Fission vs. Fusion – What’s the Difference? Fission vs. Fusion – What’s the Difference?

Fission vs. Fusion – What’s the Difference?

While different, the two processes have an important role in the past, present and future of energy creation

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Look up during the day to see one of the most powerful examples of a nuclear reactor: the sun. Inside the sun, fusion reactions take place at very high temperatures and enormous gravitational pressures.

The foundation of nuclear energy is harnessing the power of atoms by splitting them apart, a process called fission, or combining them, called fusion. Both fission and fusion alter atoms to create energy, so what is the difference between the two?

A nuclear reactor needs fuel that will fission (split)

Fission, a term coined by scientists Lise Meitner and Otto Frisch, is named after the term “binary fission” in biology to describe cell division. Just as cells divide, in fission an atom splits into smaller particles. This takes place when a large, somewhat unstable isotope (atoms with the same number of protons but different number of neutrons) is bombarded by high-speed particles, usually neutrons.

This graphic demonstrates how a nuclear reactor uses uranium 235 because its atoms will easily split, emitting heat and causing a chain reaction.
Nuclear reactors use uranium 235 (U235) because its atoms will easily split, emitting heat and causing a chain reaction.

These neutrons are accelerated and then slammed into the unstable isotope, causing it to fission, or break into smaller particles. During the process, a neutron is accelerated and strikes the target nucleus, which in most nuclear power reactors today is uranium-235. This splits the target nucleus and breaks it down into two smaller isotopes (the fission products), three high-speed neutrons and a large amount of energy.

The resulting energy is then used to heat water in nuclear reactors and ultimately produces electricity. The high-speed neutrons that are ejected become projectiles that initiate other fission reactions, or chain reactions.

Fusion reactions power the Sun and other stars

Conversely, fusion takes place when two low-mass isotopes, typically isotopes of hydrogen, unite under conditions of extreme pressure and temperature. Atoms of tritium and deuterium (isotopes of hydrogen, hydrogen-3 and hydrogen-2, respectively) unite under extreme pressure and temperature to produce a neutron and a helium isotope. Along with this, an enormous amount of energy is released, which is several times the amount produced from fission.

This graphic demonstrates how uranium is used as nuclear fuel by turning water into steam.
Uranium to Electricity: How nuclear power plants work

While fission is used in nuclear power reactors since it can be controlled, fusion is not yet utilized to produce power. Some scientists believe there are opportunities to do so. Fusion offers an appealing opportunity, since fusion creates less radioactive material than fission and has a nearly unlimited fuel supply.

These benefits are countered by the difficulty in harnessing fusion. Fusion reactions are not easily controlled, and it is expensive to create the needed conditions for a fusion reaction.

However, research continues into ways to better harness the power of fusion, but research is in experimental stages as scientists continue to work on controlling nuclear fusion to make a fusion reactor to produce electricity.

Both fission and fusion are nuclear reactions that produce energy, but the processes are very different. Fission is the splitting of a heavy, unstable nucleus into two lighter nuclei, and fusion is the process where two light nuclei combine, releasing vast amounts of energy. While different, the two processes have an important role in the past, present and future of energy creation.

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