RA-20-0364, 1 & 2 - Response to RAI for License Amendment Request to Modify Approved 10 CFR 50.69, Risk-Informed Categorization and Treatment of Structures, Systems, and Components for Nuclear Power Reactors Categorization Process

1 & 2 - Response to RAI for License Amendment Request to Modify Approved 10 CFR 50.69, Risk-Informed Categorization and Treatment of Structures, Systems, and Components for Nuclear Power Reactors Categorization Process

ML20329A466
Person / Time
Site:	Brunswick
Issue date:	11/24/2020
From:	Ratliff J Duke Energy Progress
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-20-0364
Download: ML20329A466 (17)

Text

Jay Ratliff Plant Manager Brunswick Nuclear Plant 8470 River Rd SE Southport, NC 28461 o: 910.832.3480 Serial: RA-20-0364 10 CFR 50.90 November 24, 2020 United States Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 BRUNSWICK STEAM ELECTRIC PLANT, UNIT NOS. 1 AND 2 RENEWED FACILITY OPERATING LICENSE NOS. DPR-71 AND DPR-62 DOCKET NOS. 50-325 AND 50-324

SUBJECT:

Response to Request for Additional Information (RAI) for License Amendment Request to Modify Approved 10 CFR 50.69, "Risk-Informed Categorization and Treatment of Structures, Systems, and Components for Nuclear Power Reactors Categorization Process

REFERENCES:

1. Duke Energy Letter to the U.S. Nuclear Regulatory Commission, RA-19-0437, License Amendment Request to Modify Approved 10 CFR 50.69, "Risk-Informed Categorization and Treatment of Structures, Systems, and Components for Nuclear Power Reactors Categorization Process, dated July 9, 2020 (ADAMS Accession Number ML20191A054).

2. Electronic Mail from Andy Hon to Art Zaremba, Brunswick License Amendment Request to modify its approved 10 CFR 50.69, Risk-Informed Categorization and Treatment of SSC categorization process (EPID: L-2020-LLA-0152), dated October 29, 2020 (ADAMS Accession Number ML20309A521).

Ladies and Gentlemen:

By letter dated July 9, 2020 (Reference 1), Duke Energy Progress, LLC (Duke Energy) submitted a license amendment request for Brunswick Steam Electric Plant (BSEP), Units 1 and

2. The proposed amendment would modify the approved 10 CFR 50.69 categorization process.

By electronic mail dated October 29, 2020 (Reference 2), the U.S. Nuclear Regulaory Commission (NRC) requested additional information (RAI) required to complete its review. The Enclosure to this letter provides Duke Energys response to the NRC RAIs. Attachment 1 provides a list of categorization prerequisites in support of the response to RAI 6. Attachment 1 of this letter supersedes Attachment 1 of Reference 1.

This document contains no new regulatory commitments.

U.S. Nuclear Regulatory Commission Page 2 Serial: RA-20-0364 Should you have any questions concerning this letter, or require additional information, please contact Art Zaremba, Manager - Nuclear Fleet Licensing, at 980-373-2062.

Sincerely, Jay Ratliff Plant Manager Brunswick Steam Electric Plant

Enclosure:

Duke Energy Response to Request for Additional Information Attachment

1. List of Categorization Prerequisites

U.S. Nuclear Regulatory Commission Page 3 Serial: RA-20-0364 Cc (with enclosure):

L. Dudes, Regional Administrator U. S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA 30303-1257 A.L. Hon, Project Manager (BSEP) (Electronic Copy only)

U. S. Nuclear Regulatory Commission One White Flint North, Mail Stop 8 G9A 11555 Rockville Pike Rockville, MD 20852-2738 Andrew.Hon@nrc.gov G. Smith, NRC Senior Resident Inspector 8470 River Road Southport, NC 28461-8869 Chair - North Carolina Utilities Commission (Electronic Copy only) 4325 Mail Service Center Raleigh, NC 27699-4300 swatson@ncuc.net W. Lee Cox III, Section Chief (Electronic Copy Only)

Radiation Protection Section North Carolina Department of Health and Human Services 1645 Mail Service Center Raleigh, NC 27699-145 lee.cox@dhhs.nc.gov

RA-20-0364 Enclosure Page 1 of 12 Enclosure Duke Energy Progress, LLC Brunswick Steam Electric Plant Units 1 and 2 Duke Energy Response to Request for Additional Information

RA-20-0364 Enclosure Page 2 of 12 REQUESTS FOR ADDITIONAL INFORMATION REGULATORY BASIS The regulation at 10 CFR 50.69(c)(1)(ii) states, in part, that the SSC categorization process must determine SSC functional importance using an integrated, systematic process for addressing initiating events (internal and external), and all aspects of the integrated, systematic process used to characterize SSC importance must reasonably reflect the current plant configuration and operating practices, and applicable plant and industry operational experience.

