About nuclear power
How does it work?
The heart of a nuclear power plant is the nuclear reactor. The most common type is the Pressurised Water Reactor (PWR). Inside a very strong pressure vessel is an array of fuel assemblies containing uranium rods enriched to about 4 percent U 235, each rod clad in zircaloy sheathing. The reactor contains water, at high pressure to prevent boiling, and also neutron absorbing control rods. The fuel array can be made to produce a nuclear chain reaction, in which U235 nuclei fission or split, releasing heat which is transferred to the water which is circulated to an external circuit. Here heat is transferred to a secondary water circuit where steam is produced which feeds a steam turbine/generator. The reactor power output is controlled by the control rods and also soluble boron poisoning. When loaded with fresh fuel the reactor has excess reactivity which is controlled by these means, during operation the fuel is gradually used up and eventually, at intervals of roughly 2 years, it has to be shutdown for fresh fuel to be loaded in place of spent fuel.
There are other types of reactor, including gas cooled ones, but the PWR is now established as the type most often built, from experience of cost and reliability.
