Nuclear Fission

Nuclear fission involves splitting large and unstable nuclei into smaller ones. This process releases a lot of energy. There are two main ways that nuclear fission can take place:

  • Spontaneously, which takes place naturally, without the help of a neutron
  • By absorbing a neutron, which makes the nucleus more unstable

In a nuclear reactor, we use neutrons to start the process, because spontaneous fission is extremely rare. Let’s break down how the process works:

1. A slowed neutron is fired at a large, unstable nucleus (usually uranium-235).

2. The large nucleus absorbs the neutron, becoming uranium-236, which is unstable.

3. As the nucleus becomes unstable, it splits into smaller nuclei, known as daughter nuclei.

4. In the process, the nucleus fires out two or three more neutrons and releases energy in the form of gamma radiation.

5. The released neutrons collide with more uranium nuclei, leading to more fission reactions. This is known as a chain reaction.

If this process is not controlled, the system can malfunction, which could potentially lead to the release of vast amounts of energy. This is what happens in a nuclear bomb.

In nuclear reactors, the rate of fission has to be controlled, which can be achieved by using control rods. They are inserted and removed from the reactor to increase or decrease the rate of reaction and absorb neutrons.

The energy released in the process is used to heat water, which turns into steam. The steam rises and drives turbines, which are connected to an electricity generator.

Advantages and Disadvantages of Nuclear Fission


  • Uranium and plutonium fuels are relatively cheap, resulting in low running costs.
  • Nuclear fission produces a large and steady supply of energy.
  • Nuclear fission does not produce gas emissions.


  • Nuclear power plants are quite expensive to build and dismantle.
  • They produce radioactive waste, which is expensive to dispose of. This waste must be buried underground in metal containers and then stored in concrete-lined vaults.
  • Nuclear fission emits ionising radiation, which is harmful to humans.
  • Although rare, there’s a risk of catastrophe if the process goes wrong. This potential risk makes many people hesitant about using nuclear energy.

Comparing Nuclear Fission and Nuclear Fusion

Try not to confuse nuclear fission with nuclear fusion.

Nuclear fission is when unstable nuclei split into smaller nuclei. This process releases a lot of energy but not as much as nuclear fusion. On Earth, we use nuclear fission to generate electricity as it occurs at much lower temperatures and pressures compared to nuclear fusion.

In contrast, nuclear fusion involves the joining of lighter nuclei to form heavier ones, releasing a significant amount of energy. Nuclear fusion takes place in stars at very high temperatures and pressures.