ML22067A213

Level 3 PRA Project, Volume 3b: Reactor, At-Power, Level 1 PRA for Internal Floods (Draft)

ML22067A213
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Issue date:	04/05/2022
From:	Alan Kuritzky NRC/RES/DRA/PRAB
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U.S. NRC Level 3 Probabilistic Risk Assessment (PRA) Project Volume 3b: Reactor, At-Power, Level 1 PRA for Internal Flooding April 2022

iii ABSTRACT The U.S. Nuclear Regulatory Commission (NRC) performed a full-scope site Level 3 probabilistic risk analysis (PRA) project (L3PRA project) for a two-unit pressurized-water reactor reference plant, responding to Commission direction in the staff requirements memorandum (SRM) (Agencywide Documents and Management System [ADAMS] Accession No. ML112640419) resulting from SECY-11-0089, Options for Proceeding with Future Level 3 Probabilistic Risk Assessment (PRA) Activities (ADAMS Accession No. ML11090A039).

As described in SECY-11-0089, the objectives of the L3PRA project are to:

Develop a Level 3 PRA, generally based on current state-of-practice methods, tools, and data,0F1 that (1) reflects technical advances since the last NRC-sponsored Level 3 PRAs (NUREG-11501F2), which were completed over 30 years ago, and (2) addresses scope considerations that were not previously considered (e.g., low power and shutdown

[LPSD] risk, multi-unit risk, other radiological sources).

Extract new insights to enhance regulatory decision making and to help focus limited NRC resources on issues most directly related to the agencys mission to protect public health and safety.

Enhance PRA staff capability and expertise and improve documentation practices to make PRA information more accessible, retrievable, and understandable.

Demonstrate technical feasibility and evaluate the realistic cost of developing new Level 3 PRAs.

The scope of the L3PRA project encompasses all major radiological sources on the site (i.e.,

reactors, spent fuel pools, and dry cask storage), all internal and external hazards, and all modes of plant operation. Fresh nuclear fuel, radiological waste, and minor radiological sources (e.g., calibration devices) are not included as part of the scope. In addition, deliberate malevolent acts (e.g., terrorism and sabotage) are excluded from the scope of this study.

This report, one of a series of reports documenting the models and analyses supporting the L3PRA project, specifically addresses the reactor, at-power, Level 1 PRA model for internal floods for a single unit. The analyses documented herein are based information for the reference plant as it was designed and operated as of 2012 and does not reflect the plant as it is currently designed, licensed, operated, or maintained.2F3 1 State-of-practice methods, tools, and data refer to those that are routinely used by the NRC and industry or have acceptance in the PRA technical community. While the L3PRA project is intended to be a state-of-practice study, note that there are several technical areas within the project scope that necessitated advancements in the state-of-practice (e.g., modeling of multi-unit site risk, modeling of spent fuel in pools or casks, and of human reliability analysis for other than internal events and internal fires).

2 NUREG-1150, Severe Accident Risk: An Assessment for Five U.S. Nuclear Power Plants, December 1990.

3 An overview report, which covers all three PRA levels, has been created for each major element of the L3PRA project scope (e.g., for the combined internal event and internal flood PRAs for a single reactor unit operating at full power). These overview reports include a reevaluation of plant risk based on a set of updated plant equipment and PRA model assumptions (e.g., incorporation of the current reactor coolant pump shutdown seal design at the

iv A full-scope site Level 3 PRA for a nuclear power plant site can provide valuable insights into the importance of various risk contributors by assessing accidents involving one or more reactor cores as well as other site radiological sources. Furthermore, some future advanced light water reactor (ALWR) and advanced non-light water reactor (NLWR) applicants may rely heavily on results of analyses similar to those used in the L3PRA project to establish their licensing basis and design basis by using the Licensing Modernization Project (LMP) (NEI 18-04, Rev. 1) which was recently endorsed via RG 1.233. Licensees who use the LMP framework are required to perform Level 3 PRA analyses. Therefore, another potential use of the methodology and insights generated from this study is to inform regulatory, policy, and technical issues pertaining to ALWRs and NLWRs.

CAUTION:

While the L3PRA project is intended to be a state-of-practice study, due to limitations in time, resources, and plant information, some technical aspects of the study were subjected to simplifications or were not fully addressed. As such, inclusion of approaches in the L3PRA project documentation should not be viewed as an endorsement of these approaches for regulatory purposes.

reference plant and the potential impact of the U.S. nuclear power industry's proposed safety strategy, called Diverse and Flexible Mitigation Capability [FLEX], both of which reduce the risk to the public).

v FOREWORD The U.S. Nuclear Regulatory Commission (NRC) performed a full-scope site Level 3 probabilistic risk analysis (PRA) project (L3PRA project) for a two-unit pressurized-water reactor reference plant, responding to Commission direction in the staff requirements memorandum (SRM) (Agencywide Documents and Management System [ADAMS] Accession No. ML112640419) resulting from SECY-11-0089, Options for Proceeding with Future Level 3 Probabilistic Risk Assessment (PRA) Activities (ADAMS Accession No. ML11090A039).

Licensee information used in performing the Level 3 PRA project was voluntarily provided based on a licensed, operating nuclear power plant. The information provided reflects the plant as it was designed and operated as of 2012 and does not reflect the plant as it is currently designed, licensed, operated, or maintained. In addition, the information provided for the reference plant was changed based on additional information, assumptions, practices, methods, and conventions used by the NRC in the development of plant-specific PRA models used in its regulatory decisionmaking. As such, use of L3PRA project reports to assess the risk from the reference plant is not appropriate and these reports will not be the basis for any regulatory decision associated with the reference plant.

Each set of L3PRA project reports covering the Level 1, 2, and 3 PRAs for a specific site radiological source, plant operating state, and hazard group is accompanied by an overview report. The overview reports summarize the results and insights from all three PRA levels.

In order to provide results and insights better aligned with the current design and operation of the reference plant, the overview reports also provide a reevaluation of the plant risk based on a set of new plant equipment and PRA model assumptions and compare the results of the reevaluation to the original study results. This reevaluation reflects the current reactor coolant pump (RCP) shutdown seal design at the reference plant, as well as the potential impact of FLEX strategies,3F4 both of which reduce the risk to the public.

A full-scope site Level 3 PRA for a nuclear power plant site can provide valuable insights into the relative importance of various risk contributors by assessing accidents involving one or more reactor cores as well as other site radiological sources (i.e., spent fuel in pools and dry storage casks). These insights may be used to further enhance regulatory policy and decisionmaking and to help focus limited agency resources on issues most directly related to the agencys mission to protect public health and safety. More specifically, potential future uses of the Level 3 PRA project can be categorized as follows (a more detailed list is provided in SECY 0123, Update on Staff Plans to Apply the Full-Scope Site Level 3 PRA Project Results to the NRCs Regulatory Framework, dated September 13, 2012):

enhancing the technical basis for the use of risk information (e.g., obtaining updated and enhanced understanding of plant risk as compared to the Commissions safety goals) improving the PRA state-of-practice (e.g., demonstrating new methods for site risk assessments, which may be particularly advantageous in addressing the risk from advanced reactor designs, or in supporting the evaluation of the potential impact that a multi-unit accident, or an accident involving spent fuel, may have on the efficacy of the emergency planning zone in protecting public health and safety) 4 FLEX refers to the U.S. nuclear power industry's proposed safety strategy, called Diverse and Flexible Mitigation Capability. FLEX is intended to maintain long-term core and spent fuel cooling and containment integrity with installed plant equipment that is protected from natural hazards, as well as backup portable onsite equipment. If necessary, similar equipment can be brought from offsite.

vi identifying safety and regulatory improvements (e.g., identifying potential safety improvements that may lead to either regulatory improvements or voluntary implementation by licensees) supporting knowledge management (e.g., developing or enhancing in-house PRA technical capabilities)

In addition, the overall Level 3 PRA project model can be exercised to provide insights with regard to other issues not explicitly included in the current project scope (e.g., security-related events or the use of accident tolerant fuel). Furthermore, some future advanced light water reactor (ALWR) and advanced non-light water reactor (NLWR) applicants may rely heavily on the results of analyses similar to those used in the L3PRA project to establish their licensing basis and design basis by using the Licensing Modernization Project (LMP) (NEI 18-04, Rev. 1) which was recently endorsed via RG 1.233. Licensees who use the LMP framework are required to perform Level 3 PRA analyses. Therefore, another potential use of the methodology and insights generated from this study is to inform regulatory, policy, and technical issues pertaining to ALWRs and NLWRs.

The results and perspectives from this report, as well as all other reports prepared in support of the Level 3 PRA project, will be incorporated into a summary report to be published after all technical work for the Level 3 PRA project has been completed.

vii ABBREVIATIONS AND ACRONYMS ACCW auxiliary component cooling water AFW auxiliary feedwater ANS American Nuclear Society ARV atmospheric relief valve ASME American Society of Mechanical Engineers CCDP conditional core damage probability CCW component cooling water CDF core damage frequency CS containment spray CVCS chemical and volume control system CW circulating water ECCS emergency core cooling system EDG emergency diesel generator EPRI Electric Power Research Institute FW feedwater HEP human error probability HFE human failure event HVAC heating, ventilation and air conditioning IFPRA internal flooding probabilistic risk assessment KV AC kilovolts alternating current LCO limiting condition for operation LOCA loss-of-coolant accident LOCHS loss of condenser heat sink LOMFW loss of main feedwater LOOP loss of offsite power LO4160VA loss of safety-related 4160 volt bus train A MDP motor-driven pump MOV motor-operated valve MFIV main feedwater isolation valves MFW main feedwater MS main steam MSIV main steam isolation valve MSLB main steam line break NRC Nuclear Regulatory Commission NSCW nuclear service cooling water PORV power-operated relief valve PRA probabilistic risk assessment PWR pressurized-water reactor RAT reserve auxiliary transformer RCP reactor coolant pump RCS reactor coolant system RHR residual heat removal

viii RPS reactor protection system RTRIP reactor trip RWST refueling water storage tank SBO station blackout SG steam generator SI safety injection SRM staff requirements memorandum SSBI secondary-side break upstream of MSIVs / downstream of MFIVs SSC structures, systems, and components TDAFWP turbine-driven AFW pump TPCCW turbine plant closed cooling water TPCW turbine plant cooling water system TRANS other transient resulting in reactor trip TTRIP turbine trip VAC volts alternating current VDC volts direct current

ix Table of Contents FOREWORD............................................................................................................................. iii ABBREVIATIONS AND ACRONYMS....................................................................................... vii

1.

INTRODUCTION............................................................................................................. 1 1.1.

Approach.................................................................................................................... 2 1.2.

Arrangement of This Report......................................................................................... 3

2.

Internal Flood PRA Model Overview................................................................................ 4 2.1.

Internal Flood Plant Partitioning................................................................................... 4 2.2.

Internal Flood Source Identification and Characterization............................................ 5 2.3.

Internal Flood Scenarios.............................................................................................. 6 2.3.1.

Qualitative Screening Analysis.............................................................................. 6 2.3.2.

Characterization of Flood Scenarios..................................................................... 7 2.4.

Internal Flood-Induced Initiating Events....................................................................... 9 2.4.1.

Identification of Flood-Induced Initiating Events.................................................... 9 2.4.2.

Flood Initiating Event Frequency Estimates.........................................................10 2.5.

Internal Flood Accident Sequences and Quantification...............................................11 2.5.1.

Quantitative Screening Analysis...........................................................................11 2.5.2.

Quantification of Human Failure Events...............................................................11

3.

Internal Flood PRA Model Analysis.................................................................................13 3.1.

Internal Flood Model Assumptions..............................................................................13 3.2.

Internal Flood Modeled Scenarios...............................................................................15 3.2.1.

Internal Flood Scenario: 1-FLI-AB_108_SP1.......................................................15 3.2.2.

Internal Flood Scenario: 1-FLI-AB_108_SP2.......................................................17 3.2.3.

Internal Flood Scenario: 1-FLI-AB_A20................................................................18 3.2.4.

Internal Flood Scenario: 1-FLI-AB_C113_LF1.....................................................18 3.2.5.

Internal Flood Scenario: 1-FLI-CB_122_SP.........................................................19 3.2.6.

Internal Flood Scenario: 1-FLI-CB_123_SP.........................................................20 3.2.7.

Internal Flood Scenario: 1-FLI-CB_A48...............................................................21 3.2.8.

Internal Flood Scenario: 1-FLI-CB_A60...............................................................22 3.2.9.

Internal Flood Scenario: 1-FLI-TB_500_HI1.........................................................23 3.2.10. Internal Flood Scenario: 1-FLI-TB_500_LF..........................................................24 3.2.11. Internal Flood Scenario: 1-FLI-AB_B08_LF.........................................................25 3.2.12. Internal Flood Scenario: 1-FLI-AB_B24_LF2.......................................................25 3.2.13. Internal Flood Scenario: 1-FLI-AB_B50_JI...........................................................26 3.2.14. Internal Flood Scenario: 1-FLI-AB_C115_LF.......................................................27 3.2.15. Internal Flood Scenario: 1-FLI-AB_C118_LF.......................................................27 3.2.16. Internal Flood Scenario: 1-FLI-AB_C120_LF.......................................................28 3.2.17. Internal Flood Scenario: 1-FLI-AB_D74_FP.........................................................29 3.2.18. Internal Flood Scenario: 1-FLI-DGB_101_LF.......................................................29

x 3.2.19. Internal Flood Scenario: 1-FLI-DGB_103_LF.......................................................30 3.2.20. Internal Flood Scenario: 1-FLI-AB_A20_FP.........................................................31 3.2.21. Internal Flood Scenario: 1-FLI-AB_D78_FP.........................................................31 3.2.22. Internal Flood Scenario: 1-FLI-TB_500_LF-CDS.................................................32 3.2.23. Internal Flood Scenario: 1-FLI-TB_500_HI2.........................................................33

4.

Internal Flood Model Results..........................................................................................35 4.1.

Internal Flooding Scenario and Overall CDF Results..................................................35 4.2.

Internal Flooding Accident Sequences........................................................................36 4.3.

Internal Flooding Cut Set Results................................................................................41 4.4.

Internal Flooding CDF Parameter Uncertainty Analysis..............................................57 4.5.

Internal Flood PRA Model Uncertainty and Sensitivity Cases.....................................59 4.5.1.

Internal Flooding Initiating Event Frequencies......................................................69 4.5.2.

Human Error Probabilities for Maintenance-Induced Flooding Scenarios.............69 4.5.3.

Human Error Probabilities for Failures Unrelated to Flood Mitigation...................70 4.5.4.

Crediting Improved RCP Shutdown Seals............................................................71 4.5.5.

Propagation Factor for Flooding Scenario 1-FLI-CB_A48....................................73 4.5.6.

Potential Flood Propagation Impacting Both Safety-Related 4160 VAC Switchgears.......................................................................................................................73 4.5.7.

Application of Spray Direction Factor...................................................................74 4.5.8.

Credit for Manual Action to Start Service Water Cooling Tower Fans..................76 4.5.9.

Impact of Consequetial Loss of Offsite Power on Internal Flooding Scenarios.....77 4.6.

Comparison of Results to Similar Plant.......................................................................80 4.7.

Key Insights................................................................................................................82

5.

References.....................................................................................................................85 Appendix A:

Flood Initiating Event Frequency Analysis...................................................... A-1 Appendix B:

Internal Flooding PRA Significant Cut Sets and Basic Event Importance....... B-1 B.1 Internal Flooding PRA Significant Cut Set Results.................................................... B-1 B.2 Internal Flooding PRA Basic Event Importance Measures...................................... B-35 Appendix C:

Internal Flooding Topics for Future Work........................................................ C-1 LIST OF FIGURES IN MAIN REPORT Figure 4-1 Cumulative Distribution Function for Internal Flooding CDF.....................................59 Figure 4-2 Probability Density for Internal Flooding CDF...........................................................59 LIST OF TABLES IN MAIN REPORT Table 4.1 Internal Flooding Results by Scenario.......................................................................36 Table 4.2 Significant Internal Flooding Accident Sequences.....................................................38

xi Table 4.3 Internal Flooding Top 100 Cut Set Results................................................................41 Table 4.4 Internal Flooding CDF Model Parameter Uncertainty Results....................................58 Table 4.5 Sources of Model Uncertainty....................................................................................60 Table 4.6 Internal Flooding Adjustments to HEP Values for Actions Outside the Control Room 71 Table 4.7 Internal Flooding Accident Sequences with RCP Shutdown Seals............................72 Table 4.8 Internal Flooding Scenario Results With Propagation to Both Safety-Related 4160 VAC Switchgear Rooms............................................................................................................74 Table 4.9 Internal Flooding Scenario Results With Spray Direction Factor................................75 Table 4.10 Internal Flooding Scenario Results With Credit for Manual Action to Start Service Water Cooling Tower Fans........................................................................................................77 Table 4.11 Internal Flooding Accident Sequences Suppressing Consequential LOOP for Flooding Scenarios Not Causing Plant Trip...............................................................................78 LIST OF TABLES IN APPENDIX A Table A.1-1 Plant-Specific Flooding Events....................................................................... A-2 Table A.1-2 Generic Pipe Lengths Used for Reference Plant Systems.............................. A-2 Table A.1-3 Internal Flooding Scenario Initiating Event Frequencies................................. A-4 Table A.2-1 Flood Sources 1-FLI-CB_122_SP and 1-FLI-CB_123_SP.............................. A-5 Table A.2-2 Conditional Rupture Probability Parameters 1-FLI-CB_122_SP and 1-FLI-CB_123_SP

...A-5 Table A.2-3 Failure Rate Parameters 1-FLI-CB_122_SP and 1-FLI-CB_123_SP.............. A-6 Table A.2-4 Initiating Event Frequency Estimate for 1-FLI-CB_122_SP and 1-FLI-CB_123_SP

...A-6 Table A.3-1 Flood Sources 1-FLI-AB_108_SP.................................................................. A-7 Table A.3-2 Conditional Rupture Probability Parameters 1-FLI-AB_108_SP..................... A-7 Table A.3-3 Failure Rate Parameters 1-FLI-AB_108_SP................................................... A-8 Table A.3-4 Initiating Event Frequency Estimate for 1-FLI-AB_108_SP............................. A-8 Table A.4-1 Flood Sources 1-FLI-AB_ A20........................................................................ A-9 Table A.4-2 Conditional Rupture Probability Parameters 1-FLI-AB_A20 and 1-FLI-AB_A20_FP

.A-9 Table A.4-3 Failure Rate Parameters 1-FLI-AB_A20 and 1-FLI-AB_A20_FP.................. A-10 Table A.4-4 Initiating Event Frequency Estimate for 1-FLI-AB_A20................................. A-11 Table A.4-5 Initiating Event Frequency Estimate for 1-FLI-AB_A20_FP.......................... A-11 Table A.5-1 Flood Sources 1-FLI-CB_ A60...................................................................... A-11 Table A.5-2 Conditional Rupture Probability Parameters 1-FLI-CB_ A60........................ A-12 Table A.5-3 Failure Rate Parameters 1-FLI-CB_ A60...................................................... A-12 Table A.5-4 Initiating Event Frequency Estimate for 1-FLI-CB_A60................................. A-13 Table A.6-1 Flood Sources 1-FLI-TB_500_LF and 1-FLI-TB_500_LF-CDS..................... A-14 Table A.6-2 Conditional Rupture Probability Parameters 1-FLI-TB_500_LF and 1-FLI-TB_500_LF-CDS.................................................................................................................. A-14 Table A.6-3 Failure Rate Parameters 1-FLI-TB_ 500_LF and 1-FLI-TB_500_LF-CDS.... A-16 Table A.6-4 Initiating Event Frequency Estimate for 1-FLI-TB_ 500_LF.......................... A-17 Table A.6-5 Initiating Event Frequency Estimate for 1-FLI-TB_ 500_LF-CDS.................. A-17 Table A.7-1 Flood Sources 1-FLI-AB_ C113_LF1............................................................ A-17

xii Table A.7-2 Conditional Rupture Probability Parameters 1-FLI-AB_ C113_LF1.............. A-18 Table A.7-3 Failure Rate Parameters 1-FLI-AB_ C113_LF1............................................ A-18 Table A.7-4 Initiating Event Frequency Estimate for 1-FLI-AB_ C113_LF1...................... A-19 Table A.8-1 Flood Sources 1-FLI-CB_ A48...................................................................... A-19 Table A.8-2 Conditional Rupture Probability Parameters 1-FLI-CB_A48......................... A-20 Table A.8-3 Failure Rate Parameters 1-FLI-CB_A48....................................................... A-20 Table A.8-4 Initiating Event Frequency Estimate for 1-FLI-CB_A48................................. A-21 Table A.9-1 Events Contributing to Flood Frequency for Scenario 1-FLI-TB_500_HI1.... A-21 Table A.9-2 Events Contributing to Flood Frequency for Scenario 1-FLI-TB_500_HI2.... A-22 Table A.9-3 Initiating Event Frequency Estimate for 1-FLI-TB_500_HI1 and 1-FLI-TB_500_HI2

.A-22 Table A.10-1 Flood Sources 1-FLI-AB_C120_LF.............................................................. A-22 Table A.10-2 Conditional Rupture Probability Parameters 1-FLI-AB_C120_LF................. A-22 Table A.10-3 Failure Rate Parameters 1-FLI-AB_C120_LF............................................... A-23 Table A.10-4 Initiating Event Frequency Estimate for 1-FLI-AB_C120_LF......................... A-24 Table A.11-1 Flood Sources 1-FLI-AB_C115_LF.............................................................. A-24 Table A.11-2 Conditional Rupture Probability Parameters 1-FLI-AB_C115_LF................. A-24 Table A.11-3 Failure Rate Parameters 1-FLI-AB_C115_LF............................................... A-25 Table A.11-4 Initiating Event Frequency Estimate for 1-FLI-AB_C115_LF......................... A-25 Table A.12-1 Flood Sources 1-FLI-AB_C118_LF.............................................................. A-25 Table A.12-2 Conditional Rupture Probability Parameters 1-FLI-AB_C118_LF................. A-26 Table A.12-3 Failure Rate Parameters 1-FLI-AB_C118_LF............................................... A-26 Table A.12-4 Initiating Event Frequency Estimate for 1-FLI-AB_C118_LF......................... A-26 Table A.13-1 Flood Sources 1-FLI-AB_B08_LF................................................................. A-27 Table A.13-2 Conditional Rupture Probability Parameters 1-FLI-AB_B08_LF.................... A-27 Table A.13-3 Failure Rate Parameters 1-FLI-AB_B08_LF................................................. A-28 Table A.13-4 Initiating Event Frequency Estimate for 1-FLI-AB_B08_LF........................... A-28 Table A.14-1 Flood Sources 1-FLI-AB_B24_LF2............................................................... A-28 Table A.14-2 Conditional Rupture Probability Parameters 1-FLI-AB_B24_LF2.................. A-29 Table A.14-3 Failure Rate Parameters 1-FLI-AB_B24_LF2............................................... A-29 Table A.14-4 Initiating Event Frequency Estimate for 1-FLI-AB_B24_LF2......................... A-29 Table A.15-1 Flood Sources 1-FLI-AB_B50_JI.................................................................. A-29 Table A.15-2 Conditional Rupture Probability Parameters 1-FLI-AB_B50_JI..................... A-30 Table A.15-3 Failure Rate Parameters 1-FLI-AB_B50_JI.................................................. A-30 Table A.15-4 Initiating Event Frequency Estimate for 1-FLI-AB_B50_JI............................ A-30 Table A.16-1 Flood Sources 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF....................... A-31 Table A.16-2 Conditional Rupture Probability Parameters 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF.A-31 Table A.16-3 Failure Rate Parameters 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF........ A-32 Table A.16-4 Initiating Event Frequency Estimate for 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF.A-32 Table A.17-1 Flood Sources 1-FLI-AB_D74_FP................................................................ A-32 Table A.17-2 Conditional Rupture Probability Parameters 1-FLI-AB_D74_FP................... A-33 Table A.17-3 Failure Rate Parameters 1-FLI-AB_D74_FP................................................ A-33

xiii Table A.17-4 Initiating Event Frequency Estimate for 1-FLI-AB_D74_FP.......................... A-33 Table A.18-1 Flood Sources 1-FLI-AB_D78_FP................................................................ A-34 Table A.18-2 Conditional Rupture Probability Parameters 1-FLI-AB_D78_FP................... A-34 Table A.18-3 Failure Rate Parameters 1-FLI-AB_D78_FP................................................ A-34 Table A.18-4 Initiating Event Frequency Estimate for 1-FLI-AB_D78_FP.......................... A-35 LIST OF TABLES IN APPENDIX B Table B-1 Internal Flooding Significant Cut Sets................................................................ B-1 Table B-2 Internal Flooding Basic Event Importance Measures....................................... B-35 LIST OF TABLES IN APPENDIX C Table C-1 Internal Flooding Topics for Future Work........................................................... C-1

1

1. INTRODUCTION This report documents a description and results for the reactor, at-power, Level 1 probabilistic risk assessment (PRA) model for internal floods that supports the U.S. Nuclear Regulatory Commission (NRC) full-scope site Level 3 PRA project (L3PRA project) for a two-unit pressurized-water reactor (PWR) reference plant. The results provided in this report are for a single unita subsequent report in this series addresses multi-unit risk.

Licensee information used in performing the L3PRA project was voluntarily provided based on a licensed, operating nuclear power plant. The information provided reflects the plant as it was designed and operated as of 2012 and does not reflect the plant as it is currently designed, licensed, operated, or maintained. In addition, the information provided for the reference plant was changed based on additional information, assumptions, practices, methods, and conventions used by the NRC in the development of plant-specific PRA models used in its regulatory decisionmaking. As such, use of this report to assess the risk from the reference plant is not appropriate and this report will not be the basis for any regulatory decision associated with the reference plant.

Since the L3PRA project involves multiple PRA models, each of these models should be considered a living PRA until the entire project is complete. It is anticipated that the models and results of the L3PRA project are likely to evolve over time, as other parts of the project are developed, or as other technical issues are identified. As such, the final models and results of the project (which will be documented in a summary report to be published after all technical work for the L3PRA project has been competed) may differ in some ways from the models and results provided in the current report.

The series of reports for the L3PRA project are organized as follows:

Volume 1: Summary (to be published last)

Volume 2: Background, site and plant description, and technical approach Volume 3: Reactor, at-power, internal event and flood PRA Volume 3x: Overview Volume 3a: Level 1 PRA for internal events (Part 1 - Main Report; Part 2 - Appendices)

Volume 3b: Level 1 PRA for internal floods Volume 3c: Level 2 PRA for internal events and floods Volume 3d: Level 3 PRA for internal events and floods Volume 4: Reactor, at-power, internal fire and external event PRA Volume 4x: Overview Volume 4a: Level 1 PRA for internal fires Volume 4b: Level 1 PRA for seismic events Volume 4c: Level 1 PRA for high wind events and other hazards evaluation Volume 4d: Level 2 PRA for internal fires and seismic and wind-related events Volume 4e: Level 3 PRA for internal fires and seismic and wind-related events Volume 5: Reactor, low power and shutdown, internal event PRA Volume 5x: Overview Volume 5a: Level 1 PRA for internal events Volume 5b: Level 2 PRA for internal events

2 Volume 5c: Level 3 PRA for internal events Volume 6: Spent fuel pool all hazards PRA Volume 6x: Overview Volume 6a: Level 1 and Level 2 PRA Volume 6b: Level 3 PRA Volume 7: Dry cask storage, all hazards, Level 1, Level 2, and Level 3 PRA Volume 8: Integrated site risk, all hazards, Level 1, Level 2, and Level 3 PRA The details of the internal flooding analysis, including modeling assumptions, scenario descriptions, and sources of uncertainty are documented in this report. Section 1.1 describes the overall approach for developing the NRC internal flooding PRA (IFPRA). Section 1.2 describes the arrangement of this report. Simplified diagrams for key systems are provided in Volume 2 of this NUREG series (see Agencywide Documents Access and Management System Accession No. ML22067A232).

CAUTION:

While the L3PRA project is intended to be a state-of-practice study, due to limitations in time, resources, and plant information, some technical aspects of the study were subjected to simplifications or were not fully addressed. As such, inclusion of approaches in the L3PRA project documentation should not be viewed as an endorsement of these approaches for regulatory purposes.

1.1.

Approach The purpose of this section is to describe the process of developing the internal flooding PRA model and documentation. Each of the internal flooding technical elements and associated requirements were addressed in accordance with the ASME/ANS PRA Standard (Ref. IF-7).

The licensee had completed an internal flooding PRA for the reference plant at the time this study was initiated. The reference plants PRA was reviewed and much of the analysis was adopted for this study. The NRCs IFPRA also leverages the NRCs internal events Level 1 PRA model for the reference plant (Ref. IF-16).

The NRC staff performed a plant walkdown to confirm aspects of the internal flooding analysis.

The walkdown allowed the staff to gain familiarity with the plant layout, equipment locations, flood sources, and flood mitigation features.

While the reference plant had completed an internal flooding PRA, new analyses were performed for this study in support of the overall objectives of the Level 3 PRA project. The focus of the new analyses included:

Incorporating insights from NRCs confirmatory plant walkdown.

Evaluating the internal flood scenario qualitative and quantitative screening approach Updating the internal flood initiating event frequency estimates Quantifying the internal flooding modeling, including integrating the model with NRCs internal events PRA model Identifying sources of model uncertainty and performing sensitivity studies

3 1.2.

Arrangement of This Report The IFPRA analysis is described in the subsequent sections of this report. Section 2 describes the approach for addressing each of the internal flooding technical elements in the NRC IFPRA.

Section 3 provides the overarching modeling assumptions and describes each of the modeled internal flooding scenarios. The IFPRA model results and uncertainty analysis are presented in Section 4, with a summary of key insights in Section 4.7. Section 5 provides a list of references.

Additional supporting information for the NRC IFPRA is provided in appendices. Appendix A contains details of the internal flood initiating event frequency analysis for each modeled flood scenario. Appendix B provides a listing of the risk-significant IFPRA cut sets, as well as the importance measures for all risk-significant basic events. Appendix C identifies a number of topics that were not addressed as part of the IFPRA, but for which additional study may be warranted. These modeling improvements should be implemented to maximize the value of the insights obtained from the study.

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2. INTERNAL FLOOD PRA MODEL OVERVIEW This section includes an overview of the technical elements that were analyzed in developing the IFPRA. The section is organized in terms of the five technical elements of an internal flooding PRA, as defined in the ASME/ANS PRA Standard (Ref. IF-7). The following subsections describe the analyses performed for each of the internal flooding PRA technical elements. Section 2.1 addresses Internal Flood Plant Partitioning. Section 2.2 covers Internal Flood Source Identification and Characterization. Section 2.3 addresses Internal Flood Scenarios. Section 2.4 covers Internal Flood-Induced Initiating Events. And, Section 2.5 addresses Internal Flood Accident Sequences and Quantification.

2.1.

Internal Flood Plant Partitioning The main objective of the internal flood plant partitioning is to identify plant areas susceptible to internal flooding that could lead to core damage. Plant partitioning consists of two high-level requirements: (1) to identify a reasonably complete set of flood areas of the plant, and (2) to document internal flood plant partitioning consistent with the applicable supporting requirements from the ASME/ANS PRA Standard.

The identification of flood areas uses plant information resources and is supplemented by walkdowns and interviews with plant staff to confirm the plant configurations. The following information sources from the reference plant were used by the licensee in developing the flood areas:

Plant architectural drawings Piping and instrumentation diagrams Design basis flood calculation documents Appendix R fire areas, fire hazard analysis, and the associated drawings High-energy line break areas Individual Plant Examination internal flooding analysis notebooks Risk-informed inservice inspection documenation The plant partitioning analysis identified hundreds of potential flood areas. The licensee further evaluated the flood areas to identify the structures, systems, and components (SSCs) that are susceptible to flood damage and/or can mitigate the flooding effects.

For each flood area, flood mitigating features that have the ability to terminate or contain the flood were identified in the reference plants PRA documentation. The flood mitigating features are considered in the qualitative screening of flood areas. The flood mitigating features can include:

Flood alarms Flood auto-trip logic for circulating water pumps Flood dikes, curbs, sumps, or structures that allow for the accumulation and retention of water Sump pumps Drainage systems Spray or drip shields Water-tight doors Blowout panels or dampers Various other types of flood barriers, including walls and other structures

5 The licensee evaluated the potential flood areas to identify the SSCs contained in each area that are susceptible to flood damage. The focus was specifically on those SSCs whose failure may result in accident initiation and/or negatively impact an accident mitigation function.

Prior to adopting the licensees flood area analysis, the NRC visited the reference plant site in June 2013. The visit included confirmatory walkdowns of flooding areas, review of design basis flooding calculations, and interviews with plant staff familiar with the plant design and operation.

This effort was intended to provide confirmation of key information for risk-significant flooding areas. It was not an exhaustive or complete walkdown of all flood areas in the plant. Prior to performing the walkdowns, the staff generated a list of priority flood areas to be evaluated during the plant visit. This focused the walkdown effort on those areas that were initially considered to be risk significant or of particular interest for the IFPRA. The following criteria were used to identify the priority flood areas:

Flood areas containing high risk achievement worth importance measure SSCs based on the internal events PRA The top CDF contributors to internal flooding from the reference plants internal flooding PRA Areas of potential cross-unit or multi-unit flooding impacts Other areas of interest for the NRC IFPRA The confirmatory plant walkdown was completed for the selected risk-significant flooding areas and confirmed the information regarding equipment layout, flood sources, protective features, and susceptibilities. As such, the licensees internal flood plant partitioning analysis was adopted for use in the NRC IFPRA.

2.2.

Internal Flood Source Identification and Characterization The purpose of this section is to describe the internal flood source identification and characterization analysis. The main objective of the internal flood source identification is to identify the plant-specific sources of internal flooding that could lead to accident sequences resulting in core damage. This task identifies the various sources of floods and equipment spray within the plant, along with the mechanisms resulting in flood or spray from these sources, and characterizes the flood/spray sources (e.g., in terms of liquid amounts and flowrates).

Flood sources include any equipment located in a flood area that can cause flooding. Examples of flood sources include: piping, flanges, valves, pumps, tanks, heat exchangers, pools, external sources of water connected to the area through systems or structures, and in-leakage from other flood areas. Primary system piping whose failure would result in a loss-of-coolant accident (LOCA) and selected high-energy line breaks4F5 are not treated in the internal flooding analysis, since they were addressed and analyzed in the internal events analysis.

The licensee performed a systematic review of the flood sources for each flood area. The most prevalent sources of flooding for most flood areas are piping systems. For each flood area, the following information was collected for the piping located in the area: the system, the pipe diameter, and the length of pipe in the area. This information was used in the subsequent analysis tasks for developing the internal flood scenarios.

5 Main feedwater line breaks were included as internal flooding initiating events, and these contribute to several of the modeled flooding scenarios described in Section 3.2. However, main steam line breaks were not included as internal flooding initiating events. Main steam line breaks are evaluated in the internal events PRA model.

6 2.3.

Internal Flood Scenarios The purpose of this section is to describe the internal flood scenario analysis performed by the licensee. The internal flood scenarios were developed by incorporating aspects of the plant partitioning and flood source analyses discussed in the previous sections. Next, a qualitative screening evaluation was performed to identify the potential internal flooding scenarios. Section 2.3.1 discusses this qualitative screening analysis. The remaining flood areas and flood sources were evaluated to develop the detailed characteristics of the potential flooding scenarios.

Section 2.3.2 summarizes this characterization of flood scenarios.

2.3.1. Qualitative Screening Analysis The purpose of the qualitative screening analysis is to identify and remove flood areas that are not important for the internal flooding PRA. A set of qualitative screening criteria was used to screen flood areas and associated flood sources. These criteria were based on the requirements of the ASME/ANS PRA standard (Ref. IF-7). The qualitative screening criteria are presented below:

a. If there is no flood source in the room or location, the room or location can be screened out, even if it contains accident initiation/mitigation SSCs. However, rooms with no flood sources, but that contain accident initiation/mitigation SSCs, need to be further evaluated if there is a potential for flood water from adjacent room(s) or location(s) to propagate to these rooms.

b. If flooding of the area would not cause an initiating event or a need for immediate plant shutdown, and The flood area (including areas where flood sources can propagate to) contains no accident initiation/mitigation equipment susceptible to flood damage, or The flood area has no flood sources sufficient (e.g., through spray, submergence, or other flood-induced hazards) to cause failure of accident initiation/mitigation equipment susceptible to flood damage in the area (including areas where flood sources can propagate to).

c. If flooding of the area would not cause an initiating event or a need for immediate plant shutdown, and the area contains flooding mitigation systems (e.g., drains or sump pumps) capable of preventing unacceptable flood levels, and the nature of the flood would not cause failure of the accident initiation/mitigation equipment susceptible to flood damage (e.g.,

through spray, submergence, or other flood-induced hazards).

d. If potential human mitigating actions could be used for screening (and meet ASME/ANS PRA standard Capability Category II) given that:

flood indication is available in the control room flood sources in the area can be isolated mitigating actions can be performed with high reliability for the worst flooding initiator, which can be established by demonstrating, for example, that the actions are procedurally directed, that adequate time is available for response, that the area is accessible, and that there is sufficient manpower available to perform the action

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e. If the flood source is insufficient (e.g., through spray, submergence, or other flood induced hazards) to cause failure of accident initiation/mitigation equipment susceptible to flood damage.

f. If the area flood mitigating systems (e.g., drains or sump pumps) are capable of preventing unacceptable flood levels and the nature of the flood does not cause failure of accident initiation/mitigation equipment susceptible to flood damage through spray, submergence, or other flood-induced hazards.

g. If the flood only affects the system that is the flood source and the system analysis addresses this type of failure, then this flood source need not be treated as a separate internal flooding initiating event.

In applying these criteria, the ASME/ANS PRA standard specifies that the potential flood impacts on accident initiation/mitigation equipment shall include consideration of impacts on support systems (e.g., electric power, cooling water systems) whose failure would result in accident initiation or failure of mitigation functions. The licensee evaluated each of the identified flood areas and associated flood sources against the criteria above. The flood areas not screened by this process were evaluated further by defining and characterizing flood scenarios.

2.3.2. Characterization of Flood Scenarios This section describes the overall approach to assembling the elements that were considered in defining potential flooding scenarios for the IFPRA model. Each flood scenario description includes the relevant information required for incorporation into the model. This information includes a description of the flooding initiating event (i.e., the pipe break or component failure that initiates the flood), the flood location, and attributes of the flood source (e.g., flow rate and type). The scenario description also includes the impacts of the flood and plant response, identifies the SSCs that are damaged due to the flood, and identifies the corresponding initiating event from the internal events PRA that is used to model the flood impacts. If no corresponding internal initiating event exists, then a new initiating event type is created to model the flood response. The plant response also includes identifying the plant systems and functions that are needed to prevent core damage. The detailed descriptions of each modeled flood scenario in the IFPRA are provided in Section 3.2.

The scenarios consider the flooding effects (i.e., submergence, humidity, condensation, and temperature) that could cause equipment failures. In addition, due to the energy associated with failures of high-energy piping systems, these events may cause additional consequences, such as pipe whip or jet impingement. The flood scenarios are categorized by flood type to distinguish the types of flood effects that can occur. Each flood area may have more than one flood type associated with it. The following flood types are defined:

Local flooding - The flooding effects are considered within the same flood area where the flood initiated. The flooding effects due to submergence, humidity, condensation, and temperature are considered. The primary consideration for most flood scenarios is submergence.

Flood propagation - The flood propagates to other flood areas. The same flooding effects as local flooding are considered.

Human-induced local flooding - The flood is initiated by human error. The same flooding effects as local flooding are considered.

8 Spray - In addition to the above mentioned flooding effects, spray events consider impacts to SSCs that are within a direct line-of-sight of the flood source. SSCs located above the maximum flood height can fail from spray before submergence. Spray events are characterized by small through-wall failures resulting in low leak rates, but may have a higher contribution to the flood initiating event frequency. Sprays are considered for both high-energy piping and non-high-energy piping.

Jet impingement - Jet impingement is only considered for high-energy piping. The flooding effects are similar to spray events, with additional consideration for the high-energy impact of the jet stream from the flood source.

Pipe whip - The flooding effects include consideration for pipe whip due to failure of high-energy piping.

The criteria for determining susceptibility to sprays can vary in different internal flooding analyses. The specific criteria for this study considers the adverse effects from spray sources if the susceptible equipment is within 10 feet of horizontal distance from overhead flood sources and the equipment is in the line-of-sight of pressurized-water sources. The distance is extended to include SSCs within 20 feet for high-energy flood sources. The IFPRA considers piping systems with pressures in excess of 275 psig or the maximum normal operating temperature exceeding 200ºF to be high-energy piping. The same definition of high-energy piping is used for determining which flood sources are potential sources for jet impingement and pipe whip.

The potential impacts due to submergence are evaluated by examining the maximum flood water height for each flood area. The licensee for the reference plant used the design basis flood calculations to estimate the maximum flood water height for each flood area. The flood water level estimates considered the flood propagation paths and areas of accumulation by accounting for flow through non-water-tight doors, drains, penetrations, and other features that can contribute to the flood accumulation level. The licensee did not directly use the flood level calculations to determine potential equipment failures, though they did use them to inform bounding assumptions on flood impacts. For example, for local flooding scenarios, the design basis flood calculations support the assumption that all eaqupment in a given flood area would be failed. However, for some flood propagation scenarios, the flood calculations are not conclusive regarding equipment damage. Nonetheless, the licensee assumed that for both local flooding scenarios and flood propagation scenarios, all SSCs located in a flooded room would be damaged by the flood water. The IFPRA uses the same set of flooding impact assumptions as the licensee.

The flooding scenario analysis considers actions and systems that may be used to mitigate the impacts of flood scenarios. These include flood alarms; level, pressure, and flow indicators; and post-flood operator actions. The flood mitigating actions that have the ability to terminate or contain flood propagation were identified for each flood scenario. The licensee assigned screening human error probability (HEP) values for each action. For most scenarios, the licensee assumed no credit for mitigating actions, and the screening HEP is set to 1.0. The lone exeception involved mitigating actions for scenarios due to charging system line breaks.

Operator action to restore charging and seal injection according to applicable procedures was assigned a screening HEP of 0.1. The screening HEPs were used in the initial screening quantification of CDF contributions. If risk significant operator actions were identified from the initial screening quantification, then a detailed human reliability analysis would have been performed for those actions. However, no risk-significant operator actions were identified from the screening quantification. The licensees analysis of flood scenario mitigation was adopted for use in the NRC IFPRA.

9 2.4.

Internal Flood-Induced Initiating Events The purpose of this section is to describe the internal flood-induced initiating event analysis. The main objectives of the analysis are to identify flood-induced initiating events and to estimate their frequencies. The approach to initiating event identification is described in Section 2.4.1. An overview of the initiating event frequency estimation approach is discussed in Section 2.4.2.

Initiating event frequency analysis for each of the modeled flood scenarios is described in detail in Appendix A.

2.4.1. Identification of Flood-Induced Initiating Events For each of the identified flood scenarios, the licensee considered two types of flood-induced initiating events:

1. Floods that cause an initiating event

2. Floods that result from an initiating event The first type of flood initiator begins with a pressure boundary failure and likely causes an automatic actuation resulting in an initiating event. The frequency of these failures, which are primarily piping system failures, were quantified using generic industry data along with plant-specific operating experience.

For the second type of flood initiator, plant conditions that could result in a flooding event were evaluated. This included the consideration of human-induced floods and induced pipe failures resulting from a random initiating event. A random initiating event could involve stresses on a piping system from any of the following:

Water hammer Rapid pressurization Valve slamming open or closed High vibration Void collapse A review of the pipe failure operating experience (as documented in Ref. IF-9) suggests that the probability of a conditional pipe break resulting from a random initiating event is expected to be much lower than other failure probabilities that would impact a given plant systems reliability.

Combined with the frequency of a random initiating event, the flood initiating sequence frequency would be very low. Therefore, this type of pipe failure is screened from further consideration.

The reference plant provided an analysis of maintenance activities that could result in human-induced flooding. The analysis considered the following maintenance activities:

Circulating water (CW) system maintenance work Component cooling water (CCW)/auxiliary CCW heat exchanger maintenance work Turbine plant closed cooling water (TPCCW) heat exchanger maintenance work Fire protection water system maintenance work To estimate the frequency of causing a human-induced flooding event, the licensee used screening values for HEPs that lead to flooding events. The human-induced flooding scenarios involve two types of human failures: (1) failure to properly restore the system or component after maintenance work, and (2) failure of the maintenance crew to mitigate the flooding event when the system or component is returned to service. The first type of failure was assigned a screening HEP of 0.01. The second type of failure was assigned a screening HEP of 0.1. The restoration of equipment from maintenance is directed by applicable procedures. Also, the

10 reference plant has a general practice of staging operations and maintenance staff locally to identify leakage when a system/component is being refilled and placed back in service. For these reasons, human failures associated with restoring equipment and mitigating flooding are expected to be unlikely.

The licensee identified flood scenarios that may impact accident initiation or mitigating equipment. The internal event initiator that would result due to the flood was identified for each scenario. For certain pipe failures, the associated flooding effects may be inconsequential to the resulting internal event accident scenarios. Examples of these failures include pipe breaks resulting in loss-of-coolant accidents (LOCAs) and main steam line breaks (MSLBs). These scenarios are not addressed in the internal flooding analysis. The impacts from these events are captured by the internal events PRA model.

2.4.2. Flood Initiating Event Frequency Estimates This section describes the quantitative analysis used by the L3PRA project staff to estimate the internal flooding scenario frequencies for the IFPRA. The initiating event frequency analysis is based on the approach described in the Electric Power Research Institute (EPRI) report, Pipe Rupture Frequencies for Internal Flooding PRAs, Revision 3 (Ref. IF-9). The initiating event frequency, f, for a given pipe break flooding scenario is given by the following expression:

= x x (l)

[1]

where, l is the length of pipe (in feet) located in the flood area pipe is the failure rate of the pipe per feet-critical reactor year Ppipe(RlF) is the conditional rupture probability given pipe failure The EPRI report defines failure as any condition in which pipe repair or replacement was performed. Failures can include wall thinning, cracks, pinhole leaks, leaks, and major structural failures. A failure will not necessarily result in a flooding event, but the occurrence of any failure will be associated with the conditional probability of a rupture. A rupture is a substantial failure that results in the initiation of a flooding event. In this report, the terms rupture and break are used interchangeably to refer to substantial pipe failures that result in flooding events.

Similarly, the initiating event frequency can be expressed in terms of component failures that may be relevant to a flood scenario (e.g., failure of rubber expansion joints), as follows:

= x x (l)

[2]

where, n is the number of components located in the flood area component is the failure rate per component-critical reactor year Pcomponent(RlF) is the conditional rupture probability given component failure The EPRI report provides generic failure data for different types of plant systems. The data are further categorized in terms of the severity of pipe failure (e.g., wall thinning, pinhole leak, leak, major structural failure) and pipe size. The category definitions may vary depending on the type of system. The generic data and failure rates in the report were used in the IFPRA to develop prior distributions for the pipe (or component) failure rates and conditional rupture probabilities.

The prior distributions are updated with plant-specific data. The plant-specific data considered for the IFPRA cover the period from January 1, 1990 through December 31, 2012.

11 Additional details regarding the initiating event frequency estimates for the NRC IFPRA are provided in Appendix A.

2.5.

Internal Flood Accident Sequences and Quantification This section describes the analysis and quantification of the internal flood accident sequences performed by the L3PRA project staff. The main objective of this task is to identify the internal-flood-induced accident sequences and quantify the likelihood of core damage (Ref. IF-7). Each internal flooding scenario is related to an internal events scenario that would be caused by the flood and accounts for flood-specific impacts on equipment and operator actions. The modeled scenarios that were adopted for the IFPRA are described in Section 3.2 of this report. For each scenario, the related internal event sequences and flood-specific impacts were reviewed to ensure the flood-related phenomena are appropriately modeled. The following sections provide a description of the quantification process used for the IFPRA. Section 2.5.1 discusses the quantitative screening analysis, and Section 2.5.2 discusses quantification of human failure events. Additional information on the IFPRA model quantification can be found in the discussion of model results in Section 4.

2.5.1. Quantitative Screening Analysis After the licensee applied the qualitative screening criteria, 78 potential internal flooding scenarios were identified for further quantitative evaluation. A quantitative screening process was performed by the L3PRA project staff to estimate the CDF contribution of each scenario.

The scenarios representing the top 95 percent of the total estimated internal flood CDF and each scenario contributing greater than 1 percent to total internal flood CDF were selected to be incorporated into the IFPRA model.

The quantitative screening approach used the NRC internal events PRA to assess the plant impacts resulting from each of the flooding scenarios. The internal events model was used to calculate the conditional core damage probability (CCDP) for each flooding scenario based on the initiating event that was caused and the SSCs that were failed due to the flooding impacts.

The initiating event frequency for each flooding scenario was estimated based on generic data from the EPRI technical report, Pipe Rupture Frequencies for Internal Flooding Probabilistic Risk Assessments (Ref. IF-9).

This process was used to estimate the CDF of each flooding scenario and determine its contribution to the overall flooding CDF. The scenarios with the highest contributions to CDF were evaluated further to assess whether they should be incorporated into the NRC IFPRA model. This process was repeated for the top contributing scenarios until the modeled scenarios represented greater than 95 percent of the total flooding CDF and each scenario contributing greater than 1 percent to total flooding CDF was identified. This process resulted in 23 internal event flood scenarios being incorporated into the IFPRA model.

2.5.2. Quantification of Human Failure Events The analysis of human failure events consists of three types of failures: pre-initiator human failures, post-initiator actions for flood mitigation, and post-flood actions unrelated to the flood but required for responding to the accident scenario.

The licensees internal flooding PRA identified pre-initiator human actions that may lead to flooding events. They then reviewed plant-specific maintenance practices, procedures and experience to identify potential human errors that could result in flooding. The identified human-induced flooding scenarios were previously discussed in Section 2.4.1. Also as discussed in

12 Section 2.4.1, in estimating the human-induced flooding scenario frequencies, the licensee assigned screening values for the HEPs that contribute to the floods.

The licensees internal flooding analysis identified post-initiator flood mitigation actions that may be performed to limit or prevent impacts after a flood is initiated. The plant procedures, instrumentation, and indications were reviewed to assess how operators become aware that a flooding situation has occurred. The plant features that could alert operators may include:

Flood alarms - The presence of flood alarms will reduce the time to discover a flood and take action to islote the flood.

Flow and pressure indicators - Many systems contain flow indicators that are monitored from the main control room. Operators may use flow indications to recognize flooding conditions. Similarly, low pressure indications may assist in flood indentificaiton.

Radwaste control panels - These panels provide diagnostic information for locating leaks inside plant buildings.

Radiation detectors - These may be considered in identifying flood source failures where high radiation may be involved.

As discussed previously in Section 2.3.2, flood mitigating actions were identified based on plant procedures and available flood indication inside the control room. The licensee applied a screening HEP of 1.0 to most of these actions (exceptions are described in Section 2.3.2). As previously stated, there is no credit given for flood mitigation actions in the modeled flooding scenarios.

The internal flooding analysis also considers the impact on post-flood human failure events that are unrelated to flood mitigation. These are actions that are performed to mitigate the resulting plant accident scenario and may be influenced by the flooding conditions. In the IFPRA, post-flood actions are assumed to fail if local action occurs in an area impacted by the flood. For actions that are performed in locations unaffected by the flood, the failure probabilities of those actions may be influenced by the flood occurrence. For actions that are not located in areas affected by the flooding, the stress level is expected to be the primary performance shaping factor that impacts the change in the HEP value. The time window for the action should also be considered. If the time window is sufficiently long (e.g., > 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />), then the increase in the stress level due to the flooding event may be insignificant. A consensus approach for scaling the HEP values for actions unaffected by the flood location was not identified for this study. Potential impacts on HEP values were considered, but ultimately there was no method implemented in the model. Future work in this area may be needed to develop a consensus approach for adjusting HEP values. For this study, the issue is addressed by considering a sensitivity case with increased HEP values. The sensitivity case is discussed in Section 4.5.3.

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3. INTERNAL FLOOD PRA MODEL ANALYSIS The purpose of this section is to describe the NRC IFPRA modeled flood scenarios. Section 3.1 identifies the important model assumptions that were made in developing the NRC IFPRA.

Section 3.2 describes the internal flooding scenarios as they are modeled in the NRC IFPRA.

3.1.

Internal Flood Model Assumptions The following assumptions were made in developing the NRC IFPRA models internal flooding scenarios. Assumptions were made in cases where information about the plants flooding risk was unavailable or not well developed. Additional effort to develop analyses or gather more information was deemed to be unwarranted because the significance of these issues to the overall plant core damage frequency (CDF) from all hazards was considered to be low.

