ML19248C756
| ML19248C756 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 10/08/2019 |
| From: | Peter Bamford Beyond-Design-Basis Management Branch |
| To: | Bryan Hanson Exelon Generation Co |
| Peter Bamford 301-415-2833 | |
| References | |
| EPID L-2018-JLD-0010 | |
| Download: ML19248C756 (6) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 October 8, 2019 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:
PEACH BOTIOM ATOMIC POWER STATION, UNITS 2 AND 3-CORRECTION REGARDING STAFF REVIEW OF SEISMIC PROBABILISTIC RISK ASSESSMENT ASSOCIATED WITH REEVALUATED SEISMIC HAZARD IMPLEMENTATION OF THE NEAR-TERM TASK FORCE RECOMMENDATION 2.1: SEISMIC (EPIO NO. L-2018-JLD-0010)
Dear Mr. Hanson:
The purpose of this letter is to provide a correction regarding the staff's evaluation of the Peach Bottom Atomic Power Station, Units 2 and 3 (Peach Bottom), seismic probabilistic risk assessment (SPRA), which was submitted in response to Near~Term Task Force (NTIF)
Recommendation 2.1 "Seismic." The correction does not change the U.S. Nuclear Regulatory Commission (NRC) staff's previous conclusion that no further response or regulatory action associated with NTIF Recommendation 2.1 "Seismic" is required for Peach Bottom.
By letter dated March 12, 2012 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12053A340), the NRC issued a request for information under Title 10 of the Code of Federal Regulations Section 50.54(f) (hereafter referred to as the 50.54(f) letter). The request 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 that licensees reevaluate seismic hazards at their sites using present-day methodologies and guidance. Enclosure 1, Item (8), of the 50.54(f) letter requested that certain licensees complete an SPRA to determine if plant enhancements are warranted due to the change in the reevaluated seismic hazard compared to the site's design-basis seismic hazard.
By letter dated August 28, 2018 (ADAMS Accession No. ML18240A065), Exelon Generation Company, LLC (Exelon, the licensee), provided its SPRA submittal in response to Enclosure 1, Item (8) of the 50.54(f) letter, for Peach Bottom. The NRC staff reviewed the SPRA submittal and provided its evaluation by letter dated June 10, 2019 (ADAMS Accession No. ML19053A469). This review used the guidance in NRC staff memorandum dated August 29, 2017, titled, "Guidance for Determination of Appropriate Regulatory Action Based on Seismic Probabilistic Risk Assessment Submittals in Response to Near Term Task Force Recommendation 2.1: Seismic" (ADAMS Accession No. ML17146A200; hereafter referred to as the SPRA Screening Guidance) to develop a recommendation based on its review of the SPRAs submitted by licensees in response to the 50.54{f) letter.
During an internal self-assessment review, the staff recently uncovered an error in the spreadsheet used in the SPRA Screening Guidance to evaluate the Peach Bottom SPRA submittal. The correction of the error resulted in changes to certain numerical values that were documented in the staff's Peach Bottom SPRA evaluation. A description of the error and corrected values for the affected portions of the staff evaluation are provided in the enclosure to this letter. The staff has confirmed that the changes to the numerical values presented in the enclosure to this letter do not impact or change the NRC decision documented by the previously referenced staff evaluation dated June 10, 2019.
The NRC staff regrets any inconvenience this may have caused. If you have any questions, please contact me at (301) 415-2833, or via e-mail at Peter.Bamford@nrc.gov.
Docket Nos. 50-277 and 50-278
Enclosure:
NRC Staff Correction Description cc w/encl: Distribution via Listserv Sincerely,
~
Peter Bamford, Senior Project Manager Beyond-Design-Basis Management Branch Division of Licensing Projects Office of Nuclear Reactor Regulation
NRC Staff Correction Description By letter dated August 28, 2018 (ADAMS Accession No. ML18240A065), Exelon Generation Company, LLG (Exelon, the licensee), provided its seismic probabilistic risk assessment (SPRA) submittal in response to Enclosure 1, Item (8) of the 50.54(f) letter [Title 10 of the Code of Federal Regulations Section 50.54(f), dated March 12, 2012] for Peach Bottom Atomic Power Station, Units 2 and 3 (Peach Bottom). The U.S. Nuclear Regulatory Commission (NRG) staff reviewed the SPRA submittal and provided its evaluation by letter dated June 10, 2019 (ADAMS Accession No. ML19053A469). This review used the guidance in NRG staff memorandum dated August 29, 2017, titled, "Guidance for Determination of Appropriate Regulatory Action Based on Seismic Probabilistic Risk Assessment Submittals in Response to Near Term Task Force Recommendation 2.1: Seismic" (ADAMS Accession No. ML17146A200; hereafter referred to as SPRA Screening Guidance) to develop a recommendation based on its review of the SPRAs submitted by licensees in response to the 50.54(f) letter.
During an internal self-assessment review, the staff recently uncovered an error in the spreadsheet used to implement the SPRA Screening Guidance for evaluating the Peach Bottom SPRA submittal. The correction of the error resulted in changes to certain numerical values documented in the staff evaluation letter. The staff has confirmed that the changes to the numerical values do not impact or change the NRC decision documented by the previously referenced staff evaluation dated June 10, 2019. to the staff evaluation letter dated June 12, 2019 (page 2 of Enclosure 2) contains a sentence that states the following:
The target RRWs [risk reduction worths] based on the mean and 95th percentile SCDF
[seismic core damage frequency] and SLERF [seismic large early release frequency]
were also calculated by the NRC staff and ranged between 1.63 and 1.96 for both units.
