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Nuclear Reactors

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Nuclear Reactors

An immense amount of energy is contained within the nucleus of atoms. For example, one kilogram of uranium-235 can provide between two and three million times the amount of energy as an equivalent kilogram of coal! If the public's concerns over safety could be alleviated and the technology perfected, then nuclear power would free us from reliance on our limited reserves of polluting fossil fuels.

Nuclear power has several advantages over non-renewable energy sources. While the waste produced by nuclear reactors is toxic, the radioactive waste will eventually decay into harmless substances such as lead, even though this might take up to 1 million years. Also, nuclear fuels such as uranium are far denser than traditional fossil fuels, so much less waste is physically produced. Lastly, green renewable energy sources such as solar or wind power can't produce nearly as much energy as Nuclear and are usually dependent on weather conditions.

Nuclear reactor explanation and fundamentals

The nuclear reactor is the heart of any nuclear power plant. However, outside of the main reactor, a nuclear power plant generates electricity in a surprisingly similar way to a coal power plant. Ultimately, the energy released from the nuclear reactions inside a reactor is simply used to heat and boil water. The steam then produces mechanical work to spin a turbine to generate electricity. The steam is later cooled inside the condenser to be reused in the reactor. Nuclear power plants are an example of a heat engine.

Nuclear Reactors Nuclear Reactor Diagram StudySmarterDiagram of how electricity is generated in a nuclear powerplant, Flickr CC BY-NC-SA 2.0

There are two methods of heating the water by utilising nuclear reactions. The first is nuclear fission, where a parent nucleus is split into two daughter nuclei. The mass of the two daughter nuclei is always less than the parent nucleus, this missing mass is released as energy.

The second possible method of heating is through nuclear fusion, where two light atomic nuclei are forced together and merged into a single nucleus. Similarly to fission, the resultant nucleus from a fusion reaction has a lower mass than the two original nuclei. The leftover mass is released as energy.

To figure out exactly how much energy is released in both of these nuclear reactions we must refer to the most famous equation in all of physics. Einstein's equation! Which helps us understand how mass can be converted into energy.

, whereis energy,is mass andis the speed of light.

To calculate the energy released from a nuclear fission reaction you must determine the difference in mass between the parent nucleus and the daughter nuclei. (A periodic table can help you with this). Einstein's equation shows you can then multiply this mass difference by the speed of light squared to reveal the mass that has been converted into energy in the reaction.

Nuclear reactor examples

As of March 2022, there are currently 11 nuclear reactors in 5 different locations currently in operation in the UK. Nuclear power generated over 16% of the nation's energy requirements in 2020 and that percentage is rising due to recently introduced incentives and subsidies from the government. The list of active nuclear power plants in the UK includes Hinkley Point B, Hartlepool, Heysham 1, Heysham 2, Torness, and Sizewell B.

Nuclear Reactors Nuclear Reactor Examples StudysmarterSizewell B Nuclear Power Plant, Geograph CC BY-SA 2.0

Nuclear fission reactor

In a nuclear fission reaction, a parent nucleus is split to produce two daughter nuclei. The difference in mass before and after the reaction is converted directly into energy. The most common type of nuclear fuel used in fission reactors is Uranium-235. Unfortunately, the energy released from splitting just one uranium-235 atom is only. This is insignificant compared to our modern energy requirements as the average UK home requires aboutjoules of energy per year. Thankfully, within just a single kilogram of Uranium exist an unfathomably large number of Uranium-235 atoms. So how do we split more than one atomic nucleus at once? The answer is nuclear chain reactions.

Nuclear Reactors The fission of uranium-235 StudySmarterThe fission of Uranium-235 into its daughter products, adapted from image by Wikimedia Commons CC-BY-SA-3.0

Inside a nuclear fission reactor, when a neutron is absorbed by a Uranium-235 isotope, it briefly becomes Uranium-236. U-236 is extremely unstable and will quickly decay into two daughter nuclei, Caesium-140 and Rubidium-92 while releasing energy. However, the two daughter nuclei are not the only products of nuclear fission. Two or three neutrons are also emitted. If the uranium fuel source is dense enough, then these neutrons can then be absorbed by other U-235 isotopes, causing more nuclei to split in further nuclear fission reactions, releasing more energy!

Nuclear Reactors A nuclear chain reaction StudySmarterA diagram of a nuclear chain reaction, flickr CC BY 2.0

In the diagram above you can see that the fission of the example nucleus above produces 3 new neutrons, which in turn are absorbed by 3 more atomic nuclei. Those nuclei will split too, emitting 9 new neutrons in total! So if every instance of fission produces 3 new neutrons, then the number of fission reactions will triple in each new generation (assuming all emitted neutrons actually collide with an atomic nucleus).

