Proposed Revisions to Standard Review Plan Section 2.4.6, Tsunami Hazards; Section 2.4.9, Channel Migration or Diversion; and Section 2.3.3, Onsite Meteorological Measurements Program, 49132-49138 [2018-21140]

Agencies

• NUCLEAR REGULATORY COMMISSION

[Federal Register Volume 83, Number 189 (Friday, September 28, 2018)]
[Notices]
[Pages 49132-49138]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-21140]


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NUCLEAR REGULATORY COMMISSION

[NRC-2018-0176]


Proposed Revisions to Standard Review Plan Section 2.4.6, Tsunami 
Hazards; Section 2.4.9, Channel Migration or Diversion; and Section 
2.3.3, Onsite Meteorological Measurements Program

AGENCY: Nuclear Regulatory Commission.

[[Page 49133]]


ACTION: Standard review plan-draft section revision; request for 
comment.

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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is soliciting 
public comment on proposed updates to NUREG-0800, ``Standard Review 
Plan for the Review of Safety Analysis Reports for Nuclear Power 
Plants: LWR Edition'' (or SRP). The staff is proposing changes to a 
select number of sections of SRP Chapter 2 taking into account some of 
the lessons-learned from the flooding hazard re-evaluations performed 
by the operating power reactor fleet. Specific changes are being 
proposed to Section 2.4.6, ``Tsunami Hazards''; Section 2.4.9, 
``Channel Migration or Diversion''; and Section 2.3.3, ``Onsite 
Meteorological Measurements Program''.

DATES: Comments must be filed no later than October 29, 2018. 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 on or before this date.

ADDRESSES: You may submit comments by any of the following methods:
     Federal Rulemaking website: Go to https://www.regulations.gov and search for Docket ID NRC-2018-0176. Address 
questions about NRC dockets to Jennifer Borges; telephone: 301-287-
9127; email: [email protected]. For technical questions, contact 
the individual(s) listed in the FOR FURTHER INFORMATION CONTACT section 
of this document.
     Mail comments to: May Ma, Office of Administration, Mail 
Stop: TWFN-7-A60M, U.S. Nuclear Regulatory Commission, Washington, DC 
20555-0001.
    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: Mark D. Notich, Office of New 
Reactors, telephone: 301-415-3053; email: [email protected]; U.S. 
Nuclear Regulatory Commission, Washington DC 20555-0001.

SUPPLEMENTARY INFORMATION: 

I. Obtaining Information and Submitting Comments

A. Obtaining Information

    Please refer to Docket ID NRC-2018-0176 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-2018-0176.
     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]. For the convenience of the reader, 
instructions about obtaining materials referenced in this document are 
provided in the ``Availability of Documents'' section.
     NRC's PDR: You may examine and purchase copies of public 
documents at the NRC's PDR, Room O1-F21, One White Flint North, 11555 
Rockville Pike, Rockville, Maryland 20852.

B. Submitting Comments

    Please include Docket ID NRC-2018-0176 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

    In connection with the current update to the SRP hydrology chapter, 
the staff is proposing to place greater emphasis on reviewing the 
flood-causing mechanism (or mechanisms) consequential to defining the 
site characteristic for flooding. Consistent with the Commission's 
policy approach to risk-informed regulation, the updates the staff is 
proposing will support a simplified review by staff of flood-causing 
mechanisms determined to not pose a threat to the safe operation of a 
nuclear power plant. The staff proposes making additional revisions to 
some of the remaining SRP sections in Chapters 2.3 and 2.4 in the next 
fiscal year. The scope of these revisions and a timetable for updates 
would be discussed at a public meeting later this calendar year. In 
addition, the staff is looking to apply the type of risk-informed 
approach used in the SRP Sections 2.3 and 2.4 in other SRP sections in 
the future. Additional meetings will be scheduled in FY19 to discuss 
specific revisions to the remaining SRP sections in Chapters 2.3, 2.4, 
and/or other SRP sections. The current update cycle for NRC's SRP 
Chapter 2.4 on hydrology coincides with the NRC staff's recent 
completion of its reviews of section 50.54(f) of title 10 of the Code 
of Federal Regulations (10 CFR), flooding hazard re-evaluations 
performed by the operating power reactor fleet in response to the 
Fukushima--Dai-ichi nuclear power plant accident. A key focus of the 
flood hazard re-evaluations was to determine whether the current design 
basis flood elevation had been exceeded based on the hazard re-
evaluations. The flood-causing mechanisms examined in connection with 
the flood hazard re-evaluations correspond implicitly to review areas 
currently found in Chapter 2.4 of the SRP for license applications to 
construct new nuclear power plants. The flood-causing mechanisms that 
were examined either alone or in combination included:

