[Federal Register Volume 76, Number 170 (Thursday, September 1, 2011)]
[Notices]
[Pages 54507-54510]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2011-22422]


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NUCLEAR REGULATORY COMMISSION

[NRC-2011-0204]


Proposed Generic Communication; Draft NRC Generic Letter 2011-XX: 
Seismic Risk Evaluations for Operating Reactors

AGENCY: Nuclear Regulatory Commission.

ACTION: Notice of opportunity for public comment.

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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is issuing this 
generic letter to inform addressees that the NRC requests addressees to 
evaluate their facilities to determine the current level of seismic 
risk and to submit the requested information to facilitate the NRC's 
determination if there is a need for additional regulatory action.

DATES: Comment period expires October 31, 2011. Comments submitted 
after this date will be considered if it is practical to do so, but 
assurance of consideration cannot be given except for comments received 
on or before this date.

ADDRESSES: Please include Docket ID NRC-2011-0201 in the subject line 
of your comments. For additional instructions on submitting comments 
and instructions on accessing documents related to this action, see 
``Submitting Comments and Accessing Information'' in the SUPPLEMENTARY 
INFORMATION section of this document. You may submit comments by any 
one of the following methods:
     Federal Rulemaking Web Site: Go to http://www.regulations.gov and search for documents filed under Docket ID NRC-
2011-0201. Address questions about NRC dockets to Carol Gallagher, 
telephone: 301-492-3668; e-mail: [email protected].
     Mail comments to: Cindy Bladey, Chief, Rules, 
Announcements, and Directives Branch (RADB), Office of Administration, 
Mail Stop: TWB-05-B01M, U.S. Nuclear Regulatory Commission, Washington, 
DC 20555-0001.
     Fax comments to: RADB at 301-492-3446.

SUPPLEMENTARY INFORMATION: 

Submitting Comments and Accessing Information

    Comments submitted in writing or in electronic form will be posted 
on the NRC Web site and on the Federal rulemaking Web site, http://www.regulations.gov. Because your comments will not be edited to remove 
any identifying or contact information, the NRC cautions you against 
including any information in your submission that you do not want to be 
publicly disclosed.
    The NRC requests that any party soliciting or aggregating comments 
received from other persons for submission to the NRC inform those 
persons that the NRC will not edit their comments to remove any 
identifying or contact information, and therefore, they should not 
include any information in their comments that they do not want 
publicly disclosed.
    You can access publicly available documents related to this 
document using the following methods:
     NRC's Public Document Room (PDR): The public may examine 
and have copied, for a fee, publicly available documents at the NRC's 
PDR, O1-F21,

[[Page 54508]]

One White Flint North, 11555 Rockville Pike, Rockville, Maryland 20852.
     NRC's Agencywide Documents Access and Management System 
(ADAMS): Publicly available documents created or received at the NRC 
are available online in the NRC Library at http://www.nrc.gov/reading-rm/adams.html. From this page, the public can gain entry into ADAMS, 
which provides text and image files of the NRC's public documents. If 
you do not have access to ADAMS or if there are problems in accessing 
the documents located in ADAMS, contact the NRC's PDR reference staff 
at 1-800-397-4209, 301-415-4737, or by e-mail to [email protected].
     Federal Rulemaking Web Site: Public comments and 
supporting materials related to this notice can be found at http://www.regulations.gov by searching on Docket ID NRC-2011-0201.

FOR FURTHER INFORMATION CONTACT: Kamal Manoly, NRR/DE, 301-415-2765, e-
mail: [email protected].

SUPPLEMENTARY INFORMATION: 

NRC Generic Letter 2011-XX Seismic Risk Evaluations for Operating 
Reactors

Addressees

    All holders of an operating license or construction permit for a 
nuclear power reactor issued under Title 10 of the Code of Federal 
Regulations (10 CFR) part 50, ``Domestic Licensing of Production and 
Utilization Facilities,'' except those who have permanently ceased 
operation and have certified that fuel has been removed from the 
reactor vessel.

Intent

    The NRC is issuing this generic letter (GL) to inform addressees 
that the NRC requests addressees to evaluate their facilities to 
determine the current level of seismic risk and to submit the requested 
information to facilitate the NRC's determination if there is a need 
for additional regulatory action.

