How India's nuclear energy journey has led to a new route for production of green hydrogen

Last month, scientists at the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam (Tamil Nadu), demonstrated something remarkable. Besides using the Fast Breeder Test Reactor (FBTR) to advance India's thorium programme, they successfully produced green hydrogen using the reactor's waste heat. The technology for this feat had been developed by those at the Bhabha Atomic Research Centre (BARC) in Mumbai.

The achievement shows that a nuclear reactor can do more than generate electricity. It can also become a source of clean, green hydrogen.

To understand why this development matters, we must go back nearly seventy years, to the three-stage nuclear power programme conceived by physicist Homi Jehangir Bhabha. The strategy arose from India's unique geological endowment.

India possesses only modest reserves of uranium suitable for nuclear fuel. Much of the ore is of relatively low grade, making extraction and processing expensive. Thorium presents a striking contrast. The beach sands of Kerala, Tamil Nadu, Odisha and Andhra Pradesh contain one of the world's largest reserves of this element.

There is, however, one complication.

Thorium-232 (Th-232), the naturally occurring isotope, is not a fissile material. It cannot sustain a nuclear chain reaction on its own. Freshly cut wood cannot be used efficiently as firewood until it has dried. Likewise, thorium has to undergo a transformation inside a nuclear reactor before it becomes useful as fuel. When it absorbs neutrons, it is gradually converted into Uranium-233 (U-233), an excellent reactor fuel. This process is known as breeding.

This simple idea forms the foundation of India's three-stage nuclear programme.

The programme may be compared to preparing a traditional meal in stages. First, the vegetables are cleaned and cooked. Then spices and coconut are added and allowed to simmer. Finally comes the tempering that completes the dish. Each stage prepares the way for the next.

In a three-stage nuclear power programme, the first stage employs Pressurised Heavy Water Reactors (PHWRs) fuelled by natural uranium. These reactors generate electricity while producing plutonium as a by-product. In the second stage, this plutonium becomes the fuel for Fast Breeder Reactors, which are designed to produce more fissile material than they consume. Around the reactor core is a blanket of thorium. As fast neutrons escape from the core, they are absorbed by the thorium blanket, converting thorium into Uranium-233. In the third stage, this Uranium-233 becomes the fuel for advanced reactors while fresh thorium is added to the blanket. The result is a self-sustaining fuel cycle capable of producing both energy and fresh nuclear fuel.

The backbone of this long-term strategy is the IGCAR at Kalpakkam.

Since 1985, the Fast Breeder Test Reactor (FBTR) here has enabled Indian scientists to master sodium-cooled fast reactor technology. Unlike conventional reactors, Fast Breeder Reactors use high-energy, or "fast", neutrons. Liquid sodium serves as the coolant because it transfers heat efficiently without slowing these neutrons. Over four decades, the FBTR has provided valuable experience in reactor operation, fuel behaviour and specialised materials. Like learning to ride a bicycle before venturing onto a busy road, this small experimental reactor laid the foundation for India's 500-megawatt Prototype Fast Breeder Reactor (PFBR), which achieved first criticality(the point at which a continuous nuclear reaction spontaneously establishes itself inside the reactor without any external trigger) in 2026.

The same research infrastructure has now yielded another outcome. Scientists at the IGCAR, using technology developed by those at BARC, have shown that the heat normally released as waste from the Fast Breeder Test Reactor can be used to produce green hydrogen. In other words, a nuclear reactor need no longer be viewed merely as a source of electricity. It can also supply the energy needed to manufacture a clean fuel. Killing two birds with one stone.

That is the broader significance of the achievement at Kalpakkam. It marks the beginning of a new role for nuclear energy, one that extends well beyond electricity generation.

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Water is one of the most stable compounds found in nature. Every molecule consists of two hydrogen atoms tightly bound to one oxygen atom. Break this bond and hydrogen is released, a clean fuel that produces only water when it burns or when it is used in a fuel cell.

The idea sounds simple. The challenge is anything but.

Breaking apart a water molecule is rather like scratching the surface of a diamond. Breaking an ordinary stone is easy; leaving even a small mark on a diamond demands far greater effort. Likewise, separating hydrogen from water requires a considerable amount of energy.

