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
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.
The Neutron Bridge — Part 1 | Prof. Prabhat Ranjan
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.
What changed in fusion while you were busy keeping the grid running
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 That perception is now out of date in two specific ways.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.
Why a fusion neutron is different
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.
The fusion neutron is born about seven times more energetic than a fission neutron, clearing the thresholds for neutron multiplication and hard-spectrum fission that a reactor spectrum cannot.
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.
The probe Indian industry has been doing without — Prabhat Ranjan
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.
📣 Breaking — 6 April 2026
India’s Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, Tamil Nadu achieved first criticality at 20:25 IST — marking India’s formal entry into Stage 2 of the three-stage nuclear programme. This historic milestone, coming just as this article goes to press, makes the question of accelerating Stage 3 more urgent and more actionable than ever. ASPL Fusion’s Project PRABHA is designed to be exactly that accelerant.
India sits atop the world’s largest thorium reserves — enough to power the country for centuries. Yet the gateway to this abundance, Stage 3 of the three-stage nuclear programme, remains decades away under the current trajectory. ASPL Fusion’s fusion-fission hybrid technology offers a credible, privately-funded shortcut: producing ²³³U directly from thorium using fusion neutrons, bypassing the central bottleneck of the Fast Breeder Reactor fleet, and potentially compressing a 40-year wait into 20.
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.
2. The Missing Accelerant: An External Neutron Source
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.
What is a fusion-fission hybrid?
A fusion-fission hybrid marries two nuclear processes. Fusion — the joining of light nuclei (deuterium and tritium, or deuterium alone) — releases vast energy and, crucially, a flood of energetic neutrons. Fission — the splitting of heavy nuclei like thorium or uranium when struck by neutrons — releases further energy and breeds new fissile material. In a conventional fission reactor, a precise critical mass of fissile fuel must be maintained to keep the chain reaction going, demanding expensive enrichment and creating inherent safety challenges.
In a fusion-fission hybrid, the fusion core acts as a powerful, controllable neutron gun, firing neutrons into a surrounding “blanket” of thorium. The blanket undergoes breeding reactions, but it never reaches criticality on its own: its neutron multiplication factor keff is kept below 1.0 by design. This means the reaction halts the instant the fusion source is switched off — an intrinsic safety property no conventional reactor can match, since no self-sustained runaway chain reaction is physically possible. However, subcritical systems still accumulate decay heat from fission products after shutdown, requiring continued cooling; they are not free from thermal-hydraulic safety requirements. Yet the neutron economy within the blanket can be made substantial. The neutron multiplication factor M = 1/(1−keff) = 33 means that one source neutron ultimately produces approximately 33 neutrons across all cascade generations — not 33 breeding reactions. Of these, a fraction (typically 10–30%, depending on blanket design and spectrum) are usefully absorbed in Th-232 to initiate the transmutation chain to ²³³U. The remainder sustain the multiplication, compensate for parasitic absorption in structural materials, and manage leakage. This neutron amplification, combined with a carefully optimised multi-zone blanket, is what enables meaningful ²³³U production from a modest fusion source.
ASPL Fusion’s PRABHA-Hybrid is a subcritical fusion-fission hybrid with the following design parameters:
keff = 0.97 — deeply subcritical, inherently safe
Neutron multiplication M = 33× — one source neutron produces ~33 neutrons in cascade across all generations (M = 1/(1−keff)); a fraction of these are usefully absorbed in Th-232 for ²³³U breeding
~80 kg of ²³³U per unit per year from the thorium zone — a design-target based on internal neutronics calculations at ~53 MWth blanket power; subject to detailed validation accounting for Pa-233 capture losses, spectrum effects, and geometric efficiency
33 MWe net electrical output at 87.5% capacity factor (253 GWh/yr)
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.
India’s electricity demand will nearly quadruple by 2047. Solar and wind cannot carry that load alone. The time to build the next generation of baseload is not 2040 — it is today and why fusion must be a strong part of it.
India’s electricity demand will nearly quadruple by 2047. Solar and wind cannot carry that load alone. The time to build the next generation of baseload is not 2040 — it is today.
Disclosure: The author is co-founder of ASPL Fusion, a private Indian fusion company. This article presents an industry perspective on national energy policy. The policy arguments are grounded in publicly available data; the ASPL programme description in Section 5 is provided as a concrete illustration of what a domestic fusion development path can look like in practice.
At a Glance — For Decision-Makers
708 GW peak demand and 2,100 GW total capacity needed by 2047 — the equivalent of building a new US power grid from scratch.
Intermittent renewables alone cannot provide firm power — grid stability requires large-scale dispatchable baseload even with abundant storage.
