Editing Pressurized water reactor (section)

=== Coolant ===

[[Water|Light water]] is used as the primary coolant in a PWR. Water enters through the bottom of the reactor's core at about {{convert|548|K|lk=in}} and is heated as it flows upwards through the reactor core to a temperature of about {{convert|588|K}}. The water remains liquid despite the high temperature due to the high pressure in the primary coolant loop, usually around 155 [[bar (unit)|bar]] (15.5&nbsp;[[megapascal|MPa]] 153&nbsp;[[Atmosphere (unit)|atm]], 2,250&nbsp;[[Pounds per square inch|psi]]).
The water in a PWR cannot exceed a temperature of {{convert|647|K}} or a pressure of 22.064&nbsp;MPa (3200 psi or 218 atm), because those are the [[critical point (thermodynamics)|critical point]] of water.<ref>International Association for the Properties of Water and Steam, 2007.</ref> [[Supercritical water reactor]]s are (as of 2022) only a proposed concept in which the coolant would never leave the [[supercritical fluid|supercritical]] state. However, as this requires even higher pressures than a PWR and can cause issues of corrosion, so far no such reactor has been built.