ML21131A221

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Westinghouse AP1000 Rev 19 DC Extension Verification Evaluation Report
ML21131A221
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Issue date: 05/11/2021
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U.S. NUCLEAR REGULATORY COMMISSION VERIFICATION EVALUATION REPORT

1.0 INTRODUCTION

The final and approved AP1000 Design Control Document (DCD), Revision 19, dated June 13, 2011 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML11171A500), expired on February 27, 2021. By letter dated June 26, 2020 (ADAMS Accession No. ML20178A640), Westinghouse Electric Company, LLC (Westinghouse),

requested that the U.S. Nuclear Regulatory Commission (NRC) extend the duration of the AP1000 design certification (DC) by 5 years, retroactive to the expiration date. This request would extend the period for which a combined license (COL) applicant could reference the AP1000 DC from 15 to 20 years, resulting in a new expiration date of February 27, 2026. It would also allow the AP1000 DC to remain valid for reference by future applicants under Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic licensing of production and utilization facilities, or 10 CFR Part 52, Licenses, certifications, and approvals for nuclear power plants, while the NRC considers other approaches to the duration and renewal of future and currently valid DCs in a separate and ongoing rulemaking.

In the staff requirements memorandum (SRM) for SECY-20-0082, Rulemaking Plan to Extend the Duration of the AP1000 Design Certification, dated September 8, 2020 (ADAMS Accession No. ML20322A047), the Commission approved the staffs recommendations to initiate a limited-scope rulemaking to amend Section VII, Duration of This Appendix, in Appendix D, Design Certification Rule for the AP1000 Design, to 10 CFR Part 52, to extend the duration of the AP1000 DC for an additional 5 years beyond the current expiration date of February 27, 2021, and to use the direct final rule process. In the rulemaking plan, the NRC staff acknowledged that there are known design issues that it would need to assess in the rulemaking to determine their impact on the necessary safety and environmental findings (ADAMS Accession No. ML20196L652). These design issues were discovered in the certified design following December 30, 2011, and AP1000 DC, Revision 19: (1) passive core cooling system containment condensate return, (2) main control room (MCR) dose, (3) MCR heatup, (4) hydrogen vent inspections, tests, analyses, and acceptance criteria (ITAAC), and (5) neutron flux logic operating bypass. COL applicants have previously resolved and referenced these five design issues, and the NRC has approved the changes in multiple COL proceedings.

The timeline below highlights the milestones of the AP1000 design relevant to the five design issues:

  • The NRC staff issued the final safety evaluation report (FSER) for the AP1000 DCD (ADAMS Accession No. ML112061231) in August 2011 and subsequently published the FSER as Supplement 2, Volumes 1 and 2, to NUREG-1793, Final Safety Evaluation Report Related to Certification of the AP1000 Standard Design, in September 2011.
  • On December 30, 2011, the NRC published the AP1000 DC amendment final rule in Volume 76 of the Federal Register (FR), page 82079 (76 FR 82079).
  • Two months later, on February 10, 2012, the Commission issued a license referencing AP1000 DC, Revision 19, to Southern Nuclear Company (SNC) Vogtle Electric Generating Plant (VEGP), Units 3 and 4 (Unit 3ADAMS Accession No. ML14100A106 1

and Unit 4ADAMS Accession No. ML14100A135). License amendment requests (LARs) were issued to the NRC on these five design issues and are covered below in Section 4 of this report.

  • On May 31, 2016, the NRC staff published FSER Chapter 21, Design Changes Proposed in Accordance with ISG-11 (ADAMS Accession No. ML16068A418), for Duke Energy Floridas Levy Nuclear Plant (LNP) in Levy County. This FSER addressed the five design issues and would be used as a reference for the remaining AP1000 COL applicants.
  • On October 26, 2016, the Commission issued a license referencing AP1000 DC, Revision 19, to LNP Units 1 and 2 (Unit 1ADAMS Accession No. ML12265A029 and Unit 2ADAMS Accession No. ML12265A042).
  • On August 1, 2016, the NRC staff published FSER Chapter 21, Design Changes Proposed in Accordance with ISG-11 (ADAMS Accession No. ML16137A123), for William States Lee III Nuclear Station (WLS), Units 1 and 2. This FSER addressed the five design issues. On December 19, 2016, the Commission issued a license referencing AP1000 DC, Revision 19, to WLS Units 1 and 2 (Unit 1ADAMS Accession No. ML16333A329 and Unit 2ADAMS Accession No. ML16333A331).
  • On November 10, 2016, the NRC staff published FSER Chapter 21, Design Changes Proposed in Accordance with ISG-11 (ADAMS Accession No. ML16263A433), for Florida Power and Light Company (FPL) Turkey Point Nuclear Generating Units 6 and 7.

