Process for shutting down and controlling gas cooled nuclear reactors

The gas cooled 1000 MWe output pebble bed reactor has three independent control systems with absorber rods. One is used for complete and longterm shutdown, where the absorber rods are driven into the pebble bed. The second provides absorber rods, which are used for fast load changes and fine control and which can be lowered into the side reflector. The third control system also uses absorber rods, which consist of boron steel of Y-shape crossection and can be moved up and down in the space between the pebble bed and the top reflector and through the latter. They are used for partial of 'scram'shutdown, for increasing load from part load to full load or vice versa. These three control systems render the introduction of absorbing gas unnecessary and the sude reflector is protected against too high a dose of fast neutrons. (DG)