MW PHWR units at Kakrapar and Rawatbhata representing the current Stage 1 fleet.
• Stage 2: Stage 2 of India's three-stage nuclear power programme uses Fast Breeder Reactors fuelled by the plutonium recovered from Stage 1 spent fuel in mixed-oxide (MOX) form. With a uranium-238 blanket they breed more plutonium than they consume, and with a thorium-232 blanket they convert thorium into fissile uranium-233 for the final stage. Stage 2 became operational when the 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam achieved first criticality on 6 April 2026. Example: The PFBR at Kalpakkam, a sodium-cooled reactor built by BHAVINI, which makes India only the second country after Russia to operate a commercial-scale fast breeder.
• Stage 3: Stage 3 is the final phase of India's three-stage nuclear power programme, in which advanced reactors are fuelled by uranium-233 bred from thorium-232 in Stage 2 breeders. It is designed to exploit India's vast thorium reserves (among the world's largest) for long-term energy independence, since thorium itself is not fissile and needs the uranium-233 bred in Stage 2 to start the cycle. The Advanced Heavy Water Reactor (AHWR) is the reference design for this stage. Example: The proposed AHWR, designed to run largely on thorium with uranium-233, demonstrating a near-inexhaustible domestic fuel cycle.
• ITER: ITER, the International Thermonuclear Experimental Reactor, is the world's largest tokamak fusion experiment, being built at Cadarache in France by a 35-partner international collaboration. It aims to demonstrate self-burning plasma and a fusion energy gain above ten, proving that magnetic confinement fusion can become a future energy source. Example: India, which joined ITER in 2005, fabricated the machine's cryostat, the world's largest.
• tokamak: A tokamak is a doughnut-shaped (toroidal) magnetic-confinement device designed to contain plasma hot enough for nuclear fusion, using powerful magnetic coils to keep the plasma from touching the walls. It is the most researched design for achieving controlled fusion power. The international ITER project in southern France, in which India is a partner, is building the world's largest tokamak. Example: ITER at Cadarache, France, being built by 35 countries including India, will be the largest tokamak ever constructed.
• magnetic confinement fusion: Magnetic confinement fusion is the approach to fusion energy in which super-hot plasma, at temperatures exceeding 100 million degrees Celsius, is held away from any material wall by powerful magnetic fields shaped into a doughnut-like chamber called a tokamak. No container could survive the plasma's heat, so magnetic fields act as the invisible bottle. It is the most advanced route to practical fusion power, with the international ITER project aiming to demonstrate net energy gain. Example: ITER, being built at Cadarache in France by 35 partners including India, the EU, the US, Russia, China, Japan and South Korea, is the world's largest magnetic confinement fusion experiment and aims to produce ten times more fusion power than the heat put in.
• fusion gain: The ratio of fusion energy released to the energy put into the fusion fuel, usually written as Q. A fusion gain greater than one (Q > 1) means the reaction produces more energy than was supplied to it, the milestone known as scientific breakeven. Fusion gain is the key performance metric for fusion experiments, distinct from engineering breakeven, which would require the whole plant to produce net electricity. Example: The National Ignition Facility's December 2022 experiment achieved a fusion gain above 1, the first time a laboratory fusion reaction produced more energy than the laser energy driving it.
• cryostat: A large, heavily insulated vessel or enclosure used to maintain extremely low (cryogenic) temperatures for scientific or industrial equipment. In fusion-energy research it denotes the giant vacuum chamber that houses the tokamak reactor, keeping superconducting magnets cold and thermally isolating the machine. Building one is an extreme engineering challenge because of its size, vacuum requirements and precision tolerances. Example: Larsen and Toubro built the ITER cryostat at Hazira, Gujarat, the world's largest stainless-steel high-vacuum chamber (about 3,850 tonnes), for the fusion reactor being assembled in France.
• ITER-India: ITER-India is India's domestic agency for the ITER fusion project, supervised by the Institute for Plasma Research (IPR) under the Department of Atomic Energy. It delivers India's in-kind contributions to ITER at Cadarache while simultaneously operating India's own tokamaks, ADITYA-U and SST-1, to build indigenous fusion expertise. Example: ITER-India operates the ADITYA-U and SST-1 tokamaks at Gandhinagar for domestic fusion research.
• ADITYA-U: India's upgraded indigenous tokamak at the Institute for Plasma Research, Gandhinagar, used for magnetic-confinement fusion research. It studies high-temperature plasma behaviour relevant to future fusion power plants and supports India's scientific contributions to the international ITER project in France. Example: it succeeded the original ADITYA tokamak, which operated at IPR from 1989, with upgraded operations beginning around 2020. Example: Upgraded tokamak at IPR Gandhinagar succeeding ADITYA (1989), supporting fusion research for ITER.