This FSER addressed the five design issues. On April 12, 2018, the NRC issued a license to FPLs Turkey Point Units 6 and 7, referencing AP1000 DC, Revision 19 (Unit 6ADAMS Accession No. ML17088A329 and Unit 7ADAMS Accession No. ML17088A330).

After the NRC staff began assessing the known design issues for the rulemaking, Westinghouse indicated its preference to update the design to reflect the changes requested in the various combined license applications (COLAs). By letter dated March 19, 2021 (ADAMS Accession No. ML21081A023), Westinghouse submitted applicable AP1000 DC markups and references that illustrate how (1) the five issues have been corrected based on construction of the current AP1000 reactors for VEGP Units 3 and 4, and (2) Westinghouse has marked up the referenced DCD in accordance with those changes. The NRC staff is using this document to verify the Westinghouse submittal. Westinghouse is using SNC for VEGP Units 3 and 4 (under construction) as the current lead AP1000 design in its submittal, but throughout this report, the staff references other AP1000 COLAs as needed for clarity. In addition, Westinghouse compared changes to the generic technical specifications to the Turkey Point Technical Specification because the relevant SNC Technical Specification were reformatted in a fashion that makes comparison of the generic AP1000 Technical Specification to the SNC Technical Specification impractical. Although multiple other licensing proceedings are referenced 2

depending on various factors (e.g., when the NRC first evaluated each change), the changes to address these five design issues were the same for each COL.

This verification evaluation report is the staffs assessment of the Westinghouse submittal and is divided into five sections. Section 1 is the introduction, Section 2 summarizes applicable regulatory criteria, Section 3 discusses the five design issues presented in the Westinghouse document, Section 4 verifies the technical updates, and Section 5 presents the conclusions of this review.

2.0 REGULATORY CRITERIA In order for the direct final rule to proceed, the NRC must conclude that the design continues to meet the criteria for issuance of a DC under 10 CFR 52.54, Issuance of standard design certification. Moreover, 10 CFR 52.54(a)(1) requires a determination that the design meets the applicable standards and requirements of the Atomic Energy Act of 1954, as amended (AEA),

and the Commissions regulations, and 10 CFR 52.54(a)(3) requires a determination that there is reasonable assurance that the standard design conforms with the provisions of the AEA and the Commissions regulations.

In this evaluation, the staff is comparing the changes supplied by Westinghouse to the changes previously approved in COL proceedings. If the changes are the same, the NRCs previous approval supports the findings required under the AEA and 10 CFR 52.54 for a DC that incorporates these changes.

3.0

SUMMARY

OF THE FIVE DESIGN ISSUES 3.1 Passive Core Cooling System Containment Condensate Return Westinghouse identified the need to make changes to the AP1000 design to increase the passive core cooling system (PXS) condensate return to achieve compliance with General Design Criterion (GDC) 34, Residual heat removal, in Appendix A, General Design Criteria for Nuclear Power Plants, to 10 CFR Part 50. The AP1000 design provides for closed-loop cooldown and passive heat removal under accident conditions not involving loss of coolant.

Reactor coolant circulates naturally through a passive residual heat removal (PRHR) heat exchanger (HX) located within the in-containment refueling water storage tank (IRWST). The PRHR HX converts IRWST water to steam, and the subsequent condensation of this steam on the containment vessels interior surface passively transfers residual heat by conduction through the containment wall to the outside air. This closed-loop cooling requires that sufficient condensed water be returned to the IRWST to ensure the inventory needed to maintain the cooldown status and to continue the PRHR process for as long as necessary. The required changes are needed to increase the fraction of condensate returning to the IRWST for prolonged non-loss-of-coolant accident (non-LOCA) events. Specifically, the design changes include additional gutters, dams, downspouts, and the blocking of drain holes.

