Pressurised water reactor PWR

The most common reactor on earth. Ordinary water under roughly 155 bar of pressure serves as both coolant and moderator, staying liquid at over 300 °C. Because the primary water never boils, it stays in a sealed loop and gives up its heat to a separate steam generator; the turbine side is therefore not radioactive. That separation is the design's defining feature and the reason it dominates both civil and naval propulsion. Fuel is low-enriched uranium dioxide, replaced roughly a third at a time on an 18-to-24-month cycle.