The best-known method is electrolysis. An electric current is passed through water, splitting it into hydrogen and oxygen. The drawback is that electrolysis consumes large amounts of electricity. If the electricity comes from renewable sources such as solar or wind power, the product is known as green hydrogen. If the electricity is generated using fossil fuels such as coal or natural gas, the hydrogen carries a significant carbon footprint, despite being chemically identical. This hydrogen is called grey hydrogen.

As demand for green hydrogen grows, so does the need for abundant, low-cost clean electricity. Renewable energy can supply much of this demand, but solar panels produce electricity only during the day, and wind turbines generate power only when the wind blows. Researchers have therefore been searching for other ways to split water without depending entirely on electricity.

One possibility is to use heat.

In principle, water begins to dissociate into hydrogen and oxygen if it is heated to around 2,000°C. But generating and sustaining such extreme temperatures requires enormous amounts of energy, making the process impractical for industrial use.

Scientists therefore looked for a chemical shortcut. Instead of forcing water to split in a single step, they divided the reaction into a series of smaller chemical reactions. Each reaction takes place at a much lower temperature, yet together they achieve the same result; the water molecule is broken into hydrogen and oxygen. Such processes are known as thermochemical cycles.

Scientists at BARC have developed one such process known as the Copper–Chlorine (Cu–Cl) thermochemical cycle.

Imagine a kitchen where the same set of cooking vessels is used repeatedly. They help prepare the meal but are neither consumed nor discarded. The Copper–Chlorine cycle works in much the same way. Copper and chlorine compounds pass through a sequence of chemical reactions with water and steam. Hydrogen is released during one stage and oxygen during another. At the end of the cycle, the copper and chlorine compounds are regenerated and reused. Only water is consumed; the chemical intermediates continue to circulate through the process.

The greatest advantage of this cycle is that it operates at about 500–550°C, a fraction of the temperature required for the direct thermal decomposition of water. Such temperatures are readily available from certain nuclear reactors.

This is where Kalpakkam re-enters the story.

A nuclear power plant converts only about one-third of the heat produced inside the reactor into electricity. The remaining two-thirds is normally discharged through cooling systems. Like the radiator of a running car carrying away excess engine heat, this thermal energy has traditionally been regarded as unavoidable waste.

For many years, engineers have explored ways to put this heat to productive use.

At the IGCAR, scientists integrated the Copper–Chlorine thermochemical cycle with the Fast Breeder Test Reactor (FBTR). Instead of allowing the reactor's process heat to dissipate unused, they employed it to drive the chemical reactions needed to split water.

The hydrogen production facility commissioned at Kalpakkam last month has successfully demonstrated this concept. By combining reactor heat with the Copper–Chlorine cycle, it has shown that green hydrogen can be produced using energy that would otherwise have gone unused.

Kalpakkam has already shown that Fast Breeder Reactors can generate electricity while converting thorium into nuclear fuel. It has now demonstrated a third capability: using the reactor's waste heat to produce green hydrogen. A single reactor, therefore, can contribute simultaneously to electricity generation, fuel breeding and clean hydrogen production.

Electricity cannot be seen, yet it travels through wires to light our homes and power our machines. Hydrogen plays a similar role. It is not an energy source like coal, natural gas or sunlight. Rather, it is an energy carrier, a medium that stores energy produced elsewhere and delivers it where it is needed. Much like money transferred from one bank account to another, hydrogen enables energy to be stored, transported and used at a different place or time.

This ability is becoming increasingly important as countries rely more on renewable energy.

The sun does not shine at night and the wind does not blow all the time. Consequently, solar panels and wind turbines do not generate electricity continuously. There are periods when electricity production exceeds demand and others when demand exceeds supply. One way to bridge this gap is to use surplus electricity to produce hydrogen. The hydrogen can then be stored and used later to generate electricity or as a fuel for industry and transport.

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Not all hydrogen, however, is produced in the same way.

Today, most of the hydrogen used worldwide comes from natural gas or coal, thus grey hydrogen, because its production releases large quantities of carbon dioxide into the atmosphere. Green hydrogen, in contrast, produced by splitting water using renewable electricity or other low-carbon energy sources, such as nuclear heat, has a much smaller carbon footprint, since the process does not depend on fossil fuels.

This distinction matters because hydrogen is already indispensable to modern industry. Ammonia, the raw material for urea fertiliser, cannot be produced without hydrogen. Petroleum refineries use it to remove sulphur from fuels, while the chemical industry depends on it to manufacture products such as methanol. Much of the hydrogen used in these industries today is derived from fossil fuels. Replacing it with green hydrogen could significantly reduce their greenhouse gas emissions.