3.2 Main Control Room Dose Westinghouse identified several discrepancies in the certified design analyses supporting the determination of MCR operator dose following a design-basis accident (DBA). Specifically, (1) the analyses did not account for the direct dose from the MCR emergency habitability 3

system (VES) filter, (2) the nuclear island nonradioactive ventilation system (VBS) radiation monitor setpoints were not based upon all DBA release scenarios, and (3) the methodology used to estimate the MCR dose contribution from direct radiation and sky-shine was not up to date.

3.3 Main Control Room Heatup Applicable AP1000 COLAs identified that heat sources in the MCR had increased with detailed design development and now exceed those assumed in the certified design. Also, the design had not considered an event in which the MCR could be isolated and dependent on the VES, while offsite power remained available and powering certain MCR equipment. This event results in significantly higher heat loads than are considered in the certified design.

3.4 Hydrogen Vent Inspections, Tests, Analyses, and Acceptance Criteria Westinghouse identified the need to make changes based on the error with the certified designs ITAAC. This error required changes related to locations where hydrogen venting could occur during specific severe accident sequences in openings inside PXS rooms inside containment.

3.5 Neutron Flux Logic Operating Bypass Westinghouse identified the need to make changes to the AP1000 protection and safety monitoring system (PMS) design to meet the requirements in Institute of Electrical and Electronics Engineers (IEEE) Standard (Std.) 603-1991, IEEE Standard Criteria for Safety Systems for Nuclear Power Generating Stations. In the certified AP1000 design, the PMS initiates safety functions. In AP1000 DCD, Revision 19, Chapter 7, Instrumentation and Control, all safety functions initiated by the PMS comply with IEEE Std. 603-1991, Clause 6.6, Operating Bypasses, with one exception. The exception is the manually activated operating bypass of the safety function, called the boron dilution block, from the source range neutron flux doubling logic. The boron dilution blocking function is normally activated when neutron flux doubles too quickly while reactor power is in the source range. However, bypassing this block is permitted above a certain temperature when boron dilution can no longer lead to inadvertent criticality. The certified AP1000 design of the PMS flux doubling logic for the boron dilution block did not meet the operating bypass requirements of IEEE Std. 603-1991 because the logic programmed into the PMS did not include a permissive to allow the block of the flux doubling function under the appropriate conditions.

4.0 VERIFICATION AND EVALUATION OF TECHNICAL UPDATES 4.1. Passive Core Cooling System Containment Condensate Return 4.1.1 Established Technical Evaluation GDC 34 requires a system to remove residual heat with a system safety function to transfer fission product decay heat and other residual heat from the reactor core at a rate such that specified acceptable fuel design limits and the design conditions of the reactor coolant pressure boundary are not exceeded. SECY-94-084, Policy and Technical Issues Associated with the Regulatory Treatment of Non-Safety Systems in Passive Plant Designs, establishes the position 4

that reactor designs using passive safety systems must include a residual heat removal system capable of bringing the reactor to a safe-shutdown condition of 420 degrees Fahrenheit (F) or lower following non-LOCA events.

Westinghouse identified the need to make changes to the AP1000 design to address PXS condensate return to meet GDC 34. Westinghouse and COL applicants previously addressed and resolved these issues as part of the AP1000 COLAs for LNP Units 1 and 2, WLS Units 1 and 2, and FPLs Turkey Point Units 6 and 7 and through the amendment process for the COL for VEGP Units 3 and 4.

By letter dated November 4, 2016 (ADAMS Accession No. ML16319A120), SNC submitted LAR 16-026 with changes to ITAAC and updated final safety analysis report (UFSAR) descriptions to increase the fraction of condensate returning to the IRWST for prolonged non-LOCA events. Specifically, the design changes included additional gutters, dams, downspouts, and the blocking of drain holes. SNC stated in its LAR that the changes are necessary to ensure the capability of the PRHR HX to maintain the reactor coolant system in a safe, stable, condition, as described in licensing basis documents, and to demonstrate that the existing non-LOCA analyses in Chapter 15, Accident Analyses, that credit the PRHR HX remain valid.

