ML18128A384: Difference between revisions
StriderTol (talk | contribs) (Created page by program invented by StriderTol) |
StriderTol (talk | contribs) (Created page by program invented by StriderTol) |
||
Line 26: | Line 26: | ||
==Subject:== | ==Subject:== | ||
CALVERT CLIFFS NUCLEAR POWER PLANT, UNITS 1 AND 2 - DRAFT REQUEST FOR ADDITIONAL INFORMATIONREGARDING RISK-INFORMED TECHNICAL SPECIFICATION COMPLETION TIMES (CAC NOS. MF7415 ANDMF7416; EPID L-2016-LLA-0001)Date:Tuesday, May 08, 2018 2:34:00 PMHello Glenn, By letter dated February 25, 2016 (ADAMS Accession No. ML16060A223), assupplemented by letters dated April 3, 2017 (ADAMS Accession No. ML17094A591),January 11, 2018 (ADAMS Accession No. ML18011A665), and January 18, 2018 (ADAMSAccession No. ML18018B340), Exelon Generation Company, LLC (Exelon; licensee)submitted a License Amendment Request (LAR) proposing to modify the Calvert CliffsNuclear Power Plant (CCNPP), Units 1 and 2 Technical Specification requirements topermit the use of risk-informed completion times. The Nuclear Regulatory Commission (NRC) staff has determined that additional informationis needed to complete its review of the request. The purpose of this e-mail is to provide adraft copy of the request for additional information (RAI) for your review to ensure that: ~ the draft RAI questions are understandable,~ the bases for the questions are clear, and~ to determine whether the information being requested was previously docketed. The draft RAI questions listed below are not a complete listing of the additional informationneeded to complete the NRC staff's review. Additional RAI questions were provided viaseparate correspondence. RAIs numbers 1 through 19 were sent to Exelon in letters datedNovember 13, 2017 (ADAMS Accession No. ML17304A941) and December 21, 2017(ADAMS Accession No. ML17346A909). If Exelon has any questions or comments concerning the clarity or basis for the RAIquestions, please plan to share your questions or comments with the cognizant NRC staffat the public meeting scheduled for May 16, 2018 (ADAMS Accession No. ML18123A280). Additionally, be prepared to confirm that Exelon will be able to provide responses to the RAIquestions within 30 days of the issuance of the final RAIs. Draft RAIs 20. Enclosure 4 of the letter dated February 25, 2016, states that a total seismic coredamage frequency (CDF) contribution of 1.1E-6/year and a seismic large early releasefrequency (LERF) contribution of 1.1E-7/year will be added to the configuration specificdelta CDF and delta LERF from the internal events and fire initiating event contributionsto estimate the risk-informed completion time. The LAR states that these seismicestimates are based on the re-evaluated seismic hazard for CCNPP performed inresponse to the Near-Term Task Force 2.1 (ADAMS Accession No. ML14099A196) andan estimated plant level high confidence of low probability of failure (HCLPF) of 0.27gpeak ground acceleration (PGA) as used in the 2003 LAR entitled "Extension of DieselGenerator Required Action Completion Time" (ADAMS Accession No. ML031360410). | CALVERT CLIFFS NUCLEAR POWER PLANT, UNITS 1 AND 2 - DRAFT REQUEST FOR ADDITIONAL INFORMATIONREGARDING RISK-INFORMED TECHNICAL SPECIFICATION COMPLETION TIMES (CAC NOS. MF7415 ANDMF7416; EPID L-2016-LLA-0001)Date:Tuesday, May 08, 2018 2:34:00 PMHello Glenn, By letter dated February 25, 2016 (ADAMS Accession No. ML16060A223), assupplemented by letters dated April 3, 2017 (ADAMS Accession No. ML17094A591),January 11, 2018 (ADAMS Accession No. ML18011A665), and January 18, 2018 (ADAMSAccession No. ML18018B340), Exelon Generation Company, LLC (Exelon; licensee)submitted a License Amendment Request (LAR) proposing to modify the Calvert CliffsNuclear Power Plant (CCNPP), Units 1 and 2 Technical Specification requirements topermit the use of risk-informed completion times. The Nuclear Regulatory Commission (NRC) staff has determined that additional informationis needed to complete its review of the request. The purpose of this e-mail is to provide adraft copy of the request for additional information (RAI) for your review to ensure that: ~ the draft RAI questions are understandable,~ the bases for the questions are clear, and~ to determine whether the information being requested was previously docketed. The draft RAI questions listed below are not a complete listing of the additional informationneeded to complete the NRC staff's review. Additional RAI questions were provided viaseparate correspondence. RAIs numbers 1 through 19 were sent to Exelon in letters datedNovember 13, 2017 (ADAMS Accession No. ML17304A941) and December 21, 2017(ADAMS Accession No. ML17346A909). If Exelon has any questions or comments concerning the clarity or basis for the RAIquestions, please plan to share your questions or comments with the cognizant NRC staffat the public meeting scheduled for May 16, 2018 (ADAMS Accession No. ML18123A280). Additionally, be prepared to confirm that Exelon will be able to provide responses to the RAIquestions within 30 days of the issuance of the final RAIs. Draft RAIs 20. Enclosure 4 of the letter dated February 25, 2016, states that a total seismic coredamage frequency (CDF) contribution of 1.1E-6/year and a seismic large early releasefrequency (LERF) contribution of 1.1E-7/year will be added to the configuration specificdelta CDF and delta LERF from the internal events and fire initiating event contributionsto estimate the risk-informed completion time. The LAR states that these seismicestimates are based on the re-evaluated seismic hazard for CCNPP performed inresponse to the Near-Term Task Force 2.1 (ADAMS Accession No. ML14099A196) andan estimated plant level high confidence of low probability of failure (HCLPF) of 0.27gpeak ground acceleration (PGA) as used in the 2003 LAR entitled "Extension of DieselGenerator Required Action Completion Time" (ADAMS Accession No. ML031360410). | ||
