Nuclear Energy: Reactors and India's Three-Stage Programme
Fission, reactor components, PHWRs and fast breeders, India's three-stage programme and PFBR, SMRs, CLNDA 2010, the 2008 NSG waiver, fusion and ITER — for UPSC.
SyllabusGS III · Infrastructure: energy; science and technology — developments and their applications in everyday life
Prerequisites: Nuclear Technology and Energy — overview · Mineral and Energy Resources
The Hook: Kalpakkam Begins Loading Its Breeder
In March 2024, core loading began at India’s 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, Tamil Nadu — a step towards the second stage of the nuclear programme that Homi J. Bhabha outlined in the 1950s. A breeder reactor produces more fissile fuel than it consumes.
Why would India build such a complex machine when most of the world runs simpler reactors? The answer lies in geology — India has modest uranium but large thorium reserves — and it is the thread that runs through this whole topic.
The Core Concept
What nuclear energy is — and how a reactor works (in one paragraph)
When a heavy nucleus such as uranium-235 absorbs a slow neutron, it splits (fission) into two lighter nuclei, releasing a large amount of energy and two or three new neutrons. If on average one of those neutrons causes another fission, the reaction sustains itself — a chain reaction. A reactor controls this chain reaction: fuel supplies the fissile atoms; a moderator slows neutrons so they are more likely to cause fission; control rods absorb surplus neutrons to regulate or stop the reaction; a coolant carries the heat away to raise steam, which spins a turbine exactly as in a coal plant. The difference is that no fuel is burnt and no carbon dioxide is emitted at the plant.
| Component | Job | Common materials |
|---|---|---|
| Fuel | Supplies fissile atoms | Natural uranium, enriched uranium, plutonium (MOX) |
| Moderator | Slows down neutrons | Heavy water (D₂O), light water, graphite |
| Control rods | Absorb neutrons | Boron, cadmium, hafnium |
| Coolant | Removes heat | Light water, heavy water, liquid sodium, gas |
| Containment | Prevents release of radioactivity | Thick reinforced concrete and steel |
Fissile and fertile
| Fissile (can sustain a chain reaction) | Fertile (becomes fissile after absorbing a neutron) |
|---|---|
| Uranium-235 (about 0.7% of natural uranium) | Uranium-238 → Plutonium-239 |
| Plutonium-239 | Thorium-232 → Uranium-233 |
| Uranium-233 | — |
Enrichment raises the share of U-235. Light-water reactors typically use uranium enriched to a few per cent; weapons need very high enrichment. India’s main reactor type, the PHWR, runs on natural (unenriched) uranium because heavy water absorbs very few neutrons.
Reactor types
| Type | Fuel | Moderator / coolant | Indian example |
|---|---|---|---|
| PHWR (Pressurised Heavy Water Reactor) | Natural uranium | Heavy water / heavy water | Most Indian reactors; Kakrapar-3 — first indigenous 700 MWe unit |
| BWR (Boiling Water Reactor) | Enriched uranium | Light water / light water | Tarapur 1 and 2 — India’s first nuclear power station (1969) |
| PWR / VVER | Enriched uranium | Light water / light water | Kudankulam (Russian VVER design) |
| Fast Breeder Reactor | Plutonium–uranium mixed fuel | No moderator / liquid sodium | FBTR (1985) and PFBR, Kalpakkam |
| Small Modular Reactor (SMR) | Varies | Varies | Planned; up to about 300 MWe per unit, factory-built modules |
India’s three-stage programme
graph LR
A[Stage 1: PHWRs burn natural uranium] --> B[Spent fuel yields plutonium-239]
B --> C[Stage 2: Fast breeders burn plutonium, breed more fuel]
C --> D[Thorium blanket converts Th-232 to U-233]
D --> E[Stage 3: Reactors run on thorium and U-233]- Stage 1 — PHWRs use natural uranium and produce electricity plus plutonium-239 in their spent fuel.
- Stage 2 — Fast breeder reactors use that plutonium. Fast neutrons convert surrounding uranium-238 into more plutonium, building up the fissile inventory; later, a thorium blanket produces uranium-233.
- Stage 3 — reactors using thorium-232 with uranium-233, tapping India’s large thorium reserves in monazite beach sands of Kerala, Tamil Nadu, Odisha and Andhra Pradesh. BARC has designed an Advanced Heavy Water Reactor (AHWR) for this stage.
The logic: thorium is not fissile, so it cannot start a reactor on its own. India must first build up fissile material (stages 1 and 2) before it can use thorium at scale (stage 3). India follows a closed fuel cycle — spent fuel is reprocessed, not simply buried.
