Pressurized Water Reactor (PWR)

Pressurized Water Reactor (PWR)

The pressurized water reactor is a type of nuclear reactor. This type of reactor's main characteristic is that the water uses high pressure in the primary circuit to prevent it from boiling. Otherwise, the high temperature inside the reactor would convert it into steam.

It is currently the most widely used type of nuclear reactor in nuclear power plants worldwide. At present, there are more than 230 nuclear reactors in the world manufactured with this system.

The first purpose of the PWR model was to use it in a nuclear submarine.

Pressurized water reactors (PWR) use enriched uranium as nuclear fuel.

Along with boiling water reactors (BWR), the pressurized water reactor is a light water reactor.

How does a pressurized nuclear reactor work?

The pressurized water reactor (PWR) works in 4 steps:

  1. The reactor core within the reactor vessel generates heat through fission reactions.

  2. The high-pressure water from the primary circuit transports this thermal energy to a steam generator.

  3. Inside the steam generator, the heat that comes from the primary circuit converts the water from the secondary circuit into steam.

  4. The steam generated drives a turbine that produces electricity.

During these four points, the pressurized water reactor PWR has converted nuclear energy from nuclear fuel into electrical energy. From here, the cycle begins again: the resulting steam is converted back into liquid water through a condenser. 

The condenser puts the secondary circuit in thermal contact with a tertiary course through which cold water circulates outside (seawater, rivers, lakes, etc.). Once converted into liquid water, it returns to the steam generator driven by a series of water pumps.

The reactor core and nuclear reactions

The reactor core contains the nuclear fuel rods. Inside, the atomic reactor generates a large amount of thermal energy.

For safety reasons, the PWR pressurized water reactor cannot exceed a specific temperature to avoid melting. The reactor coolant system keeps the fuel rods at the right temperature.

The cooling is carried out using water that circulates thanks to a set of reactor coolant pumps.

The reactor must do the heat exchange between the primary and secondary without the water mixing. This mixture must be avoided because the water in the primary circuit is radioactive.

Pressurized Water Reactor (PWR)

Coolant for pressurized water reactors

Ordinary water is the coolant used to keep water at the right temperature. In the field of nuclear engineering, it is called light water. The water can reach temperatures of up to 315 degrees Celsius. The water remains in the liquid phase due to the high pressure (around 16 megapascals) at which the primary circuit operates.

Nuclear moderator in pressurized water nuclear reactors

Nuclear fission reactions occur when a neutron collides with a fuel atom. Atomic reactions release one or two fast neutrons.

The pressurized water reactor (PWR) requires fast neutrons to slow down to generate more reactions.

The moderator is in charge of the neutrons losing speed. In PWR reactors, the water used as coolant also acts as a neutron moderator.

Another way to control power reactors is by using control rods. Control rods can absorb neutrons. Introducing them deeper into the reactor makes the reactions go down.



Published: June 16, 2017
Last review: September 28, 2020