: a. The staff notes that the CCNPP Expedited Seismic Evaluation Process Report(ESEP), submitted to the NRC on December 17, 2014 (ADAMS Accession No.ML14365A138), indicates that certain components, such as safety injectiontanks, motor control centers, electrical buses, main control room panels, wouldfail in a seismic event through interaction with nearby block walls, and thosecomponents were assigned a lower HCLPF of 0.175 g due to the block walllower capacity. This lower HCLPF could increase the seismic CDF and LERFestimates provided in the LAR. Justify the plant level HCLPF of 0.27 g PGA, given the noted block walls failuresat 0.175 g indicated in the ESEP, or provide, with justification, updated seismicCDF and LERF estimates. b. The 2003 LAR for extension of emergency diesel generator (EDG) completiontimes shows differences in estimated seismic CDF and LERF between Unit 1and Unit 2. According to the NRC Technical Evaluation Report for the IndividualPlant Examination for External Events, because the EDGs dedicated to Unit 2are more dependent on service water cooling, which has a low fragility, the CDFvalue is higher for Unit 2 than for Unit 1. Explain and justify how the seismic CDF and LERF estimates apply to bothunits. To estimate the seismic LERF, in the LAR assumes a 0.1 conditional large early releaseprobability (CLERP) for seismic events, based on the internal events LERF to CDFratio. The staff notes that a seismic event could lead to seismic-specific failures ofstructures, systems, and components, resulting in additional LERF sequences that arenot in the internal events probabilistic risk assessment (PRA) model or potentiallyconverting non-LERF sequences in the internal events PRA model to seismic LERFsequences. The LAR does not provide sufficient justification for the selected CLERPbeing able to capture or bound such considerations. c. Explain why the containment is not expected to fail for seismic events andtherefore would not noticeably affect the assumed 0.1 CLERP, andconsequently, the seismic LERF estimate. d. Identify other containment failure or bypass scenarios and discuss the impact ofrelatively frequent seismic events on these scenarios. 21. In RAI 10 (see letter dated November 13, 2017), the staff asked the licensee to explainhow common cause failures (CCFs) are included in the PRA model and how thetreatment of CCF either meets the guidance in Regulatory Guide (RG) 1.177, "AnApproach for Plant-Specific, Risk-Informed Decisionmaking: Technical Specifications,"Revision 1 (ADAMS Accession No. ML100910008) or meets the intent of this guidancewhen quantifying a risk-informed completion time (RICT) for preventative maintenancefor components from a CCF group of three or more components. The response to theRAI states that "common cause failures are modeled as separate basic events, withcommon cause combinations in the fault tree as different basic events." The licenseefurther stated that the "common cause grouping is not dynamically changed when acomponent is removed from service for preventative maintenance" and that this is appropriate because "the component, though not out of service for a reason subject tocommon cause failure, remains a participant in the common cause events for theremainder of the component operation." It is unclear how the out of service component"remains a participant in the common cause events for the remainder of the componentoperation" and therefore it is unclear how the intent of RG 1.177 is met. Please explain clearly how CCFs are modeled in the CCNPP PRA and justify whyadjusting the common cause grouping is not necessary for preventative maintenance. In the explanation, include examples of fault trees for a CCF group of three componentsand the associated numerical results. 22. In RAI 11.a (see letter dated November 13, 2017), the staff requested the licensee toconfirm and describe how the treatment of CCF in the case of emergent failures eithermeets the guidance in RG 1.177 or meets the intent of this guidance when quantifying aRICT. In response to RAI 11.a the licensee stated that risk management actions will beimplemented. However in the response to RAI 11.b the licensee added the option to"numerically account for the increased possibility of CCF in the RICT calculation" to thetext for the CCNPP Technical Specification Administrative Section 5.5.18, withoutfurther justification on how it meets the intent of the guidance in RG 1.177 requested inRAI 11.a. a. Explain how the task to "numerically account for the increased possibility of CCFin the RICT calculation" will be performed for emergent failures. b. Justify the treatment of CCF meets the intent of the guidance in RG 1.177. 