1. Local Intense Precipitation and Associated Drainage
2. Streams and Rivers
3. Failure of Dams and Onsite Water Control/Storage Structures
4. Storm Surge
5. Seiche
6. Tsunami
7. Ice-Induced
8. Channel Migrations or Diversions

    In its March 12, 2012, 10 CFR 50.54(f) letter to operating reactor 
licensees\1\, the NRC staff requested that licensees reevaluate all 
flood-causing hazards for their respective sites using present-day 
methods and regulatory guidance used by the NRC staff when reviewing 
applications for early site permits (ESPs) and combined licenses 
(COLs). In connection with those flood hazard re-evaluations, licensees 
were to address information on the flood event duration associated with 
the respective flood hazards, which included warning times necessary to 
take preventive measures, the expected duration of site

[[Page 49134]]

inundation, and flood recession times until unimpeded site access could 
be restored. Licensees were also to estimate the effects associated 
with the respective consequential flood-causing mechanisms being 
investigated, such as hydrostatic and hydrodynamic loads, water 
velocities, potential for erosion, and other parameters. In response to 
the March 12, 2012, 10 CFR 50.54(f) flood information request, hazard 
re-evaluations at approximately 60 operating reactor sites were 
submitted by licensees. In most cases, licensees reported that local 
intense precipitation (LIP) in addition to one or more other flood-
causing mechanisms could be consequential enough to exceed the level 
(water surface elevation) of the current design basis flood. Following 
a review of the information provided, the staff identified which flood-
causing mechanisms were consequential for defining, and in some cases 
redefining, the design basis flood for each of the operating nuclear 
power plants covered by the 10 CFR 50.54(f) flooding reviews.\2\
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    \1\ Letter from Michael R. Johnson, Director, Office of New 
Reactors, to All Power Reactor Licensees and Holders of Construction 
Permits in Active or Deferred Status, March 12, 2012 (ADAMS 
Accession No. ML12053A340).
    \2\ In parallel with the March 12, 2012, 10 CFR 50.54(f) 
flooding request, the NRC staff were also in the process of 
reviewing a handful of ESPs and COLs for new operating power 
reactors. In connection with those reviews, the licensees also 
evaluated the potential for flooding consistent with guidance found 
in the SRP.
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    The staff is now proposing changes to Chapter 2.4 of the SRP taking 
into account some of the lessons-learned from the 10 CFR 50.54(f) 
flooding reevaluation reviews as well as the ESP/COL reviews. For 
example, where simplified analytical (manual) solutions were performed 
decades ago and prior to the widespread availability of digital 
computers, licensees are now relying on more-detailed numerical models 
to perform these very same calculations. It was also learned that 
licensees made extensive use of geo-spatial databases in connection 
with those computer simulations. Through these efforts, many of the 
licensees submitted flood inundation maps for the first time comparing 
the elevations of the power plant site and as-built structures with the 
water surface elevations produced by the respective flood-causing 
mechanisms.
    Another key lesson-learned was that a majority of the sites had 
multiple re-evaluated flooding hazards in excess of the design basis 
previously used in licensing. In particular, the majority of the 
exceedances were associated with LIP, which was a flooding hazard not 
generally evaluated as part of the original design basis for several of 
the operating-reactor sites. Previously, it was assumed that the 
consequences of LIP would be addressed by a combination of site grading 
and some type of storm water management system integrated into the 
site's drainage design. In many cases it was found that earlier design 
decisions underestimated the effects of LIP and associated drainage on 
structures, systems, and components (SSCs) important to safety. 
Consequently, the staff intends to propose that one of the current SRP 
chapters be repurposed (SRP Section 2.4.2--``Floods'') to specifically 
focus on evaluating the effects of LIP and associated site drainage.

