Nuclear Power Technologies

This note covers nuclear technology types and mechanisms: fission, fusion and radioisotope decay. India's commercial reactor fleet, the minerals behind it, and why plants are sited where they are, is covered in Energy Resources of India.

Three genuinely different ways to get energy from the nucleus

Nuclear technology covers three distinct physical processes, and confusing them is the standard trap on this topic.

Nuclear fission is what every commercial nuclear power plant uses: splitting a heavy atomic nucleus (uranium or plutonium) into lighter fragments, releasing energy, in a controlled, self-sustaining chain reaction.

Nuclear fusion is the opposite process: fusing light nuclei, typically isotopes of hydrogen, into a heavier one, which is what powers the Sun and every other star, and releases even more energy per unit of fuel than fission does. No commercial fusion power plant exists anywhere in the world yet; it remains at the experimental stage.

Radioactive decay is neither of these. It is the natural, spontaneous breakdown of an unstable atomic nucleus over time, releasing energy steadily as heat, with no chain reaction, no controlled reaction of any kind, and nothing that could be described as "splitting" in the fission sense.

RTGs: catching decay heat, not splitting atoms

A Radioisotope Thermoelectric Generator (RTG) generates electricity from the heat given off by a radioactive isotope's natural decay, most commonly plutonium-238, converted directly into electrical current through a thermoelectric effect, with no moving parts and no chain reaction whatsoever. This is precisely the point a past question tested: describing an RTG as generating electricity "through controlled nuclear fission reactions" is false, since an RTG's fuel is never used in a reactor and cannot sustain a chain reaction at all; it simply decays at its own natural rate regardless of anything the RTG does.

RTGs are the standard power source for deep-space missions travelling too far from the Sun for solar panels to be practical. Voyager 1 and Voyager 2, launched in 1977, each carry RTGs that have continued supplying power for close to fifty years, since the plutonium-238 fuel's radioactive decay, and the heat it produces, continues steadily for a very long time (its output only halves roughly every 87.7 years, the isotope's half-life).

ITER: chasing commercial fusion, and why India joined

ITER (International Thermonuclear Experimental Reactor) is a large international experimental fusion reactor under construction, designed to prove that controlled nuclear fusion can produce net positive energy at a meaningful scale, a milestone no fusion device has yet achieved.

India is one of ITER's members, alongside the European Union, the United States, China, Russia, Japan and South Korea, and contributes significant hardware to the project rather than only funding, including the massive cryostat (the vacuum vessel housing the reactor's superconducting magnets) and cryogenic distribution systems. If ITER succeeds in demonstrating sustained, net-positive fusion, the practical significance for India, given its stated participation, is direct access to frontier fusion technology and expertise as a full research partner rather than as an outside observer, positioning India among the states with genuine advanced capability in the technology if and when it eventually becomes commercially viable.

Quick revision points

• Fission (splitting heavy nuclei, chain reaction, what all commercial plants use), fusion (combining light nuclei, powers the Sun, no commercial plant exists yet), and radioactive decay (spontaneous, no chain reaction, no reactor) are three genuinely different processes.
• RTG: generates electricity from decay heat (commonly plutonium-238) via a thermoelectric effect, NOT via fission, and involves no chain reaction. This is the specific false claim a past question tested. Used to power deep-space probes like Voyager 1 and 2 (launched 1977, RTGs still functioning after nearly 50 years, since output halves only every 87.7 years).
• ITER: international experimental fusion reactor, aiming to prove net-positive fusion at scale. India is a full member, contributing hardware including the cryostat, giving it direct access to frontier fusion research as a partner rather than merely a funder.
• India's actual commercial reactor fleet, fuel minerals and plant siting are covered separately in Energy Resources of India.