23. In RAI 14 (see letter dated November 13, 2017), the staff requested explanation on howthe containment spray and the containment cooling systems are modeled, and how aRICT based on CDF and LERF can be quantitatively determined for these systems. Inresponse to RAI 14 the licensee stated that both systems are explicitly modeled in thePRA and that the PRA modeling "includes system components, such as pumps, valvesand heat exchangers, and system dependencies, such as electrical and cooling watersystems." The licensee further explained that the PRA success criteria is one of the twoheaders for the containment spray system, and two out of four air coolers for thecontainment air recirculation and cooling system. The licensee stated that thesesystems "can be numerally quantified for impact on CDF and LERF," however did notexplain how these systems impact core damage or large early release. Since thecontainment spray and containment cooling systems are generally related to the long-term release sequences (not large early release), it is not immediately clear to the NRCstaff the impact that these systems have on the core damage and large early release inthe licensee's PRA model. Further, the iodine removal function of the containmentspray system is not usually captured in the PRA. Explain and justify how these systems impact CDF and LERF. 24. In RAI 15 (see letter dated November 13, 2017), the staff provided wording for aproposed license condition, consistent with the license condition included in NRC-approved Amendment Nos. 188 and 171 for the pilot risk-informed completion timelicense amendment request (ADAMS Accession No. ML15127A669). In response, thelicensee proposed the following text to be added to the CCNPP Technical Specification Administrative Section 5.5.18: a. A RICT must be calculated using the PRA and non-PRA methodsapproved by the NRC, including internal events, internal floods, andfire PRA. Changes to these PRA and non-PRA methods require priorNRC approval. The PRA maintenance and upgrade process willvalidate that changes to the PRA models used in the RICT programfollow the guidance in Appendix 1-A of ASME/ANS RA-Sa-2009,"Standard for Level 1/Large Early Release Frequency ProbabilisticRisk Assessment for Nuclear Power Plant Applications." b. A report shall be submitted following each PRA upgrade andassociated peer review, and prior to using the upgraded PRA tocalculate a RICT. The report shall describe the scope of the upgrade. The license condition approved for the pilot contains both the terms "method" and"approach." The license condition approved for the pilot would require prior NRCapproval when: ~ Switching from a non-PRA process, such as seismic margin analysis, to aseismic PRA, or vice-versa and ~ Changing processes within a PRA model. Describe, with examples, what constitutes a PRA and non-PRA methods that if changed,would require prior NRC approval. Best Regards,Michael L. Marshall, Jr.Senior Project Manager Plant Licensing Branch I-2Division of Operating Reactor LicensingOffice of Nuclear Reactor Regulation 301-415-2871 Docket No. 50-317 and 50-318 | : a. The staff notes that the CCNPP Expedited Seismic Evaluation Process Report(ESEP), submitted to the NRC on December 17, 2014 (ADAMS Accession No.ML14365A138), indicates that certain components, such as safety injectiontanks, motor control centers, electrical buses, main control room panels, wouldfail in a seismic event through interaction with nearby block walls, and thosecomponents were assigned a lower HCLPF of 0.175 g due to the block walllower capacity. This lower HCLPF could increase the seismic CDF and LERFestimates provided in the LAR. Justify the plant level HCLPF of 0.27 g PGA, given the noted block walls failuresat 0.175 g indicated in the ESEP, or provide, with justification, updated seismicCDF and LERF estimates. b. The 2003 LAR for extension of emergency diesel generator (EDG) completiontimes shows differences in estimated seismic CDF and LERF between Unit 1and Unit 2. According to the NRC Technical Evaluation Report for the IndividualPlant Examination for External Events, because the EDGs dedicated to Unit 2are more dependent on service water cooling, which has a low fragility, the CDFvalue is higher for Unit 2 than for Unit 1. Explain and justify how the seismic CDF and LERF estimates apply to bothunits. To estimate the seismic LERF, in the LAR assumes a 0.1 conditional large early releaseprobability (CLERP) for seismic events, based on the internal events LERF to CDFratio. The staff notes that a seismic event could lead to seismic-specific failures ofstructures, systems, and components, resulting in additional LERF sequences that arenot in the internal events probabilistic risk assessment (PRA) model or potentiallyconverting non-LERF sequences in the internal events PRA model to seismic LERFsequences. The LAR does not provide sufficient justification for the selected CLERPbeing able to capture or bound such considerations. c. Explain why the containment is not expected to fail for seismic events andtherefore would not noticeably affect the assumed 0.1 CLERP, andconsequently, the seismic LERF estimate. d. Identify other containment failure or bypass scenarios and discuss the impact ofrelatively frequent seismic events on these scenarios. 