Prof. Prabhat Ranjan CEO and Co-founder of a nuclear fusion company called ASPL Fusion. He is former Vice Chancellor of D Y Patil International University, Akurdi, Pune
This blog tries to summarize my research journey from Universe to Sun to Moon to Earth to Body to Brain.
[ This blog tries to summarize my research journey from Universe to Sun to Moon to Earth to Body to Brain. Some of this is covered in a talk I gave at IIASA, Vienna – https://youtu.be/327A01oYqdo ]
Continue reading “My Research Journey to Brain”The SHANTI Act ended a six-decade monopoly and opened India’s nuclear sector to private enterprise — but its framework was written for fission. Drawing on how the United States, the United Kingdom and Japan now regulate fusion for its actual hazard, here is what India should change next, and where the lighter touch must not apply.
When the SHANTI Act took effect in December 2025, it ended a monopoly that had defined Indian nuclear policy since 1962. For the first time, an Indian private company can hold a licence to build and operate facilities that involve nuclear materials and ionising radiation, under the oversight of a regulator — the Atomic Energy Regulatory Board — that the same Act finally placed on a statutory footing. This is a structural reset, and it deserves the praise it has received.
But a law written principally for fission power generation cannot, on its own, settle how fusion should be governed. That is the next question, and it is a narrower and more technical one than the debate that produced SHANTI. It is also one the rest of the world has spent the last three years answering. India now has the rare advantage of being able to learn from settled precedent rather than improvise.
Those of us who have spent careers operating India’s experimental tokamaks know that a fusion device and a fission reactor are not variants of the same hazard. A fission reactor sustains a chain reaction in a large inventory of fissile material; its central safety problems are criticality control, the management of decay heat after shutdown, and a very large radioactive source term that must be contained in any conceivable accident. None of these apply to a magnetic-confinement fusion machine. There is no chain reaction to run away. The fuel present in the plasma at any instant is measured in fractions of a gram, and any disturbance — a loss of heating, a loss of vacuum, a magnet trip — causes the reaction to stop within seconds. The plasma cannot melt down because there is nothing sustaining it once conditions are lost.
This does not make fusion free of radiological concern, and no serious person claims it does. There are two real hazards, and they are bounded and well understood: the handling of tritium, a low-energy beta emitter used as fuel; and the neutron activation of the structure surrounding the plasma, which produces radioactive materials in the machine’s own components. These are radiation-safety problems. They are the kind of problem a regulator manages every day for medical accelerators, industrial radiography, and radioisotope production. They are not reactor-safety problems, and a regime designed for reactor safety is the wrong instrument for them.
That mismatch — applying high-hazard rules to a low-hazard technology — is precisely what the world’s leading jurisdictions have now moved to correct.
The pattern across countries is strikingly consistent, and it amounts to a single principle: regulate fusion in proportion to the hazard it actually presents, which is the hazard of radioactive materials, and keep it legally distinct from fission.
In the United States, the Nuclear Regulatory Commission decided in 2023 to regulate fusion machines not as power reactors but under its byproduct-material framework — the same regime that governs radioisotopes and particle accelerators. The reasoning was explicit: fusion does not generate the decay heat that requires engineered emergency cooling, so the regulatory focus should sit on tritium, activation products, and activated dust, which existing materials licensing already handles well. Congress wrote that choice into law in the 2024 ADVANCE Act, and the NRC issued its proposed rule in February 2026. The resulting framework is described, in the agency’s own terms, as performance-based, technology-inclusive and risk-informed — deliberately less prescriptive than the rules for fission plants.
The United Kingdom went further in statute. Its Energy Act 2023 confirmed that fusion energy facilities fall outside the Nuclear Installations Act 1965, so they do not require a nuclear site licence and are not overseen by the Office for Nuclear Regulation. Instead they are regulated by the Health and Safety Executive and the environmental regulators, under rules judged proportionate to fusion’s lower hazard. The government’s stated motive was as much economic as scientific: early regulatory clarity, it found, was a decisive factor in where private fusion companies chose to locate.