This sentence should have said (changes in bold):
The target RRWs based on the mean and 95th percentile SCDF and SLERF were also calculated by the NRG staff and ranged between 1.04 and 1.60 for both units.
In addition, the correction of the spreadsheet error impacts certain values presented in Tables 1 and 2 of Enclosure 2 to the staff's evaluation letter dated June 1.0, 2019. The following corrected versions of the impacted portions of Tables 1 and 2 are provided. The numbers that have changed are shown in bold.
Enclosure Table 1. lmoortance Analvsis Results of Too Contributors to Unit 2 and 3 SCDF Unit 2 Unit 3 MCR MCR Fragility Group/Event Description Failure Mode RRW
(/rx-yr)
(/rx-yr)
SSC Fragiliry Groups - Seismically Failed OSP Offsite Power Functional 52.632 2.63E-05 52.632 2.63E-05 S-DCBT1-DC Batteries 2(A-D)D01, 3(A-D)D01 Anchorage 1.136 3.22E-06 1.135 3.19E-06 S-CNWG2-Conowingo Hydroelectric Plant Functional 1.046 1.18E-06 1.056 1.41E-06 (OSP)
S-CEP1-Panel 20C003, 20C004C, 30c003, Anchorage 1.040 1.02E-06 1.039 1.01E-06 30C004C, OOC29(A-D)
S-CC359A-Correlated Relay Chatter Group Functional 1.011 2.87E-07 1.012 3 06E-07 359A (52B-TD5 relays) (All EDGs -
Unrecoverable)
S-DCBS4-DC Panel 20D24, 30D21 Anchorage NA NA 1.010 2.71E-07 S-DGPA1 D/G Room Supply Temp Control Functional 1.007 1.82E-07 1.007 1.95E-07 Panel O(A-D)C479 Table 2. Importance Analysis Results of Top Contributors to Unit 2 and 3 SLERF Unit 2 Unit3 MLR MLR Fragility Group/Event Description Failure Mode RRW (lrx-yr)
RRW (lrx-yr)
SSC Fragilitf Groups - Seismically Failed OSP Offsite Power Functional 10.204 6.62E-06 10.417 6.64E-06 SCRAM RPV Internals (Scram)
Anchorage 1.266 1.54E-06 1.253 1.48E-06 S-DCBT1-DC Batteries 2(A-D)D01. 3(A-Anchorage 1.144 9.25E-07 1.114 7.49E-07 0)001 S-CNWG2-Conowingo Hydroelectric Plant Functional 1.054 3.75E-07 1.052 3.61E-07 (OSP)
BOC Break Outside Containment Anchorage 1.040 2.84E-07 1.039 2.75E-07 SML Seismic Induced Medium LOCA Anchorage 1.032 2.29E-07 1.031 2.21E-07 S-CEPA1-Pane120C003,20C004C,30c003.
Anchorage 1.027 1.95E-07 1.055 3.84E-07 30C004C, OOC29(A-D)
S-DCBS4 DC Panel 20D24, 30D21 Anchorage NA NA 1.026 1.84E-07 S-PCl2 Primary Containment Isolation Functional 1.025 1.80E-07 1.024 1.74E-07 (Inboard and Outboard MSIVs)
S-CEPA7-Panel 20C32 (U2 Engineering Sub Functional 1.014 1.D4E-07 NA NA Systems I Relay Cabinet)
S-CNCT1-Condensate Storage Tank 20T010, Anchorage 1.014 1.D1E-07 1.015 1.09E-07 30E010 S-DCBS10 250 voe Bus 30D11 Anchorage NA NA 1.014 1.01E-07 S-SGTK1-SGIG Nitrogen Tank Anchorage 1.012 8.51E-D8 1.011 7.85E-08 S-CEPA6-Panel 20C32 (U2 HPCI Relay Functional 1.012 8.44E-08 NA NA Panel}
S-CC190A-Correlated Relay Chatter Group Functional 1.009 6.74E-D8 1.008 6.0JE-08 190A (526-151 N relays}(EDGs A and D - Unrecoverable)
S-CEPA8-Panel 20C33 (U2 Engineering Sub Functional 1.008 5.60E-08 NA NA Systems II Relay Cabinet}
S-CC138-Relay Chatter Group 138 (150G Functional 1.007 5.29E-08 NA NA relay) (4KV Bus 20A15-Recoverable)
S-DCBS6-DC Panel 2(A-D)D17, 3AD17.
Functional 1.006 4.SSE-08 NA NA 3CD17, 3DD17
- concurrence via email OFFICE NRR/DLP/PBMB/PM NRR/DLP/PBMB/PM NRR/DLP/PBMB/LA NRR/DRA/APLB/TL NAME PBamford JSebrosky SLent SVasavada DATE 9/5/19 9/9/19 9/6/19 9/20/19 OFFICE NRR/DLP/PBMB/BC NRR/DLP/PBMB/PM NAME BTitus PBamford DATE 10/8/19 10/8/19