21. In RAI 10 (see letter dated November 13, 2017), the staff asked the licensee to explainhow common cause failures (CCFs) are included in the PRA model and how thetreatment of CCF either meets the guidance in Regulatory Guide (RG) 1.177, "AnApproach for Plant-Specific, Risk-Informed Decisionmaking: Technical Specifications,"Revision 1 (ADAMS Accession No. ML100910008) or meets the intent of this guidancewhen quantifying a risk-informed completion time (RICT) for preventative maintenancefor components from a CCF group of three or more components. The response to theRAI states that "common cause failures are modeled as separate basic events, withcommon cause combinations in the fault tree as different basic events." The licenseefurther stated that the "common cause grouping is not dynamically changed when acomponent is removed from service for preventative maintenance" and that this is appropriate because "the component, though not out of service for a reason subject tocommon cause failure, remains a participant in the common cause events for theremainder of the component operation." It is unclear how the out of service component"remains a participant in the common cause events for the remainder of the componentoperation" and therefore it is unclear how the intent of RG 1.177 is met. Please explain clearly how CCFs are modeled in the CCNPP PRA and justify whyadjusting the common cause grouping is not necessary for preventative maintenance. In the explanation, include examples of fault trees for a CCF group of three componentsand the associated numerical results. 22. In RAI 11.a (see letter dated November 13, 2017), the staff requested the licensee toconfirm and describe how the treatment of CCF in the case of emergent failures eithermeets the guidance in RG 1.177 or meets the intent of this guidance when quantifying aRICT. In response to RAI 11.a the licensee stated that risk management actions will beimplemented. However in the response to RAI 11.b the licensee added the option to"numerically account for the increased possibility of CCF in the RICT calculation" to thetext for the CCNPP Technical Specification Administrative Section 5.5.18, withoutfurther justification on how it meets the intent of the guidance in RG 1.177 requested inRAI 11.a. a. Explain how the task to "numerically account for the increased possibility of CCFin the RICT calculation" will be performed for emergent failures. b. Justify the treatment of CCF meets the intent of the guidance in RG 1.177. 23. In RAI 14 (see letter dated November 13, 2017), the staff requested explanation on howthe containment spray and the containment cooling systems are modeled, and how aRICT based on CDF and LERF can be quantitatively determined for these systems. Inresponse to RAI 14 the licensee stated that both systems are explicitly modeled in thePRA and that the PRA modeling "includes system components, such as pumps, valvesand heat exchangers, and system dependencies, such as electrical and cooling watersystems." The licensee further explained that the PRA success criteria is one of the twoheaders for the containment spray system, and two out of four air coolers for thecontainment air recirculation and cooling system. The licensee stated that thesesystems "can be numerally quantified for impact on CDF and LERF," however did notexplain how these systems impact core damage or large early release. Since thecontainment spray and containment cooling systems are generally related to the long-term release sequences (not large early release), it is not immediately clear to the NRCstaff the impact that these systems have on the core damage and large early release inthe licensee's PRA model. Further, the iodine removal function of the containmentspray system is not usually captured in the PRA. Explain and justify how these systems impact CDF and LERF. 24. In RAI 15 (see letter dated November 13, 2017), the staff provided wording for aproposed license condition, consistent with the license condition included in NRC-approved Amendment Nos. 188 and 171 for the pilot risk-informed completion timelicense amendment request (ADAMS Accession No. ML15127A669). In response, thelicensee proposed the following text to be added to the CCNPP Technical Specification Administrative Section 5.5.18: a. A RICT must be calculated using the PRA and non-PRA methodsapproved by the NRC, including internal events, internal floods, andfire PRA. Changes to these PRA and non-PRA methods require priorNRC approval. The PRA maintenance and upgrade process willvalidate that changes to the PRA models used in the RICT programfollow the guidance in Appendix 1-A of ASME/ANS RA-Sa-2009,"Standard for Level 1/Large Early Release Frequency ProbabilisticRisk Assessment for Nuclear Power Plant Applications." b. A report shall be submitted following each PRA upgrade andassociated peer review, and prior to using the upgraded PRA tocalculate a RICT. The report shall describe the scope of the upgrade. The license condition approved for the pilot contains both the terms "method" and"approach." The license condition approved for the pilot would require prior NRCapproval when: ~ Switching from a non-PRA process, such as seismic margin analysis, to aseismic PRA, or vice-versa and ~ Changing processes within a PRA model. Describe, with examples, what constitutes a PRA and non-PRA methods that if changed,would require prior NRC approval. Best Regards,Michael L. Marshall, Jr.Senior Project Manager Plant Licensing Branch I-2Division of Operating Reactor LicensingOffice of Nuclear Reactor Regulation 301-415-2871 Docket No. 50-317 and 50-318}} | ||
}} |
Revision as of 23:22, 16 May 2018
ML18128A384 | |
Person / Time | |
---|---|
Site: | Calvert Cliffs ![]() |
Issue date: | 05/08/2018 |
From: | Marshall M L Plant Licensing Branch 1 |
