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Guidance on the Treatment of Uncertainties Associated with PRAs in Risk-Informed Decision Making (NUREG-1855)- Draft Report For CommentOn this page: Download complete document The following links on this page are to documents in Adobe Portable Document Format (PDF). See our Plugins, Viewers, and Other Tools page for more information. For successful viewing of PDF documents on our site please be sure to use the latest version of Adobe. Publication InformationManuscript Completed: November 2007 Prepared by: Other Contributors: 3Brookhaven National Laboratory Upton, NY 11973 4Sandia National Laboratories Albuquerque, NM 87185 M. Drouin, NRC Project Manager 1Office of Nuclear Regulatory Research AbstractThis document provides guidance on how to treat uncertainties associated with probabilistic risk assessment (PRA) in risk-informed decision making. The objectives of this guidance include fostering an understanding of the uncertainties associated with PRA, the impact of the uncertainties on the results of the PRA, and the uncertainties in the context of the decision making. The guidance in this document focuses on the use of PRA insights and results and ways to address the associated uncertainties. Consequently, the scope of the guidance contained in this report is limited to addressing the uncertainties associated with the use of the results of risk models. In implementing risk-informed decision making, the US Nuclear Regulatory Commission expects that appropriate consideration of uncertainty will be given in analyses and interpretation of findings. Such consideration should include using a program of monitoring, feedback, and corrective action to address significant uncertainties. To meet this objective, it is necessary to understand the role that PRA results play in the context of the decision process. Defining the context includes providing an overview of the risk-informed decision making process itself. With the context defined, the characteristics of a risk model and, in particular, a PRA need to be understood. This understanding includes a recognition of the different forms of uncertainty which include aleatory and epistemic. A PRA, as a probabilistic model already characterizes aleatory uncertainty. The focus of this document is epistemic uncertainty. Therefore, guidance is given on identifying and describing the different types of sources of epistemic uncertainty including the different ways that they are treated. The different types of epistemic uncertainty include parameter, model, and completeness uncertainties. The final part of the guidance includes addressing the uncertainty in PRA results in the context of risk-informed decision making and, in particular, the interpretation of the results of the uncertainty analysis when comparing PRA results with the acceptance criteria established for a specified application. In addition, guidance is provided for addressing the other elements contributing to completeness uncertainty in risk-informed decision making (e.g., unknown phenomena that have not been recognized or factors that have been identified but for which there is no agreed on method for addressing them in PRAs). |
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