1. Dual-unit or cross-unit flooding scenarios: Based on information reviewed from the reference plant flooding analysis and confirmatory walkdowns performed by NRC staff for the NRC IFPRA, potential dual-unit or cross-unit flooding scenarios were screened from further analysis. The key fluid systems at the reference plant include dedicated systems for each unit. There is limited dependency on shared or cross-tied systems that could act as a dual-unit flood source. The potential for flood propagation between units is limited by sufficient use of compartment walls, doors (including watertight doors for significant flood sources), curbs, drains, and spatial separation. No risk-significant internal flooding propagation paths were identified that would impact accident initiation or mitigating equipment in both units. Also, no risk-significant propagation paths were identified that could initiate in one unit and impact accident initiation or mitigating equipment in the other unit.

These assumptions are supported by the NRC staffs analysis of the reference plant; however, they may not be applicable to other multi-unit plant sites. Also, changes in plant conditions that could increase internal flooding risks may require revisiting these assumptions. For example, if cross-unit flood barriers are defeated or potential flood sources are aligned in off-normal alignments, then the potential for cross-unit flooding may need to be reevaluated. Nevertheless, for normal plant operating conditions at the reference plant, the NRC staff deemed the potential for dual-unit or cross-unit internal flooding to be unlikely.

Note, further analysis of floods impacting both units is identified as a consideration for future work in Appendix C.

2. Applicability of results to Unit 2: The flooding scenarios were based on analysis of Unit 1 of the reference plant. The Unit 1 internal flooding analysis was deemed applicable to corresponding flooding areas located in Unit 2. No major differences between the two reactor units at the reference plant were identified that would impact the internal flooding analysis.

3. Loss-of-coolant accidents (LOCAs) and main steam line breaks (MSLBs): Loss of primary coolant accidents and main steam line breaks are addressed in the internal events analysis, and were not addressed in the internal flooding analysis. This approach appears to be consistent with the current internal events PRA state of practice. However, additional analysis could be pursued to consider multiple locations for these breaks and incorporate the local impacts in the plant response model. This would improve the realism of these scenarios, but was not pursued for this study. The internal events PRA evaluation of high-energy line breaks was deemed sufficient for this study. Note, the contribution of steam line breaks to the internal flooding analysis is identified as a potential model enhancement in Appendix C.

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4. Flood source flow rate characterization: The flow rate from a failed flood source can vary depending on the type of failure that occurs. The Electric Power Research Institute (EPRI) pipe rupture report (IF-9) defines three flood failure categories, with associated break flow rate ranges: spray events with 100 gpm; flood events with break sizes that produce 100 gpm to 2000 gpm; and major flood events with flow rates greater than 2000 gpm. The same categories were adopted for the NRC IFPRA.

Each flood scenario may include multiple flood sources that could fail in a variety of ways and result in a range of break flow rates. A representative flow rate was selected for each scenario, according to the following:

For spray events, the representative flow rate was assumed to be 100 gpm.

For flood events where all failed pipes have a diameter of 2 in. or less, the representative flow rate was assumed to be 1000 gpm.

For flood events where at least one failed pipe has a diameter greater than 2 in., the representative flow rate was assumed to be 2000 gpm.

For major floods, the representative flow rate was assumed to be 100,000 gpm.5F6 The choice of representative flow rate for the flooding scenarios does not have a significant impact on the NRC IFPRA results. Assumptions regarding equipment failures due to flooding (see assumption 5, below) make the results insensitive to the choice of representative flow rate.

5. Equipment damage due to flooding: For the NRC IFPRA, the structures, systems, and components (SSCs) that may contribute to accident initiation and mitigation were assumed to fail if the room was impacted by a flood, regardless of flood height.

6. Impact of sprays: Failures resulting in spraying or splashing are assumed to affect components located within a 10-foot radius and within line-of-sight of a pressurized-water source.6F7 The spray impact assessment should include consideration of the spatial and directional effects of sprays. In some PRA studies, a spray directional factor that accounts for the sprays direction with respect to the pipes circumference is applied when supported by a detailed engineering evaluation. For the spray scenarios modeled in the NRC IFPRA, there was not sufficient information available to support a detailed evaluation of the directional effects of sprays. Therefore, a spray directional factor was not applied in any of the modeled flood scenarios.

7. Flood mitigation operator actions: For all of the modeled flooding scenarios, there was no credit given for flood mitigation actions. In other words, there was no credit given for operator actions prior to scenario flood damage occurring. It was assumed that each flooding scenario is eventually terminated by automatic or operator actions after initial flooding damage and accident initiation occur. Long-term actions to terminate floods may or may not be required to place the plant in a safe and stable condition, depending on (1) the capacity of the source and (2) location of the breach and flood water accumulation areas.

6 100,000 gpm is assumed for major floods that involve failures of the circulating water system. The EPRI flooding frequency report (IF-9) reports significant circulating water failure historical events that resulted in estimated flow rates ranging from 3,000 gpm to 200,000 gpm. Based on this range, 100,000 gpm is deemed to be a reasonable estimate for major floods.

7 EPRIs Guidelines for Performing of Internal Flooding Probabilistic Risk Assessment (Ref. IF-14) suggests a general guideline that spraying or splashing water should be assumed to affect electrical components located within a minimum 10-foot radius and within line-of-sight of a pressurized-water source. This guideline is considered to be consistent with current internal flooding PRA state of practice.

15 Long-term actions to terminate floods were not modeled. It was assumed that any additional damage from long-term flooding was bounded by the initial flood damage and accident initiation that was captured in the modeled scenarios.

3.2.

Internal Flood Modeled Scenarios The purpose of this section is to describe the internal flooding scenarios that were modeled in the NRC IFPRA model. Each flooding scenario description consists of:

Flooding initiating event - the pipe break or component failure that initiates the flooding Flood location - flood area(s) impacted by the flood Flood type - spray, local flooding, or flood propagation Representative flow rate - flood sources can produce a range of possible flow rates. A representative flow rate was selected using guidlines consistent with those provided in the first revision of EPRIs flooding frequency report (Ref. IF-8).

Corresponding internal initiating event - each flooding scenario results in impacts to the plant that map to an internal initiating event that is modeled in the internal events PRA. For example, a flooding event from a feedwater pipe break that results in isolation of main feedwater (MFW) maps to the internal event loss of MFW.

Flood impact - the impacts on the plant due to flooding (i.e., the SSCs included in the PRA model that are assumed to be failed due to the flood)

Plant response - the plant systems and functions that are needed to prevent core damage given the SSC failures associated with the flood The NRC IFPRA model includes 23 internal flood scenarios. The flooding scenarios were primarily based on the reference plants internal flooding analysis; however, some modifications were made to support the NRC IFPRA. The motivations for modifying the scenarios are described below.

Update to Initiating Event Frequency Estimates: For the NRC IFPRA, the staff used generic data from the EPRI technical report, Pipe Rupture Frequencies for Internal Flooding PRAs, Revision 3, (IF-9IF-8). The revised initiating event frequencies have generally increased (by factors ranging from approximately 2 to 4) with respect to the values published in previous versions of EPRIs report.

Subsuming Related Scenarios: For the NRC IFPRA, related flood scenarios that have the same or similar plant impacts were subsumed into a single flood scenario. For example, a spray scenario and a local flooding scenario that both affect the same equipment in the same room were treated as a single scenario, and the initiating event frequency includes both spray and local flooding contributions. These related scenarios were subsumed to provide more inclusive coverage of the flooding risk, rather than modeling only the highest contributing scenario from a group of related scenarios.

The internal flooding scenarios are described below. Each scenario description includes information on the flood location, type of scenario, and impacts on the plant. The scenario descriptions also identify the corresponding event tree from the internal events PRA that was used to model the flooding scenaro.

3.2.1. Internal Flood Scenario: 1-FLI-AB_108_SP1

16 Flooding Initiating Event Feedwater (FW) or auxiliary component cooling water (ACCW) pipe failure results in a spray that impacts steam generator relief and isolation valves.

Location:

Auxiliary building - south main steam valve room Flood type:

Spray Representative flow rate:

100 gpm Corresponding internal event:

Secondary-side break upstream of MSIVs /

downstream of MFIVs (SSBI)

Flood Impact The scenario impact involves the spurious operation of steam generator 1 (SG1) MSIVs, MS isolation bypass valves, and atmospheric relief valve (ARV). Assuming the SG1 ARV fails open and operators cannot quickly close it, a plant trip would occur. The modeled impact on the SG1 ARV may be pessimistic, since the spray directional factor and the likelihood of equipment damage given it is sprayed were not factored into the spray scenario frequency. Spray has no impact on code safety valves. The room is not susceptible to local flooding. Flood water would accumulate at a lower level of this room, and not propagate to other flood areas.

Spray from FW or ACCW pipe failures can only impact either the SG1 or SG4 valves due to a wall partition. It is assumed that half of the time the source pipe rupture will impact the SG1 valves (i.e., initiating event frequency for this scenario = 0.5 x total pipe rupture frequency).

Stated differently, half of the source pipe length was assumed to impact SG1 and is modeled in this scenario. The other half of the source pipe length was assumed to impact SG4 and is modeled in scenario 1-FLI-AB_108_SP2, described in 3.2.2.

Plant Response Auxiliary feedwater (AFW) is the primary means of heat removal for this scenario. After a secondary-side break, the MSIVs will close on low steam line pressure. This eliminates the use of steam dump valves as a means of removing decay heat. Therefore, heat removal needs to be accomplished using the ARV or 1 of 5 code safety valves for at least one SG. Although the ARV for SG1 is assumed to fail open to initiate the event, heat removal by this ARV may not be available. Due to the flood impacts, the ARV is susceptible to spurious operation and could re-close. The worst-case assumption is applied to this scenario, and therefore, heat removal by the ARV for SG1 is assumed unavailable. The operator action to open the SG1 ARV locally with a hydraulic pump will be directly impacted by a flooding event in this location and cannot be credited. Successful operation of secondary-side cooling (AFW) can place the reactor in a stable condition provided (1) successful isolation of the faulted SG, (2) no reactor coolant pump (RCP) seal LOCA occurs, and (3) a power-operated relief valve (PORV) did not open. Feed-and-bleed cooling with high-pressure recirculation is also a viable success path.

Main steam lines are located in this room, but they do not contribute to the spray event modeled in this scenario. The impact of main steam line failures were modeled as separate initiating events in the internal events model.

17 3.2.2. Internal Flood Scenario: 1-FLI-AB_108_SP2 Flooding Initiating Event FW or ACCW system pipe failure results in a spray that impacts SG relief and isolation valves.

Location:

Auxiliary building - south main steam valve room Flood type:

Spray Representative flow rate:

100 gpm Corresponding internal event:

Secondary-side break upstream of MSIVs /

downstream of MFIVs (SSBI)

Flood Impact The scenario impact involves the spurious operation of SG4 MSIVs, MS isolation bypass valves, and ARV. Assuming the SG4 ARV fails open and operators cannot quickly close it, a plant trip would occur. The modeled impact on the SG4 ARV may be pessimistic, since the spray directional factor and the likelihood of equipment damage given it is sprayed were not factored into the spray scenario frequency. Spray has no impact on code safety valves. The room is not susceptible to local flooding. Flood water would accumulate at a lower level of this room, and not propagate to other flood areas.

Spray from FW or ACCW pipe failures can only impact either the SG1 or SG4 valves due to a wall partition. It is assumed that half of the time the source pipe rupture will impact the SG4 valves (i.e., initiating event frequency for this scenario = 0.5 x total pipe rupture frequency).

Stated differently, half of the source pipe length was assumed to impact SG4 and is modeled in this scenario. The other half of the source pipe length was assumed to impact SG1 and is modeled in scenario 1-FLI-AB_108_SP1, described in 3.2.1.

Plant Response AFW is the primary means of heat removal for this scenario. After a secondary-side break, the MSIVs will close on low steam line pressure. This eliminates the use of steam dump valves as a means of removing decay heat. Therefore, heat removal needs to be accomplished using the ARV or 1 of 5 code safety valves for at least one SG. Although the ARV for SG4 is assumed to fail open to initiate the event, heat removal by this ARV may not be available. Due to the flood impacts, the ARV is susceptible to spurious operation and could re-close. The worst-case assumption is applied to this scenario, and therefore, heat removal by the ARV for SG4 is assumed unavailable. The operator action to open the SG4 ARV locally with a hydraulic pump will be directly impacted by a flooding event in this location and cannot be credited. Successful operation of secondary-side cooling (AFW) can place the reactor in a stable condition provided (1) successful isolation of the faulted SG, (2) no RCP seal LOCA occurs, and (3) a PORV did not open. Feed-and-bleed cooling with high-pressure recirculation is also a viable success path.

Main steam lines are located in this room, but they do not contribute to the spray event modeled in this scenario. The impact of main steam line failures are modeled as separate initiating events in the internal events model.

18 3.2.3. Internal Flood Scenario: 1-FLI-AB_A20 Flooding Initiating Event Condensate pipe failure in room A06 results in flood propagation to room A20, or feedwater pipe failure results in spray impacting equipment in room A20. For the flood sources in room A20, this scenario only considers spray due to small leaks in feedwater piping. Large leaks that could cause local flooding are modeled in scenario 1-FLI-AB_A20_FP.

Pipe failure frequencies for flooding sources in both rooms A06 and A20 were included in this scenario. Flood water propagates from room A06 to room A20 via piping penetrations at various heights from the floor. The propagation of flood water from room A06 to room A20 was assumed to be unmitigated.

Location:

Auxiliary building, rooms A06 and A20 Flood type:

Spray from sources in room A20 and propagation from sources in A06 to A20 (Local flooding from room A20 sources is modeled in scenario 1-FLI-AB_A20_FP, which impacts room A20 and also propagates to rooms A11 and A12.)

Representative flow rate:

2000 gpm Corresponding internal event:

Loss of MFW (LOMFW)

Flood Impact The impacted components in room A20 include the FW control/regulator valves and the FW control/regulator bypass valves for feed lines to SG 1 and SG 4. The FW bypass valves are assumed to fail to full open, resulting in a loss of MFW transient.

Plant Response Successful operation of secondary-side cooling (AFW) can place the reactor in a stable condition provided there is no RCP seal LOCA and a PORV did not open. Feed-and-bleed cooling with high-pressure recirculation can also provide successful decay heat removal if secondary-side cooling is unavailable.

3.2.4. Internal Flood Scenario: 1-FLI-AB_C113_LF1 Flooding Initiating Event The scenario involves failure of the nuclear service cooling water (NSCW) piping located in the boric acid batching tank room. This scenario only considers NSCW pipe failures as a flood source. Other potential flood sources are located in the room.

The other flooding sources were determined to not be significant contributors to overall internal flooding risk and were not modeled in the NRC IFPRA. No propagation scenarios were identified for this flood area.

Location:

Auxiliary building - boric acid batching tank room Flood type:

Local flooding

19 Representative flow rate:

1000 gpm Corresponding internal event:

Other transient resulting in reactor trip (TRANS)

Flood Impact The failure of the flood source results in unavailability of NSCW train A. Local flooding impacts the refueling water storage tank (RWST) to a charging pump suction isolation valve that fails to open. The NSCW failure would not result in an immediate plant trip. The NSCW failure could lead to a subsequent plant shutdown if required action and associated completion time were not met under a limiting condition for operation (LCO). For the purposes of modeling the scenario, a plant trip with loss of NSCW train A was assumed.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path, but one centrifugal charging pump is unavailable due to the dependency on the failed NSCW train.

3.2.5. Internal Flood Scenario: 1-FLI-CB_122_SP Flooding Initiating Event FW pipe failure results in a spray that impacts SG relief and isolation valves.

Location:

Control Building - north main steam valve room Flood type:

Spray Representative flow rate:

100 gpm Corresponding internal event:

Secondary-side break upstream of MSIVs /

downstream of MFIVs (SSBI)

Flood Impact The scenario impact involves the spurious operation of SG3 MSIVs, MS isolation bypass valves, and ARV. Assuming the SG3 ARV fails open and operators cannot quickly close it, a plant trip would occur. The modeled impact on the SG3 ARV may be pessimistic, since the spray directional factor and the likelihood of equipment damage given it is sprayed were not factored into the spray scenario frequency. Spray has no impact on code safety valves. The room is not susceptible to local flooding. Flood water would accumulate at a lower level of this room, and not propagate to other flood areas.

Plant Response AFW is the primary means of heat removal for this scenario. After a secondary-side break, the MSIVs will close on low steam line pressure. This eliminates the use of steam dump valves as a means of removing decay heat. Therefore, heat removal needs to be accomplished using the

20 ARV or 1 of 5 code safety valves for at least one SG. Although the ARV for SG3 is assumed to fail open to initiate the event, heat removal by this ARV may not be available. Due to the flood impacts, the ARV is susceptible to spurious operation and could re-close. The worst-case assumption is applied to this scenario, and therefore, heat removal by the ARV for SG3 is assumed unavailable. The operator action to open the SG3 ARV locally with a hydraulic pump will be directly impacted by a flooding event in this location and cannot be credited. Successful operation of secondary-side cooling (AFW) can place the reactor in a stable condition provided (1) successful isolation of the faulted SG, (2) no RCP seal LOCA occurs, and (3) a PORV did not open. Feed-and-bleed cooling with high-pressure recirculation is also a viable success path.

Main steam lines are located in this room, but they do not contribute to the spray event modeled in this scenario. The impact of main steam line failures were modeled as separate initiating events in the internal events model.

3.2.6. Internal Flood Scenario: 1-FLI-CB_123_SP Flooding Initiating Event FW pipe failure results in a spray that impacts SG relief and isolation valves.

Location:

Control Building - north main steam valve room Flood type:

Spray Representative flow rate:

100 gpm Corresponding internal event:

Secondary-side break upstream of MSIVs /

downstream of MFIVs (SSBI)

Flood Impact The scenario impact involves the spurious operation of SG2 MSIVs, MS isolation bypass valves, and ARV. Assuming the SG2 ARV fails open and operators cannot quickly close it, a plant trip would occur. The modeled impact on the SG2 ARV may be pessimistic, since the spray directional factor and the likelihood of equipment damage given it is sprayed were not factored into the spray scenario frequency. Spray has no impact on code safety valves. The room is not susceptible to local flooding. Flood water would accumulate at a lower level of this room, and not propagate to other flood areas.

Plant Response AFW is the primary means of heat removal for this scenario. After a secondary-side break, the MSIVs will close on low steam line pressure. This eliminates the use of steam dump valves as a means of removing decay heat. Therefore, heat removal needs to be accomplished using the ARV or 1 of 5 code safety valves for at least one SG. Although the ARV for SG4 is assumed to fail open to initiate the event, heat removal by this ARV may not be available. Due to the flood impacts, the ARV is susceptible to spurious operation and could re-close. The worst-case assumption is applied to this scenario, and therefore, heat removal by the ARV for SG2 is assumed unavailable. The operator action to open the SG2 ARV locally with a hydraulic pump will be directly impacted by a flooding event in this location and cannot be credited. Successful operation of secondary-side cooling (AFW) can place the reactor in a stable condition provided (1) successful isolation of the faulted SG, (2) no RCP seal LOCA occurs, and (3) a PORV did not open. Feed-and-bleed cooling with high-pressure recirculation is also a viable success path.

21 Main steam lines are located in this room, but they do not contribute to the spray event modeled in this scenario. The impact of main steam line failures were modeled as separate initiating events in the internal events model.

3.2.7. Internal Flood Scenario: 1-FLI-CB_A48 Flooding Initiating Event The train A 4.16 KV AC switchgear room does not contain flood sources. However, flood water may propagate to the train A 4.16 KV AC switchgear room by flowing through the gap under the normally closed double doors from an adjacent hallway. The likelihood of propagation to the switchgear room depends on break size, location, and effectiveness of the flood mitigation features (e.g., floor drains). For the purposes of the NRCs IFPRA model, an NRC staff walkdown of the reference plant in ths location supported the assumption that flood propagation to the 4.16 KV AC switchgear room was unlikely; therefore, a flood propagation factor of 0.1 was assumed.

Location:

Control building, room A48 - train A 4.16 KV AC swithgear room and room A58 - train A corridor Flood type:

Flood propagation Representative flow rate:

1000 gpm Corresponding internal event:

Loss of safety-related (Class 1E) 4160V bus train A (LO4160VA)

Flood Impact The switchgear cabinets located in the room were assumed to be impacted by flood water that propagates to the room. The failed switchgear results in a loss of power to Class 1E 4160 VAC bus train A. Power to the bus is assumed to be non-recoverable. The loss of Class 1E 4160 VAC bus A will cause loss of power to multiple 480 VAC switchgears and battery chargers for dc buses. After four hours, power to the affected Class 1E 125 vdc buses will be lost as the batteries deplete. This will cause a reactor trip and will affect the actuation and control of train A engineered safety features.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path. The redundancy of equipment available for the plant response is significantly impacted by the loss of power to the Class 1E 4160 VAC bus train A. The train A AFW motor-driven pump and centrifugal charging pump are unavailable, as well as many other train A engineered safety feature electrical loads.

22 3.2.8. Internal Flood Scenario: 1-FLI-CB_A60 Flooding Initiating Event The scenario considers impacts from flood sources located in adjacent rooms A60 and A59. The flood sources include fire protection and utility water pipes that can lead to local flooding and flood propagation.

Location:

Control building, room A60 - HVAC room and room A59 - corridor Flood type:

Local flooding in room A60 and propagation from A59 to A60 Representative flow rate:

1000 gpm Corresponding internal event:

Secondary-side break upstream of MSIVs /

downstream of MFIVs (SSBI)

Flood Impact The flood sources impact the ARV signal converter for either SG2 or SG3, both located in room A60. The flood sources located in room A60 contribute to local flooding and spray impacts on one of the ARV signal converters. No spray directional factor is applied. The flood scenario also includes a contribution from flood sources in room A59 that can propagate to room A60 by flowing through the gap under the normally closed double doors. Room A59 contains no accident initiation or mitigating equipment. The modeled scenario subsumes different flood types (e.g., spray, propagation) and simplified assumptions were made about the impacts on equipment. A detailed analysis including flood water height, spray directional effects, and flood water impact on signal converters was not performed. Rather, a pessimistic assumption was made that any flood impacting room A60 will result in a single stuck open ARV and an effective secondary-side line break (assumed to be associated with SG2). If operators cannot quickly close the SG2 ARV, this would lead to a plant trip.

23 Plant Response AFW is the primary means of heat removal for this scenario. After a secondary-side break, the MSIVs will close on low steam line pressure. This eliminates the use of steam dump valves as a means for removing decay heat. Therefore, heat removal needs to be accomplished using an ARV or 1 of 5 code safety valves for at least one SG. Although the ARV for SG2 is assumed to fail open to initiate the event, heat removal by this ARV may not be available. Due to the flood impacts, the ARV is susceptible to spurious operation and could re-close. The worst-case assumption is applied to this scenario, and therefore, heat removal by the ARV for SG2 is assumed unavailable. Successful operation of secondary-side cooling (AFW) can place the reactor in a stable condition provided (1) successful isolation of the faulted SG, (2) no RCP seal LOCA occurs, and (3) a PORV did not open. Feed-and-bleed cooling with high-pressure recirculation is also a viable success path.

3.2.9. Internal Flood Scenario: 1-FLI-TB_500_HI1 Flooding Initiating Event Human failures associated with the circulating water system and condenser water box manways can lead to human-induced local flooding. This scenario considers circulating water system maintenance work leading to a flooding event. Maintenance work requiring the opening of the condenser water box for tube cleaning/plugging was estimated to occur during plant operation at a frequency of 9.4x10-2 per reactor-critical-year. Human errors that result in failure to properly secure the manway cover(s) after completion of the work would lead to spilling of water out of the condenser water box and impacting equipment on level A of the turbine building. Screening values were assumed for human error probabilities. These were deemed to be conservative estimates of the likelihood of operator failure. The frequency of the flood scenario is expected to be lower than the estimate provided here if more realistic HEP values are used.7F8 A screening value of 0.01 was assigned for the probability of the crew failing to properly secure the manway cover(s). The flood scenario can be mitigated by the control room operators tripping the circulating water pumps, if they are notified before significant flooding occurs. A screening value of 0.1 was assigned for operator failure to mitigate the flooding event. The frequency of this human-induced flood scenario was estimated by assuming the occurrence of all three of the following events:

condenser water box maintenance during plant operation maintenance crew failure to properly secure the manway cover(s) operator failure to mitigate the flood scenario The frequency of this human-induced flooding scenario was estimated to be:

9.4x10-2 per reactor-critical-year x 0.01 x 0.1 = 9.4x10-5 per reactor-critical-year Location:

Turbine building, level A fire zone 500 Flood type:

Human-induced local flooding Representative flow rate:

100,000 gpm Corresponding internal event:

Loss of condenser heat sink (LOCHS) 8 A sensitivity analysis documented in Section 4.5.2 shows that the overall internal flooding CDF is relatively insensitive to the HEP values chosen.

24 Flood Impact The loss of circulating water through the condenser manway(s) would cause a plant trip due to loss of condenser vacuum. With the condenser unavailable, the steam dump system cannot dump steam to the condenser. The MFW pump will trip on low condenser vacuum, which causes a total loss of MFW flow. Although feedwater could be used after resetting feedwater isolation, the MFW and condensate systems were assumed to be unavailable. The large flow volume from the circulating water system through the condenser manway(s) would also cause significant flooding in the turbine building. All the equipment on level A of the turbine building would be impacted.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators. Secondary-side pressure control and heat removal are accomplished using the ARVs. The main condenser is unavailable due to the initiating event. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open. Feed-and-bleed cooling with high-pressure recirculation is also a viable success path.

3.2.10.

Internal Flood Scenario: 1-FLI-TB_500_LF Flooding Initiating Event The scenario considers flood sources that contribute to local flooding of level A of the turbine building. The largest contribution to local flooding in the turbine building is due to failure of circulating water piping or expansion joints. Other flood sources include fire protection, heater drain, demineralized water, and TPCCW system piping.

Location:

Turbine building, level A fire zone 500 Flood type:

Local flooding Representative flow rate:

100,000 gpm Corresponding internal event:

Loss of condenser heat sink (LOCHS)

Flood Impact The loss of circulating water would cause a plant trip due to loss of condenser vacuum. With the condenser unavailable, the steam dump system cannot dump steam to the condenser. The MFW pump will trip on low condenser vacuum, which causes a total loss of MFW flow.

Although feedwater could be used after resetting feedwater isolation, the MFW and condensate systems were assumed to be unavailable. The large flow volume from the circulating water system would impact all the equipment on level A of the turbine building.

Failures of other flood sources would be limited in their impacts. For example, failures of the TPCCW system would be expected to only impact the equipment of that system. However, this scenario conservatively assumes the bounding conditions of a circulating water piping failure for all modeled flood sources. The condensate system piping is another potential flood source located in the turbine building, but this source was not included in this scenario. The condensate system flooding impact was modeled separately in scenario 1-FLI-TB_500_LF-CDS.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators. Secondary-side pressure control and

25 heat removal are accomplished using the ARVs. The main condenser is unavailable due to the initiating event. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open. Feed-and-bleed cooling with high-pressure recirculation is also a viable success path.

3.2.11.

Internal Flood Scenario: 1-FLI-AB_B08_LF Flooding Initiating Event The scenario involves failure of the NSCW piping located in room B08. This scenario only considers NSCW pipe failure as a flood source. Other potential flood sources are located in the room. The other flooding sources were determined to not be significant contributors to overall internal flooding risk and were not modeled in the NRC IFPRA.

No propagation scenarios were identified for this flood area.

Location:

Auxiliary building, room B08 - pipe penetration room Flood type:

Local flooding Representative flow rate:

2000 gpm Corresponding internal event:

Reactor trip (RTRIP)

Flood Impact The failure of the flood source results in unavailability of NSCW train A. Local flooding impacts a safety-related containment pressure transmitter. Failure of the containment pressure transmitter is assumed to result in a reactor protection system (RPS) actuation and reactor trip. A basic event representing containment pressure transmitter failure was not modeled, but the impact of the pressure transmitter failure was modeled by assuming a reactor trip occurs.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path, but one centrifugal charging pump is unavailable due to the dependency on the failed NSCW train.

3.2.12.

Internal Flood Scenario: 1-FLI-AB_B24_LF2 Flooding Initiating Event The scenario involves failure of the NSCW piping located in room B24. The failure of the flood source results in unavailability of NSCW train A. This scenario only considers NSCW pipe failure as a flood source. Other potential flood sources are located in the room. The other flooding sources were determined to not be significant contributors to overall internal flooding risk and were not modeled in the NRC IFPRA. No propagation scenarios were identified for this flood area.

Location:

Auxiliary building, room B24 - ACCW pump room Flood type:

Local flooding

26 Representative flow rate:

1000 gpm Corresponding internal event:

Other transient resulting in reactor trip (TRANS)

Flood Impact Local flooding impacts ACCW pump 1 and fails the pumps discharge pressure interlock. The NSCW failure would not result in an immediate plant trip. The NSCW failure could lead to a subsequent plant shutdown if required action and associated completion time are not met under LCO conditions. For the purposes of modeling the scenario, a plant trip with loss of NSCW train A was assumed.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path, but one centrifugal charging pump is unavailable due to the dependency on the failed NSCW train.

3.2.13.

Internal Flood Scenario: 1-FLI-AB_B50_JI Flooding Initiating Event Chemical and volume control system (CVCS) pipe failure results in spray and jet impingement on a nearby cable tray in pipe chase room B50. No propagation scenarios were identified for this flood area.

Location:

Auxiliary building, room B50 - pipe chase train B Flood type:

Jet impingement Representative flow rate:

100 gpm Corresponding internal event:

Other transient resulting in reactor trip (TRANS)

Flood Impact The failure of the cable tray results in loss of instrumentation and control for several pieces of equipment, including ACCW pump 1, all three CCW train B pumps, and all three NSCW train B pumps. The equipment controlled via the cable tray were assumed failed for this scenario. The failed equipment would ultimately result in a reactor trip or a plant shutdown under LCO conditions.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

27 Feed-and-bleed cooling with high-pressure recirculation is also a viable success path, but one centrifugal charging pump is unavailable due to the dependency on the failed NSCW train.

3.2.14.

Internal Flood Scenario: 1-FLI-AB_C115_LF Flooding Initiating Event The scenario involves failure of the NSCW piping located in the train A centrifugal charging pump room. This scenario only considers NSCW pipe failure as a flood source. Other potential flood sources are located in the room. The other flooding sources were determined to not be significant contributors to overall internal flooding risk and were not modeled in the NRC IFPRA. No propagation scenarios were identified for this flood area.

Location:

Auxiliary building - CVCS centrifugal charging pump room train A Flood type:

Local flooding Representative flow rate:

2000 gpm Corresponding internal event:

Other transient resulting in reactor trip (TRANS)

Flood Impact The failure of the flood source results in the unavailability of NSCW train A. Local flooding impacts the train A centrifugal charging pump. The NSCW failure would not result in an immediate plant trip. The NSCW failure could lead to a subsequent plant shutdown if required action and associated completion time were not met under LCO conditions. For the purposes of modeling the scenario, a plant trip with loss of NSCW train A was assumed.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path, but one centrifugal charging pump is unavailable due to the dependency on the failed NSCW train.

3.2.15.

Internal Flood Scenario: 1-FLI-AB_C118_LF Flooding Initiating Event The scenario involves failure of the NSCW piping located in the train B centrifugal charging pump room. This scenario only considers NSCW pipe failure as a flood source. Other potential flood sources are located in the room. The other flooding sources were determined to not be significant contributors to overall internal flooding risk and were not modeled in the NRC IFPRA. No propagation scenarios were identified for this flood area.

28 Location:

Auxiliary building - CVCS centrifugal charging pump room train B Flood type:

Local flooding Representative flow rate:

1000 gpm Corresponding internal event:

Other transient resulting in reactor trip (TRANS)

Flood Impact The failure of the NSCW piping results in the unavailability of NSCW train B. The local flooding impacts the train B centrifugal charging pump. The NSCW failure would not result in an immediate plant trip. The NSCW failure could lead to a subsequent plant shutdown if required action and associated completion time were not met under LCO conditions. For the purposes of modeling the scenario, a plant trip with loss of NSCW train B was assumed.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path, but one centrifugal charging pump is unavailable due to the dependency on the failed NSCW train.

3.2.16.

Internal Flood Scenario: 1-FLI-AB_C120_LF Flooding Initiating Event The scenario involves failure of the NSCW piping located in the vestibule area outside of the charging pump rooms. This scenario only considers NSCW pipe failure as a flood source. Other potential flood sources are located in the room. The other flooding sources were determined to not be significant contributors to overall internal flooding risk and were not modeled in the NRC IFPRA. No propagation scenarios were identified for this flood area.

Location:

Auxiliary building - vestibule area charging pump rooms Flood type:

Local flooding Representative flow rate:

1000 gpm Corresponding internal event:

Other transient resulting in reactor trip (TRANS)

Flood Impact The failure of the NSCW piping results in the unavailability of NSCW train A. The local flooding would impact the RWST to charging pump suction isolation valve, which is assumed to fail to open if demanded. The NSCW failure would not result in an immediate plant trip. The NSCW

29 failure could lead to a subsequent plant shutdown if required action and associated completion time were not met under LCO conditions. For the purposes of modeling the scenario, a plant trip with loss of NSCW train A was assumed.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path, but one centrifugal charging pump is unavailable due to the dependency on the failed NSCW train.

3.2.17.

Internal Flood Scenario: 1-FLI-AB_D74_FP Flooding Initiating Event Fire protection pipe failure in room D74 results in flooding that propagates to safety-related 480 VAC switchgear room D105. There is no significant equipment located in room D74; however, the propagation of flood waters to room D105 results in failure of a class 1E 480 VAC switchgear and a 4160/480 VAC transformer.

Location:

Auxiliary building - spray additive tank room Flood type:

Flood propagation Representative flow rate:

1000 gpm Corresponding internal event:

Other transient resulting in reactor trip (TRANS)

Flood Impact Flood propagation results in failure of a class 1E 480 VAC switchgear and a 4160/480 VAC transformer. Failure of the switchgear is assumed to cause a plant trip. The loss of power to the 480 VAC bus results in unavailability of NSCW train A.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path, but one centrifugal charging pump is unavailable due to the dependency on the failed NSCW train.

3.2.18.

Internal Flood Scenario: 1-FLI-DGB_101_LF Flooding Initiating Event The scenario involves failure of the NSCW piping located in the emergency diesel generator (EDG) train B room. This scenario only considers NSCW pipe failure as a flood source. Other potential flood sources are located in the room. The other flooding sources were determined to not be significant contributors to overall internal flooding risk and were not modeled in the NRC IFPRA. No propagation scenarios were identified for this flood area.

30 Location:

Diesel generator building - diesel generator train B room Flood type:

Local flooding Representative flow rate:

2000 gpm Corresponding internal event:

Other transient resulting in reactor trip (TRANS)

Flood Impact The failure of the NSCW piping results in the unavailability of NSCW train B. The local flooding impacts the train B EDG and a safety-related 480 VAC motor control center. The NSCW failure would not result in an immediate plant trip. The NSCW failure could lead to a subsequent plant shutdown if required action and associated completion time are not met under LCO conditions.

For the purposes of modeling the scenario, a plant trip with loss of NSCW train B was assumed.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path, but one centrifugal charging pump is unavailable due to the dependency on the failed NSCW train.

3.2.19.

Internal Flood Scenario: 1-FLI-DGB_103_LF Flooding Initiating Event The scenario involves failure of the NSCW piping located in the EDG train A room. This scenario only considers NSCW pipe failure as a flood source. Other potential flood sources are located in the room. The other flooding sources were determined to not be significant contributors to overall internal flooding risk and were not modeled in the NRC IFPRA.

No propagation scenarios were identified for this flood area.

Location:

Diesel generator building - diesel generator train A room Flood type:

Local flooding Representative flow rate:

2000 gpm Corresponding internal event:

Other transient resulting in reactor trip (TRANS)

Flood Impact The failure of the NSCW piping results in the unavailability of NSCW train A. The local flooding impacts the train A EDG and a safety-related 480 VAC motor control center. The NSCW failure would not result in an immediate plant trip. The NSCW failure could lead to a subsequent plant

31 shutdown if required action and associated completion time are not met under LCO conditions.

For the purposes of modeling the scenario, a plant trip with loss of NSCW train A is assumed.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path, but one centrifugal charging pump is unavailable due to the dependency on the failed NSCW train.

3.2.20.

Internal Flood Scenario: 1-FLI-AB_A20_FP Flooding Initiating Event Feedwater pipe failure results in local flooding in room A20 and flood propagation to rooms A11 and A12. Pipe failure frequencies for flooding sources in room A20 are included in this scenario. No flood sources are identified in rooms A11 and A12. The impacts on rooms A11 and A12 are only due to the propagation of flood water from room A20.

The propagation is assumed to be unmitigated.

Location:

Auxiliary building, rooms A11 and A12 with propagation from A20 Flood type:

Local flooding in room A20 and propagation to rooms A11 and A12.

Representative flow rate:

2000 gpm Corresponding internal event:

Loss of MFW (LOMFW)

Flood Impact The impacted components in room A20 include the FW control/regulator valves and the FW control/regulator bypass valves for feed lines to SG1 and SG4. The valves are assumed to fail to open resulting in a loss of MFW transient. The impacted components in room A11 include the SG1 FW isolation valve and turbine-driven AFW pump (TDAFWP) discharge valves. The impacted components in room A12 include the SG4 FW isolation valve, ACCW supply/return isolation valves, and AFW motor-driven pump (MDP) train A discharge valves to SG1 and SG4.

The AFW pump discharge valves were assumed to fail in their normally open state. The ACCW valves were assumed to fail closed.

Plant Response In response to the loss of MFW transient, successful operation of secondary-side cooling (AFW) can place the reactor in a stable condition provided there is no RCP seal LOCA and a PORV did not open. Feed-and-bleed cooling with high-pressure recirculation can also provide successful decay heat removal, if secondary-side cooling is unavailable.

3.2.21.

Internal Flood Scenario: 1-FLI-AB_D78_FP Flooding Initiating Event The scenario involves failure of the residual heat removal (RHR) system piping and piping from the RWST located in rooms D78 and D79. The flooding

32 propagates to Class 1E 480 VAC switchgear room D105 via a non-water-tight door and piping penetrations.

Location:

Auxiliary building, train A piping rooms D78 and D79 with propagation to 480 VAC switchgear room D105 Flood type:

Flood propagation Representative flow rate:

2000 gpm Corresponding internal event:

Other transient resulting in reactor trip (TRANS)

Flood Impact The flood results in the failure of the 480 VAC switchgear and 4.16 KV AC / 480 VAC transformer located in room D105. The loss of power to the 480 VAC bus results in unavailability of NSCW train A. The RWST is also assumed to be unavailable due to the pipe failure. The switchgear failure and RWST unavailability would not result in an immediate plant trip. The failures could lead to a subsequent plant shutdown if required action and associated completion time are not met under LCO conditions. For the purposes of modeling the scenario, a plant trip with loss of the impacted equipment was assumed.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling is not available due to the flood impacting the ability to align suction to the RWST.

3.2.22.

Internal Flood Scenario: 1-FLI-TB_500_LF-CDS Flooding Initiating Event The scenario considers only the condensate system flood sources that contribute to local flooding of level A of the turbine building. Other flood sources in the area are modeled in scenario 1-FLI-TB_500_LF.

Location:

Turbine building, level A fire zone 500 Flood type:

Local flooding Representative flow rate:

2000 gpm Corresponding internal event:

Loss of MFW (LOMFW)

Flood Impact The failure of condensate system piping results in a loss of MFW and a plant trip. The flood fails the condensate pumps. The MFW system is assumed unavailable through the duration of the event due to the failed condensate pumps. The condensate system flood sources are expected to have less severe impacts compared to other large capacity, high flow rate sources in the area

33 (e.g., circulating water). Therefore the condensate system flood sources are modeled separately in this scenario.

Plant Response In response to the loss of MFW transient, successful operation of secondary-side cooling (AFW) can place the reactor in a stable condition provided there is no RCP seal LOCA and a PORV did not open. Feed-and-bleed cooling with high-pressure recirculation can also provide successful decay heat removal, if secondary-side cooling is unavailable.

3.2.23.

Internal Flood Scenario: 1-FLI-TB_500_HI2 Flooding Initiating Event Human failures in restoring the turbine plant closed cooling water (TPCCW) heat exchangers after maintenance can lead to human-induced local flooding. This scenario considers failure of the maintenance crew to properly close up the heat exchanger (on the turbine plant cooling water [TPCW] system side) after maintenance work.

Maintenance work requiring the opening of a TPCCW heat exchanger was estimated to occur during plant operation at a frequency of 9.4x10-2 per reactor-critical-year. Human errors that result in failure to properly close the heat exchanger would lead to TPCW water spilling out of the heat exchanger and impacting TPCCW equipment on level A of the turbine building. The types of human errors that can lead to flooding include:

failure to isolate the tube-side (TPCW) drain valve after maintenance failure to install the gasket for the end bell of the heat exchanger failure to properly bolt or torque the end bell of the heat exchanger Screening values were assumed for human error probabilities. These were deemed to be conservative estimates of the likelihood of operator failure. The frequency of the flood scenario is expected to be lower than the estimate provided here if more realistic HEP values are used.8F9 The screening value for the probability of the crew failing to properly close the drain valve or install the heat exchanger end bell was 0.01. The flood scenario can be mitigated if the crew re-closes the TPCW inlet isolation valve near the heat exchanger when they detect water flowing out of the system. The screening value for operator failure to mitigate the flooding event was 0.1. The frequency of the human induced flood scenario is estimated by assuming the occurrence of all three of the following events:

TPCCW heat exchanger maintenance during plant operation maintenance crew failure to properly secure the heat exchanger maintenance crew failure to mitigate the flood scenario The frequency of the human-induced flooding scenario was estimated as:

9.4x10-2 per reactor-critical-year x 0.01 x 0.1 = 9.4x10-5 per reactor-critical-year Location:

Turbine building, level A fire zone 500 Flood type:

Human-induced local flooding Representative flow rate:

2000 gpm 9 A sensitivity analysis documented in Section 4.5.2 shows that the overall internal flooding CDF is relatively insensitive to the HEP values chosen.

34 Corresponding internal event:

Turbine trip (TTRIP)

Flood Impact The impact of the flooding scenario associated with the TPCCW heat exchanger was conservatively assumed to be the loss of the TPCW leading to a turbine trip.

Plant Response After the plant trip, the primary means of heat removal is secondary-side cooling with steam generators. AFW is used for feeding steam generators and MFW is available, if needed.

Secondary-side pressure control and heat removal are accomplished using the ARVs or steam dumps to the main condenser. Successful operation of secondary-side cooling can place the reactor in a stable condition provided no RCP seal LOCA occurs and a PORV did not open.

Feed-and-bleed cooling with high-pressure recirculation is also a viable success path.

35

4. INTERNAL FLOOD MODEL RESULTS The objective of this section is to describe the results of NRCs Level 1, at-power, internal flooding PRA (IFPRA) model for a single unit. The NRCs IFPRA consists of 23 internal flooding scenarios that were integrated into the NRCs Level 1 PRA for at-power internal events. The combined model was developed and is maintained using the NRCs SAPHIRE software (IF-5).

The results of the internal flooding scenarios are presented here for the Unit 1 model. The Unit 1 internal flooding results were deemed applicable to corresponding flooding areas located in Unit 2, based on the symmetry between the two units. No major differences between the two reactor units were identified that would impact the internal flooding analysis.

The internal flooding scenarios include the flooding initiating event (i.e., the pipe break or component failure that initiates the flooding), the impacts on the plant due to flooding, and the plant response to the event. Each internal flooding scenario was represented by a unique event tree in the NRC IFPRA model. Each scenario can comprise several flooding accident sequences, which involve different combinations of operator errors and/or mitigating system failures resulting in core damage. Each accident sequence represents a unique event tree branch in the NRC IFPRA model. The following sections provide the NRC IFPRA results. 4.1 presents the CDF results obtained for each of the modeled internal flooding scenarios. 4.2 provides results for the significant internal flooding accident sequences. 4.3 presents the significant internal flooding cut set results. 4.4 shows the results of parameter uncertainty analysis for the IFPRA CDF results. Section 4.5 discusses sources of model uncertainty and sensitivity cases to demonstrate the potential effects of uncertainties on the model results.

Section 4.6 compares the results to the results from a similar plant. Section 4.7 presents a summary of key insights.

4.1.

Internal Flooding Scenario and Overall CDF Results The internal flooding scenarios were quantified to estimate CDF. The truncation level for quantification was set to 10-12. The internal flooding scenarios were also quantified at truncations of 10-11 and 10-13 to check for convergence of the CDF results. The change in CDF was less than 5 percent for each decade of truncation value. The minimal cut set upper bound method was used for quantifying the cut set results. The total estimated CDF result for internal flooding scenarios was calculated to be 7.9x10-7 per reactor-critical-year, which is less than 1 percent of the total single unit CDF for all hazards. The model was developed and quantified using the NRCs SAPHIRE software (IF-5). The SAPHIRE version number used for the quantification is 8.1.5. The model revision number used for the quantification is SVN285. The results by internal flooding initiating event scenario are shown in Table 4.1.

36 Table 4.1 Internal Flooding Results by Scenario Scenario Name IE frequency per reactor-critical-year CCDP*

CDF per reactor-critical-year

% of CDF Cut Set Count 1 1-FLI-AB_C113_LF1 2.2E-04 6.9E-04 1.6E-07 19.6 348 2 1-FLI-AB_C120_LF 1.8E-04 7.2E-04 1.3E-07 16.5 347 3 1-FLI-CB_123_SP 2.8E-04 3.7E-04 1.0E-07 12.9 1393 4 1-FLI-CB_122_SP 2.8E-04 3.7E-04 1.0E-07 12.9 1389 5 1-FLI-AB_C115_LF 1.3E-04 6.9E-04 9.2E-08 11.7 300 6 1-FLI-AB_108_SP1 2.8E-04 2.1E-04 5.9E-08 7.5 1135 7 1-FLI-AB_108_SP2 2.8E-04 2.1E-04 5.9E-08 7.5 1127 8 1-FLI-CB_A60 5.2E-05 3.6E-04 1.9E-08 2.4 493 9 1-FLI-TB_500_LF 2.2E-03 7.6E-06 1.6E-08 2.1 701 10 1-FLI-CB_A48 9.2E-05 1.5E-04 1.4E-08 1.8 332 11 1-FLI-DGB_101_LF 7.3E-06 8.5E-04 6.2E-09 0.8 70 12 1-FLI-AB_D74_FP 8.6E-06 6.9E-04 5.9E-09 0.8 89 13 1-FLI-AB_C118_LF 7.5E-06 7.3E-04 5.5E-09 0.7 75 14 1-FLI-AB_B08_LF 7.7E-06 6.9E-04 5.3E-09 0.7 72 15 1-FLI-DGB_103_LF 7.3E-06 7.0E-04 5.1E-09 0.7 79 16 1-FLI-TB_500_LF-CDS 6.3E-04 7.2E-06 4.5E-09 0.6 303 17 1-FLI-AB_B24_LF2 3.5E-06 7.1E-04 2.5E-09 0.3 74 18 1-FLI-AB_B50_JI 3.4E-06 7.3E-04 2.4E-09 0.3 56 19 1-FLI-AB_A20 2.7E-04 6.8E-06 1.8E-09 0.2 153 20 1-FLI-TB_500_HI2 9.4E-05 7.2E-06 6.7E-10 0.1 59 21 1-FLI-TB_500_HI1 9.4E-05 6.1E-06 5.7E-10 0.1 58 22 1-FLI-AB_D78_FP 3.6E-07 6.7E-04 2.4E-10 0.0 24 23 1-FLI-AB_A20_FP 2.3E-05 8.5E-06 1.9E-10 0.0 51 Total:

5.1E-03 7.9E-07 8728

• CCDP - conditional core damage probability 4.2.

Internal Flooding Accident Sequences The significant internal flooding accident sequences are shown in Table 4.2. The significant accident sequences are those sequences whose summed CDF contributes more than 95 percent of the total internal flooding CDF and all sequences that individually contribute more than 1 percent to total internal flooding CDF. The top 10 sequences, each contributing more than 5 percent of the total internal flooding CDF, are described below.

1. 1-FLI-AB_C113_LF1: 1-10-1 Flood occurs in auxiliary building resulting in unavailability of train A NSCW, as described in 3.2.4 of this report. The reactor is tripped. Offsite power is lost due to consequential failures related to the plant transient. Subsequent failures or maintenance unavailabilities result in loss of emergency power train B (train A is lost due to

37 unavailability of NSCW). The loss of all AC power sources renders the AFW system and feed and bleed unavailable for providing core cooling (the TDAFWP is assumed to fail after battery depletion). The sequence frequency is 7.8x10-8 per reactor-critical-year, contributing approximately 9.9 percent to the internal flooding CDF.

2. 1-FLI-AB_C113_LF1: 1-11-08-1 Flood occurs in auxiliary building resulting in unavailability of train A NSCW, as described in 3.2.4 of this report. The reactor is tripped. Equipment and human failures contribute to the failure of all RCP seal injection and cooling. The RCP seals fail resulting in a small LOCA. High-pressure and low-pressure injection with train A emergency core cooling system (ECCS) pumps are unavailable due to the dependency on train A NSCW. Subsequent failures of train B electrical distribution equipment or train B NSCW result in unavailability of high-pressure and low-pressure injection with train B ECCS pumps. The sequence frequency is 7.7x10-8 per reactor-critical-year, contributing approximately 9.8 percent to the internal flooding CDF.

3. 1-FLI-AB_C120_LF1: 1-10-1 Flood occurs in auxiliary building resulting in unavailability of train A NSCW, as described in 3.2.16 of this report. The reactor is tripped. Offsite power is lost due to consequential failures related to the plant transient. Subsequent failures or maintenance unavailabilities result in loss of emergency power train B (train A is lost due to unavailability of NSCW). The loss of all AC power sources renders the AFW system and feed and bleed unavailable for providing core cooling (the TDAFWP is assumed to fail after battery depletion). The sequence frequency is 6.8x10-8 per reactor-critical-year, contributing approximately 8.6 percent to the internal flooding CDF.

4. 1-FLI-AB_C120_LF1: 1-11-08-1 Flood occurs in auxiliary building resulting in unavailability of train A NSCW, as described in 3.2.16 of this report. The reactor is tripped. Equipment and human failures contribute to the failure of all RCP seal injection and cooling. The RCP seals fail resulting in a small LOCA. High-pressure and low-pressure injection with train A ECCS pumps are unavailable due to the dependency on train A NSCW. Subsequent failures of train B electrical distribution equipment or train B NSCW result in unavailability of high-pressure and low-pressure injection with train B ECCS pumps. The sequence frequency is 6.2x10-8 per reactor-critical-year, contributing approximately 7.9 percent to the internal flooding CDF.

5. 1-FLI-AB_C115_LF1: 1-10-1 Flood occurs in auxiliary building resulting in unavailability of train A NSCW, as described in Section 3.2.14 of this report. The reactor is tripped. Offsite power is lost due to consequential failures related to the plant transient. Subsequent failures or maintenance unavailabilities result in loss of emergency power train B (train A is lost due to unavailability of NSCW). The loss of all AC power sources renders the AFW system and feed and bleed unavailable for providing core cooling (the TDAFWP is assumed to fail after battery depletion). The sequence frequency is 4.6x10-8 per reactor-critical-year, contributing approximately 5.9 percent to the internal flooding CDF.

6. 1-FLI-AB_C115_LF1: 1-11-08-1 Flood occurs in auxiliary building resulting in unavailability of train A NSCW, as described in Section 3.2.14 of this report. The reactor is tripped.

Equipment and human failures contribute to the failure of all RCP seal injection and cooling.

The RCP seals fail resulting in a small LOCA. High-pressure and low-pressure injection with train A ECCS pumps are unavailable due to the dependency on train A NSCW. Subsequent failures of train B electrical distribution equipment or train B NSCW result in unavailability of high-pressure and low-pressure injection with train B ECCS pumps. The sequence frequency is 4.6x10-8 per reactor-critical-year, contributing approximately 5.8 percent to the internal flooding CDF.

38

7. 1-FLI-AB_108_SP1: 1-11-08-1 Flood occurs in the south main steam valve room resulting in a failed open ARV on SG1, as described in Section 3.2.1 of this report. The impact of the failed ARV results in a secondary-side break upstream of the MSIV. Equipment and human failures contribute to the failure of all RCP seal injection and cooling. The RCP seals fail resulting in a small LOCA. Combinations of failures result in unavailability of high-pressure and low-pressure injection. The predominant equipment failures are related to the safety injection sequencer, NSCW, and electrical distribution equipment. The sequence frequency is 4.2x10-8 per reactor-critical-year, contributing approximately 5.3 percent to the internal flooding CDF.

8. 1-FLI-AB_108_SP2: 1-11-08-1 Flood occurs in the south main steam valve room resulting in a failed open ARV on SG4, as described in Section 3.2.2 of this report. The impact of the failed ARV results in a secondary-side break upstream of the MSIV. Equipment and human failures contribute to the failure of all RCP seal injection and cooling. The RCP seals fail resulting in a small LOCA. Combinations of failures result in unavailability of high-pressure and low-pressure injection. The predominant equipment failures are related to the safety injection sequencer, NSCW, and electrical distribution equipment. The sequence frequency is 4.2x10-8 per reactor-critical-year, contributing approximately 5.3 percent to the internal flooding CDF.

