eli5 How does a nuclear reactor in a nuclear power plant work?
In: Engineering
There are lots of designs of reactors which work in completely different ways but the basic principle is the same. Nuclear fuel consists of isotopes of heavy elements like thorium, uranium and plutonium which is able to absorb neutrons and split into smaller atoms releasing a lot of energy and new neutrons. In addition to the fuel a nuclear reactor consists of other elements which acts as neutron reflectors, absorbers and moderators. These change the chance of a neutron getting absorbed by a fuel isotope by reflecting neutrons back into the fuel, absorbing the neutrons so they are not reflected back and slowing down the neutrons increasing their chance of absorbtion. The reactor can be controlled by changing these elements by inserting or removing control rods from the reactor. This way you can control exactly how much heat is produced by the reactor. In order to extract the energy from the reactor it also have some sort of cooling medium flowing through it. Again, different reactors have different designs but this heat is most of the time used to boil water in order to create pressure to force the steam through turbines to generate electricity. The steam which is now at atmospheric pressures is cooled down so it condensates and can be used again. This is why you see cooling towers next to nuclear reactors or they are placed next to a large body of water. In some cases they can also provide heating for nearby houses.
When a uranium atom falls apart, it produces energy, some fragments and some free neutron. When a neutron hits another uranium atom, that one falls apart, too. So, the more atoms fall apart, the more neutrons you have flying around and even more atoms fall apart. Obviously, too much is not good, so you use other stuff that can catch neutrons without falling apart and insert that stuff between your uranium fuel rods. Those are the control rods. With them, you make sure that just the right amount of uranium falls apart.
The energy that is released by the falling apart of the uranium turns water into steam, and that runs a turbine and a generator, just like in a coal plant.
Fissible material is brought to a controlled chainreaction. If it gets too fast it gets slowed down with neutron absorbers so it’s basically a nuclear explosion in slow.
The heat of that is carried away with water, wich is then used to create steam wich powers a turbine wich in turn powers a generator, so except for the heat source it’s the same as a coal powerplant.
Nuclear reactors use special metals that that give off a strange heat. This strange heat can make us very sick if we stay around it too long.
The more of this metal that we put together the hotter it will get as the metal heat makes itself heat up and that makes it go even hotter and hotter. And it can get so hot that it will eventually explode if there’s enough of it in a small enough space.
Nuclear reactors use a controlled form of this. carbon rods made of the same stuff as pencil lead are used to absorb and control the release of this strange heat. These are called control rods. And in this example the special metal is uranium
The strange heat is used to heat up water, The water also helps control the temperature of the special metal so it doesn’t get too hot.
This water is moved in a series of coils to heat up a separate set of coils of water. This is important to make sure that none of the water that’s been in contact with the strange heat leaves the system.
This second coil of water also gets really really hot. And that is used to make steam turbines spin. The steam turbines turn the spin into electrical energy.
This is done with magnets, The spinning part of the turbine spins magnets around inside coils of wire, This produces electricity.
Now these second coils of water are also really hot even after they’ve made the steam turbine spin. To be reused it needs to cool down A lot of plants will use a third set of coiled water tubes to exchange heat again. These coils use outside water from something like a river or the ocean. Cold water comes in it gets warmed up and then gets pumped back out into the river or ocean.
This three coil system of water make sure none of the strange heat leaves the power plant.
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