In its safety evaluation (SE) (ADAMS Accession No. ML17024A307), the staff stated that its review confirmed that SNC had addressed the required information relating to the design change for the PXS. Further, the staff concluded the relevant information presented in LAR 16-026 is acceptable and satisfies GDC 34.

In its DC extension letter issued March 2021, Westinghouse stated that the proposed DCD changes are consistent with the licensing basis markups in SNC LAR 16-026, except for those in DCD Tier 2, Chapter 16, Technical Specifications Bases B3.3.3, which are consistent with the licensing basis markups in the Technical Specification for FPLs Turkey Point Units 6 and 7 (ADAMS Accession No. ML16250A350). Westinghouse noted that the Turkey Point Technical Specification changes were referenced since the SNC Technical Specification for those sections were reformatted before implementing LAR 16-026 for SNC VEGP Units 3 and 4. In November 2016, in its FSER for Chapter 16 of the COLA for FPLs Turkey Point, Units 6 and 7 (ADAMS Accession No. ML16266A185), the staff confirmed that the applicant had addressed the relevant information relating to Chapter 16, to ensure that the Technical Specification and bases accurately reflect the updated design and that no outstanding information remained to be addressed.

4.1.2 Staff Evaluation of Westinghouse Submittal The staff verified the information presented in the enclosures to the Westinghouse DC extension request submittal on the PXS condensate return against the information provided in the previous licensing submittals on this issue. The staff also reviewed associated NRC SEs documenting approval of changes to the DCD information on the PXS condensate return. The staff concludes that the AP1000 DC markups are consistent with the design changes to the PXS condensate return previously reviewed and approved by the NRC for SNC for VEGP Units 3 and 4, and Technical Specification changes for FPLs Turkey Point Units 6 and 7.

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4.2. Main Control Room Dose 4.2.1 Established Technical Evaluation GDC 19, Control Room, requires that a control room be provided from which actions can be taken to operate the nuclear power unit safely under normal conditions and to maintain it in a safe condition under accident conditions. This includes providing for the protection of the control room operators under normal and accident conditions against the threat of radiological hazards. After the NRC issued the certified design documented in AP1000 DCD, Revision 19, Westinghouse identified the need to update the DBA radiological analyses to show compliance with the control room habitability regulatory requirements in GDC 19, because (1) the analyses did not account for the MCR VES filter direct dose in the control room, (2) the nuclear island nonradioactive VBS radiation monitor setpoints for control room VBS actuation did not account for all DBA release scenarios, and (3) the analyses that estimated the MCR dose contribution from direct radiation and sky-shine used methodologies that were not up to date. Westinghouse developed changes that address and resolve these issues, which the NRC approved as part of its review of the AP1000 COLAs for LNP Units 1 and 2, WLS Units 1 and 2, and FPLs Turkey Point Units 6 and 7 and through the amendment process for VEGP Units 3 and 4 COLs. A summary of the staffs verification and review of the information is provided below.

1. MCR VES filter direct dose in the control room Westinghouse identified deficiencies in the design-basis MCR radiological dose evaluations.

Westinghouse found that, in AP1000 DCD, Revision 19, the radiation contributions from MCR heating, ventilation, and air conditioning (HVAC) filters were not considered in the MCR dose analyses reported in DCD Chapter 6, Engineered Safety Features, Section 6.4, Habitability Systems, and Chapter 15. To address this deficiency, Westinghouse revised its MCR DBA dose consequence analyses to include the radiation contributions to the total MCR operator dose due to direct radiation from radioactive material estimated to accumulate on the VES and VBS filters during the accident. The revised analyses resulted in departures from Tier 1 and Tier 2 information in the DCD and the generic Technical Specification for the AP1000.

During the licensing of the AP1000 COLAs for LNP Units 1 and 2, WLS Units 1 and 2, and FPLs Turkey Point Units 6 and 7, each applicant submitted departures from the AP1000 MCR DBA dose consequence analyses. A license amendment request to update information in the final safety analysis report, based on the revised MCR dose analyses, was also submitted for VEGP Units 3 and 4. The submittals included markups of the COLAs for review and approval by the NRC. The changes incorporated encompass modifications to the physical plant design, Technical Specification, and analyses changes. The markups to the DCD submitted with the AP1000 DCD extension request incorporate changes that were included in the approved AP1000 COLAs.

