[en] As the chimney does not belong to the higher-safety-class structures of a nuclear power plant, it is normally not designed for such extreme loading conditions as the safe-shutdown earthquake and the aircraft impact. Nevertheless, the behaviour of the chimney for these loads has to be investigated, as a possible collapse onto adjacent safety-relevant structures (reactor building, reactor auxiliary building, fuel-handling building) may significantly influence the design of these structures and of the equipment in them. The loading cases which might cause a collapse are outlined. The mathematical models used to calculate the highly physically and geometrically non-linear behaviour are described. The resulting response of the structures subjected to impact is determined and compared to that caused by other external extreme loading conditions. The safe-shutdown earthquake is represented by an artificially generated time history which fits a specified design-response spectrum. For preliminary calculations the response for simple sine wave excitation is determined. The ground acceleration at which collapse first occurs is calculated for different soil parameters and dimensions of the chimney. As an additional loading case, the direct impact of an aircraft or its freely flying debris on the chimney is investigated approximately. For different locations of impact, the impulse causing collapse is established. Under normal circumstances, debris such as engines can hardly lead to a collapse of the entire chimney. Overall consideration of the balance of energy and of impulse as well as detailed solutions of the resulting differential equations of motion are performed. (Auth.)