Fusion now has serious private capital behind it: Microsoft, Google, and OpenAI are structuring power purchase agreements with fusion companies. India risks being a technology importer.
Three budget-cycle asks for 2026: fusion in National Energy Plan · dedicated component development fund · AERB regulatory engagement mandate.
Key Number
India’s Central Electricity Authority projects peak power demand reaching 708 GW by 2047 — four times today’s installed capacity. Meeting it requires 2,100 GW of generation: close to the entire current installed capacity of the US and EU combined. That is the scale of infrastructure build India must manage across the next two decades.
A young mother in Knightdale, North Carolina recently learned that her tap water contained uranium at twelve times the safe limit — and that her infant son had been drinking it for a year. The uranium was natural. But it points to a much deeper problem: the millions of tonnes of spent nuclear fuel buried in geological repositories worldwide, isolated by engineered barriers designed to last thousands of years while the waste inside remains hazardous for hundreds of thousands. Does fusion technology offer the only real solution?
And why fusion technology may hold the key to breaking its millennia-long grip on our environment
📰 What sparked this post
Earlier this month, a young mother in Knightdale, North Carolina, received two letters in her mailbox from Carolina Water Service informing her that uranium levels in her tap water had tested at 250 picocuries per litre — twelve times the US federal safety standard. Her one-year-old son had been drinking that water, mixed into his formula, for the entirety of his short life. The well had been testing clean for five consecutive years. Nobody had any warning. The utility, WRAL News reported on 20 February 2026, tests for uranium only once a year.
I read that report and felt the familiar, uncomfortable weight of a problem I have spent decades worrying. The uranium in that Knightdale well was almost certainly natural — leached from granite bedrock by groundwater as it has been doing since long before human civilisation. But the story it tells becomes far more urgent when you consider what we have deliberately added to the geological environment over the past eighty years: millions of tonnes of radioactive material, far more concentrated and persistent than anything nature placed there, buried across hundreds of sites worldwide. If natural uranium can contaminate a neighbourhood well quietly, over years, undetected — what does that tell us about the long-term safety of the radioactive legacy we are choosing to leave underground?
There is a kind of danger that does not announce itself. It moves silently through cracks in bedrock and channels of groundwater, carrying with it some of the most persistent poisons humanity has ever created — thousands of tonnes of spent nuclear fuel and high-level waste from decades of fission power generation, stored in temporary facilities and deep geological repositories, with the quiet hope that they will remain isolated for the ten thousand years or more that their radioactivity demands. That hope, I am afraid, rests on a geological optimism that the story from Knightdale does not entirely justify.
The Burial Problem: Out of Sight Is Not Out of Mind
The logic behind deep geological disposal is sound in principle. Take the waste deep enough — typically 300 to 1,000 metres underground — into stable rock formations of granite, clay, or salt, and isolate it from the biosphere for geological timescales. Countries including Finland, Sweden, and Canada have invested heavily in this approach. India, too, through its Department of Atomic Energy, manages vitrified high-level waste in stainless steel canisters awaiting eventual deep burial.
The problem is the word eventually. Spent nuclear fuel contains a cocktail of long-lived radionuclides. Plutonium-239 has a half-life of 24,100 years. Technetium-99 has a half-life of 211,000 years. Iodine-129 decays over 15.7 million years. The engineered barriers — steel canisters, bentonite clay buffers, concrete vaults — are designed to last centuries, perhaps a few thousand years. But the radioactive material inside them demands isolation for hundreds of thousands of years. No engineered structure in human history has lasted that long. The Egyptian pyramids are 4,500 years old and already substantially degraded.
⚠ Critical Context
The Timescale Mismatch
The engineered barriers in deep geological repositories are designed to last at most a few thousand years. The long-lived actinides inside them — plutonium, americium, neptunium — remain radiologically hazardous for hundreds of thousands to millions of years. No engineered containment system in history has bridged this gap.
When Water Meets Radioactivity
Water is the great dissolver. Given enough time, groundwater will find every crack, every imperfection, every microscopic flaw in the engineered barriers of a repository. When it does, it will begin to leach radionuclides and carry them outward through the rock, toward aquifers, rivers, and ultimately the food chain.
This is not a hypothetical case. At the Hanford Site in Washington State, USA — the largest nuclear waste site in the Western Hemisphere — radioactive contamination has migrated into the Columbia River through groundwater. Tritium, strontium-90, and technetium-99 have all been detected in monitoring wells between the site and the river. The US government has spent over $20 billion on cleanup, and the problem remains unresolved. In the Marshall Islands, the Runit Dome — a concrete cap built over nuclear test debris — sits at sea level, and rising ocean waters are already infiltrating its base, mobilising radioactive material into the Pacific.
