WE have all heard the idiom — killing two birds with one stone. Scientists at the Bhabha Atomic Research Centre (BARC), Mumbai, and the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam, appear to have gone one better. Using the Fast Breeder Test Reactor (FBTR), they have demonstrated that a single reactor can simultaneously perform three functions: generate electricity, convert non-fissile thorium into nuclear fuel and now produce green hydrogen using its waste heat.

Several industries depend on hydrogen as a raw material. It is indispensable for manufacturing ammonia, the starting point for urea fertilisers. It is also used to produce methanol, an important feedstock for plastics, paints and other industrial chemicals and in petroleum refineries to remove sulphur from fuels through hydrodesulphurisation.

Hydrogen is also expected to play an important role in future transport systems. In fuel cells, which power e-vehicles, hydrogen combines with oxygen from the air to generate electricity, producing only water vapour as the exhaust. Fuel-cell vehicles can be refuelled within minutes, much like petrol or diesel vehicles, making them favourable for heavy trucks, ships and potentially aircraft, where battery-powered systems face limitations due to their weight and long charging times.

Hydrogen is not found in nature in a free form. It needs to be taken from water or hydrocarbons, where the hydrogen atoms are securely attached. Breaking these strong chemical bonds requires a lot of energy.

Today, most of the world's hydrogen is produced either by steam methane reforming, which extracts hydrogen from natural gas, or by electrolysis. When the electricity for electrolysis comes from coal — or gas-fired power stations, the process also results in significant carbon emissions.

Hydrogen produced through such fossil-fuel-dependent routes is known as grey hydrogen. In effect, the pollution is shifted from the point of use to the point of production, with little overall reduction in greenhouse gas emissions.

This is why countries are investing in green hydrogen, hydrogen produced with little or no carbon emissions. Scientists are studying several approaches — from solar- and wind-powered electrolysis to biological methods that use microorganisms. India has chosen a novel route.

India has one of the largest thorium reserves in the world, but only limited uranium reserves, which is the fuel used in most nuclear reactors today. Much of its uranium ore is of relatively low quality, making extraction and processing costly. However, thorium cannot be used directly as nuclear fuel, just as freshly cut green wood cannot be used right away as firewood. It must first go through a transformation.

This is where fast breeder reactors (FBRs) come in. Around the reactor core, engineers place a blanket of thorium. As high-energy, or 'fast', neutrons escape from the core, they are absorbed by the thorium blanket.

Through a series of nuclear transformations, the thorium is gradually converted into uranium-233 (U-233), an excellent reactor fuel. Because these reactors produce fresh nuclear fuel while generating electricity, they are called breeder reactors.

Developing this technology was far from straightforward. For several decades, India's nuclear programme operated under technology denial regimes imposed by western countries. Indian scientists therefore had to develop fast breeder reactor technology largely on their own.

To gain the necessary experience in designing, constructing and operating sodium-cooled fast reactors, IGCAR commissioned the FBTR in 1985. Four decades of operating experience built the scientific and engineering foundation for the 500-megawatt prototype fast breeder reactor (PFBR), which achieved first criticality in 2026.

A nuclear reactor produces heat. The heat from nuclear fission turns water into steam. This steam drives a turbine connected to an electrical generator. However, only about one-third of this thermal energy gets converted into electricity. The remaining two-thirds is released as waste heat through cooling systems.

For decades, engineers have sought ways to put this heat to productive use. One established application is district heating. In countries with severe winters, including Russia, China and several European nations, waste heat from nuclear power stations is piped to nearby towns and cities to heat homes, offices and industrial buildings, reducing the consumption of coal and natural gas.

Another application is desalination. Coastal nuclear power plants use reactor heat to convert seawater into fresh drinking water. For example, at Kalpakkam, a desalination plant coupled to the Madras Atomic Power Station (MAPS) uses a hybrid multi-stage flash (MSF) and reverse osmosis (RO) system to produce drinking water from seawater.

The next frontier is hydrogen production. Researchers around the world are exploring two broad approaches. One seeks to improve the efficiency of conventional electrolysis by using reactor heat to generate steam before electricity splits the water into hydrogen and oxygen, thereby reducing electricity consumption. The other relies on thermochemical cycles, in which heat rather than electricity drives a sequence of chemical reactions that split water.

Here, reactor temperature becomes the deciding factor. Conventional pressurised water and pressurised heavy water reactors, including those at MAPS, operate with coolant temperatures of about 300-330°C, whereas most thermochemical cycles require much higher temperatures.

China, for example, is investigating the sulfur-iodine (S-I) thermochemical cycle using its high-temperature reactor pebble-bed module (HTR-PM) at Shidao Bay, where helium coolant leaves the reactor at around 750°C.

India has taken a different approach. The sodium coolant in the FBTR leaves the reactor at about 480-520°C. Scientists at BARC developed the copper-chlorine (Cu-Cl) thermochemical cycle to operate efficiently within this temperature range.

Working with engineers at IGCAR, they integrated the process into the reactor and demonstrated that the reactor's waste heat can be used to produce green hydrogen. In doing so, the FBTR has demonstrated that a single reactor can generate electricity, breed nuclear fuel and now produce green hydrogen, a combination that could broaden the role of nuclear energy beyond power generation.

The hydrogen plant attached to the FBTR is a technology demonstrator rather than a commercial facility. The next challenge is to scale up the process and develop commercial thermochemical hydrogen plants that can utilise the waste heat from future fast breeder reactors.