III. Discussion of Update Rationale by SRP Section

    In the past the Commission has adopted the concept of the 
``probable maximum event'' when estimating the design bases for nuclear 
power plants. The probable maximum event, which is determined by 
accounting for the physical limits of a natural phenomenon, is 
considered to be the most severe event reasonably (physically) possible 
at the location of interest and is thought to exceed the severity of 
all historically-observed events. The concept of ``probable maximum 
event'' is consistent with General Design Criterion (GDC) 2 of Appendix 
A (``General Design Criteria for Nuclear Power Plants'') to CFR part 50 
(``Domestic Licensing of Production And Utilization Facilities'') which 
requires that nuclear power plant SSCs important to safety be designed 
to withstand the most severe effects of natural phenomena such as 
earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches 
without loss of capability to perform their intended safety functions.
    The Commission's reactor siting criteria at 10 CFR 100.20(c)(3) 
calls for the estimation of the ``. . . maximum probable flood [PMF] . 
. . using historical data.'' Floods (or flooding), corresponding to the 
hypothetical PMF, is thus one of the site characteristics \3\ to be 
evaluated in the context of GDC 2. Historically, the PMF at a nuclear 
power plant has been estimated based on some plausible maximum water 
surface elevation that would occur across the footprint of the power 
plant site in relation to the elevations of SSCs important to safety. 
As noted below, the staff is now proposing to expand the flood hazard 
definition to more explicitly address what is meant by associated 
flooding effects and the flood event duration.
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    \3\ Section 52.1(a) defines site characteristics ``. . . as the 
actual physical, environmental and demographic features of a site. 
Site characteristics are specified in an early site permit or in a 
final safety analysis report for a combined license. Site 
characteristics are specified in an early site permit or in a final 
safety analysis report for a combined operating license.'' (63 FR 
1897) The staff considers the identification of flooding hazards, 
such as tsunamis, as one of the physical features of the site to be 
described in an ESP or COL.
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    The focus of the hydrology reviews in Chapter 2.4 has always been 
to review and assess applications for the potential flood elevations at 
the site for the purposes of designing SSCs important to safety. Having 
reviewed the various flood-causing mechanisms listed in Chapter 2.4, 
applicants for new power reactors have historically selected the flood-
causing mechanism (or mechanisms) consequential to defining the flood 
elevation site characteristic. The results of that decision-making by 
the applicant were documented in the Safety Analysis Report (SAR). In 
many cases, the SAR documentation would be extensive, irrespective of 
whether the flooding hazard in question was consequential to defining 
the site characteristic flood. The staff observed that licensees still 
adhered to this practice in their responses to the staff's recent 10 
CFR 50.54(f) flood reevaluation request.
    In connection with the current update to the SRP hydrology chapter, 
the staff has decided to place greater emphasis in its SER on reviewing 
the flood-causing mechanism (or mechanisms) consequential to defining 
the site characteristic for flooding. In August 1995, the Commission 
issued a Policy Statement concerning the use of probabilistic risk 
assessment (PRA) methods. In that Policy Statement, the Commission 
stated that the use of those methods should be ``. . . increased to the 
extent supported by the state of the art in PRA methods and data, and 
in a manner that complements the NRC's deterministic approach and 
supports the NRC's traditional defense-in-depth philosophy. . . .'' (60 
FR 42628). Consistent with the Commission's policy, the staff is now 
proposing to simplify the SER review requirements by focusing on those 
flood-causing mechanisms determined to pose a threat to the safe 
operation of a nuclear power plant. In conducting its review of the 10 
CFR 50.54(f) flood hazard re-evaluations submitted by licensees, the 
staff found that consequences (location, magnitude, duration, timing) 
of a flooding event within the reactor powerblock could vary depending 
on the particular flood-causing mechanism under consideration. In light 
of this observation, it is now being proposed that only those 
mechanisms producing a consequential flood (defined in the appendix 
included in this document) at the site in question would be reviewed in 
detail in the SER. Under this

[[Page 49135]]