9. 1-FLI-CB_123_SP: 1-11-08-1 Flood occurs in the north main steam valve room resulting in a failed open ARV on SG2, as described in Section 3.2.6 of this report. The impact of the failed ARV results in a secondary-side break upstream of the MSIV. Equipment and human failures contribute to the failure of all RCP seal injection and cooling. The RCP seals fail resulting in a small LOCA. Combinations of failures result in unavailability of high-pressure and low-pressure injection. The predominant equipment failures are related to the safety injection sequencer, NSCW, and electrical distribution equipment. The sequence frequency is 4.1x10-8 per reactor-critical-year, contributing approximately 5.2 percent to the internal flooding CDF.

10. 1-FLI-CB_122_SP: 1-11-08-1 Flood occurs in the north main steam valve room resulting in a failed open ARV on SG3, as described in Section 3.2.5 of this report. The impact of the failed ARV results in a secondary-side break upstream of the MSIV. Equipment and human failures contribute to the failure of all RCP seal injection and cooling. The RCP seals fail resulting in a small LOCA. Combinations of failures result in unavailability of high-pressure and low-pressure injection. The predominant equipment failures are related to the safety injection sequencer, NSCW, and electrical distribution equipment. The sequence frequency is 4.1x10-8 per reactor-critical-year, contributing approximately 5.2 percent to the internal flooding CDF.

Table 4.2 Significant Internal Flooding Accident Sequences Scenario Name Sequence Number CDF/ry

% of CDF Cumulative

% of CDF Cut Set Count 1

1-FLI-AB_C113_LF1 1-10-1 7.8E-08 9.9 9.9 177 2

1-FLI-AB_C113_LF1 1-11-08-1 7.7E-08 9.8 19.6 150 3

1-FLI-AB_C120_LF 1-10-1 6.8E-08 8.6 28.2 181

39 Table 4.2 Significant Internal Flooding Accident Sequences Scenario Name Sequence Number CDF/ry

% of CDF Cumulative

% of CDF Cut Set Count 4

1-FLI-AB_C120_LF 1-11-08-1 6.2E-08 7.9 36.1 146 5

1-FLI-AB_C115_LF 1-10-1 4.6E-08 5.9 41.9 153 6

1-FLI-AB_C115_LF 1-11-08-1 4.6E-08 5.8 47.7 136 7

1-FLI-AB_108_SP1 1-11-08-1 4.2E-08 5.3 53.0 303 8

1-FLI-AB_108_SP2 1-11-08-1 4.2E-08 5.3 58.3 303 9

1-FLI-CB_123_SP 1-11-08-1 4.1E-08 5.2 63.5 292 10 1-FLI-CB_122_SP 1-11-08-1 4.1E-08 5.2 68.8 292 11 1-FLI-CB_123_SP 1-15-1 3.6E-08 4.5 73.3 105 12 1-FLI-CB_122_SP 1-15-1 3.6E-08 4.5 77.8 105 13 1-FLI-CB_122_SP 1-21-1 1.3E-08 1.7 79.5 525 14 1-FLI-CB_123_SP 1-21-1 1.3E-08 1.7 81.1 525 15 1-FLI-TB_500_LF 1-10-1 1.0E-08 1.3 82.4 401 16 1-FLI-CB_A60 1-11-08-1 7.6E-09 1.0 83.4 104 17 1-FLI-AB_108_SP2 1-21-1 7.2E-09 0.9 84.3 309 18 1-FLI-AB_108_SP1 1-21-1 7.2E-09 0.9 85.2 309 19 1-FLI-CB_A60 1-15-1 6.6E-09 0.8 86.1 51 20 1-FLI-AB_108_SP1 1-04-1 6.6E-09 0.8 86.9 111 21 1-FLI-AB_108_SP2 1-04-1 6.6E-09 0.8 87.7 105 22 1-FLI-CB_A48 2-10-1 5.7E-09 0.7 88.4 43 23 1-FLI-CB_123_SP 1-04-1 4.9E-09 0.6 89.1 69 24 1-FLI-CB_122_SP 1-04-1 4.9E-09 0.6 89.7 66 25 1-FLI-CB_A48 2-04-1 4.6E-09 0.6 90.3 142 26 1-FLI-DGB_101_LF 1-10-1 4.5E-09 0.6 90.8 41 27 1-FLI-CB_122_SP 1-14-1 4.0E-09 0.5 91.3 175 28 1-FLI-CB_123_SP 1-14-1 4.0E-09 0.5 91.8 175 29 1-FLI-AB_D74_FP 1-10-1 3.0E-09 0.4 92.2 41 30 1-FLI-TB_500_LF-CDS 1-10-1 2.9E-09 0.4 92.6 157

40 Table 4.2 Significant Internal Flooding Accident Sequences Scenario Name Sequence Number CDF/ry

% of CDF Cumulative

% of CDF Cut Set Count 31 1-FLI-AB_C118_LF 1-11-08-1 2.9E-09 0.4 92.9 34 32 1-FLI-TB_500_LF 1-04-1 2.8E-09 0.4 93.3 86 33 1-FLI-CB_A48 2-07-1 2.7E-09 0.3 93.6 16 34 1-FLI-AB_B08_LF 1-10-1 2.6E-09 0.3 94.0 39 35 1-FLI-AB_B08_LF 1-11-08-1 2.6E-09 0.3 94.3 33 36 1-FLI-AB_C118_LF 1-10-1 2.6E-09 0.3 94.6 41 37 1-FLI-DGB_103_LF 1-10-1 2.6E-09 0.3 95.0 44 38 1-FLI-AB_D74_FP 1-11-10-1 2.6E-09 0.3 95.3 22 The significant sequence results identify the types of failures that are significant to the overall plant risk from internal flooding. The consequential loss of offsite power contributes to several significant sequences, including the top contributing sequence. Failures related to emergency power systems are significant contributors to these sequences. It should be noted that the modeling assumptions for these sequences may be over-estimating the actual risk. Many of these sequences involved a break in the NSCW system, and the model assumed a reactor trip occurs. An automatic reactor trip is not likely to occur, but the plant would be required to shutdown if the technical specification requirements are not met. The likelihood of a consequential loss of offsite power may be lower for this case compared to an unanticipated plant trip.

Seven of the top ten flooding sequences involve failures subsequent to the plant transient that result in loss of RCP seal cooling, leading to a small LOCA. Additional failures leading to unavailability of high-pressure and low-pressure injection result in core damage. Not reflected in this model are the improved passive shutdown RCP seals. The new seals are expected to reduce the likelihood of an RCP seal LOCA, which, in turn, would reduce the core damage frequency for these sequences.

Failures of the safety injection sequencer, NSCW, and electrical distribution equipment dominate the results due to common functional dependencies on these systems. For all significant sequences the flood-related impacts contribute directly to the failure or loss of redundancy for the functions required to prevent core damage. Some of the significant flood-related impacts include failures that result in unavailability of an NSCW train, unavailability of secondary-side cooling using the steam generators, and loss of an AC power support system.

The internal flooding event trees are structured to directly transfer to the relevant accident sequences of the internal events model. All credible equipment failures that were considered in the internal events model were also considered possible to occur coincident with the flooding events. Accordingly, the internal flooding cut set results include many of the same failures that were important to the internal events risk. The basic events important to the plant core damage risk from internal flooding and their importance measures are presented in Appendix B, Table B-2.

41 4.3.

Internal Flooding Cut Set Results The top 100 highest contributing cut sets are displayed in Table 4.3. The top 100 cut sets account for 75 percent of the total internal flooding CDF. The significant internal flooding cut sets include all those whose summed CDF contributes more than 95 percent of the total internal flooding CDF and all cut sets that individually contribute more than one percent to total internal flooding CDF. Per this definition, there are 996 significant internal flooding cut sets. All of these cut sets are included in Appendix B: Internal Flooding PRA Significant Cut Sets and Basic Event Importance of this report.

In accordance with ASME/ANS PRA Standard (IF-7) requirement QU-D1, a sampling of the significant cut sets were reviewed to ensure they were reasonable and represented realistic accident sequences. In accordance with ASME/ANS PRA Standard (IF-7) requirement QU-D5, a sampling of non-significant cut sets were also reviewed to ensure that they also represented reasonable and realistic accident sequences.

Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 1

3.914E-8 6.65 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 3.297E-2 1-EPS-DGN-FR-G4002___ DG1B fails to run by random cause (24 hr mission) 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 2

3.145E-8 5.34 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 3.297E-2 1-EPS-DGN-FR-G4002___ DG1B fails to run by random cause (24 hr mission) 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3

2.324E-8 3.95 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 3.297E-2 1-EPS-DGN-FR-G4002___ DG1B fails to run by random cause (24 hr mission) 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 4

1.974E-8 3.35 2.800E-4 1-IE-FLI-AB_108_SP2 Internal flooding in AB 108 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 1.000E+0 1-OA-NSCWFAN---H Operator fails to start NSCW fan manually (place holder )

42 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 5

1.974E-8 3.35 2.800E-4 1-IE-FLI-AB_108_SP1 Internal flooding in AB 108 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 1.000E+0 1-OA-NSCWFAN---H Operator fails to start NSCW fan manually (place holder )

9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 6

1.960E-8 3.33 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 1.000E+0 1-OA-NSCWFAN---H Operator fails to start NSCW fan manually (place holder )

9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 7

1.960E-8 3.33 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 1.000E+0 1-OA-NSCWFAN---H Operator fails to start NSCW fan manually (place holder )

9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 8

1.595E-8 2.71 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 3.297E-2 1-EPS-DGN-FR-G4001___ DG1A fails to run by random cause (24 hr mission) 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 9

1.595E-8 2.71 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122

43 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 3.297E-2 1-EPS-DGN-FR-G4001___ DG1A fails to run by random cause (24 hr mission) 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 10 1.581E-8 2.68 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 2.150E-4 1-ACP-BAC-MA-BA03____ 4.16KV bus 1BA03 in maintenance 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 11 1.581E-8 2.68 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 2.150E-4 1-ACP-BAC-MA-BB16____ 480V switchgear 1BB16 in maintenance 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 12 1.496E-8 2.54 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 1.260E-2 1-EPS-DGN-MA-G4002___ DG1B in maintenance 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 13 1.270E-8 2.16 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 2.150E-4 1-ACP-BAC-MA-BA03____ 4.16KV bus 1BA03 in maintenance 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 14 1.270E-8 2.16 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 2.150E-4 1-ACP-BAC-MA-BB16____ 480V switchgear 1BB16 in maintenance 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 15 1.203E-8 2.04 2.800E-4 1-IE-FLI-AB_108_SP1 Internal flooding in AB 108 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate

44 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 1.000E+0 1-OA-NSCWFAN---H Operator fails to start NSCW fan manually (place holder) 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 16 1.203E-8 2.04 2.800E-4 1-IE-FLI-AB_108_SP2 Internal flooding in AB 108 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 1.000E+0 1-OA-NSCWFAN---H Operator fails to start NSCW fan manually (place holder) 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 17 1.202E-8 2.04 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 1.260E-2 1-EPS-DGN-MA-G4002___ DG1B in maintenance 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 18 1.194E-8 2.03 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 1.000E+0 1-OA-NSCWFAN---H Operator fails to start NSCW fan manually (place holder) 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 19 1.194E-8 2.03 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 1.000E+0 1-OA-NSCWFAN---H Operator fails to start NSCW fan manually (place holder) 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 20 9.632E-9 1.64 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 2.150E-4 1-ACP-BAC-MA-BA03____ 4.16KV bus 1BA03 in maintenance 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 21 9.632E-9 1.64 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113

45 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 2.150E-4 1-ACP-BAC-MA-BB16____ 480V switchgear 1BB16 in maintenance 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 22 9.386E-9 1.59 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 2.150E-4 1-ACP-BAC-MA-BA03____ 4.16KV bus 1BA03 in maintenance 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 23 9.386E-9 1.59 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 2.150E-4 1-ACP-BAC-MA-BB16____ 480V switchgear 1BB16 in maintenance 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 24 8.882E-9 1.51 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 1.260E-2 1-EPS-DGN-MA-G4002___ DG1B in maintenance 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 25 7.740E-9 1.31 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 2.150E-4 1-ACP-BAC-MA-BA03____ 4.16KV bus 1BA03 in maintenance 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 26 7.740E-9 1.31 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 2.150E-4 1-ACP-BAC-MA-BB16____ 480V switchgear 1BB16 in maintenance 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 27 6.352E-9 1.08 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 5.350E-3 1-ACP-CRB-CC-BA0301__ RAT B supply CRB randomly fails to open 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient

46 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 28 6.095E-9 1.03 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 1.260E-2 1-EPS-DGN-MA-G4001___ DG1A in maintenance 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 29 6.095E-9 1.03 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 1.260E-2 1-EPS-DGN-MA-G4001___ DG1A in maintenance 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 30 5.719E-9 0.97 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 2.150E-4 1-ACP-BAC-MA-BA03____ 4.16KV bus 1BA03 in maintenance 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 31 5.719E-9 0.97 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 2.150E-4 1-ACP-BAC-MA-BB16____ 480V switchgear 1BB16 in maintenance 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 32 5.104E-9 0.87 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 5.350E-3 1-ACP-CRB-CC-BA0301__ RAT B supply CRB randomly fails to open 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 33 4.005E-9 0.68 2.160E-3 1-IE-FLI-TB_500_LF Internal flooding in TB Fire Zone 500 3.498E-4 1-ACP-CRB-CF-A205301 CCF of switchyard AC breakers AA205 &

BA301 to open 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 34 3.953E-9 0.67 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113

47 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 3.330E-3 1-EPS-SEQ-FO-1821U302 Sequencer B fails to operate 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 35 3.771E-9 0.64 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 5.350E-3 1-ACP-CRB-CC-BA0301__ RAT B supply CRB randomly fails to open 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 36 3.659E-9 0.62 5.190E-5 1-IE-FLI-CB_A60 Internal flooding in CB A60 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 1.000E+0 1-OA-NSCWFAN---H Operator fails to start NSCW fan manually (place holder) 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 37 3.512E-9 0.60 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 4.776E-5 1-ACP-BAC-FC-BA03____ 4.16KV bus 1BA03 fails 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 38 3.512E-9 0.60 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 4.776E-5 1-ACP-BAC-FC-BB16____ 480V switchgear 1BB16 randomly fails 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 39 3.490E-9 0.59 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 2.940E-3 1-EPS-DGN-FS-G4002___ DG1B fails to start by random cause 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 40 3.467E-9 0.59 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 2.150E-4 1-ACP-BAC-MA-AA02____ Bus 1AA02 in maintenance 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient

48 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 41 3.467E-9 0.59 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 2.150E-4 1-ACP-BAC-MA-AA02____ Bus 1AA02 in maintenance 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 42 3.229E-9 0.55 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 2.720E-3 1-DCP-BAT-MA-BD1B____ Battery 1BD1B in maintenance 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 43 3.177E-9 0.54 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 3.330E-3 1-EPS-SEQ-FO-1821U302 Sequencer B fails to operate 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 44 3.000E-9 0.51 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 4.080E-5 1-SWS-CTF-MA-_B_1234_ All 4 NSCW train B tower fans unavailable due to maintenance 45 2.977E-9 0.51 5.190E-5 1-IE-FLI-CB_A60 Internal flooding in CB A60 3.297E-2 1-EPS-DGN-FR-G4001___ DG1A fails to run by random cause (24 hr mission) 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 46 2.939E-9 0.50 2.800E-4 1-IE-FLI-AB_108_SP1 Internal flooding in AB 108 3.498E-4 1-ACP-CRB-CF-A205301 CCF of switchyard AC breakers AA205 &

BA301 to open 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 47 2.939E-9 0.50 2.800E-4 1-IE-FLI-AB_108_SP2 Internal flooding in AB 108 3.498E-4 1-ACP-CRB-CF-A205301 CCF of switchyard AC breakers AA205 &

BA301 to open

49 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 48 2.918E-9 0.50 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 3.498E-4 1-ACP-CRB-CF-A205301 CCF of switchyard AC breakers AA205 &

BA301 to open 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 49 2.918E-9 0.50 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 3.498E-4 1-ACP-CRB-CF-A205301 CCF of switchyard AC breakers AA205 &

BA301 to open 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 50 2.862E-9 0.49 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 3.000E-3 1-AFW-MDP-MA-P4002___

MDAFWP B unavailable due to test and maintenance 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 51 2.822E-9 0.48 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 4.776E-5 1-ACP-BAC-FC-BA03____ 4.16KV bus 1BA03 fails 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 52 2.822E-9 0.48 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 4.776E-5 1-ACP-BAC-FC-BB16____ 480V switchgear 1BB16 randomly fails 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 53 2.805E-9 0.48 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 2.940E-3 1-EPS-DGN-FS-G4002___ DG1B fails to start by random cause 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient

50 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 54 2.699E-9 0.46 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 9.040E-1 1-NSCWCT-SPRAY NSCW CTS in spray mode (fraction of time) 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 4.060E-5 1-SWS-MOV-MA-1669ACT_

NSCW train B spray valve closed for CT maintenance 55 2.595E-9 0.44 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 2.720E-3 1-DCP-BAT-MA-BD1B____ Battery 1BD1B in maintenance 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 56 2.588E-9 0.44 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 5.350E-3 1-ACP-CRB-CC-AA0205__ RAT A supply CRB randomly fails to open 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 57 2.588E-9 0.44 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 5.350E-3 1-ACP-CRB-CC-AA0205__ RAT A supply CRB randomly fails to open 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 58 2.459E-9 0.42 2.160E-3 1-IE-FLI-TB_500_LF Internal flooding in TB Fire Zone 500 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 59 2.411E-9 0.41 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient

51 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 4.080E-5 1-SWS-CTF-MA-_B_1234_ All 4 NSCW train B tower fans unavailable due to maintenance 60 2.347E-9 0.40 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 3.330E-3 1-EPS-SEQ-FO-1821U302 Sequencer B fails to operate 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 61 2.229E-9 0.38 5.190E-5 1-IE-FLI-CB_A60 Internal flooding in CB A60 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 1.000E+0 1-OA-NSCWFAN---H Operator fails to start NSCW fan manually (place holder) 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 62 2.169E-9 0.37 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 9.040E-1 1-NSCWCT-SPRAY NSCW CTS in spray mode (fraction of time) 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 4.060E-5 1-SWS-MOV-MA-1669ACT_

NSCW train B spray valve closed for CT maintenance 63 2.140E-9 0.36 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 4.776E-5 1-ACP-BAC-FC-BA03____ 4.16KV bus 1BA03 fails 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 64 2.140E-9 0.36 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 4.776E-5 1-ACP-BAC-FC-BB16____ 480V switchgear 1BB16 randomly fails 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 65 2.085E-9 0.35 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 4.776E-5 1-ACP-BAC-FC-BA03____ 4.16KV bus 1BA03 fails

52 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 66 2.085E-9 0.35 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 4.776E-5 1-ACP-BAC-FC-BB16____ 480V switchgear 1BB16 randomly fails 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 67 2.072E-9 0.35 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 2.940E-3 1-EPS-DGN-FS-G4002___ DG1B fails to start by random cause 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 68 1.980E-9 0.34 9.210E-5 1-IE-FLI-CB_A48 Internal flooding in CB A48 2.150E-4 1-ACP-BAC-MA-BA03____ 4.16KV bus 1BA03 in maintenance 1.000E-1 1-FLI-CB-A58A48-FP Propagation factor for internal flooding from corridor A58 to 4160 VAC switchgear room A48 69 1.980E-9 0.34 9.210E-5 1-IE-FLI-CB_A48 Internal flooding in CB A48 2.150E-4 1-ACP-BAC-MA-BB16____ 480V switchgear 1BB16 in maintenance 1.000E-1 1-FLI-CB-A58A48-FP Propagation factor for internal flooding from corridor A58 to 4160 VAC switchgear room A48 70 1.941E-9 0.33 2.160E-3 1-IE-FLI-TB_500_LF Internal flooding in TB Fire Zone 500 1.549E-5 1-AFW-PMP-CF-RUN CCF of AFW pumps to run (excluding driver) 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 71 1.917E-9 0.33 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 2.720E-3 1-DCP-BAT-MA-BD1B____ Battery 1BD1B in maintenance 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 72 1.852E-9 0.31

53 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 2.800E-4 1-IE-FLI-AB_108_SP1 Internal flooding in AB 108 3.000E-3 1-AFW-MDP-MA-P4002___

MDAFWP B unavailable due to test and maintenance 3.802E-2 1-AFW-TDP-FR-P4001___ TDAFWP fails to run 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 73 1.852E-9 0.31 2.800E-4 1-IE-FLI-AB_108_SP2 Internal flooding in AB 108 3.000E-3 1-AFW-MDP-MA-P4002___

MDAFWP B unavailable due to test and maintenance 3.802E-2 1-AFW-TDP-FR-P4001___ TDAFWP fails to run 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 74 1.839E-9 0.31 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 3.000E-3 1-AFW-MDP-MA-P4003___

MDAFWP A unavailable due to test and maintenance 3.802E-2 1-AFW-TDP-FR-P4001___ TDAFWP fails to run 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 75 1.839E-9 0.31 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 3.000E-3 1-AFW-MDP-MA-P4003___

MDAFWP A unavailable due to test and maintenance 3.802E-2 1-AFW-TDP-FR-P4001___ TDAFWP fails to run 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 76 1.828E-9 0.31 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 4.080E-5 1-SWS-CTF-MA-_B_1234_ All 4 NSCW train B tower fans unavailable due to maintenance 77 1.804E-9 0.31 2.800E-4 1-IE-FLI-AB_108_SP1 Internal flooding in AB 108 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 78 1.804E-9 0.31 2.800E-4 1-IE-FLI-AB_108_SP2 Internal flooding in AB 108

54 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 79 1.791E-9 0.30 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 80 1.791E-9 0.30 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 2.148E-4 1-EPS-SEQ-CF-FOAB Sequencers fail from common cause to operate 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 81 1.781E-9 0.30 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs 4.080E-5 1-SWS-CTF-MA-_B_1234_

All 4 NSCW train B tower fans unavailable due to maintenance 82 1.719E-9 0.29 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 4.776E-5 1-ACP-BAC-FC-BA03____

4.16KV bus 1BA03 fails 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 83 1.719E-9 0.29 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 4.776E-5 1-ACP-BAC-FC-BB16____

480V switchgear 1BB16 randomly fails 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 84 1.644E-9 0.28 2.240E-4 1-IE-FLI-AB_C113_LF1 Internal flooding in AB C113 9.040E-1 1-NSCWCT-SPRAY NSCW CTS in spray mode (fraction of time) 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails

55 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 4.060E-5 1-SWS-MOV-MA-1669ACT_

NSCW train B spray valve closed for CT maintenance 85 1.611E-9 0.27 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 3.330E-3 1-EPS-SEQ-FO-1821U301 Sequencer A fails to operate 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 86 1.611E-9 0.27 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 3.330E-3 1-EPS-SEQ-FO-1821U301 Sequencer A fails to operate 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 87 1.609E-9 0.27 9.210E-5 1-IE-FLI-CB_A48 Internal flooding in CB A48 3.297E-2 1-EPS-DGN-FR-G4002___

DG1B fails to run by random cause (24 hr mission) 1.000E-1 1-FLI-CB-A58A48-FP Propagation factor for internal flooding from corridor A58 to 4160 VAC switchgear room A48 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 88 1.603E-9 0.27 9.210E-5 1-IE-FLI-CB_A48 Internal flooding in CB A48 3.000E-3 1-AFW-MDP-MA-P4002___

MDAFWP B unavailable due to test and maintenance 1.000E-1 1-FLI-CB-A58A48-FP Propagation factor for internal flooding from corridor A58 to 4160 VAC switchgear room A48 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 89 1.602E-9 0.27 1.330E-4 1-IE-FLI-AB_C115_LF Internal flooding in AB C115 due to NSCW pipe failure 9.040E-1 1-NSCWCT-SPRAY NSCW CTS in spray mode (fraction of time) 9.947E-1

/1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 3.300E-1 1-RCS-XHE-XM-TRIP Operator fails to trip RCPs

56 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 4.060E-5 1-SWS-MOV-MA-1669ACT_

NSCW train B spray valve closed for CT maintenance 90 1.574E-9 0.27 7.320E-6 1-IE-FLI-DGB_101_LF Internal flooding in DG1B room 101 due to NSCW pipe failure 2.150E-4 1-ACP-BAC-MA-AA02____ Bus 1AA02 in maintenance 91 1.497E-9 0.25 8.570E-6 1-IE-FLI-AB_D74_FP Internal flooding in AB D74 propagates to480 VAC switchgear room D105 3.297E-2 1-EPS-DGN-FR-G4002___ DG1B fails to run by random cause (24 hr mission) 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 92 1.469E-9 0.25 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 4.080E-5 1-SWS-CTF-MA-_B_1234_ All 4 NSCW train B tower fans unavailable due to maintenance 93 1.422E-9 0.24 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 2.940E-3 1-EPS-DGN-FS-G4001___ DG1A fails to start by random cause 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 94 1.422E-9 0.24 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 2.940E-3 1-EPS-DGN-FS-G4001___ DG1A fails to start by random cause 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 95 1.340E-9 0.23 7.670E-6 1-IE-FLI-AB_B08_LF Internal flooding in AB B08 due to NSCW pipe failure 3.297E-2 1-EPS-DGN-FR-G4002___ DG1B fails to run by random cause (24 hr mission) 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 96 1.321E-9 0.22

57 Table 4.3 Internal Flooding Top 100 Cut Set Results Cut Set #

Frequency

% of CDF Basic Event Name Basic Event Description Probability 1.800E-4 1-IE-FLI-AB_C120_LF Internal flooding in AB C120 due to NSCW pipe failure 9.040E-1 1-NSCWCT-SPRAY NSCW CTS in spray mode (fraction of time) 2.000E-1 1-RCS-MDP-LK-BP2 RCP seal stage 2 integrity (binding/popping open) fails 4.060E-5 1-SWS-MOV-MA-1669ACT_

NSCW train B spray valve closed for CT maintenance 97 1.316E-9 0.22 2.780E-4 1-IE-FLI-CB_123_SP Internal flooding in CB 123 2.720E-3 1-DCP-BAT-MA-AD1B____ Battery 1AD1B in maintenance 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 98 1.316E-9 0.22 2.780E-4 1-IE-FLI-CB_122_SP Internal flooding in CB 122 2.720E-3 1-DCP-BAT-MA-AD1B____ Battery 1AD1B in maintenance 5.800E-2 1-OAB_TR-------H Operator fails to feed and bleed -

transient 3.000E-2 1-OEP-VCF-LP-CLOPL Consequential loss of offsite power -

LOCA 99 1.314E-9 0.22 7.520E-6 1-IE-FLI-AB_C118_LF Internal flooding in AB C118 due to NSCW pipe failure 3.297E-2 1-EPS-DGN-FR-G4001___ DG1A fails to run by random cause (24 hr mission) 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 100 1.279E-9 0.22 7.320E-6 1-IE-FLI-DGB_101_LF Internal flooding in DG1B room 101 due to NSCW pipe failure 3.297E-2 1-EPS-DGN-FR-G4001___ DG1A fails to run by random cause (24 hr mission) 5.300E-3 1-OEP-VCF-LP-CLOPT Consequential loss of offsite power -

transient 4.4.

Internal Flooding CDF Parameter Uncertainty Analysis The uncertainty of the IFPRA CDF results are addressed in two ways: parameter uncertainty sampling and sensitivity studies. The parameter uncertainty sampling is discussed further in this section. In Section 4.5 sources of model uncertainty are identified. The impacts of these model uncertainties are evaluated through sensitivity cases that examine how the results change if

58 alternate modeling assumptions are made. Both the parameter uncertainty analysis and the model uncertainty sensitivity cases are considered in evaluating the uncertainty in the model results.

The mean CDF is estimated using a Monte Carlo sampling approach using the uncertainty distributions of the contributing basic events. The state-of-knowledge correlations are addressed by assigning correlation classes to basic events with similar component types and failure modes, as described in the SAPHIRE technical reference manual (IF-5). The CDF mean value and uncertainty results are provided in Table 4.4. The internal flooding CDF cumulative distribution function is shown in Figure 4-1, and the probability density is shown in Figure 4-2.

Table 4.4 Internal Flooding CDF Model Parameter Uncertainty Results Point Estimate CDF Mean CDF 5th Percentile Median 95th Percentile Standard Deviation 7.91E-07 7.99E-07 1.62E-07 5.67E-07 2.17E-06 7.79E-07

59 Figure 4-1 Cumulative Distribution Function for Internal Flooding CDF Figure 4-2 Probability Density for Internal Flooding CDF 4.5.

Internal Flood PRA Model Uncertainty and Sensitivity Cases The purpose of this section is to identify sources of model uncertainty in the NRC IFPRA and develop sensitivity cases to assess the effects of this uncertainty. The modeling approaches and related assumptions can have a significant impact on the CDF results, and the impacts of these choices are often not well characterized by the parameter uncertainty distributions. A systematic review of each technical element of the NRC IFPRA model was performed to identify sources of model uncertainty. The potential impacts on the NRC IFPRA model are discussed for each identified source of uncertainty. The technical element, as defined in the ASME/ANS PRA Standard (IF-7), is identified for each source of uncertainty. The EPRI report, Treatment of Parameter and Model Uncertainty for Probabilistic Risk Assessments, (Ref. IF-13), was consulted for generic sources of model uncertainty for an internal flooding PRA. The sources of model uncertainty are listed in Table 4.5.

60 One method to address the impacts of modeling assumptions is to develop sensitivity cases to examine how the results change if alternate assumptions are made. Several sensitivity cases are examined here to explore the impacts of modeling assumptions and sources of model uncertainty on the internal flooding CDF results. The impacts of these sensitivity cases are evaluated in the following sections, as indicated below:

Internal flooding initiating event frequencies (Section 4.5.1)

Human error probabilities for maintenance-induced flooding scenarios (Section 4.5.2)

Human error probabilities for failures unrelated to flood mitigation (Section 4.5.3)

Crediting improved RCP shutdown seals (Section 4.5.4)

Propagation factor for flooding scenario 1-FLI-CB_A48 (Section 4.5.5)

Potential flood propagation impacting both safety-related 4160 VAC switchgears (Section 4.5.6)

Application of spray direction factor (Section 4.5.7)

Credit for manual action to start service water cooling tower fans (Section 4.5.8)

Impact of consequential loss of offsite power on internal flooding scenarios (Section 4.5.9)

A table summarizing the results of all of the sensitivity analyses is provided in Section 4.5.10.

Not all sources of model uncertainty discussed in Table 4.5 are addressed by the sensitivity cases. For some cases, the sources of uncertainty may not be easily quantifiable or able to be assessed by a sensitivity case. The potential areas for future work in Appendix C describe additional work that could be pursued that may help in understanding the impacts of model uncertainties, including those that are not addressed by sensitivity cases in this study.

Table 4.5 Sources of Model Uncertainty Technical Element Source of NRC IFPRA Model Uncertainty Impact on NRC IFPRA Model Internal Flood Plant Partitioning (IFPP)

The flood areas are primarily defined in terms of the rooms and compartments that are physically divided with walls, curbs, doors, etc., between them. Some areas are connected via passage ways or corridors, but are deemed to be independent with respect to flooding effects.

No significant impact. The definitions of flood areas are reasonable based on available information and confirmatory walkdowns. Potential propagation between flood areas was considered.

The modeled plant is a two-unit site with limited structures and systems that are shared between units. Shared flood areas have the potential to impact both units.

No significant impact. Confirmatory walkdowns for the NRC IFPRA did not identify any significant multi-unit internal flooding scenarios. Shared areas were qualitatively screened due to no flood sources and/or limited impact on accident initiation/mitigation equipment. Further quantitative analysis of postulated multi-unit flooding scenarios could supplement the screening analysis.

61 Table 4.5 Sources of Model Uncertainty Technical Element Source of NRC IFPRA Model Uncertainty Impact on NRC IFPRA Model Internal Flood Source Identification (IFSO)

Flood areas that do not contain flood sources may be screened from further analysis. However, flood areas with no flood sources that contain accident initiation/mitigation equipment should be evaluated further if there is potential for flood water propagation from adjacent areas.

Several flood areas, including those containing risk-significant electrical equipment, were screened because they do not contain flood sources. Flood propagation from adjacent areas was considered. For example, the flood scenario FLI-CB_A48 was included in the NRC IFPRA model and considers propagation from a corridor to Class 1E 4160 KV AC switchgear room. However, flood propagation to adjacent areas does not account for the failure probabilities of flood mitigating features (e.g., curbs, doors, drains). Though this could result in the omission of some flood scenarios in the model, these scenarios should have relatively lower frequencies when accounting for the mitigating feature failure probabilities.

The performance of flood mitigating features (e.g., drains or flood barriers) may be evaluated based on qualitative features and engineering judgment. Flood areas may be qualitatively screened based on the assumption of successful performance of flood mitigating features that would prevent flood water from reaching accident initiation/mitigation equipment.

Lack of well-established method(s) for evaluating the reliability of flood mitigating features contributes to model uncertainty. In some cases, no well-established method for quantitatively estimating flood barrier reliability exists. Generic assumptions regarding expected performance of flood barriers may be used in assessing flood sources and scenario development.

Flood areas may be qualitatively screened. The screening may include implicit assumptions about the successful performance of flood mitigating features.

For example, control building, spreading room train B, was screened because the area has no flood sources sufficient to fail accident initiation/mitigation equipment, including in areas where the flood can propagate. Failure of flood mitigating features may result in the flood propagating to areas that contain accident initiation/mitigation equipment. However, the assumptions applied to flood mitigating features do not necessarily result in flood prevention. For example, the presence non-water-tight doors and drains are not assumed to prevent flood propagation, but they are assumed to slow the flood progression. Water-tight doors, solid walls, and curbs are assumed to prevent flood propagation, given the maximum flood height would not exceed the height of those barriers.

62 Table 4.5 Sources of Model Uncertainty Technical Element Source of NRC IFPRA Model Uncertainty Impact on NRC IFPRA Model The flood source analysis requires characterization of failure mechanism and release including:

(a) the type of breach (e.g., leak, rupture, spray), (b) flow rate, (c) capacity of source, and (d) pressure and temperature of the source. Engineering judgment and assumptions applied to the source characterization may impact the IFPRA.

No significant impact. Each flood source that was modeled in the NRC IFPRA was characterized. The modeled breach may encompass a range of break sizes and flow rates. A representative flow rate was assumed. The impacts due to the flood source breach were generally pessimistic and have limited dependence on the flow rate assumptions.

Steam lines can be important flood source contributors. Though some steam line failures might not contribute to flooding impacts that are typically considered (e.g.,

submergence or spray), they can result in other potentially important impacts, such as elevated humidity and temperature, and condensation. There is generally less experience in assessing these types of impacts.

Consequently, consideration of steam lines as a flooding source may rely on simplifying assumptions that lead to uncertainty in the modeling.

There are many steam lines that were identified as potential flooding sources in the IFPRA, but many were not included in the estimation of flooding frequency. First, main steam lines were excluded from the IFPRA because these are included as an initiating event in the internal events PRA.

Secondly, contributions from some types of smaller steam lines are also excluded, based on qualitative assessment that the potential sources do not contribute to flood impacts. However, there may not be sufficient consideration of other flooding impacts, such as elevated humidity and temperature, and condensation. Further evaluation of these potential flood sources could result in additional contributions to the flooding scenario initiaiting event frequencies.

63 Table 4.5 Sources of Model Uncertainty Technical Element Source of NRC IFPRA Model Uncertainty Impact on NRC IFPRA Model Internal Flood Scenario Development (IFSN)

Flood scenario characterization includes consideration of automatic or operator actions that have the ability to terminate or contain the flood. Simplifying assumptions regarding post-flood operator actions were used in defining flood scenarios for the NRC IFPRA model.

Automatic or operator actions that have the ability to terminate or contain the flood were identified. Post-flood operator actions to limit or prevent flood impacts were generally not credited and were not modeled. These actions were assumed to have high failure probabilities due to limited time available to prevent flood damage/accident initiation. Long-term actions to terminate or contain floods were not modeled. It is possible that long-term floods could result in extensive propagation and additional plant impacts that would hinder safe shutdown of the plant; however, this is not the case for most scenarios. The long-term flooding is likely to accumulate in areas like sumps, corridors, and stairwells, with limited impact on plant operation. It was assumed that long-term flood damage was bounded by the initial flood damage, which occurs in the area containing the flood source and those adjacent areas that are identified in flood propagation scenarios.

Flood scenario characterization includes consideration of flood rate, time to reach SSCs, capacity of drains, and the amount of water retained by sumps, berms, dikes, and curbs. Design basis flooding calculations account for these factors in estimating flood volumes and SSC impacts. The design basis flooding calculations were used as a reference, but they do not directly define the PRA flood scenario impacts.

Flood impacts were based on assumptions that were considered to be pessimistic.

Design basis flooding calculations may have different boundary conditions (e.g.,

postulated break type and size) than the modeled NRC IFPRA scenarios. The model assumes that all identified SSCs are failed by flood water that reaches the room. Additional scenario-specific analysis of flood water volumes is not expected to identify additional impacted equipment or higher failure probabilities, but may be able to provide a basis for equipment survivability.

64 Table 4.5 Sources of Model Uncertainty Technical Element Source of NRC IFPRA Model Uncertainty Impact on NRC IFPRA Model In developing flood scenarios, qualitative screening criteria are applied to flood areas and flood scenarios in accordance with the ASME/ANS PRA standard. In applying these qualitative criteria, analysts may rely on judgement and assumptions, which can be a source of uncertainty. In particular, the assessment of flood propagation can introduce uncertainty when there are many potential propagation paths, or if the propagation depends on the occurrence of a very large flood that is beyond the typical design basis flood analysis.

The qualitative screening criteria involve consideration of potential flood propagation. However, some potential propagation paths may be overlooked or assumed to be unlikely. For example, a past operating experience event involved charging of a fire protection sprinkler header and water from a leakoff valve propagating to the main control room from the upper cable spreading room. Sealant was applied to floor penetrations to prevent future propagation. However, it could not be confirmed that the sealant would be leak tight if a significant flooding event occurred in the room. Degradation of the sealant (e.g., developing cracks) over time might be possible. The frequency of a large flood occurring and propagating to the main control room is expected to be low.

SSCs were evaluated for susceptibility to flood-induced failure mechanisms. Simplifying failure assumptions were made for SSCs susceptible to spray.

Spraying was assumed to fail components located within a 10-foot radius and within line-of-sight of a pressurized-water source.

The direction of the spray was not considered.

A spray directional factor may be applied to reduce the spatial impact of a failed flood source. The directional factor should be applied based on engineering analysis and judgment. A spray directional factor would reduce the initiating event frequency for flood scenarios involving sprays.

Assumptions regarding equipment susceptibility to all flood-induced failure mechanisms introduce model uncertainty. For most flood scenarios, the impacts are considered to be restricted to the flood areas and propagation paths, with local effects from spray and submergence being the primary concerns. However, some flood-induced failure mechanisms (e.g., high humidity) may affect The IFPRA considers the impacts of all flood-induced failure mechanisms.

However, the flood impacts are limited to the identified flood areas and propagation paths. It is possible that some flooding mechanisms (e.g., a large steam release) could have broader impacts on plant equipment. For example, insights from the internal events PRA identify the importance of non-safety related batteries located in the turbine building for restoring offsite power. The batteries are not located on the lower level of the turbine building,

65 Table 4.5 Sources of Model Uncertainty Technical Element Source of NRC IFPRA Model Uncertainty Impact on NRC IFPRA Model equipment that is located outside the analyzed propagation path(s).

are not in an identified flood propagation path, and are not impacted by any of the modeled turbine building floods. However, a large flood or steam release in the turbine building could impact the performance of these batteries. It should be noted that the potential importance of these batteries depends on a consequential loss of offsite power (LOOP) occurring. For a non-LOOP flood scenario, the loss of the batteries would have little impact on the accident response.

Selected high-energy line break events were excluded from the scope of the IFPRA. Secondary-side steam line break events were modeled as part of the internal events PRA, but these events do not consider impacts at the location of the break. Flood-related impacts (e.g., sprays) could fail accident mitigation equipment.

The plant response due to steam line breaks is expected to be dominated by the break itself. Accounting for local flooding impacts could increase the conditional core damage probability (CCDP) for those events, but the impacted equipment is not expected to have a significant effect on overall results. The unscreened flood areas containing steam lines were reviewed to identify potential impacts of steam line breaks. These flood areas, including the main steam valve rooms and a room containing FW control/regulator valves, were modeled in the NRC IFPRA due to other flood sources in the rooms.

The impacts due to steam line breaks can be inferred from these internal flooding scenarios.

Simplifying assumptions were made with respect to the impacts due to flood propagation. For most internal flooding scenarios, if a propagation path was identified, then the propagation was assumed to proceed unmitigated to the target flood area. One exception is the flood scenario, 1-FLI-CB_A48, where a propagation factor of 0.1 was assigned to the target flood area due to the For most internal flood scenarios assuming unmitigated propagation was reasonable. Identified equipment in the target flood area was assumed to fail.

Additional analysis of flood propagation mitigating features, timing, flood water heights, and operator actions may be able to support crediting successful operation of equipment. Additional analysis was not warranted due to the relative significance of the internal flooding scenarios. For scenario 1-FLI-CB_A48, only one of several potential propagation paths for the

66 Table 4.5 Sources of Model Uncertainty Technical Element Source of NRC IFPRA Model Uncertainty Impact on NRC IFPRA Model uncertainty of how the flood would propagate.

flood source was modeled. Propagation to room A48 depends on break size, location, and effectiveness of the flood mitigation features (e.g., floor drains). The uncertainty in the propagation factor was addressed by assigning an uncertainty distribution to this parameter.

Internal Flood-Induced Initiating Event Analysis (IFEV)

Internal flooding scenarios were modeled that include feedwater lines as a flood source. The flood areas include the main steam valve rooms and a room containing FW control/regulator valves. Feedwater line breaks were also considered as a contributor to secondary-side breaks downstream of MSIVs/upstream of MFIVs in the internal events model, under the IE-SSBO initiating event.

Feedwater line breaks contribute to the SSBO internal event initiator and as flood sources in NRC IFPRA scenarios. The inclusion of the feedwater line breaks in both studies may result in overestimating their overall contribution to plant risk.

Removing the feedwater line break contribution from SSBO would reduce the frequency for that initiator, but that may result in an overall under-estimation of their contribution, since the modeled NRC IFPRA scenarios only account for a fraction of the potential feedwater line breaks. Contributions from screened or unmodeled flood areas were not included in the NRC IFPRA. The two initiating event categories as currently modeled are expected to give a small overestimation of the feedwater line break contribution.

Internal flooding scenario 1-FLI-TB_500_LF includes circulating water piping, expansion joints, and other non-safety piping in the turbine building as potential flood sources. Some of these flood sources are also included in the estimation of the internal event initiator, Loss of Condenser Heat Sink (LOCHS).

Expansion joint failures contribute to both the loss of condenser heat sink (LOCHS) initiator in the internal event model and as a flood source in NRC IFPRA scenarios.

The inclusion of expansion joint failures in both studies may result in overestimating the contribution to plant risk. The LOCHS initiating event analysis incorporates a number of expansion joint failures into the frequency estimate. Expansion joint failures were included under the subcategory Condenser Leakage, as defined in NUREG/CR-5750. Removing the expansion joint contribution to 1-FLI-TB_500_LF would reduce the frequency for that initiator. The two initiating event categories as currently modeled are expected to give a small overestimation of

67 Table 4.5 Sources of Model Uncertainty Technical Element Source of NRC IFPRA Model Uncertainty Impact on NRC IFPRA Model the contribution from expansion joint failures.

Internal flooding scenarios that have the same or similar impacts are subsumed into a group. The resulting grouped scenario may lose some level of modeling fidelity with respect to the subsumed scenarios.

Scenarios may be subsumed when the same flood area is affected. In most cases, the impacts for the subsumed scenarios are the same. The only differences are the flood sources and the failure mechanisms of the flood sources (e.g., spray, local flood, or flood propagation). Subsuming these scenarios does not impact the NRC IFPRA model results. For scenario 1-FLI-TB_500_LF, several potential flood sources are subsumed. The impacted equipment can vary depending on the flood source. The bounding impacts are assumed to apply to all subsumed scenarios. In this particular case, the sum of the CDF contributions from the individual flood scenarios may be less than the CDF of the grouped scenario.

68 Table 4.5 Sources of Model Uncertainty Technical Element Source of NRC IFPRA Model Uncertainty Impact on NRC IFPRA Model Internal flooding initiating event frequencies are based on generic data from EPRI's report on pipe rupture frequencies (IF-9) and plant-specific data from the reference plant. The EPRI report provides a range of failure data for different plant systems and failure mechanisms, including sprays, floods, and major floods. Although the EPRI report provides a systematic approach for frequency estimation, there are several modeling choices that can impact the frequency results. Some examples of modeling choices include evaluation of pipe size categories and effective break sizes, estimation of total system piping length, incorporation of plant-specific failure/flooding experience, and choice of statistical models. Analyst judgment was exercised in determining the applicability and appropriateness of data and models used to support frequency estimates in the L3PRA project.

In the L3PRA project, internal flooding initiating event frequencies were based on the most recent available data sources.

Additional analysis is not expected to significantly change initiating event frequency values. The uncertainty in the initiating event frequencies was addressed by performing parameter uncertainty analysis.

Internal Flood Accident Sequences and Quantification (IFQU)

The screening HEPs that are selected for maintenance-related human errors for maintenance-induced flooding scenarios represent a source of model uncertainty.

Maintenance-induced internal flooding initiating event frequencies incorporate screening HEP values in estimating the event frequencies. The frequency estimates involve a combination of human failure events: failure to properly restore system after maintenance (screening HEP of 0.01) and failure to mitigate flooding when system is returned to service (screening HEP of 0.1). To account for uncertainty in these screening HEP values, the combined HEP value is varied in sensitivity analyses.

The internal flooding analysis identified post-flood human failure events (HFEs) that are unrelated While there are several post-flood HFEs that are important to the model results, most are not expected to be impacted by

69 Table 4.5 Sources of Model Uncertainty Technical Element Source of NRC IFPRA Model Uncertainty Impact on NRC IFPRA Model to flood mitigation. These HFEs can be influenced by stress and other factors related to the flooding scenarios. A set of HEP multiplier values to scale HEP values for flood scenarios could be developed. Such HEP multipliers were not implemented in the NRC IFPRA model due to insignificant contribution from the post-flood HFEs that are expected to be affected by the flooding.

flooding effects. Implementing the HEP multipliers would result in a small increase in the CCDP for a small number of internal flooding scenarios.

4.5.1. Internal Flooding Initiating Event Frequencies Description - Some internal flooding scenarios can have significant impacts on important-to-safety SSCs. The risk associated with internal flooding is often limited by the relatively low frequency of flooding initiating events. However, estimates of flooding initiating event frequencies can include significant uncertainties. Limited flooding data, size of piping systems at the plant, choice of system and pipe diameter categorization, use of surrogate data, incorporation of plant-specific data, choice of prior distribution, and other factors can all influence the flooding frequency estimates. In addition, the widely-used model for internal flooding frequencies is based on a product of the length of pipe, failure rate per length of pipe, and conditional rupture probability. One can question whether this model is appropriate for all piping systems, and the choice of this model itself introduces uncertainty. The point estimate value for internal flooding CDF can be estimated with initiating events set to different values within their uncertainty distributions to explore the sensitivity to these frequencies.

Sensitivity Case - For this sensitivity case, the IFPRA is quantified using the 95th percentile upper bound estimate for all inititiating event frequencies. The 95th percentile upper bound values for each flooding initiating event are shown in Table A.1-3 of Appendix A.

Results - This sensitivity resulted in a significant increase to the overall internal flooding CDF from 7.9x10-7 to 2.2x10-6 per reactor-critical-year. The individual contribution of every flooding scenario is increased in this sensitivity case, but the relative CDF contributions of the flooding scenarios are largely unchanged from the base case.

Sensitivity Case - Another sensitivity case was quantified using the 5th percentile lower bound estimate for all inititiating event frequencies.

Results - This sensitivity resulted in a significant decrease to the overall internal flooding CDF from 7.9x10-7 to 1.0x10-7 per reactor-critical-year.

4.5.2. Human Error Probabilities for Maintenance-Induced Flooding Scenarios Description - Maintenance-induced internal flooding initiating event frequencies incorporate screening HEP values in estimating the event frequency. The selection of these screening

70 values introduces uncertainty in the model. The HEP values are intended to be conservative screening values; however, considering variations in the conditions associated with the failure evnets could drive these failure probabilities to be either higher or lower than the screening values. The frequency estimates involve a combination of human failure events: failure to properly restore system after maintenance (screening HEP of 0.01) and failure to mitigate flooding when system is returned to service (screening HEP of 0.1). The combined HEP values are varied higher and lower by a factor of 10 to account for uncertainty in these screening HEP values.

Sensitivity Case - The combined HEP values for the maintenance-induced flooding scenarios are increased by a factor of 10.

Results - This sensitivity case has a small impact on the overall internal flooding CDF. The CDF increased from 7.9x10-7 to 8.0x10-7 per reactor-critical-year. The two maintenance-induced flooding scenarios, 1-FLI-TB_500_HI1 and 1-FLI-TB_500_HI2, do not contribute significantly to the base case CDF results. With this sensitivity case, the two scenarios show increased CDF values, but both are still under 1 percent of the total internal flooding CDF. The CDF for scenario 1-FLI-TB_500_HI1 increased from 5.7x10-10 to 6.9x10-9 per reactor-critical-year. The CDF for scenario 1-FLI-TB_500_HI2 increased from 6.7x10-10 to 7.8x10-9 per reactor-critical-year.

Sensitivity Case - The combined HEP values for the maintenance-induced flooding scenarios are decreased by a factor of 10.

Results - This sensitivity case has minimal impact on the overall internal flooding CDF. The CDF is unchanged from 7.9x10-7, though the number of cut sets is slightly reduced from 8728 to 8630. The CDF for scenario 1-FLI-TB_500_HI1 decreased from 5.7x10-10 to 4.3x10-11 per reactor-critical-year. The CDF for scenario 1-FLI-TB_500_HI2 decreased from 6.7x10-10 to 5.3x10-11 per reactor-critical-year.

4.5.3. Human Error Probabilities for Failures Unrelated to Flood Mitigation Description - For evaluation of post-flood human failure events in the portion of the plant response not related to flood mitigation, the flooding impacts should be taken into consideration in the performance shaping factors that influence these failures. For the areas that are impacted by the flood, it is assumed that local actions are not possible. For actions that are not located in areas affected by the flood, the impacts on human performance can vary depending on the specific performance shaping factors that are present. For actions in the main control room, increased stress due to the flooding event is the primary concern for influencing actions. For actions outside the main control room, accessibility and additional time required to perform actions can influence the failure events. This sensitivity case is developed to explore the impacts on HEP values for human failures unrelated to the flood mitigation.

Sensitivity Case - All HEP values are set to 10 times their nominal values. If the HEP is 0.1 or higher, then the value is set to 0.9. For one of the modeled human failure events (basic event 1-OA-NSCWFAN---H), the basic event is assigned a failure probability of 1.0 (i.e., the event is failed) in the base model. That event failure probability is also set to 1.0 in this sensitivity case.

Results - For this sensitivity case the CDF increased from 7.9x10-7 to 2.4x10-6 per reactor-critical-year. The resulting cut sets show that human failure events associated with operator failure to initiate feed and bleed (basic event 1-OAB_TR-------H) and operator failure to trip reactor coolant pumps (basic event 1-RCS-XHE-XM-TRIP) are significant contributors to CDF.

For many of the significant human failure events, the actions take place in the main control room. Also, the baseline HEP estimate for most events assumes high stress level. The increased stress associated with the flooding event is expected to have a small impact on the

71 HEP value. Therefore, this sensitivity case is expected to overestimate the impacts of flooding on HEP values. A second sensitivity case is developed to focus only on actions performed outside of the main control room.

Sensitivity Case - All the modeled HFEs in the IFPRA were reviewed to identify the locations of where the actions are performed. Only four HFEs were identified that represent actions performed outside the main control room. Several other ex-control room actions were considered, but ultimately only these four events were modeled in the internal events and internal flooding models. For these HFEs, the HEP values are set to 10 times their nominal values. The adjustments to the HEP values for internal flooding events are shown in Table 4.6 Table 4.6 Internal Flooding Adjustments to HEP Values for Actions Outside the Control Room Basic Event Name Description Base HEP Location for Operator Action HEP Used for Flooding 1-OA-ALIGNPW-01HR OPERATOR FAILS TO ALIGN PLANT WILSON TO 4.16KV BUS WITHIN 1 HR AFTER SBO 9.2E-02 Switchyard 9.2E-01 1-OA-ALIGNPW-02HR OPERATOR FAILS TO ALIGN PLANT WILSON TO 4.16KV BUS WITHIN 2 HR AFTER SBO 1.2E-02 Switchyard 1.2E-01 1-OA-HURGXFMR--H OPERATOR FAILS LOCAL CHANGE 120VAC SUPPLY FROM INVERTER TO RGXFMR 3.4E-03 Control Building 3.4E-02 1-OA-NSCWCT-MV-H OPERATOR FAILS TO LOCALLY OPEN NSCW CT SPRAY MOV NO SI 1.1E-02 Service Water Pump House 1.1E-01 Results - This sensitivity case has minimal impact on the overall internal flooding CDF. The CDF is unchanged from 7.9x10-7, though the number of cut sets is slightly increased from 8728 to 8984.

