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The major types of reactors in commercial operation
  1. Pressurised Water Reactor (PWR)
    PWR is a light water reactor using ordinary water as the coolant and moderator. The PWR has a primary coolant circuit with water circulating through the reactor core at high pressure above 150 bars (1 bar = 100 kPa) to extract the heat generated by nuclear fission. The water then passes through steam generators to deliver heat to the secondary circuit. The steam generator produces steam on the secondary side to drive the turbine and generator. Water in the primary circuit is maintained at a high temperature of over 300 degree C under high pressure of above 150 bars to prevent it from boiling.

  2. Boiling Water Reactor (BWR)
    BWR is a light water reactor using ordinary water as coolant and moderator similar to the PWR except it only has a single circuit connecting the reactor and the turbine without a steam generator. Water in the reactor is kept at a lower pressure of about 75 bars such that it will boil at about 285 degree C. The steam produced from the reactor will directly feed into the turbine after passing through steam separators above the reactor core. The steam leaving the turbine is condensed into liquid water (feed water) after passing through the condenser and then re-circulated back to the reactor for conversion into steam again. The reactors involved in the Fukushima accident belong to this type.

  3. Pressurised Heavy Water Reactor (CANDU)
    CANDU is a pressurised heavy water reactor operated on natural uranium fuel (U-238) and uses heavy water (D2O) as coolant and moderator. CANDU is an acronym for CANada Deuterium Uranium. The CANDU reactor is capable of on-line refuelling during operation.

  4. Graphite Moderated, Direct Cycle (Boiling Water) Pressure Tube Reactor (RBMK)
    RBMK is a type of pressure tube reactor designed in the former Soviet Union, which uses ordinary boiling water as the coolant and graphite as the moderator. This type of reactor is capable of on-line refuelling. The reactor involved in the Chernobyl accident belongs to this type.
The above information is provided by EMSD
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Last revision date: <19 Dec 2012>