[en] Nuclear power plants are under permanent supervision by the government regulatory authorities. This supervision covers the phases of planning, construction, operation, and decommissioning as well as any plant modifications and changes in its mode of operation, and extends to all safety-related aspects. The German Advisory Committee on Reactor Safeguards (RSK) and the competent Federal Ministry for the Environment, Nature Conservation, and Nuclear Safety (BMU) recommended in the late eighties to have a supplementary safety review of nuclear power plants conducted roughly every ten years. The PSR Working Party of the Federal States Committee on Atomic Energy established guidelines for a standardized nationwide execution of periodic safety reviews (PSR) on the basis of hearings involving plant operators and expert consultants. From the official point of view, PSR serve to advance the safety status of a nuclear plant by analyzing the actual state of technical safety and the mode of plant operation in a holistic stocktaking exercise assessing all the findings made. Accordingly, guidelines containing the objectives, requirements, and the scope of PSR have been compiled for these areas: 'Basic Principles of Periodic Safety Reviews of Nuclear Power Plants', 'Safety Status Analysis', 'Probabilistic Safety Analysis', and 'Deterministic Safety Analysis'. For the time being there is no legal obligation to conduct PSR; however, this requirement is to be incorporated in the 10th amendment to the German Atomic Energy Act now under preparation. A PSR for the Obrigheim Nuclear Power Station was completed in 1998; activities for another six nuclear power plants are under way or being prepared. (orig.)