• SST-1: SST-1 (Steady State Superconducting Tokamak-1) is India's first superconducting tokamak, a plasma confinement experimental device at the Institute for Plasma Research in Gandhinagar, Gujarat. It uses superconducting magnets to confine million-degree plasma for long durations, building domestic expertise in the magnetic-confinement fusion technologies needed for future fusion power plants. Along with ADITYA-U, it underpins India's contribution to the international ITER fusion project, for which India built the giant cryostat. Example: Long-duration plasma confinement experiments at SST-1 advancing India's fusion research.
• Nuclear Energy Mission: A mission-mode programme announced in the Union Budget 2025-26 with an outlay of Rs 20,000 crore to scale India's nuclear power capacity to 100 GW by 2047 (the Viksit Bharat target), up from about 8.7 GW today. It is pursued alongside private-sector participation enabled by the SHANTI Act and a national programme for Small Modular Reactors (SMRs). The mission aims to make nuclear a large, steady source of clean electricity rather than a marginal contributor. Example: The mission underpins India's plan to use nuclear power as firm, non-intermittent clean electricity in its net-zero pathway, complementing solar and wind capacity.
• BARC: The Bhabha Atomic Research Centre (BARC) is India's premier nuclear research institution, functioning under the Department of Atomic Energy and headquartered at Trombay in Mumbai. Established in 1954 as the Atomic Energy Establishment, Trombay, it was renamed in 1967 in memory of Homi J. Bhabha, the founder of India's nuclear programme. BARC designs India's indigenous pressurised heavy water reactors, conducts research across nuclear science and its applications, and is the technical backbone of India's three-stage nuclear power programme. Example: BARC designed the 220 MWe Indian pressurised heavy water reactor (IPHWR) line operating at several Indian nuclear power stations.
• Bharat Small Reactors: Bharat Small Reactors is the umbrella name for India's small modular reactor programme being developed by BARC under the Department of Atomic Energy. The programme covers multiple designs, including the 200 MWe BSMR-200, a 55 MWe SMR-55, and a high-temperature gas-cooled reactor of up to 5 MW thermal capacity meant for hydrogen generation. Supported by the Nuclear Energy Mission's 20,000 crore rupee allocation in the 2025-26 Budget, the programme is part of India's target of 100 GW of nuclear power capacity by 2047. Example: The 55 MWe SMR-55 variant is aimed at flexible power supply for smaller industrial units and remote locations.
• Atomic Energy Act, 1962: The Atomic Energy Act, 1962 is the principal law governing the development, control and use of atomic energy in India, replacing the 1948 Act. It vests the Central Government with exclusive authority over atomic energy, restricts disclosure of sensitive information, and keeps uranium and thorium mining and the nuclear fuel cycle under state control. It underpins regulators like the Atomic Energy Regulatory Board and is central to UPSC questions on nuclear governance. Example: A 2015 amendment enabled the Nuclear Power Corporation of India to form joint ventures.
• Civil Liability for Nuclear Damage Act, 2010: The Civil Liability for Nuclear Damage Act, 2010 channels liability for a nuclear accident onto the operator, capped at Rs 1,500 crore, with the government covering compensation beyond that. Its debated Section 17(b) gives the operator a right of recourse against suppliers of defective equipment, which foreign vendors read as supplier liability and cite for staying out of India's reactor market. India joined the global CSC regime in 2016. Example: The supplier-recourse clause has slowed several planned foreign reactor projects.
• India-US civil nuclear agreement: The India-US civil nuclear agreement of 2005, operationalised in 2008, is the deal that ended India's decades of nuclear isolation. It secured an India-specific IAEA safeguards agreement and a 2008 Nuclear Suppliers Group waiver, letting India trade nuclear fuel and technology despite not signing the Non-Proliferation Treaty, while placing civilian reactors under IAEA safeguards. Example: The 2008 NSG waiver opened the way for India's civil nuclear trade, including the Russian-built reactors at Kudankulam.
• Nuclear Suppliers Group waiver: The September 2008 decision by the Nuclear Suppliers Group (NSG), a 48-nation export-control regime, granting India a country-specific exemption from its rule requiring full-scope IAEA safeguards as a condition for nuclear trade. The waiver opened India to international civil nuclear commerce in fuel, reactors and technology despite India not being a signatory to the NPT, and made the India-US 123 Agreement operational. It marked India's effective integration into the global civilian nuclear order. Example: After the 2008 waiver, India signed uranium supply agreements with countries such as France, Russia and Kazakhstan for its safeguarded reactors.
