The steam which drives the steam turbine is generated by heating water.
In a nuclear power plant, the conventional steam boiler is replaced by a steam generator.
This is a heat exchanger in which two water circuits meet each other: hot water under extremely high pressure in the primary circuit leaves the reactor and flows through thousands of U-shaped heat conducting tubes.
Depending on the reactor power, two, three or four steam generators are provided. Together with the reactor, they are installed in the hermetically-sealed doubled-walled reactor building.
How does a steam generator operate ?
A steam generator is a cylindrical reservoir containing approximately 5.000 inverted U-shaped pipes. The hot water in the primary circuit, coming from the reactor, circulates through the steam generator pipes. The water in the secondary circuit flows along the outside of the tube bundle. When it comes into contact with the heated pipes, the secondary circuit water starts boiling and is converted in steam.
Therefore, the water and steam in the secondary circuit do not come into contact with the primary water from the reactor which absorbs the heat from the fuel rods. In this manner the steam generator acts as an additional safety barrier between the nuclear reactor and the outside world.
|2.||Secondary moisture separator|
|5.||Primary moisture separator|
|9.||Feed water inlet|
|12.||Reactor coolant outlet|
|13.||Reactor coolant inlet|