Fast Breeder Reactor (FBR):
A fast breeder reactor produces heat and at the same time converts fertile material into fissionable material. The central portion of this reactor is a stainless steel pot in which a core of fissionable material is kept. The Fuel used is natural or enriched Uranium. This core of fissionable material is surrounded by a blanket of breeder (fertile) material (U238 or Th232).In this type of reactor, two heat exchangers are used. The reactor core is cooled by liquid sodium / potassium. In the second heat exchanger, the coolant is again liquid sodium/potassium which transfers heat to feed water. A neutron shield (graphite) separates the reactor core and primary heat exchanger. The fertile material absorbs neutrons produced by chain reaction and thus produces fissile material (Pu239 or U233).A true breeder reactor produces more new fuel than it consumes. The term "fast" comes from the fact that the majority of the fission events are caused by fast neutrons, rather than slow or thermal neutrons. In fact no moderator is present at all to slow down the fast neutrons.