The mechanisms are well understood by hydrogeologists. Radionuclides differ dramatically in their mobility through soil and rock. Cesium-137 and strontium-90 tend to adsorb onto mineral surfaces and migrate slowly. Tritium (radioactive hydrogen) and iodine-129 behave like water itself and can travel enormous distances rapidly. Technetium-99, in its pertechnetate form, is highly mobile and poorly retained by most geological materials. Once these isotopes enter an aquifer, remediation is extraordinarily difficult.
24,100YearsHalf-life of Plutonium-239, the dominant actinide in spent fuel
~250kTonnesSpent nuclear fuel in storage worldwide, growing ~10,000 t/year
106YearsIsolation time needed for Iodine-129 to reach background levels
The Indian Context: A Growing Inventory
India operates 24 nuclear reactors with more under construction, and the DAE’s vision for a three-stage fuel cycle — natural uranium pressurised heavy water reactors, fast breeder reactors, and eventually thorium-fuelled reactors — will produce substantial quantities of spent fuel and radioactive waste for decades. The Bhabha Atomic Research Centre manages this waste responsibly by global standards, with vitrification plants at Tarapur and Trombay converting liquid high-level waste into borosilicate glass, and interim storage in air-cooled vaults. But interim is not permanent. The waste continues to accumulate, and the long-term disposal solution remains to be finalised.
India’s geology presents both opportunities and challenges for deep disposal. The Deccan Traps basalts, Precambrian granites of Rajasthan and Karnataka, and Gondwana sedimentary formations are all under investigation. However, India is seismically active, and the hydrological connectivity of hard-rock aquifers in peninsular India is not fully characterised. The consequences of a repository breach — even a slow, diffusive one — for communities dependent on groundwater in rural India would be severe and essentially irreversible. This is why India needs a two-pronged strategy: continued, well-funded site characterisation to identify the safest possible repository locations, pursued in parallel with fusion-driven transmutation research that progressively reduces the volume and longevity of the material that must be stored. ASPL Fusion sees itself as a partner in that national strategy — not as a replacement for rigorous geological work, but as the scientific complement to it.
“The question we must ask is not only where to store nuclear waste safely — but whether we can transform it from a millennial burden into a resource. That is the question fusion science must answer.”
What if the answer to radioactive waste is not better burial, but transformation? This is the principle of nuclear transmutation — using neutrons to convert long-lived radioisotopes into shorter-lived or even stable nuclides. The physics is straightforward: a neutron capture event can convert a problematic long-lived nucleus into one that decays much faster, or even into a stable, non-radioactive element. Transmutation does not eliminate radioactivity immediately, but it can dramatically reduce the required isolation time from hundreds of thousands of years to hundreds — a difference of three orders of magnitude that makes engineered containment genuinely feasible.
The challenge has always been producing neutrons in sufficient intensity and at the right energies to drive transmutation efficiently. Fast neutrons — those with energies in the MeV range — are particularly effective at inducing fission in transuranic actinides, the most radiologically hazardous long-lived components of spent nuclear fuel. This is precisely where fusion technology enters the picture.
It is worth being precise about what we are actually trying to destroy. Of the spent fuel discharged from a fission reactor, roughly 95% is uranium — material that can be recycled into new fuel in a closed fuel cycle. Another 4% or so is fission products, most of which decay to benign levels within a few hundred years. The true long-term problem is the remaining fraction: the minor actinides — americium, neptunium, and curium — which constitute barely 0.1% of spent fuel by mass but are responsible for the overwhelming majority of the radiological hazard beyond 1,000 years. Remove that 0.1% through transmutation, and the isolation time required for the remainder drops from hundreds of thousands of years to roughly 300 years — a timescale within the credible reach of engineered barriers and, crucially, within human institutional memory.
The Fusion-Fission Hybrid: How It Works
A fusion-fission hybrid couples a fusion neutron source to a sub-critical fission blanket loaded with spent nuclear fuel or separated minor actinides. The fusion device — in ASPL Fusion’s case, a Gas Dynamic Trap (GDT) operating on deuterium-tritium fuel — produces intense fluxes of 14.1 MeV neutrons directed into the surrounding blanket, driving fission of the actinide inventory without the blanket ever sustaining a chain reaction on its own.
The choice of the GDT as the neutron source is deliberate. Unlike toroidal devices such as tokamaks, a GDT is a linear magnetic mirror machine: its open, cylindrical geometry makes it inherently well suited for surrounding with a concentric fission blanket, since there is no toroidal geometry to work around. The GDT also operates in steady state rather than producing pulsed neutron bursts, which matters enormously for the thermal and mechanical engineering of the blanket and for achieving sustained transmutation rates.
