Nuclear energy is released when you interfere with the nucleus that sits at the centre of an atom.
There are two ways to release nuclear energy: nuclear fission and nuclear fusion.
What's the difference between fission and fusion?
During nuclear fission, a heavy nucleus either splits spontaneously or splits because it collides with another particle. Fission is another word for splitting.
During nuclear fusion, a light nucleus is fused with another light nucleaus to form a heavy nucleus.
Here's a quick Lego example where two nuclei are fused together to form a bigger nucleus, and some energy is released.
Are both fission and fusion used to generate electricity?
No. Only nuclear fission can be used to generate electricity in nuclear reactors.
Uranium or plutonium isotopes are often used in fission because these large nuclei are easy to split. (Isotopes are just atoms with a few extra neutrons shoved in.) Neutrons are fired at the large isotopes to help them split up.
Let's look at another example. Ironman fires a tiny yellow neutron at a large nucleus. This causes the nucleus to split into two smaller nuclei, a couple of neutrons and some energy is released.
If you have lots of uranium or plutonium isotopes, then these two or three released neutrons may also hit other uranium or plutonium nuclei.
Then, these nuclei will split and release more neutrons and energy. This, in turn, can cause more nuclei to split. And so on. This is called a chain reaction.
The chain reaction in a nuclear reactor is controlled to stop it getting out of control. And the nuclear energy released is captured and used to create electricity.
What about nuclear fusion?
The Sun and other stars use a sequence of nuclear fusion reactions to release energy. In simple terms, hydrogen nuclei are fused together to form helium, which causes an energy release.
However, in the Sun massive gravitational forces create the right conditions for fusion - and these are incredibly difficult to replicate on Earth. If we could recreate fusion, then we would have an energy source that produces very short-lived nuclear waste.
The waste produced in nuclear fission, however, takes much longer to decay. The Plutonium-239 isotope, for example, takes 24,000 years for its radioactivity to drop by half.
Fusion has a chequered past in the scientific community, but progress is being made in the nuclear fusion field.
If a stable nuclear fusion power plant was created on Earth, it could solve the planet's energy crisis.
Extra reading and watching
Here's a great explanation covering nuclear fusion and the challenges it presents from the World Nuclear Association. And New Scientist covers the topic of nuclear energy quite extensively.
This week, the Chinese reportedly got one step closer to a steady state nuclear fusion operation. Here's a nice retro video from the BBC explaining the differences between nuclear fission and fusion:
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