• Question: Sam, I think that you are the perfect person to ask this question to: How Nuclear Reactors are created and how do they work?

    Asked by anon-253333 to Sam on 15 Jun 2020.
    • Photo: Sam Smith

      Sam Smith answered on 15 Jun 2020:


      Hi Aditya, really good question! I’ll answer it as best I can without going into too much technical detail. If you are looking for more detail, I’ve included some useful links at the bottom of my answer!

      When talking about nuclear reactors its useful to know how a power station generates electricity. In most power stations, water is heated to 100’s of degrees Celsius until it becomes steam, like in a giant kettle. This steam is then used to turn to spin a turbine (often more than one) to generate electricity. Where power stations differ is in how they generate the steam. Some burn pulverised coal (eg. Ratcliffe-on-Soar), some burn gas (eg. Connah’s Quay) and some burn biofuels (eg. 4 of Drax’s 6 units). Nuclear power stations also work on the principle of turning a turbine to make electricity but they don’t burn anything, they get the energy that they convert to electricity through nuclear fission.

      A very basic explanation of nuclear fission is the process of unstable atoms breaking apart to become more stable, and in the process releasing neutrons, energy and other atoms. The neutrons cause more atoms to become unstable and release energy, and so on; we call these unstable elements radioactive. If there is enough of the radioactive element, you get a chain reaction that produces lots of energy. A nuclear reactor makes use of this process to make the energy that the spinning turbine converts to electricity.

      The reactors use fuel that is made up of the radioactive elements (uranium and plutonium) to cause a chain reaction (what we call ‘criticality’) to happen, but under controlled conditions which prevent the reaction from going out of control. This is done using control rods which can change the rate of the reaction or make it start/stop, and a moderator which helps make the conditions right for the reaction to happen at the correct rate. A coolant is used to keep the reactor under ideal temperature conditions, and this coolant is what is used to spin the turbines. Different types of nuclear reactor do this differently, the old designs (eg. Magnox design) used carbon dioxide as coolant and to spin the turbines, more modern designs use water as coolant (eg. Pressurised water reactors), and some of the future designs are looking to use liquid metals (eg. Sodium cooled fast reactors). An alternative option for the future that is being explored by a lot of people is nuclear fusion. This works around the idea fusing atoms together to make huge quantities of energy, and is a lot cleaner than a power station based on nuclear fission.

      In terms of what the power station is made from, it really does depend on the type of reactor. Where it can vary includes: fuel material, fuel cladding material, moderator material, material used for control rods, material used for coolant and the material used for shielding. That list doesn’t include the rest of the power station surrounding the reactor, which has huge variation, and as a result very few power stations look the same!

      I’ve given quite a generic answer, so I’d recommend going to the World Nuclear Association’s information library which I’ve used a lot during my training (https://www.world-nuclear.org/information-library.aspx), and exploring the International Atomic Energy Agency website (https://www.iaea.org/). Some of it can be really technical so I’d recommend this article about US nuclear reactors from the US Office for Nuclear Energy (https://www.energy.gov/ne/articles/nuclear-101-how-does-nuclear-reactor-work) and some of the articles by BBC Science Focus magazine (https://www.sciencefocus.com/).

      Hopefully I’ve not made it too complicated, it’s a really complex topic which can very very technical! I am always happy to answer any follow up questions you might have!

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