proposal, applicants would still be required to perform their due 
diligence and evaluate all flood-causing mechanisms described in the 
SRP against GDC 2. However, only those flood-causing mechanisms found 
to be instrumental in identifying consequential flooding at a site 
would be subject to a detailed regulatory review in the SER.
    In identifying consequential flooding, the staff would review and 
assess flood inundation and topographic maps for those consequential 
flood-causing mechanisms, if available. The staff's review would focus 
primarily on the flood-causing mechanism (or mechanisms) found to be 
consequential for the purposes of defining the site characteristic 
flood elevations. Similarly, the detailed discussion contained in the 
SER would focus primarily on those identified consequential flood-
causing mechanisms, including LIP. With this change in emphasis, the 
SER discussions for those inconsequential flood-causing mechanisms 
would not need to be fully developed because they are not relevant to 
defining the site characteristic flood elevations. The only exception 
to this proposal is LIP. As mentioned above, LIP occurs at all reactor 
sites, and in many cases was found to exceed the current design basis 
as part of the recent 10 CFR 50.54(f) flood reevaluation request.
Generic Flooding Changes Proposed to SRP Chapter 2.4
    There are several areas for which the staff seeks public comment on 
the generic changes now being proposed to Chapter 2.4 of the SRP. To 
determine the bounding flood causing mechanism consequential to 
defining the site characteristic flood, the staff will review and 
assess which flood-causing mechanisms are physically plausible and 
capable of inundating SSCs important to safety at the site. For some 
sites, based on the physical geography, certain flood-causing 
mechanisms may be eliminated from consideration by virtue of being 
located at inland locations well away from large bodies of water such 
as an ocean or large lake. Such sites would not be expected to be 
threatened by the effects of storm surge or tsunamis of marine origin. 
Still other sites might be located in Mediterranean or Subtropical 
climatic settings for which average daily temperatures do not drop 
below the freezing point of water and thus may not be susceptible to 
ice effects. Lastly, some sites might be located adjacent to large 
inland lakes or the open coast for which there is an absence of rivers 
or streams; such sites can be expected to be free from flooding due to 
riverine-based events. Hence, the need for water surface elevation 
estimates within the reactor powerblock due to these flooding 
mechanisms would be obviated. However, there could be a scenario in 
which a proposed reactor site might be vulnerable to flooding by 
multiple scenarios; for example, a site located in a watershed occupied 
by multiple upstream dams of different impoundment volumes and 
distances from the reactor site. The timing and sequencing of the 
failure of any of these dams could result in significantly different 
inundation depths at the site in question. As a result, all potential 
flooding scenarios need to be examined and considered in detail to 
calculate the site's inundation map, associated effects, and flood 
event duration for those consequential (bounding) flood-causing 
mechanisms.
    As illustrated by the examples described above, the staff's 
proposed detailed review of the hydrology portion of the application 
would focus primarily only on those flood-causing mechanisms, including 
LIP, which could result in consequential flooding at a reactor site. 
Under such an approach, the staff may also need to review multiple 
scenarios for the same flood-causing mechanism to determine which 
scenario is the bounding flooding event. The staff intends to review 
and assess inundation maps to assure that they are prepared consistent 
with Federal standards for inundation mapping, such as the Federal 
Emergency Management Agency (FEMA) Publication 64-P, entitled ``Federal 
Guidelines for Dam Safety: Emergency Action Planning for Dams'' \4\.
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    \4\ Available on-line at https://www.fema.gov/technical-manuals-and-guides.
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    The staff also proposes to expand the flood hazard PMF definition 
to include associated flooding effects and the flood event duration and 
reduce the use of terms in the respective SRP chapters such as 
``maximum,'' ``probable maximum,'' and ``PMF'' when referring to flood-
causing mechanisms and instead refer to consequential and non-
consequential flood-causing mechanisms. As part of staff's recent 10 
CFR 50.54(f) flood reevaluation, staff noted the terms ``maximum,'' or 
``probable maximum,'' could be misinterpreted since these terms refer 
to deterministic methodologies that are not frequency based. In 
addition, staff continues to pursue probabilistic flood hazard analysis 
(PFHA) methodologies, and removal of staff's discussion of maximum 
flood elevation is aligned with this pursuit.
    The term ``safety-related SSCs'' is being replaced with the term 
``SSCs important to safety'' to better track with the definition of 
that phrase currently found in Appendix A to 10 CFR part 50 of the 
Commission's regulations.
    The staff is also proposing to introduce a glossary of some 
standard flooding terms to avoid confusion between applicants and the 
NRC staff when communicating on certain flooding concepts. A tentative 
list of those concepts and their definitions is included as an appendix 
to this document. Some of these definitions have been previously 
published by the Nuclear Energy Institute (NEI) and used by the NRC 
staff with the recent 10 CFR 50.54(f) flood reevaluation. Included in 
the list of terms is a proposed definition for ``consequential 
flooding.'' Public comment on these concepts and definitions is 
welcomed as the staff intends to propose that they will be added to an 
update of SRP Section 2.4.1 (``Hydrologic Description'') at a later 
date.
    Lastly, other generic changes proposed to SRP Chapter 2.4 include 
technical editing, as appropriate, to improve the readability of the 
various SRP sections as well as to better convey lessons-learned from 
the recent 10 CFR 50.54(f) flooding reviews. For example, among the 
lessons-learned was the need to re-organize and update the 
``References'' Section (Section VI) to the respective SRP sections.
Proposed Future Changes to SRP Chapter 2.4 Sections
    The staff plans on making additional revisions to the remaining SRP 
sections in Chapter 2.4 next fiscal year (FY19) based on the lessons-
learned from the 10 CFR 50.54(f) and ESP/COL flooding reviews. The 
scope of these future revisions is consistent with the generic 
revisions described above (e.g., focus on descriptions of the 
consequential mechanism(s), preparation of inundation maps, updating of 
references, etc.). In addition to the generic changes being proposed, 
the staff also plans specific changes to other SRP sections as 
described below.
    Hydrologic Description--SRP Section 2.4.1: The staff intends to 
propose in the future that this SRP section be re-written to place 
increased emphasis on differentiating between consequential and 
inconsequential flood-causing mechanisms. Consequential flood-causing 
mechanism (or mechanisms), including LIP, that would be used to define 
the site characteristic for design-basis flooding, will continue to be 
fully-developed in the appropriate hazard-mechanism specific section of 
Chapter

[[Page 49136]]

