Structured Hazard Assessment Committee Process for Flooding (SHAC-F) for Local Intense Precipitation, Riverine, and Coastal Flooding (NUREG/CR-7292)

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Publication Information

Manuscript Completed: September 2021
Date Published: March 2026

Prepared by:
R. Prasad, N.C. Nadal-Caraballo, P.D. Meyer,
V.M. Gonzalez, and K.J. Coppersmith

Pacific Northwest National Laboratory
P.O. Box 999
Richland, Washington 99352

Joseph F. Kanney, NRC Project Manager

Prepared for:
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, D.C. 20555

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Abstract

This report describes the Structured Hazard Assessment Committee Process for Flooding (SHAC-F). The process was developed to enable users to perform probabilistic flood hazard assessments (PFHAs) in a consistent, transparent, and reproducible manner. Concepts and principles from the Senior Seismic Hazard Analysis Committee (SSHAC) process, which is widely used to perform probabilistic seismic hazard analyses for nuclear power plants (NPPs), were adapted for performing the PFHAs. This report focuses on three flooding mechanisms: (1) site-scale flooding from local intense precipitation (LIP), (2) riverine flooding, and (3) coastal flooding from storm surges.

The SHAC-F approach is delineated using three study levels that support a range of NPP oversight, permitting, and licensing activities—from least to most complex. The level of SHAC-F Study complexity increases to match that of the U.S. Nuclear Regulatory Commission (NRC) reviews. SHAC-F studies are sponsored by an agency or entity (or a group) that has a need to perform a PFHA for specific NPP safety review needs. A Level 1 SHAC-F Study is expected to be a rapid assessment supported by a small group of analysts and reviewers. A Level 2 SHAC-F Study is expected to be performed by a larger group of analysts and reviewers commensurate with the scope of the replacement or update and/or refinement of an existing or an initial analysis. A Level 3 SHAC-F Study, the most detailed one, is expected to be performed by a larger group of analysts, Resource Experts, Proponent Experts, computational experts, and an appropriately sized review group. Regardless of the level at which a SHAC-F Study is performed, the hazard assessment must include a comprehensive treatment of uncertainty. The information provided here is expected to assist both the NPP permittees and licensees in performing and the NRC staff in reviewing PFHAs that are consistent, transparent, reproducible, and commensurate with the safety significance of the risk-informed decisions that they support.

This report (1) describes the purpose and scope of the work performed while developing SHAC-F; (2) provides background information about and a description of the approaches for performing PFHAs; (3) describes the frequency analysis and process-model simulation approaches for estimating flood hazard curves; (4) describes how aleatory variabilities and epistemic uncertainties can be treated; (5) delineates the three levels of SHAC-F studies; (6) describes key SHAC-F concepts, study participants’ roles and responsibilities, and essential study steps; and (7) describes the SHAC-F studies for LIP flooding, riverine flooding, and coastal flooding from storm surges.