4.5.4. Crediting Improved RCP Shutdown Seals Description - To assess the impact on risk from improvements in RCP Shutdown seals, a sensitivity study was done based on low leakage RCP seals (Westinghouse SHIELD Passive Shutdown Seal). For these seals, RCP seal leakage was assumed to be 1 gpm per RCP after seal actuation. The inclusion of these seals can have a significant effect on the model results.

Sensitivity Case - To evaluate the effect of the RCP shutdown RCP seals on the Level 1 IFPRA model results, basic event 1-RCS-SDS-FC-ACTUATE (shutdown seals fail to actuate), which is set to TRUE in the base model, was assigned a failure probability.9F10 This basic event was located in the 1-SDS (shutdown seal actuation), 1-RCPSC (RCP seal cooling/integrity), 1-10 The failure probability for the low leakage RCP seals was taken from the Final Safety Evaluation by the Office Of Nuclear Reactor Regulation, PWROG-14001-P, Revision 1, "PRA Model for the Generation III Westinghouse Shutdown Seal," (Ref. IF-15). The failure probability is proprietary and is redacted from the public version of the safety evaluation report.

72 RCPSC-BP (RCP seal integrity-binding/popping), and 1-OPR-RCPS (RCP seal integrity lost during SBO) fault trees. In addition to the failure of the shutdown seals to actuate, there was potential that the seals may not remain sealed. Therefore, an additional basic event, 1-RCS-SDS-SEALED (shutdown seals fail to remain sealed), was added under the same OR gates (1-SDS, 1-RCPSC2223, 1-RCPS-BP21, and 1-OPR-RCPS-02, respectively) with basic event 1-RCS-SDS-FC-ACTUATE. The assumed hourly failure rate is based on NRCs evaluation of the improved RCP seal (Ref. IF-15).

The station blackout (SBO) event tree was also modified to account for the RCP shutdown seals. The changes are consistent with the sensitivity case discussed in Section 10.8 of the internal events Level 1 PRA model report (Ref. IF-16). However, the SBO event tree does not contribute to any of the significant accident sequences for the IFPRA. Refer to the internal events Level 1 PRA report for more information on the SBO changes.

Results - This sensitivity resulted in a decrease of the overall internal flooding CDF from 7.9x10-7 to 6.4x10-7 per reactor-critical-year (an approximately 19 percent decrease). In the base model, seven of the top ten accident sequences involve RCP seal failures resulting in small LOCAs (sequences identified by sequence number 1-11-08-1). In the sensitivity case, these sequences are still significant contributors to overall CDF, though to a lesser extent than the base model. The top 20 accident sequences for the sensitivity case are shown in Table 4.7.

After accounting for the reduced failure rate of the shutdown seals, the highest contribution to the RCP seal failure is due to the human error associated with failing to trip the running RCPs (basic event 1-RCS-XHE-XM-TRIP). In some of the significant flood scenarios, the flood intiator impacts the availability of service water, and this impacts the likelihood of reactor coolant system (RCS) injection failure after the small LOCA occurs. This is another factor that contributes to the importance of these sequences.

Table 4.7 Internal Flooding Accident Sequences with RCP Shutdown Seals Scenario Name Sequence Number CDF/ry

% of CDF Cumulative

% of CDF Cut Set Count 1

1-FLI-AB_C113_LF1 1-10-1 7.8E-08 12.1 12.1 177 2

1-FLI-AB_C120_LF 1-10-1 6.8E-08 10.6 22.7 181 3

1-FLI-AB_C113_LF1 1-11-08-1 4.7E-08 7.4 30.1 91 4

1-FLI-AB_C115_LF 1-10-1 4.6E-08 7.2 37.3 153 5

1-FLI-AB_C120_LF 1-11-08-1 3.8E-08 5.9 43.2 84 6

1-FLI-CB_122_SP 1-15-1 3.6E-08 5.5 48.7 105 7

1-FLI-CB_123_SP 1-15-1 3.6E-08 5.5 54.3 105 8

1-FLI-AB_C115_LF 1-11-08-1 2.8E-08 4.4 58.6 82 9

1-FLI-AB_108_SP1 1-11-08-1 2.6E-08 4.0 62.6 167 10 1-FLI-AB_108_SP2 1-11-08-1 2.6E-08 4.0 66.6 167 11 1-FLI-CB_123_SP 1-11-08-1 2.5E-08 3.9 70.5 167 12 1-FLI-CB_122_SP 1-11-08-1 2.5E-08 3.9 74.4 167 13 1-FLI-CB_123_SP 1-21-1 1.3E-08 2.1 76.5 525 14 1-FLI-CB_122_SP 1-21-1 1.3E-08 2.1 78.6 525 15 1-FLI-TB_500_LF 1-10-1 1.0E-08 1.6 80.2 401 16 1-FLI-AB_108_SP1 1-21-1 7.2E-09 1.1 81.3 309 17 1-FLI-AB_108_SP2 1-21-1 7.2E-09 1.1 82.4 309

73 Scenario Name Sequence Number CDF/ry

% of CDF Cumulative

% of CDF Cut Set Count 18 1-FLI-CB_A60 1-15-1 6.6E-09 1.0 83.4 51 19 1-FLI-AB_108_SP1 1-04-1 6.6E-09 1.0 84.5 111 20 1-FLI-AB_108_SP2 1-04-1 6.6E-09 1.0 85.5 105 Total CDF 6.4E-07 7510 4.5.5. Propagation Factor for Flooding Scenario 1-FLI-CB_A48 Description - The potential for flood propagation from a corridor to the train A safety-related 4.16 KV AC switchgear room is modeled in flooding scenario 1-FLI-CB_A48. A propagation factor was assumed that represents the likelihood of flood sources propagating to the switchgear room. The likelihood of propagation to the switchgear room depends on break size, location, and effectiveness of the flood mitigation features (e.g., floor drains).

Sensitivity Case - To address uncertainty in the likelihood of propagation, the propagation factor is set to 1.0 from the base case value of 0.1.

Results - This sensitivity resulted in an increase of the overall internal flooding CDF from 7.9x10-7 to 9.2x10-7 per reactor-critical-year (an approximately 16% increase). The increase in CDF is attributed to the increased contribution from flooding scenario 1-FLI-CB_A48. The CDF of flood scenario 1-FLI-CB_A48 increased from 1.4x10-8 to 1.4x10-7 per reactor-critical-year.

4.5.6. Potential Flood Propagation Impacting Both Safety-Related 4160 VAC Switchgears Description - Given the importance of the 4160 VAC essential switchgear rooms, additional evaluation of flood propagation that could impact both safety-related trains may be warranted.

Flood propagation to the train A switchgear room is described in scenario 1-FLI-CB_A48. The train B switchgear room is located adjacent to the train A room, but there are several features in place that inhibit flood propagation. Neither of the switchgear rooms contain any flood sources.

There are no direct propagation paths between the two rooms. The flood scenario would have to initiate in the adjoining corridor and then propagate to both rooms. The train B switchgear room is protected by a 6-inch high curb at the door, and the equipment in the room is mounted on a 6-inch high pedestal. There are multiple flood propagation paths and drains that would slow the flood height increase and would likely prevent overtopping the 6-inch curb. As such, flood propagation to both switchgear rooms is very unlikely.

Sensitivity Case - Flooding scenario 1-FLI-CB_A48 is modified to address the potential for flood propagation to both safety-related 4160 VAC switchgear rooms. The probability of flood propagation to both rooms is assumed to be 1x10-2. This is considered to be a conservative estimate, since the propagation to the train B room is unlikely due to the protection from a curb at the door and the presence of several other potential propagation paths and floor drains. Even if such a flood were to occur, then plant staff would be expected to have time to pursue flood mitigating actions (e.g., isolating the flood source) before the train B room was impacted. These flood mitigating actions are not credited in the sensitivity case. Also, the impacts of the flood are assumed to fail all switchgears in both rooms. A more detailed analysis of the flood height may support less severe flooding impacts. If the flooding does cause loss of power to both safety-related 4160 VAC buses, then power will be unavailable to safety-related equipment required for core cooling (e.g., AFW and ECCS motor-driven pumps). No credit is given for continued operation of the turbine-driven AFW pump after battery depletion (4-hour battery life). No credit

74 is given to recovering the safety-related loads after the switchgear equipment is failed. If the flood impacts both switchgear rooms, then core damage is assumed.

Results - This sensitivity resulted in a significant increase to the internal flooding CDF from 7.9x10-7 to 1.7x10-6 per reactor-critical-year. In this sensitivity case, the flooding scenario impacting both safety-related 4160 VAC switchgear rooms (scenario 1-FLI-CB_A48) contributes more than half of the total internal flooding CDF. This is expected to be a bounding assessment of the scenario for the reasons discussed above. The individual flooding scenario contributions for this sensitivity study are shown in Table 4.8.

Table 4.8 Internal Flooding Scenario Results With Propagation to Both Safety-Related 4160 VAC Switchgear Rooms Scenario Name IE frequency per reactor-critical-year CCDP CDF per reactor-critical-year

% of CDF Cut Set Count 1

1-FLI-CB_A48 9.2E-05 1.0E-02 9.2E-07 54.2 1

2 1-FLI-AB_C113_LF1 2.2E-04 6.9E-04 1.6E-07 9.2 348 3

1-FLI-AB_C120_LF 1.8E-04 7.2E-04 1.3E-07 7.7 347 4

1-FLI-CB_123_SP 2.8E-04 3.7E-04 1.0E-07 6.0 1393 5

1-FLI-CB_122_SP 2.8E-04 3.7E-04 1.0E-07 6.0 1389 6

1-FLI-AB_C115_LF 1.3E-04 6.9E-04 9.2E-08 5.4 300 7

1-FLI-AB_108_SP1 2.8E-04 2.1E-04 5.9E-08 3.5 1135 8

1-FLI-AB_108_SP2 2.8E-04 2.1E-04 5.9E-08 3.5 1127 9

1-FLI-CB_A60 5.2E-05 3.6E-04 1.9E-08 1.1 493 10 1-FLI-TB_500_LF 2.2E-03 7.6E-06 1.6E-08 1.0 701 11 1-FLI-DGB_101_LF 7.3E-06 8.5E-04 6.2E-09 0.4 70 12 1-FLI-AB_D74_FP 8.6E-06 6.9E-04 5.9E-09 0.3 89 13 1-FLI-AB_C118_LF 7.5E-06 7.3E-04 5.5E-09 0.3 75 14 1-FLI-AB_B08_LF 7.7E-06 6.9E-04 5.3E-09 0.3 72 15 1-FLI-DGB_103_LF 7.3E-06 7.0E-04 5.1E-09 0.3 79 16 1-FLI-TB_500_LF-CDS 6.3E-04 7.2E-06 4.5E-09 0.3 303 17 1-FLI-AB_B24_LF2 3.5E-06 7.1E-04 2.5E-09 0.1 74 18 1-FLI-AB_B50_JI 3.4E-06 7.3E-04 2.4E-09 0.1 56 19 1-FLI-AB_A20 2.7E-04 6.8E-06 1.8E-09 0.1 153 20 1-FLI-TB_500_HI2 9.4E-05 7.2E-06 6.7E-10 0.0 59 21 1-FLI-TB_500_HI1 9.4E-05 6.1E-06 5.7E-10 0.0 58 22 1-FLI-AB_D78_FP 3.6E-07 6.7E-04 2.4E-10 0.0 24 23 1-FLI-AB_A20_FP 2.3E-05 8.5E-06 1.9E-10 0.0 51 Total:

5.1E-03 1.7E-06 8397 4.5.7. Application of Spray Direction Factor Description - In some PRA studies, a spray direction factor that accounts for the sprays direction with respect to the pipes circumference is applied when supported by a detailed

75 engineering evaluation. Spray events are generally characterized as having small through-wall pipe failures and low break flow rates. Accordingly, the impacts on nearby equipment can be expected to be less severe than those of larger flooding events. The equipment impacted by spray events are assumed to be within a direct line-of-sight of the pipe failure and result in spraying or splashing on the affected component(s). The approach for estimating spray frequency does not account for the direction of the spray. Applying a spray direction factor has the effect of reducing the spray frequency to account for the fraction of spray events that would be directed toward the impacted equipment. This assumes that some spray events would be directed away from the equipment and would not result in equipment failure.

Sensitivity Case - To evaluate the effect of the spray direction a factor of 1/8 is multiplied by the initiating event frequency for flooding scenarios that model impacts from sprays or jet impingment.10F11 The spray direction factor is applied to the following internal flooding scenarios:

1-FLI-AB_108_SP1, 1-FLI-AB_108_SP2, 1-FLI-CB_122_SP, 1-FLI-CB_123_SP, and 1-FLI-AB_B50_JI.

Results - This sensitivity resulted in a decrease to the internal flooding CDF from 7.9x10-7 to 5.0x10-7 per reactor-critical-year (an approximately 37 percent decrease). The individual flooding scenario contributions for this sensitivity study are shown in Table 4.9.

Table 4.9 Internal Flooding Scenario Results With Spray Direction Factor Scenario Name IE frequency per reactor-critical-year CCDP CDF per reactor-critical-year

% of CDF Cut Set Count 1

1-FLI-AB_C113_LF1 2.2E-04 6.9E-04 1.6E-07 30.8 348 2

1-FLI-AB_C120_LF 1.8E-04 7.2E-04 1.3E-07 25.8 347 3

1-FLI-AB_C115_LF 1.3E-04 6.9E-04 9.2E-08 18.3 300 4

1-FLI-CB_A60 5.2E-05 3.6E-04 1.9E-08 3.7 493 5

1-FLI-TB_500_LF 2.2E-03 7.6E-06 1.6E-08 3.2 701 6

1-FLI-CB_A48 9.2E-05 1.5E-04 1.4E-08 2.8 332 7

1-FLI-CB_123_SP 3.5E-05 3.6E-04 1.2E-08 2.5 400 8

1-FLI-CB_122_SP 3.5E-05 3.6E-04 1.2E-08 2.5 399 9

1-FLI-AB_108_SP1 3.5E-05 2.0E-04 7.1E-09 1.4 230 10 1-FLI-AB_108_SP2 3.5E-05 2.0E-04 7.1E-09 1.4 229 11 1-FLI-DGB_101_LF 7.3E-06 8.5E-04 6.2E-09 1.2 70 12 1-FLI-AB_D74_FP 8.6E-06 6.9E-04 5.9E-09 1.2 89 13 1-FLI-AB_C118_LF 7.5E-06 7.3E-04 5.5E-09 1.1 75 14 1-FLI-AB_B08_LF 7.7E-06 6.9E-04 5.3E-09 1.0 72 15 1-FLI-DGB_103_LF 7.3E-06 7.0E-04 5.1E-09 1.0 79 16 1-FLI-TB_500_LF-CDS 6.3E-04 7.2E-06 4.5E-09 0.9 303 17 1-FLI-AB_B24_LF2 3.5E-06 7.1E-04 2.5E-09 0.5 74 11 The authors are not aware of any rigorous analyses that have been performed to justify a particular spray direction factor. For this sensitivity case, a spray direction factor of 1/8 was selected based on engineering judgment and its use in at least one other internal flooding PRA.

76 Table 4.9 Internal Flooding Scenario Results With Spray Direction Factor Scenario Name IE frequency per reactor-critical-year CCDP CDF per reactor-critical-year

% of CDF Cut Set Count 18 1-FLI-AB_A20 2.7E-04 6.8E-06 1.8E-09 0.4 153 19 1-FLI-TB_500_HI2 9.4E-05 7.2E-06 6.7E-10 0.1 59 20 1-FLI-TB_500_HI1 9.4E-05 6.1E-06 5.7E-10 0.1 58 21 1-FLI-AB_B50_JI 4.2E-07 7.0E-04 2.9E-10 0.1 26 22 1-FLI-AB_D78_FP 3.6E-07 6.7E-04 2.4E-10 0.1 24 23 1-FLI-AB_A20_FP 2.3E-05 8.5E-06 1.9E-10 0.0 51 Total:

4.2E-03 5.0E-07 4912 4.5.8. Credit for Manual Action to Start Service Water Cooling Tower Fans Description - One of the significant basic events in the IFPRA model involves an operator failure to manually start service water cooling tower fans following a safety injection or loss of offsite power signal (basic event 1-OA-NSCWFAN---H). In the base model, no credit is given for this action, which is consistent with the modeling approach in the reference plant PRA. The basic event is included in the model with failure probability set to 1.0. The event is present in several significant cut sets. The Fussell-Vesely importance measure for this basic event indicates an approximately 21 percent contribution to internal flooding CDF. The accident sequences that contain these cut sets involve a secondary-side break upstream of the MSIVs that is induced by the flooding initiating event, resulting in a reactor trip, main steamline isolation, and safety injection actuation. Subsequent failures result in an RCP seal LOCA. The success criterion requires 3 out of 4 service water cooling tower fans for successful operation during safety injection. The relevant cut sets include combinations of the fans failure to start and operator failure to manually start the fans. These cut sets are potentially conservative because there is no credit given for the manual actions. Also, the safety injection can be terminated after RCS level has been recovered and is stable. At that time, the success criterion is 1 out of 4 service water cooling tower fans for successful operation.

Sensitivity Case - To evaluate the effect of applying credit for manual action to start service water cooling tower fans, the basic event failure probability is set to 0.1.

Results - This sensitivity resulted in a decrease to the internal flooding CDF from 7.9x10-7 to 6.4x10-7 per reactor-critical-year (an approximately 19 percent decrease). The contributions from accident sequences that involve a flood-related secondary-side break resulting in an RCP seal LOCA are significantly reduced. The flooding scenarios that include these sequences are 1-FLI-AB_108_SP1, 1-FLI-AB_108_SP2, 1-FLI-CB_122_SP, 1-FLI-CB_123_SP, and 1-FLI-CB_A60. The CDF contributions from all these scenarios are reduced with this sensitivity case.

The flooding scenario contributions to CDF are shown in Table 4.10.

77 Table 4.10 Internal Flooding Scenario Results With Credit for Manual Action to Start Service Water Cooling Tower Fans Scenario Name IE frequency per reactor-critical-year CCDP CDF per reactor-critical-year

% of CDF Cut Set Count 1

1-FLI-AB_C113_LF1 2.2E-04 6.9E-04 1.6E-07 24.4 348 2

1-FLI-AB_C120_LF 1.8E-04 7.2E-04 1.3E-07 20.4 347 3

1-FLI-AB_C115_LF 1.3E-04 6.9E-04 9.2E-08 14.5 300 4

1-FLI-CB_123_SP 2.8E-04 2.3E-04 6.6E-08 10.3 1105 5

1-FLI-CB_122_SP 2.8E-04 2.3E-04 6.6E-08 10.3 1101 6

1-FLI-AB_108_SP1 2.8E-04 8.1E-05 2.3E-08 3.6 824 7

1-FLI-AB_108_SP2 2.8E-04 8.1E-05 2.3E-08 3.6 816 8

1-FLI-TB_500_LF 2.2E-03 7.6E-06 1.6E-08 2.6 697 9

1-FLI-CB_A48 9.2E-05 1.5E-04 1.4E-08 2.2 300 10 1-FLI-CB_A60 5.2E-05 2.3E-04 1.2E-08 1.9 385 11 1-FLI-DGB_101_LF 7.3E-06 8.5E-04 6.2E-09 1.0 70 12 1-FLI-AB_D74_FP 8.6E-06 6.9E-04 5.9E-09 0.9 89 13 1-FLI-AB_C118_LF 7.5E-06 7.3E-04 5.5E-09 0.9 75 14 1-FLI-AB_B08_LF 7.7E-06 6.9E-04 5.3E-09 0.8 72 15 1-FLI-DGB_103_LF 7.3E-06 7.0E-04 5.1E-09 0.8 79 16 1-FLI-TB_500_LF-CDS 6.3E-04 7.2E-06 4.5E-09 0.7 302 17 1-FLI-AB_B24_LF2 3.5E-06 7.1E-04 2.5E-09 0.4 74 18 1-FLI-AB_B50_JI 3.4E-06 7.3E-04 2.4E-09 0.4 56 19 1-FLI-AB_A20 2.7E-04 6.8E-06 1.8E-09 0.3 153 20 1-FLI-TB_500_HI2 9.4E-05 7.2E-06 6.7E-10 0.1 59 21 1-FLI-TB_500_HI1 9.4E-05 6.1E-06 5.7E-10 0.1 58 22 1-FLI-AB_D78_FP 3.6E-07 6.7E-04 2.4E-10 0.0 24 23 1-FLI-AB_A20_FP 2.3E-05 8.5E-06 1.9E-10 0.0 51 Total:

5.2E-03 6.4E-07 7385 4.5.9. Impact of Consequetial Loss of Offsite Power on Internal Flooding Scenarios Description - A consequential loss of offsite power (LOOP) can occur in response to a reactor trip or other plant transients as electrical loads are transferred to power sources supplied from the offsite grid. The consequential LOOP modeling approach is described in the internal events Level 1 PRA model report (Ref. IF-16), and the same approach is adopted for the IFPRA model. Consequential LOOPs are a significant contributor to the internal flooding CDF, as can be seen in the discussion of significant accident sequences in Section 4.2. However, many of the flooding scenarios would not result in an immediate plant trip. Operators may initiate a manual reactor trip or a controlled plant shutdown. If a controlled plant shutdown is initiated,

78 then this would not have the same impacts on the electrical distribution system as a reactor trip or other plant transients.

Sensitivity Case - To evaluate the impacts of the consequential LOOP modeling, a sensitivity case is developed to suppress the consequential LOOP failures in the internal flooding scenarios that do not result in an immediate plant trip. The internal flooding scenarios that do not result in an immediate plant trip are:

1-FLI-AB_B24_LF2 1-FLI-AB_B50_JI 1-FLI-AB_C113_LF1 1-FLI-AB_C115_LF 1-FLI-AB_C118_LF 1-FLI-AB_C120_LF 1-FLI-AB_D74_FP 1-FLI-AB_D78_FP 1-FLI-DGB_101_LF 1-FLI-DGB_103_LF The basic event used to model the consequential LOOP probability (basic event 1-OEP-VCF-LP-CLOPT) is ignored in these flooding scenarios.

Results - This sensitivity resulted in a decrease to the internal flooding CDF from 7.9x10-7 to 5.9x10-7 per reactor-critical-year (an approximately 25 percent decrease). The contribution from accident sequences involving consequtial LOOPs are significantly reduced. In the base model, one of the significant accident sequences involves a failure of NSCW piping and a subsequent LOOP. The sequence is identified by sequence number 1-10-1 (see base model accident sequence results in Table 4.2). For the sensitivity case, the CDF contributions from sequence number 1-10-1 are significantly reduced. The top 20 accident sequences for the sensitivity case are shown in Table 4.11. Sequence number 1-10-1 does not appear in the top 20 accident sequences for any of the flooding scenarios that would not result in an immediate plant trip.

Table 4.11 Internal Flooding Accident Sequences Suppressing Consequential LOOP for Flooding Scenarios Not Causing Plant Trip Scenario Name Sequence Number CDF/ry

% of CDF Cumulative

% of CDF Cut Set Count 1

1-FLI-AB_C113_LF1 1-11-08-1 7.8E-08 13.2 13.2 150 2

1-FLI-AB_C120_LF 1-11-08-1 6.2E-08 10.6 23.8 146 3

1-FLI-AB_C115_LF 1-11-08-1 4.6E-08 7.8 31.6 136 4

1-FLI-AB_108_SP1 1-11-08-1 4.2E-08 7.1 38.6 303 5

1-FLI-AB_108_SP2 1-11-08-1 4.2E-08 7.1 45.7 303 6

1-FLI-CB_123_SP 1-11-08-1 4.1E-08 7.0 52.7 292 7

1-FLI-CB_122_SP 1-11-08-1 4.1E-08 7.0 59.8 292 8

1-FLI-CB_122_SP 1-15-1 3.6E-08 6.0 65.8 105 9

1-FLI-CB_123_SP 1-15-1 3.6E-08 6.0 71.9 105 10 1-FLI-CB_123_SP 1-21-1 1.3E-08 2.3 74.1 525 11 1-FLI-CB_122_SP 1-21-1 1.3E-08 2.3 76.4 525 12 1-FLI-TB_500_LF 1-10-1 1.0E-08 1.8 78.1 401

79 Table 4.11 Internal Flooding Accident Sequences Suppressing Consequential LOOP for Flooding Scenarios Not Causing Plant Trip Scenario Name Sequence Number CDF/ry

% of CDF Cumulative

% of CDF Cut Set Count 13 1-FLI-CB_A60 1-11-08-1 7.6E-09 1.3 79.4 104 14 1-FLI-AB_108_SP2 1-21-1 7.2E-09 1.2 80.6 309 15 1-FLI-AB_108_SP1 1-21-1 7.2E-09 1.2 81.9 309 16 1-FLI-CB_A60 1-15-1 6.6E-09 1.1 83.0 51 17 1-FLI-AB_108_SP1 1-04-1 6.6E-09 1.1 84.1 111 18 1-FLI-AB_108_SP2 1-04-1 6.6E-09 1.1 85.2 105 19 1-FLI-CB_A48 2-10-1 5.7E-09 1.0 86.2 43 20 1-FLI-CB_123_SP 1-04-1 4.9E-09 0.8 87.0 69 Total CDF 5.9E-07 8116 4.5.10. Summary of Sensitivity Analysis Results A summary of the results of the sensitivity cases documented in this report is provided below.

As evident from the table, the largest increases in CDF occur in the following cases:

Increasing the HEPs for all human failure events unrelated to flood mitigation (204 percent increase in internal flooding CDF)

Using the 95th percentile upper bound estimate for all flooding initiating event frequencies (178 percent increase in internal flooding CDF)

Assuming a safety-related 4160 VAC switchgear room flood propagates to the room for the other train of safety-related 4160 VAC switchgear (115 percent increase in internal flooding CDF)

In the first case above, most of the impact comes from the failure of operator actions in the main control room (MCR). Since the baseline HEPs for most of these human failure events already assume a high stress level, the increased stress associated with a flooding event is not expected to have a significant impact on the HEPs. A follow-up sensitivity analysis showed that if operator actions in the MCR are excluded, there is virtually no increase in internal flooding CDF.

In the second case above, it is clear that the total internal flooding CDF is very sensitive to the flooding initiating event frequencies. In fact, using the 5th percentile lower bound estimate for all flooding initiating event frequencies results in the greatest decrease in internal flooding CDF of all of the sensitivity analyses performed. As such, estimation of flooding initiating event frequencies is a prime candidate for future research.

In the last case above, it is clear that a flood that can propagate and damage both trains of safety-related 4160 VAC switchgear will have a severe impact on plant safety (in the sensitivity case, this situation was assumed to lead directly to core damage). However, as discussed in Section 4.5.6, the likelihood of such an occurrence is extremely low.

80 Table 4.12 Summary of Sensitivity Cases Results Description Base CDF (per ry)

Sensitivity CDF (per ry)

Percent Change 1

Internal flooding initiating event frequencies Use 95th percentile frequencies Use 5th percentile frequencies 7.9E-07 7.9E-07 2.2E-06 1.0E-07

+178%

-87%

2 Human error probabilities for maintenance-induced flooding scenarios Increased HEPs (x10)

Decreased HEPs (x10) 7.9E-07 7.9E-07 8.0E-07 7.9E-07

+1%

3 Human error probabilities for failures unrelated to flood mitigation All HEPs increased (x10)

Ex-MCR HEPs increased (x10) 7.9E-07 7.9E-07 2.4E-06 7.9E-07

+204%

4 Crediting improved RCP shutdown seals 7.9E-07 6.4E-07

-19%

5 Propagation factor for flooding scenario 1-FLI-CB_A48 7.9E-07 9.2E-07

+16%

6 Potential flood propagation impacting both safety-related 4160 VAC switchgears 7.9E-07 1.7E-06

+115%

7 Application of spray direction factor 7.9E-07 5.0E-07

-37%

8 Credit for manual action to start service water cooling tower fans 7.9E-07 6.4E-07

-19%

9 Impact of consequential loss of offsite power on internal flooding scenarios 7.9E-07 5.9E-07

-25%

4.6.

Comparison of Results to Similar Plant The NRC IFPRA results were compared to the flooding results from the SPAR model and IPE11F12 of a similar four-loop PWR plant. The comparison plants internal events and internal flooding PRA results were reviewed. The internal flooding scenarios contribute approximately 0.5 percent of the total internal events and internal flooding CDF for the comparison plant. The top 100 cut sets from the comparison plants internal flooding scenarios were reviewed to identify similarities and differences compared to the NRC IFPRA.

Notable similarities between the NRC IFPRA and the comparison plant internal flooding results are observed:

Both internal flooding PRAs have significant contributions from service water flood sources.

These flood scenarios limit the availability of service water that is used to support the mitigating systems needed to respond to the plant transient.

12 The Standardized Plant Analysis Risk (SPAR) models are SAPHIRE-based nuclear power plant PRA models primary used by the NRC to support risk assessments performed as part of the Significance Determination Process (SDP), Accident Sequence Precursor (ASP) Program, Management Directive (MD) 8.3, Incident Investigation Program, and evaluation of notices of enforcement discretion (NOEDs). The individual plant evaluation (IPE) models are nuclear power plant PRA models for internal events and internal floods prepared by licensees in response to Generic Letter (GL) 88-20, Individual Plant Examination for Severe Accident Vulnerabilities - 10 CFR 50.54(f), dated November, 23, 1988.

81 Both internal flooding PRAs have significant contributions from accident sequences that initiate with a flood event and subsequent failure(s) resulting in RCP seal LOCA.

The comparison plants internal flooding CDF is similar to that of NRC IFPRA. The comparison plants internal flooding CDF is 3.4x10-7 per reactor-critical-year compared to the NRC IFPRA value of 7.9x10-7 per reactor-critical-year. While both plants have similar overall internal flooding results and both have significant contributions form service water pipe failures, the contributions due to other types of flooding scenarios are different. The following differences are noted:

Other significant internal flooding contributors to the NRC IFPRA are scenarios involving pipe failures in the main steam valve rooms resulting in spurious operation of an atmospheric relief valve. The comparison plant does not include any type of similar internal flooding scenario.

After the service water-related flooding scenarios, the next highest contributing scenarios in the comparison plants internal flooding PRA is a failure of ECCS-related piping in the auxiliary building resulting in unavailability of the RWST and other ECCS equipment. This is comparable to the NRC IFPRA flooding scenario 1-FLI-AB_D78_FP, which involves failure of RHR system piping in the auxiliary building. The biggest difference between the comparison plant scenario and the NRC IFPRA scenario is the initiating event frequency.

The NRC IFPRA has a significantly lower frequency for the similar scenario (3.6x10-7 per reactor-critical-year versus 2.7x10-3 per reactor-critical-year for the comparison plant).

However, this comparison does not evaluate the many factors that can influence the initiating event frequency estimates (e.g., size of the flood source piping system or plant-specific operating experience). This level of detail was beyond the scope of this comparison of model results.

Both the NRC IFPRA and the comparison plant modeled turbine building internal flooding scenarios. The CDF results for turbine building flooding is similar for both models. In both models the turbine building floods are characterized by high initiating event frequencies and low conditional core damage probabilities. This results in a modest contribution to overall internal flooding CDF. The modeled impacts of the flooding scenario are also similar in both models. The turbine building floods result in unavailability of the main condenser and loss of instrument air.

The NRC IFPRA appears to include a broader range of internal flooding scenarios with different flooding sources, locations and impacts. The NRC IFPRA includes 23 modeled internal flooding scenarios and many other scenarios that were assessed quantitatively and screened. The comparison plants internal flooding PRA includes eight modeled flood scenarios with five of the eight involving floods related to service water pipe failures.

The comparison plants initiating event frequencies for similar types of flooding scenarios are greater than those for the NRC IFPRA. The comparison plants significant cut sets include flooding scenarios with frequencies of 2.7x10-3 per year and 1.0x10-3 per year.

Similar scenarios in the NRC IFPRA model have frequencies of less than 3x10-4 per year.

The differences in the internal flooding PRA results for the comparison plant and NRC IFPRA results appear to be reasonable given the differences in the models scopes. The two models include service water failure flooding and turbine building flooding scenarios that show similar impacts and similar CDF results. Both models have significant contributions from RCP seal failures that occur after the flooding initiating event. The two models have differences in the other types of internal flooding scenarios that are modeled. The differences in screening of flood areas and flood sources, initiating event frequencies, and modeling of flooding impacts

82 may be driven by many factors, including: locations and lengths of piping at the plants, equipment locations, physical layout of plant rooms, and flood mitigation features (i.e., curbs, drains, doors, etc.). Confirmation of these plant differences is beyond the scope of the NRC IFPRA study.

4.7. Key Insights This section discusses the key insights obtained from the L3PRA Level 1 model for internal flooding (i.e., the IFPRA model).

The total internal flooding CDF results show that internal flooding scenarios are not a dominant risk contributor for the reference plant, compared to other internal and external hazards. The total internal flooding CDF is approximately 1 percent of the internal events CDF (as reported in Ref. IF-16). Both failure of RCP seal cooling and consequential LOOP events contribute significantly to the dominant internal flooding accident sequences. Other important contributors to the internal flooding results are service water failures, which act as a flooding source and also impact the availability of accident mitigating equipment to respond to the event. Additional key insights are discussed below. Note that many of these insights are not solely relevant to this project, but likely affect internal flooding PRAs at other plants.

Consequential Loss of Offsite Power A consequential LOOP can occur in response to a reactor trip or other plant transients as electrical loads are transferred to power sources supplied from the offsite grid. The IFPRA model adopts the same consequential LOOP modeling approach as described in the internal events Level 1 PRA model report (Ref. IF-16). The basic event representing consequential LOOP following a reactor trip (basic event 1-OEP-VCF-LP-CLOPT) contributes approximately 28 percent to the total internal flooding CDF. As discussed in the sensitivity analysis in Section 4.5.9, the consequential LOOP modeling may overestimate the risk for flooding scenarios that would not result in an immediate plant trip. If operators initiate a controlled plant shutdown, then this would not cause the same stresses on the electrical system as a reactor trip or other plant transients. Assuming a reactor trip occurs for these flooding scenarios is a modeling simplification. The same simplifying assumption is used in the reference plants internal flooding PRA. While most PRAs rely on some simplifying assumptions, as the impacts of these assumptions become significant, it is important to reevaluate the assumptions and strive for realism in the modeling.

Reactor Coolant Pump Seal Failure Failures that result in loss of RCP seal cooling and lead to a small LOCA are significant contributors to the internal flooding CDF. However, not reflected in this model are the improved passive shutdown RCP seals at the reference plant. The inclusion of these seals can have a significant effect on the model results, decreasing the total internal flooding CDF by approximately 19 percent. The impacts of the improved RCP seals are discussed in the sensitivity case in Section 4.5.4.

Service Water Failures as a Flood Source Several of the significant internal flooding scenarios involve failures of service water piping. The service water failures have important contributions both as a flood initiator and impacting accident mitigation capabilities. Several safety significant systems (e.g., ECCS and emergency diesel generators) depend on service water for successful operation. Also, the evaluation in EPRIs report on pipe rupture frequencies (Ref. IF-9) suggests that service water pipe failure rates tend to be relatively high compared to those of other piping systems.

83 Internal Flooding Initiating Event Frequencies and Uncertainty The internal flood initiating event frequency estimates are a significant factor in assessing the uncertainty of the internal flooding CDF results. Section 4.5.1 discusses sensitivity cases performed to evaluate the impacts of initiating event frequency uncertainty. The approach for estimating internal flooding initiating event frequencies is discussed in Appendix A.

The frequency analysis is based on the approach described in EPRIs pipe rupture frequency report (Ref. IF-9). That report provides a systematic approach for estimating flooding frequencies based on system type, pipe size, failure mechanism, and other attributes. The report also provides a thorough assessment of industry-wide pipe failure and flooding operating experience; however, this operating experience is limited to the time frame available when the report was published. At the time of this study, Revision 3 of the EPRI report was available.

Revision 3 evaluates piping operating experience through 2008 for most systems, though some systems include data through portions of years 2009 and 2010. For circulating water expansion joints, an important flooding source, the data are limited to 2004 and earlier. Revision 3 of the EPRI report shows comparisons of the failure rates for different piping systems that were calculated in the 2010 study and those calculated in an earlier revision in 2006. Many significant flooding sources show increased failure rates over this time frame. An ongoing piping data collection and analysis arrangement would be helpful to ensure that the most relevant data are being used in initiating event frequency analysis. This ongoing analysis of piping failure data is important, not only for the industry-wide results that are reported by EPRI, but also for incorporating plant-specific experience into the failure rate and flood frequency estimates.

There are many modeling choices in the initiating event frequency analysis that can introduce uncertainty. The evaluation of plant-specific data can have important impacts on the frequency estimates. Several modeling questions can arise. Are there consistent approaches for how the plant-specific data are defined as pipe failures and flood occurrences? Are there consistent approaches for evaluating pipe size categories, effective break sizes, and the total feet of system piping at the plant? How is uncertainty in these choices being incorporated into the frequency estimates? Other areas of uncertainty can include the choices of prior data to use for plant-specific updates and the statistical models used to represent the frequency distributions.

Overall there are several modeling choices that introduce uncertainty in the frequency estimates. Although the EPRI report lays out a systematic framework for evaluating flooding frequencies, a plant-specific application of that framework involves many modeling choices that contribute to uncertainty.

Impact of Intiating Event Frequency Analysis on Internal Flooding Results As discussed above, the initating event frequency analysis is an important part of the IFPRA model. An example of the impact that the initiating event frequency analysis has on the model results can be seen by the importance of the flooding scenarios involving spray events in the main steam valve rooms (scenarios 1-FLI-AB_108_SP1, 1-FLI-AB_108_SP2, 1-FLI-CB_122_SP, and 1-FLI-CB_123_SP). These scenarios have significant contributions to the overall internal flooding CDF.

These spray scenarios have relatively large initiating event frequencies compared to other internal flooding scenarios. Three key areas are identified that influence the initiating event frequency analysis for these scenarios:

The scenarios model spray events, which are associated with small break sizes and small break flow rates. These scenarios generally have higher failure rates compared to larger flood events.

84 In some internal flooding analyses, a spray direction factor is applied to reduce spray frequency. This approach assumes that some sprays will be directed away from susceptible equipment and cause no damage. For the spray scenarios modeled in the NRC IFPRA, there was not sufficient information available to support the application of a spray direction factor. However, the impact of a spray direction factor is assessed in a sensitivity study (Section 4.5.7).

Plant-specific operating experience is incorporated, which results in a failure rate that is higher than the generic failure rate reported in the EPRI pipe rupture frequency report (Ref. IF-9). A summary of the approach for incorporating plant-specific experience is provided in Appendix A.

These factors combine to result in relatively large initiating event frequencies for the main steam valve room spray scenarios.

Electrical Power Distribution Equipment in Flooding Scenarios Safety-related electrical distribution equipment (e.g., switchgears, breakers, and motor control centers) are often important risk contributors in PRA models. Protecting this equipment from flooding impacts is an important aspect of internal flooding risk. This study identifies five internal flooding scenarios where safety-related electrical equipment is impact by flooding (scenarios 1-FLI-CB_A48, 1-FLI-AB_D74_FP, 1-FLI-AB_D78_FP, 1-FLI-DGB_101_LF, and 1-FLI-DGB_103_LF). The risk significance of these scenarios is relatively low compared to other internal flooding and internal event accident scenarios. These results suggest the flood mitigation features at the reference plant are generally effective in limiting the flooding impacts to electrical equipment. However, the impacts could be more significant if more pressimistic assumptions are made regarding flood propagation. These alternative assumptions are explored in the sensitivity cases discussed in Section 4.5.5 and Section 4.5.6. Also, the internal flooding risk associated with impacting electrical equipment can be significant at other plants, if good flood mititgation features are not present. Examples of good flood mitigation features include (1) separation of flood sources from risk-significant equipment; (2) separation of redundant trains; and (3) the use of curbs and drains, and mounting equipment on raised pedestals, to limit impacts from flood propagation.

Turbine Building Flooding The turbine building can be an important contributor to internal flooding risk. The flood sources located in this area (e.g., circulating water system, main steam lines, feedwater lines) have the potential to produce very large floods, and there are many flood sources in the area. One of the highest flood initiating event frequencies in this study is associated with a turbine building flood scenario (1-FLI-TB_500_LF). Despite the high initiating event frequency, the CDF results of the turbine building flood scenarios are relatively low compared to other internal flooding and internal event accident scenarios. The CCDP values for turbine building flood scenarios are lower than the CCDP values for other internal flooding scenarios, as is shown in Table 4.1. Yet, the turbine building flood sources may be more important for internal flooding PRAs for other plants. The impacts on equipment that is located in the turbine building, or equipment that can be impacted by flood propagation, will depend on the specific plant design and layout.

85

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U.S. Nuclear Regulatory Commission, Final Safety Evaluation by the Office of Nuclear Reactor Regulation PWROG-14001-P, Revision 1, PRA Model for the Generation III Westinghouse Shut-Down Seal, August 23, 2017, ADAMS Accession No. ML17200C876.

86 IF-16 U.S. Nuclear Regulatory Commission, Level 3 PRA Project, Volume 3a: Reactor, At-Power, Level 1 PRA for Internal Events, April 2022, ADAMS Accession No. ML22067A211.

A-1 APPENDIX A:

FLOOD INITIATING EVENT FREQUENCY ANALYSIS A.1. Initiating Event Frequency Analysis Approach The initiating event frequency analysis was based on the approach described in EPRIs Pipe Rupture Frequencies for Internal Flooding PRAs, Revision 3 (IF-9). The initiating event frequency, f, for a given pipe break flooding scenario is given by the following expression,

= x x (l)

[1]

where, l is the length of pipe (in feet) located in the flood area.

pipe is the failure rate of the pipe per feet-critical reactor year.

Ppipe(RlF) is the conditional rupture probability given pipe failure.

Similarly, the initiating event frequency can be expressed in terms of component failures that may be relevant to a flood scenario (e.g., failure of rubber expansion joints.)

= x x (l)

[2]

where, n is the number of components located in the flood area.

component is the failure rate per component-critical reactor year.

Pcomponent(RlF) is the conditional rupture probability given component failure.

The EPRI report provides generic failure data for different types of plant systems. The data were further categorized in terms of the severity of pipe failure (e.g., wall thinning, pinhole leak, leak, major structural failure) and pipe size. The category definitions may vary depending on the type of system. The generic data and failure rates in the report were used to develop prior distributions for the pipe (or component) failure rates and conditional rupture probabilities.

The prior distributions were updated with plant-specific data. The plant-specific data considered for the NRC IFPRA cover the period from January 1, 1990 through December 31, 2012. The plant-specific flooding date are shown in Table A.1-1. The plant-specific data were taken from the following sources:

Plant-specific operating experience submitted to the CODAP international database (Ref. IF-

10) covering data collected and analyzed through December 2012.

Search of plant-specific Licensee Event Reports (LERs) for events including leak, leakage, or flood in the title through December 2012.

INLs NROD site, which includes plant-specific EPIX records through December 2012 (Ref.

IF-11).

A-2 Table A.1-1 Plant-Specific Flooding Events System Nominal Pipe Size /

Diameter (in.)

Non Through Wall Spray

( 100 gpm)

Flooding (100-2000 gpm)

Major Flooding (>

2000 gpm NSCW NPS 2 0

0 0

0 2 < NPS 4 5

1 0

0 4 < NPS 10 0

0 0

0 NPS > 10 0

0 0

0 Fire protection NPS 4 0

1 0

0 4 < NPS 6 0

0 0

0 NPS > 6 0

0 0

0 Circulating water pipe NPS 24 0

0 0

0 Circulating water expansion joints 24 0

0 0

0 Component cooling water; applicable to other closed, low temp., low-pressure water systems NPS 2 0

0 0

0 2 < NPS 6 0

0 0

0 NPS > 6 0

1 0

0 RWST piping (includes CVCS, SI, CS, and RHR piping outside containment) 2 < NPS 6 0

1 0

0 6 < NPS 10 0

0 0

0 NPS > 10 0

0 0

0 (PWR) Condensate and feedwater NPS 2 2

0 0

0 2 < NPS 10 3

1 0

0 NPS > 10 0

0 0

0 Another input into the plant-specific update of flood data was the plants system pipe length for the various pipe size categories defined in Table A.1-1 above. For this study, generic pipe lengths are used based on the generic system sizes given in References IF-8 and IF-9. The system pipe lengths are given in Table A.1-2. A lognormal distribution with an error factor of 3 was assumed for the system pipe lengths to account for uncertainty in the generic estimates.

Table A.1-2 Generic Pipe Lengths Used for Reference Plant Systems System Nominal Pipe Size /

Diameter (in.)

5th percentile Median pipe length Mean pipe length 95th percentile NSCW NPS 2 311 933 1166 2799 2 < NPS 4 138 414 517 1242 4 < NPS 10 451 1354 1692 4062 NPS > 10 2103 6307 7883 18919 Fire protection NPS 4 1004 3012 3765 9035 4 < NPS 6 640 1920 2400 5759 NPS > 6 463 1390 1737 4170 Circulating water pipe NPS 24 333 1000 1250 3000 Circulating water expansion joints 24 12 expansion joints

A-3 System Nominal Pipe Size /

Diameter (in.)

5th percentile Median pipe length Mean pipe length 95th percentile Component cooling water; applicable to other closed, low temp., low-pressure water systems NPS 2 not estimated(1) 2 < NPS 6 366 1099 1374 3297 NPS > 6 2844 8532 10664 25593 RWST piping (includes CVCS, SI, CS, and RHR piping outside containment) 2 < NPS 6 1340 4020 5024 12059 6 < NPS 10 4467 13400 16748 40196 NPS > 10 3127 9380 11723 28137 (PWR) Condensate and feedwater NPS 2 not estimated(2) 2 < NPS 10 1520 4560(3) 5699 13679 NPS > 10 4679 14037 17544 42107 Notes:

(1) Data for 2 < NPS 6 are used as a surrogate for CCW pipe sizes 2.

(2) This pipe size category is not estimated and does not contribute to frequency estimates in this study.

(3) The most recent available estimate for pipe lengths for PWR feedwater and condensate systems was obtained from Table 5-3 of IF-9. The median length for pipes > 10 in. diameter is given as 14,037 ft. This length is also estimated to be the upper bound for pipe sizes between 2 and 10 in. An estimated length for all feedwater and condensate pipes > 2 in. is given as 18,597 ft. in a previous revision (IF-8, Table 4-22). For this study the median length for sizes between 2 and 10 in. is given by 18,597 ft -

14,037 ft = 4,560 ft. Assuming an error factor of 3 gives an upper bound for this size range that is similar to the upper bound indicated in Table 5-3 of IF-9.

Analyst judgment was exercised to determine the appropriate statistical models to use for the initiating event frequencies in the NRC IFPRA. The NRCs Handbook of Parameter Estimation for Probabilistic Risk Assessment, NUREG/CR-6823 (IF-12), was referenced for guidance in selecting distributions and performing Bayesian updates. Failure rates were assumed to have a gamma uncertainty distribution. The failure rate data were assumed to be exponential. A Poisson likelihood function was used. A constrained noninformative prior distribution was used with the prior mean taken from the generic estimates in the EPRI report (IF-9). Conditional rupture probabilities were assumed to have a beta uncertainty distribution. The data were assumed to be binomially distributed. A beta prior distribution was used with parameters selected based on analyst judgment.

A Gibbs sampling process was used to generate the combined initiating event frequency posterior distributions. The sampling was performed using the OpenBUGS version 3.2.2 software. For each frequency estimate, 10,000 samples were run. Sampling simulations were performed for two separate chains. Trace history plots of the two sampling chains were reviewed for evidence of parameter convergence. The sampling process produces an empirical posterior distribution. The resulting empirical distribution was expected to resemble a gamma distribution based on the choice of prior distribution for the failure rates. Also, gamma distributions are routinely used to model initiating event frequency uncertainty distributions.

Gamma function parameters were fit to the empirical distribution using a maximum likelihood estimate approach. The fit was performed using the R statistical computing environment (64-bit version 2.15.2) with the MASS function package. The fitted gamma distribution parameters were used to specify the mean initiating event frequencies and shape parameters in the NRC IFPRA model.

A-4 The plant-specific reactor years of operation were estimated for the operating period from January 1, 1990 to December 31, 2012, based on a capacity factor of 0.9078 to estimate critical years for the NRC IFPRA. This yielded a combined estimate of 41.76 critical years for units 1 and 2. If an estimate of frequency per calendar year was desired, then the capacity factor can be used to scale the frequency estimate. Assume that F is a random variable representing the initiating event frequency that has a gamma distribution and is estimated based on number of critical reactor years. The distribution is characterized by two parameters: the mean value and the shape parameter,. The capacity factor, c, can be applied to scale the initiating event frequency distribution as shown below. The mean value is scaled by c and the shape parameter is unchanged.

F ~ gamma(,)

mean(F) = /

Applying a capacity factor, c, yields:

cF ~ gamma(,/c) mean(cF) = c/ = c x mean(F)

Two of the modeled internal flooding scenarios (scenario TB_500_HI1 and TB_500_HI2) use initiating event frequencies that were based on a combination of human error probabilities using the assumptions of the reference plants internal flooding PRA model. For these scenarios the uncertainty distribution parameters were selected based on the authors judgment and common practices used for HEP uncertainty analysis. See A.9 for additional details.

The results of the NRC IFPRA initiating event frequency analysis are shown in Table A.1-3.

Table A.1-3 Internal Flooding Scenario Initiating Event Frequencies Scenario Name Mean IE frequency per reactor-critical-year Shape parameter or error factor 5th percentile Median value 95th percentile 1-FLI-AB_108_SP1 2.8E-04 2.8 7.3E-05 2.5E-04 6.0E-04 1-FLI-AB_108_SP2 2.8E-04 2.8 7.3E-05 2.5E-04 6.0E-04 1-FLI-AB_A20 2.7E-04 2.6 6.3E-05 2.4E-04 5.9E-04 1-FLI-AB_A20_FP 2.3E-05 2.3 4.6E-06 1.9E-05 5.2E-05 1-FLI-AB_B08_LF 7.7E-06 0.38 5.3E-09 2.5E-06 3.2E-05 1-FLI-AB_B24_LF2 3.5E-06 0.35 1.5E-09 1.1E-06 1.5E-05 1-FLI-AB_B50_JI 3.4E-06 0.67 4.8E-08 1.9E-06 1.1E-05 1-FLI-AB_C113_LF1 2.2E-04 0.95 9.9E-06 1.5E-04 6.9E-04 1-FLI-AB_C115_LF 1.3E-04 0.89 4.7E-06 8.7E-05 4.2E-04 1-FLI-AB_C118_LF 7.5E-06 0.38 4.7E-09 2.6E-06 3.2E-05 1-FLI-AB_C120_LF 1.8E-04 0.93 7.6E-06 1.2E-04 5.5E-04 1-FLI-AB_D74_FP 8.6E-06 0.43 1.4E-08 3.4E-06 3.5E-05 1-FLI-AB_D78_FP 3.6E-07 0.35 1.7E-10 1.1E-07 1.6E-06 1-FLI-CB_122_SP 2.8E-04 2.8 7.1E-05 2.5E-04 5.9E-04 1-FLI-CB_123_SP 2.8E-04 2.8 7.1E-05 2.5E-04 5.9E-04 1-FLI-CB_A48 9.2E-05 0.98 4.8E-06 6.4E-05 2.8E-04 1-FLI-CB_A60 5.2E-05 0.97 2.3E-06 3.5E-05 1.6E-04 1-FLI-DGB_101_LF 7.3E-06 0.37 4.1E-09 2.2E-06 3.2E-05

A-5 Table A.1-3 Internal Flooding Scenario Initiating Event Frequencies Scenario Name Mean IE frequency per reactor-critical-year Shape parameter or error factor 5th percentile Median value 95th percentile 1-FLI-DGB_103_LF 7.3E-06 0.37 4.1E-09 2.2E-06 3.2E-05 1-FLI-TB_500_HI1 9.4E-05 12.5 2.3E-06 2.9E-05 3.6E-04 1-FLI-TB_500_HI2 9.4E-05 12.5 2.3E-06 2.9E-05 3.6E-04 1-FLI-TB_500_LF 2.2E-03 0.75 4.9E-05 1.3E-03 7.2E-03 1-FLI-TB_500_LF-CDS 6.3E-04 2.3 1.4E-04 5.5E-04 1.4E-03 A.2. Initiating Event Frequencies for Scenarios 1-FLI-CB_122_SP and 1-FLI-CB_123_SP Both rooms CB_122 and CB_123 contain the same contributing flood source pipes and the same length of pipe. The only piping in these rooms that contributes to the flooding estimate was a 10-inch diameter FW pipe with a length of 75 feet. Steam lines located in these rooms were not considered to contribute to the spray in this flooding scenario. Impacts due to main steam line breaks were modeled as separate initiating events. The flood sources used to estimate the initiating event frequencies for scenarios 1-FLI-CB_122_SP and 1-FLI-CB_123_SP are summarized in Table A.2-1. The initiating event frequency that was quantified in this section was applied to both rooms.