Background

    Structures, systems, and components (SSCs) important to safety at 
nuclear power reactors must be designed to withstand the effects of 
natural phenomena, including earthquakes, without losing the capability 
to perform their intended safety functions. SSCs in operating nuclear 
power plants are designed either in accordance with, or have been 
revised to meet the intent of Appendix A to 10 CFR part 100 and 
Appendix A to 10 CFR part 50, General Design Criteria (GDC) 2. The 
state of knowledge of seismic hazard within the United States has 
evolved to the point that the NRC has concluded that, in view of the 
potential safety significance of this issue, it is necessary to 
reexamine the level of conservatism in the determination of original 
seismic design estimates. Analyses performed under the Generic Issue 
program (GIP) indicated the need to evaluate in more detail the impact 
of updated seismic hazard information with respect to operating 
commercial nuclear reactors. The background information relevant to 
this GL includes the individual plant examinations of external events 
(IPEEE) and Generic Issue (GI)-199, ``Implications of Updated 
Probabilistic Seismic Hazard Estimates in Central and Eastern United 
States on Existing Plants,'' dated June 9, 2005 (ADAMS Accession No. 
ML051600272). The following paragraphs summarize these two studies.
Individual Plant Examination of External Events
    On June 28, 1991, the NRC issued Supplement 4 to GL 88-20, 
``Individual Plant Examination of External Events (IPEEE) for Severe 
Accident Vulnerabilities,'' (ADAMS Accession No. ML031150485) to 
request that each licensee identify and report to the NRC all plant-
specific vulnerabilities to severe accidents caused by external events. 
The IPEEE program included the following four supporting objectives:
    (1) Develop an appreciation of severe accident behavior.
    (2) Understand the most likely severe accident sequences that could 
occur at the licensee's plant under full-power operating conditions.
    (3) Gain a qualitative understanding of the overall likelihood of 
core damage and fission product releases.
    (4) Reduce, if necessary, the overall likelihood of core damage and 
radioactive material releases by modifying, where appropriate, hardware 
and procedures that would help prevent or mitigate severe accidents.
    The external events to be considered in the IPEEE were seismic 
events; internal fires; and high winds, floods, and other external 
initiating events, including accidents related to transportation or 
nearby facilities and plant-unique hazards.
    In June 1991, at about the same time the NRC issued Supplement 4 to 
GL 88-20, the NRC issued NUREG-1407, ``Procedure and Submittal Guidance 
for the Individual Plant Examination of External Events (IPEEE) for 
Severe Accident Vulnerabilities,'' (ADAMS Accession No. ML063550238) 
which provided guidelines for conducting IPEEEs. On September 8, 1995, 
the NRC issued Supplement 5 to GL 88-20 (ADAMS Accession No. 
ML031130465) to notify licensees of modifications to the recommended 
scope of the seismic portion of the IPEEE for certain plant sites in 
the Central and Eastern United States (CEUS).
    NUREG-1742, ``Perspectives Gained from the Individual Plant 
Examination of External Events (IPEEE) Program,'' issued April 2002, 
(ADAMS Accession Nos. ML021270070 and ML021270674) provides insights 
gained by the NRC from the IPEEE program. Almost all licensees reported 
in their IPEEE submittals that no plant vulnerabilities were identified 
with respect to seismic risk (the use of the term ``vulnerability'' 
varied widely among the IPEEE submittals). However, most licensees did 
report at least some seismic ``anomalies,'' ``outliers,'' or other 
concerns. In the few submittals that did identify a seismic 
vulnerability, the findings were comparable to those identified as 
outliers or anomalies in other IPEEE submittals. Seventy percent of the 
plants proposed improvements as a result of their seismic IPEEE 
analyses. In several responses, neither the IPEEE analyses nor 
subsequent assessments documented the potential safety impacts of these 
improvements, and in most cases, plants have not reported completion of 
these improvements to the NRC.
Generic Issue 199
    In support of early site permits (ESPs) and combined license 
applications (COLs) for new reactors, the NRC staff reviewed updates to 
the seismic source and ground motion models provided by applicants. 
These seismic updates included new Electric Power Research Institute 
models to estimate earthquake ground motion and updated models for 
earthquake sources in the CEUS, such as around Charleston, SC, and New 
Madrid, MO. These reviews identified higher seismic hazard estimates 
than previously assumed that may result in the increased likelihood of 
exceeding the safe-shutdown earthquake (SSE) at operating facilities in 
the CEUS. The staff determined that based on the evaluations of the 
IPEEE program, seismic designs of operating plants in the CEUS do not 
pose an imminent safety concern. At the same time, the staff also 
recognized that, because the probability of exceeding the SSE at some 
currently operating sites in the CEUS is higher than previously 
understood, further study was warranted. As a result, the staff 
concluded on May 26, 2005 (ADAMS Accession No. ML051450456), that the