GenerationNumber of Fission Reactions
1st1
2nd3
3rd9
4th27
5th
81
10th
19,683
50th
2.4 x 1023

You can see from the table above how a nuclear chain reaction could quickly get out of hand, releasing an enormous amount of energy in a very short time. This is actually how nuclear weapons work. An uncontrolled nuclear chain reaction that leads to a catastrophic explosion. Clearly, for our energy requirements, we would need to be able to regulate this reaction to control the amount of energy released.

Nuclear reactor diagram

To understand how to control a nuclear chain reaction for use in our powerplants we should study the design of a nuclear fission reactor. A fission reactor has mechanisms engineered to moderate a chain reaction so that we can extract the exact amount of energy desired. This is particularly useful as the UK's energy demands on the national grid change based on many different factors, including the time of day, weather, season, and so on.

Nuclear Reactors Nuclear Reactor Diagram StudySmarterThe primary components of a nuclear fission reactor, Wikimedia Commons CC-BY-2.5

A nuclear fission reactor contains many important parts. The nuclear fuel source (uranium, plutonium, thorium etc.) is held in fuel rods which are encased with a graphite moderator. The graphite between the fuel rods slows down any emitted neutrons, which makes them more likely to be absorbed by the nuclear fuel in another rod which will induce a higher rate of nuclear fission.

The main mechanism that controls the rate of the nuclear chain reaction inside the fission reactor is the control rods. They are typically made out of elements such as silver or boron, which can readily absorb neutrons without splitting themselves. A nuclear chain reaction can therefore be controlled by lowering or raising these control rods. You can slow the reaction rate by lowering the control rods further into the core. Oppositely, you can increase the rate of the reaction by steadily removing the control rods. With multiple control rods, it is simple to maintain real-time control of the fission process.

Radiation shielding (typically made of concrete) is used to protect the external environment from the radioactive and harmful daughter products of the fission reactions. The energy generated by nuclear fission in the reactor is used to heat water, so the steam can perform useful work by turning a steam turbine, which is ultimately used to generate electricity.

Nuclear Fusion Reactor

In a nuclear fusion reaction, two atomic nuclei are forced together and combined into one nucleus. The difference in mass before and after a fusion reaction is converted directly into energy. Nuclear fusion powers our Sun, where a near-countless number of nuclear fusion reactions occur every second. The mass difference is then radiated away as energy.

Nuclear fusion can create immense amounts of energy, several times greater than fission. The fuel used in fusion is extremely abundant and cheap, unlike heavier, radioactive elements used in fission. Also, none of the products of fusion are themselves radioactive, so a nuclear fusion power plant would be a green and renewable energy source. Finally, a nuclear fusion reactor would be incapable of having a nuclear meltdown even with human error, so they would be much safer.

It is obvious then that a lot of energy can be extracted through nuclear fusion. It may shock you then that there are currently zero nuclear fusion reactors in the world to help generate our electricity! For fusion to occur you need to overcome the repelling force between two positively charged atomic nuclei. The two nuclei must be close enough that the nuclear force will be strong enough to induce nuclear fusion. An environment with extremely high temperature and pressure is needed to accomplish this, like that found inside a star.

Nuclear Reactors Electrostatic repulsion of nuclei StudySmarterThe force repelling two positively charged nuclei that must be overcome for nuclear fusion, Wikimedia Commons CC-BY-2.5

Unfortunately, the amount of energy needed to artificially create this environment takes more energy to sustain than we receive from the fusion itself. Scientists and engineers have been making steady progress on this problem over the past few decades, but currently, nuclear fusion reactors exist as experimental technology only.

Scientists have decided that in any future nuclear fusion reactor two different Hydrogen isotopes, Deuterium and Tritium will probably be the fuel. This fuel can fuse at lower temperatures than other sources and releases more energy than many other fusion reactions. Furthermore, deuterium is easily found in seawater and while it is rare for Tritium to occur naturally, it can be artificially produced easily and cheaply.

Deuterium (D) nuclei possess 1 proton and 1 neutron each, while Tritium (T) contains 1 proton and 2 neutrons each. When Deuterium and Tritium undergo fusion they merge into an ordinary Helium nucleus, releasing a single neutron and a lot of useful energy!