Table A.2-1 Flood Sources 1-FLI-CB_122_SP and 1-FLI-CB_123_SP Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet)

CB 122 CB_122_SP FW 10 75 CB 123 CB_123_SP FW 10 75 The conditional rupture probability was estimated from data provided in Table 5-1 of Ref. IF-9.

The data from the period 1988-2008 were selected for this estimate because the period aligns closely to the reference plants operating history, and it was the most recent data available for feedwater and condensate piping. A rupture in this flooding scenario can include spray events resulting from effective break sizes that were less than the nominal pipe size of 10 in. The conditional rupture probability includes both rupture events and leak events as both types of events were deemed relevant for the sprays considered in this scenario. The parameters used to estimate the conditional rupture probability for scenarios 1-FLI-CB_122_SP and 1-FLI-CB_123_SP are summarized in Table A.2-2.

Table A.2-2 Conditional Rupture Probability Parameters 1-FLI-CB_122_SP and 1-FLI-CB_123_SP Beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst.

Evidence ruptures failures 24 57 IF-9 Table 5-1 Data for FWC 2 < NPS 10, 1988-2008, includes leaks and ruptures

A-6 The failure rate for feedwater and condensate piping was estimated in IF-9 in Table 5-6 for pipe sizes 10 in. The mean value of the failure rate prior distribution was assigned the value 3.16x10-6, which was given for pipe sizes 10 in. A constrained noninformative gamma distribution, as defined in IF-12, is used as the prior. The estimated feet of condensate and feedwater piping was taken from Table A.1-2 above. A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above.

A review of reference plant operating experience identified four failures that were relevant to this scenario. Ultrasonic thickness measurements were performed on selected feedwater and condensate components in 2000. Twenty-three large-bore components were identified to have wall thickness measurements that indicated possible wear due to flow-accelerated corrosion.

Based on these measurements and measurements during prior outages, the wall thickness degradations in three components were determined to be significant enough to require replacement. All other measured large-bore components were determined to be acceptable for continued service. The three components that required replacement included:

A portion of heater drain pump 1B discharge piping FW heater 6A shell wall Additional portion of heater drain pump 1B discharge piping These three wall thickness degradations are considered failures for this analysis. The parameters used to estimate the failure rate for scenarios 1-FLI-CB_122_SP and 1-FLI-CB_123_SP are summarized in Table A.2-3.

Table A.2-3 Failure Rate Parameters 1-FLI-CB_122_SP and 1-FLI-CB_123_SP Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 158228 IF-9 Table 5-6 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value Evidence failures feet - critical years 4

1.904E+05 Tables A.1-1 and A.1-2, CODAP database 4,560 ft of FW/Cond piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenarios 1-FLI-CB_122_SP and 1-FLI-CB_123_SP is shown in Table A.2-4.

Table A.2-4 Initiating Event Frequency Estimate for 1-FLI-CB_122_SP and 1-FLI-CB_123_SP Mean value Shape parameter 5th percentile Median value 95th percentile 2.78E-04 2.82 7.12E-05 2.47E-04 5.91E-04 A.3. Initiating Event Frequencies for Scenarios 1-FLI-AB_108_SP1 and 1-FLI-AB_108_SP2 For room AB_108 due to a wall partition spray can only impact the SG1 or SG4 valves. It is assumed that half of the time the source pipe rupture will result in spray scenario 1 (impacting the SG1 valves) and the other half will result in spray scenario 2 (impacting the SG4 valves),

that is, the initiating event frequency for each scenario is one-half of the total pipe rupture

A-7 frequency. Steam lines located in these rooms were not considered to contribute to the spray in this flooding scenario. Impacts due to main steam line breaks were modeled as separate initiating events. The flood sources used to estimate the initiating event frequencies for scenarios 1-FLI-AB_108_SP1 and 1-FLI-AB_108_SP2 are summarized in Table A.3-1. The initiating event frequency that is quantified in this section was applied to both rooms.

Table A.3-1 Flood Sources 1-FLI-AB_108_SP Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet)

AB 108 AB_108_SP ACCW 10 50 ACCW 8

20 FW 10 150 The conditional rupture probability for feedwater and condensate piping was estimated from data provided in Table 5-1 of IF-9. The data from the period 1988-2008 were selected for this estimate because the period aligns closely to the reference plants operating history, and it is the most recent data available for feedwater and condensate piping. The data for feedwater and condensate nominal pipe sizes between 2 and 10 in. were used. The conditional rupture probability for auxiliary CCW piping was estimated from data provided in Table 4-2 of EPRIs flooding frequency report (IF-9). The failure data in EPRIs flooding frequency report span the period from January 1970 through March 2010. Data for all CCW pipe sizes greater than 6 in.

were selected. The conditional rupture probability includes both rupture events and leak events as both types of events were deemed relevant for the sprays considered in this scenario. The parameters used to estimate the conditional rupture probability for scenarios 1-FLI-AB_108_SP1 and 1-FLI-AB_108_SP2 are summarized in Table A.3-2.

Table A.3-2 Conditional Rupture Probability Parameters 1-FLI-AB_108_SP FW Beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst.

FW Evidence ruptures failures 24 57 IF-9 Table 5-1 Data for FWC 2 < NPS 10, 1988-2008, includes leaks and ruptures ACCW beta prior distribution alpha prior beta prior Reference Notes 1

99 Based on judgment of the analyst.

ACCW Evidence ruptures failures 0

7 IF-9 Table 4-2 Data for all CCW pipe sizes > 6",

1970-2010.

The failure rate for feedwater and condensate piping was estimated in IF-9 in Table 5-6 for pipe sizes 10 in. The failure rate for CCW piping was estimated in IF-9 in Table 4-7 for nominal pipe size of 24 in., which was consistent with the > 6 in. size category. For both systems a constrained noninformative gamma distribution, as defined in IF-12, was used as the prior. The estimated feet of piping for condensate and feedwater and CCW systems were taken from Table A.1-2 above. A lognormal distribution with an error factor of 3 was assumed for the feet of

A-8 piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above.

A review of reference plant operating experience has identified four failures that were relevant to this scenario. Ultrasonic thickness measurements were performed on selected feedwater and condensate components in 2000. Twenty-three large-bore components were identified to have wall thickness measurements that indicated possible wear due to flow-accelerated corrosion.

Based on these measurements and measurements during prior outages, the wall thickness degradations in three components were determined to be significant enough to require replacement. All other measured large-bore components were determined to be acceptable for continued service. The three components that required replacement included:

A portion of heater drain pump 1B discharge piping FW heater 6A shell wall Additional portion of heater drain pump 1B discharge piping These three wall thickness degradations are considered failures for this analysis. In addition, one CCW failure is identified by the reference plant. The parameters used to estimate the failure rate for scenarios 1-FLI-AB_108_SP1 and 1-FLI-AB_108_SP2 are summarized in Table A.3-3.

Table A.3-3 Failure Rate Parameters 1-FLI-AB_108_SP FW Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 158228 IF-9 Table 5-6 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value FW Evidence failures feet - critical years 4

1.904E+05 Tables A.1-1 and A.1-2, CODAP database 4,560 ft of FW/Cond piping, 41.76 critical years CCW Gamma CNI prior dist.

alpha prior beta prior Reference Notes 0.5 694444 Ref. IF-9 Table 4-7 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value CCW Evidence failures feet - critical years 1

3.563E+05 Reference plant identified 8,532 ft of CCW piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenarios 1-FLI-AB_108_SP1 and 1-FLI-AB_108_SP2 is shown in Table A.3-4.

Table A.3-4 Initiating Event Frequency Estimate for 1-FLI-AB_108_SP Mean value Shape parameter 5th percentile Median value 95th percentile 2.80E-04 2.83 7.34E-05 2.45E-04 5.95E-04 A.4. Initiating Event Frequency for Scenario 1-FLI-AB_A20 and 1-FLI-AB_A20_FP Scenario 1-FLI-AB_A20 subsumes two reference plant scenarios that impact the feedwater control and regulating valves located in room A20. The flood sources in room A20 can impact

A-9 the valves by spray or local flooding, but only spray was modeled in scenario 1-FLI-AB_A20.

The flood sources in room A06 can propagate to room A20. Sprays from sources in room A06 do not contribute to the propagation to room A20 and were not applicable to this scenario.

Scenario 1-FLI-AB_A20_FP subsumes two reference plant scenarios related to local flooding from room A20 sources impacting equipment in room A20 and propagating to rooms A11 and A12.

Steam lines located in these rooms were not considered to contribute to the flooding scenario.

Impacts due to main steam line breaks being modeled as separate initiating events. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-AB_A20 are summarized in Table A.4-1.

Table A.4-1 Flood Sources 1-FLI-AB_ A20 Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet)

AB A20 AB_A20 FW 8

20 FW 20 40 AB A06 AB_A06_FP Condensate 4

100 Condensate 3

30 Cond Sample Cooler 3

30 Cond Sample Cooler 6

40 The conditional rupture probability for feedwater and condensate piping was estimated from data provided in Table 5-1 of IF-9. The data from the period 1988-2008 were selected for this estimate because the period aligns closely to the reference plants operating history, and it is the most recent data available for feedwater and condensate piping. For room A20 sources the 8-in. pipe uses feedwater and condensate pipe data in the 2 to 10 in. size category. The 20-in.

pipe uses data in the greater than 10 in. size category. The conditional rupture probabilities for room A20 sources were separated into sprays and local flooding. The data for leak events were relevant for sprays, and the data for rupture events were relevant for local flooding. For room A06 sources (pipe sizes between 3 and 6 in.), the data for nominal pipe sizes between 2 and 10 in. were used. The conditional rupture probability for room A06 sources includes only rupture events (sprays were not relevant for this room). The parameters used to estimate the conditional rupture probability for scenarios 1-FLI-AB_A20 and 1-FLI-AB_A20_FP are summarized in Table A.4-2.

Table A.4-2 Conditional Rupture Probability Parameters 1-FLI-AB_A20 and 1-FLI-AB_A20_FP Room A20 Beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst Room A20 Spray Evidence 2<NPS<=10 ruptures failures 18 57 IF-9 Table 5-1 Data for FWC 2 < NPS < 10, 1988-2008, includes leaks only

A-10 Room A20 LF Evidence 2<NPS<=10 ruptures failures 6

57 IF-9 Table 5-1 Data for FWC 2 < NPS < 10, 1988-2008, includes ruptures only Room A20 Beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst Room A20 Spray Evidence NPS > 10 ruptures failures 23 155 IF-9 Table 5-1 Data for all FWC pipe sizes > 10",

1988-2008, includes leaks only Room A20 LF Evidence NPS > 10 ruptures failures 6

155 IF-9 Table 5-1 Data for all FWC pipe sizes > 10",

1988-2008, includes ruptures only Room A06 beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst Room A06 Evidence ruptures failures 6

57 IF-9 Table 5-1 Data for FWC 2 < NPS < 10, 1988-2008 The failure rate for feedwater and condensate piping was estimated in IF-9 in Table 5-6 for pipe sizes 10 in. and in Table 5-7 for pipe sizes > 10 in. The mean value of the failure rate prior distribution was 3.16x10-6 for pipe sizes 10 in. and 5.72x10-6 for pipe sizes > 10 in. The estimated feet of piping for the feedwater and condensate systems for > 10 inch pipes was given in Table 5-3 of IF-9 as 14,037 ft. For pipe sizes from 2 in. to 10 in., Table 5-3 of IF-9 indicates that 14,037 ft was an upper bound. The median length for 2 in. to 10 in. pipes was estimated to be 4,560 ft, as described in Table A.1-2 above.

A review of reference plant operating experience identified four feedwater and condensate failures that are relevant to this scenario. The four failures are identified in Table A.1-1 above.

The parameters used to estimate the failure rates for scenarios 1-FLI-AB_A20 and 1-FLI-AB_A20_FP are summarized in Table A.4-3.

Table A.4-3 Failure Rate Parameters 1-FLI-AB_A20 and 1-FLI-AB_A20_FP Gamma CNI prior distribution NPS<=10 alpha prior beta prior Reference Notes 0.5 158228 IF-9 Table 5-6 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value Evidence NPS<=10 failures feet - critical years 4

1.904E+05 Tables A.1-1 and A.1-2, CODAP database 4560 ft of FW/Cond piping, 41.76 critical years Gamma CNI prior distribution NPS>10 alpha prior beta prior Reference Notes 0.5 87413 IF-9 Table 5-7 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value

A-11 Evidence NPS>10 failures feet - critical years 0

5.862E+05 Tables A.1-1 and A.1-2, IF-9 Table 5-3 14,037 ft of FW/Cond piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_A20 is shown in Table A.4-4.

Table A.4-4 Initiating Event Frequency Estimate for 1-FLI-AB_A20 Mean value Shape parameter 5th percentile Median value 95th percentile 2.71E-04 2.63 6.31E-05 2.38E-04 5.93E-04 The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_A20_FP is shown in Table A.4-5.

Table A.4-5 Initiating Event Frequency Estimate for 1-FLI-AB_A20_FP Mean value Shape parameter 5th percentile Median value 95th percentile 2.27E-05 2.27 4.59E-06 1.93E-05 5.16E-05 A.5. Initiating Event Frequency for Scenario 1-FLI-CB_A60 Scenario CB_A60 subsumes three reference plant scenarios that impact the atmospheric relief valve signal converters located in room A60. The flood sources in room A60 can impact the signal converters by spray or local flooding. The flood sources in room A59 can propagate to room A60. Sprays from sources in room A59 do not contribute to the propagation to room A60 and were not applicable to this scenario. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-CB_A60 are summarized in Table A.5-1.

Table A.5-1 Flood Sources 1-FLI-CB_ A60 Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet)

CB A59 CB_A59_FP Fire protection 4

100 CB A60 AB_A60 Fire protection 2

60 Utility water 1

40 The conditional rupture probability for fire protection piping was estimated from data provided in Table 3-43 of IF-9. The data for fire protection nominal pipe sizes less than or equal to 4 in.

were used. The data were based on service experience from 1970 through March 31, 2009. The conditional rupture probability estimate for room A59 sources includes only major structural failures. The conditional rupture probability for room A60 sources includes both major structural failures and leak events as both types of events were deemed relevant for the sprays considered in this room. The data for fire protection systems includes water hammer events.

The NRC IFPRA uses the service data and frequency estimates for the component cooling water system for other closed water systems with low temperature and pressure conditions, such as utility water. The data provided in Table 4-2 of IF-9 were used to estimate the conditional rupture probability for utility water piping. The estimate was based on data for pipe

A-12 diameters less than 2 in. The parameters used to estimate the conditional rupture probability for scenario 1-FLI-CB_A60 are summarized in Table A.5-2.

Table A.5-2 Conditional Rupture Probability Parameters 1-FLI-CB_ A60 Room A59 Beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst Room A59 Evidence ruptures failures 1

35 IF-9 Table 3-43 Data for NPS <= 4, only MSF events are considered ruptures Rm A60 FP beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst Rm A60 FP Evidence ruptures failures 6

35 IF-9 Table 3-43 Data for NPS <= 4, includes MSF and leak events Rm A60 UW beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst Rm A60 UW Evidence ruptures failures 1

49 IF-9 Table 4-2 Data for pipe dia. <= 2, includes MSF and leak events The failure rate for fire protection piping was estimated in IF-9 in Table 3-47 for nominal pipe size of 4 in. All pipe sizes were considered applicable for this scenario. The mean value of the failure rate prior distributions were assigned the value 1.23x10-5 for fire protection piping (4 in.).

The failure rate prior distribution for utility water piping uses the CCW failure rate reported in Table 4-6 of IF-9. The failure rate for the smallest nominal pipe size (6 in.) was used, 4.84x10-6.

The estimated feet of piping for fire protection piping was given in IF-9 Table 3-42. The feet of CCW piping reported in IF-9 Table 4-3 was used as a surrogate for utility water. The parameters used to estimate the failure rate for scenario 1-FLI-CB_A60 are summarized in Table A.5-3.

Table A.5-3 Failure Rate Parameters 1-FLI-CB_ A60 Rm A59 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 40650 IF-9 Tables 3-47 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value Rm A59 Evidence failures feet - critical years 0

1.26E+05 IF-9 Table 3-42 3012 ft of FP piping, 41.76 critical years Rm A60 FP Gamma CNI prior distribution alpha prior beta prior 0.5 40650 IF-9 Tables 3-47 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value

A-13 Table A.5-3 Failure Rate Parameters 1-FLI-CB_ A60 Rm A60 FP Evidence failures feet - critical years 0

1.26E+05 IF-9 Table 3-42 3,012 ft of FP piping, 41.76 critical years Rm A60 UW Gamma CNI prior distribution alpha prior beta prior 0.5 103306 IF-9 Table 4-6 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value Rm A60 UW Evidence failures feet - critical years 0

45894 IF-9 Table 4-3 1,099 ft of CCW was used as a surrogate estimate, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-CB_A60 is shown in Table A.5-4.

Table A.5-4 Initiating Event Frequency Estimate for 1-FLI-CB_A60 Mean value Shape parameter 5th percentile Median value 95th percentile 5.19E-05 0.971 2.33E-06 3.49E-05 1.55E-4 A.6. Initiating Event Frequency for Scenario 1-FLI-TB_500_LF and 1-FLI-TB_500_LF-CDS Scenario 1-FLI-TB_500_LF subsumes two reference plant scenarios that models impacts from local flooding. Sprays were not applicable to this scenario. The flood area contains 10 different flood sources. These can be condensed into six flood source categories. The two TPCW piping sources were grouped, and their failure was based on operating experience for service water systems with river water intake sources. The demineralized water source was a clean closed water system with low temperature and pressure conditions. The service data for component cooling water were used to estimate the flood frequency for demineralized water. The circulating water and fire protection sources were each estimated from generic and plant-specific data for those respective systems. The circulating water expansion joints were treated as a separate flood source. The failure rate for expansion joints is estimated in terms of component-critical years, rather than feet-critical years.

The condensate and heater drain piping was grouped as a single flood source category, and this category was addressed in a separate scenario, 1-FLI-TB_500_LF-CDS. All other flood sources in the area were included in scenario 1-FLI-TB_500_LF.

The flood sources used to estimate the initiating event frequency for scenarios 1-FLI-TB_500_LF and 1-FLI-TB_500_LF-CDS are summarized in Table A.6-1.

A-14 Table A.6-1 Flood Sources 1-FLI-TB_500_LF and 1-FLI-TB_500_LF-CDS Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or #

components TB Fire Zone 500 TB_500_LF Circulating water 72 1000 Condensate 24 250 Condensate 48 140 Condensate 10 350 Demin water 10 200 Fire protection 10 900 Heater drain 8

250 TPCW 14 500 TPCW 18 200 Circulating water expansion joints 72 12 The conditional rupture probability for all piping systems was estimated from data provided in IF-

9. Refer to Table A.6-2 for additional details on the data used for these estimates. The most recent revision of the EPRI internal flooding frequency report (IF-9) does not include an update for failure of expansion joints. The failure estimates were based on data provided in the first revision of the report (IF-8). The parameters used to estimate the conditional rupture probability for scenarios 1-FLI-TB_500_LF and 1-FLI-TB_500_LF-CDS are summarized in Table A.6-2.

Table A.6-2 Conditional Rupture Probability Parameters 1-FLI-TB_500_LF and 1-FLI-TB_500_LF-CDS CW Beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst CW Evidence ruptures failures 6

20 IF-9 Table 3-61 Includes all CW data (NPS>30) from 1970 through March 2010 Cond/HD beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst Cond/HD Evidence 2<NPS10 ruptures failures 6

57 IF-9 Table 5-1 Includes all FWC 2 < pipe size <= 10, 1988-2008 Cond/HD beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst Cond/HD ruptures failures

A-15 Table A.6-2 Conditional Rupture Probability Parameters 1-FLI-TB_500_LF and 1-FLI-TB_500_LF-CDS Evidence NPS > 10 6

155 IF-9 Table 5-1 Includes all FWC pipe sizes > 10, 1988-2008 Demin water beta prior distribution alpha prior beta prior Reference Notes 1

99 Based on judgment of the analyst Demin water Evidence ruptures failures 0

7 IF-9 Table 4-2 Data for CCW pipe sizes > 6 were used as a surrogate. 1970-2010 FP Beta prior distribution alpha prior beta prior Reference Notes 1

99 Based on judgment of the analyst FP Evidence ruptures failures 1

74 IF-9 Table 3-43 Includes data for FP NPS > 6 TPCW beta prior distribution alpha prior beta prior Reference Notes 1

99 Based on judgment of the analyst TPCW Evidence ruptures failures 0

74 IF-9 Table 3-5 Based on PWR operating experience for SW systems with river water intake.

Data for NPS > 10 was used.

Exp Joints beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst Exp Joints Evidence ruptures failures 3

36 IF-8 Table 4-12 Ruptures include all events resulting in leakage flow > 2000 gpm.

The piping failure rates are estimated using a prior distribution base on the generic mean value reported in Ref. IF-9. The prior is updated with plant-specific failure data. The plant-specific failures relevant to this flood area were obtained from the reference plant, the CODAP database (IF-10), and a reference-plant-specific Licensee Event Report that describes failures of NSCW pump discharge pipes that were relevant to the TPCW failure rate estimate.

The failure rate for expansion joints was taken from IF-8 Table A-35. The rate for sprays was used as the generic failure rate for expansion joints. The parameters used to estimate the failure rate for scenarios 1-FLI-TB_500_LF and 1-FLI-TB_500_LF-CDS are summarized in Table A.6-3.

A-16 Table A.6-3 Failure Rate Parameters 1-FLI-TB_ 500_LF and 1-FLI-TB_500_LF-CDS CW Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 25253 IF-9 Table 3-64 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value CW Evidence failures feet - critical years 0

41760 Reference plant data 1000 ft of CW piping is reference-plant-specific estimate, 41.76 critical years FWC 2-10 Gamma CNI prior distribution alpha prior beta prior 0.5 158228 IF-9 Table 5-6 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value Cond/HD Evidence 2<NPS10 failures feet - critical years 4

1.904E+05 Tables A.1-1 and A.1-2 4560 ft of FW/Cond piping, 41.76 critical years Cond >10 Gamma CNI prior distribution alpha prior beta prior 0.5 94877 IF-9 Table 5-7 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value Cond/HD Evidence NPS>10 failures feet - critical years 0

5.862E+05 Tables A.1-1 and A.1-2, IF-9 Table 5-3 14,037 ft of FW/Cond piping, 41.76 critical years Demin water Gamma CNI prior distribution alpha prior beta prior 0.5 103306 IF-9, Table 4-6 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value Demin water Evidence failures feet - critical years 1

3.563E+05 Reference plant data 8,532 ft of CCW was used as a surrogate estimate, 41.76 critical years FP Gamma CNI prior distribution alpha prior beta prior 0.5 8834 IF-9 Table 3-49 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value FP Evidence failures feet - critical years 0

5.8E+04 IF-9 Table 3-42, reference plant data 1,390 ft of FP piping for NPS>6, 41.76 critical years TPCW Gamma alpha prior beta prior

A-17 Table A.6-3 Failure Rate Parameters 1-FLI-TB_ 500_LF and 1-FLI-TB_500_LF-CDS CNI prior distribution 0.5 30675 IF-9 Table 3-9 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value TPCW Evidence failures feet - critical years 0

2.63E+05 IF-9 Table 3-2 6,037 ft of SW piping, 41.76 critical years Exp Joints Gamma CNI prior distribution alpha prior beta prior 0.5 3571 IF-8 Table A-35 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value Exp Joints Evidence failures feet - critical years 0

501 Reference plant data 12 expansion joints, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-TB_500_LF is shown in Table A.6-4.

Table A.6-4 Initiating Event Frequency Estimate for 1-FLI-TB_ 500_LF Mean value Shape parameter 5th percentile Median value 95th percentile 2.16E-03 7.49E-01 4.87E-05 1.28E-03 7.18E-03 The initiating event frequency estimate for internal flooding scenario 1-FLI-TB_500_LF-CDS is shown in Table A.6-5.

Table A.6-5 Initiating Event Frequency Estimate for 1-FLI-TB_ 500_LF-CDS Mean value Shape parameter 5th percentile Median value 95th percentile 6.32E-04 2.33 1.37E-04 5.48E-04 1.42E-03 A.7. Initiating Event Frequency for Scenario 1-FLI-AB_C113_LF1 Scenario 1-FLI-AB_C113_LF1 models impacts from local flooding. Sprays were not applicable to this scenario. The flood sources applicable to this scenario were the NSCW pipes located in the room. Other potential flood sources were located in the room, but those sources were addressed in other flooding scenarios and were not modeled here. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-AB_C113_LF1 are summarized in Table A.7-1.

Table A.7-1 Flood Sources 1-FLI-AB_ C113_LF1 Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or # components

A-18 AB C113 AB_C113_LF1 NSCW 1.5 120 NSCW 4

120 The conditional rupture probability for all piping systems was estimated from generic data for PWR raw water service water systems provided in IF-9. Table 3-5 of IF-9 identifies the number of failure events for PWR plants with lake suction source. The lake suction source was deemed applicable to the NSCW system that take suction from cooling towers with makeup water provided from underground wells. Data was provided for pipe sizes less than 2 in. and sizes between 2 and 4 in. The parameters used to estimate the conditional rupture probability for scenario 1-FLI-AB_C113_LF1 are summarized in Table A.7-2.

Table A.7-2 Conditional Rupture Probability Parameters 1-FLI-AB_ C113_LF1 NSCW < 2 Beta prior distribution alpha prior beta prior Reference Notes 1

99 Based on judgment of the analyst NSCW < 2 Evidence ruptures failures 0

90 IF-9 Table 3-5 Based on PWR operating experience for SW systems with lake water intake.

Data for NPS 2 was used.

NSCW 2-4 Beta prior distribution alpha prior beta prior 1

99 Based on judgment of the analyst NSCW 2-4 Evidence ruptures failures 0

71 IF-9 Table 3-5 Based on PWR operating experience for SW systems with lake water intake.

Data for 2 < NPS 4 was used.

The failure rate for PWR service water piping was estimated in IF-9 in Table 3-9 for pipe sizes 2 in. and for pipe sizes > 2 in. and 4 in. A constrained noninformative gamma distribution, as defined in IF-12, was used as the prior. Six plant-specific NSCW failures were identified as discussed in a Licensee Event Report. The failures involved welds where a 4-in. bypass line joins an 18-in. pump discharge line. The failures were deemed applicable to the NSCW pipe sizes from 2 to 4 in. The estimated feet of PWR service water piping was taken from Table 3-2 of IF-9. A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above. The parameters used to estimate the failure rate for scenario 1-FLI-AB_C113_LF1 are summarized in Table A.7-3.

Table A.7-3 Failure Rate Parameters 1-FLI-AB_ C113_LF1 NSCW < 2 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 4505 IF-9 Table 3-9 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value NSCW < 2 Evidence failures feet - critical years

A-19 0

38962 IF-9 Table 3-2 0 failures identified, 933 ft of SW piping, 41.76 critical years NSCW 2-4 Gamma CNI prior distribution alpha prior beta prior 0.5 2538 IF-9 Table 3-9 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value NSCW 2-4 Evidence failures feet - critical years 6

17289 IF-9 Table 3-2, LER 6 failures identified, 414 ft of SW piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_C113_LF1 is shown in Table A.7-4.

Table A.7-4 Initiating Event Frequency Estimate for 1-FLI-AB_ C113_LF1 Mean value Shape parameter 5th percentile Median value 95th percentile 2.24E-04 9.45E-01 9.88E-06 1.52E-04 6.88E-04 A.8. Initiating Event Frequency for Scenario 1-FLI-CB_A48 Scenario 1-FLI-CB_A48 models impacts on room A48 from flood water propagating from adjacent corridor A58. Switchgear room A48 contains no flood sources. All flood sources applicable to this scenario wre located in corridor A58. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-CB_A48 are summarized in Table A.8-1.

Table A.8-1 Flood Sources 1-FLI-CB_ A48 Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or # components CB A58 CB_A58_FP Fire Protection 2

60 Fire Protection 4

290 Fire Protection 6

60 Utility water 1

200 The conditional rupture probability for fire protection piping systems was estimated from generic data in IF-9. Table 3-43 of IF-9 identifies the number of failure events fire protection pipes with nominal pipe sizes less than 4 in. and between 4 and 6 in. The service data for component cooling water were used to estimate the flood frequency for utility water, which was a clean closed water system with low temperature and pressure conditions. The failure data for component cooling water was taken from Table 4-2 of IF-9. The parameters used to estimate the conditional rupture probability for scenario 1-FLI-CB_A48 are summarized in Table A.8-2.

A-20 Table A.8-2 Conditional Rupture Probability Parameters 1-FLI-CB_A48 FP < 4 Beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on judgment of the analyst FP < 4 Evidence ruptures failures 1

35 IF-9 Table 3-43 Data for NPS 4 was used.

FP 4-6 Beta prior distribution alpha prior beta prior 1

9 Based on judgment of the analyst FP 4-6 Evidence ruptures failures 1

29 IF-9 Table 3-43 Data for 4 < NPS 6 was used.

CCW < 2 Beta prior distribution alpha prior beta prior 1

9 Based on judgment of the analyst CCW < 2 Evidence ruptures failures 1

49 IF-9 Table 4-2 Data for NPS 2 was used.

The failure rates for fire protection piping are estimated in IF-9 in Tables 3-47 and 3-48 for nominal pipe sizes of 4 in. and 6 in. The failure rate prior distribution for utility water piping uses the CCW failure rate reported in Table 4-6 of IF-9. The failure rate for the smallest nominal pipe size (6 in.) was used, 4.84x10-6. A constrained non-informative gamma distribution, as defined in IF-12, was used as the prior. The estimated feet of piping for fire protection piping was given in IF-9 Table 3-42. The feet of CCW piping reported in IF-9 Table 4-3 was used as a surrogate for utility water. A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above. The parameters used to estimate the failure rate for scenario 1-FLI-CB_A48 are summarized in Table A.8-3.

Table A.8-3 Failure Rate Parameters 1-FLI-CB_A48 FP < 4 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 40650 IF-9 Tables 3-47 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value FP < 4 Evidence failures feet - critical years 0

1.26E+05 IF-9 Table 3-42 3,012 ft of FP piping, 41.76 critical years FP 4-6 Gamma CNI prior distribution alpha prior beta prior 0.5 31447 IF-9 Tables 3-48 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value FP 4-6 Evidence failures feet - critical years 0

80179 IF-9 Table 3-42 1,920 ft of FP piping, 41.76 critical years alpha prior beta prior

A-21 CCW < 2 Gamma CNI prior distribution 0.5 103306 IF-9 Table 4-6 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value CCW < 2 Evidence failures feet - critical years 1

45894 Reference plant information, IF-9 Table 4-3 1,099 ft of CCW was used as a surrogate estimate, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-CB_A48 is shown in Table A.8-4.

Table A.8-4 Initiating Event Frequency Estimate for 1-FLI-CB_A48 Mean value Shape parameter 5th percentile Median value 95th percentile 9.21E-05 0.979 4.77E-06 6.42E-05 2.80E-04 A.9. Initiating Event Frequency for Scenarios 1-FLI-TB_500_HI1 and 1-FLI-TB_500_HI2 The initiating event frequency for scenarios 1-FLI-TB_500_HI1 and 1-FLI-TB_500_HI2 were based on analysis of human error(s) that induce a flooding event. The uncertainty distributions were assigned based on analysts judgment and common practices for HEP uncertainty.

The frequency of the human induced flood scenario 1-FLI-TB_500_HI1 was estimated by assuming the occurrence of all three of the following events:

Condenser water box maintenance during plant operation Maintenance crew failure to properly secure the manway cover(s)

Operator failure to mitigate the flood scenario A lognormal distribution was assumed for each event. The mean values and error factors used for each event is shown in Table A.9-1 below.

Table A.9-1 Events Contributing to Flood Frequency for Scenario 1-FLI-TB_500_HI1 Failure Event Uncertainty Distribution Mean Value Error Factor Condenser maintenance occurs during plant operation Lognormal 9.4E-02 3

Failure to secure manway cover(s)

Lognormal 1.0E-02 5

Failure to mitigate flood Lognormal 1.0E-01 5

The frequency of the human induced flood scenario 1-FLI-TB_500_HI2 was estimated by assuming the occurrence of all three of the following events:

TPCCW heat exchanger maintenance during plant operation Maintenance crew failure to properly secure the heat exchanger Maintenance crew failure to mitigate the flood scenario

A-22 A lognormal distribution was assumed for each event. The mean values and error factors used for each event is shown in Table A.9-2 below.

Table A.9-2 Events Contributing to Flood Frequency for Scenario 1-FLI-TB_500_HI2 Failure Event Uncertainty Distribution Mean Value Error Factor TPCCW heat exchanger maintenance occurs during plant operation Lognormal 9.4E-02 3

Failure to secure heat exchanger Lognormal 1.0E-02 5

Failure to mitigate flood Lognormal 1.0E-01 5

The frequency of the human induced flooding scenario was estimated by the product of the three events discussed above. As both scenarios were using the same input distribution, the same resulting frequency distribution was used for both scenarios. The product distribution was also lognormal. The product distribution is characterized by mean value and error factor given in Table A.9-3.

Table A.9-3 Initiating Event Frequency Estimate for 1-FLI-TB_500_HI1 and 1-FLI-TB_500_HI2 Mean value Error factor 5th percentile Median value 95th percentile 9.4E-05 12.5 2.3E-06 2.9E-05 3.6E-04 A.10. Initiating Event Frequency for Scenario 1-FLI-AB_C120_LF Scenario 1-FLI-AB_C120_LF models impacts from local flooding. Sprays were not applicable to this scenario. The flood sources applicable to this scenario were the NSCW pipes located in the room. Other potential flood sources were located in the room, but those sources were addressed in other flooding scenarios and were not modeled here. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-AB_C120_LF are summarized in Table A.10-1.

Table A.10-1 Flood Sources 1-FLI-AB_C120_LF Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or # components AB C120 AB_C120_LF NSCW 1.5 70 NSCW 3

100 The conditional rupture probability for NSCW piping system was estimated from generic data for PWR raw water service water systems provided in IF-9. Table 3-5 of IF-9 identifies the number of failure events for PWR plants with lake suction source. The lake suction source was deemed applicable to the NSCW system that take suction from cooling towers with makeup water provided from underground wells. Data was provided for pipe sizes less than 2 in. and sizes between 2 and 4 in. The parameters used to estimate the conditional rupture probability for scenario 1-FLI-AB_C120_LF are summarized in Table A.10-2.

Table A.10-2 Conditional Rupture Probability Parameters 1-FLI-AB_C120_LF alpha prior beta prior Reference Notes

A-23 NSCW < 2 Beta prior distribution 1

99 Based on judgment of the analyst NSCW < 2 Evidence ruptures failures 0

90 IF-9 Table 3-5 Based on PWR operating experience for SW systems with lake water intake.

Data for NPS 2 was used.

NSCW 2-4 Beta prior distribution alpha prior beta prior 1

99 Based on judgment of the analyst NSCW 2-4 Evidence ruptures failures 0

71 IF-9 Table 3-5 Based on PWR operating experience for SW systems with lake water intake.

Data for 2 < NPS 4 was used.

The failure rate for PWR service water piping was estimated in IF-9 in Table 3-9 for pipe sizes 2 in. and for pipe sizes > 2 in. and 4 in. A constrained noninformative gamma distribution, as defined in IF-12, was used as the prior. Six plant-specific NSCW failures were identified as discussed in a Licensee Event Report. The failures involved welds where a 4-in. bypass line joins an 18-in. pump discharge line. The failures were deemed applicable to the NSCW pipe sizes from 2 to 4 in. The estimated feet of PWR service water piping was taken from Table 3-2 of IF-9. A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above. The parameters used to estimate the failure rate for scenario 1-FLI-AB_C120_LF are summarized in Table A.10-3.

Table A.10-3 Failure Rate Parameters 1-FLI-AB_C120_LF NSCW < 2 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 4505 IF-9 Table 3-9 For CNI prior, alpha prior = 0.5, beta prior

= 0.5/mean value NSCW < 2 Evidence failures feet - critical years 0

38962 IF-9 Table 3-2 0 failures identified, 933 ft of SW piping, 41.76 critical years NSCW 2-4 Gamma CNI prior distribution alpha prior beta prior 0.5 2538 IF-9 Table 3-9 For CNI prior, alpha prior = 0.5, beta prior

= 0.5/mean value NSCW 2-4 Evidence failures feet - critical years 6

17289 IF-9 Table 3-2, LER 6 failures identified, 414 ft of SW piping, 41.76 critical years

A-24 The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_C120_LF is shown in Table A.10-4.

Table A.10-4 Initiating Event Frequency Estimate for 1-FLI-AB_C120_LF Mean value Shape parameter 5th percentile Median value 95th percentile 1.80E-04 9.26E-01 7.65E-06 1.20E-04 5.49E-04 A.11. Initiating Event Frequency for Scenario 1-FLI-AB_C115_LF Scenario 1-FLI-AB_C115_LF models impacts from local flooding. Sprays were not applicable to this scenario. The flood sources applicable to this scenario awere the NSCW pipes located in the room. Other potential flood sources were located in the room, but those sources were addressed in other flooding scenarios and were not modeled here. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-AB_C115_LF are summarized in Table A.11-1.

Table A.11-1 Flood Sources 1-FLI-AB_C115_LF Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or

1. components AB C115 AB_C115_LF NSCW 2.5 80 The conditional rupture probability for NSCW piping system was estimated from generic data for PWR raw water service water systems provided in IF-9. Table 3-5 of IF-9 identifies the number of failure events for PWR plants with lake suction source. The lake suction source was deemed applicable to the NSCW system that take suction from cooling towers with makeup water provided from underground wells. Data was provided for pipe sizes between 2 and 4 in. The parameters used to estimate the conditional rupture probability for scenario 1-FLI-AB_C115_LF are summarized in Table A.11-2.

Table A.11-2 Conditional Rupture Probability Parameters 1-FLI-AB_C115_LF NSCW 2-4 Beta prior distribution alpha prior beta prior 1

99 Based on judgment of the analyst NSCW 2-4 Evidence ruptures failures 0

71 IF-9 Table 3-5 Based on PWR operating experience for SW systems with lake water intake.

Data for 2 < NPS 4 is used.

The failure rate for PWR service water piping was estimated in IF-9 in Table 3-9 for pipe sizes >

2 in. and 4 in. A constrained noninformative gamma distribution, as defined in IF-12, was used as the prior. Six plant-specific NSCW failures were identified as discussed in a Licensee Event Report. The failures involved welds where a 4-in. bypass line joins an 18-in. pump discharge line. The failures were deemed applicable to the NSCW pipe sizes from 2 to 4 in. The estimated feet of PWR service water piping was taken from Table 3-2 of IF-9. A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above. The parameters used to estimate the failure rate for scenario 1-FLI-AB_C115_LF are summarized in Table A.11-3.

A-25 Table A.11-3 Failure Rate Parameters 1-FLI-AB_C115_LF NSCW 2-4 Gamma CNI prior distribution alpha prior beta prior 0.5 2538 IF-9 Table 3-9 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value NSCW 2-4 Evidence failures feet - critical years 6

17289 IF-9 Table 3-2, LER 6 failures identified, 414 ft of SW piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_C115_LF is shown in Table A.11-4.

Table A.11-4 Initiating Event Frequency Estimate for 1-FLI-AB_C115_LF Mean value Shape parameter 5th percentile Median value 95th percentile 1.33E-04 8.90E-01 4.69E-06 8.66E-05 4.21E-04 A.12. Initiating Event Frequency for Scenario 1-FLI-AB_C118_LF Scenario 1-FLI-AB_C118_LF models impacts from local flooding. Sprays were not applicable to this scenario. The flood sources applicable to this scenario were the NSCW pipes located in the room. Other potential flood sources were located in the room, but those sources were addressed in other flooding scenarios and were not modeled here. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-AB_C118_LF were summarized in Table A.12-1.

Table A.12-1 Flood Sources 1-FLI-AB_C118_LF Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or # components AB C118 AB_C118_LF NSCW 2

80 The conditional rupture probability for NSCW piping system was estimated from generic data for PWR raw water service water systems provided in IF-9. Table 3-5 of IF-9 identifies the number of failure events for PWR plants with lake suction source. The lake suction source was deemed applicable to the NSCW system that take suction from cooling towers with makeup water provided from underground wells. Data was provided for pipe sizes less than or equal to 2 in.

The parameters used to estimate the conditional rupture probability for scenario 1-FLI-AB_C118_LF are summarized in Table A.12-2.

A-26 Table A.12-2 Conditional Rupture Probability Parameters 1-FLI-AB_C118_LF NSCW 2 Beta prior distribution alpha prior beta prior Reference Notes 1

99 Based on judgment of the analyst NSCW 2 Evidence ruptures failures 0

90 IF-9 Table 3-5 Based on PWR operating experience for SW systems with lake water intake. Data for NPS 2 is used.

The failure rate for PWR service water piping was estimated in IF-9 in Table 3-9 for pipe sizes 2 in. A constrained noninformative gamma distribution, as defined in IF-12, was used as the prior. The estimated feet of PWR service water piping was taken from Table 3-2 of IF-9. A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above.

The parameters used to estimate the failure rate for scenario 1-FLI-AB_C118_LF are summarized in Table A.12-3.

Table A.12-3 Failure Rate Parameters 1-FLI-AB_C118_LF NSCW 2 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 4505 IF-9 Table 3-9 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value NSCW 2 Evidence failures feet - critical years 0

38962 IF-9 Table 3-2 0 failures identified, 933 ft of SW piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_C118_LF is shown in Table A.12-4.

Table A.12-4 Initiating Event Frequency Estimate for 1-FLI-AB_C118_LF Mean value Shape parameter 5th percentile Median value 95th percentile 7.52E-06 3.76E-01 4.72E-09 2.55E-06 3.22E-05 A.13. Initiating Event Frequency for Scenario 1-FLI-AB_B08_LF Scenario 1-FLI-AB_B08_LF models impacts from local flooding. Sprays were not applicable to this scenario. The flood sources applicable to this scenario were the NSCW pipes located in the room. Other potential flood sources were located in the room, but those sources were addressed in other flooding scenarios and were not modeled here. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-AB_B08_LF are summarized in Table A.13-1.

A-27 Table A.13-1 Flood Sources 1-FLI-AB_B08_LF Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or #

components AB B08 AB_B08_LF NSCW 8

110 The conditional rupture probability for NSCW piping system was estimated from generic data for PWR raw water service water systems provided in IF-9. Table 3-5 of IF-9 identifies the number of failure events for PWR plants with lake suction source. The lake suction source was deemed applicable to the NSCW system that take suction from cooling towers with makeup water provided from underground wells. Data was provided for pipe sizes between 4 and 10 in. The prior was based on the EPRI model described in Table 3-12 of IF-9. The prior rupture probability for flood events was used. A more specific, informed prior could not be justified for this case given the sparse service data for the pipe category. The parameters used to estimate the conditional rupture probability for scenario 1-FLI-AB_B08_LF are summarized in Table A.13-2.

Table A.13-2 Conditional Rupture Probability Parameters 1-FLI-AB_B08_LF NSCW 4-10 Beta prior distribution alpha prior beta prior Reference Notes 1

99 IF-9 Table 3-12 Based on generic flood rupture probability of 0.01.

NSCW 4-10 Evidence ruptures failures 0

60 IF-9 Table 3-5 Based on PWR operating experience for SW systems with lake water intake. Data for NPS 4-10 was used.

The failure rate for PWR service water piping was estimated in IF-9 in Table 3-9 for pipe sizes 4 to 10 in. A constrained noninformative gamma distribution, as defined in IF-12, was used as the prior. The estimated feet of PWR service water piping was taken from Table 3-2 of IF-9. A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above.

The parameters used to estimate the failure rate for scenario 1-FLI-AB_B08_LF are summarized in Table A.13-3.

A-28 Table A.13-3 Failure Rate Parameters 1-FLI-AB_B08_LF NSCW 4-10 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 9804 IF-9 Table 3-9 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value NSCW 4-10 Evidence failures feet - critical years 0

56543 IF-9 Table 3-2 0 failures identified, 1354 ft of SW piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_B08_LF is shown in Table A.13-4.

Table A.13-4 Initiating Event Frequency Estimate for 1-FLI-AB_B08_LF Mean value Shape parameter 5th percentile Median value 95th percentile 7.67E-06 3.84E-01 5.34E-09 2.49E-06 3.25E-05 A.14. Initiating Event Frequency for Scenario 1-FLI-AB_B24_LF2 Scenario 1-FLI-AB_B24_LF2 models impacts from local flooding. Sprays were not applicable to this scenario. The flood sources applicable to this scenario were the NSCW pipes located in the room. Other potential flood sources were located in the room, but those sources were addressed in other flooding scenarios and were not modeled here. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-AB_B24_LF2 are summarized in Table A.14-1.

Table A.14-1 Flood Sources 1-FLI-AB_B24_LF2 Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or # components AB C118 AB_B24_LF2 NSCW 1.5 40 The conditional rupture probability for NSCW piping system was estimated from generic data for PWR raw water service water systems provided in IF-9. Table 3-5 of IF-9 identifies the number of failure events for PWR plants with lake suction source. The lake suction source was deemed applicable to the NSCW system that takes suction from cooling towers with makeup water provided from underground wells. Data was provided for pipe sizes less than or equal to 2 in.

The parameters used to estimate the conditional rupture probability for scenario 1-FLI-AB_B24_LF2 are summarized in Table A.14-2.

A-29 Table A.14-2 Conditional Rupture Probability Parameters 1-FLI-AB_B24_LF2 NSCW 2 Beta prior distribution alpha prior beta prior Reference Notes 1

99 Based on judgment of the analyst NSCW 2 Evidence ruptures failures 0

90 IF-9 Table 3-5 Based on PWR operating experience for SW systems with lake water intake. Data for NPS 2 was used.

The failure rate for PWR service water piping was estimated in IF-9 in Table 3-9 for pipe sizes 2 in. A constrained noninformative gamma distribution, as defined in Ref. IF-12, was used as the prior. The estimated feet of PWR service water piping was taken from Table 3-2 of IF-9. A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above.

The parameters used to estimate the failure rate for scenario 1-FLI-AB_B24_LF2 are summarized in Table A.14-3.

Table A.14-3 Failure Rate Parameters 1-FLI-AB_B24_LF2 NSCW 2 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 4505 IF-9 Table 3-9 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value NSCW 2 Evidence failures feet - critical years 0

38962 IF-9 Table 3-2 0 failures identified, 933 ft of SW piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_B24_LF2 is shown in Table A.14-4.

Table A.14-4 Initiating Event Frequency Estimate for 1-FLI-AB_B24_LF2 Mean value Shape parameter 5th percentile Median value 95th percentile 3.53E-06 3.53E-01 1.54E-09 1.12E-06 1.52E-05 A.15. Initiating Event Frequency for Scenario 1-FLI-AB_B50_JI Scenario 1-FLI-AB_B50_JI models impacts from jet impingement. The frequency for spray events was used for the jet impingement scenario. The flood sources applicable to this scenario were the Safety Injection/Recirculation system pipes located in the room, referred to as RWST piping. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-AB_B50_JI are summarized in Table A.15-1.

Table A.15-1 Flood Sources 1-FLI-AB_B50_JI Building Flood Area Designator Flood Source Pipe Size (inch) Pipe Length (feet) or

1. components

A-30 AB B50 AB_B50_JI RWST 3

50 The conditional rupture probability for RWST piping was estimated from generic data for safety injection and recirculation systems provided in IF-9. Table 4-1 of IF-9 identifies the number of failure events for PWR safety injection system piping. The prior was based on the EPRI model described in Table 3-12 of IF-9. The prior rupture probability for spray events was used. A more specific, informed prior was not developed for this case due the sparse service data for the pipe category. Data was provided for pipe sizes less than or equal to 2 in. The parameters used to estimate the conditional rupture probability for scenario 1-FLI-AB_B50_JI are summarized in Table A.15-2.

Table A.15-2 Conditional Rupture Probability Parameters 1-FLI-AB_B50_JI RWST 2-6 Beta prior distribution alpha prior beta prior Reference Notes 1

9 IF-9 Table 3-12 Based on generic spray rupture probability of 0.1.

RWST 2-6 Evidence ruptures failures 0

31 IF-9 Table 4-1 Based on SI/recirc operating experience. Data for 2 < NPS 6 is used.

The failure rate for PWR service water piping was estimated in IF-9 in Table 4-8 for nominal pipe size of 6 in. A constrained noninformative gamma distribution, as defined in IF-12, was used as the prior. The estimated feet of RWST piping was taken from Table 4-3 of IF-9. A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above.

The parameters used to estimate the failure rate for scenario 1-FLI-AB_B50_JI are summarized in Table A.15-3.

Table A.15-3 Failure Rate Parameters 1-FLI-AB_B50_JI RWST 2-6 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 320513 IF-9 Table 4-8 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value RWST 2-6 Evidence failures feet - critical years 1

167875 IF-9 Table 4-3, reference plant information 1 failure identified, 4,020 ft of RWST piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_B50_JI is shown in Table A.15-4.

Table A.15-4 Initiating Event Frequency Estimate for 1-FLI-AB_B50_JI Mean value Shape parameter 5th percentile Median value 95th percentile 3.35E-06 6.69E-01 4.75E-08 1.87E-06 1.14E-05

A-31 A.16. Initiating Event Frequency for Scenarios 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF Scenarios 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF both model the impacts from NSCW pipes located in the rooms. The contributing pipes in each room were from the same system, same size, and same length. Therefore, the same initiating event frequency was used for both scenarios. The scenarios model impacts from local flooding. Sprays were not applicable to these scenarios. Other potential flood sources besides the NSCW pipes were located in the rooms, but those sources were addressed in other flooding scenarios and were not modeled here. The flood sources used to estimate the initiating event frequency for scenarios 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF are summarized in Table A.16-1.

Table A.16-1 Flood Sources 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or

1. components DGB 101 DGB_101_LF NSCW 10 120 DGB 103 DGB_103_LF NSCW 10 120 The conditional rupture probability for NSCW piping system was estimated from generic data for PWR raw water service water systems provided in IF-9. Table 3-5 of IF-9 identifies the number of failure events for PWR plants with lake suction source. The lake suction source was deemed applicable to the NSCW system that take suction from cooling towers with makeup water provided from underground wells. Data was provided for pipe sizes between 4 and 10 in. The prior was based on the EPRI model described in Table 3-12 of IF-9. The prior rupture probability for flood events was used. A more specific, informed prior could not be justified for this case given the sparse service data for the pipe category. The parameters used to estimate the conditional rupture probability for scenarios 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF are summarized in Table A.16-2.

Table A.16-2 Conditional Rupture Probability Parameters 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF NSCW 4-10 Beta prior distribution alpha prior beta prior Reference Notes 1

99 IF-9 Table 3-12 Based on generic flood rupture probability of 0.01.

NSCW 4-10 Evidence ruptures failures 0

60 IF-9 Table 3-5 Based on PWR operating experience for SW systems with lake water intake. Data for NPS 4-10 was used.

The failure rate for PWR service water piping was estimated in IF-9 in Table 3-9 for pipe sizes 4 to 10 in. A constrained noninformative gamma distribution, as defined in IF-12, was used as the prior. The estimated feet of PWR service water piping was taken from Table 3-2 of IF-9. A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above.

The parameters used to estimate the failure rate for scenarios 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF are summarized in Table A.16-3.

A-32 Table A.16-3 Failure Rate Parameters 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF NSCW 4-10 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 9804 IF-9 Table 3-9 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value NSCW 4-10 Evidence failures feet - critical years 0

56543 IF-9 Table 3-2 0 failures identified, 1,354 ft of SW piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenarios 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF is shown in Table A.16-4.

Table A.16-4 Initiating Event Frequency Estimate for 1-FLI-DGB_101_LF and 1-FLI-DGB_103_LF Mean value Shape parameter 5th percentile Median value 95th percentile 7.32E-06 3.66E-01 4.06E-09 2.24E-06 3.19E-05 A.17. Initiating Event Frequency for Scenario 1-FLI-AB_D74_FP Scenario 1-FLI-AB_D74_FP models impacts on auxiliary building switchgear room D105 from flood water propagating from adjacent room D74. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-AB_D74_FP are summarized in Table A.17-1.