• Non-Proliferation Treaty: The 1968 international treaty, in force since 1970, aimed at preventing the spread of nuclear weapons, promoting peaceful uses of nuclear energy and pursuing disarmament. It recognises five nuclear-weapon states (the US, Russia, the UK, France and China) and obliges others to forgo weapons and accept IAEA safeguards; India has never signed it, calling it discriminatory, yet secured a 2008 Nuclear Suppliers Group waiver for civilian nuclear trade. Example: India's civilian reactors are placed under IAEA safeguards even though India remains outside the treaty.
• International Atomic Energy Agency (IAEA) safeguards: The system of inspections, monitoring and nuclear material accounting through which the IAEA verifies that nuclear material and facilities are used only for peaceful purposes and are not diverted to weapons. As a non-NPT nuclear-weapon state, India concluded an India-specific safeguards agreement with the IAEA in 2009, placing its declared civilian nuclear facilities under inspection in a phased manner under its Separation Plan. Example: Civilian power reactors that India identified in its Separation Plan are subject to IAEA safeguards inspections under the 2009 agreement.
• Rosatom: Rosatom is Russia's state atomic energy corporation, responsible for the country's nuclear power programme and its overseas reactor exports. It built the Kudankulam Nuclear Power Plant in Tamil Nadu, India's largest nuclear station with 2,000 MWe of operating capacity from its VVER units. Rosatom remains India's key foreign partner for nuclear power equipment and fuel. Example: Kudankulam units 1 and 2, each a 1,000 MWe VVER reactor built by Rosatom, supply power to southern India.
• EDF: EDF (Electricite de France) is the French multinational electric utility and one of the world's largest nuclear power operators, running France's fleet of around 56-58 nuclear reactors that supply most of the country's electricity. It is the vendor of the EPR (European Pressurised Reactor) design and is slated to supply EPR reactors for India's proposed Jaitapur nuclear power plant in Maharashtra. EDF's nuclear expertise also makes it central to Franco-Indian civil nuclear cooperation. Example: EDF's techno-commercial offer for six EPR reactors at Jaitapur has been under negotiation between India and France.
• Holtec: Holtec International is a US nuclear technology company founded by Indian-American entrepreneur Kris Singh, best known for spent-fuel storage and transport systems and for its SMR-300 small modular reactor design. In March 2025 the US Department of Energy granted it authorisation under 10CFR810 to transfer unclassified small modular reactor technology to India. The clearance allows Holtec to share SMR technology with three Indian entities, Larsen and Toubro, Tata Consulting Engineers and its own subsidiary Holtec Asia, for manufacture in India under IAEA safeguards. Example: The March 2025 US clearance lets Holtec partner with Larsen and Toubro, Tata Consulting Engineers and Holtec Asia to build SMR-300 reactors in India.
• net-zero: Net-zero describes a balance between the greenhouse gases released into the atmosphere and those removed from it, so that net additions to the atmosphere are zero. It is achieved by cutting emissions as deeply as possible and then offsetting the remainder through sinks such as forests or technologies like carbon capture and storage. Countries, companies, and cities adopt net-zero targets with a specified year to align with the Paris Agreement's temperature goals. Example: A country reaches net-zero when its remaining emissions are fully matched by verified removals, such as afforestation or direct air capture.
• three-stage programme: The three-stage programme is shorthand for India's three-stage nuclear power programme, the Bhabha-designed strategy for energy independence based on the country's thorium reserves. It sequences natural-uranium reactors first, then plutonium-fuelled fast breeders, and finally thorium-based reactors, with each stage producing the fuel for the next. The closed fuel cycle design minimises nuclear waste while multiplying India's fissile material from limited uranium. Example: The 500 MWe Prototype Fast Breeder Reactor at Kalpakkam, Tamil Nadu, whose core-loading was witnessed in March 2024, marks India's entry into the programme's second stage.
• PFBR: The Prototype Fast Breeder Reactor is a 500 MWe sodium-cooled fast reactor at Kalpakkam in Tamil Nadu, built by BHAVINI and designed to breed more plutonium fuel than it consumes. It is the centrepiece of Stage 2 of India's three-stage nuclear programme, converting the plutonium and depleted uranium produced in Stage 1 into fuel for thorium-based Stage 3 reactors. Its commissioning marks India's formal entry into fast-breeder technology. Example: The PFBR's attainment of criticality represents India's entry into Stage 2 of Homi Bhabha's three-stage programme, unlocking the use of the country's thorium reserves.
