Pressurized Water Reactors (also known as PWRs) keep water under
pressure so that it heats, but does not boil. This heated water is
circulated through tubes in steam generators, allowing the water in the
steam generators to turn to steam, which then turns the turbine
generator. Water from the reactor and the water that is turned into
steam are in separate systems and do not mix.
View animated image of a Pressurized Water Reactor
Source: Nuclear Regulatory Commission
View animated image of a Pressurized Water Reactor
Source: Nuclear Regulatory Commission