[Federal Register Volume 85, Number 249 (Tuesday, December 29, 2020)]
[Pages 85683-85685]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2020-28708]




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

AGENCY: Nuclear Regulatory Commission.

ACTION: Draft NUREG; request for comment.


SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is issuing for 
public comment a draft NUREG, 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: Submit comments by March 1, 2021. Comments received after this 
date will be considered if it is practical to do so, but the Commission 
is able to ensure consideration only for comments received before this 

[[Page 85684]]

ADDRESSES: You may submit comments by any of the following methods; 
however, the NRC encourages electronic comment submission through the 
Federal Rulemaking website:
     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 Jennifer Borges; 
telephone: 301-287-9127; email: [email protected]. For technical 
questions, contact the individual listed in the FOR FURTHER INFORMATION 
CONTACT section of this document.
     Mail comments to: Office of Administration, Mail Stop: 
TWFN-7-A60M, U.S. Nuclear Regulatory Commission, Washington, DC 20555-
0001, ATTN: Program Management, Announcements and Editing Staff.
    For additional direction on obtaining information and submitting 
comments, see ``Obtaining Information and Submitting Comments'' in the 
SUPPLEMENTARY INFORMATION section of this document.

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].


I. Obtaining Information and Submitting Comments

A. Obtaining Information

    Please refer to Docket ID NRC-2020-0237 when contacting the NRC 
about the availability of information for this action. You may obtain 
publicly available information related to this action by any of the 
following methods:
     Federal Rulemaking Website: Go to https://www.regulations.gov and search for Docket ID NRC-2020-0237.
     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, at 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. ML20356A293.
     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 
between 8:00 a.m. and 4:00 p.m. (EST), Monday through Friday, except 
Federal holidays.

B. Submitting Comments

    The NRC encourages electronic comment submission through the 
Federal Rulemaking website (https://www.regulations.gov). Please 
include Docket ID NRC-2020-0237 in your comment submission.
    The NRC cautions you not to include identifying or contact 
information that you do not want to be publicly disclosed in your 
comment submission. The NRC will post all comment submissions at 
https://www.regulations.gov as well as enter the comment submissions 
into ADAMS. The NRC does not routinely edit comment submissions to 
remove identifying or contact information.
    If you are requesting or aggregating comments from other persons 
for submission to the NRC, then you should inform those persons not to 
include identifying or contact information that they do not want to be 
publicly disclosed in their comment submission. Your request should 
state that the NRC does not routinely edit comment submissions to 
remove such information before making the comment submissions available 
to the public or entering the comment into ADAMS.

II. 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 
section 50.54(f)--``Conditions of Licenses''--of the Commission's 
regulations found at part 50 of title of the Code of Federal 
Regulations (10 CFR). 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
 Storm Representative Dew Point Selection

[[Page 85685]]

 Precipitable Water Estimation
 Dew Point Climatology, Moisture Maximization, and Moisture 
 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 

III. 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: December 22, 2020.

    For the Nuclear Regulatory Commission.
Luissette Candelario,
Project Manager, External Hazards Branch, Division of Engineering and 
External Hazards, Office of Nuclear Reactor Regulation.
[FR Doc. 2020-28708 Filed 12-28-20; 8:45 am]