2.4. However, staff will propose that the discussion for those 
inconsequential flood-causing mechanisms at the site does not need to 
be fully developed in a hazard-specific section of Chapter 2.4. 
Documentation of inconsequential mechanisms can be simplified because 
they were found to be not relevant to defining the site characteristic 
flood elevations for SSCs important-to-safety. Applicants would still 
be expected to account for the effects of plausible combined event 
hazards when describing the flood-causing mechanism (or mechanisms) 
consequential for defining the site characteristic for flooding. SRP 
Section 2.4.1 currently requests detailed discussions of the 
hydrosphere without clear acceptance guidelines. Staff will propose 
that topics not directly associated with defining the flooding site 
characteristic, and hence the staff's safety conclusion, no longer be 
required for the FSAR.\5\ A glossary of terms (attached as an appendix 
to this notice) would be added to the document.
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    \5\ This information would still be called for in any EIS/EA 
prepared for the site as currently required by 10 CFR part 51.
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    Floods--SRP Section 2.4.2: The staff intends to propose in the 
future that this SRP section be re-purposed to focus on defining the 
characteristic flood due to LIP and associated site drainage in and 
around the powerblock and controlled area. All applicants would be 
expected to prepare a flood inundation map for their sites showing the 
effects of LIP. Depending on a site's climate, applicants may need to 
consider different types of storms, including general and tropical 
storms, to obtain a bounding LIP value for a precipitation event that 
produces plausible maximum associated flooding effects and flood event 
duration, in addition to water level variations. If applicants choose 
to rely on a site-specific precipitation estimate from sources other 
than the Hydrometeorological Reports (or HMRs) prepared by the National 
Weather Service,\6\ then the staff would describe how those site-
specific estimates would be reviewed. Review instructions for riverine-
based floods currently in this section would be migrated into Section 
2.4.3 (``Streams and Rivers'').
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    \6\ Available on-line at https://nws.noaa.gov/oh/hdsc/studies/pmp.html.
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    Groundwater--SRP Section 2.4.12: The staff intends to propose in 
the future that this SRP section will be updated based on the 
experience gained through the review of the recent design certification 
(DC)/ESP/COL applications. The main purpose of this SRP section is to 
establishing the future maximum groundwater elevations associated with 
the reactor site and its environs. In examining the water table, this 
section also discusses the pathway and travel time of potential plumes 
containing radionuclide contaminants. In connection with any 
radionuclide fate and transport analysis, the staff must consider the 
effects of any geotechnical backfill used during site construction on 
groundwater flow. The review activities associated with the specific 
engineering properties of backfill are reviewed in SRP Section 2.5.4, 
``Stability of Subsurface Materials and Foundations.'' Review 
activities associated with the groundwater monitoring programs required 
by the regulations would be incorporated into one section describing 
groundwater use and characteristics, aquifers, pathways and, 
radionuclide fate and transport scenarios in SRP Section 2.4.13, 
``Accidental Releases of Radioactive Liquid Effluents in Ground and 
Surface Water.'' Content from DC/COL-ISG-014, ``Assessing the 
Radiological Consequences of Accidental Releases of Radioactive 
Materials from Liquid Waste Tanks in Ground and Surface Waters for 
Combined License Applications,'' would be incorporated into this new 
SRP section.
Probabilistic Flood Hazard Analyses in the SRP
    Following publication of the 1995 PRA Policy Statement, the 
Advisory Committee on Reactor Safeguards and the Advisory Committee on 
Nuclear Waste prepared a White Paper defining certain PRA-related 
terms. In that White Paper, designated SECY-98-144, the two NRC 
Advisory Committees defined what was meant by a risk-informed, 
performance-based approach. A risk-informed approach was defined to be 
a regulatory decision-making philosophy whereby risk insights are 
considered together with other factors to establish requirements that 
better focus licensee and regulatory attention on design and 
operational issues commensurate with their importance to health and 
safety. A risk-informed approach enhances the traditional approach by: 
(a) Allowing explicit consideration of a broader set of potential 
challenges to safety, (b) providing a logical means for prioritizing 
these challenges based on risk significance, operating experience, and/
or engineering judgment, (c) facilitating consideration of a broader 
set of resources to defend against these challenges, (d) explicitly 
identifying and quantifying sources of uncertainty in the analysis, and 
(e) leading to better decision-making by providing a means to test the 
sensitivity of the results to key assumptions. Where appropriate, a 
risk-informed regulatory approach can also be used to reduce 
unnecessary conservatism in deterministic approaches, or can be used to 
identify areas with insufficient conservatism and provide the bases for 
additional requirements or regulatory actions.
    SECY-98-144 also noted that the Commission's regulations 
requirements that are either prescriptive or performance-based. A 
prescriptive requirement specifies particular features, actions, or 
programmatic elements to be included in the design or process, as the 
means for achieving a desired objective. A performance-based 
requirement relies upon measurable (or calculable) outcomes (i.e., 
performance results) to be met, but provides more flexibility to the 
licensee as to the means of meeting those outcomes.
    Risk-informed, performance-based approaches are becoming more 
widespread in regulatory decision-making owing to improved methods, 
models, and approaches. Probabilistic seismic hazard analysis is just 
one example that has been in use in regulatory applications since the 
early 1980s. As the staff prepares updates to Chapter 2.4 of the SRP in 
FY19, the staff intends to seek stakeholder views on review methods and 
acceptance criteria that might be appropriate for implementation in the 
context of probabilistic flood hazard analyses for nuclear power 
plants. Later in FY19, the staff will issue a second Federal Register 
Notice announcing a public meeting on this topic to be held in 
connection with additional SRP updates for Chapter 2.4.
Specific Changes to Chapter 2.4 SRP Sections Covered in This Document
    In light of the new review philosophy envisioned for future license 
applications (as described above), the staff seeks public comment on 
other specific revisions proposed in the following SRP chapters. 
Electronic copies of these SRP chapters are available through the NRC's 
Agencywide Documents Access and Management System (ADAMS), at https://www.nrc.gov/reading-rm/adams.html, under the ADAMS accession numbers 
indicated below along with a summary of the section-specific changes.
    Tsunami--SRP Section 2.4.6 (ADAMS Accession No. ML18190A200): New 
language has been proposed to this SRP section reflecting the nuances 
of the recently-completed 10 CFR 50.54(f) flooding reviews (for 
example, the potential for multiple water surface elevations across the 
reactor site due to