COL submittals and the DCD markups also included changes related to the VBS filter and its dose contribution, including information on added shielding to the VES filter and the increase of the assumed VES HVAC filter absorption efficiency.

By letter dated August 31, 2017 (ADAMS Accession No. ML17243A351), and supplemented by letters dated February 8 and March 9, 2018 (ADAMS Accession Nos. ML18040A487 and ML18067A648, respectively), SNC submitted LAR 17-023 for VEGP Units 3 and 4. The 6

amendment request proposed changes to licensing basis information about the nuclear island nonradioactive VBS, the MCR habitability system VES, and post-accident operator dose analyses. It also added a new ITAAC to ensure installation of radiation shielding below the VES filter, which is needed to meet the regulatory requirements of GDC 19. In its SE of LAR 17-023, dated April 20, 2018 (ADAMS Accession No. ML18085A628), the staff found that the proposed revisions were acceptable because they were based on radiological dose analyses that include direct radiation contributions from filters in the VES and VBS HVAC systems during DBA events. The change was incorporated by reference into the VEGP Units 3 and 4 COLs from the WLS Units 1 and 2 COLs, and the staff approved the technical evaluation of the changes to the MCR dose analyses in Section 21.2, Main Control Room Dose Departure of the FSER for the WLS Units 1 and 2 COLs (ADAMS Accession No. ML16137A123).

In the FSER, the staff stated that, through the addition of shielding at the VES filter and the addition of the related ITAAC, the deficiency in the DCD analyses related to the direct dose contributions from the VES filter has been resolved. Under the conditions analyzed, the additional shielding ensures that the incremental increase in the MCR dose resulting from the use of the VES filter would not result in exceeding the operator dose requirements of GDC 19.

2. Nuclear island nonradioactive VBS radiation monitor setpoints for control room VBS actuation Westinghouse noted that, in AP1000 DCD, Revision 19, the VBS radiation monitor setpoints in the AP1000 DCD, which were based on loss-of-coolant accident releases, were not selected in a manner that ensures that GDC 19 is met for non-LOCA DBAs. For postulated accident conditions involving a reduced source term or release rate other than that evaluated for DBAs as part of the certified design, there may not be sufficient radioactivity within the MCR envelope to prompt VES actuation, and yet enough radioactivity could exist that would lead to operator doses in excess of 5 rem (0.05 sievert) without manual actuation. To address this deficiency, the radiation monitor setpoint values in the DCD were updated to ensure VBS or VES filtration mode actuation occurs for any radiological release event, regardless of release or accident scenario, that could result in MCR operator doses in excess of the limits described in GDC 19.

In its SE of LAR 17-023, the staff found that, for VEGP Units 3 and 4, SNC incorporated by reference previously approved changes pertaining to the radiation monitor setpoint values to ensure VES actuation and VBS supplemental filtration mode (SFM) actuation occurs for any radiological release event that could result in MCR personnel doses in excess of GDC 19. This change also implemented a nonsafety-related High-1 signal to actuate VBS SFM (gaseous, particulate, or iodine) and the existing safety-related High-2 signal to actuate VES (iodine or particulate) in a manner that ensures High-2 would only be reached if VBS SFM were not functioning properly or were functioning insufficiently. The staff found the change, which was incorporated by reference into the VEGP Units 3 and 4 COLs, acceptable. LNP FSER, Section 21.2, Sections B.3 and B.4.2, describes the staffs previous evaluation of this change.

The AP1000 DCD markups included in the AP1000 DC extension submittal are consistent with the information that was approved for the COLs for VEGP Units 3 and 4 and WLS Units 1 and 2.

3. MCR direct radiation and sky-shine dose methodology not up to date Westinghouse noted that, in AP1000 DCD, Revision 19, the MCR dose contribution from direct radiation and sky-shine calculations used a methodology that was not up to date. In its SE of LAR 17-023, the NRC staff found that, to maintain compliance with GDC 19, SNC incorporated 7

by reference previously approved changes from LNP Units 1 and 2 that ensure that radiological sources are accounted for and modeled accurately. The staff found acceptable the incorporation by reference of the previously approved analysis of sky-shine and direct radiation dose. LNP FSER, Section 21.2, Section B.1, describes the staffs previous evaluation of this change.

