Before we get into nuclear fission, I would like to take you on a visual journey in your mind's eye to give you an understanding of the scale of minuscule we are talking about here.
To understand nuclear fission, we will be talking about a nucleus (and plural nuclei) quite a lot. A Nucleus is tiny, too tiny to comprehend unless we apply some perspective.
Let's start with a grain of sand, a single grain of sand about 1mm from end to end.
We can all picture a grain of sand. Just try to forget the beach, daydreaming about where you are going on your next holiday, and focus on the single grain of sand.
Now, let's gradually increase the size of the grain of sand until it is the size of a house, now a city, now a country and now the size of the earth (12,472 km in diameter).
If a single grain of sand is the size of the earth, then a uranium atom would be the size of an average double-storey house.
Can you picture this? Good.
If you can't, head over to Google Earth, enter your address and zoom in and out to get a sense of the scale. (Earth to house = grain of sand to atom).
Now we are looking at a house-sized atom. However, from this perspective, we still cannot see the atom's nucleus with the human eye. To help with this, in your minds-eye, now expand your house-sized atom into a large stadium - think Wembley Stadium.
If you look, floating above the centre of the pitch, you can see a grain of sand - this is the nucleus of a single proton hydrogen atom. Our uranium atom comprises hundreds of protons and neutrons and is classed as a large nucleus. The nucleus of a uranium atom would be a marble in this scenario.
To finish the exercise, let's zoom back out again to return to our initial perspective;
Zoom out from the marble-sized nucleus to the stadium-sized uranium atom.
Shrink the stadium-sized atom to an average double-storey house-sized atom.
Zoom out from the house-sized atom to an earth-sized grain of sand.
Now shrink the grain of sand back down to its original 1mm size.
There are 43,000,000,000,000,000,000 (43 million million million) atoms within that grain of sand, each containing a 'marble in a stadium' sized nucleus. We are talking incredibly small when we are discussing nuclei!
Now we have a sense of size, we are ready to look into the process of nuclear fission.
What is Nuclear Fission?
Nuclear Fission is the process of splitting a large nucleus (our marble), generating a huge amount of energy in the process. This energy can be used to turn water into steam to generate electricity for our grid or allowed to run away and create the incredible payload seen in a nuclear bomb.
You can find a nice video below explaining nuclear fission from Cognito at the bottom of this article. We have used a couple of screenshots of their video to help us explain.
Fun fact: the term nucleus comes from the Latin word used for the seed inside of a fruit.So, how do we split the nucleus?
To release energy from the nucleus, we can wait for the nucleus to spontaneously split by itself, but this is very rare and happens at such a slow rate, or we can get the process started by firing neutrons at the nucleus, forcing it to split. We'll come back to firing neutrons later.
As the nucleus splits, it forms two nuclei, some neutrons and a lot of energy.
So much energy! A million times more than burning fossil fuels, in fact. (Keep this fact in mind for later).
The 'daughter' neutrons released as part of the fission process find other nuclei and form with them, causing them to split, creating more daughter nuclei, which find more daughter nuclei which split - you get the point. And every time you get a split, you get a huge release of energy.
This is called a chain reaction.
Nuclear Bomb
Each of these fissions with subsequent energy release happened in fractions of seconds.
When using nuclear fission in a nuclear bomb, it's easy to see that when the pit (centre) of the bomb is pierced, introducing neutrons to nuclei, a chain reaction can quickly run away with itself and generate a huge payload (a million times that of TNT).
We have a separate post that goes into the details of nuclear bombs if you want to read further.
Nuclear Energy
If we can control the rate of the chain reaction - accelerating, slowing down or stopping the nuclei from splitting- we can control the energy generated.
Nuclear fission reactors do just this. Using just a small amount of fuel (think our marble-in-a-stadium with a million times more energy than coal), a moderator to slow the speed of the neutrons down (often water) and control rods to govern the rate of fission.
Control rods are made of material that is more likely to absorb neutrons than fuel. Whenever they are placed into the reactor, the neutrons stop nuclei from splitting, slowing down or stopping the chain reactions. With this control, we can control the energy (heat) generated and the amount of steam available to power the electric generator.
To simplify things further, a moderator slows down the neutrons, just like taking a Lamborghini off-roading. And control rods attract the neutrons away from the nuclei, just like... me being distracted by YouTube videos like this for over an hour before finishing this sentence.
