Two types of nuclear reactor are in use in Germany's nuclear power plants: pressurized-water reactors (PWRs) and boiling-water reactors (LWRs). Both types of reactor use water both as a coolant and as a moderator.


Pressurized-water reactor

In pressurized-water reactors the water in the primary cooling circuit absorbs the heat released by nuclear fission. This circuit is pressurized to prevent the water from boiling. The primary cooling circuit transfers the heat generated in the reactor to the steam generators, which are connected to the water-steam circuit (secondary circuit). The steam generators form a barrier between the primary circuit and the secondary circuit, thereby preventing radioactive material from escaping from the primary circuit.

Boiling-water reactor

In boiling-water reactors, the pressure is set so that some of the water evaporates while flowing through the reactor core. The resulting steam is separated off and fed directly through to the turbines, which are coupled to the generator. Boiling-water reactors differ from pressurized-water reactors in that the steam produced by the former is slightly radioactive. Consequently, it is possible for radioactive deposits to build up in the steam lines, turbines, condenser and condensate lines. For this reason special safety facilities are installed in the turbine rooms of boiling-water reactors.