This sub-criticality is the system’s defining safety feature. Unlike a conventional fission reactor, the assembly cannot run away: switch off the fusion source and all fission reactions stop immediately. There is no possibility of a Chernobyl or Fukushima-type criticality event. The physics simply does not permit it.
Inside the blanket, the fast neutrons accomplish two things simultaneously. First, they fission transuranic actinides — plutonium, americium, neptunium, curium — converting them into shorter-lived fission products. A nuclide requiring 24,000 years of isolation becomes one requiring roughly 300 years. Second, neutron capture in a lithium layer breeds tritium, replenishing the fusion fuel. The system can in principle be self-sustaining in tritium and generate net electrical power while consuming the most hazardous fraction of the waste inventory.
Figure 1: The fusion-fission hybrid closed loop. D-T fusion drives a sub-critical fission blanket; fission heat generates electricity; lithium breeds tritium to replenish fusion fuel.
🔬 Science Note
Why 14 MeV Neutrons Matter for Transmutation
Fast neutrons from D-T fusion carry 14.1 MeV of energy — far above the fission thresholds of minor actinides like americium-241 and curium-244, which are very difficult to fission with the lower-energy neutrons available in a conventional thermal reactor. D-T fusion neutron sources can therefore access and destroy actinides that conventional reactors largely cannot.
What Transmutation Can — and Cannot — Do
Transmutation is not a silver bullet. The global inventory of spent nuclear fuel — approximately 250,000 tonnes and growing by around 10,000 tonnes each year — is enormous, and no single device will process all of it. Critics rightly raise the economics: transmutation is energy-intensive, and the costs are significant. But the fusion-fission hybrid addresses this directly. The fission reactions in the sub-critical blanket generate substantial heat, which can be converted to electricity. In a mature system, this electricity generation partially or fully offsets the cost of waste processing — turning a pure liability into a partial energy asset. Regulatorily, sub-critical systems present new challenges; most existing nuclear frameworks were designed around critical reactors. Updated regulatory pathways for driven sub-critical assemblies will need to be developed in dialogue with AERB in India and equivalent bodies internationally. This is work that needs to begin now, in parallel with the physics.
ASPL Fusion is advancing this programme in India, working toward a GDT-based fusion neutron device capable of driving a sub-critical blanket — a system that addresses the waste hazard at its root rather than managing its symptoms indefinitely underground.
Comparison: Deep Burial vs. Fusion-Driven Transmutation
Feature
Conventional Burial
Fusion-Driven Transmutation
Isolation Time Required
100,000+ Years
~300 Years
Primary Barrier
Geological Formations
Engineered Containment
Actinide Hazard
Passively Decaying
Actively Fissioned
Economic Value
Pure Liability
Partial Energy Asset
Safety Basis
Geological Stability
Sub-critical Physics
The radioactive waste buried under our mountains and stored in our cooling ponds will not simply go away. The water will, eventually, find it. The question is whether we act now, with the best science available, to transform the problem before it transforms our groundwater. Fusion technology — specifically the intense fast-neutron fluxes that only fusion can produce — offers a path that fission alone cannot. I have spent my career in this field, from the plasma physics laboratories of UC Berkeley to leading India’s Technology Vision 2035 as Head of TIFAC, and I have never been more confident that this path is real, achievable, and urgently necessary.
We owe it to the generations who will inherit this planet to do more than bury the problem deeper. We owe them a solution.
Learn More About ASPL Fusion’s Work
Fusion-driven transmutation research, the Gas Dynamic Trap programme, and India’s path to closing the nuclear waste cycle.
Thorium-232 can power India for centuries. Converting it to usable fuel requires neutrons — and fusion may be our best answer.
The four things you need to know
⛏️
The Resource
India holds 846,000 tonnes of thorium oxide — worth more than Saudi Arabia’s oil reserves.
⚡
The Challenge
Thorium needs a neutron “spark” to become uranium-233 fuel. The conversion process is called breeding.
☀️
The Tool
14.1 MeV D-T fusion neutrons are the most efficient “spark” in physics — uniquely suited to thorium breeding.
🚀
The Opportunity
ASPL Fusion’s PRABHA project is building the world’s first fusion-fission hybrid to unlock this energy.
