On an AGR nuclear power station boilers sit within the concrete outer layer of the reactor. This means that they cannot be replaced, so a lot of effort goes into maintaining them and ensuring they continue to do their jobs throughout the life of the power station.
At the bottom of each boiler, large gas circulators pump high-pressure carbon dioxide gas through the graphite core and up through the fuel channels, where the gas picks up the heat generated by the nuclear reaction. As it passes through the boiler, the gas gives up its heat to the water in the boiler tubes. This forms superheated high-pressure steam which is piped away to drive the turbines.
The boilers operate at very high temperatures and require an extensive and careful monitoring and maintenance regime to ensure that they are operating efficiently. Each site has teams of highly trained engineers who are responsible for their maintenance and operations.
Alongside normal maintenance work, a pro-active programme of detailed technical assessments, modelling and inspection is carried out, backed up by significant investment. The programme will continue through the lifetime of the stations to ensure the boilers operate reliably.
Our Sizewell B station, a Pressurised Water Reactor, has a different arrangement using steam generators. This heats water in thousands of tubes, creating very hot steam which then turns the turbines.