To: | Stewart G H Exelon Generation Co |
Marshall M L, NRR/DORL/LPLI, 415-2871 | |
References | |
CAC MF7415, CAC MF7416, EPID L-2016-LLA-0001 | |
Download: ML18128A384 (4) | |
Text
From:Marshall, MichaelTo:"Stewart, Glenn H:(GenCo-Nuc)"Cc:"Villar, Enrique:(GenCo-Nuc)"; James Danna (James.Danna@nrc.gov)
Subject:
CALVERT CLIFFS NUCLEAR POWER PLANT, UNITS 1 AND 2 - DRAFT REQUEST FOR ADDITIONAL INFORMATIONREGARDING RISK-INFORMED TECHNICAL SPECIFICATION COMPLETION TIMES (CAC NOS. MF7415 ANDMF7416; EPID L-2016-LLA-0001)Date:Tuesday, May 08, 2018 2:34:00 PMHello Glenn, By letter dated February 25, 2016 (ADAMS Accession No. ML16060A223), assupplemented by letters dated April 3, 2017 (ADAMS Accession No. ML17094A591),January 11, 2018 (ADAMS Accession No. ML18011A665), and January 18, 2018 (ADAMSAccession No. ML18018B340), Exelon Generation Company, LLC (Exelon; licensee)submitted a License Amendment Request (LAR) proposing to modify the Calvert CliffsNuclear Power Plant (CCNPP), Units 1 and 2 Technical Specification requirements topermit the use of risk-informed completion times. The Nuclear Regulatory Commission (NRC) staff has determined that additional informationis needed to complete its review of the request. The purpose of this e-mail is to provide adraft copy of the request for additional information (RAI) for your review to ensure that: ~ the draft RAI questions are understandable,~ the bases for the questions are clear, and~ to determine whether the information being requested was previously docketed. The draft RAI questions listed below are not a complete listing of the additional informationneeded to complete the NRC staff's review. Additional RAI questions were provided viaseparate correspondence. RAIs numbers 1 through 19 were sent to Exelon in letters datedNovember 13, 2017 (ADAMS Accession No. ML17304A941) and December 21, 2017(ADAMS Accession No. ML17346A909). If Exelon has any questions or comments concerning the clarity or basis for the RAIquestions, please plan to share your questions or comments with the cognizant NRC staffat the public meeting scheduled for May 16, 2018 (ADAMS Accession No. ML18123A280). Additionally, be prepared to confirm that Exelon will be able to provide responses to the RAIquestions within 30 days of the issuance of the final RAIs. Draft RAIs 20. Enclosure 4 of the letter dated February 25, 2016, states that a total seismic coredamage frequency (CDF) contribution of 1.1E-6/year and a seismic large early releasefrequency (LERF) contribution of 1.1E-7/year will be added to the configuration specificdelta CDF and delta LERF from the internal events and fire initiating event contributionsto estimate the risk-informed completion time. The LAR states that these seismicestimates are based on the re-evaluated seismic hazard for CCNPP performed inresponse to the Near-Term Task Force 2.1 (ADAMS Accession No. ML14099A196) andan estimated plant level high confidence of low probability of failure (HCLPF) of 0.27gpeak ground acceleration (PGA) as used in the 2003 LAR entitled "Extension of DieselGenerator Required Action Completion Time" (ADAMS Accession No. ML031360410).
- a. The staff notes that the CCNPP Expedited Seismic Evaluation Process Report(ESEP), submitted to the NRC on December 17, 2014 (ADAMS Accession No.ML14365A138), indicates that certain components, such as safety injectiontanks, motor control centers, electrical buses, main control room panels, wouldfail in a seismic event through interaction with nearby block walls, and thosecomponents were assigned a lower HCLPF of 0.175 g due to the block walllower capacity. This lower HCLPF could increase the seismic CDF and LERFestimates provided in the LAR. Justify the plant level HCLPF of 0.27 g PGA, given the noted block walls failuresat 0.175 g indicated in the ESEP, or provide, with justification, updated seismicCDF and LERF estimates. b. The 2003 LAR for extension of emergency diesel generator (EDG) completiontimes shows differences in estimated seismic CDF and LERF between Unit 1and Unit 2. According to the NRC Technical Evaluation Report for the IndividualPlant Examination for External Events, because the EDGs dedicated to Unit 2are more dependent on service water cooling, which has a low fragility, the CDFvalue is higher for Unit 2 than for Unit 1. Explain and justify how the seismic CDF and LERF estimates apply to bothunits. To estimate the seismic LERF, in the LAR assumes a 0.1 conditional large early releaseprobability (CLERP) for seismic events, based on the internal events LERF to CDFratio. The staff notes that a seismic event could lead to seismic-specific failures ofstructures, systems, and components, resulting in additional LERF sequences that arenot in the internal events probabilistic risk assessment (PRA) model or potentiallyconverting non-LERF sequences in the internal events PRA model to seismic LERFsequences. The LAR does not provide sufficient justification for the selected CLERPbeing able to capture or bound such considerations. c. Explain why the containment is not expected to fail for seismic events andtherefore would not noticeably affect the assumed 0.1 CLERP, andconsequently, the seismic LERF estimate. d. Identify other containment failure or bypass scenarios and discuss the impact ofrelatively frequent seismic events on these scenarios. 