Aspects of probabilistic risk assessment for nuclear safety in the Federal Republic of Germany

This paper discusses the current status of application and further development of probabilistic risk assessment (PRA) methodology in the Federal Republic of Germany. Referring to the experience obtained so far, especially to the insights gained from the German Risk Study, graduated levels for application of PRA methods are briefly described. Thereby the following items are pointed out: (a) the use of PRA to identify weak points in the systems and to evaluate plant system modifications; (b) evaluation of the database, identification and quantification of common-mode failures, human intervention, and (c) modelling of accident progression, description of core-melt sequences and containment response. In the second part of the paper, aspects concerning the assessment of risk and appropriate forms for setting up quantitative safety goals are considered. Although this topic is still under discussion the paper examines the possibility for quantitative criteria which can give guidance for further improvement of safety features. Two approaches are outlined briefly: (a) a plant-oriented engineering approach considering graduated levels of safety requirements, and (b) a risk criterion, setting limits to frequencies of dose commitments with respect to the individual mortality risk. (author)