The Silent Contamination : What Nuclear Waste Does to Our Water

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.

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.

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.

Transmutation: Changing the Problem at Its Root

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.

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.

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.