Indian Council of World Affairs

Introduction

India’s nuclear programme has always been shaped by a paradox. While the country has pursued nuclear energy as a means of ensuring energy security, its limited domestic uranium reserves have constrained the expansion of a conventional, uranium-based nuclear power programme. At the same time, India possesses one of the world’s largest reserves of thorium, a resource that has influenced the country’s nuclear planning since the early years of its atomic energy programme. Recognising this unique position, Dr Homi J. Bhabha proposed a three-stage nuclear power programme that would progressively transition from uranium-based reactors to a closed fuel cycle centred on thorium. This strategy has remained the cornerstone of India’s civilian nuclear policy for more than seven decades.

This vision has grown significantly in recent years. As countries seek reliable low-carbon sources of electricity while reducing dependence on imported fuels, India’s long-term investment in thorium has attracted renewed attention globally. The achievement of the first criticality of the 500 MWe Prototype Fast Breeder Reactor at Kalpakkam in April 2026 represents an important milestone in this journey, bringing India closer to the technological capabilities required for the eventual utilisation of  thorium on a larger scale.^[i]

India’s pursuit of thorium is driven by considerations that extend beyond electricity generation. It is closely linked to the country’s objective of achieving long-term energy security, reducing dependence on imported fuel and strengthening indigenous technology. Against this backdrop, this paper examines the evolution of India's three-stage nuclear programme, the country's progress towards a thorium-based fuel cycle, India's thorium reserves and technological capabilities, and assesses the place of thorium within India's broader nuclear policy.

India’s Three-Stage Nuclear Power Programme: The Foundation of the Thorium Strategy

The three-stage nuclear programme is one of India’s most distinctive long-term nuclear strategies. Developed by Dr. Homi J. Bhabha during the 1950s, the programme was designed around India’s unique resource profile. Unlike countries, such as the United States, Canada, or Russia, which possess substantial uranium reserves, India has relatively modest deposits of natural uranium but abundant thorium resources. More specifically, India holds roughly 1.07 million tonnes of thorium deposits, accounting for almost 25% of the global thorium reserves^[ii]. This resource imbalance made it impractical for India to rely indefinitely on conventional uranium-fuelled reactors. Instead, Dr. Bhabha proposed a phased nuclear programme that would maximise the energy extracted from India’s limited uranium resources while gradually building the technological and material foundation required to utilise thorium on a larger scale. More than seven decades later, this three-stage strategy continues to guide India’s civilian nuclear programme and remains central to the country’s long-term objective of achieving energy security through indigenous resources.

The programme is based on a closed nuclear fuel cycle, in which the spent fuel generated by one stage is reprocessed to produce the fissile material required for the next. Unlike the once-through fuel cycle followed by many countries, where spent nuclear fuel is treated largely as waste, India’s approach views spent fuel as a valuable resource that can be chemically reprocessed and recycled. This enables the recovery of plutonium and, eventually, uranium-233, extracting a substantial amount of energy from the original fuel while reducing long-term dependence on fresh uranium supplies.^[iii] The three stages are therefore not independent reactor technologies but successive components of an integrated strategy, with each stage creating the material base for the next.

The first stage of the programme employs Pressurised Heavy Water Reactors (PHWRs) fuelled by natural uranium. India’s decision to adopt PHWR technology was itself influenced by resource constraints. Since heavy water is an efficient moderator, PHWRs can operate using natural uranium without the need for expensive enrichment facilities. During electricity generation, uranium fuel undergoes fission while a portion of the uranium-238 present in the fuel is converted into plutonium-239.^[iv] This plutonium is recovered through reprocessing and becomes the principal fuel for the second stage of the programme. Over the past several decades, India has successfully established an indigenous PHWR fleet and developed capabilities across the entire fuel cycle, including fuel fabrication, reactor construction, operation, spent-fuel reprocessing, and waste management. The maturity of this stage has provided the technological foundation on which the subsequent stages depend.

The second stage centres on Fast Breeder Reactors (FBRs), which differ fundamentally from conventional thermal reactors. Instead of consuming fissile material only, breeder reactors are designed to generate more fissile fuel than they use. India's 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam uses mixed oxide fuel containing plutonium recovered from the spent fuel of PHWRs.^[v] The reactor core is surrounded by a blanket of fertile material that is converted into additional fissile material through the process of “neutron irradiation”.^[vi] In doing so, Fast Breeder Reactors significantly increase the utilisation of India’s limited uranium resources while simultaneously creating the conditions for the eventual introduction of thorium into the fuel cycle. The PFBR’s attainment of first criticality in April 2026 marked India’s formal entry into the second stage of the programme, representing one of the most significant milestones in the country’s nuclear history.^[vii]

The third stage represents the culmination of India’s long-term vision. Unlike uranium, thorium-232 is a fertile rather than a fissile material; it cannot by itself sustain a nuclear chain reaction. It must first absorb a neutron and be converted into uranium-233, a fissile isotope capable of serving as reactor fuel. The production of uranium-233 depends upon the successful operation of fast breeder reactors in the second stage, making the entire programme sequential in nature. Once sufficient uranium-233 becomes available, advanced reactors designed to utilise thorium can establish a self-sustaining thorium fuel cycle, allowing India to draw upon its extensive domestic thorium resources^[viii]. It is this final stage that distinguishes India's nuclear programme from those of most other countries and reflects a strategic vision for long-term fuel security and energy self-reliance.