The requirement of 10 CFR 50.69(b)(2)(ii) states that the licensees application contain a description of the measures taken to assure that the quality and level of detail of the systematic processes that evaluate the plant for internal and external events during normal operation, low power, and shutdown (including the plant-specific PRA, margins-type approaches, or other systematic evaluation techniques used to evaluate severe accident vulnerabilities) are adequate for the categorization of SSCs.

In addition, Regulatory Guide (RG) 1.201, Guidelines for Categorizing Structures, Systems, and Components in Nuclear Power Plants According to Their Safety Significance, endorses NEI 00-04, which provides guidance on including external events in the categorization of SSCs. Figure 5-6 in Section 5.4 of NEI 00-04 illustrates the process that begins with the SSCs selected for categorization and then proceeds through the flow chart for each external hazard.

RAI 1

Issue The LAR requested to use screening of the external flooding (XF) instead of the use of an XF probabilistic risk assessment (PRA) in its 10 CFR 50.69 program. The XF PRA was approved for use in Brunswicks 10 CFR 50.69 program as part of the NRC staffs approval (ADAMS Accession No. ML19149A471). The current LAR proposes screening of the XF hazard in Brunswicks categorization process. The SSCs necessary for mitigation of an XF hazard at Brunswick were included in the XF PRA. The licensees response in letter dated November 2, 2018 (ADAMS Accession No. ML18306A523), to Request for Additional Information (RAI) 18(e) for the previously approved LAR, identified changes to the internal events PRA model to develop the XF PRA. It is unclear to the NRC staff if any of the SSCs included in the XF PRA are unique to mitigation of the XF hazard at Brunswick, and therefore, are not included in Brunswicks internal events and/or internal fire PRAs. Further, the NRC staff is also unclear whether the proposed screening of XF hazard will appropriately evaluate the categorization of SSC necessary for mitigation of the XF hazard, especially those that are unique to mitigation of the XF hazard.

RAI

a. Describe the mitigation of the XF hazard at Brunswick, comparing the SSCs necessary for such mitigation against those necessary for mitigation of other initiators, such as those from

RA-20-0364 Enclosure Page 3 of 12 internal events and internal fires. The description should identify SSCs that are unique to mitigation of the XF hazard at Brunswick and are not included in the internal events and/or internal fire PRAs.

b. Describe how the proposed screening of the XF hazard, in conjunction with the previously approved categorization process, will evaluate the categorization of SSCs necessary for mitigation of the XF hazard, especially those that are unique to mitigation of the XF hazard.

Response a.:

The XF hazard at BSEP is mitigated by crediting the flood protection features that protect the equipment needed for safe shutdown. Flood protection features are identified in BSEP documentation and include, but are not limited to building walls, penetration seals, watertight doors, and temporary flood barriers. As described in the License Amendment Request (LAR)

(Reference 1), some of these features are permanent (e.g., seals around piping, personnel access doors) and some are installed during an impending storm (e.g., temporary flood barriers). By crediting these features, all safe shutdown equipment is protected from flood waters. When a system is to be categorized, all SSCs in the system will be reviewed against the XF hazard during the categorization process to ensure that the NEI 00-04 Section 5.4 process is followed. Per NEI 00-04 Section 5.4, any SSC being categorized will be evaluated to determine if the component participates in the screened scenario, and those that do participate in the scenario are then evaluated to determine if failure of the component results in the scenario becoming unscreened.

There were no XF-unique components modeled in the XF PRA. The flood protection features were not directly modeled. There are no SSCs unique to XF modeled in the internal events or fire PRA, which is consistent with industry practice.