21. In RAI 10 (see letter dated November 13, 2017), the staff asked the licensee to explainhow common cause failures (CCFs) are included in the PRA model and how thetreatment of CCF either meets the guidance in Regulatory Guide (RG) 1.177, "AnApproach for Plant-Specific, Risk-Informed Decisionmaking: Technical Specifications,"Revision 1 (ADAMS Accession No. ML100910008) or meets the intent of this guidancewhen quantifying a risk-informed completion time (RICT) for preventative maintenancefor components from a CCF group of three or more components. The response to theRAI states that "common cause failures are modeled as separate basic events, withcommon cause combinations in the fault tree as different basic events." The licenseefurther stated that the "common cause grouping is not dynamically changed when acomponent is removed from service for preventative maintenance" and that this is appropriate because "the component, though not out of service for a reason subject tocommon cause failure, remains a participant in the common cause events for theremainder of the component operation." It is unclear how the out of service component"remains a participant in the common cause events for the remainder of the componentoperation" and therefore it is unclear how the intent of RG 1.177 is met. Please explain clearly how CCFs are modeled in the CCNPP PRA and justify whyadjusting the common cause grouping is not necessary for preventative maintenance. In the explanation, include examples of fault trees for a CCF group of three componentsand the associated numerical results. 22. In RAI 11.a (see letter dated November 13, 2017), the staff requested the licensee toconfirm and describe how the treatment of CCF in the case of emergent failures eithermeets the guidance in RG 1.177 or meets the intent of this guidance when quantifying aRICT. In response to RAI 11.a the licensee stated that risk management actions will beimplemented. However in the response to RAI 11.b the licensee added the option to"numerically account for the increased possibility of CCF in the RICT calculation" to thetext for the CCNPP Technical Specification Administrative Section 5.5.18, withoutfurther justification on how it meets the intent of the guidance in RG 1.177 requested inRAI 11.a. a. Explain how the task to "numerically account for the increased possibility of CCFin the RICT calculation" will be performed for emergent failures. b. Justify the treatment of CCF meets the intent of the guidance in RG 1.177. 23. In RAI 14 (see letter dated November 13, 2017), the staff requested explanation on howthe containment spray and the containment cooling systems are modeled, and how aRICT based on CDF and LERF can be quantitatively determined for these systems. Inresponse to RAI 14 the licensee stated that both systems are explicitly modeled in thePRA and that the PRA modeling "includes system components, such as pumps, valvesand heat exchangers, and system dependencies, such as electrical and cooling watersystems." The licensee further explained that the PRA success criteria is one of the twoheaders for the containment spray system, and two out of four air coolers for thecontainment air recirculation and cooling system. The licensee stated that thesesystems "can be numerally quantified for impact on CDF and LERF," however did notexplain how these systems impact core damage or large early release. Since thecontainment spray and containment cooling systems are generally related to the long-term release sequences (not large early release), it is not immediately clear to the NRCstaff the impact that these systems have on the core damage and large early release inthe licensee's PRA model. Further, the iodine removal function of the containmentspray system is not usually captured in the PRA. Explain and justify how these systems impact CDF and LERF. 24. In RAI 15 (see letter dated November 13, 2017), the staff provided wording for aproposed license condition, consistent with the license condition included in NRC-approved Amendment Nos. 188 and 171 for the pilot risk-informed completion timelicense amendment request (ADAMS Accession No. ML15127A669). In response, thelicensee proposed the following text to be added to the CCNPP Technical Specification Administrative Section 5.5.18: a. A RICT must be calculated using the PRA and non-PRA methodsapproved by the NRC, including internal events, internal floods, andfire PRA. Changes to these PRA and non-PRA methods require priorNRC approval. The PRA maintenance and upgrade process willvalidate that changes to the PRA models used in the RICT programfollow the guidance in Appendix 1-A of ASME/ANS RA-Sa-2009,"Standard for Level 1/Large Early Release Frequency ProbabilisticRisk Assessment for Nuclear Power Plant Applications." b. A report shall be submitted following each PRA upgrade andassociated peer review, and prior to using the upgraded PRA tocalculate a RICT. The report shall describe the scope of the upgrade. The license condition approved for the pilot contains both the terms "method" and"approach." The license condition approved for the pilot would require prior NRCapproval when: ~ Switching from a non-PRA process, such as seismic margin analysis, to aseismic PRA, or vice-versa and ~ Changing processes within a PRA model. Describe, with examples, what constitutes a PRA and non-PRA methods that if changed,would require prior NRC approval. Best Regards,Michael L. Marshall, Jr.Senior Project Manager Plant Licensing Branch I-2Division of Operating Reactor LicensingOffice of Nuclear Reactor Regulation 301-415-2871 Docket No. 50-317 and 50-318 From:Marshall, MichaelTo:"Stewart, Glenn H:(GenCo-Nuc)"Cc:"Villar, Enrique:(GenCo-Nuc)"; James Danna (James.Danna@nrc.gov)
