Uranium-235 can undergo nuclear fission, and is therefore the portion of the fuel we’re interested in. The majority of uranium in the fuel is uranium-238, but a small percentage (3-5%) is uranium-235. Uranium comes in different forms, or isotopes – these are atoms of uranium that have the same number of protons in the nucleus, but a different number of neutrons. These consist of pellets of uranium oxide, packed into pellets and sealed in a zirconium metal tube. The fuel in the reactor core is contained in fuel rods. This reactor differs from the two described above – but to understand how, we first need to know a little more about what’s going on inside the reactor itself. The Chernobyl reactor was of a different type, known as the RBMK reactor. The majority of western nuclear reactors are PWRs. In pressurised water reactors (PWR), the water heated in the reactor is contained under pressure, and used to produce steam in a secondary loop of water which then goes on to turn the turbines. In boiling water reactors (BWR), the source of the steam that drives the turbine is water in the reactor core this means that short-lived radioactive substances pass through the turbines, so they must be shielded when the reactor is active. The variations are related to the water that’s heated to produce the steam that drives the turbine. ![]() In terms of types of reactor, there are two main variations on the above theme for western reactors. The steam that drive the turbine is cooled and condensed back to water, which can then be recycled back through the reactor continuously. This in turn drives a generator producing electricity. The heat generated by these reactions is used to heat water and produce steam, which goes on to turn a turbine. Let’s start with the basics: how do nuclear plants generate electricity? The manner in which they do this is actually not too dissimilar from how it is produced in coal or gas power plants, with the key different being that the fuel is in the form of heat-producing nuclear reactions instead of these fossil fuels. As is often the case, however, the truth is slightly more complicated, and an understanding of how modern nuclear reactors work can help make sense of what happened 30 years ago today. Chernobyl’s legacy is a perhaps understandable wariness and distrust in the safety of nuclear power from a significant proportion of the public, to many of whom it stands as an example of a dangerous series of events that could befall any nuclear plant. I recall staring down into the reactor hall and being amazed at the thought of the invisible atomic processes occurring below, eventually resulting in the generation of electricity for hundreds of thousands of people.Īn interest in the workings of nuclear reactors inevitably leads to an interest in Chernobyl, the one nuclear plant that likely anyone can name. In part, it probably stems from a visit to the Hinckley Point nuclear power plant at the age of around eight (part of a family holiday – you end up having some occasionally weird excursions when one of your parents works in nuclear safety). Though I’m a chemistry teacher by trade, the physics behind nuclear power has always held something of a fascination for me. Here, we look at how nuclear reactors work generally, what led to the accident at Chernobyl 30 years ago, and the differences between Chernobyl and modern reactors. The narrative seems to be a classic cautionary tale against the utilisation of nuclear reactors to generate power, but the reality is more nuanced. Early in the morning on 26 April 1986, a safety system test at the Chernobyl power plant in Pripyat, now part of Northern Ukraine, ended in a nuclear disaster with catastrophic consequences for both those working at the plant and those living in the surrounding area.
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