A pressurized water reactor is a type of nuclear reactor used to generate nuclear power. It works by placing nuclear fuel in a reactor pressure vessel, which is then engaged in a controlled fission chain reaction, producing heat. This heats water in the primary coolant loop by thermal conduction through the fuel cladding. The hot primary coolant is pumped into a heat exchanger called the steam generator, where it flows through several thousand small tubes. Heat is transferred through the walls of these tubes to the lower pressure secondary coolant located on the sheet side of the exchanger where the secondary coolant evaporates to pressurized steam. This transfer of heat is accomplished without mixing the two fluids to prevent the secondary coolant from becoming radioactive. This digital animation was produced by the Tennessee Valley Authority, a federally owned electric utility corporation in the United States, and narrates the operation of a pressurized water reactor.Animation credit: Tennessee Valley Authority