While achieving criticality is a crucial step in its nuclear energy programme, India requires a calculated and flexible approach to nuclear energy to align with its broader visions of Viksit Bharat and its net-zero target.
After a long and troubled development cycle, India’s Prototype Fast Breeder Reactor (PFBR) finally achieved criticality on 6 April 2026, marking a significant step forward for India’s nuclear energy programme. It could bridge the gap between India’s current suite of primarily indigenously developed Pressurised Heavy Water Reactors (PHWRs) and its future plans for thorium-based reactors.
Though this endeavour still requires significant design and R&D progress, India’s recent push towards nuclear energy privatisation and Small Modular Reactors (SMRs) is encouraging, and it exemplifies its commitment to a multi-pronged nuclear energy strategy. However, the technological and economic obstacles associated with continuing to pursue a closed fuel cycle will require a flexible approach to nuclear energy, in line with the country’s broader visions of Viksit Bharat 2047 and net-zero 2070.
Pioneered by the vision and efforts of Dr Homi Bhabha, India decided to adopt a three-stage NEP employing a closed fuel cycle, with the intent of exploiting its vast thorium reserves rather than relying on foreign supplies to supplement its relatively limited uranium reserves.
After centuries of colonial subjugation, achieving technological sovereignty was a foremost priority for independent India. India’s nuclear energy programme (NEP) emerged as the bulwark in its efforts to reduce dependence on the West. Pioneered by the vision and efforts of Dr Homi Bhabha, India decided to adopt a three-stage NEP employing a closed fuel cycle, with the intent of exploiting its vast thorium reserves rather than relying on foreign supplies to supplement its relatively limited uranium reserves.
Figure 1: India's Three-Stage Nuclear Energy Programme
Source: CSTEP
The basic idea behind pursuing a closed fuel cycle was that it would allow each stage to function independently, eventually leading to a self-sustaining nuclear energy ecosystem.
India’s PFBR at Kalpakkam is a 500 MWe sodium-cooled Fast Breeder Reactor (FBR) that utilises a Uranium-Plutonium Mixed Oxide (MOX) fuel with a core surrounded by a blanket of Uranium-238 (U-238). As the nuclear fission reaction proceeds, fast neutrons transmute the fertile U-238 into fissile Plutonium-239 (Pu-239), thereby essentially “breeding” the latter.
The PFBR is operated under the oversight of the Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI), a government enterprise created under the Department of Atomic Energy (DAE) in 2003. Designed by the Indira Gandhi Centre for Atomic Research (IGCAR), the PFBR was fabricated and constructed indigenously with significant contributions from academia and industry partners.
Though construction of the reactor was initially planned to be completed by 2010, the project was plagued by multiple delays and cost overruns. However, on 6 April 2026, the PFBR finally achieved criticality—the point at which a sustained and controlled nuclear fission reaction is initiated—marking a key step before full operationalisation. Consequently, it represents a landmark moment for India’s NEP, bringing it one step closer to completing Stage 2 of its closed fuel cycle.
While reaching criticality is a crucial step towards achieving India’s long-envisioned goal of a closed fuel cycle, it will nevertheless take significant time and effort to be realised. There are several subsequent hurdles and caveats which must be addressed.
While reaching criticality is a crucial step towards achieving India’s long-envisioned goal of a closed fuel cycle, it will nevertheless take significant time and effort to be realised.
Post-achieving criticality, the next step is to achieve full operationalisation, which, though relatively straightforward, will still take time. Furthermore, to complete the second stage of India’s NEP, the DAE will need to decide on and approve the design for a Uranium-233 (U-233) breeder reactor, followed by the construction of another prototype reactor to test the design. Subsequently, the DAE will face the substantial task of FBR commercialisation, which presents several challenges, with achieving spent fuel reprocessing on a commercial scale arguably the most significant of these challenges. One of the chief obstacles in this regard is the extraction of U-233 from spent thorium fuel, as it gets invariably contaminated by uranium-232 (U-232), making the resulting mixture highly radioactive over time and rendering handling and extraction extremely challenging.
Assuming completion of Stage 2, the next task would be to build a prototype Advanced Heavy Water Reactor (AHWR) similar to the PFBR. An effort has already been made in this direction by the Bhabha Atomic Research Centre (BARC) through the development of a lower-power research reactor, the Advanced Heavy Water Reactor – Critical Facility (AHWR-CF), as well as a proposed design for a 300 MWe AHWR. This would be followed by the commercialisation of AHWRs, thereby finally completing Stage 3 of the NEP.
