[Federal Register Volume 86, Number 174 (Monday, September 13, 2021)]
[Notices]
[Pages 50913-50914]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-19636]


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NUCLEAR REGULATORY COMMISSION

[NRC-2020-0237]


Considerations for Estimating Site-Specific Probable Maximum 
Precipitation at Nuclear Power Plants in the United States of America

AGENCY: Nuclear Regulatory Commission.

ACTION: NUREG; issuance.

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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is issuing a 
knowledge management NUREG, NUREG/KM-0015, ``Considerations for 
Estimating Site-Specific Probable Maximum Precipitation at Nuclear 
Power Plants in the United States of America.'' The NRC staff and Oak 
Ridge National Laboratory have prepared a reference document 
summarizing recent lessons-learned in connection with a review of the 
site-specific probable maximum precipitation (SSPMP) estimates used by 
some nuclear power plant owners and operators in connection with a 
recent re-evaluation of external flooding at their respective project 
sites.

DATES: NUREG/KM-0015 is available on September 13, 2021.

ADDRESSES: Please refer to Docket ID NRC-2020-0237 when contacting the 
NRC about the availability of information regarding this document. You 
may obtain publicly available information related to this document 
using any of the following methods:
     Federal Rulemaking Website: Go to https://www.regulations.gov and search for Docket ID NRC-2020-0237. Address 
questions about Docket IDs in Regulations.gov to Stacy Schumann; 
telephone: 301-415-0624; email: [email protected]. For technical 
questions, contact the individual listed in the FOR FURTHER INFORMATION 
CONTACT section of this document.
     NRC's Agencywide Documents Access and Management System 
(ADAMS): You may obtain publicly available documents online in the 
ADAMS Public Documents collection at https://www.nrc.gov/reading-rm/adams.html. To begin the search, select ``Begin Web-based ADAMS 
Search.'' For problems with ADAMS, please contact the NRC's Public 
Document Room (PDR) reference staff at 1-800-397-4209, 301-415-4737, or 
by email to [email protected]. NUREG/KM-0015, ``Considerations for 
Estimating Site-Specific Probable Maximum Precipitation at Nuclear 
Power Plants in the United States of America'' is available in ADAMS 
under Accession No. ML21245A418.
     Attention: The PDR, where you may examine, and order 
copies of public documents, is currently closed. You may submit your 
request to the PDR via email at [email protected] or call 1-800-397-
4209 or 301-415-4737, between 8:00 a.m. and 4:00 p.m. (ET), Monday 
through Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Kevin Quinlan, Office of Nuclear 
Reactor Regulation, U.S. Nuclear Regulatory Commission, Washington, DC 
20555-0001; telephone: 301-415-6809, email: [email protected].

SUPPLEMENTARY INFORMATION:

I. Background

    By letter dated March 12, 2012, the NRC issued a request for 
information to all power reactor licensees and holders of construction 
permits in active or deferred status licensees to reevaluate seismic 
and external flooding for their sites against current Commission 
requirements and guidance. This request was made consistent with 
paragraph 50.54(f) of title of the Code of Federal Regulations (10 
CFR), ``Conditions of licenses.'' The request was issued in connection 
with implementing lessons-learned identified by the staff, and 
described in their Near-Term Task Force Report, following the 2011 
accident at the Fukushima Dai-ichi nuclear power plant. In connection 
with this request, owners and operators were to re-evaluate flood 
hazards at their respective sites using present-day methods and 
regulatory guidance used by the NRC staff when reviewing 10 CFR part 52 
applications for Early Site Permits and Combined Operating Licenses.
    In response to the staff's 2012 Sec.  50.54(f) information request, 
owners and licensees submitted about 60 external flood hazard re-
evaluation reports (FHRRs) corresponding to the operating fleet of 
power reactors. In the matter of the probable maximum precipitation 
(PMP) value used for some of the flood-hazard re-evaluations (primarily 
the estimation of local intense precipitation and riverine-based 
floods), current NRC guidance documents recommend the use of the PMP 
estimation methods described in a series of Hydrometeorological Reports 
(HMRs) developed by the National Oceanographic and Atmospheric 
Administration (NOAA). The PMP event itself is generally defined as the 
greatest depth of precipitation for a given duration meteorologically 
possible for a design watershed or a given storm area at a particular 
time of year. The estimated PMP over a particular watershed or basin 
results in a flood magnitude for which there is virtually no risk of 
exceeding. The challenge, however, is that HMR-derived PMP estimates 
are based on methodologies and data which have not been updated with 
rainfall and storm events which have occurred in the decades since the 
HMRs were last published.
    Upon review of the FHRRs, the staff found that about 26 project 
sites responding to the Sec.  50.54(f) information request submitted 
PMP estimates that were not based on NOAA HMRs but were developed by a 
commercial interest. As part of the FHRR process, the staff conducted 
an audit of the commercial vendor who developed the site-specific PMP 
estimates to better-understand the technical basis underlying the 
approach. In all cases, these SSPMP estimates were less than those 
obtained from the applicable HMR. Although the development and 
estimation of the SSPMP studies reviewed by the staff 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 HMR methodology.
    Based on the staff's Sec.  50.54(f) review experience and in 
anticipation of its continued use, this NUREG summarizes the lessons-
learned concerning the review and application of a SSPMP. To that end, 
this NUREG addresses the following topics:

 Storm Selection
 Storm Reconstruction
 Storm Transposition

[[Page 50914]]

 Storm Representative Dew Point Selection
 Precipitable Water Estimation
 Dew Point Climatology, Moisture Maximization, and Moisture 
Transposition
 Terrain Adjustment
 Envelopment and Probable Maximum Precipitation Determination
 Spatial and Temporal Distributions for SSPMP Applications

    This reference document describes the technical theory, data 
sources, and analysis methodology that could be used to derive a SSPMP 
estimate. Certain new terms are also introduced and defined. This 
reference document also identifies key technical (meteorological) 
considerations when reviewing a SSPMP estimate.
    To date, there is no clear NRC guidance on this topic or a commonly 
agreed-to approach on the estimation of SSPMP. As the staff may be 
reviewing additional SSPMP estimates in the future in connection with 
its regulatory responsibilities, it was decided to elicit stakeholder 
views on the matters and approaches discussed in this draft document.
    This document contains no regulatory guidance or regulatory 
positions.
    A request for comments on draft NUREG/KM-0015, (ADAMS Accession No. 
ML20356A293) was published in the Federal Register on December 29, 2020 
(85 FR 85683), with a 60-day comment period ending on March 1, 2021. 
Comments received on NUREG/KM-0015 can be found on the Federal 
Rulemaking website (https://www.regulations.gov) under Docket ID NRC-
2020-0237.

II. Knowledge Management

    Since its inception, the Atomic Energy Commission and its 
successor, the NRC, have focused on preserving the (explicit) 
documentary record of its decision-making in the form of NUREGs, SECY 
Papers, Regulatory Guides, and other documents. However, in 2006, the 
agency recognized that there was a need to engage in a more-formal 
program of knowledge management that also reflects the less-tangible 
(implicit) human capital aspect of the agencies' knowledge base. This 
feature was particularly important as the agency enters its fifth 
decade of operation--a period characterized by an increasing number of 
retirements among long-serving staff involved in many of the agencies' 
early regulatory programs and associated licensing actions. Staff 
efforts thus far in preserving this legacy of experience that describe 
important historical events, facts, and research that were instrumental 
in shaping NRC's regulatory programs, can be found at https://www.nrc.gov/reading-rm/doc-collections/nuregs/knowledge/.
    The purpose of this knowledge management NUREG (or NUREG/KM) is 
intended to satisfy an NRC goal of maintaining and preserving knowledge 
concerning the lessons-learned from the recent flood hazard re-
evaluations at current and planned nuclear power plant sites performed 
most recently in connection with the staff 2012 Sec.  50.54(f) reviews.

    Dated: September 8, 2021.

    For the Nuclear Regulatory Commission.
Luissette Candelario-Quintana,
Project Manager, External Hazards Branch, Division of Engineering and 
External Hazards, Office of Nuclear Reactor Regulation.
[FR Doc. 2021-19636 Filed 9-10-21; 8:45 am]
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