I have spent most of my career thinking about what powers India’s future. As the former head of TIFAC and key contributor to India’s Technology Vision 2035, I have watched the country debate energy security for decades. We import over 80% of our oil, a significant portion of our gas, and nearly all of our uranium. And yet, sitting in the mineral sands along our coastlines — in Kerala, Tamil Nadu, Andhra Pradesh, Odisha — lies something most Indians have never heard of: 846,000 tonnes of thorium oxide. At current energy prices, that is worth more than all of Saudi Arabia’s oil reserves.
The question is not whether India has the fuel. We do. The question is whether we can unlock it.
India holds the world’s largest confirmed thorium reserves — approximately 846,000 tonnes — under both IAEA and USGS estimates.
This article is my attempt to explain, plainly, what thorium breeding is, why it matters more than almost anything else in India’s energy policy, and why I believe fusion — the same process that powers the sun — may be the most powerful tool we have to unlock it.
First, Why Can’t We Just ‘Burn’ Thorium?
This is the first question everyone asks, and it is a fair one. If we have so much thorium, why not simply put it in a reactor?
The answer is that thorium is ‘fertile’ but not ‘fissile’. Think of it this way: thorium is like a log of wood that will not light on its own. You need a spark. In nuclear terms, that spark is a neutron. When a neutron strikes a thorium-232 nucleus, it transforms through a two-step radioactive decay into uranium-233 — a remarkable fissile material that can sustain a chain reaction and produce energy.
The chain looks like this: thorium-232 absorbs a neutron, becomes thorium-233, which decays in 22 minutes into protactinium-233, which then decays over 27 days into uranium-233. That uranium-233 is your fuel.
Figure 1 — The Thorium-232 Breeding Chain: How a Neutron Spark Creates Fuel
Step 4 is the engineering challenge: ²³³Pa must decay (good path → ²³³U fuel) rather than capture another neutron (bad path → ²³⁴U, wasted). High neutron flux increases the risk of the bad path — this is the “Pa-233 penalty” all breeding methods must manage.
This is what nuclear scientists call ‘breeding’ — using one type of nuclear reaction to produce the fuel for another. Dr. Homi Bhabha, the father of India’s atomic programme, designed our entire nuclear strategy around this concept sixty years ago. He called it the Three-Stage Programme. Stage One: use natural uranium in heavy water reactors to produce plutonium. Stage Two: use that plutonium in fast breeder reactors to produce more plutonium and begin converting thorium into uranium-233. Stage Three: run thorium-uranium-233 fuel cycles that are essentially self-sustaining. We are currently somewhere between Stage One and Stage Two. Stage Three — the thorium stage — is still decades away under conventional approaches.
The challenge is not the physics. The physics is settled and beautiful. The challenge is producing enough neutrons, of the right energy, efficiently enough to make thorium breeding economically viable at scale.
Five Ways to Breed Uranium-233 from Thorium
Over the past year, my team at ASPL Fusion has conducted a detailed technical assessment of every known method for converting thorium to uranium-233. Let me summarise what we found in plain terms.
1. Heavy Water Reactors — and the ANEEL Breakthrough
India’s 22 pressurised heavy water reactors — the workhorses of our nuclear fleet — can be loaded with thorium fuel alongside uranium. The thermal neutrons breed some uranium-233, but not enough to be self-sustaining. The Advanced Heavy Water Reactor (AHWR) being developed by BARC targets near-unity breeding. This is our most mature near-term option.
But something important happened recently that changes this picture substantially. A Chicago-based company, founded by Shri Mehul Shah, called Clean Core Thorium Energy (CCTE) has developed a fuel called ANEEL — Advanced Nuclear Energy for Enriched Life — that fits India’s existing PHWR fuel bundle dimensions without any reactor modification. ANEEL blends thorium with a small amount of High-Assay Low-Enriched Uranium (HALEU). The results from testing at Idaho National Laboratory are remarkable: burnup of 45–60 GWd per tonne, compared to just 7 GWd/tonne for natural uranium — six to eight times more energy from the same fuel load. Waste drops by over 85 per cent. And as the thorium in the pellet absorbs neutrons, it steadily converts to uranium-233, beginning to build India’s strategic fissile inventory right now, in reactors that are already running.
Dr. Anil Kakodkar, former chairman of the Atomic Energy Commission and one of India’s most respected nuclear scientists, has called this a transformational opportunity. NTPC, India’s largest power company, has approved a minority equity investment in CCTE. Larsen & Toubro signed a manufacturing partnership in 2024. The US Department of Energy granted CCTE an export licence for India in August 2025 — only the second such authorisation in twenty years.
There is one important caveat: ANEEL needs HALEU, which India does not currently produce. That enriched uranium would need to come from the United States, introducing a supply chain dependency that must be managed carefully. India should develop ANEEL fuel while simultaneously building the domestic enrichment capability to eventually produce HALEU independently. The two goals are not contradictory — they are sequential.
