Nuclear Fission

Overview

Nuclear fission is a process in which a large, unstable nucleus splits up or fragments into two smaller, less massive nuclei.
The resulting fragments have combined mass less than the original nucleus. This “missing” mass transforms into energy according to Einstein’s equation, E=mc².

In nuclear reactors, the fission process is typically initiated using either uranium-235 or plutonium-239.
An unstable uranium-235 or plutonium-239 nucleus can absorb a slow-moving neutron, turning it into uranium-236 or plutonium-240 respectively.
This makes the nucleus extremely unstable, causing it to undergo fission.
The fission of a single nucleus releases two or three neutrons along with a large amount of energy. The released neutrons can then trigger further fissions, leading to a chain reaction.

In a controlled chain reaction, used in nuclear power plants, the rate of reaction is carefully regulated to prevent a dangerous build-up of energy.
In an uncontrolled chain reaction, there is no attempt to regulate the reaction rate. This is what occurs in atomic bombs.

The energy released during nuclear fission is mainly in the form of kinetic energy of the fragments and gamma radiation.
This energy is then transformed into heat, which can be used to produce steam to power turbines and generate electricity.
This energy release per gram of fuel is more than a million times greater than that from chemical reactions, such as those in fossil fuels.

The fission of uranium-235 and plutonium-239 produces a large number of different fission products, many of which are highly radioactive.
The generation of radioactive waste, including these fission products, is a major challenge associated with the use of nuclear fission for energy production.