India’s overall nuclear energy strategy hinges on various facets. It currently envisions employing a combination of indigenously built PHWRs alongside imported light water reactors (LWRs). Keeping India’s goal of reaching 100 GW of nuclear energy generation capacity by 2047, this has been supplemented by the recent push towards developing SMRs through the Nuclear Energy Mission, as well as the enactment of the “Sustainable Harnessing and Advancement of Nuclear Energy for Transforming India (SHANTI) Act, 2025,” which aims to refurbish and revitalise India’s nuclear energy framework by enabling more substantial private participation within India’s nuclear energy sector.
On the other hand, India’s pursuit of a closed fuel cycle continues, with the full operationalisation of the PFBR serving as its next major step. While the ultimate goal of India’s NEP remains an uphill task, the possibility of enhanced private participation in the nuclear energy sector in the aftermath of the passage of the SHANTI Act is likely to bolster these efforts, particularly given the significant contributions already made to the PFBR by multiple private entities such as Larsen & Toubro (L&T), Godrej, and Walchandnagar Industries.
However, there is a viewpoint that the pursuit of a closed fuel cycle was a product of its time, driven by the ambitions of technological and energy sovereignty of a newly independent India, and may not be the most practical or economically sound strategy in the current era. For instance, though India’s NEP suffered from Western sanctions following its 1974 “Smiling Buddha” nuclear test, the situation was largely eased after the finalisation of the US–India nuclear deal in 2008, which gave India substantial access to uranium imports. Furthermore, India has signed Inter-Governmental Agreements (IGAs) on civil nuclear cooperation with 18 countries, rendering the issue of uranium shortage largely redundant at this point.
The situation is further complicated by the possibility of multiple pathways for thorium-based reactors, each involving distinct advantages and trade-offs. For instance, the development of molten salt breeder reactors (MSBRs) and accelerator-driven reactor systems (ADS) offers noteworthy alternatives to the AHWRs proposed under the initial NEP. An example of this has already been provided by China, which recently successfully demonstrated its thorium-based molten salt reactor (TMSR-LF1).
Moreover, there are pathways for utilising thorium which do not even require FBRs, relying instead on existing technologies such as PHWRs and pressurised water reactors (PWRs).
As India pursues Viksit Bharat 2047, alongside its 2070 net-zero strategy, India’s NEP has acquired unprecedented significance. The achievement of first criticality by the PFBR marks a watershed moment in India’s nuclear energy journey, not only as a technological milestone, but as an opportunity to determine the direction of its NEP in the coming years. Should India remain committed to its ambitious but costly vision of a closed fuel cycle, or should it pursue a more practical and economical approach based on traditional reactor technologies?
The achievement of first criticality by the PFBR marks a watershed moment in India’s nuclear energy journey, not only as a technological milestone, but as an opportunity to determine the direction of its NEP in the coming years.
The answer lies in balance. To identify an optimal path forward, India must pursue a modern and flexible approach to nuclear energy that reflects emerging trends while retaining the fundamental tenets of technological and energy sovereignty. Consequently, enhancing nuclear energy output through a diverse range of reactor technologies, including PHWRs, LWRs, and SMRs, should be a near-term goal, in line with the country’s 2047 vision, while achieving a closed fuel cycle should be the long-term goal, more aligned with its 2070 net-zero vision. Though the latter presents a challenging prospect, necessitating the exploration of multiple and potentially costly pathways, it offers the possibility of energy sovereignty unlike that achieved by any other nation to date.
This is particularly relevant in the current geopolitical climate, which has exposed the fragility of global energy supply chains and the negative consequences of overreliance on foreign energy sources and technology. In particular, threats to clean energy technology imports arising from the weaponisation of critical mineral export controls by major powers, alongside disruptions to global fuel and gas supplies following the closure of the Strait of Hormuz, make the continued pursuit of a closed fuel cycle by India—though not immediately rewarding—warranted in the long run.
Prateek Tripathi is an Associate Fellow with the Centre for Security, Strategy and Technology (CSST) at the Observer Research Foundation.
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Prateek Tripathi is an Associate Fellow at the Centre for Security, Strategy and Technology. His work focuses on an emerging technologies and deep tech including quantum ...
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