The description of the XF PRA model in response to RAI 18, Part e from Duke Energy letter dated Nov 2, 2018 (ADAMS Accession No. ML18306A523) provided specific details on how the external flood initiator was coupled to the plant response model. The table in the RAI describes the XF specific initiator gate and what existing basic events in the model are failed due to those specific XF initiators. There were no unique components added to the XF PRA model that are not in the internal events or fire PRA models.

There are no specific SSCs that were added to the XF PRA model that are not addressed in the internal events, internal fire and/or high winds PRA models.

Response b:

The only categorization process step different from the NRC-approved process for categorizing components at BSEP is the process step for evaluating components against the XF hazard. BSEP will use the approved screening process (non-PRA) for the XF hazard, as described in NEI 00-04 Section 5.4 as endorsed by the NRC, including Figure 5-6. As stated above, there are no unique components in the XF PRA model necessary for mitigation of the XF hazard that are not already aligned with components in the other PRA models. When a system is categorized, the components of that system will be evaluated against the XF hazard

RA-20-0364 Enclosure Page 4 of 12 scenario and any component whose failure would cause the scenario to become unscreened will be assessed as high safety significant. This ensures that modeled components will continue to be evaluated per the NRC-approved process. Components assessed as high safety significant for non-modeled hazards will remain high safety significant and cannot be over-ridden, and changed to low safety significant, by the Integrated Decision Making Panel (IDP).

As stated in the response to RAI 1.a, SSCs necessary for mitigation of the XF hazard are the flood protection features that protect the equipment needed for safe shutdown. These are the only SSCs unique to the mitigation of the XF hazard.

RAI 2

Issue Section 3.1.5, SSCs Required for External Flood Screening, of the enclosure to the LAR provides a list of SSCs that, if failed, would result in an unscreened XF scenario for the Combined Effects (CE) storm surge event. The LAR does not mention the use of Figure 5-6 other than for the list in Section 3.1.5 of the enclosure to the LAR. Section 3.1.2, Local Intense Precipitation Disposition, of the enclosure to the LAR states that water accumulation in the equipment access area behind door D-3 will be handled via a permanent passive floor drain and the Reactor Building sump system. However, the floor drains are not included in the list in Section 3.1.5 of the enclosure to the LAR. The licensee's supplement dated February 13, 2019, to the previously approved LAR discussed the potential categorization of floor drains as implicitly modeled components in the context of the XF PRA.

Section 3.1.4 of the enclosure to the LAR discusses the licensees procedure 0AI-68, Brunswick Nuclear Plant Response to Severe Weather Warnings, Revision 52, for response to a CE storm surge event. The licensees February 13, 2019, supplement is consistent with Section 9.2.2 of NEI 00-04, in that if the failure of an SSC by itself will prevent the successful completion of a risk-significant human action, the SSC will become a candidate high-safety-significant.

However, the current LAR appears to present the list in Section 3.1.5 of the enclosure to the LAR as the complete list of SSCs if Figure 5-6 in NEI 00-04 were for the XF hazard during categorization of SSCs. It is unclear to the NRC staff whether all potential impacts of XF using Figure 5-6 of NEI 00-04 on categorization have been evaluated and how these can be known before the selection of an SSC for categorization.

RAI

a. Clarify whether the guidance in NEI 00-04 and Figure 5-6 therein will be followed as part of Brunswicks 10 CFR 50.69 program during categorization of SSCs to evaluate the impact of XF on the categorization. If Figure 5-6 will not be followed, justify the deviation from the NRC-endorsed guidance only for XF.

b. Explain whether the list in Section 3.1.5 of the enclosure to the LAR is a complete list or only a representative list based on the identified modifications. If the list is considered

RA-20-0364 Enclosure Page 5 of 12 complete, justify how all potential impacts of XF using Figure 5-6 of NEI 00-04 on categorization have been evaluated prior to the selection of an SSC for categorization. Such impacts include, but are not limited to, floor drains, human actions in procedures applicable to the XF hazard, vents and barriers on the fuel oil tank chamber (FOTC) roof (see RAI 6), and any XF-specific mitigation equipment (see RAI 1).

Response a:

BSEP will use the approved screening process (non-PRA) for the XF hazard as described in NEI 00-04 Section 5.4, as endorsed by the NRC, including Figure 5-6. When a system is categorized, the components of that system will be evaluated against the XF hazard scenario and any component whose failure would cause the scenario to become unscreened will be assessed as high safety significant. This ensures that modeled components will continue to be evaluated per the NRC-approved process. Components assessed as high safety significant for non-modeled hazards will remain high safety significant and cannot be over-ridden, and changed to low safety significant, by the IDP.