4.2.2 Staff Evaluation of Westinghouse Submittal The AP1000 DCD markups included in the March 2021 Westinghouse AP1000 DC extension submittal incorporate the information that was in the previously mentioned COLAs. The markups provide the information necessary to update the generic certified design with the same information that the NRC previously reviewed and approved to address the identified issues.

For this issue, the staff verified the information presented in the Westinghouse DC extension request enclosures against the information provided in the previous licensing submittals. The AP1000 DCD markups included in the AP1000 DC extension submittal are consistent with the information that was approved for the COLs for VEGP Units 3 and 4 and WLS Units 1 and 2.

4.3. Main Control Room Heatup 4.3.1 Established Technical Evaluation GDC 19 requires, in part, that a control room be provided from which actions can be taken to operate the nuclear power unit safely under normal conditions and to maintain it in a safe condition under accident conditions.

Westinghouse identified the need to make changes to the AP1000 design to address increased MCR heat sources that exceed those assumed in the certified design and are necessary for GDC 19 compliance. Westinghouse and COL applicants previously addressed and resolved these issues as part of the AP1000 COLAs for LNP Units 1 and 2, WLS Units 1 and 2, and FPLs Turkey Point Units 6 and 7 and through the amendment process for VEGP Units 3 and 4 COLs.

By letter dated May 9, 2017 (ADAMS Accession No. ML17129A608), as supplemented by letter dated September 15, 2017 (ADAMS Accession No. ML17258B211), SNC submitted LAR 17-001, requesting that the NRC amend the COLs for VEGP Units 3 and 4 for changes to the UFSAR, plant-specific Tier 1 information, and plant-specific Technical Specification to reflect design changes to the VES. Section 1 of Enclosure 1 to SNC LAR 17-001 states the following:

The proposed changes affect the Combined License (COL) concerning the safety-related main control room (MCR) emergency habitability system (VES).

Because of design finalization and completion of calculations for main control room envelope (MCRE) temperature response, the following design changes to the VES are required:

1. Load Shed Capability An automatic and manual, Class 1E, electrical load shed of nonessential nonsafety-related equipment within the MCRE is added. The automatic electrical load shed is actuated from the existing VES actuation signals 8

(i.e., whenever ac power is not available for more than 10 minutes or high-2 radioactivity is detected in the MCRE air supply).

2. Main Control Room Habitability
a. Wet Bulb Globe Temperature (WBGT) Index The temperature acceptance criterion in the MCR following a Design Basis Accident (DBA) is changed from MIL STD 1472E to the WBGT Index of 90°F. This limit is based on the recommendations of NUREG-0700. The WBGT Index in NUREG-0700 describes allowable stay times for workers in heated environments, with an allowable 90°F (32.2°C) WBGT Index for unlimited stay times. In post-design basis accident scenarios, the temperature in the AP1000 MCR remains below this limit, allowing for unlimited operator stay times in the MCR.
b. Surveillance Requirements The Technical Specifications are revised in four ways: to provide specified initial temperature conditions for the required rooms in the MCRE and adjacent rooms, to specify a measurement for the moisture content of the air in the VES air storage tanks, to verify load shed function actuates on receipt of actual or simulated signal, and to clarify verification of main air delivery valve actuation on receipt of actual or simulated signal.
c. Instrument Valve Changes A description of the requirements for maintaining habitability of the MCRE beyond 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following a DBA is added to the design and licensing basis, to change the designation of existing safety-related temporary instrument valves to active valves required for providing clean, breathable replenishment air to the VES beyond 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following a DBA. These temporary instrument valves allow the use of a continued ventilation and pressurization requirements of the MCRE after the 72-hour supply of breathable quality air in the VES air storage tanks is exhausted. This is only necessary if: 1) the breathable quality air compressor in the compressed and instrument air system (CAS) is not available to replenish the VES air storage tanks; 2) the nuclear island nonradioactive ventilation system (VBS) is not available; and 3) the MCR ancillary fans are not available.

In its SE for LAR 17-001, dated February 1, 2018 (ADAMS Accession No. ML18011A894), the staff stated that its review of SNCs analysis as provided in LAR 17-001 found that (1) the proposed changes do not adversely affect the existing safety standard of VES and approved systems, and (2) the proposed changes provided additional clarity to existing documentation.

