Power from the nucleus
Nuclear power generation begins in the core of a reactor, where
neutrons are fired into uranium-235 nuclei causing them to split into lighter nuclei plus further
neutrons. These neutrons must be slowed down by a moderator so that they are able to initiate
further fission reactions and sustain a chain reaction. In the case of a pressurized water reactor
(PWR, shown) water is used as the moderator, but graphite or heavy water are used in other
designs. Neutron-absorbing "control rods", which can be inserted into the reactor core at will,
enable the reaction rate to be tweaked or shut down. Collisions between the fission products
and surrounding atoms generate heat, which is extracted by a coolant (water in the case of a
PWR) that circulates through the core and generates steam in a secondary circuit. The steam
drives a turbine and generator, which are connected up to the electricity grid.