The architecture of the three-stage programme shows that India’s pursuit of thorium was never a short-term technological project. Rather, it is the outcome of a carefully sequenced strategy in which every stage performs a distinct function within a larger objective. The success achieved in the first stage and the recent transition into the second have brought India closer to realising the final stage. Yet, despite this progress, the commercial deployment of thorium-based reactors remains dependent on overcoming significant technological and fuel-cycle challenges, making the third stage both the programme's greatest ambition and its most complex undertaking. 

Figure 1: India’s three-stage nuclear programme

Source: Napkin AI

India’s Progress Towards the Third Stage

The attainment of first criticality by the 500 MWe Prototype Fast Breeder Reactor at Kalpakkam in 2026 marked a watershed moment in India’s three-stage nuclear programme. It signified India’s successful transition to the second stage of the programme. While the achievement of criticality of the PFBR has brought India closer to the third stage, the transition to a thorium-based fuel cycle largely depends on the successful operation and gradual expansion of the fast breeder reactor programme. As noted above, thorium-232 is a fertile material and must first be converted into the fissile isotope uranium-233 before it can be used as reactor fuel. The production of uranium-233 on a commercially meaningful scale is therefore a prerequisite for the deployment of thorium-based reactors, making the second and third stages intrinsically interconnected rather than isolated.

The next phase of this transition is expected to centre on the Advanced Heavy Water Reactor (AHWR), developed by the Bhabha Atomic Research Centre. Designed to utilise thorium-based fuel, the AHWR is intended to demonstrate the technical and commercial viability of the thorium fuel cycle^[ix]. Although the reactor design has reached an advanced stage of development, its commercial deployment will largely determine how quickly India can move beyond breeder technology towards the sustained utilisation of its abundant thorium reserves. The realisation of a self-sustaining thorium fuel cycle will depend on the continued expansion of breeder reactor capacity, the efficient production and management of uranium-233, and the successful deployment of advanced thorium-based reactor technologies. India's progress towards the third stage should therefore be viewed as an evolutionary process rather than a single technological milestone.

India’s Thorium Reserves: Resource Base and Distribution

India possesses one of the world's largest reserves of thorium, a resource that forms the cornerstone of its long-term nuclear strategy. India accounts for nearly one-quarter of the world's identified thorium resources, making it among the most thorium-rich countries globally, unlike uranium, which occurs in relatively limited quantities within the country.^[x]

Thorium in India occurs predominantly in the form of monazite, a phosphate mineral containing thorium along with rare earth elements. These heavy mineral sands are primarily found along India’s eastern and south-western coastlines. The concentration of thorium within monazite varies depending on the geological composition of the deposit, but the mineral remains the country’s principal commercial source of thorium.^[xi] The largest deposits are located on the coasts of Kerala, Tamil Nadu, Andhra Pradesh, and Odisha, with additional occurrences reported in parts of Maharashtra and Gujarat. The beach sand deposits of Kerala's Chavara coast, Tamil Nadu’s Manavalakurichi region, and Odisha's Chhatrapur belt are some of the country’s most significant monazite-bearing deposits.^[xii] These regions collectively account for the bulk of India’s identified thorium resources and have been the focus of exploration and mineral development activities.

While India’s resource base is considerable, thorium is not found in a readily usable form. Monazite contains thorium along with rare earth elements, uranium, and other minerals, requiring extensive physical and chemical processing before thorium can be separated and converted into nuclear-grade material. Thorium is chemically extracted and converted into thorium oxide (ThO₂) before it can be introduced into the nuclear fuel cycle. Extraction and refining of thorium are undertaken through a network of specialised institutions, with Indian Rare Earths Limited responsible for mineral processing, the Atomic Minerals Directorate for resource exploration, and the Bhabha Atomic Research Centre and Indira Gandhi Centre for Atomic Research leading research on fuel fabrication, reprocessing, and reactor technologies. 

