Risk Metrics and Measures for an Extended PSA

This report provides a review of the main used risk measures for Level 1 and Level 2 PSA. It depicts their advantages, limitations and disadvantages and develops some more precise risk measures relevant for extended PSAs and helpful for decision-making. This report does not recommend or suggest any quantitative value for the risk measures. It does not discuss in details decision-making based on PSA results neither. The choice of one appropriate risk measure or a set of risk measures depends on the decision making approach as well as on the issue to be decided. The general approach for decision making aims at a multi-attribute approach. This can include the use of several risk measures as appropriate. Section 5 provides some recommendations on the main risk metrics to be used for an extended PSA. For Level 1 PSA, Fuel Damage Frequency and Radionuclide Mobilization Frequency are recommended. For Level 2 PSA, the characterization of loss of containment function and a total risk measure based on the aggregated activity releases of all sequences rated by their frequencies is proposed. (authors)