Abstract: A device for controlling the power output of a core reactor and for turning ff the same, in which that portion of the device which contains absorber material comprises a first component in the form of absorber rods for turning off the core reactor which absorber rods are movable into the filling provided in the reflector of the reactor. That portion of the device which contains absorber material furthermore comprises a second component in the form of plates which serve for controlling the output of the core reactor and are displaceable in that chamber portion of the reflector which is defined by the top surface of the filling and by the reflector wall above the filling.

Abstract: A core reactor and method of operating same, according to which fuel elems, preferably of ball shape, are provided with an envelope of graphite and are passed in downward direction through reflector means of graphite which is simultaneously passed through by a heat transfer means and includes a ceiling reflector, a side reflector and a bottom reflector so that the fuel elements after once passing through the reactor core have reached the desired end burn-off conditions. Within or in the vicinity of that portion of the wall of the ceiling reflector and/or of the upper portion of the wall of the side reflector there are provided neutrons absorbing substances or additional substances reducing the speed of the neutrons.