Subject:
CALVERT CLIFFS NUCLEAR POWER PLANT, UNITS 1 AND 2 - DRAFT REQUEST FOR ADDITIONAL INFORMATIONREGARDING RISK-INFORMED TECHNICAL SPECIFICATION COMPLETION TIMES (CAC NOS. MF7415 ANDMF7416; EPID L-2016-LLA-0001)Date:Tuesday, May 08, 2018 2:34:00 PMHello Glenn, By letter dated February 25, 2016 (ADAMS Accession No. ML16060A223), assupplemented by letters dated April 3, 2017 (ADAMS Accession No. ML17094A591),January 11, 2018 (ADAMS Accession No. ML18011A665), and January 18, 2018 (ADAMSAccession No. ML18018B340), Exelon Generation Company, LLC (Exelon; licensee)submitted a License Amendment Request (LAR) proposing to modify the Calvert CliffsNuclear Power Plant (CCNPP), Units 1 and 2 Technical Specification requirements topermit the use of risk-informed completion times. The Nuclear Regulatory Commission (NRC) staff has determined that additional informationis needed to complete its review of the request. The purpose of this e-mail is to provide adraft copy of the request for additional information (RAI) for your review to ensure that: ~ the draft RAI questions are understandable,~ the bases for the questions are clear, and~ to determine whether the information being requested was previously docketed. The draft RAI questions listed below are not a complete listing of the additional informationneeded to complete the NRC staff's review. Additional RAI questions were provided viaseparate correspondence. RAIs numbers 1 through 19 were sent to Exelon in letters datedNovember 13, 2017 (ADAMS Accession No. ML17304A941) and December 21, 2017(ADAMS Accession No. ML17346A909). If Exelon has any questions or comments concerning the clarity or basis for the RAIquestions, please plan to share your questions or comments with the cognizant NRC staffat the public meeting scheduled for May 16, 2018 (ADAMS Accession No. ML18123A280). Additionally, be prepared to confirm that Exelon will be able to provide responses to the RAIquestions within 30 days of the issuance of the final RAIs. Draft RAIs 20. Enclosure 4 of the letter dated February 25, 2016, states that a total seismic coredamage frequency (CDF) contribution of 1.1E-6/year and a seismic large early releasefrequency (LERF) contribution of 1.1E-7/year will be added to the configuration specificdelta CDF and delta LERF from the internal events and fire initiating event contributionsto estimate the risk-informed completion time. The LAR states that these seismicestimates are based on the re-evaluated seismic hazard for CCNPP performed inresponse to the Near-Term Task Force 2.1 (ADAMS Accession No. ML14099A196) andan estimated plant level high confidence of low probability of failure (HCLPF) of 0.27gpeak ground acceleration (PGA) as used in the 2003 LAR entitled "Extension of DieselGenerator Required Action Completion Time" (ADAMS Accession No. ML031360410).
- a. The staff notes that the CCNPP Expedited Seismic Evaluation Process Report(ESEP), submitted to the NRC on December 17, 2014 (ADAMS Accession No.ML14365A138), indicates that certain components, such as safety injectiontanks, motor control centers, electrical buses, main control room panels, wouldfail in a seismic event through interaction with nearby block walls, and thosecomponents were assigned a lower HCLPF of 0.175 g due to the block walllower capacity. This lower HCLPF could increase the seismic CDF and LERFestimates provided in the LAR. Justify the plant level HCLPF of 0.27 g PGA, given the noted block walls failuresat 0.175 g indicated in the ESEP, or provide, with justification, updated seismicCDF and LERF estimates. b. The 2003 LAR for extension of emergency diesel generator (EDG) completiontimes shows differences in estimated seismic CDF and LERF between Unit 1and Unit 2. According to the NRC Technical Evaluation Report for the IndividualPlant Examination for External Events, because the EDGs dedicated to Unit 2are more dependent on service water cooling, which has a low fragility, the CDFvalue is higher for Unit 2 than for Unit 1. Explain and justify how the seismic CDF and LERF estimates apply to bothunits. To estimate the seismic LERF, in the LAR assumes a 0.1 conditional large early releaseprobability (CLERP) for seismic events, based on the internal events LERF to CDFratio. The staff notes that a seismic event could lead to seismic-specific failures ofstructures, systems, and components, resulting in additional LERF sequences that arenot in the internal events probabilistic risk assessment (PRA) model or potentiallyconverting non-LERF sequences in the internal events PRA model to seismic LERFsequences. The LAR does not provide sufficient justification for the selected CLERPbeing able to capture or bound such considerations. c. Explain why the containment is not expected to fail for seismic events andtherefore would not noticeably affect the assumed 0.1 CLERP, andconsequently, the seismic LERF estimate. d. Identify other containment failure or bypass scenarios and discuss the impact ofrelatively frequent seismic events on these scenarios. 