Figure 2: Map of India’s thorium deposits

Source: The Hindu

Conclusion

India’s commitment to thorium has remained consistent despite significant changes in the international nuclear landscape. The 2008 India-US Civil Nuclear Agreement and the subsequent waiver granted by the Nuclear Suppliers Group enabled India to participate in international nuclear commerce and eased constraints on uranium imports. Yet India has continued to invest in breeder reactors, thorium fuel research and advanced reactor technologies, indicating that thorium occupies a role in national policy that extends beyond uranium scarcity.

The continued emphasis on thorium reflects India's vision of strategic autonomy. Imported uranium has undoubtedly facilitated the expansion of nuclear power generation, but it remains vulnerable to geopolitical uncertainties, changing market conditions, and external supply arrangements. Thorium, on the other hand, is an abundant domestic resource that offers the prospect of a self-sustaining nuclear fuel cycle and reduces dependence on external fuel supplies. Successive governments have therefore viewed thorium not just as a substitute for imported uranium but as the foundation of India's long-term nuclear security. India’s thorium policy has been largely pragmatic rather than urgent.

Policymakers have recognised that commercial deployment of thorium-based reactors will require advanced technological development and cannot replace conventional uranium-based reactors in the near future. As a result, India’s nuclear policy has followed a dual-track approach: expanding nuclear generation through uranium-fuelled reactors while simultaneously investing in the infrastructure and technologies necessary for the eventual transition to a thorium-based fuel cycle. In this sense, thorium represents more than an alternative nuclear fuel. It reflects a strategic choice to leverage India's natural resource endowment in pursuit of long-term energy security, technological self-reliance, and fuel independence. The continued investment in thorium despite improved access to international uranium supplies suggests that India views the resource not simply as an energy asset but as a cornerstone of its future nuclear strategy. Although commercial deployment of thorium-based reactors remains a long-term objective, continued investments in fast breeder technology, fuel-cycle research, and reactor development reflect India's sustained commitment to realising Dr. Bhabha's vision.

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*Tripti Neb, Research Intern, Indian Council of World Affairs, New Delhi
Disclaimer: Views expressed are personal. 

Endnotes 

^[i] World Nuclear News, "First Criticality for Indian Fast Breeder Reactor," World Nuclear News, April 7, 2026, https://world-nuclear-news.org/articles/first-criticality-for-indian-fast-breeder-reactor.

^[ii] Press Information Bureau, "A New Chapter in India’s Nuclear Journey," Factsheet ID 150617, Ministry of Information and Broadcasting, Government of India, April 7, 2026, https://www.pib.gov.in/FactsheetDetails.aspx?id=150617.

^[iii] J. Srivastava, "Journey from Scarcity to Surplus—Success Story of India’s Heavy Water Production," in Atomic Energy in India: Achievements since Independence, ed. A. K. Tyagi and P. R. Vasudeva Rao (Mumbai: Homi Bhabha National Institute / Bhabha Atomic Research Centre, 2022), https://www.barc.gov.in/ebooks/9789356590526/paper08.pdf.

^[iv] Ibid.

^[v] Shiv Parekh, "India’s Three Stage Nuclear Program," coursework for PH241, Stanford University, March 22, 2014, http://large.stanford.edu/courses/2014/ph241/parekh1/.

^[vi] “Nuclear irradiation” is the exposure of nuclear fuel and reactor components to a flux of free neutrons during the reactor operation stage, leading to atomic-level material damage, isotope transmutation, and energy generation.

^[vii] David Dalton, "India Hails 'Defining Step' In Nuclear Programme As Fast Breeder Reactor Reaches First Criticality," NucNet, April 8, 2026, https://www.nucnet.org/news/india-hails-defining-step-in-nuclear-programme-as-fast-breeder-reactor-reaches-first-criticality-4-3-2026.

^[viii] J. Srivastava, "Journey from Scarcity to Surplus—Success Story of India’s Heavy Water Production," in Atomic Energy in India: Achievements since Independence, ed. A. K. Tyagi and P. R. Vasudeva Rao (Mumbai: Homi Bhabha National Institute / Bhabha Atomic Research Centre, 2022), https://www.barc.gov.in/ebooks/9789356590526/paper08.pdf.

^[ix] Bhabha Atomic Research Centre, ”Advanced Heavy Water Reactor (AHWR),” Research Projects, Department of Atomic Energy, Government of India, https://www.barc.gov.in/randd/ahwr.html.

^[x] Harsh Parikh, "Thorium in India," coursework for PH241, Stanford University, March 6, 2024, http://large.stanford.edu/courses/2024/ph241/parikh1/.

^[xi] Energy Portal, "Thorium Exploration in India," Energy Portal, https://www.energyportal.in/nuclear/thorium-exploration-in-india.

^[xii] Harsh Parikh, "Thorium in India," coursework for PH241, Stanford University, March 6, 2024, http://large.stanford.edu/courses/2024/ph241/parikh1/.