PWR – Pressurized water reactor

The pressurized water reactor, abbreviated as PWR, is a light water reactor, in which light water (ordinary water) is used as a moderator as well as the reactor coolant. In PWRs, the reactor coolant is maintained under the high pressure (16 MPa) and at normal operation the flow is considered to be single-phase (without boiling). It is the most common type of nuclear reactor.

Pressurized water reactors use a reactor pressure vessel (RPV) to contain the nuclear fuel, moderator, control rods and coolant. They are cooled and moderated by high-pressure liquid water (e.g. 16MPa). At this pressure water boils at approximately 350°C (662°F).  This high pressure is maintained by pressurizer. Inlet temperature of the water is about 290°C (554°F). The water (coolant) is heated in the reactor core to approximately 325°C (617°F) as the water flows through the core. As it can be seen, the reactor has approximately 25°C subcooled coolant (distance from the saturation).

The hot water that leaves the pressure vessel through hot leg nozzle and is looped through a steam generator, which in turn heats a secondary loop of water to steam that can run turbines and generator. Secondary water in the steam generator boils at pressure approximately 6-7 MPa, what equals to 260°C (500°F) saturated steam. Typical reactor nominal thermal power is about 3400MW, thus corresponds to the net electric output 1100MW. Therefor the typical efficiency of the Rankine cykle is about 33%.

The unused steam (45°C) is exhausted to the condenser, where it is condensed into water. The secondary side of the condenser extracts the waste heat (2000MW; 30°C) and the waste heat is released into environment. The resulting secondary water is pumped out of the condenser with a series of pumps, reheated, and pumped back to the steam generator.


Nuclear reactor - WWER 1200
Nuclear reactor and primary coolant system of WWER-1200.