Nuclear Reactors - Key takeaways

  • Immense amounts of energy are contained within the nuclei of atoms that we can utilise in power generation.
  • Nuclear Powerplants produce less waste than fossil fuels and the radioactive waste does eventually decay into harmless substances. Plus they can generate far more electricity than renewable energy sources like solar, wind or tidal power.
  • The energy released during a nuclear reaction is used to heat water like other types of power plants. The heated water turns into steam, which uses mechanical work to spin a turbine. The turbine ultimately generates electricity. The steam can then be cooled in a condenser to be reused in the reactor.
  • In nuclear fission, one heavier atomic nuclei is split apart into two daughter nuclei. The total mass of the daughter nuclei is always less than the parent nucleus. The mass difference is converted into energy.
  • In nuclear fusion, two light atomic nuclei are forced together to merge into a single nucleus. The mass of the resultant nucleus is always less than the original two nuclei. The mass difference is converted into energy.
  • Nuclear chain reactions are used to split more than one atom at a time. Uncontrolled chain reactions are used in weapons and controlled chain reactions are used in nuclear power plants.
  • Nuclear fission reactors have many important parts. Fuel rods, control rods, graphite moderator and radiation shielding.
  • Nuclear fusion can produce several times more energy than nuclear fission. Fuel is abundant and cheap and the process produces no radioactive waste. Fusion power plants are also safer than fission power plants.
  • Nuclear fusion requires a high temperature and pressure environment to overcome the repelling force between the two positive nuclei.

Frequently Asked Questions about Nuclear Reactors

A nuclear fission reactor splits heavy atomic nuclei in a process called nuclear fission. Splitting these nuclei causes a nuclear chain reaction which releases a lot of energy.

A nuclear reactor is the part of a nuclear power plant that is used to heat and boil water using nuclear reactions.

  1. Nuclear Fission Reactor, where atomic nuclei are split to release energy.
  2. Nuclear Fusion Reactor, where atomic nuclei are forced together to release energy.

A nuclear reactor uses nuclear reactions to release energy. One of the primary purposes of the reactor is to moderate these reactions using control rods, so that the exact amount of energy is desired.

Fukushima (Japan), Chernobyl (Ukraine), Torness (UK)

Final Nuclear Reactors Quiz

Question

What can provide more useful energy in our power plants?

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Answer

Nuclear fuels 

(Uranium, Plutonium, Thorium etc.)

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Question

Write three sentences or less describing a nuclear fission reaction.

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Answer

A heavier parent nucleus is split into two lighter daughter nuclei. The daughter nuclei always have less total mass than the parent nucleus, the mass difference is released as energy.

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Question

Write three sentences or less describing a nuclear fusion reaction.

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Answer

Two light atomic nuclei are forced together and combined into a single nucleus. The resultant nucleus has less mass than the two original nuclei, that mass difference is released as energy.

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Question

Which one of these is not a fuel used in a nuclear fission reactor?

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Answer

Helium

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Question

What product of nuclear fission is the key component that allows nuclear chain reactions to occur?

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Answer

Neutrons

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Question

In a specific nuclear fission reaction, two neutrons are emitted as products. These neutrons are used in a nuclear chain reaction. How many fission reactions will occur during the 5th generation?

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Answer

16

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Question

What sort of nuclear reactions do nuclear weapons use?

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Answer

Uncontrolled

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Question

In two sentences or less, describe the role of the graphite moderator in a nuclear fission reactor.

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Answer

The graphite between the fuel rods slows down the emitted neutrons during the fission reaction, which means they are more likely to be absorbed by the nuclear fuel in another rod.  

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Question

In a nuclear fission reactor, would you raise or lower the control rods to quicken the reaction rate?

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Answer

Raise the rods

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Question

Describe in one sentence, why control rods in a nuclear power plant made from elements such as boron or silver?

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Answer

They can readily absorb neutrons without undergoing nuclear fission themselves. 

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Question

What is the safest type of Nuclear Powerplant?

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Answer

Nuclear Fusion 

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Question

What sort of environment is required to induce nuclear fusion between two atomic nuclei?

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Answer

High Pressure and High Temperature

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Question

Describe in two sentences or less, why it is difficult to get two light atomic nuclei to undergo nuclear fusion.

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Answer

Atomic nuclei are always positively charged, so they repel each other. The two nuclei must be forced together close enough for the nuclear force to become stronger and fuse them.

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Question

Why do we currently have zero nuclear fusion reactors to generate our electricity?

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Answer

The energy needed to create the right environment for nuclear fusion requires more energy than we receive from the reaction. 

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