Institutions and law
| Body / law | Year | Role |
|---|---|---|
| Atomic Energy Commission | 1948 | Policy |
| Department of Atomic Energy | 1954 | Directly under the Prime Minister |
| Atomic Energy Act | 1962 | Nuclear power only by the Central Government or its companies; 2015 amendment allowed joint ventures of public sector companies |
| Atomic Energy Regulatory Board (AERB) | 1983 | Safety regulator, created by executive order under the 1962 Act |
| NPCIL | 1987 | Builds and runs power reactors |
| BHAVINI | 2003 | Builds and runs fast breeder reactors |
| Civil Liability for Nuclear Damage Act (CLNDA) | 2010 | Operator’s liability up to ₹1,500 crore; Section 17(b) gives the operator a right of recourse against suppliers for defective equipment or material |
International framework
- India has not signed the NPT or the CTBT, considering them discriminatory. It tested in May 1974 (Pokhran-I) and May 1998 (Pokhran-II).
- 2008 — the IAEA approved an India-specific safeguards agreement; the NSG granted a waiver (September 2008) allowing civil nuclear trade; India and the USA concluded the civil nuclear (“123”) agreement. Civilian reactors were placed under IAEA safeguards under a separation plan.
- India ratified the Convention on Supplementary Compensation (CSC) in 2016; the India Nuclear Insurance Pool (2015) covers operators’ and suppliers’ liability risk.
Fusion
Fusion joins light nuclei — usually deuterium and tritium — into helium, releasing energy. It needs temperatures of the order of 100 million °C, achieved either by magnetic confinement (the doughnut-shaped tokamak) or inertial confinement (lasers compressing a fuel pellet). The fuel is abundant and the process produces no long-lived high-level waste, but no fusion power plant yet exists. ITER, at Cadarache in France, is a tokamak built by seven members — the EU, China, India (member since 2005), Japan, South Korea, Russia and the USA. India’s Institute for Plasma Research, Gandhinagar, runs the SST-1 and Aditya tokamaks. In December 2022, the US National Ignition Facility achieved fusion “ignition” — more energy from the reaction than the laser energy delivered to the target.
Applications beyond electricity
- Medicine: cobalt-60 for cancer radiotherapy (BARC’s indigenous Bhabhatron teletherapy machine); iodine-131 for thyroid disorders; technetium-99m for diagnostic imaging.
- Agriculture and food: radiation-induced mutation breeding of crop varieties; food irradiation to inhibit sprouting in onions and potatoes and extend shelf life; the sterile insect technique for pest control.
- Industry and research: radiography of welds, carbon-14 dating, tracers in hydrology.
India’s status and plans
- Nuclear power remains a small share of India’s electricity, supplied by a fleet dominated by indigenous PHWRs; ten 700 MWe PHWRs were sanctioned in fleet mode in 2017.
- Union Budget 2025-26 announced a Nuclear Energy Mission for small modular reactors (₹20,000 crore; at least five indigenously designed SMRs operational by 2033), a target of 100 GW of nuclear capacity by 2047, and amendments to the Atomic Energy Act and the CLNDA to enable private participation.
Issues
- Safety and public trust — lessons from Chernobyl (April 1986) and Fukushima (March 2011); local protests at Kudankulam and Jaitapur.
- Regulatory independence — AERB is not a statutory body and reports within the DAE structure.
- Supplier liability under Section 17(b) has deterred foreign vendors.
- High capital cost and long construction periods; land and water needs.
- Spent fuel and long-lived radioactive waste.
- Uranium import dependence for the first stage.
Memory Anchors
Reactor parts: “Fast Moving Cars Crash” → Fuel, Moderator, Control rods, Coolant (and containment keeps the crash inside).
Three stages in three words: “Uranium → Plutonium → Thorium”.
Fertile pairs: “238 makes 239, 232 makes 233” → U-238 → Pu-239; Th-232 → U-233.
| Confusable pair | Difference |
|---|---|
| Moderator vs control rod | Moderator slows neutrons; control rod absorbs them |
| PHWR vs fast breeder | Natural uranium + heavy water moderator vs plutonium fuel + no moderator + sodium coolant |
| Fissile vs fertile | Fissile sustains fission; fertile must first absorb a neutron |
| Fission vs fusion | Splitting heavy nuclei vs joining light ones |
One-line Mains hook: India’s three-stage programme is a strategy written by geology — modest uranium, abundant thorium.
For Prelims
- PHWRs use natural uranium with heavy water as both moderator and coolant.
- Fast breeders use no moderator and are cooled by liquid sodium.
- Thorium-232 is fertile, not fissile; it is converted to U-233. Main Indian source: monazite.
- CLNDA 2010: operator liability ₹1,500 crore; Section 17(b) — recourse against suppliers.
- NSG waiver: September 2008. India is not a party to the NPT or CTBT.
- ITER: tokamak at Cadarache, France; India a member since 2005.
For Mains
- Dimensions: energy security; climate (low-carbon baseload to complement variable solar and wind); strategic (fuel supply, non-proliferation diplomacy); economic (capital cost, private participation); safety and environment (waste, accidents); social (land acquisition, local consent).
- Keywords: baseload power, closed fuel cycle, fleet mode, SMRs, supplier liability, regulatory independence, energy mix, net zero by 2070.
