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
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 strategic shift hidden in three words
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 DOE strategy in one line: the state builds shared capability so that companies can build reactors.
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.
Public money belongs where private money cannot go
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.
Learn the mechanisms, not just the intent
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.
Four instruments, four bargains — the same rupee deployed against four different kinds of risk.
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.
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.
