Guidance for the Definition and Application of Probabilistic Safety Criteria

Safety goals are defined in different ways in different countries and also used differently. Many countries are presently developing them in connection to the transfer to risk-informed regulation of both operating nuclear power plants (NPP) and new designs. However, it is far from self-evident how probabilistic safety criteria should be defined and used. On one hand, experience indicates that safety goals are valuable tools for the interpretation of results from a probabilistic safety assessment (PSA), and they tend to enhance the quality and realism of a risk assessment. On the other hand, strict use of probabilistic criteria is usually avoided, due to the large number of different uncertainties in a PSA model. This report aims at providing general guidance concerning the formulation, application and interpretation of probabilistic criteria based on work carried in the Nordic project "The Validity of Safety Goals" and a survey on PSA safety criteria which was initiated in 2006 within the OECD/NEA Working Group Risk.