Response b:

The list in Section 3.1.5 of Reference 1 was intended to be only a representative list based on the identified modifications. As described in Part a of this RAI, all SSCs within a given categorization will be assessed for the components role in the screened hazard in accordance with NEI 00-04 Section 5.4, including Figure 5-6.

RAI 3

Issue Section 3.1.5 of the enclosure to the LAR states that components in the table in that section would not be categorized as low safety significant (LSS) unless adequate justification is provided to demonstrate that their failure would not result in an unscreened scenario in accordance with NEI 00-04 Figure 5-6. This statement would be applicable to other components that would be identified as high-safety-significant after following Figure 5-6 in NEI 00-04 (see RAI 1). Table 3-1 of the LAR for Brunswicks previously approved 10 CFR 50.69 program shows that categorization from Other External Hazards cannot be changed by the Integrated Decision-Making Panel (IDP). Therefore, it appears to the NRC staff that the discussion in Section 3.1.5 of the enclosure to this LAR is inconsistent with, and potentially a deviation from, the approved 10 CFR 50.69 program.

RAI Explain how the proposed approach for categorization of SSCs using Figure 5-6 of NEI 00-04 is consistent with the approved 10 CFR 50.69 program. The explanation should address and justify the apparent inconsistency between the ability of the IDP to change categorization in Table 3-1 of the previous LAR and the statements in Section 3.1.5 of the enclosure to this LAR.

RA-20-0364 Enclosure Page 6 of 12

Response

The LAR (Reference 1) language in Section 3.1.5 was not intended to contradict the NEI 00-04 Figure 5-6 process. The language was intended to explain that the components in the LAR (Reference 1) Section 3.1.5 table are credited in the external flooding screening, and therefore, if they are categorized, would be evaluated to determine whether their failure would result in an unscreened scenario. Additional components not listed in the LAR (Reference 1) Section 3.1.5 table are also credited in the screening and would go through the same process if categorized.

BSEP will use the approved screening process (non-PRA) for the XF hazard as described in NEI 00-04 Section 5.4 as endorsed by the NRC, including Figure 5-6. When a system is categorized, the components of that system will be evaluated against the XF hazard scenario and any component whose failure would cause the scenario to become unscreened will be assessed as high safety significance. This ensures that modeled components will continue to be evaluated per the NRC-approved process. Components assessed as high safety significant for non-modeled hazards will remain high safety significant and cannot be over-ridden, and changed to low safety significant, by the IDP.

RAI 4

Issue Section 3.1.2 of the enclosure to the LAR states that tsunamis, failure of dams and onsite water control/storage structures, and flooding in streams and rivers is considered screened per the initial preliminary screening criteria identified in Attachment 3 of the enclosure to the LAR. Section 3.1.3 of the enclosure to the LAR discusses the initial screening criteria for local intense precipitation. Section 3.1.4 of the enclosure to the LAR discusses the preliminary initial screening criteria for the CE storm surge mechanism. It is unclear why the screening criteria are preliminary, initial, and preliminary initial, as well as how and when the screening criteria will be finalized for review.

The licensee has proposed the use of screening criterion C1, Event damage potential is less than events for which plant is designed, for the CE storm surge mechanism in addition to C5, Event develops slowly, allowing adequate time to eliminate or mitigate the threat. It appears that the basis for proposing to use the C1 criterion is the flood protection barriers. However, the NRC staffs understanding is that the current Brunswick licensing basis has not been changed because of the reevaluated flood hazard. Therefore, it is unclear how the plant is designed for the reevaluated CE storm surge mechanism.

RAI

a. Explain why the screening criteria in the above-mentioned sections of the enclosure to the LAR are preliminary, initial, and preliminary initial. Provide the final screening criteria with any additional basis for review by the NRC staff.

RA-20-0364 Enclosure Page 7 of 12

b. Justify the use of the criterion C1, Event damage potential is less than events for which plant is designed for the CE storm surge mechanism, given that the current Brunswick licensing basis does not appear to have been changed by the reevaluated hazard.

