The most common type of nuclear reactor, which uses ordinary water circulating through the core under high pressure to cool the uranium fuel. Water also serves as a moderator. It has a pressure of 15 MPa and a temperature of around 300 °C. As fuel, PWR uses uranium enriched to 3—5 percent with the isotope ²³⁵U. Ceramic uranium dioxide pellets are stacked in zirconium alloy coated fuel rods, which are bundled into fuel assemblies four metres long. Regulating rods are inserted between them from above. The heat from the primary circuit is transferred to the secondary circuit in the steam generator, and the steam generated drives the turbine.

The Russian modification of the PWR is called the VVER (an acronym based on the Russian words vodo-vodjanoj energetičeskij reaktor, water-water energetic reactor). In 2023, a total of 307 pressurized water reactors were in operation.