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| Fig. 1: Map of Indias thorium reserves. they are mostly found in a belt formed by its eastern coastal states. [4] (Source: Wikimedia Commons) |
India's economic growth and expanding population have led to a drastic rise in energy demand. Electricity consumption in the country is projected to exceed roughly 2500 TWh by 2030. [1] However, India's electricity generation remains mostly dependent on coal. It accounts for more than half of the country's power production. [1] While coal has provided reliable and cheap electricity, its dominance and proliferation in recent times poses challenges for India's ambitious climate commitments, rising air pollution, and long term energy security goals.
In response to these challenges the government has committed to an ambitious energy transition. The country has pledged to achieve net-zero carbon emissions by 2070. Achieving this goal will require a substantial expansion of low carbon energy sources. Renewable energy technologies such as solar and wind are expected to play a major role in this transition but their unreliability presents challenges for maintaining stable electricity generation. Therefore, nuclear power with the ability to deliver continuous, low-carbon electricity represents an important component of India's long-term energy strategy.
Despite these advantages, nuclear energy currently contributes only a small fraction of India's electricity supply, with an installed capacity of roughly 6 - 7 GW across 22 operational reactors. [1] This limited capacity reflects both technological and resource constraints. Unlike many other nuclear-powered nations, India possesses relatively modest domestic uranium reserves - around 70,000 tones. [1] Nevertheless, at the same time the country is known to have the largest thorium reserves in the world along coastal regions - 846,000 tonnes (see Fig. 1). [1]
This resource distribution has influenced India's nuclear strategy. Since the early years of its nuclear program, Indian scientists such as Homi J. Bhabha envisioned that long term energy independence would require utilising the country's abundant thorium resources. This vision led to the development of India's three stage nuclear power program - a roadmap designed to transition from uranium to a thorium based fuel cycle. If successfully implemented, a thorium fuel cycle could enable India to utilise its domestic resources far more effectively while reducing dependence on imported uranium. It would be one big step towards energy independence.
Unlike U-235 or Pu-239, which are fissile, the most common isotope of Thorium (Th-232) is a fertile material. This means that thorium cannot itself sustain a nuclear chain reaction needed to generate energy. [2] Instead, it can absorb a neutron and undergo a sequence of beta decays that ultimately produce U-233. U-233 is a fissile isotope capable of sustaining fission reactions in nuclear reactors thus capable of generating energy.
The thorium fuel cycle begins when Th-232 captures a neutron to form Th-233, which then undergoes beta decay to form Pa-233, and finally decays into U-233. [2] The world is interested because thorium offers several potential advantages over conventional uranium fuel cycles. Firstly, thorium is estimated to be three to four times more abundant in the Earth's crust than uranium, making it an attractive long-term resource for nuclear power. [3] Secondly, Thorium fuel cycle is an attractive way to produce long term nuclear energy because it produces fewer long-lived minor actinides compared to conventional uranium reactors. [3] However, thorium cycles also introduce technical challenges. The bred U-233 is frequently contaminated with U-232, whose strong gamma emissions complicate fuel handling and reprocessing. [3] Additionally, the need to first breed fissile material means that thorium fuel cycles require more complex reactor designs and fuel management strategies. [3]
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| Fig. 2: A Fast-Breeder Test Reactor at the Kalpakkam Nuclear Complex, India. (Source: Wikimedia Commons) |
India holds the largest thorium deposits in the world, primarily contained in monazite sands along its eastern and southern coastal regions (see Fig. 1). Estimates suggest that 25% of the world's thorium resources are located in India, particularly in the beach sands of states such as Kerala, Tamil Nadu, Andhra Pradesh, and Odisha. [1] India's growing energy demand as mentioned earlier along with strong climate commitments, restricted uranium supply and thorium abundance have all played a role in influencing the direction of energy policy, specifically nuclear energy policy.
Recognizing the uranium constraints and thorium opportunities early in the development of India's nuclear program, Homi J. Bhabha proposed a strategy designed to gradually transition from uranium-based reactors to a thorium based fuel cycle. Developed in the 1950s, this approach commonly known as India's three-stage nuclear power program guides the country's nuclear energy development. [1]
To offer a concise explanation, the first stage relies on pressurised heavy water reactors (PHWRs) fueled by natural uranium. In addition to generating electricity, these reactors produce plutonium as a byproduct in the spent fuel. This plutonium forms the fuel for the second stage of the program, which uses fast breeder reactors (FBRs) designed to generate more fissile material than they consume. In these systems, plutonium is used to sustain the reactor while also enabling the production of additional fissile isotopes such as uranium-233. The final stage is intended to fully exploit India's thorium reserves. In this phase, thorium is used as the primary fertile material and is gradually converted into fissile U-233, which then sustains the reactors chain reaction. Advanced reactor designs proposed for this stage aim to operate using a combination of thorium and bred U-233, enabling a self-sustaining fuel cycle. More information about the three-stage nuclear power program can be found in Salvam et al. and Joshi. [1,5]
Research reactors, fuel cycle facilities, and prototype fast breeder reactors such as those developed at Kalpakkam (see Fig. 2) form part of the technological infrastructure required to transition between the different stages of the program. Nevertheless, significant engineering and economic challenges remain.