Table A.17-1 Flood Sources 1-FLI-AB_D74_FP Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or # components AB D74 AB_D74_FP Fire Protection 4

35 Fire Protection 2

20 The conditional rupture probability for fire protection piping systems was estimated from generic data in IF-9. Table 3-43 of IF-9 identifies the number of failure events fire protection pipes with nominal pipe sizes less than or equal to 4 in. According to the simple EPRI model used to inform the choice for prior conditional rupture probabilities (Table 3-12 of IF-9), flood events were assigned a mean conditional rupture probability of 0.01. However, a review of the fire protection service data suggests that a higher conditional rupture probability may be appropriate for this system. The data in Table 3-43 of IF-9 show three major structural failures (out of 138 total failures) and several significant leakage events. The susceptibility of fire protection piping to water hammer events also contributes to a higher likelihood of significant failures in comparison to other system piping. For these reasons a mean value of 0.1 was selected for the prior conditional rupture probability. The parameters used to estimate the conditional rupture probability for scenario 1-FLI-AB_D74_FP are summarized in Table A.17-2.

A-33 Table A.17-2 Conditional Rupture Probability Parameters 1-FLI-AB_D74_FP FP 4 Beta prior distribution alpha prior beta prior Reference Notes 1

9 Based on review of FP system service data.

FP 4 Evidence ruptures failures 1

35 IF-9 Table 3-43 Data for NPS 4 is used.

The failure rates for fire protection piping were estimated in IF-9 in Table 3-47 for nominal pipe size of 4 in. A constrained non-informative gamma distribution, as defined in IF-12, was used as the prior. The estimated feet of piping for fire protection piping was given in IF-9 Table 3-42.

A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above. The parameters used to estimate the failure rate for scenario 1-FLI-AB_D74_FP are summarized in Table A.17-3.

Table A.17-3 Failure Rate Parameters 1-FLI-AB_D74_FP FP 4 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 40650 IF-9 Tables 3-47 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value FP 4 Evidence failures feet - critical years 0

1.26E+05 IF-9 Table 3-42 3,012 ft of FP piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_D74_FP is shown in Table A.17-4.

Table A.17-4 Initiating Event Frequency Estimate for 1-FLI-AB_D74_FP Mean value Shape parameter 5th percentile Median value 95th percentile 8.57E-06 4.28E-01 1.39E-08 3.45E-06 3.52E-05 A.18. Initiating Event Frequency for Scenario 1-FLI-AB_D78_FP Scenario 1-FLI-AB_D78_FP models impacts on auxiliary building switchgear room D105 from flood water propagating from adjacent rooms D78 and D79. The flood sources used to estimate the initiating event frequency for scenario 1-FLI-AB_D78_FP are summarized in Table A.18-1.

A-34 Table A.18-1 Flood Sources 1-FLI-AB_D78_FP Building Flood Area Designator Flood Source Pipe Size (inch)

Pipe Length (feet) or # components AB D78 AB_D78_FP RHR 8

20 RHR 10 20 RWST 8

15 AB D79 AB_D79_FP RWST 8

25 The conditional rupture probability for the RHR and RWST piping was estimated from generic safety injection piping data in IF-9. Table 4-1 of IF-9 identifies the number of failure events safety injection pipes with nominal pipe sizes greater than 6 in. and less than or equal to 10 in.

According to the simple EPRI model used to inform the choice for prior conditional rupture probabilities (Table 3-12 of IF-9), flood events were assigned a mean conditional rupture probability of 0.01. A mean value of 0.01 was selected for the prior conditional rupture probability. The parameters used to estimate the conditional rupture probability for scenario 1-FLI-AB_D78_FP are summarized in Table A.18-2.

Table A.18-2 Conditional Rupture Probability Parameters 1-FLI-AB_D78_FP 6 < SI 10 Beta prior distribution alpha prior beta prior Reference Notes 1

99 Based on review of FP system service data.

6 < SI 10 Evidence ruptures failures 0

31 IF-9 Table 4-1 Data for 6 < NPS 10 was used.

The failure rates for safety injection piping were estimated in IF-9 in Table 4-9 for nominal pipe size of 10 in. A constrained non-informative gamma distribution, as defined in IF-12, was used as the prior. The estimated feet of piping for safety injection piping was given in IF-9 Table 4-3.

A lognormal distribution with an error factor of 3 was assumed for the feet of piping to account for uncertainty in the estimate. The reactor-critical-years were estimated as described in A.1 above. The parameters used to estimate the failure rate for scenario 1-FLI-AB_D78_FP are summarized in Table A.18-3.

Table A.18-3 Failure Rate Parameters 1-FLI-AB_D78_FP FP 4 Gamma CNI prior distribution alpha prior beta prior Reference Notes 0.5 1061571 IF-9 Tables 4-9 For CNI prior, alpha prior = 0.5, beta prior = 0.5/mean value FP 4 Evidence failures feet - critical years 0

559584 IF-9 Table 4-3 13,400 ft of SI piping, 41.76 critical years The initiating event frequency estimate for internal flooding scenario 1-FLI-AB_D78_FP is shown in Table A.18-4.

A-35 Table A.18-4 Initiating Event Frequency Estimate for 1-FLI-AB_D78_FP Mean value Shape parameter 5th percentile Median value 95th percentile 3.55E-07 3.55E-01 1.73E-10 1.12E-07 1.57E-06

B-1 APPENDIX B: INTERNAL FLOODING PRA SIGNIFICANT CUT SETS AND BASIC EVENT IMPORTANCE Appendix B contains the significant results from the Internal Flooding PRA (IFPRA). The significant cut sets are provided in B.1 Internal Flooding PRA Significant Cut Set Results and the importance measures for all significant basic events are provided in B.2 Internal Flooding PRA Basic Event Importance Measures.

B.1 Internal Flooding PRA Significant Cut Set Results The significant cut sets contributing to IFPRA core damage frequency (CDF) are provided in Table B-1. The significant internal flooding cut sets include all those whose summed CDF contributes more than 95 percent of the total internal flooding CDF and all cut sets that individually contribute more than 1 percent to total internal flooding CDF.

Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 1

3.914E-8 5.21 1-IE-FLI-AB_C113_LF1,1-EPS-DGN-FR-G4002___,1-OEP-VCF-LP-CLOPT 2

3.145E-8 4.19 1-IE-FLI-AB_C120_LF,1-EPS-DGN-FR-G4002___,1-OEP-VCF-LP-CLOPT 3

2.324E-8 3.09 1-IE-FLI-AB_C115_LF,1-EPS-DGN-FR-G4002___,1-OEP-VCF-LP-CLOPT 4

1.974E-8 2.63 1-IE-FLI-AB_108_SP2,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 5

1.974E-8 2.63 1-IE-FLI-AB_108_SP1,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 6

1.960E-8 2.61 1-IE-FLI-CB_123_SP,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 7

1.960E-8 2.61 1-IE-FLI-CB_122_SP,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 8

1.595E-8 2.12 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 9

1.595E-8 2.12 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 10 1.581E-8 2.10 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 11 1.581E-8 2.10 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 12 1.496E-8 1.99 1-IE-FLI-AB_C113_LF1,1-EPS-DGN-MA-G4002___,1-OEP-VCF-LP-CLOPT 13 1.270E-8 1.69 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 14 1.270E-8 1.69 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 15 1.203E-8 1.60 1-IE-FLI-AB_108_SP1,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 16 1.203E-8 1.60 1-IE-FLI-AB_108_SP2,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 17 1.202E-8 1.60 1-IE-FLI-AB_C120_LF,1-EPS-DGN-MA-G4002___,1-OEP-VCF-LP-CLOPT 18 1.194E-8 1.59 1-IE-FLI-CB_122_SP,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 19 1.194E-8 1.59 1-IE-FLI-CB_123_SP,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 20 9.632E-9 1.28 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-BA03____,1-RCS-MDP-LK-BP2

B-2 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 21 9.632E-9 1.28 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-BB16____,1-RCS-MDP-LK-BP2 22 9.386E-9 1.25 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 23 9.386E-9 1.25 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 24 8.882E-9 1.18 1-IE-FLI-AB_C115_LF,1-EPS-DGN-MA-G4002___,1-OEP-VCF-LP-CLOPT 25 7.740E-9 1.03 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-BA03____,1-RCS-MDP-LK-BP2 26 7.740E-9 1.03 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-BB16____,1-RCS-MDP-LK-BP2 27 6.352E-9 0.85 1-IE-FLI-AB_C113_LF1,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPT 28 6.095E-9 0.81 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 29 6.095E-9 0.81 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 30 5.719E-9 0.76 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-BA03____,1-RCS-MDP-LK-BP2 31 5.719E-9 0.76 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-BB16____,1-RCS-MDP-LK-BP2 32 5.104E-9 0.68 1-IE-FLI-AB_C120_LF,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPT 33 4.005E-9 0.53 1-IE-FLI-TB_500_LF,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPT 34 3.953E-9 0.53 1-IE-FLI-AB_C113_LF1,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 35 3.771E-9 0.50 1-IE-FLI-AB_C115_LF,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPT 36 3.659E-9 0.49 1-IE-FLI-CB_A60,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 37 3.512E-9 0.47 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 38 3.512E-9 0.47 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 39 3.490E-9 0.46 1-IE-FLI-AB_C113_LF1,1-EPS-DGN-FS-G4002___,1-OEP-VCF-LP-CLOPT 40 3.467E-9 0.46 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AA02____,1-OAB_TR-------H 41 3.467E-9 0.46 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AA02____,1-OAB_TR-------H 42 3.229E-9 0.43 1-IE-FLI-AB_C113_LF1,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPT 43 3.177E-9 0.42 1-IE-FLI-AB_C120_LF,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 44 3.000E-9 0.40 1-IE-FLI-AB_C113_LF1,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_B_1234_

45 2.977E-9 0.40 1-IE-FLI-CB_A60,1-EPS-DGN-FR-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 46 2.939E-9 0.39 1-IE-FLI-AB_108_SP1,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPL 47 2.939E-9 0.39 1-IE-FLI-AB_108_SP2,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPL 48 2.918E-9 0.39 1-IE-FLI-CB_122_SP,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPL 49 2.918E-9 0.39 1-IE-FLI-CB_123_SP,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPL 50 2.862E-9 0.38 1-IE-FLI-AB_C120_LF,1-AFW-MDP-MA-P4002___,1-OEP-VCF-LP-CLOPT 51 2.822E-9 0.38 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 52 2.822E-9 0.38 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 53 2.805E-9 0.37 1-IE-FLI-AB_C120_LF,1-EPS-DGN-FS-G4002___,1-OEP-VCF-LP-CLOPT

B-3 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 54 2.699E-9 0.36 1-IE-FLI-AB_C113_LF1,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1669ACT_

55 2.595E-9 0.35 1-IE-FLI-AB_C120_LF,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPT 56 2.588E-9 0.34 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-AA0205__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 57 2.588E-9 0.34 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-AA0205__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 58 2.459E-9 0.33 1-IE-FLI-TB_500_LF,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPT 59 2.411E-9 0.32 1-IE-FLI-AB_C120_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_B_1234_

60 2.347E-9 0.31 1-IE-FLI-AB_C115_LF,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 61 2.229E-9 0.30 1-IE-FLI-CB_A60,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 62 2.169E-9 0.29 1-IE-FLI-AB_C120_LF,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1669ACT_

63 2.140E-9 0.28 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-BA03____,1-RCS-MDP-LK-BP2 64 2.140E-9 0.28 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-BB16____,1-RCS-MDP-LK-BP2 65 2.085E-9 0.28 1-IE-FLI-AB_C115_LF,1-ACP-BAC-FC-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 66 2.085E-9 0.28 1-IE-FLI-AB_C115_LF,1-ACP-BAC-FC-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 67 2.072E-9 0.28 1-IE-FLI-AB_C115_LF,1-EPS-DGN-FS-G4002___,1-OEP-VCF-LP-CLOPT 68 1.980E-9 0.26 1-IE-FLI-CB_A48,1-ACP-BAC-MA-BA03____,1-FLI-CB-A58A48-FP 69 1.980E-9 0.26 1-IE-FLI-CB_A48,1-ACP-BAC-MA-BB16____,1-FLI-CB-A58A48-FP 70 1.941E-9 0.26 1-IE-FLI-TB_500_LF,1-AFW-PMP-CF-RUN,1-OAB_TR-------H 71 1.917E-9 0.26 1-IE-FLI-AB_C115_LF,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPT 72 1.852E-9 0.25 1-IE-FLI-AB_108_SP1,1-AFW-MDP-MA-P4002___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 73 1.852E-9 0.25 1-IE-FLI-AB_108_SP2,1-AFW-MDP-MA-P4002___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 74 1.839E-9 0.24 1-IE-FLI-CB_122_SP,1-AFW-MDP-MA-P4003___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 75 1.839E-9 0.24 1-IE-FLI-CB_123_SP,1-AFW-MDP-MA-P4003___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 76 1.828E-9 0.24 1-IE-FLI-AB_C113_LF1,1-RCS-MDP-LK-BP2,1-SWS-CTF-MA-_B_1234_

77 1.804E-9 0.24 1-IE-FLI-AB_108_SP1,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPL 78 1.804E-9 0.24 1-IE-FLI-AB_108_SP2,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPL 79 1.791E-9 0.24 1-IE-FLI-CB_122_SP,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPL 80 1.791E-9 0.24 1-IE-FLI-CB_123_SP,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPL 81 1.781E-9 0.24 1-IE-FLI-AB_C115_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_B_1234_

82 1.719E-9 0.23 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-BA03____,1-RCS-MDP-LK-BP2 83 1.719E-9 0.23 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-BB16____,1-RCS-MDP-LK-BP2 84 1.644E-9 0.22 1-IE-FLI-AB_C113_LF1,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP2,1-SWS-MOV-MA-1669ACT_

85 1.611E-9 0.21 1-IE-FLI-CB_123_SP,1-EPS-SEQ-FO-1821U301,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 86 1.611E-9 0.21 1-IE-FLI-CB_122_SP,1-EPS-SEQ-FO-1821U301,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL

B-4 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 87 1.609E-9 0.21 1-IE-FLI-CB_A48,1-EPS-DGN-FR-G4002___,1-FLI-CB-A58A48-FP,1-OEP-VCF-LP-CLOPT 88 1.603E-9 0.21 1-IE-FLI-CB_A48,1-AFW-MDP-MA-P4002___,1-FLI-CB-A58A48-FP,1-OAB_TR-------H 89 1.602E-9 0.21 1-IE-FLI-AB_C115_LF,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1669ACT_

90 1.574E-9 0.21 1-IE-FLI-DGB_101_LF,1-ACP-BAC-MA-AA02____

91 1.497E-9 0.20 1-IE-FLI-AB_D74_FP,1-EPS-DGN-FR-G4002___,1-OEP-VCF-LP-CLOPT 92 1.469E-9 0.20 1-IE-FLI-AB_C120_LF,1-RCS-MDP-LK-BP2,1-SWS-CTF-MA-_B_1234_

93 1.422E-9 0.19 1-IE-FLI-CB_123_SP,1-EPS-DGN-FS-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 94 1.422E-9 0.19 1-IE-FLI-CB_122_SP,1-EPS-DGN-FS-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 95 1.340E-9 0.18 1-IE-FLI-AB_B08_LF,1-EPS-DGN-FR-G4002___,1-OEP-VCF-LP-CLOPT 96 1.321E-9 0.18 1-IE-FLI-AB_C120_LF,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP2,1-SWS-MOV-MA-1669ACT_

97 1.316E-9 0.18 1-IE-FLI-CB_123_SP,1-DCP-BAT-MA-AD1B____,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 98 1.316E-9 0.18 1-IE-FLI-CB_122_SP,1-DCP-BAT-MA-AD1B____,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 99 1.314E-9 0.17 1-IE-FLI-AB_C118_LF,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPT 100 1.279E-9 0.17 1-IE-FLI-DGB_101_LF,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPT 101 1.279E-9 0.17 1-IE-FLI-DGB_103_LF,1-EPS-DGN-FR-G4002___,1-OEP-VCF-LP-CLOPT 102 1.270E-9 0.17 1-IE-FLI-AB_C115_LF,1-ACP-BAC-FC-BA03____,1-RCS-MDP-LK-BP2 103 1.270E-9 0.17 1-IE-FLI-AB_C115_LF,1-ACP-BAC-FC-BB16____,1-RCS-MDP-LK-BP2 104 1.172E-9 0.16 1-IE-FLI-TB_500_LF-CDS,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPT 105 1.138E-9 0.15 1-IE-FLI-CB_A60,1-EPS-DGN-MA-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 106 1.122E-9 0.15 1-IE-FLI-AB_C113_LF1,1-ACP-TFW-FC-BB16X___,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 107 1.085E-9 0.14 1-IE-FLI-AB_C115_LF,1-RCS-MDP-LK-BP2,1-SWS-CTF-MA-_B_1234_

108 1.019E-9 0.14 1-IE-FLI-AB_108_SP2,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 109 1.019E-9 0.14 1-IE-FLI-AB_108_SP1,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 110 1.012E-9 0.13 1-IE-FLI-CB_123_SP,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 111 1.012E-9 0.13 1-IE-FLI-CB_122_SP,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 112 9.763E-10 0.13 1-IE-FLI-AB_C115_LF,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP2,1-SWS-MOV-MA-1669ACT_

113 9.632E-10 0.13 1-IE-FLI-AB_108_SP1,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-CF-FS-ALL 114 9.632E-10 0.13 1-IE-FLI-AB_108_SP2,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-CF-FS-ALL 115 9.563E-10 0.13 1-IE-FLI-CB_122_SP,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-CF-FS-ALL 116 9.563E-10 0.13 1-IE-FLI-CB_123_SP,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-CF-FS-ALL

B-5 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 117 9.540E-10 0.13 1-IE-FLI-AB_C120_LF,1-AFW-MDP-FS-P4002___,1-OEP-VCF-LP-CLOPT 118 9.540E-10 0.13 1-IE-FLI-AB_C120_LF,1-OA-MISPAF5094H,1-OEP-VCF-LP-CLOPT 119 9.019E-10 0.12 1-IE-FLI-AB_C120_LF,1-ACP-TFW-FC-BB16X___,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 120 8.325E-10 0.11 1-IE-FLI-AB_108_SP2,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 121 8.325E-10 0.11 1-IE-FLI-AB_108_SP2,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 122 8.325E-10 0.11 1-IE-FLI-AB_108_SP1,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 123 8.325E-10 0.11 1-IE-FLI-AB_108_SP1,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 124 8.265E-10 0.11 1-IE-FLI-CB_123_SP,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 125 8.265E-10 0.11 1-IE-FLI-CB_123_SP,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 126 8.265E-10 0.11 1-IE-FLI-CB_122_SP,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 127 8.265E-10 0.11 1-IE-FLI-CB_122_SP,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 128 8.248E-10 0.11 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 129 8.248E-10 0.11 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 130 8.248E-10 0.11 1-IE-FLI-CB_123_SP,1-CVC-MDP-MA-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 131 8.248E-10 0.11 1-IE-FLI-CB_122_SP,1-CVC-MDP-MA-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 132 7.701E-10 0.10 1-IE-FLI-CB_122_SP,1-ACP-BAC-FC-AA02____,1-OAB_TR-------H 133 7.701E-10 0.10 1-IE-FLI-CB_123_SP,1-ACP-BAC-FC-AA02____,1-OAB_TR-------H 134 7.517E-10 0.10 1-IE-FLI-AB_108_SP1,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP1 135 7.517E-10 0.10 1-IE-FLI-AB_108_SP2,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP1 136 7.464E-10 0.10 1-IE-FLI-CB_122_SP,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP1 137 7.464E-10 0.10 1-IE-FLI-CB_123_SP,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP1 138 7.194E-10 0.10 1-IE-FLI-TB_500_LF-CDS,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPT 139 6.838E-10 0.09 1-IE-FLI-AB_C113_LF1,1-ACP-TFW-FC-BB16X___,1-RCS-MDP-LK-BP2 140 6.791E-10 0.09 1-IE-FLI-CB_123_SP,1-CVC-MDP-TE-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 141 6.791E-10 0.09 1-IE-FLI-CB_122_SP,1-CVC-MDP-TE-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 142 6.664E-10 0.09 1-IE-FLI-AB_C115_LF,1-ACP-TFW-FC-BB16X___,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP

B-6 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 143 6.472E-10 0.09 1-IE-FLI-CB_A60,1-ACP-BAC-MA-AA02____,1-OAB_TR-------H 144 6.210E-10 0.08 1-IE-FLI-AB_108_SP2,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 145 6.210E-10 0.08 1-IE-FLI-AB_108_SP1,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 146 6.174E-10 0.08 1-IE-FLI-AB_108_SP1,1-AFW-TDP-FR-P4001___,1-OA-MISPAF5094H,1-OAB_TR-------H 147 6.174E-10 0.08 1-IE-FLI-AB_108_SP2,1-AFW-TDP-FR-P4001___,1-OA-MISPAF5094H,1-OAB_TR-------H 148 6.174E-10 0.08 1-IE-FLI-AB_108_SP1,1-AFW-MDP-FS-P4002___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 149 6.174E-10 0.08 1-IE-FLI-AB_108_SP2,1-AFW-MDP-FS-P4002___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 150 6.168E-10 0.08 1-IE-FLI-AB_B24_LF2,1-EPS-DGN-FR-G4002___,1-OEP-VCF-LP-CLOPT 151 6.165E-10 0.08 1-IE-FLI-CB_123_SP,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 152 6.165E-10 0.08 1-IE-FLI-CB_122_SP,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 153 6.150E-10 0.08 1-IE-FLI-CB_A48,1-EPS-DGN-MA-G4002___,1-FLI-CB-A58A48-FP,1-OEP-VCF-LP-CLOPT 154 6.130E-10 0.08 1-IE-FLI-CB_122_SP,1-AFW-TDP-FR-P4001___,1-OA-MISPAF5095H,1-OAB_TR-------H 155 6.130E-10 0.08 1-IE-FLI-CB_123_SP,1-AFW-TDP-FR-P4001___,1-OA-MISPAF5095H,1-OAB_TR-------H 156 6.130E-10 0.08 1-IE-FLI-CB_122_SP,1-AFW-MDP-FS-P4003___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 157 6.130E-10 0.08 1-IE-FLI-CB_123_SP,1-AFW-MDP-FS-P4003___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 158 6.106E-10 0.08 1-IE-FLI-AB_108_SP1,1-AFW-TDP-FR-P4001___,1-EPS-DGN-FR-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 159 6.106E-10 0.08 1-IE-FLI-AB_108_SP2,1-AFW-TDP-FR-P4001___,1-EPS-DGN-FR-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 160 6.048E-10 0.08 1-IE-FLI-AB_D74_FP,1-ACP-BAC-MA-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 161 6.048E-10 0.08 1-IE-FLI-AB_D74_FP,1-ACP-BAC-MA-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 162 6.020E-10 0.08 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-BA03____,1-RCS-MDP-LK-BP1 163 6.020E-10 0.08 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-BB16____,1-RCS-MDP-LK-BP1 164 5.869E-10 0.08 1-IE-FLI-AB_108_SP1,1-RCS-MDP-LK-BP2,1-SWS-CTF-CF-FS-ALL 165 5.869E-10 0.08 1-IE-FLI-AB_108_SP2,1-RCS-MDP-LK-BP2,1-SWS-CTF-CF-FS-ALL 166 5.853E-10 0.08 1-IE-FLI-AB_B50_JI,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPT 167 5.827E-10 0.08 1-IE-FLI-CB_122_SP,1-RCS-MDP-LK-BP2,1-SWS-CTF-CF-FS-ALL 168 5.827E-10 0.08 1-IE-FLI-CB_123_SP,1-RCS-MDP-LK-BP2,1-SWS-CTF-CF-FS-ALL 169 5.723E-10 0.08 1-IE-FLI-AB_D74_FP,1-EPS-DGN-MA-G4002___,1-OEP-VCF-LP-CLOPT 170 5.678E-10 0.08 1-IE-FLI-TB_500_LF-CDS,1-AFW-PMP-CF-RUN,1-OAB_TR-------H 171 5.495E-10 0.07 1-IE-FLI-AB_C120_LF,1-ACP-TFW-FC-BB16X___,1-RCS-MDP-LK-BP2 172 5.447E-10 0.07 1-IE-FLI-CB_A60,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPL 173 5.413E-10 0.07 1-IE-FLI-AB_B08_LF,1-ACP-BAC-MA-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 174 5.413E-10 0.07 1-IE-FLI-AB_B08_LF,1-ACP-BAC-MA-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 175 5.342E-10 0.07 1-IE-FLI-CB_A48,1-AFW-MDP-FS-P4002___,1-FLI-CB-A58A48-FP,1-OAB_TR-------H

B-7 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 176 5.342E-10 0.07 1-IE-FLI-CB_A48,1-FLI-CB-A58A48-FP,1-OA-MISPAF5094H,1-OAB_TR-------H 177 5.307E-10 0.07 1-IE-FLI-AB_C118_LF,1-ACP-BAC-MA-AA02____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 178 5.307E-10 0.07 1-IE-FLI-AB_C118_LF,1-ACP-BAC-MA-AB15____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 179 5.166E-10 0.07 1-IE-FLI-DGB_103_LF,1-ACP-BAC-MA-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 180 5.166E-10 0.07 1-IE-FLI-DGB_103_LF,1-ACP-BAC-MA-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 181 5.166E-10 0.07 1-IE-FLI-DGB_101_LF,1-ACP-BAC-MA-AB15____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 182 5.122E-10 0.07 1-IE-FLI-AB_B08_LF,1-EPS-DGN-MA-G4002___,1-OEP-VCF-LP-CLOPT 183 5.072E-10 0.07 1-IE-FLI-AB_108_SP2,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 184 5.072E-10 0.07 1-IE-FLI-AB_108_SP1,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 185 5.072E-10 0.07 1-IE-FLI-AB_108_SP2,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 186 5.072E-10 0.07 1-IE-FLI-AB_108_SP1,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 187 5.036E-10 0.07 1-IE-FLI-CB_123_SP,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 188 5.036E-10 0.07 1-IE-FLI-CB_122_SP,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 189 5.036E-10 0.07 1-IE-FLI-CB_123_SP,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 190 5.036E-10 0.07 1-IE-FLI-CB_122_SP,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 191 5.025E-10 0.07 1-IE-FLI-AB_A20,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPT 192 5.022E-10 0.07 1-IE-FLI-AB_C118_LF,1-EPS-DGN-MA-G4001___,1-OEP-VCF-LP-CLOPT 193 4.921E-10 0.07 1-IE-FLI-CB_123_SP,1-CVC-MDP-FS-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 194 4.921E-10 0.07 1-IE-FLI-CB_122_SP,1-CVC-MDP-FS-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 195 4.888E-10 0.07 1-IE-FLI-DGB_101_LF,1-EPS-DGN-MA-G4001___,1-OEP-VCF-LP-CLOPT 196 4.888E-10 0.07 1-IE-FLI-DGB_103_LF,1-EPS-DGN-MA-G4002___,1-OEP-VCF-LP-CLOPT 197 4.837E-10 0.06 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-BA03____,1-RCS-MDP-LK-BP1 198 4.837E-10 0.06 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-BB16____,1-RCS-MDP-LK-BP1 199 4.831E-10 0.06 1-IE-FLI-CB_A60,1-ACP-CRB-CC-AA0205__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 200 4.749E-10 0.06 1-IE-FLI-AB_C113_LF1,1-EPS-TNK-MA-DFOSTKB_,1-OEP-VCF-LP-CLOPT 201 4.748E-10 0.06 1-IE-FLI-AB_C113_LF1,1-EPS-DGN-MA-G4002___,1-OEP-VCF-LP-RLOOP 202 4.508E-10 0.06 1-IE-FLI-AB_108_SP1,1-RPS-BME-CF-RTBAB 203 4.508E-10 0.06 1-IE-FLI-AB_108_SP2,1-RPS-BME-CF-RTBAB 204 4.476E-10 0.06 1-IE-FLI-CB_122_SP,1-RPS-BME-CF-RTBAB 205 4.476E-10 0.06 1-IE-FLI-CB_123_SP,1-RPS-BME-CF-RTBAB 206 4.399E-10 0.06 1-IE-FLI-CB_A48,1-ACP-BAC-FC-BA03____,1-FLI-CB-A58A48-FP 207 4.399E-10 0.06 1-IE-FLI-CB_A48,1-ACP-BAC-FC-BB16____,1-FLI-CB-A58A48-FP 208 4.271E-10 0.06 1-IE-FLI-AB_108_SP1,1-DCP-BCH-FC-AAABBABB-CC

B-8 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 209 4.271E-10 0.06 1-IE-FLI-AB_108_SP2,1-DCP-BCH-FC-AAABBABB-CC 210 4.262E-10 0.06 1-IE-FLI-CB_123_SP,1-ACP-INV-MA-AD1I11__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 211 4.262E-10 0.06 1-IE-FLI-CB_122_SP,1-ACP-INV-MA-AD1I11__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 212 4.241E-10 0.06 1-IE-FLI-CB_122_SP,1-DCP-BCH-FC-AAABBABB-CC 213 4.241E-10 0.06 1-IE-FLI-CB_123_SP,1-DCP-BCH-FC-AAABBABB-CC 214 4.153E-10 0.06 1-IE-FLI-AB_C113_LF1,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPT 215 4.060E-10 0.05 1-IE-FLI-AB_C115_LF,1-ACP-TFW-FC-BB16X___,1-RCS-MDP-LK-BP2 216 3.971E-10 0.05 1-IE-FLI-AB_C113_LF1,1-ACP-CRB-CO-BA0309__,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 217 3.971E-10 0.05 1-IE-FLI-AB_C113_LF1,1-ACP-CRB-CO-BB1601__,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 218 3.825E-10 0.05 1-IE-FLI-TB_500_LF,1-RPS-BME-CF-RTBAB,1-UET2-NOPORV-BLK 219 3.816E-10 0.05 1-IE-FLI-AB_C120_LF,1-EPS-TNK-MA-DFOSTKB_,1-OEP-VCF-LP-CLOPT 220 3.815E-10 0.05 1-IE-FLI-AB_C120_LF,1-EPS-DGN-MA-G4002___,1-OEP-VCF-LP-RLOOP 221 3.788E-10 0.05 1-IE-FLI-AB_C113_LF1,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT,1-SWS-MOV-CC-1669A___

222 3.685E-10 0.05 1-IE-FLI-AB_D74_FP,1-ACP-BAC-MA-BA03____,1-RCS-MDP-LK-BP2 223 3.685E-10 0.05 1-IE-FLI-AB_D74_FP,1-ACP-BAC-MA-BB16____,1-RCS-MDP-LK-BP2 224 3.574E-10 0.05 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-BA03____,1-RCS-MDP-LK-BP1 225 3.574E-10 0.05 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-BB16____,1-RCS-MDP-LK-BP1 226 3.496E-10 0.05 1-IE-FLI-DGB_101_LF,1-ACP-BAC-FC-AA02____

227 3.433E-10 0.05 1-IE-FLI-CB_A60,1-AFW-MDP-MA-P4003___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 228 3.388E-10 0.05 1-IE-FLI-AB_108_SP1,1-RPS-ROD-CF-RCCAS 229 3.388E-10 0.05 1-IE-FLI-AB_108_SP2,1-RPS-ROD-CF-RCCAS 230 3.368E-10 0.04 1-IE-FLI-AB_C120_LF,1-AFW-MOV-OO-FV5154__,1-OEP-VCF-LP-CLOPT 231 3.364E-10 0.04 1-IE-FLI-CB_122_SP,1-RPS-ROD-CF-RCCAS 232 3.364E-10 0.04 1-IE-FLI-CB_123_SP,1-RPS-ROD-CF-RCCAS 233 3.344E-10 0.04 1-IE-FLI-CB_A60,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPL 234 3.337E-10 0.04 1-IE-FLI-AB_C120_LF,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPT 235 3.298E-10 0.04 1-IE-FLI-AB_B08_LF,1-ACP-BAC-MA-BA03____,1-RCS-MDP-LK-BP2 236 3.298E-10 0.04 1-IE-FLI-AB_B08_LF,1-ACP-BAC-MA-BB16____,1-RCS-MDP-LK-BP2 237 3.277E-10 0.04 1-IE-FLI-TB_500_LF,1-ACP-CRB-CC-AA0205__,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPT 238 3.234E-10 0.04 1-IE-FLI-AB_C118_LF,1-ACP-BAC-MA-AA02____,1-RCS-MDP-LK-BP2 239 3.234E-10 0.04 1-IE-FLI-AB_C118_LF,1-ACP-BAC-MA-AB15____,1-RCS-MDP-LK-BP2 240 3.191E-10 0.04 1-IE-FLI-AB_C120_LF,1-ACP-CRB-CO-BA0309__,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 241 3.191E-10 0.04 1-IE-FLI-AB_C120_LF,1-ACP-CRB-CO-BB1601__,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP

B-9 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 242 3.148E-10 0.04 1-IE-FLI-DGB_101_LF,1-ACP-BAC-MA-AB15____,1-RCS-MDP-LK-BP2 243 3.148E-10 0.04 1-IE-FLI-DGB_103_LF,1-ACP-BAC-MA-BA03____,1-RCS-MDP-LK-BP2 244 3.148E-10 0.04 1-IE-FLI-DGB_103_LF,1-ACP-BAC-MA-BB16____,1-RCS-MDP-LK-BP2 245 3.085E-10 0.04 1-IE-FLI-AB_A20,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPT 246 3.044E-10 0.04 1-IE-FLI-AB_C120_LF,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT,1-SWS-MOV-CC-1669A___

247 3.028E-10 0.04 1-IE-FLI-CB_123_SP,1-EPS-TNK-MA-DFOSTKA_,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 248 3.028E-10 0.04 1-IE-FLI-CB_122_SP,1-EPS-TNK-MA-DFOSTKA_,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 249 3.007E-10 0.04 1-IE-FLI-CB_A60,1-EPS-SEQ-FO-1821U301,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 250 2.889E-10 0.04 1-IE-FLI-AB_108_SP1,1-AFW-MDP-MA-P4002___,1-AFW-TDP-FS-P4001___,1-OAB_TR-------H 251 2.889E-10 0.04 1-IE-FLI-AB_108_SP2,1-AFW-MDP-MA-P4002___,1-AFW-TDP-FS-P4001___,1-OAB_TR-------H 252 2.875E-10 0.04 1-IE-FLI-TB_500_LF,1-RPS-ROD-CF-RCCAS,1-UET2-NOPORV-BLK 253 2.868E-10 0.04 1-IE-FLI-CB_122_SP,1-AFW-MDP-MA-P4003___,1-AFW-TDP-FS-P4001___,1-OAB_TR-------H 254 2.868E-10 0.04 1-IE-FLI-CB_123_SP,1-AFW-MDP-MA-P4003___,1-AFW-TDP-FS-P4001___,1-OAB_TR-------H 255 2.820E-10 0.04 1-IE-FLI-AB_C115_LF,1-EPS-TNK-MA-DFOSTKB_,1-OEP-VCF-LP-CLOPT 256 2.819E-10 0.04 1-IE-FLI-AB_C115_LF,1-EPS-DGN-MA-G4002___,1-OEP-VCF-LP-RLOOP 257 2.749E-10 0.04 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-LPI-MDP-FS-RHRB____,1-OEP-VCF-LP-CLOPL 258 2.749E-10 0.04 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-LPI-MDP-FS-RHRB____,1-OEP-VCF-LP-CLOPL 259 2.696E-10 0.04 1-IE-FLI-AB_108_SP2,1-ACP-INV-MA-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 260 2.696E-10 0.04 1-IE-FLI-AB_108_SP1,1-ACP-INV-MA-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 261 2.677E-10 0.04 1-IE-FLI-CB_123_SP,1-ACP-INV-MA-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 262 2.677E-10 0.04 1-IE-FLI-CB_122_SP,1-ACP-INV-MA-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 263 2.655E-10 0.04 1-IE-FLI-CB_A60,1-EPS-DGN-FS-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 264 2.611E-10 0.03 1-IE-FLI-CB_A48,1-ACP-CRB-CC-BA0301__,1-FLI-CB-A58A48-FP,1-OEP-VCF-LP-CLOPT 265 2.596E-10 0.03 1-IE-FLI-CB_123_SP,1-CVC-MDP-TE-CCPB____,1-EPS-DGN-MA-G4001___,1-OEP-VCF-LP-CLOPL 266 2.596E-10 0.03 1-IE-FLI-CB_122_SP,1-CVC-MDP-TE-CCPB____,1-EPS-DGN-MA-G4001___,1-OEP-VCF-LP-CLOPL 267 2.552E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-BA03____,1-OEP-VCF-LP-CLOPT 268 2.552E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-BB07____,1-OEP-VCF-LP-CLOPT 269 2.552E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-BB16____,1-OEP-VCF-LP-CLOPT 270 2.552E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-MCCBBB__,1-OEP-VCF-LP-CLOPT 271 2.552E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-MCCBBF__,1-OEP-VCF-LP-CLOPT

B-10 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 272 2.550E-10 0.03 1-IE-FLI-AB_C113_LF1,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPT 273 2.550E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-INV-FC-BD1I12__,1-OEP-VCF-LP-CLOPT 274 2.516E-10 0.03 1-IE-FLI-AB_108_SP1,1-AFW-PMP-CF-RUN,1-OAB_TR-------H 275 2.516E-10 0.03 1-IE-FLI-AB_108_SP2,1-AFW-PMP-CF-RUN,1-OAB_TR-------H 276 2.498E-10 0.03 1-IE-FLI-CB_122_SP,1-AFW-PMP-CF-RUN,1-OAB_TR-------H 277 2.498E-10 0.03 1-IE-FLI-CB_123_SP,1-AFW-PMP-CF-RUN,1-OAB_TR-------H 278 2.491E-10 0.03 1-IE-FLI-AB_B24_LF2,1-ACP-BAC-MA-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 279 2.491E-10 0.03 1-IE-FLI-AB_B24_LF2,1-ACP-BAC-MA-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 280 2.466E-10 0.03 1-IE-FLI-AB_C115_LF,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPT 281 2.456E-10 0.03 1-IE-FLI-CB_A60,1-DCP-BAT-MA-AD1B____,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 282 2.446E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-INV-MA-BD1I12__,1-OEP-VCF-LP-CLOPT 283 2.435E-10 0.03 1-IE-FLI-AB_A20,1-AFW-PMP-CF-RUN,1-OAB_TR-------H 284 2.430E-10 0.03 1-IE-FLI-AB_D74_FP,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPT 285 2.419E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-CRB-CO-BA0309__,1-RCS-MDP-LK-BP2 286 2.419E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-CRB-CO-BB1601__,1-RCS-MDP-LK-BP2 287 2.404E-10 0.03 1-IE-FLI-AB_108_SP2,1-ACP-CRB-CC-AA0205__,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPL 288 2.404E-10 0.03 1-IE-FLI-AB_108_SP1,1-ACP-CRB-CC-AA0205__,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPL 289 2.391E-10 0.03 1-IE-FLI-TB_500_LF,1-AFW-MDP-CF-START,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 290 2.387E-10 0.03 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-AA0205__,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPL 291 2.387E-10 0.03 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-AA0205__,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPL 292 2.364E-10 0.03 1-IE-FLI-AB_B50_JI,1-ACP-BAC-MA-AA02____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 293 2.364E-10 0.03 1-IE-FLI-AB_B50_JI,1-ACP-BAC-MA-AB15____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 294 2.357E-10 0.03 1-IE-FLI-AB_C115_LF,1-ACP-CRB-CO-BA0309__,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 295 2.357E-10 0.03 1-IE-FLI-AB_C115_LF,1-ACP-CRB-CO-BB1601__,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 296 2.357E-10 0.03 1-IE-FLI-AB_B24_LF2,1-EPS-DGN-MA-G4002___,1-OEP-VCF-LP-CLOPT 297 2.334E-10 0.03 1-IE-FLI-AB_108_SP1,1-AFW-TDP-FR-P4001___,1-EPS-DGN-MA-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 298 2.334E-10 0.03 1-IE-FLI-AB_108_SP2,1-AFW-TDP-FR-P4001___,1-EPS-DGN-MA-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 299 2.315E-10 0.03 1-IE-FLI-TB_500_LF,1-NSCW-CT-NEED-SWAP,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-SWT-FC-TY16689B-CC 300 2.307E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-BYB1____,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT 301 2.249E-10 0.03 1-IE-FLI-AB_C115_LF,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT,1-SWS-MOV-CC-1669A___

302 2.237E-10 0.03 1-IE-FLI-AB_B50_JI,1-EPS-DGN-MA-G4001___,1-OEP-VCF-LP-CLOPT 303 2.220E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-SSD-MA-1821U302,1-OEP-VCF-LP-CLOPT

B-11 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 304 2.179E-10 0.03 1-IE-FLI-AB_108_SP1,1-AFW-MOV-OO-FV5154__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 305 2.179E-10 0.03 1-IE-FLI-AB_108_SP2,1-AFW-MOV-OO-FV5154__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 306 2.175E-10 0.03 1-IE-FLI-AB_B08_LF,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPT 307 2.164E-10 0.03 1-IE-FLI-CB_122_SP,1-AFW-MOV-OO-FV5155__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 308 2.164E-10 0.03 1-IE-FLI-CB_123_SP,1-AFW-MOV-OO-FV5155__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 309 2.132E-10 0.03 1-IE-FLI-AB_C118_LF,1-ACP-CRB-CC-AA0205__,1-OEP-VCF-LP-CLOPT 310 2.076E-10 0.03 1-IE-FLI-DGB_101_LF,1-ACP-CRB-CC-AA0205__,1-OEP-VCF-LP-CLOPT 311 2.076E-10 0.03 1-IE-FLI-DGB_103_LF,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPT 312 2.066E-10 0.03 1-IE-FLI-AB_C113_LF1,1-AFW-MDP-MA-P4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPT 313 2.051E-10 0.03 1-IE-FLI-AB_C113_LF1,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MDP-MA-P4_00246-3 314 2.051E-10 0.03 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-BA03____,1-OEP-VCF-LP-CLOPT 315 2.051E-10 0.03 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-BB07____,1-OEP-VCF-LP-CLOPT 316 2.051E-10 0.03 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-BB16____,1-OEP-VCF-LP-CLOPT 317 2.051E-10 0.03 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-MCCBBB__,1-OEP-VCF-LP-CLOPT 318 2.051E-10 0.03 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-MCCBBF__,1-OEP-VCF-LP-CLOPT 319 2.049E-10 0.03 1-IE-FLI-AB_C120_LF,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPT 320 2.049E-10 0.03 1-IE-FLI-AB_C120_LF,1-ACP-INV-FC-BD1I12__,1-OEP-VCF-LP-CLOPT 321 2.040E-10 0.03 1-IE-FLI-TB_500_LF,1-ACP-CRB-CC-AA0205__,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 322 2.040E-10 0.03 1-IE-FLI-TB_500_LF,1-ACP-CRB-CC-BA0301__,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPT 323 2.016E-10 0.03 1-IE-FLI-AB_C113_LF1,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-RLOOP 324 1.990E-10 0.03 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AA02____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H 325 1.990E-10 0.03 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AA02____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H 326 1.965E-10 0.03 1-IE-FLI-AB_C120_LF,1-ACP-INV-MA-BD1I12__,1-OEP-VCF-LP-CLOPT 327 1.948E-10 0.03 1-IE-FLI-AB_C118_LF,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1668ACT_

328 1.944E-10 0.03 1-IE-FLI-AB_C120_LF,1-ACP-CRB-CO-BA0309__,1-RCS-MDP-LK-BP2 329 1.944E-10 0.03 1-IE-FLI-AB_C120_LF,1-ACP-CRB-CO-BB1601__,1-RCS-MDP-LK-BP2 330 1.896E-10 0.03 1-IE-FLI-DGB_101_LF,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1668ACT_

331 1.893E-10 0.03 1-IE-FLI-AB_C120_LF,1-AFW-MDP-FR-P4002___,1-OEP-VCF-LP-CLOPT 332 1.889E-10 0.03 1-IE-FLI-CB_A60,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 333 1.886E-10 0.03 1-IE-FLI-CB_A48,1-AFW-MOV-OO-FV5154__,1-FLI-CB-A58A48-FP,1-OAB_TR-------H 334 1.881E-10 0.03 1-IE-FLI-CB_123_SP,1-CVC-MDP-FS-CCPB____,1-EPS-DGN-MA-G4001___,1-OEP-VCF-LP-CLOPL 335 1.881E-10 0.03 1-IE-FLI-CB_122_SP,1-CVC-MDP-FS-CCPB____,1-EPS-DGN-MA-G4001___,1-OEP-VCF-LP-CLOPL

B-12 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 336 1.869E-10 0.02 1-IE-FLI-AB_C113_LF1,1-ACP-DCP-FC-1B_PS4__,1-OEP-VCF-LP-CLOPT 337 1.869E-10 0.02 1-IE-FLI-AB_C113_LF1,1-ACP-DCP-FC-1B_PS1__,1-OEP-VCF-LP-CLOPT 338 1.854E-10 0.02 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-BYB1____,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT 339 1.793E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AA02____,1-LPI-MDP-MA-RHRB____

340 1.793E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AA02____,1-CVC-MDP-MA-CCPB____

341 1.793E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AA02____,1-LPI-MDP-MA-RHRB____

342 1.793E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AA02____,1-CVC-MDP-MA-CCPB____

343 1.785E-10 0.02 1-IE-FLI-CB_A60,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-CF-FS-ALL 344 1.784E-10 0.02 1-IE-FLI-AB_C120_LF,1-ACP-SSD-MA-1821U302,1-OEP-VCF-LP-CLOPT 345 1.743E-10 0.02 1-IE-FLI-TB_500_HI1,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPT 346 1.743E-10 0.02 1-IE-FLI-TB_500_HI2,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPT 347 1.666E-10 0.02 1-IE-FLI-TB_500_LF,1-ACP-CRB-CC-BA0301__,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPT 348 1.666E-10 0.02 1-IE-FLI-TB_500_LF,1-ACP-CRB-CC-AA0205__,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPT 349 1.650E-10 0.02 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-OAR_LTFB-TRA-H,1-OEP-VCF-LP-CLOPL 350 1.650E-10 0.02 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-OAR_LTFB-TRA-H,1-OEP-VCF-LP-CLOPL 351 1.648E-10 0.02 1-IE-FLI-AB_C120_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MDP-MA-P4_00246-3 352 1.643E-10 0.02 1-IE-FLI-AB_108_SP2,1-ACP-INV-MA-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 353 1.643E-10 0.02 1-IE-FLI-AB_108_SP1,1-ACP-INV-MA-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 354 1.633E-10 0.02 1-IE-FLI-AB_108_SP2,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,1-RPS-CBI-CF-6OF8,/1-RPS-CCP-TM-CHA,1-RPS-XHE-XE-NSGNL 355 1.633E-10 0.02 1-IE-FLI-AB_108_SP1,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,1-RPS-CBI-CF-6OF8,/1-RPS-CCP-TM-CHA,1-RPS-XHE-XE-NSGNL 356 1.631E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-INV-MA-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 357 1.631E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-INV-MA-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 358 1.625E-10 0.02 1-IE-FLI-CB_A48,1-EPS-SEQ-FO-1821U302,1-FLI-CB-A58A48-FP,1-OEP-VCF-LP-CLOPT 359 1.622E-10 0.02 1-IE-FLI-CB_123_SP,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,1-RPS-CBI-CF-6OF8,/1-RPS-CCP-TM-CHA,1-RPS-XHE-XE-NSGNL 360 1.622E-10 0.02 1-IE-FLI-CB_122_SP,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,1-RPS-CBI-CF-6OF8,/1-RPS-CCP-TM-CHA,1-RPS-XHE-XE-NSGNL 361 1.620E-10 0.02 1-IE-FLI-AB_C120_LF,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-RLOOP 362 1.544E-10 0.02 1-IE-FLI-CB_123_SP,1-NSCWCT-SPRAY,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CC-1668A___

363 1.544E-10 0.02 1-IE-FLI-CB_122_SP,1-NSCWCT-SPRAY,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CC-1668A___

364 1.543E-10 0.02 1-IE-FLI-CB_A60,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 365 1.543E-10 0.02 1-IE-FLI-CB_A60,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP

B-13 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 366 1.540E-10 0.02 1-IE-FLI-CB_A60,1-EPS-DGN-FR-G4001___,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 367 1.540E-10 0.02 1-IE-FLI-CB_A60,1-CVC-MDP-MA-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 368 1.518E-10 0.02 1-IE-FLI-AB_B24_LF2,1-ACP-BAC-MA-BA03____,1-RCS-MDP-LK-BP2 369 1.518E-10 0.02 1-IE-FLI-AB_B24_LF2,1-ACP-BAC-MA-BB16____,1-RCS-MDP-LK-BP2 370 1.516E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-BA03____,1-OEP-VCF-LP-CLOPT 371 1.516E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-BB07____,1-OEP-VCF-LP-CLOPT 372 1.516E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-BB16____,1-OEP-VCF-LP-CLOPT 373 1.516E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-MCCBBB__,1-OEP-VCF-LP-CLOPT 374 1.516E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-MCCBBF__,1-OEP-VCF-LP-CLOPT 375 1.514E-10 0.02 1-IE-FLI-AB_C115_LF,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPT 376 1.514E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-INV-FC-BD1I12__,1-OEP-VCF-LP-CLOPT 377 1.513E-10 0.02 1-IE-FLI-AB_D74_FP,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 378 1.511E-10 0.02 1-IE-FLI-CB_123_SP,1-CVC-MDP-FR-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 379 1.511E-10 0.02 1-IE-FLI-CB_122_SP,1-CVC-MDP-FR-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 380 1.502E-10 0.02 1-IE-FLI-AB_C120_LF,1-ACP-DCP-FC-1B_PS4__,1-OEP-VCF-LP-CLOPT 381 1.502E-10 0.02 1-IE-FLI-AB_C120_LF,1-ACP-DCP-FC-1B_PS1__,1-OEP-VCF-LP-CLOPT 382 1.497E-10 0.02 1-IE-FLI-AB_108_SP2,1-ACP-CRB-CC-AA0205__,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 383 1.497E-10 0.02 1-IE-FLI-AB_108_SP1,1-ACP-CRB-CC-AA0205__,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 384 1.497E-10 0.02 1-IE-FLI-AB_108_SP2,1-ACP-CRB-CC-BA0301__,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 385 1.497E-10 0.02 1-IE-FLI-AB_108_SP1,1-ACP-CRB-CC-BA0301__,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 386 1.486E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-AA0205__,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 387 1.486E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-AA0205__,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 388 1.486E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-BA0301__,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 389 1.486E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-BA0301__,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 390 1.476E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AA02____,1-CVC-MDP-TE-CCPB____

391 1.476E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AA02____,1-CVC-MDP-TE-CCPB____

392 1.452E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-INV-MA-BD1I12__,1-OEP-VCF-LP-CLOPT 393 1.441E-10 0.02 1-IE-FLI-AB_B50_JI,1-ACP-BAC-MA-AA02____,1-RCS-MDP-LK-BP2 394 1.441E-10 0.02 1-IE-FLI-AB_B50_JI,1-ACP-BAC-MA-AB15____,1-RCS-MDP-LK-BP2 395 1.438E-10 0.02 1-IE-FLI-CB_A60,1-ACP-BAC-FC-AA02____,1-OAB_TR-------H 396 1.436E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-CRB-CO-BA0309__,1-RCS-MDP-LK-BP2 397 1.436E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-CRB-CO-BB1601__,1-RCS-MDP-LK-BP2 398 1.435E-10 0.02 1-IE-FLI-CB_A48,1-EPS-DGN-FS-G4002___,1-FLI-CB-A58A48-FP,1-OEP-VCF-LP-CLOPT

