- 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.
- 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.
- 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.
- 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.