India's thorium program has made significant research progress, yet many of the reactor systems required for large scale thorium use remain under development. While the first stage of India's three stage nuclear program based on pressurised heavy water reactors (PHWRs) is well established, the later stages required for widespread thorium use are still advancing gradually. [6] India's Prototype Fast Breeder Reactor (PFBR) has experienced several delays during construction and commissioning.
At the same time, India has continued to pursue reactor designs intended to utilise thorium more directly in the third stage of its nuclear program. Research at the Bhabha Atomic Research Centre (BARC) has proposed several concepts including the Advanced Heavy Water Reactor (AHWR), Compact High Temperature Reactor (CHTR), Innovative High Temperature Reactor (IHTR), and Indian Molten Salt Breeder Reactor (IMSBR) that aim to efficiently breed and utilise uranium-233 from thorium. [6] However, most of these systems remain at the level of technology demonstrations or experimental designs rather than commercial power plants. For example, some proposed reactors are currently envisioned as small demonstration units intended to validate design concepts before larger power reactors can be constructed. [6]
Developing these reactor systems involves a wide range of engineering and fuel cycle challenges. These include work on advanced fuels, materials capable of operating at high temperatures, coolant technologies, fuel fabrication and reprocessing methods, as well as reactor physics and safety modeling. While these efforts demonstrate the depth of ongoing research in India's thorium program, the detailed technical aspects fall beyond the scope of this discussion. Interested readers can find comprehensive descriptions of these developments in Dulera et al. and Singh et al. [6,7]
Another important dilemma is that the economic competitiveness of thorium cycles remains limited. Thorium fuel fabrication and reprocessing are generally more complex and costly than conventional uranium fuel cycles used in existing reactors. Studies by the International Atomic Energy Agency note that while thorium offers potential long-term resource advantages, current uranium resources are sufficient for many decades and thorium systems do not yet provide a clear economic benefit compared with established uranium fuel cycles. [3]
India's pursuit of thorium based nuclear energy represents one of the most ambitious long term strategies in modern energy planning. The motivation is straightforward: while domestic uranium resources are limited, India possesses some of the world's largest thorium reserves. In principle, the thorium fuel cycle could provide a vast and largely domestic source of low carbon energy. The underlying nuclear physics is well understood, and the concept of breeding fissile U-233 from thorium has been studied for decades.
Yet the transition from concept to reality has proven difficult. As discussed, Thorium cannot be used directly as a reactor fuel and instead relies on intermediate technologies most importantly fast breeder reactors to generate the fissile material required to initiate the cycle. As a result, the success of India's thorium strategy depends on technological milestones that are still being developed. While several reactor concepts designed to utilise thorium have been proposed and studied, most remain in research or demonstration stages rather than commercial deployment.
The current status of the program highlights a clear distinction between thorium as a resource and thorium as a functioning energy system. India has developed significant expertise and continues to pursue innovative reactor designs, but the timeline for large-scale thorium deployment remains uncertain. Thorium may ultimately become an important component of India's energy future but for now the promise of a thorium powered nuclear system remains a dream still in the making.
© Tanmay Prakash. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] C. D. Selvam et al, "Harnessing Nuclear Energy For India's Energy Security: Current Status, Challenges, and Future Opportunities," Results Eng. 26, 105105 (2025).
[2] J.-P. Revol et al., eds., Thorium Energy for the World (Springer Cham, 2013).
[3] "Thorium Fuel Cycle - Potential Benefits and Challenges," International Atomic Energy Agency, IAEA-TECDOC-1450, May 2005.
[4] N. Brahma, "Select Questions and Answers from the Indian Parliament on Nuclear Issues," Centre for Nuclear and Arms Control, Institute for Defence Studies and Analyses, 2012, p. 19.
[5] A. Joshi, "Thorium-Fueled Nuclear Power in India," Physics 241, Stanford University, Winter 2023.
[6] I. V. Dulera and A. Sharma, "Shaping Third Stage of Indian Nuclear Power Programme With High Temperature Thorium Reactors," Bhabha Atomic Research Centre, BARC Newsletter 376, 22 (January/February 2021).
[7] K. P. Singh, A. Thakur, and A. Gupta, "On the Use of High-Assay Low-Enriched Uranium-Thorium Fuel Cycles in Pressurised Heavy Water Reactors," Curr. Sci. 130, 126 (2026).