Japan is moving the same way, with its expert bodies recommending that fusion be regulated under the radioisotope law rather than the law governing fission reactors, expressly to avoid over-regulation. China oversees fusion devices through its radiation-protection and radioisotope-device regulations rather than its reactor regime. Four very different systems, four different legal mechanisms, one shared conclusion.
What none of these countries did is lower their safety standards. They removed a category error. A technology whose dominant risk is contained radioactive material should be regulated as such — rigorously, but not under a rulebook written for runaway chain reactions and molten cores.
Continue reading “Regulating Fusion for What It Is”In his previous blog, Prof. Ranjan argued that America’s new fusion roadmap marks a change of posture — the state stepping back from building the first power plant and instead building the shared infrastructure that lets private companies build it. Here he asks the natural follow-up for India: not what our public institutions should build, but what they should open. A surprising share of what a private fusion industry needs already sits inside the Department of Atomic Energy.
A companion essay. This piece continues an argument begun in “Build, Innovate, Grow: What America’s New Fusion Roadmap Means for India.”
In my last essay I argued that the deepest lesson of America’s new fusion roadmap is a change of posture — the state stepping back from building the first power plant, and instead building the shared infrastructure that lets private companies build it. That argument invites an obvious question for India: if our public institutions are to enable a private fusion industry, what exactly should they build?
After some months of looking closely, I think the more urgent question is what they should open. A great deal of what India needs already exists, scattered across the units of the Department of Atomic Energy. The fastest and cheapest way to accelerate fusion here is not a greenfield campaign of new institutes; it is to upgrade, repurpose, and — above all — open a defined slice of the capability the DAE has spent six decades building.
I do not write this from the outside. I carried out my own doctoral fusion research at Berkeley; spent nine years as a scientist at the Saha Institute of Nuclear Physics, where I worked on India’s first tokamak, commissioned in 1987; and later led the ADITYA tokamak at the Institute for Plasma Research, along with the operation and control group of its SST-1 superconducting tokamak. Several of the units I describe below I have worked inside, and I have watched this establishment’s plasma capability grow from a single small tokamak into a national programme. What follows is, in part, an argument that India underestimates what it already owns.
The American roadmap calls its shared infrastructure the Tritium-Blanket Development Platform — a distributed network of test stands and loops, public and private, that any developer can draw on because no single company can justify building them alone. India can assemble an equivalent almost entirely from assets it already holds. The right unit of thinking is not a new national laboratory but a platform — a coordinated set of shared user facilities, each anchored in an existing DAE unit and opened, under clear rules, to vetted private developers. Let me walk through fusion’s hardest gaps and where, in the DAE, each could be addressed.
In June 2026 the US Department of Energy published a fusion roadmap that quietly hands the lead to its private sector. Prof. Ranjan draws the real lessons for India — the public-to-private shift, the partnership mechanisms worth copying, the lanes where India can genuinely lead, and the case for a roadmap of our own.
In June 2026, the United States Department of Energy published its Fusion Science and Technology Roadmap. It is, on the surface, a domestic planning document — a list of facilities, milestones, and gaps that one nation intends to close over the next decade. But read carefully, it is something more interesting: the clearest articulation yet of how a great scientific power intends to hand the lead in an emerging energy technology to its private sector, while keeping its public institutions firmly in the game.
For those of us trying to build a credible private fusion enterprise on Indian soil, this document repays close study. Not because we should copy it — our circumstances are different — but because it surfaces, in plain language, the choices every nation now faces. I want to set down what I take to be the real lessons for India, and where I think our own path must diverge.
The Roadmap organises everything around three verbs: Build, Innovate, Grow. Underneath the alliteration sits a genuine change of posture. For seventy years, the American public programme — like every national fusion programme, including our own — assumed that the state would design and construct the first power plant. The 2021 National Academies report said as much.
The new Roadmap quietly retires that assumption. It now treats the private sector as the builder of first-of-a-kind machines, with the public programme repositioned to do something narrower and arguably more valuable: close the common scientific and technical gaps that no single company can justify paying for on its own. To make this concrete, DOE created a stand-alone Office of Fusion in late 2025 and restructured its science programme around it.
This is the lesson India should absorb first. The question is no longer “when will the Department of Atomic Energy build a fusion reactor?” It is “what must our public institutions build so that Indian companies can build reactors?” That is a different — and in my view, far more answerable — question.