[[Page 49137]]

variable site topography; the need to account for impact of combined 
hazard effects on estimated water surface elevations; consideration of 
the impact of associated effects on the design of SSCs important to 
safety; etc.). The reference list has also been amended to now only 
cite the Commission's regulations as well as those NRC regulatory 
guides pertinent to the tsunami review. The staff made this decision 
taking into account two factors. The first is that approximately 20 
licensees recently completed tsunami-based flood evaluations in 
connection with the 10 CFR 50.54(f) request. The respective analyses 
were computer-based and reflected an up-to date knowledge of tsunami 
wave science as well as associated generating mechanisms. The second 
factor is that the staff intends to prepare a knowledge management 
document in the future that will summarize the results of those 10 CFR 
50.54(f) reviews bearing on tsunami risk. That knowledge management 
document will also address current scientific literature on the subject 
and will include a summary of NRC-sponsored tsunami research produced 
over the last decade.
    Channel Migration or Diversions-- SRP Section 2.4.9 (ADAMS 
Accession No. ML18190A201): New language placing increased emphasis on 
the use of spatial data sets has been proposed for this SRP section. 
There are new recommendations encouraging the reviewer to consult 
aerial and satellite imagery that is now widely available. When 
reviewed in time series, temporal changes in the locations of streams 
and/or rivers can confirm whether this flood-causing mechanism is 
present at a particular site. Additional language has also been added 
to reflect the staff's intent that if a site is found to be susceptible 
to flooding due to channel migration or diversion, the applicant would 
then need to review this flood-causing mechanism in the context of a 
riverine-type flood, as outlined in SRP Section 2.4.3 (``Streams and 
Rivers''). Lastly, the reference list has also been limited to 
essentially citing the Commission's regulations as well as those NRC 
regulatory guides pertinent to the channel migration or diversion 
review.
Specific Changes to SRP Chapter 2.3 (``Meteorology'') Section Covered 
in This Document
    A revision to SRP Section 2.3.3 (``Onsite Meteorological 
Measurement Programs'') is also being proposed that captures lessons-
learned from the staff's review of DC, ESP, and COL applications 
received during the previous decade.
    Changes to SRP Section 2.3.3 were made to update the text with 
editorial and clarifying statements, including utilizing consistent 
terminology within this SRP section and within planned updates to the 
other SRP Chapter 2.3 sections. For example, the term ``atmospheric 
diffusion'' was replaced with ``atmospheric dispersion'' because 
atmospheric dispersion is generally recognized as having two 
components: Transport and diffusion. The term ``atmospheric stability 
class'' was also replaced with ``atmospheric stability'' due to the 
recognition that newer atmospheric dispersion models may be using 
direct measurements of atmospheric turbulence instead of classifying 
atmospheric stability into seven district classes as is currently 
discussed in Regulatory Guide 1.23, Revision 1.\7\ Previous standard 
boiler-plate statements in the SRP that are not applicable to this SRP 
section were also eliminated and the suite of references were updated 
as well.
---------------------------------------------------------------------------

    \7\ Entitled ``Meteorological Monitoring Programs for Nuclear 
Power Plants.''
---------------------------------------------------------------------------

    The staff plans on making additional revisions to some of the 
remaining SRP sections in Chapter 2.3 in the next fiscal year.
    The staff intends to conduct a public meeting later this calendar 
year to discuss the changes being proposed to SRP Chapters 2.3 and 2.4. 
The timing and location of that public meeting will be announced in the 
Federal Register at a later date.

