Boiling Water Reactors

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Typical Boiling-Water Reactor

How Nuclear Reactors Work

In a typical design concept of a commercial BWR, the following process occurs:

  1. The core inside the reactor vessel creates heat.
  2. A steam-water mixture is produced when very pure water (reactor coolant) moves upward through the core, absorbing heat.
  3. The steam-water mixture leaves the top of the core and enters the two stages of moisture separation where water droplets are removed before the steam is allowed to enter the steamline.
  4. The steamline directs the steam to the main turbine, causing it to turn the turbine generator, which produces electricity.

The unused steam is exhausted to the condenser, where it is condensed into water. The resulting water is pumped out of the condenser with a series of pumps, reheated, and pumped back to the reactor vessel. The reactor's core contains fuel assemblies that are cooled by water circulated using electrically powered pumps. These pumps and other operating systems in the plant receive their power from the electrical grid. If offsite power is lost, emergency cooling water is supplied by other pumps, which can be powered by onsite diesel generators. Other safety systems, such as the containment cooling system, also need electric power. BWRs contain between 370-800 fuel assemblies.

See also our animated diagram.

An artists rendering of the internal makeup of a Boiling Water Reactor, showing the various components which the reactor consists of: the containment structure with walls made of concrete and steel 3-5 feet thick; the reactor Core (in a reactor vessel with control rods); separators and dryers; feedwater line; recirculation pumps; steamline; containment cooling system and emergency water supply systems