The most useful part of the American document is its honesty about where public investment is decisive. It identifies six challenge areas — structural materials, plasma-facing components, confinement, the fuel cycle, breeder blankets, and whole-plant engineering — and is candid that several of these are bounded by physics and metallurgy, not by money. Materials qualification under fusion neutrons, and closing the tritium fuel cycle, take wall-clock time that capital cannot compress. No amount of venture funding shortens an irradiation campaign.
The American answer is to pool these burdens. Shared neutron sources, blanket and tritium test platforms, and a network of test stands are to be funded publicly and made accessible to all developers, because the cost of duplicating them is ruinous and the knowledge they generate is largely non-proprietary.
India already has the raw ingredients for exactly this model — and, in some respects, a head start. The Institute for Plasma Research, BARC’s irradiation and tritium-handling facilities, and our materials laboratories are national assets that took decades to build. The strategic act now is to deliberately open a defined slice of that capability to qualified private players, with clear rules of access. This is precisely the logic behind incubating a private company within IPR’s ecosystem — a path our own work is pursuing, and which I believe should become routine rather than exceptional. The American roadmap gives that instinct an external endorsement.
Good intentions about public–private partnership are common; workable instruments are rare. Here the Americans have done the hard design work, and we should study their toolkit rather than reinvent it.
They run four distinct instruments side by side, each with a different bargain. The Milestone Program pays private companies only for achieving defined technical and business milestones — a model borrowed deliberately from NASA’s commercial cargo programme. INFUSE issues small vouchers that buy private companies access to national-laboratory expertise. The FIRE Collaboratives fund universities and laboratories to close specific gaps that industry has flagged. A newer instrument, Fusion BRIDGE, co-finances the construction of shared facilities with state governments, philanthropy, and industry together.
India does not lack funding vehicles — between the Anusandhan National Research Foundation, the Technology Development Board, and the architecture now being enabled by recent legislation, the pieces exist. What we lack is the discipline of differentiated instruments matched to differentiated risks: one for milestone-based capital, one for expertise access, one for shared infrastructure. The American experience suggests this differentiation is not bureaucratic neatness; it is what allows the same rupee to be used four different ways for four different problems.
At INEF 2026 I realised how little the fission and fusion communities still talk to each other. Yet a fusion device is, before it is ever a power plant, an intense source of fast neutrons — and that surplus can breed U-233 from India’s thorium, burn long-lived waste, and drive a sub-critical hybrid that never goes critical. Fission problems with a fusion answer.
I spent two days at the India Nuclear Energy Forum at IIT Bombay this May, and I came away with one impression more strongly than any other. The people who build and run our fission plants — some of the most capable nuclear engineers anywhere — have, for entirely understandable reasons, not been watching what has happened in fusion over the last five or six years. And the fusion community, equally guilty, has rarely bothered to explain itself in terms a reactor physicist would find useful.
That is a shame, because the two fields are closer to needing each other than either side seems to realise. I want to use this note to close a little of that gap, written deliberately for colleagues who think in cross-sections and neutron budgets rather than press releases.
For most of our careers, “fusion” meant one thing: a very large tokamak, decades away, funded by governments. ITER is real and important, but it shaped a perception that fusion is monolithic and remote. That perception is now out of date in two specific ways.
First, the magnet problem has largely been solved by materials, not by scale. High-temperature superconductors — REBCO tapes in particular — let us reach the field strengths that used to require enormous low-temperature magnets, in machines a fraction of the size. A high field at a small radius changes the entire economic argument, because confinement and reaction rate scale steeply with field. This is why the credible new private programmes are an order of magnitude smaller than ITER and still expect meaningful performance.
Second, and more relevant to this audience, the field has rediscovered configurations the fission community would find refreshingly simple. I work on the axisymmetric magnetic mirror — the Gas Dynamic Trap lineage from Budker Institute in Novosibirsk, recently validated by the WHAM experiment at Wisconsin and its commercial successor. A linear mirror is not a closed toroidal device. It is, conceptually, a long straight magnetic bottle. It is easier to build, easier to maintain, and — crucially — it is an excellent neutron source even when its energy gain is modest. Hold that last point; it is the whole argument.
