Dealing with Uncertainty Rising Out of Probabilistic Risk Assessment

This report addresses one aspect of how probabilistic risk assessment (PRA) studies should be integrated into the regulatory process. Intended for use by the Nuclear Regulatory Commission staff, it looks specifically at how uncertainty in risk estimates is to be factored into regulatory decisionmaking. Section II defines "confidence in risk" — a simple measure of the degree to which a goal or regulation is likely to be met. In Section III the authors apply the confidence in risk measure to some selected nonnuclear technologies. Section IV examines some PRAs for the Zion and Indian Point nuclear power plants; compares the estimated risks to proposed safety goals; and applies the confidence in risk measure to the frequency of core melt, and the societal risk in terms of acute or prompt deaths and latent (cancer) deaths. Section V develops some decision rules for dealing with uncertainty. Finally, some recommendations regarding the implementation of the findings are offered.