Thorium

Topic: Energy Resources of India: Conventional and Non-conventional · NCERT: Class 10, Ch 5 "Minerals and Energy Resources"; Class 12, Ch 5 "Mineral and Energy Resources"

Meaning

Thorium (Th-232) is a radioactive heavy element. It is a fertile material: inside a reactor it absorbs a neutron and changes into U-233, which is fissile (can keep a chain reaction going) [3].

• India has one of the largest thorium reserves in the world, but only limited uranium [2].
• Because of this, thorium is the planned fuel of Stage 3, the last stage of India's three-stage nuclear power programme.

Explanation

How thorium becomes a nuclear fuel

• Fissile and fertile are different [3]:
• Fissile fuel can keep a chain reaction going by itself. Examples are U-235, Pu-239 and U-233.

• Fertile material cannot keep a chain reaction going by itself. Inside a reactor it first has to change into fissile fuel. Examples are U-238 and Th-232.

• Thorium has to be converted before it can be used:

• Th-232 absorbs a neutron inside a reactor.
• It turns into U-233, which is fissile [3].

• U-233 can then split (fission) and give off heat. The heat makes steam, and the steam drives a turbine to make electricity.

• So thorium cannot run a reactor alone. It needs a supply of neutrons from fuel that is already fissile, such as plutonium.

Its place in the three-stage programme

• Who and when: Homi J. Bhabha proposed the programme in 1954 [3].
• Why it exists: India has little uranium but a lot of thorium. The plan uses a closed fuel cycle (used fuel is reprocessed and used again, not thrown away) so that in the end India can run on thorium [2].

Stage	Reactor	Fuel	What it does for thorium
1	PHWR (pressurised heavy water reactor)	Natural uranium	Its spent fuel is reprocessed to recover plutonium [2]
2	Fast breeder reactor, e.g. the PFBR	Plutonium, as MOX (mixed oxide) fuel [2]	Makes more plutonium. Later, a thorium blanket in the reactor turns into U-233 [2]
3	Thorium-based reactors	U-233 made from thorium	Uses India's large thorium reserves for long-term energy security [2]

• Link through the PFBR (Prototype Fast Breeder Reactor), Kalpakkam:
• Today a U-238 blanket (a layer of fertile material) surrounds its core and is changed into Pu-239.
• Later the blanket will hold Th-232, which will change into U-233, the Stage 3 fuel [2].
• First criticality (the point where a steady chain reaction starts) came on 6 April 2026. With this, India formally entered Stage 2 [2].

Where thorium comes from: placer sands

• Its source minerals are monazite and ilmenite. Monazite is the main thorium mineral.
• These minerals are found in placer sands:
• Rivers carry heavy minerals from inland rocks down to the coast.
• Waves and currents sort the sand. The lighter grains are washed away.

• The heavy grains collect in layers along beaches and deltas.

• So thorium in India is mostly a coastal resource. Uranium, in contrast, is found in very old inland rocks.

Where it occurs

• Main coastal monazite sands:
• Kerala: Palakkad and Kollam (the Chavara coast)
• Tamil Nadu coast
• Near Visakhapatnam (Andhra Pradesh)

• Mahanadi delta (Odisha)

• Official list of thorium-bearing sands: Kerala, Tamil Nadu, Andhra Pradesh, Odisha, West Bengal and Jharkhand [3]. Jharkhand shows that some placer sands are found inland, not only on the coast.

• Size of the resource: the Atomic Minerals Directorate (AMD) has proved 13.15 million tonnes of in-situ monazite in coastal and inland placer sands (as of September 2025) [5].
• World position: India has one of the largest thorium reserves in the world [2].
• Where it will be used: the stage-2 work that leads to thorium use is at the Kalpakkam Nuclear Complex (Chengalpattu, Tamil Nadu, on the Coromandel coast). IGCAR designed the PFBR and BHAVINI built it [2].

Don't confuse with

• Uranium: This is the fuel of Stage 1. It comes from old inland Dharwar rocks (Jaduguda in Jharkhand, Tummalapalle in Andhra Pradesh). Thorium is the fuel of Stage 3 and comes from coastal placer sands.
• U-233 vs U-235: U-233 is man-made inside a reactor from thorium. U-235 is the fissile part of natural uranium. Both are fissile [3].
• Fertile vs fissile: Th-232 is fertile (it cannot keep a chain reaction going by itself) [3]. Do not mark thorium as a fuel that "directly sustains a chain reaction".
• Ilmenite: It is found in the same beach sands as monazite, but in textbooks it is mainly known as an ore of titanium. Monazite is the main thorium mineral.

Prelims Hooks

• Thorium mineral: monazite, found in the beach sands of Kerala (Chavara/Kollam), Tamil Nadu, Andhra Pradesh (near Visakhapatnam) and Odisha (Mahanadi delta).
• Monazite resources: 13.15 million tonnes in-situ, proved by AMD (September 2025) [5].
• Conversion pair: Th-232 (fertile) + neutron → U-233 (fissile) [3].
• Three-stage fuels in order: natural uranium (PHWR) → plutonium/MOX (FBR) → U-233 from thorium.
• Trap: India's first nuclear station, Tarapur (1969), uses US-built boiling water reactors running on uranium. No Indian power station runs on thorium yet. Thorium is the fuel of the future Stage 3.
• Official thorium-sand states also include West Bengal and Jharkhand, not just the four southern and eastern coastal states [3].

Mains Points

• A resource mismatch shapes India's strategy (GS-III):
• India's uranium is limited and low grade, but its thorium is among the world's largest [2].
• So India chose a closed-fuel-cycle, three-stage path to finally run on thorium. The PFBR's criticality in 2026 opens Stage 2 [2].

• Stage 3 still depends on first breeding enough plutonium and U-233. Until then, uranium imports after the 2008 NSG waiver and fleet-mode PHWRs are vital.

• Distribution pattern (GS-I):

• Thorium comes from coastal placer sands (Kerala, Tamil Nadu, Andhra Pradesh, Odisha). Uranium comes from the Peninsular shield rocks (Singhbhum, Kadapa basin).

• Power stations are located near cooling water: on the coast or near big rivers. So mineral areas and power stations are often far apart.

• Energy security and climate (GS-III):

• Thorium-based power would give India long-term baseload power (the minimum electricity the grid needs all day and night) from its own resources [2].
• Nuclear power is low-carbon, so it supports the 100 GW by 2047 nuclear target and net zero by 2070 [2][4]. Today nuclear gives only 3.1% of India's electricity (2024-25) [2].

Related concepts

• Nuclear energy
• Uranium
• Bhabha Atomic Research Centre
• Tarapur Atomic Power Station
• Kudankulam Nuclear Power Plant
• Jaitapur nuclear project
• Three-stage nuclear power programme
• Pressurised heavy water reactor
• Prototype Fast Breeder Reactor
• Small modular reactor

Read more

• Nuclear energy: minerals, power stations and the three-stage programme