 What is a chain reaction? You know nuclear fuel is enriched uranium-235. But that's not the whole story. A nuclear reactor generates electricity because of a chain reaction. When a uranium-235 atom disintegrates, it releases some neutrons. Some of those neutrons can be made to interact with other uranium-235 atoms, causing them to disintegrate as well. Those target atoms release more neutrons when they disintegrate, and then those neutrons interact with still other uranium-235 atoms and so on. This is called a chain reaction. This process doesn't work well for other isotopes of uranium and is also why uranium-235 needs to be enriched for use in a nuclear power plant. Most of the energy released when a uranium-235 atom disintegrates is in the form of kinetic energy, vibrations that constitute heat. The fuel rods containing the uranium pellets get hot as the reaction progresses. The faster the chain reaction, that is, the larger the number of uranium-235 atoms that disintegrate each second, the faster energy is released and the hotter the fuel rods become. The people in charge of the reactor can control the chain reaction by preventing some or all of the released neutrons from interacting with uranium-235 atoms. The physical arrangement of the fuel rods, the low uranium-235 concentration, and other design factors also limit the number of neutrons that can interact with uranium-235 atoms. The chain reaction is one step in the process of making electricity.