The reactor vessel of a commercial reactor is inside this containment building. A picture of a reactor is shown in Fig. The energy released in the fission process, which is primarily in the form of the kinetic energy of the fission fragments, heats the water. The chain reaction is controlled by rods of neutron-absorbing material inserted into the core. The thermal energy is removed from the core by the water to an external thermal-energy converter.
Nuclear reactions liberate a large amount of energy compared to chemical reactions.
This 239 Pu can be reprocessed from used fuel rods and used to power other reactors. It is actually possible to generate more 239 Pu than is used up in the reactor by surrounding the core with a uranium blanket and generating 239 Pu in this blanket. This is called a breeder reactor. In a fast-breeder reactor, water cannot be used as a coolant because it would moderate the neutrons. Liquid sodium metal may be used here as a coolant and heat-transfer fluid.