The deeper shift is one of intent. A generation of fusion programmes asked only one question: when do we put electricity on the grid? The newer programmes ask a different one first: what is fusion good for before it is a power plant? And the honest answer is that a fusion device is, first and foremost, a controllable, intense source of fast neutrons. That reframing is what should interest you.
A deuterium–tritium reaction releases 17.6 MeV, of which 14.1 MeV leaves as a neutron. Compare that with the roughly 2 MeV average of a fission neutron. The factor of seven in energy is not a curiosity — it opens reaction channels that are simply closed to a thermal or even a fast fission spectrum.
At 14 MeV you get neutron multiplication almost for free. Inelastic and (n,2n) channels in beryllium and lead mean a blanket can return more neutrons than it receives. That surplus is the resource. In a critical reactor every neutron is spoken for — you live or die by the six-factor formula and you have almost no margin to spend neutrons on anything that does not sustain the chain. A fusion source hands you a neutron budget you do not have to balance against criticality.
What you choose to do with that surplus — breed fuel that has eluded our thorium programme for decades, burn the waste that fills our repositories, and generate power without the assembly ever going critical — is exactly where our two fields meet.
What does India need to do, together, to be ready to build, supply, and benefit from fusion reactors? The Dutch fusion community asks itself that question once a year, in one room, for one day. After the SHANTI Act and PFBR criticality, India needs to start asking it too.
Earlier this month, on 8 May 2026, the Dutch fusion community gathered at DIFFER in Eindhoven for the third edition of Dutch Fusion Day. Around two hundred participants — from VDL on the established-industry side to Somni Solutions on the start-up side, together with TU/e, DIFFER and BigScienceNL as conveners — spent the day asking a single, very practical question: what does the Netherlands need to do, together, to be ready to build, supply, and benefit from fusion reactors?
The framing on the event’s own retrospective page is striking in its bluntness.
I read that line several times. It is, I think, exactly the sentence India’s fusion community needs to internalise — and the reason I believe we should now have an India Fusion Day.
The Netherlands does not have a tokamak the size of SST-1. It does not have an ITER-class fabrication base. What it has is DIFFER, a strong materials and plasma-wall-interactions community at Eindhoven, a handful of serious startups, and an industrial machine-building culture — VDL, ASML’s suppliers, semiconductor precision shops — that is now being courted by Proxima Fusion in Germany, Renaissance Fusion in France, UKFE’s STEP programme in Britain, and IFMIF-DONES in Spain.
What the Dutch organisers did with Dutch Fusion Day is simply this: they put the buyers and the sellers in the same room for one day a year. That is the entire formula — one day, one venue, a tight programme, public materials, and a room engineered for partnership conversations rather than press releases. It works because it is small enough to be honest. Two hundred people cannot do a ribbon-cutting; they can only do business.
When I look at where India is today, I am convinced we have crossed a threshold that justifies — and frankly requires — a convening of the same kind. The SHANTI Act 2025 came into force this December. The IPR fusion roadmap is published. PFBR achieved first criticality at Kalpakkam in April. A real private fusion ecosystem is now visible. This is no longer a community of three labs and one diaspora WhatsApp group. It is a sector. And sectors need a forum.
What would such a forum actually look like in India? What would it do, who would host it, and why must it happen now rather than after SST-Bharat is built? Those are the questions I want to answer next.
For most failure modes that actually matter in modern manufacturing, X-rays cannot see the problem. Neutrons can. After sixty years as a tool of national laboratories, that capability is finally about to become available to Indian industry on commercial terms.
A friend who runs R&D at a major Indian cell manufacturer told me recently about a warranty problem. Their cells were failing in the field at rates substantially higher than the equivalent imported product. The chemistry was the same. The form factor was the same. The production line was new. They had spent eight months and a great deal of money on X-ray CT, electrochemical impedance, and accelerated cycling, and they still did not know why the failures were happening.
