ML17087A066

Staff Review of Mitigation Strategies Assessment Report of the Impact of the Reevaluated Seismic Hazard Developed in Response to the March 12, 2012, 50.54(f) Letter

ML17087A066
Person / Time
Site:	Limerick
Issue date:	04/12/2017
From:	Steve Wyman Japan Lessons-Learned Division
To:	Bryan Hanson Exelon Nuclear
Wyman S, NRR/JLD, 415-3041
References
Download: ML17087A066 (4)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 12, 2017 Mr. Bryan C. Hanson Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

LIMERICK GENERATING STATION, UNITS 1 AND 2 - STAFF REVIEW OF MITIGATION STRATEGIES ASSESSMENT REPORT OF THE IMPACT OF THE REEVALUATED SEISMIC HAZARD DEVELOPED IN RESPONSE TO THE MARCH 12, 2012, 50.54(f) LETTER

Dear Mr. Hanson:

The purpose of this letter is to provide the U.S. Nuclear Regulatory Commission's (NRC) assessment of the seismic hazard mitigation strategies assessment (MSA), as described in the December 1, 2016, letter (Agencywide Documents Access and Management System (ADAMS)

Accession No. ML16336A442), submitted by Exelon Generation Company, LLC (Exelon, the licensee) for Limerick Generating Station, Units 1 and 2 (Limerick). The NRC staff evaluated the Limerick strategies as developed under Order EA-12-049, and as described in the Limerick Overall Integrated Plan (OIP) (ADAMS Accession No. ML13060A127). The staff's review of Limerick's mitigation strategies will be documented in a forthcoming safety evaluation. The purpose of the safety evaluation is to ensure the licensee has developed guidance and proposed designs which, if implemented appropriately, should adequately address the requirements of Order EA-12-049. An inspection will confirm compliance with the order. The following NRC staff review confirms that the licensee has adequately addressed the reevaluated seismic hazard within Limerick's mitigation strategies for beyond-design-basis external events.

BACKGROUND By letter dated March 12, 2012 (ADAMS Accession No. ML12053A340), the NRC issued a request for information pursuant to Title 1O of the Code of Federal Regulations (1 O CFR),

Section 50.54(f) (hereafter referred to as the 50.54(f) letter). The 50.54(f) letter was issued as part of implementing lessons-learned from the accident at the Fukushima Dai-ichi nuclear power plant. Enclosure 1 to the 50.54(f) letter requested licensees reevaluate the seismic hazard using present-day methodologies and guidance. Concurrent with the reevaluation of seismic hazards, the NRC issued Order EA-12-049, "Issuance of Order to Modify Licenses with Regard to Requirements for Mitigation Strategies for Beyond-Design-Basis External Events" (ADAMS Accession No. ML12054A736). The order requires holders of operating power reactor licenses and construction permits issued under 10 CFR Part 50 to develop, implement, and maintain guidance and strategies to maintain or restore core cooling, containment, and spent fuel pool cooling following a beyond-design-basis external event. By letter dated March 31, 2014 (ADAMS Accession No. ML14090A236), the licensee, provided its reevaluated seismic hazard for Limerick in response to the 50.54(f) letter.

B. Hanson On December 10, 2015 (ADAMS Accession No. ML16005A621 ), the Nuclear Energy Institute (NEI) submitted Revision 2 to NEI 12-06, including guidance for conducting MSAs using the reevaluated hazard information. The NRC subsequently endorsed NEI 12-06, Revision 2, with exceptions, clarifications , and additions, in Japan Lessons-Learned Division (JLD) interim staff guidance {ISG) JLD-ISG-2012-01 , Revision 1, "Compliance with Order EA-12-049, Order Modifying Licenses with Regard to Requirements for Mitigation Strategies for Beyond-Design-Basis External Events" (ADAMS Accession No. ML15357A163).

MITIGATION STRATEGIES ASSESSMENT By letter dated October 6, 2015 (ADAMS Accession No. ML15296A492), the NRC staff documented its review of the licensee's reevaluated seismic hazard, also referred to as the mitigation strategies seismic hazard information. The staff found that the Limerick Ground Motion Response Spectrum (GMRS) is bounded by the safe shutdown earthquake (SSE) in the 1 to 10 Hertz (Hz) range , and exceeds the SSE above approximately 10 Hz, meriting a high frequency (HF) confirmation. In addition , the staff concluded that the GMRS determined by the licensee adequately characterizes the reevaluated seismic hazard for the Limerick site.

By letter dated November 28, 2016 (ADAMS Accession No. ML16333A084}, Exelon submitted a HF Confirmation Report for Limerick. By letter dated February 6, 2017 (ADAMS Accession No. ML17031A415} , the NRC staff concluded , based on its review, that the licensee correctly implemented the HF guidance in conducting the HF confirmation for Limerick. All evaluated components demonstrated adequate seismic capacity and no component modifications were required .

By letter dated December 1, 2016 (ADAMS Accession No. ML16336A442), Exelon submitted a MSA Report for Limerick. The licensee stated that the Limerick MSA was performed consistent with NEI 12-06, Revision 2. Appendix H of NEI 12-06, Revision 2, describes acceptable methods for demonstrating that the reevaluated seismic hazard is addressed within the Limerick mitigation strategies for beyond-design-basis external events. The NRC staff confirmed that the licensee's seismic hazard MSA is consistent with the guidance in Appendix H.4.2 of NEI 12-06, Revision 2, as endorsed by JLD-ISG-2012-01 , Revision 1. Therefore , the methodology used by the licensee is appropriate to perform an assessment of the mitigation strategies that addresses the reevaluated seismic hazard.

The staff reviewed the licensee's description of the component selection process for the MSA.

The staff concluded the licensee provided sufficient detail in describing the selection process and provided a clear list of references used to support the selection process. The staff also confirmed that the selected components support at least a single shutdown path that is consistent with the Limerick 01 P (ADAMS Accession No. ML13060A127) submitted in response to Order EA-12-049.

The licensee provided the seismic equipment list for the MSA in Table A-1 and identified 60 components for which a HF confirmation evaluation was required. The licensee stated that the components were reviewed as part of the Limerick HF confirmation . The staff confirmed that all 60 components were part of the Limerick HF confirmation report and the review of these 60 components is documented in NRC letter dated February 6, 2017 (ADAMS Accession No. ML17031A415). The staff previously found that all 60 components had seismic capacity greater than demand as part of the HF confirmation evaluation submitted in response to the 50.54(f) letter.

B. Hanson The NRC staff completed its review of the seismic hazard MSA for Limerick. The NRC staff concludes that sufficient information has been provided to demonstrate that the licensee's plans for the development and implementation of guidance and strategies under Order EA-12-049 appropriately address the reevaluated seismic hazard information stemming from the 50.54(f) letter.

If you have any questions, please contact me at (301) 415-3041 or via e-mail at Stephen.Wyman@nrc.gov.

Sincerely, Stephen Wyma Hazards Mana ment Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation Docket Nos. 50-352 and 50-353 cc: Distribution via Listserv

ML 17xxxxxxxx *via e-mail OFFICE NRR/JLD/JHMB/PM NRR/JLD/LA NRR/JLD/JHMB/BC NRR/JLD/JHMB/PM NAME SWyman Slent NSanfilippo SWyman DATE 3/31 / 17 3/31 / 17 4/11 /1 7 4/12/17