How do control rods in nuclear reactors work?
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Radioactive materials are unstable. They have too many tiny particles shoved together in the nucleus of the atom, and they won’t last forever. *At some point*, a chunk of atom will break free and shoot out like a bullet. This is radiation.
Different types of radioactive material give off radiation at different rates. Some of it (like Uranium 238) is so stable that it takes billions of years to break down. Some other types break down in fractions of a second. The thing is, if your radioactive material gets hit by the radiation of a different atom, it might trigger the release early. Think of it like a pebble rolling down a mountain, hitting other pebbles, eventually causing an avalanche. There are a bunch of equations that predict exactly how much radioactive stuff you need to start that avalanche.
Nuclear fuel is made up of radioactive elements that are ready to go. They get hit by the radiation of other atoms nearby, and they give off their own increased radiation, and it starts a chain reaction. This is done under controlled circumstances — the scientists know exactly how much material to add to create energy, but not create a big kaboom.
Control rods are made of stuff that absorbs radiation. You insert the control rods and they start absorbing all the radiation flowing around inside the reactor. This means less radiation hitting the radioactive material, which slows down the reaction and stops the avalanche. There are also some equations behind this, so the scientists know how much of the control rods to put inside the reactor. Put them in all the way and you’ll basically kill the reaction completely. Put them in a little bit and you just reduce it to a lower level.
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