[[Page 54509]]

issue of increased seismic hazard estimates in the CEUS be examined 
under the GIP.
    GI-199, ``Implications of Updated Probabilistic Seismic Hazard 
Estimates in Central and Eastern United States on Existing Plants'' was 
established on June 9, 2005 (ADAMS Accession No. ML051600272). The 
initial screening analysis for GI-199 suggested that estimates of the 
seismic hazard for some currently operating plants in the CEUS have 
increased. The NRC completed the initial screening analysis of GI-199 
on February 1, 2008 (ADAMS Accession No. ML073400477), which concluded 
that GI-199 should proceed to the safety/risk assessment stage of the 
GIP. The NRC held a public meeting on February 6, 2008 (ADAMS Accession 
No. ML080350189), at which the NRC staff discussed its ongoing 
activities related to GI-199, described the screening process and 
criteria, and explained the screening analysis results.
    Subsequently, during the safety/risk assessment stage of the GIP, 
the NRC staff reviewed and evaluated the new information received with 
the ESP/COL submittals, along with 2008 U.S. Geological Survey seismic 
hazard estimates and recent geological research literature. The staff 
compared the new seismic hazard data with the earlier evaluations 
conducted as part of the IPEEE program. From this evaluation, the staff 
concluded that the likelihood of exceeding the seismic hazard used in 
the IPEEE program could be higher than previously understood for some 
currently operating CEUS sites.
    The NRC staff completed the safety/risk assessment stage of GI-199 
on September 2, 2010 (ADAMS Accession No. ML100270582), concluding that 
GI-199 should transition to the regulatory assessment stage of the GIP. 
The NRC staff presented this conclusion at a public meeting held on 
October 6, 2010 (ADAMS Accession No. ML102950263). Information Notice 
2010-018, ``Generic Issue 199, `Implications of Updated Probabilistic 
Seismic Hazard Estimates in Central and Eastern United States on 
Existing Plants,' '' dated September 2, 2010 (ADAMS Accession No. 
ML101970221) summarizes the results of the GI-199 safety/risk 
assessment.

Discussion

    GI-199 was initiated because of the need to evaluate the effect of 
updated seismic hazard estimates on operating nuclear power plants. The 
GI-199 safety/risk assessment investigated the safety and risk 
implications of updated earthquake-related data and models. These data 
and models suggest that the probability for earthquake ground shaking 
above the seismic design basis for some nuclear power plants in the 
CEUS is greater than previous estimates.
    In the safety/risk assessment, the NRC staff used the risk metric 
of the change in seismic core damage frequency (SCDF) derived from an 
updated understanding of the site-specific seismic hazard estimates 
from those previously used in the IPEEE submittals. The changes in SCDF 
estimate in the safety/risk assessment for some plants lie in the range 
of 10-4 per year to 10-5 per year, which meet the 
numerical risk criteria for an issue to continue to the regulatory 
assessment stage of the GIP.
    It is recognized that the approach used to estimate SCDF in the 
safety/risk assessment was not based on a rigorous methodology. The 
approach merely extrapolated from the information available within the 
IPEEE submittals. As described in NUREG-1742, there are limitations 
associated with utilizing the inherently qualitative insights from the 
IPEEE submittals in a quantitative assessment. Specifically, the 
staff's assessment did not provide insight into which SSCs are 
important to seismic risk. Such knowledge is necessary for the NRC 
staff to determine, in light of the new understanding of seismic 
hazards, the safety significance associated with the new information 
regarding seismic margin. The burden to be imposed by this GL is 
justified in view of the potential safety significance of this issue.