• Pressurised Heavy Water Reactor (PHWR): A Pressurised Heavy Water Reactor is a nuclear reactor that uses natural (unenriched) uranium as fuel and heavy water, deuterium oxide, as both moderator and coolant, with the coolant kept under pressure to prevent boiling. Because heavy water absorbs few neutrons, the reactor can run on natural uranium, and India has built its nuclear fleet around this design. Example: Kakrapar Atomic Power Station's 700 MWe units are India's largest indigenously designed PHWRs, alongside the standard 220 MWe units.
• Pressurised Water Reactor (PWR): A Pressurised Water Reactor is a nuclear reactor that uses enriched uranium fuel and ordinary (light) water as both moderator and coolant, held at high pressure so it does not boil in the core. Heat is transferred to a separate secondary loop that makes steam for the turbines, keeping radioactive water away from the power-generating circuit, and PWRs are the world's most common reactor type. Example: The Kudankulam Nuclear Power Plant's VVER-1000 units are Russian-designed PWRs.
• Boiling Water Reactor (BWR): A type of light-water nuclear reactor in which water is boiled directly inside the reactor core, and the steam produced drives the turbine to generate electricity. Because coolant and steam share a single loop, the design is simpler and cheaper than a pressurised water reactor, though the turbine can become mildly radioactive. India's Tarapur Units 1 and 2, commissioned in 1969, are boiling water reactors built with American collaboration. Example: TAPS-1 and TAPS-2 at Tarapur in Maharashtra are India's operating boiling water reactors.
• Fast Breeder Reactor (FBR): A Fast Breeder Reactor is a nuclear reactor that uses fast (unmoderated) neutrons to produce more fissile material than it consumes, breeding new fuel from fertile material such as uranium-238. It is the second stage of India's three-stage nuclear programme, designed to use plutonium-based mixed oxide fuel with liquid sodium coolant and to recycle spent fuel from pressurised heavy water reactors. It is crucial for India because it opens the path to using the country's large thorium reserves in the third stage. Example: India's 500 MWe Prototype Fast Breeder Reactor at Kalpakkam, built by BHAVINI, attained first criticality in April 2026.
• Small Modular Reactors (SMRs): Small Modular Reactors are advanced nuclear reactors with power output typically up to 300 MW per unit, far smaller than conventional gigawatt-scale plants, designed for factory fabrication and modular assembly on site. They promise lower upfront costs, faster construction, passive safety features and flexible siting, including for industrial clusters and remote areas. India has expressed interest in SMRs and in Bharat Small Reactors (220 MW PHWRs for captive industrial use) under its target of 100 GW of nuclear capacity by 2047. Example: Bharat Small Reactors, 220 MW pressurised heavy water reactors that India plans to deploy for captive power at industrial sites with private participation.
• Bharat Small Modular Reactor (BSMR-200): The Bharat Small Modular Reactor (BSMR-200) is a 200 MWe indigenous small modular reactor design being developed jointly by BARC and the Nuclear Power Corporation of India. It is derived from India's proven pressurised heavy water reactor technology, will use slightly enriched uranium fuel, and incorporates passive safety features that function without operator intervention during accidents. Backed by the 20,000 crore rupee Nuclear Energy Mission announced in the 2025-26 Union Budget, it aims to operationalise indigenous SMRs by 2033, with the lead unit proposed at the Tarapur site in Maharashtra. Example: BSMR-200 units are intended as captive power plants for energy-intensive industries such as steel, aluminium and cement, and for repurposing retiring thermal power plants.
• Prototype Fast Breeder Reactor (PFBR): The Prototype Fast Breeder Reactor is India's 500 MWe sodium-cooled, pool-type fast breeder reactor at Kalpakkam, Tamil Nadu, designed by the Indira Gandhi Centre for Atomic Research and built and operated by BHAVINI. It uses uranium-plutonium mixed oxide (MOX) fuel and is called a breeder because it produces more fissile material than it consumes, converting fertile uranium-238 into fissile plutonium. Its attainment of first criticality in April 2026 marks the entry into Stage II of India's three-stage nuclear power programme and a step toward eventually harnessing India's vast thorium reserves. Example: The PFBR attaining first criticality on 6 April 2026, beginning a self-sustaining chain reaction
• Indira Gandhi Centre for Atomic Research (IGCAR): The second major research and development centre of the Department of Atomic Energy, established in 1971 at Kalpakkam, Tamil Nadu, dedicated to fast breeder reactor technology and the associated fuel cycle. It leads India's research on sodium-cooled fast reactors, materials science, and reprocessing technologies. Example: IGCAR operates the Fast Breeder Test Reactor (FBTR) and developed the design of the Prototype Fast Breeder Reactor (PFBR) at Kalpakkam.
• Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI): Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI) is a public sector company under the Department of Atomic Energy tasked with constructing and operating India's fast breeder reactors. Its flagship project is the 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam in Tamil Nadu, a sodium-cooled reactor fuelled with uranium-plutonium mixed oxide (MOX) that breeds more fissile material than it consumes. BHAVINI's reactors form the crucial second stage of India's three-stage nuclear power programme. Example: Once the Kalpakkam PFBR is fully operational, India will be only the second country after Russia operating a commercial-scale fast breeder reactor.
• Institute for Plasma Research (IPR): An autonomous research institute established in 1986 at Gandhinagar, Gujarat, devoted to plasma physics and controlled thermonuclear fusion research, now under the Department of Atomic Energy. It operates the ADITYA tokamak and the SST-1 superconducting tokamak and plays a major scientific and technical role in India's partnership in the international ITER fusion project. Example: The SST-1 tokamak at IPR is designed for long-duration, steady-state plasma operation to advance fusion energy research.
• Nuclear Power Corporation of India (NPCIL): The public-sector undertaking under the Department of Atomic Energy responsible for designing, building and operating nuclear power plants in India. Established in 1987, it operates all of India's working nuclear reactors and is the executing agency for the indigenous 700 MWe pressurised heavy water reactor (PHWR) fleet and the Prototype Fast Breeder Reactor. It is the commercial arm of India's civil nuclear programme. Example: NPCIL operates the Tarapur Atomic Power Station in Maharashtra, site of India's first commercial nuclear reactors commissioned in 1969.
• Atomic Energy Regulatory Board (AERB): The Atomic Energy Regulatory Board is India's nuclear and radiation safety regulator, constituted on 15 November 1983 under Section 27 of the Atomic Energy Act, 1962. Its mission is to ensure that the use of ionising radiation and nuclear energy does not pose undue risk to workers, the public, and the environment. It lays down safety standards, licenses nuclear facilities, and oversees radiation safety in medicine and industry, reporting to the Atomic Energy Commission. Example: AERB licenses and inspects India's nuclear power stations, including Kudankulam in Tamil Nadu and Kakrapar in Gujarat, and certifies radiation equipment in hospitals.
• strict (no-fault) liability: Strict or no-fault liability is a legal rule under which a party must compensate victims of an accident without the victims having to prove negligence or fault. The Civil Liability for Nuclear Damage Act, 2010 imposes it on the operator of a nuclear installation, so compensation flows quickly after a nuclear incident instead of waiting on years of litigation about who was careless.
• right of recourse: A right of recourse is the legal right of a party that has paid compensation to recover that money from another party actually responsible for the harm. Under Section 17 of the Civil Liability for Nuclear Damage Act, 2010, the operator of a nuclear plant has a right of recourse against the supplier where the incident resulted from the supplier's act, including defective equipment or sub-standard services, which is broader than what international conventions allow.
• patent and latent defects: Patent defects are flaws in equipment or material that are visible on reasonable inspection, while latent defects are hidden flaws that surface only later during operation. The distinction matters in nuclear liability because Section 17(b) of the Civil Liability for Nuclear Damage Act, 2010 expressly lets the operator seek recourse against suppliers for both kinds, which is why vendors fear exposure long after delivery.
• Convention on Supplementary Compensation (CSC): The Convention on Supplementary Compensation for Nuclear Damage is a 1997 convention under the International Atomic Energy Agency that sets minimum national compensation amounts for nuclear accidents and creates an international fund for catastrophic damage beyond national limits. India ratified it in 2016. Unlike India's domestic law, the CSC channels liability exclusively to the operator and permits recourse against suppliers only where a written contract provides it or the damage was intentional.
• Special Drawing Rights (SDR): Special Drawing Rights are a reserve asset created by the International Monetary Fund that serves as an international unit of account, valued against a basket of major currencies. The Civil Liability for Nuclear Damage Act, 2010 caps the Indian government's share of nuclear damage compensation at the rupee equivalent of 300 million SDRs, linking the ceiling to a stable international benchmark rather than a fixed rupee figure.
• Advanced Heavy Water Reactor (AHWR): A 300 MWe thorium-based reactor designed by BARC to anchor Stage 3 of India's three-stage nuclear programme, fuelled mainly by thorium with plutonium or uranium-233, using heavy water as moderator and boiling light water as coolant. It is designed to draw most of its energy from thorium and to use the uranium-233 bred in fast breeder reactors. Example: The AHWR is the bridge that would let India's vast thorium reserves, rather than scarce uranium, carry the programme in the long run.

Prelims practice

Test yourself with these prelims-style questions.