Pressurized Water Reactor (PWR)

Definition - What does Pressurized Water Reactor (PWR) mean?

A pressurized water reactor (PWR) is a nuclear reactor that uses water as a coolant and moderator, which produces steam to drive a turbine. Pressurized water reactors are used as source of nuclear power for submarines and power plants.

Pressurized water reactors constitute the large majority of all Western nuclear power plants. About two-thirds of the operating nuclear reactor power plants in the United States are PWRs.

PWRs were initially designed to help as nuclear propulsion for nuclear submarines and were used in the original design of the second commercial power plant at Shippingport Atomic Power Station.

Corrosionpedia explains Pressurized Water Reactor (PWR)

Pressurized water reactors are a common nuclear power reactor design in which very pure water is:

  1. Heated to a very elevated temperature by fission
  2. Kept under high pressure (to prevent it from boiling)
  3. Changed to steam by a steam generator (rather than by boiling, as in a boiling-water reactor)

The resulting steam is used to drive turbines, which stimulate generators to produce electrical power.

A pressurized water reactor essentially operates like a pressure cooker, where a lid is tightly secured over a pot of heated water, causing the pressure inside to increase as the temperature increases (because the steam cannot escape), but keeping the water from boiling at the usual 212°F (100°C).

Two things are characteristic for the pressurized water reactor when compared with other reactor types: coolant loop separation from the steam system and pressure inside the primary coolant loop. In a PWR, there are two separate coolant loops (primary and secondary), which are both filled with demineralized/deionized water. In contrast, a boiling water reactor has only one coolant loop, while more exotic designs such as breeder reactors use substances other than water as a coolant and moderator.

Advantages of PWR include:

  • Easy to operate from a stability standpoint
  • Water in the secondary loop is not contaminated by radioactive materials
  • Can passively shut down the reactor in the event that offsite power is lost to immediately stop the primary nuclear reaction
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