B-14 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 399 1.410E-10 0.02 1-IE-FLI-TB_500_LF,1-NSCW-CT-NEED-SWAP,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-SWT-FC-TY16689B-CC 400 1.406E-10 0.02 1-IE-FLI-CB_A48,1-ACP-TFW-FC-BB16X___,1-FLI-CB-A58A48-FP 401 1.393E-10 0.02 1-IE-FLI-CB_A60,1-EPS-SEQ-CF-FOAB,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP1 402 1.386E-10 0.02 1-IE-FLI-TB_500_LF,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,1-RPS-CBI-CF-6OF8,/1-RPS-CCP-TM-CHA,1-RPS-XHE-XE-NSGNL,1-UET2-NOPORV-BLK 403 1.370E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-BAC-MA-BYB1____,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT 404 1.354E-10 0.02 1-IE-FLI-AB_B08_LF,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 405 1.344E-10 0.02 1-IE-FLI-AB_D74_FP,1-ACP-BAC-FC-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 406 1.344E-10 0.02 1-IE-FLI-AB_D74_FP,1-ACP-BAC-FC-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 407 1.339E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-AA0205__,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 408 1.339E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-AA0205__,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 409 1.339E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-AA0205__,1-CVC-MDP-MA-CCPB____,1-OEP-VCF-LP-CLOPL 410 1.339E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-AA0205__,1-CVC-MDP-MA-CCPB____,1-OEP-VCF-LP-CLOPL 411 1.337E-10 0.02 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-BA03____,1-RCS-MDP-LK-BP1 412 1.337E-10 0.02 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-BB16____,1-RCS-MDP-LK-BP1 413 1.335E-10 0.02 1-IE-FLI-AB_D74_FP,1-EPS-DGN-FS-G4002___,1-OEP-VCF-LP-CLOPT 414 1.328E-10 0.02 1-IE-FLI-CB_A48,1-DCP-BAT-MA-BD1B____,1-FLI-CB-A58A48-FP,1-OEP-VCF-LP-CLOPT 415 1.327E-10 0.02 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-BA03____,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 416 1.327E-10 0.02 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-BA03____,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 417 1.327E-10 0.02 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-BB07____,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 418 1.327E-10 0.02 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-BB07____,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 419 1.327E-10 0.02 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-MCCBBF__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 420 1.327E-10 0.02 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-MCCBBF__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 421 1.327E-10 0.02 1-IE-FLI-AB_C118_LF,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPT 422 1.322E-10 0.02 1-IE-FLI-TB_500_LF,1-AFW-TDP-FR-P4001___,1-RPS-BME-CF-RTBAB 423 1.318E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-SSD-MA-1821U302,1-OEP-VCF-LP-CLOPT 424 1.318E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AB05____,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 425 1.318E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AB05____,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 426 1.318E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-MCCABF__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 427 1.318E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-MCCABF__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 428 1.292E-10 0.02 1-IE-FLI-DGB_101_LF,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPT 429 1.292E-10 0.02 1-IE-FLI-DGB_103_LF,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 430 1.271E-10 0.02 1-IE-FLI-TB_500_LF,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-RLOOP

B-15 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 431 1.269E-10 0.02 1-IE-FLI-TB_500_LF,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 432 1.268E-10 0.02 1-IE-FLI-CB_A60,1-CVC-MDP-TE-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 433 1.255E-10 0.02 1-IE-FLI-AB_C113_LF1,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-RLOOP 434 1.250E-10 0.02 1-IE-FLI-AB_C113_LF1,1-RCS-MDP-LK-BP2,1-SWS-MDP-MA-P4_00246-3 435 1.235E-10 0.02 1-IE-FLI-AB_D74_FP,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPT 436 1.233E-10 0.02 1-IE-FLI-CB_A48,1-FLI-CB-A58A48-FP,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_B_1234_

437 1.228E-10 0.02 1-IE-FLI-TB_500_LF,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT,1-SWS-MOV-CF-1668A69A 438 1.227E-10 0.02 1-IE-FLI-AB_C115_LF,1-AFW-MDP-MA-P4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPT 439 1.225E-10 0.02 1-IE-FLI-AB_108_SP1,1-AFW-MDP-FR-P4002___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 440 1.225E-10 0.02 1-IE-FLI-AB_108_SP2,1-AFW-MDP-FR-P4002___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 441 1.222E-10 0.02 1-IE-FLI-AB_108_SP2,1-ACP-CRB-CC-BA0301__,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL 442 1.222E-10 0.02 1-IE-FLI-AB_108_SP1,1-ACP-CRB-CC-BA0301__,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL 443 1.222E-10 0.02 1-IE-FLI-AB_108_SP2,1-ACP-CRB-CC-AA0205__,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPL 444 1.222E-10 0.02 1-IE-FLI-AB_108_SP1,1-ACP-CRB-CC-AA0205__,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPL 445 1.218E-10 0.02 1-IE-FLI-AB_C115_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MDP-MA-P4_00246-3 446 1.216E-10 0.02 1-IE-FLI-CB_122_SP,1-AFW-MDP-FR-P4003___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 447 1.216E-10 0.02 1-IE-FLI-CB_123_SP,1-AFW-MDP-FR-P4003___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 448 1.214E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-BA0301__,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL 449 1.214E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-BA0301__,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL 450 1.214E-10 0.02 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-AA0205__,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPL 451 1.214E-10 0.02 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-AA0205__,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPL 452 1.204E-10 0.02 1-IE-FLI-TB_500_LF,1-EPS-DGN-FR-G4002___,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT,1-SWS-MOV-CC-1668A___

453 1.204E-10 0.02 1-IE-FLI-TB_500_LF,1-EPS-DGN-FR-G4001___,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT,1-SWS-MOV-CC-1669A___

454 1.202E-10 0.02 1-IE-FLI-AB_B08_LF,1-ACP-BAC-FC-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 455 1.202E-10 0.02 1-IE-FLI-AB_B08_LF,1-ACP-BAC-FC-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 456 1.197E-10 0.02 1-IE-FLI-AB_C115_LF,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-RLOOP 457 1.195E-10 0.02 1-IE-FLI-AB_B08_LF,1-EPS-DGN-FS-G4002___,1-OEP-VCF-LP-CLOPT 458 1.187E-10 0.02 1-IE-FLI-AB_C118_LF,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP2,1-SWS-MOV-MA-1668ACT_

459 1.179E-10 0.02 1-IE-FLI-AB_C118_LF,1-ACP-BAC-FC-AA02____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 460 1.179E-10 0.02 1-IE-FLI-AB_C118_LF,1-ACP-BAC-FC-AB15____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 461 1.172E-10 0.02 1-IE-FLI-AB_C118_LF,1-EPS-DGN-FS-G4001___,1-OEP-VCF-LP-CLOPT 462 1.155E-10 0.02 1-IE-FLI-DGB_101_LF,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP2,1-SWS-MOV-MA-1668ACT_

463 1.151E-10 0.02 1-IE-FLI-CB_A60,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2

B-16 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 464 1.148E-10 0.02 1-IE-FLI-CB_A48,1-ACP-BAC-MA-MCCBBF__,1-FLI-CB-A58A48-FP,1-OAB_TR-------H 465 1.148E-10 0.02 1-IE-FLI-CB_A48,1-ACP-BAC-MA-BB07____,1-FLI-CB-A58A48-FP,1-OAB_TR-------H 466 1.148E-10 0.02 1-IE-FLI-AB_D74_FP,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_B_1234_

467 1.148E-10 0.02 1-IE-FLI-DGB_103_LF,1-ACP-BAC-FC-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 468 1.148E-10 0.02 1-IE-FLI-DGB_103_LF,1-ACP-BAC-FC-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 469 1.148E-10 0.02 1-IE-FLI-DGB_101_LF,1-ACP-BAC-FC-AB15____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 470 1.144E-10 0.02 1-IE-FLI-CB_A60,1-AFW-TDP-FR-P4001___,1-OA-MISPAF5095H,1-OAB_TR-------H 471 1.144E-10 0.02 1-IE-FLI-CB_A60,1-AFW-MDP-FS-P4003___,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 472 1.142E-10 0.02 1-IE-FLI-AB_C113_LF1,1-RCS-MDP-LK-BP1,1-SWS-CTF-MA-_B_1234_

473 1.141E-10 0.02 1-IE-FLI-DGB_101_LF,1-EPS-DGN-FS-G4001___,1-OEP-VCF-LP-CLOPT 474 1.141E-10 0.02 1-IE-FLI-DGB_103_LF,1-EPS-DGN-FS-G4002___,1-OEP-VCF-LP-CLOPT 475 1.119E-10 0.01 1-IE-FLI-TB_500_LF-CDS,1-RPS-BME-CF-RTBAB,1-UET2-NOPORV-BLK 476 1.110E-10 0.01 1-IE-FLI-AB_C115_LF,1-ACP-DCP-FC-1B_PS4__,1-OEP-VCF-LP-CLOPT 477 1.110E-10 0.01 1-IE-FLI-AB_C115_LF,1-ACP-DCP-FC-1B_PS1__,1-OEP-VCF-LP-CLOPT 478 1.110E-10 0.01 1-IE-FLI-AB_108_SP2,1-ACP-INV-FC-AD11BD12-CC,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 479 1.110E-10 0.01 1-IE-FLI-AB_108_SP1,1-ACP-INV-FC-AD11BD12-CC,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 480 1.110E-10 0.01 1-IE-FLI-CB_A48,1-FLI-CB-A58A48-FP,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1669ACT_

481 1.108E-10 0.01 1-IE-FLI-AB_C113_LF1,1-EPS-DGN-FS-G4002___,1-OEP-VCF-LP-RLOOP 482 1.107E-10 0.01 1-IE-FLI-AB_108_SP1,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,/1-RPS-CCP-TM-CHA,1-RPS-CCX-CF-6OF8,1-RPS-XHE-XE-NSGNL 483 1.107E-10 0.01 1-IE-FLI-AB_108_SP2,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,/1-RPS-CCP-TM-CHA,1-RPS-CCX-CF-6OF8,1-RPS-XHE-XE-NSGNL 484 1.106E-10 0.01 1-IE-FLI-AB_B08_LF,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPT 485 1.102E-10 0.01 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-AA0205__,1-CVC-MDP-TE-CCPB____,1-OEP-VCF-LP-CLOPL 486 1.102E-10 0.01 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-AA0205__,1-CVC-MDP-TE-CCPB____,1-OEP-VCF-LP-CLOPL 487 1.102E-10 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-FC-AD11BD12-CC,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 488 1.102E-10 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-FC-AD11BD12-CC,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 489 1.099E-10 0.01 1-IE-FLI-CB_122_SP,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,/1-RPS-CCP-TM-CHA,1-RPS-CCX-CF-6OF8,1-RPS-XHE-XE-NSGNL 490 1.099E-10 0.01 1-IE-FLI-CB_123_SP,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,/1-RPS-CCP-TM-CHA,1-RPS-CCX-CF-6OF8,1-RPS-XHE-XE-NSGNL 491 1.088E-10 0.01 1-IE-FLI-CB_A60,1-RCS-MDP-LK-BP2,1-SWS-CTF-CF-FS-ALL 492 1.084E-10 0.01 1-IE-FLI-AB_C118_LF,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPT 493 1.075E-10 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-BA03____,1-RCS-MDP-LK-BP1

B-17 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 494 1.075E-10 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-BB16____,1-RCS-MDP-LK-BP1 495 1.070E-10 0.01 1-IE-FLI-TB_500_HI2,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPT 496 1.070E-10 0.01 1-IE-FLI-TB_500_HI1,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-CLOPT 497 1.070E-10 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AA02____,1-CVC-MDP-FS-CCPB____

498 1.070E-10 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AA02____,1-CVC-MDP-FS-CCPB____

499 1.060E-10 0.01 1-IE-FLI-CB_A48,1-AFW-MDP-FR-P4002___,1-FLI-CB-A58A48-FP,1-OAB_TR-------H 500 1.055E-10 0.01 1-IE-FLI-DGB_101_LF,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPT 501 1.055E-10 0.01 1-IE-FLI-DGB_103_LF,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPT 502 1.051E-10 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-LPI-MDP-FS-RHRB____,1-OEP-VCF-LP-CLOPL 503 1.051E-10 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-LPI-MDP-FS-RHRB____,1-OEP-VCF-LP-CLOPL 504 1.049E-10 0.01 1-IE-FLI-AB_108_SP1,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-CF-1668A69A 505 1.049E-10 0.01 1-IE-FLI-AB_108_SP2,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-CF-1668A69A 506 1.042E-10 0.01 1-IE-FLI-CB_122_SP,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-CF-1668A69A 507 1.042E-10 0.01 1-IE-FLI-CB_123_SP,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-CF-1668A69A 508 1.040E-10 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-MCCABF__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 509 1.040E-10 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-MCCABF__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 510 1.040E-10 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-MCCABB__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 511 1.040E-10 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-MCCABB__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 512 1.040E-10 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AB05____,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 513 1.040E-10 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AB05____,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 514 1.040E-10 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AB15____,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 515 1.040E-10 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AB15____,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 516 1.039E-10 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-FC-AD1I11__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 517 1.039E-10 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-FC-AD1I11__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 518 1.037E-10 0.01 1-IE-FLI-TB_500_LF,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 519 1.037E-10 0.01 1-IE-FLI-TB_500_LF,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPT 520 1.035E-10 0.01 1-IE-FLI-AB_108_SP1,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-SWT-FC-TY16689B-CC 521 1.035E-10 0.01 1-IE-FLI-AB_108_SP2,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-SWT-FC-TY16689B-CC 522 1.032E-10 0.01 1-IE-FLI-AB_D74_FP,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1669ACT_

523 1.029E-10 0.01 1-IE-FLI-AB_108_SP1,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-CF-FR-ALL 524 1.029E-10 0.01 1-IE-FLI-AB_108_SP2,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-CF-FR-ALL 525 1.028E-10 0.01 1-IE-FLI-AB_C113_LF1,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP1,1-SWS-MOV-MA-1669ACT_

526 1.027E-10 0.01 1-IE-FLI-AB_B08_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_B_1234_

B-18 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 527 1.027E-10 0.01 1-IE-FLI-CB_122_SP,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-SWT-FC-TY16689B-CC 528 1.027E-10 0.01 1-IE-FLI-CB_123_SP,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-SWT-FC-TY16689B-CC 529 1.025E-10 0.01 1-IE-FLI-AB_C113_LF1,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-RLOOP 530 1.022E-10 0.01 1-IE-FLI-CB_122_SP,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-CF-FR-ALL 531 1.022E-10 0.01 1-IE-FLI-CB_123_SP,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-CF-FR-ALL 532 1.008E-10 0.01 1-IE-FLI-AB_C120_LF,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-RLOOP 533 1.007E-10 0.01 1-IE-FLI-AB_C118_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_A_1234_

534 1.004E-10 0.01 1-IE-FLI-AB_C120_LF,1-RCS-MDP-LK-BP2,1-SWS-MDP-MA-P4_00246-3 535 1.001E-10 0.01 1-IE-FLI-CB_123_SP,1-ACP-SSD-MA-1821U301,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 536 1.001E-10 0.01 1-IE-FLI-CB_122_SP,1-ACP-SSD-MA-1821U301,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 537 1.001E-10 0.01 1-IE-FLI-AB_B24_LF2,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPT 538 9.936E-11 0.01 1-IE-FLI-TB_500_LF,1-AFW-TDP-FR-P4001___,1-RPS-ROD-CF-RCCAS 539 9.909E-11 0.01 1-IE-FLI-AB_108_SP1,1-ACP-CRB-CC-BA0301__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 540 9.909E-11 0.01 1-IE-FLI-AB_108_SP2,1-ACP-CRB-CC-BA0301__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 541 9.803E-11 0.01 1-IE-FLI-DGB_103_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_B_1234_

542 9.803E-11 0.01 1-IE-FLI-DGB_101_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_A_1234_

543 9.705E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-OO-LV0112C_,1-OEP-VCF-LP-CLOPL 544 9.705E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-CC-LV0112E_,1-OEP-VCF-LP-CLOPL 545 9.705E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-CC-HV8804B_,1-OEP-VCF-LP-CLOPL 546 9.705E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-OO-HV8813__,1-OEP-VCF-LP-CLOPL 547 9.705E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-CC-HV8807B_,1-OEP-VCF-LP-CLOPL 548 9.705E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-OO-HV8508B_,1-OEP-VCF-LP-CLOPL 549 9.705E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-CC-HV8801B_,1-OEP-VCF-LP-CLOPL 550 9.705E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-OO-HV8105__,1-OEP-VCF-LP-CLOPL 551 9.705E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-OO-LV0112C_,1-OEP-VCF-LP-CLOPL 552 9.705E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-CC-LV0112E_,1-OEP-VCF-LP-CLOPL 553 9.705E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-CC-HV8804B_,1-OEP-VCF-LP-CLOPL 554 9.705E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-OO-HV8813__,1-OEP-VCF-LP-CLOPL 555 9.705E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-CC-HV8807B_,1-OEP-VCF-LP-CLOPL 556 9.705E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-OO-HV8508B_,1-OEP-VCF-LP-CLOPL 557 9.705E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-CC-HV8801B_,1-OEP-VCF-LP-CLOPL 558 9.705E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-HPI-MOV-OO-HV8105__,1-OEP-VCF-LP-CLOPL 559 9.705E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-LPI-MOV-OO-HV8812B_,1-OEP-VCF-LP-CLOPL

B-19 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 560 9.705E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-LPI-MOV-CC-HV8811B_,1-OEP-VCF-LP-CLOPL 561 9.705E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-LPI-MOV-OO-HV8812B_,1-OEP-VCF-LP-CLOPL 562 9.705E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-LPI-MOV-CC-HV8811B_,1-OEP-VCF-LP-CLOPL 563 9.698E-11 0.01 1-IE-FLI-CB_A48,1-AFW-MDP-MA-P4002___,1-FLI-CB-A58A48-FP,1-RCS-PRV-CC-RV0456A_

564 9.630E-11 0.01 1-IE-FLI-AB_108_SP1,1-AFW-TDP-FS-P4001___,1-OA-MISPAF5094H,1-OAB_TR-------H 565 9.630E-11 0.01 1-IE-FLI-AB_108_SP2,1-AFW-TDP-FS-P4001___,1-OA-MISPAF5094H,1-OAB_TR-------H 566 9.630E-11 0.01 1-IE-FLI-AB_108_SP1,1-AFW-MDP-FS-P4002___,1-AFW-TDP-FS-P4001___,1-OAB_TR-------H 567 9.630E-11 0.01 1-IE-FLI-AB_108_SP2,1-AFW-MDP-FS-P4002___,1-AFW-TDP-FS-P4001___,1-OAB_TR-------H 568 9.587E-11 0.01 1-IE-FLI-TB_500_LF-CDS,1-ACP-CRB-CC-AA0205__,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPT 569 9.562E-11 0.01 1-IE-FLI-CB_122_SP,1-AFW-TDP-FS-P4001___,1-OA-MISPAF5095H,1-OAB_TR-------H 570 9.562E-11 0.01 1-IE-FLI-CB_123_SP,1-AFW-TDP-FS-P4001___,1-OA-MISPAF5095H,1-OAB_TR-------H 571 9.562E-11 0.01 1-IE-FLI-CB_122_SP,1-AFW-MDP-FS-P4003___,1-AFW-TDP-FS-P4001___,1-OAB_TR-------H 572 9.562E-11 0.01 1-IE-FLI-CB_123_SP,1-AFW-MDP-FS-P4003___,1-AFW-TDP-FS-P4001___,1-OAB_TR-------H 573 9.524E-11 0.01 1-IE-FLI-AB_108_SP1,1-AFW-TDP-FS-P4001___,1-EPS-DGN-FR-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 574 9.524E-11 0.01 1-IE-FLI-AB_108_SP2,1-AFW-TDP-FS-P4001___,1-EPS-DGN-FR-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 575 9.499E-11 0.01 1-IE-FLI-AB_B50_JI,1-ACP-CRB-CC-AA0205__,1-OEP-VCF-LP-CLOPT 576 9.402E-11 0.01 1-IE-FLI-CB_A60,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 577 9.402E-11 0.01 1-IE-FLI-CB_A60,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 578 9.402E-11 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AYB1____,1-NSCWCT-SPRAY,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 579 9.402E-11 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AYB1____,1-NSCWCT-SPRAY,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 580 9.394E-11 0.01 1-IE-FLI-TB_500_LF,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,/1-RPS-CCP-TM-CHA,1-RPS-CCX-CF-6OF8,1-RPS-XHE-XE-NSGNL,1-UET2-NOPORV-BLK 581 9.315E-11 0.01 1-IE-FLI-AB_108_SP2,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 582 9.315E-11 0.01 1-IE-FLI-AB_108_SP1,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 583 9.248E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 584 9.248E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 585 9.241E-11 0.01 1-IE-FLI-AB_B08_LF,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1669ACT_

586 9.201E-11 0.01 1-IE-FLI-CB_A48,1-AFW-MDP-MA-P4002___,1-EPS-SEQ-FO-1821U302,1-FLI-CB-A58A48-FP,1-OA-NSCWFAN---H 587 9.188E-11 0.01 1-IE-FLI-CB_A60,1-CVC-MDP-FS-CCPB____,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 588 9.180E-11 0.01 1-IE-FLI-AB_C120_LF,1-RCS-MDP-LK-BP1,1-SWS-CTF-MA-_B_1234_

589 9.084E-11 0.01 1-IE-FLI-AB_C120_LF,1-AFW-MDP-MA-P4002___,1-OEP-VCF-LP-RLOOP 590 9.012E-11 0.01 1-IE-FLI-AB_108_SP1,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CF-1668A69A 591 9.012E-11 0.01 1-IE-FLI-AB_108_SP2,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CF-1668A69A

B-20 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 592 8.948E-11 0.01 1-IE-FLI-CB_122_SP,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CF-1668A69A 593 8.948E-11 0.01 1-IE-FLI-CB_123_SP,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CF-1668A69A 594 8.903E-11 0.01 1-IE-FLI-AB_C120_LF,1-EPS-DGN-FS-G4002___,1-OEP-VCF-LP-RLOOP 595 8.861E-11 0.01 1-IE-FLI-AB_C113_LF1,1-DCP-FUS-OP-BD104___,1-OEP-VCF-LP-CLOPT 596 8.837E-11 0.01 1-IE-FLI-AB_108_SP2,1-EPS-DGN-FR-G4002___,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CC-1668A___

597 8.837E-11 0.01 1-IE-FLI-AB_108_SP1,1-EPS-DGN-FR-G4002___,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CC-1668A___

598 8.837E-11 0.01 1-IE-FLI-AB_108_SP2,1-EPS-DGN-FR-G4001___,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CC-1669A___

599 8.837E-11 0.01 1-IE-FLI-AB_108_SP1,1-EPS-DGN-FR-G4001___,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CC-1669A___

600 8.819E-11 0.01 1-IE-FLI-DGB_103_LF,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1669ACT_

601 8.803E-11 0.01 1-IE-FLI-AB_108_SP1,1-OEP-VCF-LP-CLOPL,1-SWS-CTF-CF-FS-ALL 602 8.803E-11 0.01 1-IE-FLI-AB_108_SP2,1-OEP-VCF-LP-CLOPL,1-SWS-CTF-CF-FS-ALL 603 8.774E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4002___,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CC-1668A___

604 8.774E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4002___,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CC-1668A___

605 8.774E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CC-1669A___

606 8.774E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-CC-1669A___

607 8.740E-11 0.01 1-IE-FLI-CB_122_SP,1-OEP-VCF-LP-CLOPL,1-SWS-CTF-CF-FS-ALL 608 8.740E-11 0.01 1-IE-FLI-CB_123_SP,1-OEP-VCF-LP-CLOPL,1-SWS-CTF-CF-FS-ALL 609 8.689E-11 0.01 1-IE-FLI-AB_C113_LF1,1-NSCW-CT-NEED-SWAP,1-NSCW-MOV-F-NON-RECBLE,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-CC-1669A___

610 8.678E-11 0.01 1-IE-FLI-AB_B50_JI,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1668ACT_

611 8.445E-11 0.01 1-IE-FLI-TB_500_HI1,1-AFW-PMP-CF-RUN,1-OAB_TR-------H 612 8.445E-11 0.01 1-IE-FLI-TB_500_HI2,1-AFW-PMP-CF-RUN,1-OAB_TR-------H 613 8.412E-11 0.01 1-IE-FLI-TB_500_LF-CDS,1-RPS-ROD-CF-RCCAS,1-UET2-NOPORV-BLK 614 8.368E-11 0.01 1-IE-FLI-AB_C118_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MDP-MA-P4_00135-3 615 8.356E-11 0.01 1-IE-FLI-CB_A60,1-RPS-BME-CF-RTBAB 616 8.332E-11 0.01 1-IE-FLI-CB_123_SP,1-CVC-MDP-MA-CCPB____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 617 8.332E-11 0.01 1-IE-FLI-CB_122_SP,1-CVC-MDP-MA-CCPB____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 618 8.332E-11 0.01 1-IE-FLI-CB_123_SP,1-EPS-SEQ-FO-1821U301,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 619 8.332E-11 0.01 1-IE-FLI-CB_122_SP,1-EPS-SEQ-FO-1821U301,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 620 8.289E-11 0.01 1-IE-FLI-CB_A48,1-AFW-MDP-MA-P4002___,1-CVC-MDP-MA-CCPB____,1-FLI-CB-A58A48-FP 621 8.258E-11 0.01 1-IE-FLI-AB_C120_LF,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP1,1-SWS-MOV-MA-1669ACT_

622 8.236E-11 0.01 1-IE-FLI-AB_C120_LF,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-RLOOP 623 8.186E-11 0.01 1-IE-FLI-AB_D74_FP,1-ACP-BAC-FC-BA03____,1-RCS-MDP-LK-BP2

B-21 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 624 8.186E-11 0.01 1-IE-FLI-AB_D74_FP,1-ACP-BAC-FC-BB16____,1-RCS-MDP-LK-BP2 625 8.145E-11 0.01 1-IE-FLI-DGB_101_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MDP-MA-P4_00135-3 626 7.987E-11 0.01 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-AA0205__,1-CVC-MDP-FS-CCPB____,1-OEP-VCF-LP-CLOPL 627 7.987E-11 0.01 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-AA0205__,1-CVC-MDP-FS-CCPB____,1-OEP-VCF-LP-CLOPL 628 7.962E-11 0.01 1-IE-FLI-CB_123_SP,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL,1-RCS-PRV-CC-RV0456A_

629 7.962E-11 0.01 1-IE-FLI-CB_122_SP,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL,1-RCS-PRV-CC-RV0456A_

630 7.956E-11 0.01 1-IE-FLI-CB_A60,1-ACP-INV-MA-AD1I11__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 631 7.940E-11 0.01 1-IE-FLI-AB_C115_LF,1-ACP-BAC-FC-BA03____,1-RCS-MDP-LK-BP1 632 7.940E-11 0.01 1-IE-FLI-AB_C115_LF,1-ACP-BAC-FC-BB16____,1-RCS-MDP-LK-BP1 633 7.917E-11 0.01 1-IE-FLI-CB_A60,1-DCP-BCH-FC-AAABBABB-CC 634 7.805E-11 0.01 1-IE-FLI-TB_500_LF,1-EPS-SEQ-CF-FOAB,1-OEP-VCF-LP-RLOOP 635 7.615E-11 0.01 1-IE-FLI-CB_123_SP,1-ACP-DCP-FC-1A_PS1__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 636 7.615E-11 0.01 1-IE-FLI-CB_122_SP,1-ACP-DCP-FC-1A_PS1__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 637 7.615E-11 0.01 1-IE-FLI-CB_123_SP,1-ACP-DCP-FC-1A_PS4__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 638 7.615E-11 0.01 1-IE-FLI-CB_122_SP,1-ACP-DCP-FC-1A_PS4__,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 639 7.608E-11 0.01 1-IE-FLI-AB_108_SP2,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 640 7.608E-11 0.01 1-IE-FLI-AB_108_SP1,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 641 7.608E-11 0.01 1-IE-FLI-AB_108_SP2,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 642 7.608E-11 0.01 1-IE-FLI-AB_108_SP1,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 643 7.554E-11 0.01 1-IE-FLI-CB_123_SP,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 644 7.554E-11 0.01 1-IE-FLI-CB_122_SP,1-DCP-BAT-MA-AD1B____,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPL 645 7.554E-11 0.01 1-IE-FLI-CB_123_SP,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 646 7.554E-11 0.01 1-IE-FLI-CB_122_SP,1-DCP-BAT-MA-BD1B____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 647 7.515E-11 0.01 1-IE-FLI-CB_A48,1-AFW-MDP-MA-P4002___,1-DCP-BAT-MA-BD1B____,1-FLI-CB-A58A48-FP,1-OA-NSCWFAN---H 648 7.515E-11 0.01 1-IE-FLI-CB_A48,1-FLI-CB-A58A48-FP,1-RCS-MDP-LK-BP2,1-SWS-CTF-MA-_B_1234_

649 7.451E-11 < 0.01 1-IE-FLI-AB_C115_LF,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-RLOOP 650 7.421E-11 < 0.01 1-IE-FLI-AB_C115_LF,1-RCS-MDP-LK-BP2,1-SWS-MDP-MA-P4_00246-3 651 7.356E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FS-G4001___,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 652 7.356E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FS-G4001___,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 653 7.356E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CVC-MDP-MA-CCPB____,1-EPS-DGN-FS-G4001___,1-OEP-VCF-LP-CLOPL 654 7.356E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CVC-MDP-MA-CCPB____,1-EPS-DGN-FS-G4001___,1-OEP-VCF-LP-CLOPL 655 7.326E-11 < 0.01 1-IE-FLI-AB_B08_LF,1-ACP-BAC-FC-BA03____,1-RCS-MDP-LK-BP2 656 7.326E-11 < 0.01 1-IE-FLI-AB_B08_LF,1-ACP-BAC-FC-BB16____,1-RCS-MDP-LK-BP2

B-22 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 657 7.183E-11 < 0.01 1-IE-FLI-AB_C118_LF,1-ACP-BAC-FC-AA02____,1-RCS-MDP-LK-BP2 658 7.183E-11 < 0.01 1-IE-FLI-AB_C118_LF,1-ACP-BAC-FC-AB15____,1-RCS-MDP-LK-BP2 659 7.120E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-DCP-FUS-OP-BD104___,1-OEP-VCF-LP-CLOPT 660 6.996E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,1-AFW-MDP-CF-START,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 661 6.993E-11 < 0.01 1-IE-FLI-AB_D74_FP,1-RCS-MDP-LK-BP2,1-SWS-CTF-MA-_B_1234_

662 6.992E-11 < 0.01 1-IE-FLI-DGB_101_LF,1-ACP-BAC-FC-AB15____,1-RCS-MDP-LK-BP2 663 6.992E-11 < 0.01 1-IE-FLI-DGB_103_LF,1-ACP-BAC-FC-BA03____,1-RCS-MDP-LK-BP2 664 6.992E-11 < 0.01 1-IE-FLI-DGB_103_LF,1-ACP-BAC-FC-BB16____,1-RCS-MDP-LK-BP2 665 6.982E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-NSCW-CT-NEED-SWAP,1-NSCW-MOV-F-NON-RECBLE,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-CC-1669A___

666 6.886E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-AFW-MDP-FS-P4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPT 667 6.886E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-OA-MISPAF5094H,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPT 668 6.860E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CVC-MDP-TE-CCPB____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 669 6.860E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CVC-MDP-TE-CCPB____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 670 6.825E-11 < 0.01 1-IE-FLI-CB_A48,1-AFW-MDP-MA-P4002___,1-CVC-MDP-TE-CCPB____,1-FLI-CB-A58A48-FP 671 6.805E-11 < 0.01 1-IE-FLI-CB_123_SP,1-DCP-BAT-MA-AD1B____,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 672 6.805E-11 < 0.01 1-IE-FLI-CB_122_SP,1-DCP-BAT-MA-AD1B____,1-LPI-MDP-MA-RHRB____,1-OEP-VCF-LP-CLOPL 673 6.805E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CVC-MDP-MA-CCPB____,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL 674 6.805E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CVC-MDP-MA-CCPB____,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL 675 6.783E-11 < 0.01 1-IE-FLI-AB_C115_LF,1-RCS-MDP-LK-BP1,1-SWS-CTF-MA-_B_1234_

676 6.772E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,1-NSCW-CT-NEED-SWAP,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-SWT-FC-TY16689B-CC 677 6.761E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-INV-FC-AD11BD12-CC,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 678 6.761E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-INV-FC-AD11BD12-CC,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 679 6.761E-11 < 0.01 1-IE-FLI-CB_A48,1-FLI-CB-A58A48-FP,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP2,1-SWS-MOV-MA-1669ACT_

680 6.713E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-FC-AD11BD12-CC,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 681 6.713E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-FC-AD11BD12-CC,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 682 6.580E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-AA02____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 683 6.580E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-AB15____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 684 6.580E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-BB16____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP

B-23 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 685 6.580E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-BA03____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 686 6.580E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-AA02____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 687 6.580E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-AB15____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 688 6.580E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-BB16____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 689 6.580E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-BA03____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 690 6.578E-11 < 0.01 1-IE-FLI-AB_C115_LF,1-EPS-DGN-FS-G4002___,1-OEP-VCF-LP-RLOOP 691 6.573E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-INV-FC-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 692 6.573E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-INV-FC-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 693 6.573E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-INV-FC-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 694 6.573E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-INV-FC-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 695 6.567E-11 < 0.01 1-IE-FLI-TB_500_LF,1-AFW-MDP-MA-P4002___,1-EPS-DGN-FR-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPT 696 6.549E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-HPI-CKV-OO-189_____,1-OEP-VCF-LP-CLOPL 697 6.549E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-HPI-CKV-OO-189_____,1-OEP-VCF-LP-CLOPL 698 6.549E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CCP-DIVT-THRNCP,1-EPS-DGN-FR-G4001___,1-HPI-CKV-OO-129_____,1-OEP-VCF-LP-CLOPL 699 6.549E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CCP-DIVT-THRNCP,1-EPS-DGN-FR-G4001___,1-HPI-CKV-OO-129_____,1-OEP-VCF-LP-CLOPL 700 6.533E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AB15____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 701 6.533E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-BB16____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 702 6.533E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-BA03____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 703 6.533E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AB15____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 704 6.533E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-BB16____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP

B-24 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 705 6.533E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-BA03____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 706 6.527E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-FC-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 707 6.527E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-FC-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 708 6.527E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-FC-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 709 6.527E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-FC-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 710 6.461E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-FR-G4001___,1-OAB_SI-------H,1-OEP-VCF-LP-CLOPL,1-PI-SGTR-SCREEN 711 6.461E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-FR-G4001___,1-OAB_SI-------H,1-OEP-VCF-LP-CLOPL,1-PI-SGTR-SCREEN 712 6.394E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-MOV-CF-1668A69A 713 6.394E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-MOV-CF-1668A69A 714 6.348E-11 < 0.01 1-IE-FLI-CB_122_SP,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-MOV-CF-1668A69A 715 6.348E-11 < 0.01 1-IE-FLI-CB_123_SP,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-MOV-CF-1668A69A 716 6.335E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-SSD-MA-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 717 6.335E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-SSD-MA-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 718 6.305E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-OAR_LTFB-TRA-H,1-OEP-VCF-LP-CLOPL 719 6.305E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-OAR_LTFB-TRA-H,1-OEP-VCF-LP-CLOPL 720 6.305E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-INV-MA-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 721 6.305E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-INV-MA-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 722 6.304E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-SWT-FC-TY16689B-CC 723 6.304E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-SWT-FC-TY16689B-CC 724 6.291E-11 < 0.01 1-IE-FLI-AB_D74_FP,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP2,1-SWS-MOV-MA-1669ACT_

725 6.290E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-SSD-MA-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 726 6.290E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-SSD-MA-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 727 6.280E-11 < 0.01 1-IE-FLI-CB_A60,1-RPS-ROD-CF-RCCAS 728 6.272E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-RCS-MDP-LK-BP2,1-SWS-CTF-CF-FR-ALL

B-25 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 729 6.272E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-RCS-MDP-LK-BP2,1-SWS-CTF-CF-FR-ALL 730 6.260E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-MA-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 731 6.260E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-MA-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 732 6.259E-11 < 0.01 1-IE-FLI-AB_B08_LF,1-RCS-MDP-LK-BP2,1-SWS-CTF-MA-_B_1234_

733 6.259E-11 < 0.01 1-IE-FLI-CB_122_SP,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-SWT-FC-TY16689B-CC 734 6.259E-11 < 0.01 1-IE-FLI-CB_123_SP,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-SWT-FC-TY16689B-CC 735 6.230E-11 < 0.01 1-IE-FLI-AB_B24_LF2,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 736 6.227E-11 < 0.01 1-IE-FLI-CB_122_SP,1-RCS-MDP-LK-BP2,1-SWS-CTF-CF-FR-ALL 737 6.227E-11 < 0.01 1-IE-FLI-CB_123_SP,1-RCS-MDP-LK-BP2,1-SWS-CTF-CF-FR-ALL 738 6.203E-11 < 0.01 1-IE-FLI-AB_D78_FP,1-EPS-DGN-FR-G4002___,1-OEP-VCF-LP-CLOPT 739 6.168E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-AFW-TDP-FR-P4001___,1-EPS-SEQ-FO-1821U302,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 740 6.168E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-AFW-TDP-FR-P4001___,1-EPS-SEQ-FO-1821U302,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 741 6.136E-11 < 0.01 1-IE-FLI-AB_C118_LF,1-RCS-MDP-LK-BP2,1-SWS-CTF-MA-_A_1234_

742 6.102E-11 < 0.01 1-IE-FLI-AB_C115_LF,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP1,1-SWS-MOV-MA-1669ACT_

743 6.100E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-AFW-TDP-MA-P4001___,1-OA-MISPAF5094H,1-OAB_TR-------H 744 6.100E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-AFW-TDP-MA-P4001___,1-OA-MISPAF5094H,1-OAB_TR-------H 745 6.100E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-AFW-MDP-FS-P4002___,1-AFW-TDP-MA-P4001___,1-OAB_TR-------H 746 6.100E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-AFW-MDP-FS-P4002___,1-AFW-TDP-MA-P4001___,1-OAB_TR-------H 747 6.086E-11 < 0.01 1-IE-FLI-AB_C115_LF,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-RLOOP 748 6.056E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CVC-MDP-TE-CCPB____,1-EPS-DGN-FS-G4001___,1-OEP-VCF-LP-CLOPL 749 6.056E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CVC-MDP-TE-CCPB____,1-EPS-DGN-FS-G4001___,1-OEP-VCF-LP-CLOPL 750 6.056E-11 < 0.01 1-IE-FLI-CB_122_SP,1-AFW-TDP-MA-P4001___,1-OA-MISPAF5095H,1-OAB_TR-------H 751 6.056E-11 < 0.01 1-IE-FLI-CB_123_SP,1-AFW-TDP-MA-P4001___,1-OA-MISPAF5095H,1-OAB_TR-------H 752 6.056E-11 < 0.01 1-IE-FLI-CB_122_SP,1-AFW-MDP-FS-P4003___,1-AFW-TDP-MA-P4001___,1-OAB_TR-------H 753 6.056E-11 < 0.01 1-IE-FLI-CB_123_SP,1-AFW-MDP-FS-P4003___,1-AFW-TDP-MA-P4001___,1-OAB_TR-------H 754 6.033E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-AFW-TDP-MA-P4001___,1-EPS-DGN-FR-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 755 6.033E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-AFW-TDP-MA-P4001___,1-EPS-DGN-FR-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 756 5.983E-11 < 0.01 1-IE-FLI-DGB_103_LF,1-ACP-BAC-MA-BA03____,1-AFW-TDP-FR-P4001___

757 5.977E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AA02____,1-LPI-MDP-FS-RHRB____

758 5.977E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AA02____,1-LPI-MDP-FS-RHRB____

759 5.973E-11 < 0.01 1-IE-FLI-DGB_101_LF,1-RCS-MDP-LK-BP2,1-SWS-CTF-MA-_A_1234_

B-26 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 760 5.973E-11 < 0.01 1-IE-FLI-DGB_103_LF,1-RCS-MDP-LK-BP2,1-SWS-CTF-MA-_B_1234_

761 5.967E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,1-ACP-CRB-CC-AA0205__,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 762 5.967E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,1-ACP-CRB-CC-BA0301__,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPT 763 5.929E-11 < 0.01 1-IE-FLI-TB_500_LF,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MDP-CF-FR-ABCDEF 764 5.912E-11 < 0.01 1-IE-FLI-AB_B50_JI,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPT 765 5.911E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-MCCBBD__,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 766 5.911E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-MCCBBD__,1-EPS-DGN-FR-G4001___,1-OEP-VCF-LP-CLOPL 767 5.774E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CVC-MDP-FR-CCPB____,1-EPS-DGN-MA-G4001___,1-OEP-VCF-LP-CLOPL 768 5.774E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CVC-MDP-FR-CCPB____,1-EPS-DGN-MA-G4001___,1-OEP-VCF-LP-CLOPL 769 5.723E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-SSD-MA-1821U302,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 770 5.723E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-SSD-MA-1821U302,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 771 5.682E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-SSD-MA-1821U302,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 772 5.682E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-SSD-MA-1821U302,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 773 5.670E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-BA03____,1-OEP-VCF-LP-CLOPT 774 5.670E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-BB07____,1-OEP-VCF-LP-CLOPT 775 5.670E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-BB16____,1-OEP-VCF-LP-CLOPT 776 5.670E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-MCCBBB__,1-OEP-VCF-LP-CLOPT 777 5.670E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-MCCBBF__,1-OEP-VCF-LP-CLOPT 778 5.653E-11 < 0.01 1-IE-FLI-CB_A60,1-EPS-TNK-MA-DFOSTKA_,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 779 5.630E-11 < 0.01 1-IE-FLI-AB_B08_LF,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP2,1-SWS-MOV-MA-1669ACT_

780 5.603E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CVC-MDP-TE-CCPB____,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL 781 5.603E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CVC-MDP-TE-CCPB____,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL 782 5.534E-11 < 0.01 1-IE-FLI-AB_B24_LF2,1-ACP-BAC-FC-BA03____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 783 5.534E-11 < 0.01 1-IE-FLI-AB_B24_LF2,1-ACP-BAC-FC-BB16____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 784 5.500E-11 < 0.01 1-IE-FLI-AB_B24_LF2,1-EPS-DGN-FS-G4002___,1-OEP-VCF-LP-CLOPT 785 5.483E-11 < 0.01 1-IE-FLI-TB_500_HI2,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,1-RPS-CBI-CF-6OF8,/1-RPS-CCP-TM-CHA,1-RPS-XHE-XE-NSGNL 786 5.445E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-AFW-TDP-FR-P4001___,1-EPS-DGN-FS-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 787 5.445E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-AFW-TDP-FR-P4001___,1-EPS-DGN-FS-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 788 5.430E-11 < 0.01 1-IE-FLI-TB_500_LF,1-AFW-TNK-RP-V4001___,1-OAB_TR-------H

B-27 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 789 5.373E-11 < 0.01 1-IE-FLI-DGB_103_LF,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP2,1-SWS-MOV-MA-1669ACT_

790 5.369E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-INV-FC-BD1I12__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 791 5.369E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-INV-FC-AD1I11__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 792 5.369E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-INV-FC-BD1I12__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 793 5.369E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-INV-FC-AD1I11__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 794 5.355E-11 < 0.01 1-IE-FLI-CB_A60,1-AFW-MDP-MA-P4003___,1-AFW-TDP-FS-P4001___,1-OAB_TR-------H 795 5.331E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-FC-BD1I12__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 796 5.331E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-FC-AD1I11__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 797 5.331E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-FC-BD1I12__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 798 5.331E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-FC-AD1I11__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 799 5.294E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-NSCW-CT-NEED-SWAP,1-NSCW-MOV-F-NON-RECBLE,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-MOV-CC-1669A___

800 5.292E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-MA-MCCBBB__,1-NSCW-CT-NEED-SWAP,1-NSCW-MOV-F-NON-RECBLE,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 801 5.288E-11 < 0.01 1-IE-FLI-AB_B50_JI,1-NSCWCT-SPRAY,1-RCS-MDP-LK-BP2,1-SWS-MOV-MA-1668ACT_

802 5.261E-11 < 0.01 1-IE-FLI-AB_C115_LF,1-DCP-FUS-OP-BD104___,1-OEP-VCF-LP-CLOPT 803 5.252E-11 < 0.01 1-IE-FLI-AB_B50_JI,1-ACP-BAC-FC-AA02____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 804 5.252E-11 < 0.01 1-IE-FLI-AB_B50_JI,1-ACP-BAC-FC-AB15____,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 805 5.220E-11 < 0.01 1-IE-FLI-AB_B50_JI,1-EPS-DGN-FS-G4001___,1-OEP-VCF-LP-CLOPT 806 5.194E-11 < 0.01 1-IE-FLI-CB_A48,1-DCP-DPL-FC-BD11____,1-FLI-CB-A58A48-FP 807 5.194E-11 < 0.01 1-IE-FLI-CB_A48,1-DCP-BDC-FC-BD1_____,1-FLI-CB-A58A48-FP 808 5.159E-11 < 0.01 1-IE-FLI-AB_C115_LF,1-NSCW-CT-NEED-SWAP,1-NSCW-MOV-F-NON-RECBLE,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-CC-1669A___

809 5.133E-11 < 0.01 1-IE-FLI-CB_A60,1-EPS-DGN-FR-G4001___,1-LPI-MDP-FS-RHRB____,1-OEP-VCF-LP-CLOPL 810 5.126E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-ACP-BAC-FC-BYB1____,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT 811 5.099E-11 < 0.01 1-IE-FLI-AB_C118_LF,1-RCS-MDP-LK-BP2,1-SWS-MDP-MA-P4_00135-3 812 5.089E-11 < 0.01 1-IE-FLI-AB_B24_LF2,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPT

B-28 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 813 5.038E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-AFW-TDP-FR-P4001___,1-DCP-BAT-MA-BD1B____,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 814 5.038E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-AFW-TDP-FR-P4001___,1-DCP-BAT-MA-BD1B____,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 815 5.027E-11 < 0.01 1-IE-FLI-TB_500_LF,1-AFW-MOV-CF-MINFL,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 816 4.998E-11 < 0.01 1-IE-FLI-CB_A60,1-ACP-INV-MA-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 817 4.973E-11 < 0.01 1-IE-FLI-CB_A48,1-DCP-CRB-CO-BD105___,1-FLI-CB-A58A48-FP 818 4.973E-11 < 0.01 1-IE-FLI-CB_A48,1-ACP-CRB-CO-BA0309__,1-FLI-CB-A58A48-FP 819 4.973E-11 < 0.01 1-IE-FLI-CB_A48,1-ACP-CRB-CO-BB1601__,1-FLI-CB-A58A48-FP 820 4.971E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CVC-MDP-FS-CCPB____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 821 4.971E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CVC-MDP-FS-CCPB____,1-EPS-SEQ-FO-1821U301,1-OEP-VCF-LP-CLOPL 822 4.963E-11 < 0.01 1-IE-FLI-DGB_101_LF,1-RCS-MDP-LK-BP2,1-SWS-MDP-MA-P4_00135-3 823 4.956E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-AFW-PMP-CF-RUN,1-OAB_TR-------H-HD,1-OAF_MFW------H 824 4.946E-11 < 0.01 1-IE-FLI-CB_A48,1-AFW-MDP-MA-P4002___,1-CVC-MDP-FS-CCPB____,1-FLI-CB-A58A48-FP 825 4.874E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,1-ACP-CRB-CC-BA0301__,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPT 826 4.874E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,1-ACP-CRB-CC-AA0205__,1-DCP-BAT-MA-BD1B____,1-OEP-VCF-LP-CLOPT 827 4.846E-11 < 0.01 1-IE-FLI-CB_A60,1-CVC-MDP-TE-CCPB____,1-EPS-DGN-MA-G4001___,1-OEP-VCF-LP-CLOPL 828 4.844E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-OEP-VCF-LP-CLOPT,1-SWS-CTF-MA-_B_1234_

829 4.829E-11 < 0.01 1-IE-FLI-AB_B50_JI,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPT 830 4.821E-11 < 0.01 1-IE-FLI-TB_500_LF,1-OEP-VCF-LP-CLOPT,1-SWS-MDP-CF-FS-ABCDEF 831 4.818E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-AFW-MDP-MA-P4002___,1-EPS-DGN-FR-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 832 4.818E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-AFW-MDP-MA-P4002___,1-EPS-DGN-FR-G4001___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 833 4.818E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-DCP-FC-1A_PS4__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 834 4.818E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-DCP-FC-1A_PS1__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 835 4.818E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-DCP-FC-1B_PS4__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 836 4.818E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-DCP-FC-1B_PS1__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 837 4.818E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-DCP-FC-1A_PS4__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 838 4.818E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-DCP-FC-1A_PS1__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP

B-29 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 839 4.818E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-DCP-FC-1B_PS4__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 840 4.818E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-DCP-FC-1B_PS1__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 841 4.799E-11 < 0.01 1-IE-FLI-AB_A20,1-RPS-BME-CF-RTBAB,1-UET2-NOPORV-BLK 842 4.790E-11 < 0.01 1-IE-FLI-TB_500_LF,1-AFW-TDP-FR-P4001___,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,1-RPS-CBI-CF-6OF8,/1-RPS-CCP-TM-CHA,1-RPS-XHE-XE-NSGNL 843 4.789E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-AFW-MDP-CF-START,1-OEP-VCF-LP-CLOPT 844 4.784E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-DCP-FC-1A_PS4__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 845 4.784E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-DCP-FC-1A_PS1__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 846 4.784E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-DCP-FC-1B_PS4__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 847 4.784E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-DCP-FC-1B_PS1__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 848 4.784E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-DCP-FC-1A_PS4__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 849 4.784E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-DCP-FC-1A_PS1__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 850 4.784E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-DCP-FC-1B_PS4__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 851 4.784E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-DCP-FC-1B_PS1__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 852 4.728E-11 < 0.01 1-IE-FLI-AB_B24_LF2,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_B_1234_

853 4.663E-11 < 0.01 1-IE-FLI-CB_A60,1-AFW-PMP-CF-RUN,1-OAB_TR-------H 854 4.658E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-OC-1669A___

855 4.556E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-BA03____,1-OEP-VCF-LP-CLOPT 856 4.556E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-BB07____,1-OEP-VCF-LP-CLOPT 857 4.556E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-BB16____,1-OEP-VCF-LP-CLOPT 858 4.556E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-MCCBBB__,1-OEP-VCF-LP-CLOPT 859 4.556E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-MCCBBF__,1-OEP-VCF-LP-CLOPT 860 4.510E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-CAD-XHE-SAFESTBLE,1-EPS-SEQ-CF-FOAB 861 4.510E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-CAD-XHE-SAFESTBLE,1-EPS-SEQ-CF-FOAB 862 4.487E-11 < 0.01 1-IE-FLI-AB_B50_JI,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-CTF-MA-_A_1234_

B-30 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 863 4.478E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CAD-XHE-SAFESTBLE,1-EPS-SEQ-CF-FOAB 864 4.478E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CAD-XHE-SAFESTBLE,1-EPS-SEQ-CF-FOAB 865 4.478E-11 < 0.01 1-IE-FLI-CB_A48,1-EPS-SEQ-FO-1821U302,1-FLI-CB-A58A48-FP,1-RCS-PRV-DP-LODC,1-RCS-PRV-OO-RV0455A_

866 4.462E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-CRB-CC-AA0205__,1-LPI-MDP-FS-RHRB____,1-OEP-VCF-LP-CLOPL 867 4.462E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-CRB-CC-AA0205__,1-LPI-MDP-FS-RHRB____,1-OEP-VCF-LP-CLOPL 868 4.457E-11 < 0.01 1-IE-FLI-CB_A60,1-ACP-CRB-CC-AA0205__,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPL 869 4.421E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-FC-AA02____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H 870 4.421E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-FC-AA02____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H 871 4.389E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CVC-MDP-FS-CCPB____,1-EPS-DGN-FS-G4001___,1-OEP-VCF-LP-CLOPL 872 4.389E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CVC-MDP-FS-CCPB____,1-EPS-DGN-FS-G4001___,1-OEP-VCF-LP-CLOPL 873 4.357E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT,1-SWS-MOV-MA-1669ACT_

874 4.294E-11 < 0.01 1-IE-FLI-AB_D74_FP,1-ACP-TFW-FC-BB16X___,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 875 4.274E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-ACP-TFW-FC-BB16X___,1-RCS-MDP-LK-BP1 876 4.254E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-NSCW-CT-NEED-SWAP,1-NSCW-MOV-F-NON-RECBLE,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-MOV-CC-1669A___

877 4.253E-11 < 0.01 1-IE-FLI-AB_B24_LF2,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-MA-1669ACT_

878 4.253E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-MCCBBB__,1-NSCW-CT-NEED-SWAP,1-NSCW-MOV-F-NON-RECBLE,1-NSCWCT-BYPASS,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 879 4.209E-11 < 0.01 1-IE-FLI-AB_A20_FP,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-CLOPT 880 4.126E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,1-NSCW-CT-NEED-SWAP,1-NSCWCT-BYPASS,1-RCS-MDP-LK-BP2,1-SWS-SWT-FC-TY16689B-CC 881 4.119E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-FC-BYB1____,1-NSCWCT-SPRAY,1-OEP-VCF-LP-CLOPT 882 4.111E-11 < 0.01 1-IE-FLI-AB_A20,1-ACP-CRB-CC-AA0205__,1-ACP-CRB-CC-BA0301__,1-OEP-VCF-LP-CLOPT 883 4.088E-11 < 0.01 1-IE-FLI-AB_C115_LF,1-AFW-MDP-FS-P4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPT 884 4.088E-11 < 0.01 1-IE-FLI-AB_C115_LF,1-OA-MISPAF5094H,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPT 885 4.061E-11 < 0.01 1-IE-FLI-CB_123_SP,1-CVC-MDP-FS-CCPB____,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL 886 4.061E-11 < 0.01 1-IE-FLI-CB_122_SP,1-CVC-MDP-FS-CCPB____,1-DCP-BAT-MA-AD1B____,1-OEP-VCF-LP-CLOPL 887 4.055E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,1-RPS-CBI-CF-6OF8,/1-RPS-CCP-TM-CHA,1-RPS-XHE-XE-NSGNL,1-UET2-NOPORV-BLK 888 4.040E-11 < 0.01 1-IE-FLI-CB_A60,1-AFW-MOV-OO-FV5155__,1-AFW-TDP-FR-P4001___,1-OAB_TR-------H 889 4.034E-11 < 0.01 1-IE-FLI-CB_A48,1-FLI-CB-A58A48-FP,1-LPI-MDP-MA-RHRB____,1-RCS-PRV-DP-LODC,1-RCS-PRV-OO-RV0455A_

