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.

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: Carol.Gallagher@nrc.gov.
• 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, 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 pdr.resource@nrc.gov.
• 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: Kamal.Manoly@nrc.gov.

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 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 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 infocollects@nrc.gov 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 Kamal.manoly@nrc.gov.

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 pdr@nrc.gov.