Hydrogen is also finding new applications in transport. Hydrogen fuel-cell vehicles carry compressed hydrogen, which reacts with oxygen from the air inside a fuel cell to generate electricity. The only direct emission is water. Unlike conventional internal combustion engines, they do not produce exhaust gases containing carbon dioxide, soot or nitrogen oxides.

Battery-electric vehicles have made rapid progress in recent years and are well suited to passenger cars and urban transport. Heavy trucks, long-distance buses, ships and some industrial vehicles, however, require much larger amounts of stored energy. For such applications, hydrogen is increasingly being explored as an alternative because it can be refuelled quickly and offers a longer operating range.

India has recognised this potential through the National Green Hydrogen Mission, which aims to expand domestic production of green hydrogen and reduce dependence on imported fossil fuels.

In this context, the achievement at Kalpakkam introduces an additional route for producing green hydrogen. At present, the technology has been demonstrated only at the pilot scale. If the Copper–Chlorine thermochemical cycle can be successfully scaled up, it could complement electrolysis as another method for producing hydrogen.

The approach has one important advantage. Nuclear reactors operate continuously, producing heat day and night irrespective of weather conditions. That steady supply of process heat matches the requirements of the Copper–Chlorine thermochemical cycle, allowing hydrogen to be produced around the clock.

The Kalpakkam demonstration is therefore more than a laboratory experiment. It shows that nuclear process heat, which would otherwise go unused, can contribute to the production of a clean industrial fuel. If developed further, the technology could help decarbonise industries such as steel, fertiliser production and petroleum refining, while adding another pathway to India's transition towards a low-carbon energy system.

For more than seven decades, nuclear power stations have been viewed primarily as electricity-generating facilities. Yet electricity accounts for only part of the energy produced inside a reactor.

In a typical nuclear power plant, only about one-third of the heat released during nuclear fission is converted into electricity. The remaining two-thirds is rejected through cooling systems. It is rather like using only the fruit of a palmyra tree while overlooking the many other useful products that can be obtained from it. Engineers have long recognised that this unused heat represents an opportunity rather than a waste.

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Several countries have already begun to make use of it. In regions with severe winters, reactor heat is piped to nearby towns and cities for district heating, providing warmth to homes, offices and industries. Some coastal nuclear power stations also use waste heat for desalination, converting seawater into fresh drinking water. These applications improve the overall utilisation of the energy produced by the reactor.

Attention is now shifting to another possibility, using nuclear heat to manufacture green hydrogen.

Around the world, researchers are exploring different ways of coupling nuclear reactors with hydrogen production. In the United States, demonstration projects have used electricity generated by nuclear power plants to produce hydrogen through electrolysis. Japan is investigating the use of high-temperature gas-cooled reactors for thermochemical hydrogen production, while China, Canada and several European countries are pursuing similar technologies as part of their efforts to reduce industrial carbon emissions.

India has now joined this global effort through a different approach. Instead of relying entirely on electricity, scientists at the Bhabha Atomic Research Centre (BARC) have demonstrated the Copper–Chlorine thermochemical cycle, which uses process heat from the Fast Breeder Test Reactor at Kalpakkam to split water and produce hydrogen. The demonstration establishes that waste heat from a nuclear reactor can be harnessed to manufacture a clean industrial fuel.

The significance of this achievement extends beyond hydrogen production. Homi Jehangir Bhabha's three-stage nuclear programme was conceived to make use of India's abundant thorium resources and achieve long-term energy security. The demonstration at Kalpakkam adds a new dimension to that vision. Until now, Fast Breeder Reactors were seen primarily as systems that generated electricity while converting thorium into reactor fuel. They have now demonstrated a third capability: supplying process heat for green hydrogen production.

The technology is still at the demonstration stage, and further engineering development will be needed before it can be deployed commercially. If successfully scaled up, however, future nuclear power stations could evolve into integrated energy centres, producing electricity, breeding nuclear fuel and supplying clean hydrogen for industry.

That is the broader message from Kalpakkam. A nuclear reactor need not be viewed simply as a machine that generates electricity. It can also become a source of clean industrial heat and low-carbon fuels, extending the role of nuclear energy in India's transition towards a more sustainable energy future.