FBR

The Fast Breeder Reactor (FBR) has a core of plutonium surrounded by rods of U-238. The U-238 nuclei absorb neutrons from the core and are transformed into plutonium (P-239). For every four atoms of plutonium that are used up in the core of the breeder, five new plutonium atoms are made from the U-238. Therefore, FBRs "breed" plutonium. Fast breeder reactors work at such a high temperature that they need a special coolant such as liquid sodium. In addition, they are not equipped with a moderator to slow down neutrons, and for this reason are called "fast" breeders.