- Value-addition: Bhabha’s three-stage plan; PFBR core loading (2024); Budget 2025-26 Nuclear Energy Mission and 100 GW target; CLNDA Section 17(b); 2008 NSG waiver.
Common Traps
In the News
- March 2024 — core loading begins at the PFBR, Kalpakkam.
- February 2025 — Union Budget 2025-26 announces the Nuclear Energy Mission for small modular reactors and a 100 GW target by 2047. Track follow-ups on the current affairs page.
Practice
Prelims
Consider the following pairs of reactor components and their functions:
- Moderator — slows down neutrons
- Control rods — absorb excess neutrons
- Liquid sodium — moderator in fast breeder reactors
- Heavy water — fissile fuel in PHWRs
How many of the pairs given above are correctly matched?
Solution
Pairs 1 and 2 are correct. Pair 3 is wrong — liquid sodium is the coolant in fast breeders, which use no moderator. Pair 4 is wrong — heavy water is the moderator and coolant in PHWRs; the fuel is natural uranium. Two pairs are correct.
Answer: B
With reference to India’s three-stage nuclear power programme, consider the following statements:
- The first stage uses natural uranium in pressurised heavy water reactors.
- The second stage uses fast breeder reactors fuelled by plutonium.
- The third stage aims to use thorium through the uranium-233 cycle.
Which of the statements given above is/are correct?
Solution
All three are correct. Stage 1 PHWRs burn natural uranium and produce plutonium-239; stage 2 fast breeders use that plutonium and breed more fissile material (and U-233 from a thorium blanket); stage 3 uses thorium-232 with uranium-233.
Answer: D
Section 17(b) of the Civil Liability for Nuclear Damage Act, 2010 is significant because
Solution
Section 17(b) gives the operator a right of recourse against a supplier if the nuclear incident results from equipment or material with patent or latent defects, or sub-standard services. This departs from international conventions that channel liability only to the operator, and foreign vendors have cited it as a barrier. The Act caps the operator’s liability at ₹1,500 crore; it neither imposes unlimited government liability nor exempts suppliers, and the AERB is not made liable.
Answer: A
Mains
India’s three-stage nuclear programme was designed around its thorium reserves, yet nuclear power still forms a small part of the electricity mix. Examine the reasons and discuss whether small modular reactors and private participation can change this.
Solution
Introduction: Homi Bhabha’s three-stage plan sought to use India’s modest uranium to build up plutonium and eventually exploit abundant thorium. Seven decades later, the second stage is only now beginning with the PFBR (core loading, March 2024), and nuclear supplies a small share of electricity.
Body:
- Reasons for slow growth: technology denial after 1974 and 1998 until the 2008 NSG waiver; uranium scarcity; the complexity of fast breeders delaying stage 2; high capital cost and long gestation; land acquisition and local protests; supplier liability concerns under CLNDA Section 17(b); a state monopoly under the Atomic Energy Act, 1962.
- Case for SMRs: factory-built modules reduce construction time and cost; smaller sites, including retiring coal plants; suitable for captive industrial power; Budget 2025-26 Nuclear Energy Mission targets at least five indigenous SMRs by 2033.
- Private participation: capital and project-management capacity; needs amendments to the Atomic Energy Act and CLNDA (announced in Budget 2025-26), a strong independent regulator and clear fuel-supply arrangements.
- Concerns: safety oversight across many small units; waste management; regulatory capacity; public trust.
Conclusion: With the 100 GW by 2047 target, nuclear energy can provide low-carbon baseload alongside renewables — but only if reforms in law, regulation and financing match the ambition, while the thorium stage remains the long-term goal.
Quick Revision
| Point | One-liner |
|---|---|
| Fission | Heavy nucleus splits; energy + 2–3 neutrons; chain reaction |
| Moderator / control rods | Slow neutrons / absorb neutrons |
| PHWR | Natural uranium; heavy water moderator and coolant |
| Fast breeder | No moderator; sodium coolant; breeds fuel |
| Fertile → fissile | U-238 → Pu-239; Th-232 → U-233 |
| PFBR | 500 MWe, Kalpakkam; core loading March 2024 |
| CLNDA 2010 | ₹1,500 crore operator cap; Section 17(b) recourse |
| 2008 | IAEA safeguards, NSG waiver, India–US agreement |
| ITER | Tokamak, France; India member since 2005 |
| Budget 2025-26 | Nuclear Energy Mission (SMRs); 100 GW by 2047 |
Key Takeaways
- Learn the reactor’s four parts by function — fuel, moderator, control rods, coolant — and you can answer most Prelims questions.
- The three-stage programme exists because thorium is fertile, not fissile, and India has more thorium than uranium.
- For Mains, link nuclear power to climate goals, energy security and the reforms (SMRs, liability law, regulator) it needs.
Related Topics
- Nuclear Technology — quick revision
- Nuclear Technology — practice questions
- Mineral and Energy Resources — uranium and thorium deposits
- Climate Change — low-carbon energy
- Defence Technology — nuclear doctrine and the triad
- Industry and Infrastructure