Response a:

In Section 3.1.2 the term initial preliminary screening criteria is used to denote the left column of the table in the LAR (Reference 1) Attachment 3. Similarly, in Section 3.1.3 of the LAR (Reference 1), the term initial screening criteria and in Section 3.1.4 the term preliminary initial screening criteria, is used to denote the left column of the table in the LAR (Reference 1) . These terms are used in SR-EXT-B1 in Part 6 of the PRA standard and were not intended to imply that there are different screening criteria for the XF hazard other than those shown in Attachment 3 of the application, nor were the terms intended to imply that the final screening assessment is not complete. The screening assessment is complete, and the screening criteria used to screen the XF hazards are included in the second column of the LAR (Reference 1) Attachment 3 (i.e., column labeled Criterion).

Response b:

The re-evaluated flood hazard constitutes part of the design basis for BSEP and provides significant margin in comparison to the licensing basis flood described in the Updated Final Safety Analysis Report (i.e., the current licensing basis). The following documents the justification for the use of screening criteria C1.

The LAR (Reference 1) Section 3.1.4, states that the CE storm surge event is considered screened utilizing criteria C1 (Event damage potential is < events for which plant is designed) and C5 (Event develops slowly, allowing adequate time to eliminate or mitigate the threat). The basis for utilizing criteria C1 is that once the proposed modifications outlined in Attachment 1 are installed, the flood barriers (including permanent flood barriers, temporary flood barriers, and debris barriers) will provide permanent physical protection to the site during a CE probable maximum storm surge (CE PMSS) event such that the event damage potential (post-modification) will also be less than the event for which the plant was designed.

Regarding the basis for screening using C5, the procedure 0AI-68 provides a timeline for the event progression including warning time, site preparation and time margin available. The operator response, warning time and time required for installation was evaluated against the NRC endorsed NEI 16-05 Appendix C guidance for "Evaluating Manual Actions for the Integrated Assessment (IA)" process. It has been concluded, given the timeline presented, that a CE storm surge event is slow to develop and initial screening criteria C5 is appropriate given there is adequate time for the site to prepare and mitigate the effects from the storm.

Once the modifications described in the LAR (Reference 1) have been installed, the plant design basis will have changed to reflect the CE storm surge event and associated effects. At that point, the plant will be designed to withstand the CE storm surge and associated effects.

The design requirements for the flood protection features (including permanent flood barriers, temporary flood barriers, and debris barriers) includes the CE storm surge and associated effects. These requirements cannot be changed without a plant design change and engineering evaluation.

RA-20-0364 Enclosure Page 8 of 12 The Duke Energy Design (Engineering) Change process formally controls the design of the plant including design requirements for SSCs. Installation of the modifications described in the LAR (Reference 1) establishes the new design basis for the plant in that the flood protection features must be designed to withstand the hazard (CE storm surge and associated effects) and must be designed to the appropriate engineering standards. Changes to any flood protection features must be evaluated by the design change process to ensure the design of the plant is maintained, as well as the 10CFR 50.59 and regulatory commitment change processes. All three of these processes would recognize the requirement for flood protection features to remain capable of withstanding the CE storm surge and associated effects.

Additionally, the BSEP performance monitoring program discussed in the approved 10 CFR 50.69 program (Reference 2) reviews plant design changes and will ensure the continued validity of the plant-specific information related to hazards considered in the program, including the XF hazard. Any changes to the plant, including the XF hazard, will be captured and appropriately addressed as part of the 10 CFR 50.69 program.

Screening criterion C1 is closely related to the screening criterion EXT-B1 criterion 1 of the 2009 PRA Standard (Reference 3). This criterion also references the plant design basis - not licensing basis. As discussed above, installation of the modifications described in the LAR (Reference 1) updates the plant design basis to withstand the external flood hazard being screened in this application.

As such, the external flooding event will be mitigated by the design of the plant (i.e., the new design basis) and change control processes will recognize the required design parameters and maintain their integrity.

RAI 5

Issue Section 3.1.4 of the enclosure to the LAR states that Brunswicks procedure 0AI-68 establishes unambiguous procedural triggers, a clear organizational response, and provides a detailed timeline for carrying out the actions required for the arrival of a CE storm surge event. The same section of the enclosure to the LAR also states, it was concluded that the site response is adequate with more than twice the time margin required to re-perform actions in the event that barrier installation is not completed correctly during the first attempt. The NRC staffs assessment of Brunswicks focused evaluation (FE) based on the reevaluated flooding hazard at the site (ADAMS Accession No. ML18348B185; non-publicly available) stated that because the licensee proposed modifications to the flood protection barriers, it is expected that Administrative Instruction 0Al-68 be modified to incorporate such changes. However, the LAR does not discuss such whether the time margin available in 0AI-68 considers these changes.