Backfit Discussion

    This GL contains only the information request described in 
``Requested Response.'' The GL does not contain any recommended changes 
to the design or procedures necessary to operate the nuclear power 
plants of the addressees. This GL also does not contain any direction 
or suggestion that the addressees should consider developing or 
implementing changes to the design or procedures necessary to operate 
their nuclear power plants in light of the information requested by 
this GL. The NRC staff does not intend that the probabilistic seismic 
hazard estimates or the methods of evaluation required by this GL be 
automatically incorporated into the licensing basis (including design 
basis) of any of the addressees' nuclear power plants via this GL. The 
NRC staff is not requiring or recommending the submission of any 
addressee-initiated changes to the licensing bases for the addressees' 
nuclear power plants, as the need for such changes will have to be made 
on a case by case basis by licensees after evaluating the significance 
of the information developed as a result of this GL.
    The NRC will evaluate the information submitted by the addressees 
in response to this GL and may then determine whether there is a need 
to take additional action. If that determination results in an action 
that constitutes an NRC staff recommendation (including the issuance of 
NRC communications characterized as ``guidance'') or an NRC requirement 
(via regulation or order, including licensing action) that one or more 
of the addressees change the design or the procedures necessary to 
operate the addressees' nuclear power plants, then the NRC will treat 
that action as backfitting under the Backfit Rule at 10 CFR 50.109.
    Under the provisions of Sections 161.c, 103.b, and 182.a of the 
Atomic Energy Act of 1954, as amended, this GL requests a review and 
appropriate resulting actions to ascertain whether backfits are 
warranted. No mandated backfit is intended by the issuance of this GL. 
Therefore, the NRC staff has not performed a backfit analysis.

Federal Register Notification

    To be done after the public comment period.

Congressional Review Act

    This section is not applicable because this proposed GL is being 
issued for public comment.

Paperwork Reduction Act Statement

    This GL does not contain new or amended information collection 
requirements that are subject to the Paperwork Reduction Act of 1995 
(44 U.S.C. 3501 et seq.). Existing requirements were approved by the 
Office of Management and Budget, approval numbers 3150-0011 and 3150-
0093.
    The burden to the public for this mandatory information is 
estimated to be 1,240 hours per response for plants in the CEUS where 
the GMRS does not exceed the SSE. Western plants may require an 
additional 2,500 hours to develop seismic source characterization and 
ground motion models. For any plant where the GMRS exceeds the SSE, the 
burden is estimated to be an additional 2,880 hours if the licensee 
elects to perform an SMA or an additional 3,380 hours if the licensee 
elects to perform an SPRA. This includes time for reviewing existing 
data sources, gathering and analyzing the data needed, and completing 
and reviewing the information collection.
    Send comments on any aspect of this information collection, 
including

[[Page 54510]]

suggestions for reducing the burden, to the Records and FOIA/Privacy 
Services Branch (T5-F52), U.S. Nuclear Regulatory Commission, 
Washington, DC 20555-0001 or by e-mail to [email protected] and to 
the Desk Officer, Office of Information and Regulatory Affairs, NEOB-
10202 (3150-0011), Office of Management and Budget (OMB), Washington, 
DC 20503.
    Please direct any questions about this matter to Kamal Manoly, at 
301-415-2765 or by e-mail at [email protected].

End of Draft Generic Letter

    Documents may be examined, and/or copied for a fee, at the NRC's 
Public Document Room at One White Flint North, 11555 Rockville Pike 
(first floor), Rockville, Maryland. Publicly available records will be 
accessible electronically from the Agencywide Documents Access and 
Management System (ADAMS) Public Electronic Reading Room on the 
Internet at the NRC Web site, http://www.nrc.gov/reading-rm/adams.html. 
If you do not have access to ADAMS or if you have problems in accessing 
the documents in ADAMS, contact the NRC Public Document Room (PDR) 
reference staff at 1-800-397-4209 or 301-415-4737 or by e-mail to 
[email protected].

    Dated at Rockville, Maryland, this 25 day of August, 2011.
    For the Nuclear Regulatory Commission.
Stacey Rosenberg,
Chief, Generic Communications and Power Uprate Branch, Division of 
Policy and Rulemaking, Office of Nuclear Reactor Regulation.
[FR Doc. 2011-22422 Filed 8-31-11; 8:45 am]
BILLING CODE 7590-01-P