A pressurized water reactor (PWR) is a type of nuclear reactor that uses water as both a coolant and a neutron moderator. In a PWR, water is kept under high pressure to prevent it from boiling, allowing it to absorb heat generated from nuclear fission in the reactor core. This heat is then transferred to a secondary loop, where it produces steam to drive turbines and generate electricity. The design of a PWR includes a containment structure to ensure safety and prevent the release of radioactive materials. PWRs are widely used in commercial nuclear power plants, making them one of the most common types of reactors in operation today.