India Nuclear Journey Takes A Hanuman Leap

In many ways, this is only the beginning -- of a new chapter in India's nuclear story, and of a future where its vast thorium reserves could finally power its ambitions.

India's long and carefully charted nuclear journey reached a defining milestone on Monday at 8:25 pm when the country's first 500 MW Prototype Fast Breeder Reactor (PFBR) at Kalpakkam attached criticality-staring of nuclear fission within its core.

Announcing the achievement Prime Minister Narendra Modi described the achievement as a 'defining step' in advancing the second stage of India's three-phase nuclear programme.

'Today, India takes a defining step in its civil nuclear journey, advancing the second stage of its nuclear programme. The indigenously designed and built Prototype Fast Breeder Reactor at Kalpakkam has attained criticality,' Modi posted on X.

'This advanced reactor, capable of producing more fuel than it consumes, reflects the depth of our scientific capability and the strength of our engineering enterprise. It is a decisive step towards harnessing our vast thorium reserves in the third stage of the programme. A proud moment for India. Congratulations to our scientists and engineers,' Modi said.

Many officials who were and are associated with the project were thrilled on hearing the news and lost their sleep on Monday night.

"It is a great feeling. It really took me a long time to sleep after hearing the news," Prabhat Kumar, the first chairman and managing director of Bharatiya Nabhikiya Vidyut Nigam Ltd (BHAVINI), which built the PFBR. He was associated with the PFBR as the project director.

Designed and built indigenously, the reactor stands not just as an engineering accomplishment, but as a symbol of India's intent to unlock the vast energy potential of its thorium reserves.

Unlike conventional thermal reactors, the PFBR uses Uranium-Plutonium Mixed Oxide (MOX) fuel. The core of PFBR is surrounded by a blanket of Uranium-238.

Fast neutrons convert fertile Uranium-238 into fissile Plutonium-239, enabling the reactor to produce more fuel than it consumes. The reactor is designed to eventually use Thorium-232 in the blanket.

Through transmutation, Thorium-232 will be converted into Uranium-233, which will fuel the third stage of India's nuclear power programme.

This unique capability significantly enhances the utilisation of nuclear fuel resources and enables the country to extract far greater energy from its limited uranium reserves while also preparing for large-scale use of thorium in the future.

With the achievement of first criticality, India moves closer to realizing the full potential of its three-stage nuclear power programme.

Fast breeder technology forms the vital bridge between the current fleet of pressurised heavy water reactors and the future deployment of thorium- based reactors, leveraging the country's abundant thorium resources for long-term clean energy generation.

Beyond energy generation, the fast breeder programme strengthens strategic capabilities in nuclear fuel cycle technologies, advanced materials, reactor physics and large-scale engineering.

The knowledge and infrastructure developed through this programme will support future reactor designs and next-generation nuclear technologies.

PFBR: A Hanuman Jump

Present and past officials losing their sleep on Monday night is not without reason.

For the 500MW PFBR, the first of its kind was designed by the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam had seen several ups and downs.

Interestingly the 13.6 MW Fast Breeder Test Reactor (FBTR), Kalpakkam is the forerunner for the 500MW PFBR.

The fast breeder reactor research agency Indira Gandhi Centre for Atomic Research (IGCAR) has done the `Hanuman Jump' in designing the PFBR with the lessons learnt from FBTR.

The journey to this moment has been anything but straightforward.

Conceived in the early 2000s and taken up for construction in 2004 by BHAVINI, the PFBR project has navigated technical hurdles, cost escalations, and delays that are often inevitable in first-of-its-kind endeavours.

Even a devastating tsunami that struck the southern coast tested the resilience of the project and its leadership.

The December 26, 2004 tsunami destroyed the project under construction completely with the foundation pit flooded.

Restart of the construction required fresh safety review and addition of safety measures resulting in delay and increased costs.

Further the Fukushima accident in Japan in 2011 had its impact in PFBR and other nuclear power plants in India as safety aspects were reviewed and additional measures were taken resulting in delay and cost overrun, recalled Kumar, the retired CMD of BHAVINI.

After the completion of civil construction and installation of machinery, the project got further delayed owing to technical problems in the equipment.

Sorting them out by reworking and other manners had its negative impact on the project getting operationalised and the cost.

And finally, the Atomic Energy Regulatory Board (AERB) issued permission for Initial Fuel Loading (IFL) into the reactor core, First Approach to Criticality (FAC) and Low Power Physics Experiments (LPPE) for PFBR on 16.10.2025.

A total of 181 fuel assemblies have to be loaded into the PFBR's reactor.

The fuel loading began in October 2025 when another problem cropped up and an alternate solution had to be found.

