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# Considerations for Estimating Site-Specific Probable Maximum Precipitation at Nuclear Power Plants in the United States of America: Final Report (NUREG/KM-0015, ORNL/SPR-2021/1375)

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## Publication Information

**Manuscript Completed:** September 2021**Date Published:** September 2021

**Prepared by:**S.T. DeNeale, S.-C. Kao, and D.B. WatsonOak Ridge National LaboratoryOak Ridge, TN 37831-6038

K.R. QuinlanU.S. Nuclear Regulatory CommissionWashington, DC 20555-0001Office of Nuclear Reactor Regulation

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## Abstract

As a result of advances in data and methodology, the U.S. Nuclear Regulatory Commission (NRC) has reviewed many studies pertaining to site-specific probable maximum precipitation (SSPMP) calculated at U.S. nuclear power plants. As described in NRC guidance and hazard assessment-related documents (e.g., Regulatory Guide 1.59;1 NUREG-0800,2 NUREG/CR-70463), the NRC guides its licensees to use the National Oceanic and Atmospheric Administration's (NOAA's) hydrometeorological reports as an acceptable resource for the probable maximum precipitation estimates used to evaluate the design-basis flood for nuclear power plants. This NUREG/KM summarizes the knowledge the NRC staff has developed over the course of the reviews based on the similarities and differences between the methodologies.

The SSPMP estimates resulting from these studies were used as a critical hydrologic modeling input in multiple submittals by licensees, such as those responding to the NRC's letter of March 12, 2012, under Title 10 of the *Code of Federal Regulations* 50.54(f), requesting updated flooding hazard analyses for nuclear power plants.4 The estimates were also used in topical reports. Although the licensee's development and estimation of SSPMP studies generally followed processes similar to those described in the existing guidance, several different methods, data sources, assumptions, and procedures were used to obtain site-specific results other than those found using the NOAA hydrometeorological report methodology.

The purpose of this document is to help fulfill the NRC's goal of maintaining and preserving knowledge and deriving lessons learned from the recent flood hazard reevaluations at nuclear power plant sites performed in connection with the accident at the Fukushima Dai-ichi nuclear power plant in Japan. Specifically, this document (1) identifies terminologies, theories, methods, and lessons learned for SSPMP studies submitted to the NRC for review and (2) presents key considerations for developing and reviewing potential future SSPMP studies.

Although the NRC staff may suggest a course of action in this NUREG/KM publication, these suggestions are not legally binding, and the regulated community may use other approaches to satisfy regulatory requirements.

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1Regulatory Guide 1.59, “Design Basis Floods for Nuclear Power Plants,” Revision 2, August 1977 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML003740388).

2NUREG-0800, “Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition”, March 2007 (ADAMS Accession No. ML070810350).

3NUREG/CR-7046, “Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America,” November 2011 (ADAMS Accession No. ML11321A195).

4ADAMS Accession No. ML12053A340.

Page Last Reviewed/Updated Wednesday, September 22, 2021