Based on these findings, the staff concluded that there was reasonable assurance that the requirements of applicable regulations continued to be met with the proposed changes, and, therefore, they were acceptable.

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In its March 2021 letter, Westinghouse stated that the proposed DCD changes are consistent with the licensing basis markups in SNC LAR 17-001, except for DCD Tier 2, Chapter 16, Technical Specification 3.3.2 and Technical Specification Bases B3.3.2, which are consistent with the licensing basis markups in the Technical Specification for FPLs Turkey Point Units 6 and 7 (ADAMS Accession No. ML16250A350). Westinghouse noted that it referenced the Turkey Point Technical Specification changes because it reformatted the SNC Technical Specification for those sections before implementing LAR 17-001 for SNC VEGP Units 3 and 4.

In November 2016, in its final SE for Chapter 16 of the COLA for FPLs Turkey Point Units 6 and 7, the staff confirmed that the applicant had addressed the relevant information relating to Chapter 16, and no outstanding information remained to be addressed (ADAMS Accession No. ML16266A185).

4.3.2 Staff Evaluation of Westinghouse Submittal The staff confirmed that the Westinghouse AP1000 DC markups are technically accurate and consistent with those provided by SNC for VEGP Units 3 and 4 and FPL for Turkey Point Units 6 and 7. Therefore, the staff finds that the Westinghouse changes to address the increased MCR heat sources are consistent with those that the staff previously approved for VEGP and FPLs Turkey Point.

4.4. Hydrogen Vent Inspections, Tests, Analyses, and Acceptance Criteria 4.4.1 Established Technical Evaluation GDC 41, Containment atmosphere cleanup, requires, in part, that systems be provided to control the concentration of hydrogen or oxygen that may be released into the reactor containment following postulated accidents to ensure that containment integrity is maintained.

In 10 CFR 50.34(f)(2)(ix)(B), the NRC requires, in part, that combustible concentrations of hydrogen not collect in areas where unintended combustion or detonation could cause loss of containment integrity or loss of appropriate mitigating features. In 10 CFR 50.44(c)(2), the NRC requires, in part, that all water-cooled reactor DCs have an inerted atmosphere or provide means to limit hydrogen concentrations in containment during and following an accident that releases an equivalent amount of hydrogen as would be generated by a 100-percent fuel clad-coolant reaction, uniformly distributed, to less than 10 percent by volume and maintain containment structural integrity and appropriate accident mitigating features. In 10 CFR 50.44(c)(3), the NRC requires certified designs with containments that do not rely upon an inerted atmosphere to control combustible gases to be able to establish and maintain safe shutdown and containment structural integrity, with systems and components capable of performing their functions during and after exposure to the environmental conditions created by the burning of hydrogen. In 10 CFR 50.44(c)(5), the NRC requires that an applicant perform an analysis that demonstrates containment structural integrity. The analysis must address an accident that releases hydrogen generated from a 100-percent fuel clad-coolant reaction accompanied by hydrogen burning. Systems necessary to ensure containment integrity must also be demonstrated to perform their function under these conditions.

Westinghouse identified a need to revise the certified AP1000 design to make changes in structural details internal to the containment that are inconsistent with the certified design ITAAC for one of the compartments, relative to the venting of any hydrogen accumulated in the compartment following a severe accident. Westinghouse and COL applicants previously 10

addressed and resolved these issues as part of the AP1000 COLAs for LNP Units 1 and 2, WLS Units 1 and 2, and FPLs Turkey Point Units 6 and 7 and through the amendment process for VEGP Units 3 and 4 COLs.

By letter dated February 22, 2017 (ADAMS Accession No. ML17053A425), as supplemented by letter dated June 2, 2017 (ADAMS Accession No. ML17153A362), SNC submitted LAR 17-003 requesting that the NRC amend the COLs for VEGP Units 3 and 4 for changes to ITAAC and UFSAR descriptions related to locations where hydrogen venting could occur during specific severe accident sequences from openings inside PXS rooms inside containment.

