l          Main Reactor Types

Most of the six main reactor types were developed in the 1950’s though not all were fully exploited for commercial applications.  Of these six reactor types, only fast neutron breeder reactor makes use of fast neutrons for nuclear fission, while the other five make use of thermal neutrons for nuclear fission.  These five are collectively called thermal neutron reactors.

Ø            Pressurised Water Reactor

In a pressurised water reactor, enriched nuclear fuel undergoes nuclear fission in an enclosed pressure vessel.  Water is used both as a coolant for the nuclear fuel and as a moderator to maintain the nuclear fission process.  The water for cooling the nuclear fuel is separated from the water used to produce steam for the turbine-generator.  A certain portion, typically 25 to 40 percent, of each store of nuclear fuel will need to be replaced in between 12-24 months.