According to BHAVINI, as part of prerequisite before start of actual fuel loading, trial operations of fuel handling machines were carried out and it was observed that the Transfer pot of inclined fuel transfer machine (IFTM) on primary side was not getting lowered fully into the reactor and got stopped at a particular elevation above the intended location.

'Since liquid sodium is opaque and direct inspection was not possible, innovative methods were used to identify the root cause for the restricted movement.

'This was systematically resolved in close co-ordination with the designers by designing and developing an alternate direct fuel handling scheme for loading fresh fuel Sub-Assemblies through In-vessel Transfer port,' BHAVINI had said.

'A new direct handling flask was designed and fabricated in-house in a record time of 4 to 5 months with the available resources in IGCAR, BHAVINI and other units of DAE (Department of Atomic Energy) at Kalpakkam,' the company said in its annual report.

The flask components were successfully validated in a full scale mock-up facility erected at PFBR.

After getting the AERB's approval, fuel loading was restarted.

The future fast breeder reactors will have the direct machine' system which is simple, a source said.

For handling spent sub-assemblies which is required after two fuel campaigns, i.e. after two years of reactor operation, unshielded flask will be replaced by shielded flask with some modification in secondary side of IFTM.

In between the completion of blanket sub-assembly loading and Phase-3 clearance from AERB for Fuel loading, one of the leaky Intermediate Heat Exchangers (IHX) taken out from the pile was rectified and erected in the reactor using the Pump - IHX (PI) flask successfully.

As per BHAVINI's annual report for 2021-2022 the project cost has been revised upwards to Rs 6,840 crore from Rs 5,677 crore. The project completion date was fixed for October 2022.

Now the anticipated completion cost of the PFBR is Rs. 8,181 crore.

What PFBR Going Critical Means for India

At the heart of this milestone lies a technology that sets the PFBR apart from conventional reactors.

Fast breeder reactors are designed to produce more fissile material than they consume, effectively creating fuel even as they generate power. This characteristic makes them central to India's long-term nuclear vision, which seeks to transition from uranium-based fuel to thorium -- a resource India possesses in abundance but has yet to fully harness.

The Atomic Energy Regulatory Board (AERB) had, in October 2025, cleared a series of crucial pre-operational steps, including initial fuel loading and low-power physics experiments.

Each of these stages ensured that theoretical assumptions matched real-world performance, with acceptable margins for variation.

The sorting out the fuel loading problem reflected a broader theme in the project: the ability to combine innovation with pragmatism.

As the reactor now moves beyond criticality, the focus will shift to gradually increasing power levels -- a process that typically takes several months.

Experts estimate that it could take up to eight months for the PFBR to reach full power, with each stage carefully monitored to ensure safety and performance.

Beyond the immediate technical achievement, the implications of the PFBR are far-reaching.

It serves as a bridge between India's current nuclear capabilities and its future ambitions. By enabling the production of more fissile material, the reactor lays the groundwork for a closed fuel cycle and the eventual transition to thorium-based energy systems. In doing so, it strengthens India's quest for long-term energy security, reducing dependence on imported fuels.

The Kalpakkam site itself is poised to become a hub of this next phase, with plans already in place for two additional 500 MW fast breeder reactors.

Together, they could form the backbone of a new generation of nuclear infrastructure -- one that is more self-reliant, efficient, and aligned with India's strategic resources.

For the scientists and engineers behind the project, the moment is both culmination and commencement.

Years of calculations, simulations, and on-ground effort have converged into a sustained nuclear reaction within the reactor core.

Yet, in many ways, this is only the beginning -- of a new chapter in India's nuclear story, and of a future where its vast thorium reserves could finally power its ambitions.

In that sense, the PFBR is more than a reactor. It is a statement -- of capability, resilience, and a nation's determination to shape its own energy destiny.

Pre-project activities of FBR 1 and 2:

The fast breeder reactors 1and2 design is being thoroughly reviewed considering all the construction and commissioning feedbacks from PFBR.

Detailed design and analysis of FBR 1 and 2 are under progress incorporating all the stipulations in line with the latest codes and standards. Based on the requirements of the major components to be fabricated and assembled at site, design of the site assembly shop (SAS) has been finalised and construction of SAS has been completed.

The site-specific studies required to be taken up in line with the latest AERB codes is being reviewed. The comments of AERB with respect to the Site Evaluation Report are being addressed.

The layout and requirement for infrastructural facilities such as construction phase substation and security building has been finalised and construction activities will be taken up. Area clearance of the site earmarked for FBR 1 and 2 has been taken up in a phased manner.

Venkatachari Jagannathan can be reached at venkatacharijagannathan@gmail.com

Feature Presentation: Aslam Hunani/Rediff