SNC stated in its LAR that, to prevent the accumulation of hydrogen in a dead-ended compartment during a beyond-design-basis accident, hydrogen may be vented from the PXS-A and PXS-B compartments (Rooms 11206 and 11207, respectively) to core makeup tank (CMT)-A and CMT-B compartments (Room 11300) through openings in the floor of Room 11300. SNC proposed to reconfigure the openings in Room 11206 to allow for access to perform maintenance activities on the equipment in Room 11206, and to use actual distances to the containment vessel in analyses of hydrogen venting from those rooms. In its SE of LAR 17-003, dated August 23, 2017 (ADAMS Accession No. ML17213A224), the staff stated that its review confirmed that SNC had addressed the required information relating to the design change for the PXS dimensions due to the potential for hydrogen venting.

4.4.2 Staff Evaluation of Westinghouse Submittal Westinghouse stated in its March 2021 letter that the proposed DCD changes are consistent with the licensing basis markups in SNC LAR 17-003. The staff confirmed that the Westinghouse AP1000 DC markups are consistent with those provided by SNC for VEGP Units 3 and 4.

4.5 Neutron Flux Logic Operating Bypass 4.5.1 Established Technical Evaluation In 10 CFR 50.55a(h)(3), the NRC requires DC applications filed on or after May 13, 1999, to meet the requirements for safety systems in IEEE Std. 603-1991 and the correction sheet dated January 30, 1995. Specifically relevant here, Clause 6.6 in IEEE Std. 603-1991 imposes requirements on the operating bypasses (i.e., blocks and resets) used for safety systems.

Westinghouse identified the need to make changes to the AP1000 design to update the PMS to align with the requirements in IEEE 603-1991. Westinghouse and COL applicants previously addressed and resolved these issues as part of the AP1000 COLAs for LNP Units 1 and 2, WLS Units 1 and 2, and FPLs Turkey Point Units 6 and 7 and through the amendment process for VEGP Units 3 and 4 COLs.

By letter dated June 16, 2016 (ADAMS Accession No. ML16168A399), SNC submitted LAR 16-006 for changes to Technical Specification and UFSAR descriptions related to the safety-related PMS functional logic for blocking and resetting the source range neutron flux doubling signal. Specifically, the license amendment asked to add a new P-8 setpoint permissive, an additional reset of source range neutron flux doubling signal when the reactor coolant temperature decreases below P-8, and PMS logic to initiate a closure signal for 11

chemical and volume control system valves 136A and if the flux doubling signal is blocked when reactor coolant temperature is less than P-8.

In its SE (ADAMS Accession No. ML16320A174), the staff found the proposed Technical Specification and UFSAR changes acceptable and concluded that the proposed changes comply with the requirements in Clause 6.6 of IEEE Std. 603-1991.

Westinghouse stated, in its March 2021 DC extension letter, that the proposed DCD changes are consistent with the licensing basis markups in SNC LAR 16-006, except for DCD Tier 2, Chapter 16, Technical Specification 3.3.2 and Technical Specification Bases B3.3.2, which are consistent with the licensing basis markups in the Technical Specification for FPLs Turkey Point Units 6 and 7 (ADAMS Accession No. ML16250A350). Westinghouse noted that it referenced the Turkey Point Technical Specification changes because it reformatted the SNC Technical Specification for those sections before implementing LAR 17-006 for SNC VEGP Units 3 and 4.

In November 2016, in its FSER for COLA Chapter 16 for FPLs Turkey Point, Units 6 and 7 (ADAMS Accession No. ML16266A185), the staff confirmed that the applicant had addressed the relevant information relating to Chapter 16, and no outstanding information remained to be addressed.

4.5.2 Staff Evaluation of Westinghouse Submittal The staff verified the information presented in the enclosures to the Westinghouse DC extension request submittal against the information provided in the previous licensing submittals on this issue. The staff also reviewed associated NRC SEs documenting the approval of changes to the DCD information. The staff concludes that AP1000 DC markups are consistent with the departures previously reviewed and approved for the COLs for SNC VEGP Units 3 and 4 and FPLs Turkey Point Units 6 and 7.

5.0 STAFF CONCLUSION The staff has verified that the AP1000 DC markups and references submitted by Westinghouse on March 19, 2021, are consistent with how the five design issues identified have been addressed in applications referencing the AP1000 design that the NRC has previously reviewed and approved.

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