Their problem was that the failure was almost certainly hidden inside the sealed cell can — a gas pocket, perhaps, or a region where the electrolyte had not wet the separator uniformly, or a local lithium plating event during fast charging. A determined X-ray physicist will tell you that phase-contrast and high-resolution micro-CT can sometimes coax these features out under ideal geometry and unlimited time. But the lithium, the electrolyte, and the gas are nearly invisible to electron-density imaging, and the steel-and-aluminium can is exactly what X-rays do see. The contrast you need is buried in the noise. You can occasionally win that fight on a single cell in a research lab; you cannot win it on a sampling cadence that keeps up with a production line. Neutrons give you the same answer in one exposure, with stark and unambiguous contrast, because the physics is working for you instead of against you.
Thirty years of neutron radiography literature would have given them the answer in a day. They knew this. They could not access it. The nearest commercial neutron-imaging facility was in Switzerland.
On 6 April 2026, India’s PFBR at Kalpakkam achieved first criticality — entering Stage 2 of the three-stage nuclear programme. But Stage 3, the thorium endgame, remains 45–65 years away. The bottleneck is ²³³U, which must be bred from thorium and currently depends entirely on the slow FBR build-out. Fusion-fission hybrid technology offers a parallel route: fusion neutrons driving a subcritical thorium blanket, independently of the FBR fleet, potentially compressing the wait by 20–30 years.
When Dr. Homi Bhabha conceived India’s three-stage nuclear programme in the 1950s, it was a work of strategic genius. India had almost no uranium but enormous thorium deposits — estimated at ~25% of the world’s total reserves. The plan was to harness fission step by step, each stage feeding the next, culminating in a self-sustaining thorium-uranium fuel cycle that could power India essentially forever.
| Stage | Reactor Type | Fuel In / Out | Strategic Purpose |
|---|---|---|---|
| Stage 1 | PHWRs (Pressurised Heavy Water) | Natural U-238 → Pu-239 | Exploit domestic uranium; breed plutonium |
| Stage 2 | Fast Breeder Reactors (FBRs) | Pu-239 + Th-232 → ²³³U | Multiply fissile inventory; introduce thorium |
| Stage 3 | Advanced Heavy Water Reactors (AHWRs) | ²³³U + Th-232 → Power | Exploit vast thorium reserves at scale |
The logic is elegant. The execution has been painfully slow. Stage 1 is mature — 22 PHWRs now operate across India. Stage 2 is inching forward: the Prototype Fast Breeder Reactor (PFBR) at Kalpakkam achieved first criticality on 6 April 2026 after decades of delays. Stage 3, the thorium endgame, remains a distant prospect. At current rates, meaningful Stage 3 deployment may not arrive until 2070–2090 — over half a century away.
The central bottleneck is fissile material inventory. Stage 3 reactors require an initial loading of ²³³U — a material that does not occur in nature. It must be bred from thorium by bombarding it with neutrons. Under the classical pathway, the only source of those neutrons at scale is the FBR fleet. But FBRs take decades to build, and their early fuel is precious Pu-239 from Stage 1 — itself in limited supply. It is a slow compound-interest problem, and India is impatient.
To understand the bottleneck, it helps to understand the breeding reaction itself. When a thorium-232 nucleus absorbs a neutron, it does not immediately fission. Instead, it undergoes a two-step transmutation: first to protactinium-233, then to uranium-233 — a fissile material that can sustain a chain reaction just as uranium-235 or plutonium-239 can. This is the nuclear alchemy at the heart of Stage 3. The challenge is neutrons: you need a sustained, high-intensity neutron flux to irradiate thorium at scale, in sufficient quantity to produce meaningful amounts of ²³³U. Classically, only a working fission reactor can supply that flux — which is why Stage 3 has always depended on Stage 2 FBRs. But what if India could breed ²³³U without waiting for the FBR fleet? What if a neutron source powerful enough to drive a thorium blanket could be built faster, cheaper, and with private capital?
This is precisely the proposition at the heart of fusion-fission hybrid technology — and it is the core strategic value of ASPL Fusion’s Project PRABHA.
ASPL Fusion’s PRABHA-Hybrid is a subcritical fusion-fission hybrid with the following design parameters:
The neutron source is a Gas Dynamic Trap (GDT) driven system, with possible collaboration with BINP Novosibirsk — the world leader in tandem mirror devices. This is not speculative physics; GDT devices have operated for decades. ASPL is the first Indian private company to access this technology for a commercial fusion application.