21. In RAI 10 (see letter dated November 13, 2017), the staff asked the licensee to explainhow common cause failures (CCFs) are included in the PRA model and how thetreatment of CCF either meets the guidance in Regulatory Guide (RG) 1.177, "AnApproach for Plant-Specific, Risk-Informed Decisionmaking: Technical Specifications,"Revision 1 (ADAMS Accession No. ML100910008) or meets the intent of this guidancewhen quantifying a risk-informed completion time (RICT) for preventative maintenancefor components from a CCF group of three or more components. The response to theRAI states that "common cause failures are modeled as separate basic events, withcommon cause combinations in the fault tree as different basic events." The licenseefurther stated that the "common cause grouping is not dynamically changed when acomponent is removed from service for preventative maintenance" and that this is appropriate because "the component, though not out of service for a reason subject tocommon cause failure, remains a participant in the common cause events for theremainder of the component operation." It is unclear how the out of service component"remains a participant in the common cause events for the remainder of the componentoperation" and therefore it is unclear how the intent of RG 1.177 is met. Please explain clearly how CCFs are modeled in the CCNPP PRA and justify whyadjusting the common cause grouping is not necessary for preventative maintenance. In the explanation, include examples of fault trees for a CCF group of three componentsand the associated numerical results. 22. In RAI 11.a (see letter dated November 13, 2017), the staff requested the licensee toconfirm and describe how the treatment of CCF in the case of emergent failures eithermeets the guidance in RG 1.177 or meets the intent of this guidance when quantifying aRICT. In response to RAI 11.a the licensee stated that risk management actions will beimplemented. However in the response to RAI 11.b the licensee added the option to"numerically account for the increased possibility of CCF in the RICT calculation" to thetext for the CCNPP Technical Specification Administrative Section 5.5.18, withoutfurther justification on how it meets the intent of the guidance in RG 1.177 requested inRAI 11.a. a. Explain how the task to "numerically account for the increased possibility of CCFin the RICT calculation" will be performed for emergent failures. b. Justify the treatment of CCF meets the intent of the guidance in RG 1.177. 23. In RAI 14 (see letter dated November 13, 2017), the staff requested explanation on howthe containment spray and the containment cooling systems are modeled, and how aRICT based on CDF and LERF can be quantitatively determined for these systems. Inresponse to RAI 14 the licensee stated that both systems are explicitly modeled in thePRA and that the PRA modeling "includes system components, such as pumps, valvesand heat exchangers, and system dependencies, such as electrical and cooling watersystems." The licensee further explained that the PRA success criteria is one of the twoheaders for the containment spray system, and two out of four air coolers for thecontainment air recirculation and cooling system. The licensee stated that thesesystems "can be numerally quantified for impact on CDF and LERF," however did notexplain how these systems impact core damage or large early release. Since thecontainment spray and containment cooling systems are generally related to the long-term release sequences (not large early release), it is not immediately clear to the NRCstaff the impact that these systems have on the core damage and large early release inthe licensee's PRA model. Further, the iodine removal function of the containmentspray system is not usually captured in the PRA. Explain and justify how these systems impact CDF and LERF. 24. In RAI 15 (see letter dated November 13, 2017), the staff provided wording for aproposed license condition, consistent with the license condition included in NRC-approved Amendment Nos. 188 and 171 for the pilot risk-informed completion timelicense amendment request (ADAMS Accession No. ML15127A669). In response, thelicensee proposed the following text to be added to the CCNPP Technical Specification Administrative Section 5.5.18: a. A RICT must be calculated using the PRA and non-PRA methodsapproved by the NRC, including internal events, internal floods, andfire PRA. Changes to these PRA and non-PRA methods require priorNRC approval. The PRA maintenance and upgrade process willvalidate that changes to the PRA models used in the RICT programfollow the guidance in Appendix 1-A of ASME/ANS RA-Sa-2009,"Standard for Level 1/Large Early Release Frequency ProbabilisticRisk Assessment for Nuclear Power Plant Applications." b. A report shall be submitted following each PRA upgrade andassociated peer review, and prior to using the upgraded PRA tocalculate a RICT. The report shall describe the scope of the upgrade. The license condition approved for the pilot contains both the terms "method" and"approach." The license condition approved for the pilot would require prior NRCapproval when: ~ Switching from a non-PRA process, such as seismic margin analysis, to aseismic PRA, or vice-versa and ~ Changing processes within a PRA model. Describe, with examples, what constitutes a PRA and non-PRA methods that if changed,would require prior NRC approval. Best Regards,Michael L. Marshall, Jr.Senior Project Manager Plant Licensing Branch I-2Division of Operating Reactor LicensingOffice of Nuclear Reactor Regulation 301-415-2871 Docket No. 50-317 and 50-318