Material Insights · Understanding the Material World

Nuclear fission reactors and Thorium

Thorium cannot run a reactor on its own: it must first be bred into fissile uranium-233 inside a reactor started on uranium or plutonium. That is why it matters most to India, which has large thorium resources and has built its three-stage nuclear programme around reaching it.

Nuclear fission reactors (energy) and Thorium (commodity): 4 relationships.

How they are linked

1. Fertile fuel, not fissile

Physical flow · Weak · Thorium bred into fuel inside reactors

Thorium-232 has no isotope that can sustain a chain reaction, but when it absorbs a neutron it turns into uranium-233, which is fissile, so a reactor needs plutonium or uranium as a driver to start the cycle.

The thorium cycle has neutronic and non-proliferation attractions, but the uranium-233 it makes is accompanied by high-energy gamma emitters that complicate handling, and fast reprocessing requires separating protactinium. These hurdles are why no commercial reactor fleet runs on thorium today, and demand for thorium itself remains small.

Sources: USGS; Argonne National Laboratory

2. India's three-stage plan

Policy · High in India · Reactor build-out leads to thorium use

India planned its nuclear programme in three steps: heavy-water reactors on natural uranium make plutonium, fast breeders use that plutonium to breed more fuel, and the third stage uses uranium-233 bred from thorium.

  • 500 MWe Prototype Fast Breeder Reactor at Kalpakkam, first criticality 6 April 2026
  • 8.78 GW India's nuclear capacity, 2026
  • 100 GW India's nuclear capacity target for 2047

The fast breeder runs on uranium-plutonium mixed oxide fuel, and the programme then plans to convert thorium-232 into uranium-233 to fuel the third stage. Large-scale thorium use therefore depends on a fleet of breeders being built and operated over decades, so the first criticality is a step, not the arrival of thorium power.

Sources: Department of Atomic Energy, Government of India; Press Information Bureau, Government of India

3. Resources sit in India

Geography and ownership · Asymmetric · Thorium resources shape reactor strategy

Countries short of uranium but rich in thorium have the strongest reason to develop thorium reactors, and India is the clearest case.

  • 850,000 t India's thorium resources, the world's largest
  • 6.4 Mt identified world thorium resources
  • about 13% India's share of identified world thorium resources, derived from the two USGS figures above

Brazil, Australia and the United States also hold large resources, about 600,000 to 630,000 t each, but they have uranium access and little reason to change fuel cycles. Thorium comes mainly from monazite, a mineral produced chiefly for its rare earths, so future reactor demand would draw on rare-earth supply chains.

Sources: USGS; Argonne National Laboratory

4. Molten salt reactors

Transition · Rising · New reactor designs could use thorium

Molten salt reactors dissolve fuel in a liquid salt, which allows uranium-233 to be bred from thorium and used in the same reactor without making solid fuel pellets.

  • 2 MWt TMSR-LF1 experimental reactor at Wuwei, China
  • 100 MWt planned Chinese thorium molten salt demonstration, target 2035

China's TMSR-LF1 reached criticality in October 2023, received thorium in October 2024 and reported the first conversion of thorium to uranium fuel in such a reactor in 2025. This is still experimental scale, so thorium remains a long-dated option rather than a fuel market.

Sources: World Nuclear News

For investors

Key learnings

  1. Thorium has no fuel market today: it needs a fissile driver and a breeding step, so commercial demand for it is decades away.
  2. Milestones such as India's 500 MWe fast breeder in 2026 and China's 2 MWt molten salt reactor matter for long-term reactor vendors, not for near-term uranium demand.
  3. Thorium sits mainly in monazite, which is processed for rare earths, so rare-earth processors hold the latent supply.

What to track

  • Fast breeder operation at Kalpakkam: Steady power operation would open the path to India's thorium stage (As announced · Department of Atomic Energy, BHAVINI)
  • Chinese molten salt reactor milestones: Progress toward the 100 MWt demonstration signals whether thorium designs can scale (As announced · Chinese Academy of Sciences, World Nuclear News)

For policymakers

Key learnings

  1. India holds about 850,000 t of thorium, the largest resource, which is why its nuclear plan ends in a thorium stage.
  2. Reaching that stage depends on the second stage: a fleet of fast breeders that make enough fissile material, starting with the 500 MWe Kalpakkam unit.
  3. Thorium fuel brings handling and reprocessing difficulties from uranium-233, so licensing, fuel fabrication and waste plans need to be developed alongside reactors.

What to track

  • Nuclear capacity against the 100 GW 2047 target: Shows whether the reactor base that would later use thorium is being built (Yearly · Department of Atomic Energy, PIB)
  • Fast breeder construction starts after the prototype: More breeders are needed before thorium use can scale (As announced · Department of Atomic Energy)
  • Monazite processing and thorium stockpiles: Indicates readiness of thorium supply for future fuel (Yearly · IREL, Atomic Minerals Directorate)

India

India has the world's largest thorium resources, about 850,000 t, but limited uranium, and its fast breeder at Kalpakkam reached first criticality in April 2026 as the bridge to a thorium-fuelled third stage.

Sources

  1. Mineral Commodity Summaries 2026: Thorium, USGS (2026)
  2. India's Baseline Plan for Nuclear Energy: Self-sufficiency (ANL/NE-09/03), Argonne National Laboratory (2009)
  3. Prototype Fast Breeder Reactor at Kalpakkam attains first criticality, Department of Atomic Energy, Government of India (2026)
  4. A New Chapter in India's Nuclear Journey, Press Information Bureau, Government of India (2026)
  5. Chinese molten salt reactor achieves conversion of thorium-uranium fuel, World Nuclear News (2025)