Section 3.1.4 of the enclosure to the LAR indicates that the actions in 0AI-68 have been time validated. However, it is unclear whether the validation has been performed via actual implementation or training. It appears to the NRC staff that 0AI-68 is likely to have been invoked in response to recent hurricane events that either impacted or had the potential to impact the Brunswick site. Therefore, it appears that information related to the time margin cited in the LAR is available from actual implementation of the procedure.

RA-20-0364 Enclosure Page 9 of 12 RAI Confirm that the timeline for 0AI-68 discussed in Section 3.1.4 of the enclosure to the LAR considers changes to 0AI-68 to reflect the modifications to the flood protection barriers proposed in Brunswicks FE, as well as in Attachment 1 of the enclosure to the LAR or justify the representativeness of the timeline and the time margin for 0AI-68 to support the screening of the CE storm surge event. The response can include insights, if available, from recent operational experience in the implementation of 0AI-68 at Brunswick to support the conclusions mentioned in Section 3.1.4 of the enclosure to the LAR regarding unambiguous procedural triggers, detailed timeline for carrying out the actions, and time margin required to re-perform actions.

Response

The timeline for installation of the flood barriers as defined in 0AI-68 is not expected to change significantly after the modifications to the flood protection barriers proposed in the Brunswick FE and this LAR (Reference 1), and any change to the time is expected to decrease the barrier installation time. Modifications to the flood protection barriers proposed in Brunswicks FE will not significantly alter the installation process from that of the existing flood protection barriers, as the only difference is the height of the barriers. Maintenance and Engineering staff have already completed walkdowns of the design change for the new barriers and have confirmed the timing should not change significantly from current estimates, and, as previously stated, timelines for installation are expected to decrease due to new staging locations. Additionally, the design and modification process for the new flood protection barriers includes a requirement that the transport and installation of the barriers is validated prior to completion of the modification.

Below is a description of the overall action timeline:

This timeline is begun by unambiguous, well-defined procedural triggers. Consistent with the guidance in NEI 16-05 Appendix C, the procedural trigger to initiate site response to the flood is issuance of a hurricane watch from the National Oceanic and Atmospheric Association (NOAA), which is 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> in advance of the anticipated onset of tropical-storm-force winds in an area, and includes a prediction of the storm surge.

Per the site procedures, installation of the flood barriers is initiated no later than a hurricane watch being issued for the area with a predicted storm surge of 20 feet or greater. Flood barriers are required to be installed 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> prior to the predicted storm surge of 20 feet or greater on site.

Per NOAA and confirmed in the FE, the hurricane watch trigger with a storm surge prediction of 20 feet or greater allows 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> of warning time for site preparation. The current estimate to install all temporary flood barriers is approximately 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> if each barrier was installed in series. Typically, the barriers are installed by multiple crews in parallel, which would further reduce the duration for installation, however, it is not proceduralized how many crews would be used, so a conservative approach to determining the time margin has been presented. The conclusion of the timing analysis is that the temporary flood barriers installation has more than twice the time available as is required, such that there is sufficient

RA-20-0364 Enclosure Page 10 of 12 time to completely repeat the entire installation process at least once. The typical site response would include multiple crews performing barrier installation, so the timeline presented is conservative.

There are no special qualifications required for installation of the barriers. Maintenance personnel were trained when the original barriers were put into place. The design change for the new barriers will also require a review from training per the Accredited Training Program, to determine if additional training for maintenance personnel is warranted.

The site has been affected by several hurricanes over the last couple of years. For each instance the severe weather procedures were enacted and there were no significant challenges to the timelines required in the procedures for preparation activities. When a storm is projected, the site often utilizes all available personnel for preparation activities to get all walkdowns, materials, and equipment in place as quickly as reasonably possible.

The flood barriers have not been installed for any storms that have hit the area in the last couple of years because the criteria of receiving a warning of a storm surge in excess of 20 feet has never been met. Actual water levels observed during a storm has confirmed there was no flooding experienced at the site.