2. Fast Breeder Reactors (Our Stage Two)
Fast breeder reactors use higher-energy neutrons — the ones that are not slowed down by a moderator. These faster neutrons are better at producing more neutrons per fission, which means you can breed more thorium than you consume. The Prototype Fast Breeder Reactor at Kalpakkam, developed by IGCAR, is India’s most important near-term step. It will breed uranium-233 in thorium blankets surrounding the core while generating 500 megawatts of electricity.
3. Molten Salt Reactors (The Elegant Solution)
In a molten salt reactor, both fuel and coolant are dissolved in a fluoride salt mixture. The genius of this design is that you can continuously extract the protactinium-233 intermediate before it can accidentally absorb another neutron and waste the breeding reaction. China’s TMSR-LF1 at Wuwei, Gansu became the world’s first MSR to reach criticality since Oak Ridge’s MSRE shut down in 1969, achieving first criticality in October 2023 on uranium fuel. In October 2024 it went further — completing the world’s first thorium-to-uranium conversion inside an operating molten salt reactor, with Pa-233 detection confirming successful U-233 breeding. India has done significant molten salt research at BARC. This technology could ultimately offer the most efficient thorium breeding of any approach, but it has not yet been demonstrated at commercial scale anywhere in the world.
4. Accelerator-Driven Systems(ADS)
In an accelerator-driven system, a powerful particle accelerator fires protons at a heavy metal target, producing a shower of neutrons. These neutrons then drive a subcritical thorium assembly that cannot sustain a chain reaction on its own and is therefore inherently safe. The limitation is economic: the accelerator consumes significant electricity and produces no power of its own.
4b. Electron Accelerators and Dense Plasma Focus Devices
Two additional niche methods deserve brief mention. Electron accelerator-driven systems use bremsstrahlung photons from a high-power electron beam to drive photofission in thorium — a lower-cost accelerator alternative for small-scale breeding, though even more energy-negative than proton ADS. Dense Plasma Focus (DPF) devices, already operated at BARC and several Indian universities, produce short pulsed neutron bursts at very low cost (₹1–5 Crore for a university-scale device). These are not suitable for commercial breeding — their neutron yield is three orders of magnitude too low — but they are ideal for validating thorium irradiation geometry, neutron activation measurements, and uranium-233 separation chemistry before a full fusion device is commissioned. At ASPL Fusion, it may be worth exploring a DPF-based Phase 1.5 programme as a low-cost proof-of-concept for AERB pre-licensing engagement.
5. Fusion Neutrons (The Path We Are Building)
And now we come to fusion — the approach I find most compelling, and the one ASPL Fusion is actively developing.
When deuterium and tritium fuse — the same reaction that powers the sun — they release a neutron with 14.1 million electron volts of energy. This is far higher than any neutron produced by fission. And those high-energy neutrons do something remarkable when they strike thorium-232: they can split the thorium nucleus itself (fast fission), and they can cause a single neutron to produce two neutrons via a reaction physicists call (n,2n). The net result is that each fusion neutron is worth significantly more for thorium breeding than any fission neutron.
In a fusion-driven system, you place the thorium blanket surrounding the fusion plasma. The fusion neutrons breed uranium-233, and simultaneously breed the tritium fuel needed to sustain the fusion reaction. The blanket also absorbs the heat of the breeding reactions to generate electricity. In principle, you produce fissile fuel, generate power, and fuel your own fusion device — simultaneously.
There is a subtlety worth understanding. The blanket must do two things with the same neutrons: breed uranium-233 from thorium, and breed tritium from lithium to refuel the plasma. These goals compete directly. The solution our PRABHA-P3 blanket uses is a beryllium neutron multiplier zone between the lithium and thorium layers. Beryllium converts one high-energy neutron into two lower-energy ones via the Be(n,2n) reaction, providing the neutron budget to achieve both goals simultaneously. Getting this balance right is one of the central design tasks in Phase 3.
Figure 2 — The PRABHA-P3 Blanket: One Fusion Neutron, Two Breeding Jobs
The beryllium multiplier (Zone 3) is the engineering key: it converts each high-energy neutron into two lower-energy ones, providing enough neutrons to simultaneously breed tritium (Zone 2) and uranium-233 (Zone 4). Without it, you must sacrifice one goal for the other.
A fusion neutron at 14.1 MeV is worth more for thorium breeding than any neutron produced by fission. The physics is simply more favourable.
Why Fusion Neutrons Are Uniquely Powerful
Let me be more specific, because the physics here is worth understanding.