IV. Further Information

    In addition to the lessons-learned from the section 50.54(f) 
reviews, the changes proposed to SRP Chapter 2 also reflect the current 
staff reviews, methods, and practices based on lessons-learned from the 
NRC's reviews of design certification and combined license applications 
completed since the last revision of this chapter.
    Following NRC staff evaluation of public comments, the NRC intends 
to finalize SRP Sections 2.4.6, 2.4.9, and 2.3.3 in ADAMS and post it 
on the NRC's public website at https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0800/. The SRP is guidance for the NRC 
staff. The SRP is not a substitute for the NRC regulations, and 
compliance with the SRP is not required.

V. Backfitting and Issue Finality

    Issuance of this draft SRP section, if finalized, would not 
constitute backfitting as defined in 10 CFR 50.109, (the Backfit Rule) 
or otherwise be inconsistent with the issue finality provisions in 10 
CFR part 52. The NRC's position is based upon the following 
considerations.
    1. The draft SRP positions, if finalized, would not constitute 
backfitting, inasmuch as the SRP is internal guidance to NRC staff 
directed at the NRC staff with respect to their regulatory 
responsibilities.
    The SRP provides internal guidance to the NRC staff on how to 
review an application for NRC regulatory approval in the form of 
licensing. Changes in internal staff guidance are not matters for which 
either nuclear power plant applicants or licensees are protected under 
either the Backfit Rule or the issue finality provisions of 10 CFR part 
52.
    2. The NRC staff has no intention to impose the SRP positions on 
current licensees or already-issued regulatory approvals either now or 
in the future.
    The NRC staff does not intend to impose or apply the positions 
described in the draft SRP to existing (already issued) licenses and 
regulatory approvals. Hence, the issuance of a final SRP, even if 
considered guidance within the purview of the issue finality provisions 
in 10 CFR part 52, would not need to be evaluated as if it were a 
backfit or as being inconsistent with issue finality provisions. If, in 
the future, the NRC staff seeks to impose a position in the SRP on 
holders of already issued licenses in a manner that does not provide 
issue finality as described in the applicable issue finality provision, 
then the staff must make the showing as set forth in the Backfit Rule 
or address the criteria for avoiding issue finality as described in the 
applicable issue finality provision.
    3. Backfitting and issue finality do not--with limited exceptions 
not applicable here--protect current or future applicants.
    Applicants and potential applicants are not, with certain 
exceptions, protected by either the Backfit Rule or any issue finality 
provisions under 10 CFR part 52. This is because neither the Backfit 
Rule nor the issue finality provisions under 10 CFR part 52--with 
certain exclusions discussed below--were intended to apply to every NRC 
action that substantially changes the expectations of current and 
future applicants.
    The exceptions to the general principle are applicable whenever an 
applicant references a 10 CFR part 52 license (e.g., an early site 
permit) and/or NRC regulatory approval (e.g., a design certification 
rule) with specified issue finality provisions. The NRC staff

[[Page 49138]]

does not, at this time, intend to impose the positions represented in 
the draft SRP in a manner that is inconsistent with any issue finality 
provisions. If, in the future, the staff seeks to impose a position in 
the draft SRP in a manner which does not provide issue finality as 
described in the applicable issue finality provisions, then the staff 
must address the criteria for avoiding issue finality as described in 
the applicable issue finality provision.

VI. Availability of Documents

    The documents identified in the following table are available to 
interested persons through the following methods, as indicated.

------------------------------------------------------------------------
                                                               ADAMS
                        Document                           Accession No.
------------------------------------------------------------------------
Draft NUREG-0800, Section 2.4.6, ``Tsunami Hazards''....     ML18190A200
Current Revision of NUREG-0800, Section 2.4.6, ``Tsunami     ML070160659
 Hazards''..............................................
Draft revision to NUREG-0800, Section 2.4.9, ``Channel       ML18190A201
 Migration or Diversion''...............................
Current revision to NUREG-0800, Section 2.4.9, ``Channel     ML070730434
 Migration or Diversion''...............................
The redline-strikeout version comparing the Revision 4       ML18267A055
 of Draft NUREG-0800, Section 2.4.6, ``Tsunami Hazards''
 and the current version of Revision 3..................
The redline-strikeout version comparing the draft            ML18264A035
 Revision 4 of Draft revision to NUREG-0800, Section
 2.4.9, ``Channel Migration or Diversion'' and the
 current version of Revision 3..........................
Draft NUREG-0800, Section 2.3.3, ``Onsite Meteorological     ML18183A446
 Measurements Program''.................................
Current Revision NUREG-0800, Section 2.3.3, ``Onsite         ML063600394
 Meteorological Measurements Program''..................
The redline-strikeout version comparing the draft            ML18267A076
 Revision 4 of Draft revision to NUREG-0800, Section
 2.3.3, ``Onsite Meteorological Measurements Program''
 and the current version of Revision 3..................
------------------------------------------------------------------------


    Dated at Rockville, Maryland, this 25th day of September, 2018.

