A breeder reactor is one type of nuclear reactor. In a breeder reactor, uranium-238 is transformed in a series of nuclear reactions into plutonium-239.
The plutonium-239 can undergo fission as shown in the equation below. The X represents a missing product in the equation.
Compare the amount of energy released by completely fissioned plutonium-239 to the amount of energy released by the complete combustion of the same amount of coal.