The reaction that matters most is what happens when a 14.1 MeV fusion neutron strikes a thorium-232 nucleus. There are three things it can do, and all three are useful:
Breed uranium-233: The neutron is captured, and after two beta decays, you get U-233. This is the primary goal.
Cause (n,2n) multiplication: The neutron has enough energy to knock two neutrons out of the thorium nucleus. So one neutron in, two neutrons out. This effectively doubles the neutron population available for breeding.
Cause fast fission: Thorium-232 has a fission threshold of about 1.4 MeV. A 14.1 MeV neutron comfortably exceeds this, causing the thorium to fission and release more neutrons still.
No fission reactor produces neutrons energetic enough to trigger (n,2n) reactions in thorium at scale. Even fast breeder reactors, with neutrons at roughly 200,000 electron volts, fall short of the 14.1 million electron volt fusion threshold. This is not an engineering limitation. It is a fundamental difference in the physics of the two processes.
What ASPL Fusion Is Building
Figure 3 — GDT Mirror Geometry: Why It Is Naturally Suited to a Thorium Blanket
Left: end-on cross-section showing the concentric zone layout around the plasma. Right: side view showing how neutrons irradiate the full-length blanket uniformly — something a tokamak’s toroidal geometry makes geometrically complex. The GDT’s straight cylindrical form is a natural match for a surrounding breeding blanket.
At ASPL Fusion, being incubated at the Institute for Plasma Research in Gandhinagar, we are developing a magnetic mirror fusion device called PRABHA (Plasma Reactor for Advanced Breeding and High-energy Applications). Our approach uses a Gas Dynamic Trap (GDT) magnetic mirror geometry, which is inherently simpler and more compact than a tokamak.
Our programme has four phases. Phase 1: a proton accelerator for Boron Neutron Capture Therapy cancer treatment — generating early revenue while we establish our neutron source expertise. Phase 2: a full deuterium-deuterium GDT fusion device for medical isotope manufacturing and thorium irradiation experiments. Phase 3: deuterium-tritium operation with a subcritical thorium blanket — the fusion-fission hybrid — breeding uranium-233 at meaningful scale while generating net electricity. Phase 4: our long-term vision — a deuterium-helium-3 tandem mirror, tritium-free fusion power in its cleanest form.
The Regulatory Reality and Why We Must Move Now
I want to be honest about the challenges, because intellectual honesty is what builds credibility.
There is a materials challenge worth naming directly. The 14.1 MeV neutrons that make D-T fusion so powerful for thorium breeding are also destructive to the steel wall facing the plasma. At these energies, neutrons cause helium bubbles to form inside metal grains — helium embrittlement — and displace atoms at rates roughly ten times higher than in a fission reactor. The PRABHA-P3 first wall will need replacement every three to five full-power years. We design for this from the start: modular wall cassettes, remote handling, clear waste management. India’s IGCAR has developed a reduced-activation steel called INRAFM specifically for fusion applications, and we will work closely with them.
The regulatory pathway for a fusion-fission hybrid in India is long. The Atomic Energy Regulatory Board’s multi-stage consent process, from site evaluation to full power operation, takes eight to twelve years for a first-of-a-kind device. The SHANTI Act of 2025 opened private sector participation in nuclear activities for the first time — a landmark change. But the regulations for a privately-operated fusion-fission hybrid producing bred uranium-233 are genuinely novel territory that AERB has not charted before.
This means we need to begin the regulatory conversation now, during Phase 2 operation, not when Phase 3 construction is ready to start. Early pre-licensing engagement with AERB, formal collaboration with DAE on uranium-233 material accountancy protocols, and participation in the IAEA’s Advanced Reactor Information System — these are not bureaucratic formalities. They are the critical path items that will determine whether India’s first fusion-fission hybrid is operational in the 2030s or the 2040s.
Under the current legal framework, bred uranium-233 cannot be owned by a private company. It must be transferred to DAE. Our business model, therefore, is not to sell uranium-233 as a commodity but to operate the breeding facility as a service to the nation — analogous to how private companies operate dedicated satellites or communication infrastructure for government use.
The International Race India Cannot Afford to Lose
Let me situate this in global context, because the competitive landscape is moving faster than most people realise.
China achieved the world’s first molten salt reactor criticality in 2023, at a facility in the Gobi Desert. They have committed to a 100-megawatt demonstration MSR by 2030 and a commercial gigawatt-scale plant by 2040. China’s thorium reserves in Inner Mongolia are smaller than India’s, but their programme is more advanced.