    For the Nuclear Regulatory Commission.
Jennivine K. Rankin,
Acting Chief, Licensing Branch 3, Division of Licensing, Siting and 
Environmental Analysis, Office of New Reactors.

APPENDIX: Proposed Definitions

    [ssquf] Active flood protection feature: A flood protection 
feature that requires the change of a component's state in order for 
it to perform as intended. Examples include sump pumps, portable 
pumps, isolation and check valves, flood detection devices (e.g., 
level switches), and flood doors (e.g., watertight doors).
    [ssquf] Associated effects: Defined to include those factors 
such as wind waves and run-up effects; hydrostatic loading; 
hydrodynamic loading, including debris and water velocities; effects 
caused by sediment deposition and erosion; concurrent site 
conditions, including adverse weather conditions; and groundwater 
ingress.
    [ssquf] Cliff-edge effect: A relatively-large increase in the 
safety consequences due to a relatively small increase in flood 
severity (e.g., flood height (elevation), associated effects, or 
flood event duration).
    [ssquf] Concurrent hazard: A hazard that occurs along with the 
occurrence of another hazard as a result of a common cause (e.g., 
local intense precipitation and/or riverine flood event concurrent 
with a storm surge event caused by the same hurricane).
    [ssquf] Consequential flooding: For Construction Permits, 
Operating Licenses, and COL applications, a term used to identify 
conditions in which the flood severity exceeds the capability of 
protection features (if available), including considerations for 
flood level, duration and/or associated effects, such that SSCs 
important-to-safety may be impacted. For ESP applications, the flood 
severity is expected to be in reference to the site characteristic 
flood. Consequential flooding may occur for events that are less 
severe and with differing characteristics (e.g., shorter warning 
time) than the deterministically defined probable maximum events.
    [ssquf] Flood event duration: Defines the length of time that a 
flood event affects the site. Flood event duration typically begins 
with conditions being met for entry into a flood procedure or 
notification of an impending flood and end when the plant is in a 
safe and stable state. It typically includes site warning time (or 
preparation time, if available) and period of inundation and 
recession.
    [ssquf] Flood hazard: Those hydrometeorologic, geoseismic, or 
structural failure phenomena (or combination thereof) that may 
produce flooding at or near nuclear power plant site.
    [ssquf] Flood-response SSCs: SSCs that may be used to maintain 
key safety functions during conditions that might occur during an 
external flood scenario, including SSCs that are indirectly related 
to maintenance of key safety functions (e.g., barriers that protect 
SSCs from floodwaters or other related effects).
    [ssquf] Local intense precipitation (LIP): A locally-heavy 
rainfall event, which is typically defined by specifying three 
parameters: Total rainfall depth, total rainfall duration, and 
spatial extent (area). LIP is typically associated with small-scale 
events over geographic areas on the scale of the reactor powerblock 
and the controlled area (typically on the order of one to ten mi\2\) 
and using an assumption that the short-term rainfall rate is 
aerially uniform although the rainfall rate (intensity) typically 
varies over the total rainfall event duration. Although the rainfall 
duration parameter selected as part of evaluating this flood-causing 
mechanism will depend on site-specific characteristics (e.g., site 
drainage, susceptibility to ponding of water, etc.), LIP events are 
typically associated with a relatively short duration (e.g., 1- to 
6-hrs) of intense rainfall compared to the duration of rainfall 
events applied to the evaluation of basin-wide flooding involving 
streams and rivers. Smaller-scale intense rainfall events may be 
imbedded within longer rainfall events for streams and rivers and, 
depending on site drainage characteristics, may affect a reactor 
site for longer durations. In the context of the Standard Review 
Plan, LIP is defined generically and is not limited to stylized 
deterministic events, such as the so-called 1-hr, 1- mi\2\, probable 
maximum precipitation (PMP) event with specified duration and 
temporal distribution that produces the maximum rainfall inundation 
at a given plant site.
    [ssquf] Passive flood protection feature: A flood protection 
feature that does not require the change of state of a component in 
order for it to perform as intended. Examples include dikes, berms, 
sumps, drains, basins, yard drainage systems, walls, floors, 
structures, penetration seals, and barriers exterior to the 
immediate plant area that is under licensee control.
    [ssquf] Powerblock elevation (for purposes of plant design and 
flood hazard assessment): The as-built elevation of the ground 
surface in the area of the site's powerblock.

[FR Doc. 2018-21140 Filed 9-27-18; 8:45 am]
 BILLING CODE 7590-01-P