RAI 6

Issue Item (v) in Attachment 1 of the enclosure to the LAR states that the licensee will confirm all barriers conform to the requirements for flood protection features specified in NEI 16-05

[External Flooding Assessment Guidelines, Revision 1], including Appendix B Section 3.1.4 of the enclosure to the LAR states that the operator response, warning time and time required for installation was evaluated against the NRC endorsed NEI 16-05 Appendix C. NEI 16-05 describes the flooding impact assessment process for use by licensees to close out the 10 CFR 50.54(f) request for information arising from Near-Term Task Force Recommendation 2.1 - Flooding. The context for the development and usage of NEI 16-05, Revision 1, was different from the request by the licensee to amend its licensing basis. The LAR does not include justification for the use of the guidance in NEI 16-05, Revision 1, to support the request.

In item #5 of Enclosure 2 to the licensees FE (September 27, 2018, ML18270A372 (publicly available) and ADAMS Accession No. ML18274A336 (non-publicly available)), the licensee stated that it will raise the elevation of the smoke removal vents on the FOTC roof and that it will provide a new debris barrier that protects all penetrations on the FOTC roof. The basis for providing a new debris barrier is to protect all penetrations on the FOTC roof from debris loading associated with the CE storm surge event.

In Section 3.1.4 of the enclosure to the LAR, the licensee stated that the above-mentioned modifications are not required for implementation of 10 CFR 50.69 because the lowest elevations of these vents are above the maximum reevaluated still-water elevation level for the CE storm surge. However, the impact of loading from the flood level and debris on the FOTC vents and roof is not discussed. The loading can result in a situation that challenges the proposed approach for XF hazard consideration in the licensees approved 10 CFR 50.69

RA-20-0364 Enclosure Page 11 of 12 program. Therefore, it is unclear to the NRC staff that the modifications cited above are unnecessary for implementation of the 10 CFR 50.69 program.

RAI Justify the applicability of the guidance in NEI 16-05, Revision 1, to the request. The justification should describe how the guidance in NEI 16-05, Revision 1, provides reasonable assurance to support the screening of the external flooding hazard for the 10 CFR 50.69 program.

Response

The guidance in NEI 16-05 Revision 1 provides a systematic evaluation technique to assess the impact of external flooding hazards on a commercial nuclear power plant. The methodology provides a process for licensees to determine key vulnerabilities to the flooding hazard and to evaluate the site-specific response strategy for the full duration of the flood. This guidance document has become the industry practice for evaluating the vulnerabilities and response to XF hazard impacts at a nuclear power plant.

Specifically, as noted in the LAR (Reference 1), the barriers (including permanent flood barriers, temporary flood barriers, and debris barriers) will conform to the requirements for flood protection features specified in NEI 16-05 Rev 1, Appendix B. This appendix requires the barriers to be designed using applicable standards, codes, guidance documents and operating experience to determine whether the configuration of the temporary barrier conforms to accepted engineering practices. These requirements will ensure the barriers can reliably perform their function. These requirements are also consistent with normal engineering practice for non-safety related components at commercial nuclear power plants and are appropriate for crediting in a risk-informed application.

The operator response, warning time and time required for installation of the currently utilized temporary flood barriers was evaluated against the guidance in NEI 16-05 Appendix C and will be revisited in the design process for the larger temporary flood barriers. NEI 16-05 Appendix C provides guidance to assess the timing of actions for the external hazard mitigation activities.

The NEI 16-05 timing analysis closely resembles traditional PRA Human Reliability Analysis (HRA) taking into account the time available until unrecoverable consequences occur, cue(s),

time for execution, and time for recovery. Environmental performance shaping factors are also considered to inform the timing analysis and adjust accordingly in the face of adverse conditions. As such, it is appropriate to utilize this methodology to evaluate these actions in the context of the external hazard mitigation strategy, as it takes into account the appropriate factors to assess the reliability of a strategy that relies on manual actions.

Therefore, the barrier (including permanent flood barriers, temporary flood barriers, and debris barriers) design and timing evaluations are conducted per a systematic process using standards appropriate for reliable performance to meet the credited function. These standards are consistent with design and timing analysis used for other PRA activities and are appropriate for crediting in screening the external flooding hazard for the 10CFR50.69 program.