Belgium is building MYRRHA — a 100-megawatt accelerator-driven system that will be the world’s most advanced ADS demonstrator when it begins operations in 2036. A billion and a half euros of European investment.
Canada is testing thorium-uranium mixed oxide fuel in CANDU reactors, the same reactor technology that India’s PHWRs are derived from.
And the United States? They have 1,750 kilograms of uranium-233 sitting at Oak Ridge National Laboratory, a legacy of their 1960s thorium programme, which they are now systematically destroying because they have no plan to use it — except, quietly, one company does have a plan. Clean Core Thorium Energy’s ANEEL fuel, tested at Idaho National Laboratory, is the most advanced commercial thorium fuel programme in the world. And its primary target market is India.
Here is what I find striking about this landscape: every country is pursuing thorium breeding through fission-based methods — MSRs, ADS, fast reactors. Nobody is pursuing fusion-driven thorium breeding at demonstration scale. The field is completely open. India, through our PRABHA programme, has the opportunity to be the first country in the world to demonstrate commercially-viable fusion-fission thorium breeding. That is not an incremental advance. That is a genuine world-first.
Every major nuclear programme is pursuing thorium through fission. Nobody is doing fusion-driven breeding at demonstration scale. That gap is India’s opportunity.
I want to be clear about how ANEEL and the PRABHA programme relate to each other, because I am sometimes asked whether they compete. They do not. They operate at entirely different layers of India’s thorium strategy. ANEEL breeds uranium-233 in Stage I reactors that exist today — it is the near-term solution. The fusion approach breeds uranium-233 at much higher flux and without any dependence on imported enriched uranium — it is the long-term, strategically independent solution. India needs both. A country with our thorium reserves and our energy ambitions cannot afford to be dogmatic about which technology to back. We should back all of them that are credible, and both ANEEL and fusion-driven breeding are credible.
The Economics: Is This Actually Viable?
Science without economic viability is interesting but not transformative. So let me address the business case directly.
Our Phase 3 PRABHA-P3 fusion-fission hybrid is designed to generate multiple revenue streams simultaneously. Net electricity output of 50 to 150 megawatts at a wholesale tariff of four rupees per kilowatt-hour, with an 80% capacity factor, produces power revenue of roughly ₹250–500 Crore per year. Medical isotope production adds another ₹150 Crore per year. And the uranium-233 breeding, valued at approximately ₹8,000 per gram and transferred to DAE under a breeding service agreement, could contribute up to ₹400 Crore per year.
Total annual revenue: approximately ₹800–1,000 Crore per year from a single Phase 3 unit, against a capital cost of ₹8,000–12,000 Crore.
Two costs deserve explicit acknowledgement: decommissioning and waste disposal. The activated structural materials — first-wall modules, thorium blanket pebbles bearing trace U-232, tritium-contaminated components — are intermediate-level radioactive waste. Our 30-year decommissioning estimate is ₹700–1,400 Crore, or roughly ₹25–50 Crore per year annualised. It is real, it is budgeted, and it does not change the commercial conclusion. But it should be stated plainly.
There is an honest caveat: the first-of-a-kind premium. The first fusion-fission hybrid built anywhere in the world will cost two to three times what subsequent units cost. This is why our Phase 1 and Phase 2 revenues — from BNCT cancer treatment and medical isotope sales — are not merely nice to have. They are how we fund the technology development that makes Phase 3 possible without requiring a single additional equity raise after our Series A.
A Personal Note: Why This Matters
I have been asked many times why I left the comfortable world of technology policy to start a nuclear fusion company in my late sixties. The honest answer is that I looked at what we were building at TIFAC, at what India’s Technology Vision 2035 laid out as possible, and I realised that the most important gap was not in solar panels or electric vehicles or artificial intelligence — important as all of those are. The most important gap was in base-load energy that India can produce from its own resources, indefinitely, without importing fuel or emitting carbon.
Thorium is that resource. Fusion is the tool to unlock it. India is the country with both the thorium reserves and, at IPR and BARC and IGCAR, the scientific talent to make it happen. What has been missing is the private sector urgency — the willingness to take the risk, move faster than government timelines, and build the demonstration that converts potential into reality.
That is what we are attempting to do at PRABHA. We are not naive about the difficulty. Building a fusion device is genuinely hard. Building a fusion-fission hybrid with regulatory approvals in India is harder still. But the physics is real, the reserves are there, the talent exists, and the strategic imperative is clear.
India’s thorium future is not a distant dream. It is an engineering problem with a solution. We are working on it.
ThoriumNuclear EnergyFusion PowerIndia Energy PolicyUranium-233PRABHA ProjectGDTThree-Stage Nuclear ProgrammeBNCT