You will note that earlier, we stated that a neutron is fired into the first nucleus to start the chain reaction. In fact, by removing the control rods, the neutrons already present in the reactor are allowed to absorb into uranium neutrons in the fuel, becoming unstable and split. Less a firing and more a releasing.
Can a reactor turn into a bomb?
No.
Uranium, when mined naturally, is 99.18% diluted or 0.82% enriched. For a nuclear reactor, you typically need uranium enriched (concentrated) to 4%, and for a nuclear weapon, you are looking for around 90% enrichment - noting that 90% of the effort to getting to 90% is spent getting to 20%.
So, the reason a nuclear reactor cannot turn into a nuclear bomb is that the fuel used for a nuclear reactor is Diet Coke when you need Bourbon to get the party started.
"But I saw the Chernobyl reactor explode on HBO, and I watched the Fukushima reactor building blow up live on the news", I hear you say. And you are not wrong. But these were no atomic explosions.
With Chernobyl, a combination of very hot fuel and cooling water led to fuel damage, followed by a rapid overpressure detaching the cover plate and jamming the fuel rods. This caused intense steam generation that led to a steam explosion. A few seconds later, a second explosion was caused, most likely by the build-up of hydrogen.
The situation was different at the Fukushima plant, with the loss of cooling water causing the hot fuel to melt through the reactor's core. The series of explosions seen on the news were gas and hydrogen explosions from the failure of the equipment surrounding the reactor.
Both situations are very bad and resulted in the loss of life. But neither is an example of a nuclear reactor turning into a nuclear bomb.
Who Discovered Nuclear Fission?
There is some controversy over who received credit for the discovery of nuclear fission.
Rutherford, Curie, and Chadwick are some of the biggest names synonymous with the nuclear industry. And each of these made numerous contributions to nuclear fission, but it is not from this list that you will find the person responsible for discovering nuclear fission.
There is no debate that nuclear fission was first achieved in Berlin in 1938 by a team of scientists led by German chemist Otto Hahn.
However, a female physicist based in Sweden named Lise Meitner, working as part of Hahn's team, was the one that discovered that uranium atoms could be split when bombarded with neutrons. She was also the person that gave the process its name.
However, in 1944, during a very different time for equality, just Hahn received the Nobel Peace Prize for the discovery. In fact, Meitner was nominated for a Nobel Peace Prize no less than 48 times but never received the award.
What is the difference between Nuclear Fission and Nuclear Fusion?
Nuclear Fission and Nuclear Fusion are physical processes that produce energy from atoms. Nuclear Fission involves splitting a heavy atom, whereas Nuclear Fusion involves the joining (or fusing) of lighter atoms.
The differences between Nuclear Fission and Nuclear Fusion circle around the fuel used, the by-products generated, the amount of energy released and the ability to commercialise the technology.
Nuclear Fission uses Uranium or Plutonium with a release of energy 1 million times that of fossil fuel sources. This dense atomic energy source leads to much less fuel usage, but the process does result in small amounts of nuclear waste that has been stored and successfully managed for many years.
Nuclear Fusion uses Hydrogen, which results in Helium as a by-product. The energy release is 3-4 times that of nuclear fission. However, although there are many nuclear fusion power plants in development, there are not any currently capable of providing electricity to the grid on a commercial scale.
This was a very brief and simplistic overview of nuclear fission, but it should give you a better understanding of what's involved, how the process works and how nuclear energy technology is far removed from that of a nuclear bomb.
Without getting too nuclear activist-y, the above has hopefully helped you to better understand the benefits of nuclear energy based on facts and dispelled some of the myths surrounding the technology - its cheap to run, takes little fuel to generate clean, reliable 24/7 energy and generates very little waste that can be recycled or easily managed.
As promised, please find the full YouTube video from Cognito that provides the above in video format.
Nuclear Fission Explained
Three more Get Into Nuclear Definitions
Nuclear Fusion - An explainer similar to this post but about nuclear fusion and how it could be a game changer in the global energy market.
Nuclear Bomb - A definition of a nuclear bomb, their science and which countries have (or at least own up to) having them.
Thorium - What is thorium, why so many people are excited about it, and how it could potentially be used to 'burn' the current nuclear waste stockpile.
