Nuclear Fusion: The Science Behind Turning Water into Electricity
11 minute read
Updated on Wed Mar 03 2021
What is nuclear fusion?
Why fusion would be a great source of energy
If splitting atoms releases energy, how can joining atoms also release energy?
Splitting atoms (fission) uses heavy elements (elements that have lots of protons and neutrons) while joining atoms (fusion) uses very light elements. Why? Because, for elements lighter than iron (26 protons), fusion releases energy, and fission consumes energy. For elements heavier than iron, this is the other way around.
How does fusion work?
You could try to fuse any two elements, but we will talk about the one specific fusion reaction that would be used to generate electricity.
We’ll refer to elements by the number of protons and neutrons they have: “1p2n” is a nucleus with 1 proton and 2 neutrons. We can forget about the electrons for now - you’ll see why later.
What are these elements? 1p0n is Hydrogen “H”. 1p1n and 1p2n, as used for fusion, are isotopes of hydrogen called Deuterium and Tritium (they have the same number of protons, but different numbers of neutrons):
What about the result of this reaction? It’d be bad if 2p2n was something dangerous, like nuclear waste.
Luckily, helium is not dangerous - it's what's used to fill balloons. Now that we know the elements involved, let’s look at the reaction again:
Why does this release energy?
As weird as it sounds, Helium plus one neutron has less mass than Deuterium plus Tritium. Yes, really! By recombining the same number of protons and neutrons into a different configuration, the whole nucleus loses mass.
So why aren’t we using fusion to make energy?
The good news is we can create fusion on Earth. The bad news: it’s really difficult.
As you can see from this graph, we got so close to Q=1, but then improvements stopped happening - why? In the next chapter, we’ll explore what the graph above means, discover what prevented further progress (so far), and discuss recent work that aims to get to Q=10 and higher.Next Chapter