RA-20-0364 Enclosure Page 12 of 12 To specifically address the Fuel Oil Tank Chamber (FOTC) smoke removal vent loading impacts from the CE storm surge and associated effects, the following discussion is provided. The smoke removal vents are being raised to solely address the flood water height from the hazard.

Debris and hydrodynamic loading from the CE storm surge on the FOTC smoke removal vents and other FOTC components are addressed by installation of a permanently-installed debris barrier. The debris barrier is credited in this screening evaluation. Reference Attachment 1 for the implementation mechanism.

Hydrostatic and hydrodynamic loads of the CE storm surge event on the FOTC components have already been assessed and translated into the plant design. The hydrostatic load evaluation showed that no changes are needed to the FOTC roof or enclosure doors from the additional load from the increased storm surge.

Raising the smoke removal vents is not as a result of debris, hydrodynamic, or hydrostatic loading from the CE storm surge event and is only related to increasing the available physical margin of the vents are above the maximum reevaluated still-water elevation level for the CE storm surge. That is, the current height of the vents is above the level of the CE storm surge and is therefore adequate, but the height is being raised to provide more margin. Thus, raising the smoke removal vents is not necessary for screening the flood hazard for this application.

References:

1. Duke Energy Letter to the U.S. Nuclear Regulatory Commission, RA-19-0437, License Amendment Request to Modify Approved 10 CFR 50.69, "Risk-Informed Categorization and Treatment of Structures, Systems, and Components for Nuclear Power Reactors Categorization Process, dated July 9, 2020 (ADAMS Accession Number ML20191A054).

2. US NRC Letter to Duke Energy, Brunswick Steam Electric Plant, Units 1 and 2 -

issuance of Amendment Nos. 292 and 320 to adopt 10 CFR 50.69, "risk-informed categorization and treatment of structures, systems, and components for nuclear power reactors" (EPID L-2018-LLA-0008), ADAMS Accession Number ML19149A471, September 17, 2019.

3. ASME/ANS RA-Sa-2009, Standard for Level l/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications, Addendum A to RA-S-2008, ASME, New York, NY, American Nuclear Society, La Grange Park, Illinois, dated February 2009

RA-20-0364 Attachment 1 Attachment 1 List of Categorization Prerequisites

RA-20-0364 Attachment 1 Attachment 1: List of Categorization Prerequisites The table below identifies the items that are required to be completed prior to implementation of the proposed 10 CFR 50.69 license condition in Section 2.3 of the LAR (i.e., the proposed change) at Brunswick Nuclear Plant (BNP), Unit Nos. 1 and 2. The issues identified below will be addressed and any associated changes made. This list is a subset of the commitments found in Enclosure 2 of the Focused Evaluation [Reference 1].

Brunswick 50.69 XF PRA Implementation Items Description

i. BSEP will enhance the existing temporary passive interior door flood barriers (i.e., Cliff Edge Barriers) to provide protection for SSCs relied upon to protect KSFs in the Reactor Building (interior to external doors D-2 and D-3), Diesel Generator Building (Exterior to external door D-6) and Control Building (At CB entrance doors interior to TB external doors D-19 and D-22) from the CE Storm Surge event. The top elevation of these enhanced temporary passive barriers will be at elevation 27.5 ft NGVD29 to achieve minimum APM = 0.7 ft.

ii. For Control Building door locations, 2-CTB-DR-EL023-102 and 1-CTB-DR-EL023-105, BSEP modifications will replace the temporary barriers with permanent water-tight doors providing permanent passive flood protection.

iii. For the Service Water Building at the locations near Doors D-13 & D-14, BSEP will modify the existing security delay gate doors to shield ventilation openings from waves.

iv. For the DG Building north external personnel watertight door D-4, BSEP will provide a new debris barrier that protects this door subjected to debris loading associated with the CE Storm Surge event.

v. BSEP will confirm all barriers conform to the requirements for flood protection features specified in NEI 16-05, including Appendix B, and the time requirements of 0AI-68.

vi. BSEP will provide a new debris barrier that protects all penetrations on the FOTC Roof from debris loading associated with the CE Storm Surge event.

References

1. Duke Energy Letter to US NRC, Brunswick Steam Electric Plant (BSEP),

Unit Nos. 1 and 2, Response to March 12, 2012, Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 3, Flooding Focused Evaluation Summary Report, Agencywide Documents Access and Accession Number ML18270A372, September 27, 2018.