Understanding nuclear reactions and India’s early steps onto the nuclear stage

Nuclear reactions are processes that change the identity of an atomic nucleus itself. Although atoms are tiny, the nucleus is even smaller — it occupies less than one ten-trillionth of an atom’s volume, yet holds nearly all of its mass. Chemical reactions only rearrange electrons on the outside of atoms. Nuclear reactions, by contrast, change the number of protons or neutrons inside the nucleus and so transform one element into another.

There are two main types of nuclear reaction. In fission, a heavy nucleus such as uranium-235 or plutonium-239 splits into two smaller nuclei, releasing a large amount of energy and a few free neutrons. In fusion, two light nuclei such as isotopes of hydrogen combine to form a heavier nucleus, also releasing enormous energy. Both processes release energy because the products are more tightly bound than the original nuclei.

Fission is the basis of every nuclear power plant in commercial operation today. A controlled chain reaction inside the reactor core generates heat, which is used to make steam and drive turbines. Fusion, the process that powers the Sun, is much harder to sustain on Earth and remains in the research and demonstration stage at facilities such as ITER in France.

Nuclear power plants are now operating in around 30 countries. Their combined output is gradually rising toward the double-digit mark as a share of the world’s total electricity supply. Many governments are returning to nuclear power as part of their plans to cut carbon emissions and meet rising electricity demand without expanding fossil fuel use.

India’s nuclear journey began in the 1950s under the vision of Dr Homi Bhabha. The Atomic Energy Commission (AEC) was set up in 1948 and the Department of Atomic Energy (DAE) followed in 1954, directly under the Prime Minister. Apsara, India’s first research reactor and Asia’s first, went critical at Trombay in August 1956. The Tarapur Atomic Power Station, India’s first commercial nuclear power plant, started operating in 1969.

To deal with India’s limited reserves of natural uranium and large reserves of thorium, the country adopted a three-stage nuclear programme. The first stage uses Pressurised Heavy Water Reactors (PHWRs) fuelled by natural uranium. The second stage uses Fast Breeder Reactors that produce more fissile material than they consume, building up a stockpile of plutonium. The third stage aims to use thorium-based reactors to tap India’s vast thorium resources for long-term energy security.

Public sector entities such as the Nuclear Power Corporation of India Limited (NPCIL), Bhabha Atomic Research Centre (BARC) and Indira Gandhi Centre for Atomic Research (IGCAR) anchor different parts of this programme. Today, India operates more than 20 commercial nuclear reactors and is expanding capacity to meet its climate and energy goals, while continuing research on thorium-based and fusion technologies.