How does nuclear energy work to make a city run?

We usually make heat energy by burning fuels oil, gas, coal, or wood. In large quantities, such energy can be used to heat water, and the resulting steam can be used to run generators that make electricity for a city. Burning fuel (combustion) is a chemical reaction that converts one form of energy into another: it recombines elements from the fuel and the oxygen in the air into things like ash, smoke, and waste gases, as well as heat.

A fission-generated nuclear reaction produces heat in a different way: it breaks apart elements themselves, turning them into waste products with less mass, which creates a great amount of energy. The tiniest particles of matteratomsof heavy elements like uranium or plutonium provide the fuel for nuclear reactors. At the center of each atom is a nucleus, which is made up of even tinier particles called protons and neutrons. A nucleus is held together by a powerful force, and breaking up the nucleus releases that force. A nuclear reaction starts when fast-moving neutrons strike the nuclei of fuel atoms, causing them to break into smaller nuclei. These in turn release neutrons that break up more fuel nuclei. All this movement produces great heat, which can be used to make steam to run electric generators.