890 4.032E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-NSCWCT-BYPASS,1-OEP-VCF-LP-CLOPT,1-SWS-MOV-CC-1669A___

891 4.009E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-BA03____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 892 4.009E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-BA03____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 893 4.009E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-BB16____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2

B-31 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 894 4.009E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-BB16____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 895 4.009E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-AB15____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 896 4.009E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-AB15____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 897 4.009E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-BAC-MA-AA02____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 898 4.009E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-BAC-MA-AA02____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 899 4.005E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-INV-FC-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 900 4.005E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-INV-FC-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 901 4.005E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-INV-FC-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 902 4.005E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-INV-FC-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 903 3.983E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-FC-AA02____,1-LPI-MDP-MA-RHRB____

904 3.983E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-FC-AA02____,1-CVC-MDP-MA-CCPB____

905 3.983E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-FC-AA02____,1-LPI-MDP-MA-RHRB____

906 3.983E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-FC-AA02____,1-CVC-MDP-MA-CCPB____

907 3.982E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-AFW-PMP-CF-RUN,1-OAB_TR-------H-HD,1-OAF_MFW------H 908 3.981E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-BA03____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 909 3.981E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-BA03____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 910 3.981E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-BB16____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 911 3.981E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-BB16____,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 912 3.981E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-MA-AB15____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 913 3.981E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-MA-AB15____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 914 3.977E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-FC-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 915 3.977E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-FC-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 916 3.977E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-FC-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 917 3.977E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-FC-AD1I11__,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 918 3.936E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-DCP-FC-1B_PS4__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 919 3.936E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-DCP-FC-1B_PS1__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 920 3.936E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-DCP-FC-1A_PS4__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 921 3.936E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-DCP-FC-1A_PS1__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 922 3.936E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-DCP-FC-1B_PS4__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP

B-32 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 923 3.936E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-DCP-FC-1B_PS1__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 924 3.936E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-DCP-FC-1A_PS4__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 925 3.936E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-DCP-FC-1A_PS1__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 926 3.908E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-DCP-FC-1B_PS4__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 927 3.908E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-DCP-FC-1B_PS1__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 928 3.908E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-DCP-FC-1A_PS4__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 929 3.908E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-DCP-FC-1A_PS1__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 930 3.908E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-DCP-FC-1B_PS4__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 931 3.908E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-DCP-FC-1B_PS1__,1-DCP-BAT-MA-AD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 932 3.908E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-DCP-FC-1A_PS4__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 933 3.908E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-DCP-FC-1A_PS1__,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 934 3.892E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-OEP-VCF-LP-CLOPT,1-SWS-CTF-MA-_B_1234_

935 3.881E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP1 936 3.881E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP1 937 3.870E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-AA02____,1-AFW-MDP-FS-P4002___

938 3.870E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-ACP-BAC-MA-AA02____,1-OA-MISPAF5094H 939 3.868E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,1-AFW-TDP-FR-P4001___,1-RPS-BME-CF-RTBAB 940 3.860E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-SSD-MA-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 941 3.860E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-SSD-MA-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 942 3.853E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP1 943 3.853E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP1 944 3.843E-11 < 0.01 1-IE-FLI-AB_B08_LF,1-ACP-TFW-FC-BB16X___,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 945 3.841E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-ACP-INV-MA-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 946 3.841E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-ACP-INV-MA-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2

B-33 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 947 3.833E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-SSD-MA-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 948 3.833E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-SSD-MA-1821U301,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 949 3.817E-11 < 0.01 1-IE-FLI-CB_123_SP,1-NSCWCT-SPRAY,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-MA-1668ACT_

950 3.817E-11 < 0.01 1-IE-FLI-CB_122_SP,1-NSCWCT-SPRAY,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL,1-SWS-MOV-MA-1668ACT_

951 3.814E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-INV-MA-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 952 3.814E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-INV-MA-BD1I12__,1-EPS-SEQ-FO-1821U301,1-OA-NSCWFAN---H,1-RCS-MDP-LK-BP2 953 3.768E-11 < 0.01 1-IE-FLI-AB_C118_LF,1-ACP-TFW-FC-AB15X___,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 954 3.743E-11 < 0.01 1-IE-FLI-AB_C120_LF,1-NSCWCT-SPRAY,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MOV-OC-1669A___

955 3.729E-11 < 0.01 1-IE-FLI-TB_500_LF,1-AFW-MDP-CF-START,1-AFW-TDP-FS-P4001___,1-OAB_TR-------H 956 3.728E-11 < 0.01 1-IE-FLI-AB_B50_JI,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP,1-SWS-MDP-MA-P4_00135-3 957 3.719E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,1-ACP-CRB-CF-A205301,1-OEP-VCF-LP-RLOOP 958 3.717E-11 < 0.01 1-IE-FLI-TB_500_HI2,/1-RPS-BME-TM-RTBA,/1-RPS-BME-TM-RTBB,/1-RPS-CCP-TM-CHA,1-RPS-CCX-CF-6OF8,1-RPS-XHE-XE-NSGNL 959 3.716E-11 < 0.01 1-IE-FLI-CB_A60,1-ACP-BAC-MA-AA02____,1-EPS-SEQ-FO-1821U302,1-OA-NSCWFAN---H 960 3.714E-11 < 0.01 1-IE-FLI-TB_500_LF-CDS,1-EPS-SEQ-FO-1821U301,1-EPS-SEQ-FO-1821U302,1-OEP-VCF-LP-CLOPT 961 3.709E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-LPI-MOV-OO-HV8812B_,1-OEP-VCF-LP-CLOPL 962 3.709E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-LPI-MOV-CC-HV8811B_,1-OEP-VCF-LP-CLOPL 963 3.709E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-LPI-MOV-OO-HV8812B_,1-OEP-VCF-LP-CLOPL 964 3.709E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-LPI-MOV-CC-HV8811B_,1-OEP-VCF-LP-CLOPL 965 3.709E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-OO-LV0112C_,1-OEP-VCF-LP-CLOPL 966 3.709E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-CC-LV0112E_,1-OEP-VCF-LP-CLOPL 967 3.709E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-CC-HV8804B_,1-OEP-VCF-LP-CLOPL 968 3.709E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-OO-HV8813__,1-OEP-VCF-LP-CLOPL 969 3.709E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-CC-HV8807B_,1-OEP-VCF-LP-CLOPL 970 3.709E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-OO-HV8508B_,1-OEP-VCF-LP-CLOPL 971 3.709E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-CC-HV8801B_,1-OEP-VCF-LP-CLOPL 972 3.709E-11 < 0.01 1-IE-FLI-CB_123_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-OO-HV8105__,1-OEP-VCF-LP-CLOPL 973 3.709E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-OO-LV0112C_,1-OEP-VCF-LP-CLOPL 974 3.709E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-CC-LV0112E_,1-OEP-VCF-LP-CLOPL 975 3.709E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-CC-HV8804B_,1-OEP-VCF-LP-CLOPL 976 3.709E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-OO-HV8813__,1-OEP-VCF-LP-CLOPL 977 3.709E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-CC-HV8807B_,1-OEP-VCF-LP-CLOPL 978 3.709E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-OO-HV8508B_,1-OEP-VCF-LP-CLOPL

B-34 Table B-1 Internal Flooding Significant Cut Sets Cut Set Prob/

Freq Total Cut Set 979 3.709E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-CC-HV8801B_,1-OEP-VCF-LP-CLOPL 980 3.709E-11 < 0.01 1-IE-FLI-CB_122_SP,1-EPS-DGN-MA-G4001___,1-HPI-MOV-OO-HV8105__,1-OEP-VCF-LP-CLOPL 981 3.700E-11 < 0.01 1-IE-FLI-AB_C113_LF1,1-ACP-TFW-FC-NXRB____,1-EPS-DGN-FR-G4002___,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 982 3.668E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-RCS-MDP-LK-BP1,1-SWS-CTF-CF-FS-ALL 983 3.668E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-RCS-MDP-LK-BP1,1-SWS-CTF-CF-FS-ALL 984 3.668E-11 < 0.01 1-IE-FLI-DGB_101_LF,1-ACP-TFW-FC-AB15X___,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 985 3.668E-11 < 0.01 1-IE-FLI-DGB_103_LF,1-ACP-TFW-FC-BB16X___,/1-OEP-VCF-LP-CLOPT,1-RCS-XHE-XM-TRIP 986 3.657E-11 < 0.01 1-IE-FLI-CB_A48,1-DCP-BAT-MA-BD1B____,1-FLI-CB-A58A48-FP,1-RCS-PRV-DP-LODC,1-RCS-PRV-OO-RV0455A_

987 3.642E-11 < 0.01 1-IE-FLI-CB_122_SP,1-RCS-MDP-LK-BP1,1-SWS-CTF-CF-FS-ALL 988 3.642E-11 < 0.01 1-IE-FLI-CB_123_SP,1-RCS-MDP-LK-BP1,1-SWS-CTF-CF-FS-ALL 989 3.640E-11 < 0.01 1-IE-FLI-AB_108_SP1,1-AFW-TDP-FS-P4001___,1-EPS-DGN-MA-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 990 3.640E-11 < 0.01 1-IE-FLI-AB_108_SP2,1-AFW-TDP-FS-P4001___,1-EPS-DGN-MA-G4002___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 991 3.613E-11 < 0.01 1-IE-FLI-TB_500_LF,1-RCS-MDP-LK-BP2,1-SWS-MDP-CF-FR-ABCDEF 992 3.611E-11 < 0.01 1-IE-FLI-CB_123_SP,1-ACP-BAC-FC-AA02____,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H 993 3.611E-11 < 0.01 1-IE-FLI-CB_122_SP,1-ACP-BAC-FC-AA02____,1-DCP-BAT-MA-BD1B____,1-OA-NSCWFAN---H 994 3.610E-11 < 0.01 1-IE-FLI-CB_123_SP,1-DCP-FUS-OP-AD104___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 995 3.610E-11 < 0.01 1-IE-FLI-CB_122_SP,1-DCP-FUS-OP-AD104___,1-OAB_TR-------H,1-OEP-VCF-LP-CLOPL 996 3.607E-11 < 0.01 1-IE-FLI-AB_A20,1-RPS-ROD-CF-RCCAS,1-UET2-NOPORV-BLK Total 7.512E-7 100 Displaying 996 Cut Sets. (8728 Original)

B-35 B.2 Internal Flooding PRA Basic Event Importance Measures The following importance measures were calculated:

Fussell-Vesely (FV) - an indication of the percentage of the overall risk metric result (CDF) contributed by the cut sets containing the basic event.

Risk Increase Ratio (RIR) - also referred to as risk-achievement worth; an indication of how much the overall risk metric (CDF) would go up if the specific event had probability equal to 1.0, corresponding to totally unreliable equipment or action.

Risk Reduction Ratio (RRR) - also referred to as risk reduction worth; an indication of how much the overall risk metric (CDF) would be reduced if the specific event probability equaled zero, corresponding to a totally reliable piece of equipment or action.

Birnbaum - an indication of the sensitivity of the overall risk metric (CDF) with respect to the basic event of concern.

The importance measures for all significant basic events are included in Table B-2 (ranked by FV importance). Significant basic events are defined as those basic events that have a FV importance greater than 0.005 or a risk-achievement worth greater than 2.

In addition to the importance measures listed above, Table B-2 also includes the basic event name, the number of cut sets in which that basic event appears (listed under column heading Count), the calculated probability or frequency associated with the basic event, and the basic event description.

Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-RCS-XHE-XM-TRIP 1456 3.300E-01 2.93E-01 1.595E+00 1.415E+00 7.028E-07 Operator fails to trip RCPs 1-OEP-VCF-LP-CLOPT 2773 5.300E-03 2.81E-01 5.351E+01 1.389E+00 4.176E-05 Consequential loss of offsite power - transient 1-OA-NSCWFAN---H 1742 1.000E+00 2.15E-01 1.000E+00 1.274E+00 1.701E-07 Operator fails to start NSCW fan manually (place holder) 1-IE-FLI-AB_C113_LF1 348 2.240E-04 1.96E-01 8.775E+02 1.244E+00 6.935E-04 Internal flooding in AB C113 1-EPS-SEQ-CF-FOAB 120 2.148E-04 1.87E-01 8.726E+02 1.230E+00 6.896E-04 Sequencers fail from common cause to operate 1-RCS-MDP-LK-BP2 1088 2.000E-01 1.78E-01 1.713E+00 1.217E+00 7.051E-07 Rcp seal stage 2 integrity (binding/popping open) fails 1-IE-FLI-AB_C120_LF 347 1.800E-04 1.65E-01 9.158E+02 1.197E+00 7.237E-04 Internal flooding in AB C120 due to NSCW pipe failure 1-OEP-VCF-LP-CLOPL 2623 3.000E-02 1.53E-01 5.947E+00 1.181E+00 4.034E-06 Consequential loss of offsite power - loca 1-OAB_TR-------H 922 5.800E-02 1.39E-01 3.262E+00 1.162E+00 1.900E-06 Operator fails to feed and bleed - transient 1-EPS-DGN-FR-G4002___

346 3.297E-02 1.31E-01 4.843E+00 1.151E+00 3.143E-06 DG1B fails to run by random cause (24 hr mission) 1-IE-FLI-CB_122_SP 1389 2.780E-04 1.29E-01 4.652E+02 1.148E+00 3.673E-04 Internal flooding in CB 122 1-IE-FLI-CB_123_SP 1393 2.780E-04 1.29E-01 4.653E+02 1.148E+00 3.674E-04 Internal flooding in CB 123 1-IE-FLI-AB_C115_LF 300 1.330E-04 1.17E-01 8.772E+02 1.132E+00 6.932E-04 Internal flooding in AB C115 due to NSCW pipe failure 1-ACP-BAC-MA-BA03____

222 2.150E-04 8.82E-02 4.109E+02 1.097E+00 3.243E-04 4.16KV bus 1BA03 in maintenance 1-ACP-BAC-MA-BB16____

165 2.150E-04 8.75E-02 4.080E+02 1.096E+00 3.220E-04 480V switchgear 1BB16 in maintenance

B-36 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-IE-FLI-AB_108_SP1 1135 2.800E-04 7.50E-02 2.689E+02 1.081E+00 2.120E-04 Internal flooding in AB 108 1-IE-FLI-AB_108_SP2 1127 2.800E-04 7.50E-02 2.687E+02 1.081E+00 2.118E-04 Internal flooding in AB 108 1-EPS-DGN-FR-G4001___

420 3.297E-02 6.33E-02 2.856E+00 1.068E+00 1.518E-06 DG1A fails to run by random cause (24 hr mission) 1-EPS-DGN-MA-G4002___

192 1.260E-02 5.13E-02 5.020E+00 1.054E+00 3.221E-06 DG1B in maintenance 1-EPS-SEQ-FO-1821U302 590 3.330E-03 4.02E-02 1.303E+01 1.042E+00 9.546E-06 Sequencer B fails to operate 1-EPS-SEQ-FO-1821U301 620 3.330E-03 3.03E-02 1.005E+01 1.031E+00 7.185E-06 Sequencer A fails to operate 1-AFW-TDP-FR-P4001___

482 3.802E-02 2.63E-02 1.666E+00 1.027E+00 5.479E-07 TDAFWP fails to run 1-ACP-CRB-CC-BA0301__

178 5.350E-03 2.60E-02 5.841E+00 1.027E+00 3.850E-06 RAT B supply CRB randomly fails to open 1-ACP-CRB-CF-A205301 36 3.498E-04 2.49E-02 7.222E+01 1.026E+00 5.636E-05 CCF of switchyard AC breakers AA205 & BA301 to open 1-NSCWCT-SPRAY 634 9.040E-01 2.38E-02 1.003E+00 1.024E+00 2.081E-08 NSCW CTS in spray mode (fraction of time) 1-IE-FLI-CB_A60 493 5.190E-05 2.36E-02 4.558E+02 1.024E+00 3.598E-04 internal flooding in CB A60 1-DCP-BAT-MA-BD1B____

390 2.720E-03 2.26E-02 9.270E+00 1.023E+00 6.559E-06 Battery 1BD1B in maintenance 1-EPS-DGN-MA-G4001___

258 1.260E-02 2.25E-02 2.760E+00 1.023E+00 1.410E-06 DG1A in maintenance 1-IE-FLI-TB_500_LF 701 2.160E-03 2.06E-02 1.053E+01 1.021E+00 7.552E-06 Internal flooding in TB Fire Zone 500 1-ACP-BAC-FC-BA03____

145 4.776E-05 1.98E-02 4.156E+02 1.020E+00 3.280E-04 4.16KV bus 1BA03 fails 1-ACP-BAC-FC-BB16____

121 4.776E-05 1.97E-02 4.125E+02 1.020E+00 3.255E-04 480V switchgear 1BB16 randomly fails 1-ACP-BAC-MA-AA02____

247 2.150E-04 1.78E-02 8.365E+01 1.018E+00 6.539E-05 Bus 1AA02 in maintenance 1-FLI-CB-A58A48-FP 332 1.000E-01 1.78E-02 1.160E+00 1.018E+00 1.405E-07 Propagation factor for internal flooding from corridor A58 to 4160 VAC switchgear room A48 1-IE-FLI-CB_A48 332 9.210E-05 1.78E-02 1.938E+02 1.018E+00 1.525E-04 internal flooding in CB A48 1-DCP-BAT-MA-AD1B____

409 2.720E-03 1.63E-02 6.986E+00 1.017E+00 4.748E-06 Battery 1AD1B in maintenance 1-SWS-CTF-MA-_B_1234_

62 4.080E-05 1.63E-02 4.003E+02 1.017E+00 3.159E-04 All four NSCW train B tower fans unavailable due to maintenance 1-SWS-MOV-MA-1669ACT_

98 4.060E-05 1.48E-02 3.662E+02 1.015E+00 2.889E-04 NSCW TR B spray valve HV1669A closed for CT maintenance 1-ACP-CRB-CC-AA0205__

231 5.350E-03 1.44E-02 3.684E+00 1.015E+00 2.135E-06 RAT A supply CRB randomly fails to open 1-AFW-MDP-MA-P4002___

183 3.000E-03 1.35E-02 5.481E+00 1.014E+00 3.555E-06 MDAFWP B unavailable due to T&M 1-EPS-DGN-FS-G4002___

151 2.940E-03 1.23E-02 5.182E+00 1.012E+00 3.318E-06 DG1B fails to start by random cause 1-RCS-MDP-LK-BP1 233 1.250E-02 1.09E-02 1.861E+00 1.011E+00 6.896E-07 RCP seal stage 1 integrity (binding/popping open) fails 1-SWS-CTF-CF-FS-ALL 24 1.048E-05 8.84E-03 8.445E+02 1.009E+00 6.672E-04 4 or more (all combinations) NSCW fans fail from common cause to start 1-IE-FLI-DGB_101_LF 70 7.320E-06 7.89E-03 1.079E+03 1.008E+00 8.525E-04 Internal flooding in DG1B room 101 due to NSCW pipe failure 1-IE-FLI-AB_D74_FP 89 8.570E-06 7.50E-03 8.758E+02 1.008E+00 6.920E-04 Internal flooding in AB D74 propagates to 480 VAC switchgear room D105

B-37 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-IE-FLI-AB_C118_LF 75 7.520E-06 6.95E-03 9.255E+02 1.007E+00 7.313E-04 Internal flooding in AB C118 due to NSCW pipe failure 1-IE-FLI-AB_B08_LF 72 7.670E-06 6.67E-03 8.697E+02 1.007E+00 6.872E-04 Internal flooding in AB B08 due to NSCW pipe failure 1-IE-FLI-DGB_103_LF 79 7.320E-06 6.49E-03 8.868E+02 1.007E+00 7.007E-04 Internal flooding in DG1A room 103 due to NSCW pipe failure 1-ACP-TFW-FC-BB16X___

62 1.526E-05 6.26E-03 4.112E+02 1.006E+00 3.245E-04 Transformer 1BB16X fails 1-AFW-MDP-MA-P4003___

61 3.000E-03 6.20E-03 3.062E+00 1.006E+00 1.636E-06 MDAFWP A unavailable due to T&M 1-EPS-DGN-FS-G4001___

204 2.940E-03 5.99E-03 3.030E+00 1.006E+00 1.610E-06 DG1A fails to start by random cause 1-IE-FLI-TB_500_LF-CDS 303 6.320E-04 5.75E-03 1.009E+01 1.006E+00 7.192E-06 Internal flooding in TB impacting condensate system 1-NSCWCT-BYPASS 453 9.620E-02 5.40E-03 1.051E+00 1.005E+00 4.442E-08 NSCW CTS in bypass mode (fraction of time) 1-AFW-PMP-CF-RUN 37 1.549E-05 5.31E-03 3.436E+02 1.005E+00 2.710E-04 CCF of AFW pumps to run (excluding driver) 1-ACP-INV-MA-AD1I11__

287 8.810E-04 5.15E-03 6.839E+00 1.005E+00 4.623E-06 Inverter 1AD1I11 in maintenance 1-OEP-VCF-LP-RLOOP 206 1.682E-04 4.91E-03 3.02E+01 1.005E+00 2.310E-05 Random loss of offsite power during post-trip mission time (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) 1-AFW-MDP-FS-P4002___

129 1.000E-03 4.79E-03 5.78E+00 1.005E+00 3.785E-06 MDAFWP B (P4-002) randomly fails to start 1-OA-MISPAF5094H 129 1.000E-03 4.79E-03 5.78E+00 1.005E+00 3.785E-06 Post-test mispositioning of MDAFWP B suction manual valve HV5094 1-CVC-MDP-MA-CCPB____

109 3.000E-03 4.46E-03 2.48E+00 1.004E+00 1.175E-06 CCP-B unavailable due to maintenance 1-LPI-MDP-MA-RHRB____

110 3.000E-03 4.45E-03 2.48E+00 1.004E+00 1.174E-06 RHR pump B in maintenance 1-CVC-MDP-TE-CCPB____

98 2.470E-03 4.38E-03 2.77E+00 1.004E+00 1.401E-06 CCP-B unavailable due to test 1-ACP-BAC-FC-AA02____

168 4.776E-05 4.27E-03 9.04E+01 1.004E+00 7.075E-05 4.16KV bus 1AA02 fails 1-ACP-BAC-MA-AB15____

134 2.150E-04 4.05E-03 1.99E+01 1.004E+00 1.492E-05 480V switchgear 1AB15 in maintenance 1-RPS-BME-CF-RTBAB 67 1.610E-06 3.70E-03 2.30E+03 1.004E+00 1.815E-03 CCF RTB-A and RTB-B (mechanical) 1-IE-FLI-AB_B24_LF2 74 3.530E-06 3.16E-03 8.96E+02 1.003E+00 7.077E-04 Internal flooding in AB B24 due to NSCW pipe failure 1-CVC-MDP-FS-CCPB____

86 1.790E-03 3.16E-03 2.76E+00 1.003E+00 1.395E-06 CCP-B fails to start due to random faults 1-SWS-MOV-CC-1669A___

139 3.530E-04 3.10E-03 9.78E+00 1.003E+00 6.947E-06 NSCW CT B spray valve fails to open on demand 1-IE-FLI-AB_B50_JI 56 3.350E-06 3.08E-03 9.21E+02 1.003E+00 7.273E-04 Internal flooding in AB B50 jet impingement on cable tray 1-RPS-ROD-CF-RCCAS 55 1.210E-06 2.72E-03 2.24E+03 1.003E+00 1.774E-03 CCF 10 or more RCCAS fail to drop 1-ACP-INV-FC-BD1I12__

144 2.148E-04 2.43E-03 1.23E+01 1.002E+00 8.950E-06 Inverter 1BD1I12 randomly fails 1-DCP-BCH-FC-AAABBABB-CC 35 1.525E-06 2.41E-03 1.58E+03 1.002E+00 1.249E-03 CCF of BCHs 1AD1CA, 1AD1CB, 1BD1CA, & 1BD1CB 1-IE-FLI-AB_A20 153 2.710E-04 2.33E-03 9.59E+00 1.002E+00 6.796E-06 Internal flooding in AB A06 1-AFW-MDP-FS-P4003___

43 1.000E-03 2.25E-03 3.24E+00 1.002E+00 1.777E-06 MDAFWP A randomly fails to start 1-OA-MISPAF5095H 43 1.000E-03 2.25E-03 3.24E+00 1.002E+00 1.777E-06 Post-test mispositioning of MDAFWP A suction manual HV5095

B-38 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-ACP-CRB-CO-BA0309__

38 5.400E-06 2.20E-03 4.08E+02 1.002E+00 3.217E-04 Feeder CRB 1BA03 spuriously opens - 1BA03 to 1BB16X 1-ACP-CRB-CO-BB1601__

38 5.400E-06 2.20E-03 4.08E+02 1.002E+00 3.217E-04 Supply CRB 1BB16 spuriously opens - 1BB16X to 1BB16 1-SWS-MOV-CF-1668A69A 57 1.187E-05 1.85E-03 1.57E+02 1.002E+00 1.232E-04 NSCW CT spray valves HV1668A, 1669A fail from common cause to open 1-SWS-SWT-FC-TY16689B-CC 45 1.170E-05 1.82E-03 1.57E+02 1.002E+00 1.231E-04 NSCW return wtr temp switches TY1668B &1669B fail -

CCF 1-LPI-MDP-FS-RHRB____

67 1.000E-03 1.79E-03 2.79E+00 1.002E+00 1.413E-06 RHR pump B fails to start due to random fault 1-ACP-DCP-FC-1B_PS1__

137 1.574E-04 1.77E-03 1.23E+01 1.002E+00 8.914E-06 Failure of 48V sequencer power supply PS-1 1-ACP-DCP-FC-1B_PS4__

137 1.574E-04 1.77E-03 1.23E+01 1.002E+00 8.914E-06 Failure of 28V sequencer power supply PS-4 1-SWS-MOV-CC-1668A___

111 3.530E-04 1.76E-03 5.99E+00 1.002E+00 3.951E-06 NSCW CT A spray valve HV1668A fails to open on demand 1-ACP-INV-FC-AD1I11__

128 2.148E-04 1.75E-03 9.15E+00 1.002E+00 6.447E-06 Inverter 1AD1I11 randomly fails 1-SWS-MOV-MA-1668ACT_

122 8.730E-05 1.72E-03 2.07E+01 1.002E+00 1.556E-05 NSCW train A return isolation valve HV1668A closed for CT maintenance 1-ACP-INV-MA-BD1I12__

108 2.060E-04 1.70E-03 9.23E+00 1.002E+00 6.515E-06 inverter 1BD1I12 in maintenance 1-EPS-TNK-MA-DFOSTKB_

31 4.000E-04 1.65E-03 5.12E+00 1.002E+00 3.257E-06 Train A diesel fuel oil storage tank in maintenance 1-ACP-BAC-MA-MCCBBB__

126 2.150E-04 1.64E-03 8.65E+00 1.002E+00 6.049E-06 480V MCC 1BBB in maintenance 1-ACP-SSD-MA-1821U302 110 1.870E-04 1.64E-03 9.78E+00 1.002E+00 6.950E-06 Sequencer B unavailable due to maintenance 1-AFW-MOV-OO-FV5154__

60 3.530E-04 1.64E-03 5.63E+00 1.002E+00 3.664E-06 MDAFWP B mini flow MOV randomly fails to close 1-ACP-BAC-MA-BB07____

54 2.150E-04 1.55E-03 8.21E+00 1.002E+00 5.705E-06 480V switchgear 1BB07 in maintenance 1-ACP-BAC-MA-MCCBBF__

53 2.150E-04 1.55E-03 8.19E+00 1.002E+00 5.687E-06 480V MCC 1BBF in maintenance 1-RPS-CBI-CF-6OF8 41 2.700E-06 1.38E-03 5.11E+02 1.001E+00 4.034E-04 CCF 6 bistables in 3 of 4 channels 1-OAR_LTFB-TRA-H 102 6.000E-04 1.33E-03 3.22E+00 1.001E+00 1.754E-06 Operator fails to establish HPR for long-term F&B -

transients 1-ACP-DCP-FC-1A_PS1__

122 1.574E-04 1.28E-03 9.11E+00 1.001E+00 6.418E-06 Failure of 48V sequencer power supply PS-1 1-ACP-DCP-FC-1A_PS4__

122 1.574E-04 1.28E-03 9.11E+00 1.001E+00 6.418E-06 Failure of 28V sequencer power supply PS-4 1-EPS-TNK-MA-DFOSTKA_

108 6.260E-04 1.25E-03 2.99E+00 1.001E+00 1.573E-06 Train A diesel fuel oil storage tank in maintenance 1-ACP-SSD-MA-1821U301 97 2.070E-04 1.17E-03 6.66E+00 1.001E+00 4.475E-06 Sequencer A unavailable due to maintenance 1-ACP-BAC-FC-AB15____

88 4.776E-05 1.11E-03 2.41E+01 1.001E+00 1.830E-05 480V switchgear 1AB15 randomly fails 1-SWS-MDP-MA-P4_00246-3 23 2.790E-06 1.10E-03 3.96E+02 1.001E+00 3.127E-04 All 3 NSCW train B pumps unavailable due to maintenance 1-ACP-BAC-MA-BYB1____

73 2.150E-04 1.08E-03 6.04E+00 1.001E+00 3.988E-06 120/240V panel 1BYB1 in maintenance 1-ACP-INV-FC-AD11BD12-CC 14 1.207E-06 9.63E-04 7.98E+02 1.001E+00 6.307E-04 CCF of inverters 1AD1I11/1BD1I12

B-39 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-SWS-CTF-CF-FR-ALL 19 1.120E-06 9.43E-04 8.43E+02 1.001E+00 6.657E-04 4 or more (all combinations) NSCW fans fail from common cause to run 1-CVC-MDP-FR-CCPB____

39 5.494E-04 9.33E-04 2.70E+00 1.001E+00 1.343E-06 CCP-B fails to run due to random faults 1-RPS-CCX-CF-6OF8 28 1.830E-06 9.20E-04 5.04E+02 1.001E+00 3.976E-04 CCF 6 analog process logic modules in 3 of 4 channels 1-AFW-MDP-CF-START 45 5.020E-05 9.03E-04 1.90E+01 1.001E+00 1.422E-05 CCF of AFW MDPs to start 1-AFW-MDP-FR-P4002___

38 1.984E-04 9.00E-04 5.54E+00 1.001E+00 3.588E-06 MDAFWP B randomly fails to run 1-ACP-BAC-MA-AB05____

44 2.150E-04 8.94E-04 5.16E+00 1.001E+00 3.289E-06 480V switchgear 1AB05 in maintenance 1-ACP-BAC-MA-MCCABF__

42 2.150E-04 8.79E-04 5.09E+00 1.001E+00 3.233E-06 480V MCC 1ABF in maintenance 1-IE-FLI-TB_500_HI2 59 9.400E-05 8.51E-04 1.01E+01 1.001E+00 7.164E-06 Internal flooding in tb due to TPCCW maintenance 1-DCP-FUS-OP-BD104___

89 7.464E-05 8.16E-04 1.19E+01 1.001E+00 8.644E-06 Supply current fuse between CRB 1BD104 & inverter fails 1-AFW-MOV-OO-FV5155__

18 3.530E-04 7.75E-04 3.20E+00 1.001E+00 1.737E-06 MDAFWP A mini flow MOV randomly fails to close 1-ACP-BAC-MA-MCCABB__

74 2.150E-04 7.63E-04 4.55E+00 1.001E+00 2.808E-06 480V MCC 1ABB in maintenance 1-IE-FLI-TB_500_HI1 58 9.400E-05 7.27E-04 8.73E+00 1.001E+00 6.116E-06 Internal flooding in TB Fire Zone 500 1-SWS-CTF-MA-_A_1234_

41 4.080E-05 7.02E-04 1.82E+01 1.001E+00 1.362E-05 All four NSCW train A tower fans unavailable due to maintenance (PSA value) 1-SWS-MDP-MA-P4_00135-3 43 3.390E-05 6.47E-04 2.01E+01 1.001E+00 1.509E-05 All 3 NSCW train A pumps unavailable due to maintenance 1-HPI-MOV-CC-HV8801B_

32 3.530E-04 5.93E-04 2.68E+00 1.001E+00 1.328E-06 Charging pump BIT injection MOV fails to open -random fault 1-HPI-MOV-CC-HV8804B_

32 3.530E-04 5.93E-04 2.68E+00 1.001E+00 1.328E-06 HV8804B in hp rec. Suction line from RHR HX A fail to open - random fault 1-HPI-MOV-CC-HV8807B_

32 3.530E-04 5.93E-04 2.68E+00 1.001E+00 1.328E-06 MOV HV8807B in CCP and SIP suction X-connection fail to open-random fault 1-HPI-MOV-CC-LV0112E_

32 3.530E-04 5.93E-04 2.68E+00 1.001E+00 1.328E-06 CCP RWST suction isolation MOV fails to open - random fault 1-HPI-MOV-OO-HV8105__

32 3.530E-04 5.93E-04 2.68E+00 1.001E+00 1.328E-06 Normal Charging Isolation MOV HV8105 fails to close random fault 1-HPI-MOV-OO-HV8508B_

32 3.530E-04 5.93E-04 2.68E+00 1.001E+00 1.328E-06 CCP B mini flow valve fail to close - random 1-HPI-MOV-OO-HV8813__

32 3.530E-04 5.93E-04 2.68E+00 1.001E+00 1.328E-06 SI pumps mini flow isolation MOV fails to close - random fault 1-HPI-MOV-OO-LV0112C_

32 3.530E-04 5.93E-04 2.68E+00 1.001E+00 1.328E-06 VCT isolation LV0112C fails to close - random fault 1-LPI-MOV-CC-HV8811B_

32 3.530E-04 5.93E-04 2.68E+00 1.001E+00 1.328E-06 RHRP B containment sump suction MOV HV8811B fails to open by random cause 1-LPI-MOV-OO-HV8812B_

32 3.530E-04 5.93E-04 2.68E+00 1.001E+00 1.328E-06 RHRP B RWST suction MOV HV8812B fails to close due to random fault

B-40 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-DCP-FUS-OP-AD104___

83 7.464E-05 5.87E-04 8.86E+00 1.001E+00 6.215E-06 Supply current fuse between CRB 1AD104 & inverter fails 1-ACP-BAC-MA-AYB1____

49 2.150E-04 5.30E-04 3.47E+00 1.001E+00 1.951E-06 120/240V panel 1AYB1 in maintenance 1-AFW-MDP-FR-P4003___

14 1.984E-04 4.32E-04 3.17E+00 1.000E+00 1.720E-06 MDAFWP A (P4-003) randomly fails to run 1-HPI-CKV-OO-129_____

34 2.382E-04 4.10E-04 2.72E+00 1.000E+00 1.362E-06 NCP discharge check valve 129 fails to close 1-HPI-CKV-OO-189_____

32 2.382E-04 4.04E-04 2.70E+00 1.000E+00 1.342E-06 CCP RWST suction CV 189 fails to close 1-ACP-BAC-FC-BB07____

51 4.776E-05 4.03E-04 9.44E+00 1.000E+00 6.678E-06 480V switchgear 1BB07 randomly fails 1-ACP-BAC-FC-MCCBBF__

51 4.776E-05 4.03E-04 9.44E+00 1.000E+00 6.678E-06 480V MCC 1BBF fails 1-ACP-BAC-FC-MCCBBB__

69 4.776E-05 3.91E-04 9.19E+00 1.000E+00 6.478E-06 480V MCC 1BBB randomly fails 1-HPI-XHE-XR-XVM207 56 1.000E-04 3.63E-04 4.63E+00 1.000E+00 2.869E-06 Operator fails to restore RWST XVM 207 after test and maintenance 1-ACP-BAC-MA-MCCBBD__

28 2.150E-04 3.57E-04 2.66E+00 1.000E+00 1.312E-06 480V MCC 1BBD in maintenance 1-ACP-TFW-FC-AB15X___

43 1.526E-05 3.44E-04 2.36E+01 1.000E+00 1.785E-05 Transformer 1AB15X fails 1-ACP-TFW-FC-NXRB____

43 1.526E-05 3.44E-04 2.36E+01 1.000E+00 1.783E-05 RAT 1NXRB fails 1-IE-FLI-AB_D78_FP 24 3.550E-07 3.02E-04 8.53E+02 1.000E+00 6.736E-04 Internal flooding in AB D78 propagates to 480 VAC switchgear room D105 1-SWS-MDP-CF-FS-ABCDEF 14 4.211E-06 2.95E-04 7.11E+01 1.000E+00 5.548E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FR-ABCDEF 26 8.363E-08 2.79E-04 3.33E+03 1.000E+00 2.632E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-ACP-BAC-FC-BYB1____

48 4.776E-05 2.71E-04 6.68E+00 1.000E+00 4.494E-06 120/240V panel 1BYB1 fails 1-ACP-BAC-FC-AB05____

44 4.776E-05 2.54E-04 6.32E+00 1.000E+00 4.206E-06 480V switchgear 1AB05 randomly fails 1-ACP-BAC-FC-MCCABF__

42 4.776E-05 2.50E-04 6.24E+00 1.000E+00 4.142E-06 480V MCC 1ABF fails 1-RPS-CBI-CF-4OF6 16 8.210E-06 2.44E-04 3.08E+01 1.000E+00 2.354E-05 CCF 4 bistables in 2 of 3 channels 1-SWS-MOV-OC-1669A___

15 7.008E-07 2.44E-04 3.49E+02 1.000E+00 2.754E-04 NSCW train B spray valve HV1669A spuriously closes 1-IE-FLI-AB_A20_FP 51 2.270E-05 2.44E-04 1.17E+01 1.000E+00 8.489E-06 Internal flooding in AB A20 propagates to rooms A11 and A12 1-SWS-RLY-FC-AX36869_-

CC 25 1.538E-06 2.18E-04 1.43E+02 1.000E+00 1.120E-04 CCF of AX3 relays for open/close NSCW MOVS 1HV1668A/B & 1669A/B after LOSP 1-ACP-DPL-FC-BY2B____

38 1.802E-05 2.08E-04 1.25E+01 1.000E+00 9.131E-06 Panel 1BY2B fails 1-ACP-BAC-FC-MCCABB__

55 4.776E-05 2.07E-04 5.33E+00 1.000E+00 3.422E-06 480V MCC 1ABB randomly fails 1-RCS-PRV-CF-RV5A6A__

36 1.044E-04 2.02E-04 2.94E+00 1.000E+00 1.532E-06 PORVS PV0455A (5A) & PV0456A (6A) fail from common cause to open 1-RPS-CCX-CF-4OF6 13 6.330E-06 1.85E-04 3.03E+01 1.000E+00 2.314E-05 CCF 4 analog process logic modules in 2 of 3 channels 1-AFW-MOV-CF-MINFL 20 1.055E-05 1.76E-04 1.77E+01 1.000E+00 1.318E-05 CCF of AFW MDP mini flow valves 5155 & 5154

B-41 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-ACP-CNT-OO-_BK346__

39 2.480E-05 1.73E-04 7.96E+00 1.000E+00 5.502E-06 SFSS relay K346B contacts fails to close 1-ACP-TFW-FC-_1BSEQT1 34 1.526E-05 1.72E-04 1.22E+01 1.000E+00 8.893E-06 Sequencer transformer T1 fails 1-ACP-TFW-FC-_1BSEQT2 34 1.526E-05 1.72E-04 1.22E+01 1.000E+00 8.893E-06 Sequencer transformer T3 fails 1-ACP-BAC-FC-AYB1____

46 4.776E-05 1.58E-04 4.31E+00 1.000E+00 2.617E-06 120/240V panel 1AYB1 fails 1-DCP-BAT-FC-BD1B____

34 1.404E-05 1.58E-04 1.22E+01 1.000E+00 8.893E-06 Battery 1BD1B randomly fails (125V) 1-ACP-DPL-FC-AY2A____

32 1.802E-05 1.57E-04 9.72E+00 1.000E+00 6.900E-06 Panel 1AY2A fails 1-DCP-DPL-FC-BD11____

26 5.640E-06 1.43E-04 2.64E+01 1.000E+00 2.006E-05 Distribution panel 1BD11 fails 1-AFW-TNK-RP-V4001___

10 4.334E-07 1.40E-04 3.25E+02 1.000E+00 2.563E-04 CST 1 failure 1-SWS-MDP-CF-FS-ABCD 11 2.000E-06 1.37E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ABCF 11 2.000E-06 1.37E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ABDE 11 2.000E-06 1.37E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ABEF 11 2.000E-06 1.37E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ACDF 11 2.000E-06 1.37E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ADEF 11 2.000E-06 1.37E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BCDE 11 2.000E-06 1.37E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BCEF 11 2.000E-06 1.37E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-CDEF 11 2.000E-06 1.37E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-LPI-MDP-CF-START 31 4.878E-05 1.36E-04 3.80E+00 1.000E+00 2.212E-06 RHR pumps A, B fail from common cause to start 1-DCP-CRB-CO-BD105___

24 5.400E-06 1.34E-04 2.59E+01 1.000E+00 1.969E-05 Supply CRB 1BD105 from bus 1BD1 to 1BD11 spuriously opens 1-ACP-TFW-FC-BB07X___

19 1.526E-05 1.34E-04 9.81E+00 1.000E+00 6.965E-06 Transformer 1BB07X fails 1-ACP-CNT-OO-_AK346__

26 2.480E-05 1.33E-04 6.38E+00 1.000E+00 4.253E-06 SFSS relay K346A contacts fails to close 1-DCP-BDC-FC-BD1_____

25 5.640E-06 1.32E-04 2.44E+01 1.000E+00 1.847E-05 125V bus 1BD1 fails 1-ACP-TFW-FC-_1ASEQT1 30 1.526E-05 1.31E-04 9.57E+00 1.000E+00 6.782E-06 Sequencer transformer T1 fails 1-ACP-TFW-FC-_1ASEQT2 30 1.526E-05 1.31E-04 9.57E+00 1.000E+00 6.782E-06 Sequencer transformer T3 fails 1-SWS-MDP-CF-FR-ABCD 23 3.967E-08 1.29E-04 3.26E+03 1.000E+00 2.577E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR

B-42 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-SWS-MDP-CF-FR-ABCF 23 3.967E-08 1.29E-04 3.26E+03 1.000E+00 2.577E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-ABDE 23 3.967E-08 1.29E-04 3.26E+03 1.000E+00 2.577E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-ABEF 23 3.967E-08 1.29E-04 3.26E+03 1.000E+00 2.577E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-ACDF 23 3.967E-08 1.29E-04 3.26E+03 1.000E+00 2.577E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-ADEF 23 3.967E-08 1.29E-04 3.26E+03 1.000E+00 2.577E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BCDE 23 3.967E-08 1.29E-04 3.26E+03 1.000E+00 2.577E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BCEF 23 3.967E-08 1.29E-04 3.26E+03 1.000E+00 2.577E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-CDEF 23 3.967E-08 1.29E-04 3.26E+03 1.000E+00 2.577E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FS-ABCDE 11 1.870E-06 1.28E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ABCDF 11 1.870E-06 1.28E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ABCEF 11 1.870E-06 1.28E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ABDEF 11 1.870E-06 1.28E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ACDEF 11 1.870E-06 1.28E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BCDEF 11 1.870E-06 1.28E-04 6.94E+01 1.000E+00 5.412E-05 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-RLY-FC-AX46869_-

CC 15 1.538E-06 1.24E-04 8.15E+01 1.000E+00 6.367E-05 Relays AX4 for opening NSCW 1HV1668A/B & 1669A/B after LOSP fails - CCF 1-DCP-BAT-FC-AD1B____

30 1.404E-05 1.20E-04 9.57E+00 1.000E+00 6.782E-06 Battery 1AD1B randomly fails (125V) 1-SWS-MDP-CF-FR-ABCDE 22 3.724E-08 1.20E-04 3.23E+03 1.000E+00 2.550E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-ABCDF 22 3.724E-08 1.20E-04 3.23E+03 1.000E+00 2.550E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-ABCEF 22 3.724E-08 1.20E-04 3.23E+03 1.000E+00 2.550E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR

B-43 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-SWS-MDP-CF-FR-ABDEF 22 3.724E-08 1.20E-04 3.23E+03 1.000E+00 2.550E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-ACDEF 22 3.724E-08 1.20E-04 3.23E+03 1.000E+00 2.550E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BCDEF 22 3.724E-08 1.20E-04 3.23E+03 1.000E+00 2.550E-03 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-CVC-MDP-FS-CCPACCPB-CC 24 4.224E-05 1.17E-04 3.77E+00 1.000E+00 2.189E-06 CCF of CCP-A & CCP-B to start 1-SWS-RLY-FC-AX3_69AB 18 2.480E-05 1.15E-04 5.63E+00 1.000E+00 3.661E-06 NSCW relay AX3 for opening/closing 1HV1669A/B fails 1-ACP-CRB-CO-AA0210__

25 5.400E-06 1.06E-04 2.07E+01 1.000E+00 1.558E-05 Feeder CRB 1AA02 spuriously opens - 1AA02 to 1AB15X 1-ACP-CRB-CO-AB1501__

25 5.400E-06 1.06E-04 2.07E+01 1.000E+00 1.558E-05 Supply CRB 1AB15 spuriously opens - 1AB15X to 1AB15 1-SWS-RLY-FC-162_1X69 15 2.480E-05 1.06E-04 5.28E+00 1.000E+00 3.387E-06 relay 162-1X for opening HV1669A/B fails random 1-ACP-CRB-CO-BA0301__

22 5.400E-06 1.06E-04 2.06E+01 1.000E+00 1.546E-05 RAT B Supply CRB BA0301 to 4160V bus BA03 spuriously opens 1-DCP-BAT-CF-ALL 15 1.235E-07 1.03E-04 8.38E+02 1.000E+00 6.617E-04 CCF of 125V batteries 1-SWS-SWT-FC-TY1669B_

7 9.864E-06 1.00E-04 1.12E+01 1.000E+00 8.028E-06 NSCW train B return water temperature switch TY1669B fails - random fault 1-AFW-MDP-CF-RUN 14 6.072E-06 9.63E-05 1.69E+01 1.000E+00 1.255E-05 CCF of AFW MDPs to run 1-SWS-RLY-FC-162_1X89-CC 10 1.538E-06 9.39E-05 6.20E+01 1.000E+00 4.828E-05 Relays 162-1X for opening HV1668A /BAND 1669A /B after LOSP fails -CCF 1-ACP-TFW-FC-BBB03X__

17 1.526E-05 9.26E-05 7.06E+00 1.000E+00 4.797E-06 480V MCC Transformer 1BBB03X fails 1-ACP-TFW-FC-AB05X___

19 1.526E-05 9.16E-05 7.00E+00 1.000E+00 4.747E-06 Transformer 1AB05X fails 1-LPI-MDP-FR-RHRB____

17 5.842E-05 8.99E-05 2.54E+00 1.000E+00 1.217E-06 RHR pump B failsto run due to random fault (24hr mission) 1-HPI-MOV-OO-HV8105&6-CC 19 3.174E-05 8.25E-05 3.60E+00 1.000E+00 2.057E-06 Normal Charging Isolation MOVs HV8106 & HV8105 fails to close due to CCF 1-HPI-MOV-OO-LV0112BC-CC 19 3.174E-05 8.25E-05 3.60E+00 1.000E+00 2.057E-06 VCT isolation MOVs LV0112B & C fails to close - CCF 1-ACP-BAC-FC-MCCBBD__

16 4.776E-05 7.23E-05 2.51E+00 1.000E+00 1.198E-06 480V MCC 1BBD randomly fails 1-SWS-MDP-FR-P4_002__

12 3.816E-05 6.23E-05 2.63E+00 1.000E+00 1.291E-06 NSCW pump 2 fail to run 1-SWS-MDP-FR-P4_004__

12 3.816E-05 6.23E-05 2.63E+00 1.000E+00 1.291E-06 NSCW pump 4 fail to run 1-ACP-TFW-FC-NXRA____

13 1.526E-05 5.90E-05 4.86E+00 1.000E+00 3.056E-06 RAT 1NXRA fails 1-SWS-MOV-CF-116-ABCDEF 9

8.698E-07 5.77E-05 6.73E+01 1.000E+00 5.246E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-ACP-TFW-FC-ABB03X__

14 1.526E-05 5.61E-05 4.68E+00 1.000E+00 2.907E-06 480V MCC Transformer 1ABB03X fails

B-44 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-SWS-MDP-CF-FR-BD 6

1.563E-07 5.61E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BF 6

1.563E-07 5.61E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-DF 6

1.563E-07 5.61E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-RLY-FC-AX3_68AB 15 2.480E-05 5.58E-05 3.25E+00 1.000E+00 1.778E-06 relay AX3 for opening/closing NSCW 1HV1668A/B fails -

random fault 1-SWS-RLY-FC-162_1X68 13 2.480E-05 5.28E-05 3.13E+00 1.000E+00 1.685E-06 relay 162-1X for opening HV1668A/B fails random 1-DCP-BDC-FC-AD1_____

22 5.640E-06 4.93E-05 9.74E+00 1.000E+00 6.912E-06 125V bus 1AD1 fails 1-SWS-RLY-FC-162_1ALL-CC 8

7.440E-07 4.82E-05 6.58E+01 1.000E+00 5.127E-05 Relays 162-1 associated with opening of HV-11600 1-DCP-DPL-FC-AD11____

21 5.640E-06 4.73E-05 9.39E+00 1.000E+00 6.634E-06 Distribution panel 1AD11 fails 1-ACP-CRB-CO-BY2B02__

18 5.400E-06 4.72E-05 9.74E+00 1.000E+00 6.916E-06 CRB 1BY2B02 between inverter 1BD1I12 & 1BY2B spuriously opens 1-DCP-CRB-CO-BD101___

18 5.400E-06 4.72E-05 9.74E+00 1.000E+00 6.916E-06 CRB from battery 1BD1B to bus 1BD1 spuriously opens 1-DCP-CRB-CO-BD104___

18 5.400E-06 4.72E-05 9.74E+00 1.000E+00 6.916E-06 CRB 1BD104 between inverter 1BD1I12 & 1BD1 spuriously opens 1-DCP-CRB-CO-BD1104__

18 5.400E-06 4.72E-05 9.74E+00 1.000E+00 6.916E-06 CRB BD1104 spuriously opens on load shed logic circuits 1-DCP-CRB-CO-BY2B08__

18 5.400E-06 4.72E-05 9.74E+00 1.000E+00 6.916E-06 CRB spuriously opens (BY2B08 to sequencer B) 1-SWS-MDP-CF-FS-BD 9

8.309E-06 4.70E-05 6.65E+00 1.000E+00 4.471E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BF 9

8.309E-06 4.70E-05 6.65E+00 1.000E+00 4.471E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-DF 9

8.309E-06 4.70E-05 6.65E+00 1.000E+00 4.471E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-DCP-CRB-CO-AD105___

19 5.400E-06 4.28E-05 8.92E+00 1.000E+00 6.264E-06 Supply CRB 1AD105 from bus 1AD1 to 1AD11 spuriously opens 1-ACP-CRB-CO-BA0304__

11 5.400E-06 4.16E-05 8.71E+00 1.000E+00 6.096E-06 Feeder CRB 1BA03 spuriously opens - 1BA03 to 1BB07X 1-ACP-CRB-CO-BB0701__

11 5.400E-06 4.16E-05 8.71E+00 1.000E+00 6.096E-06 Supply CRB 1BB07 spuriously opens - 1BB07X to 1BB07 1-ACP-CRB-CO-BB0714__

11 5.400E-06 4.16E-05 8.71E+00 1.000E+00 6.096E-06 CRB from 480V switchgear 1BB07 to 480V MCC 1BBF spuriously opens 1-RPS-UVL-CF-UVDAB 9

1.040E-05 4.11E-05 4.96E+00 1.000E+00 3.128E-06 CCF UV drivers trains A and B (2 OF 2)

B-45 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-HPI-MOV-CC-HV8807AB-CC 9

3.174E-05 4.09E-05 2.29E+00 1.000E+00 1.020E-06 MOVs HV8807A & B IN CCP and SIP suctioncross connection fail to open-CCF 1-AFW-CKV-CC-002_____

6 1.070E-05 3.94E-05 4.69E+00 1.000E+00 2.916E-06 MDAFWP discharge CKV 002 randomly fails to open 1-AFW-CKV-CC-058_____

6 1.070E-05 3.94E-05 4.69E+00 1.000E+00 2.916E-06 MDAFWP B suction CKV 058 randomly fails to open 1-AFW-CKV-CC-010214__-

CC 7

1.166E-07 3.57E-05 3.07E+02 1.000E+00 2.424E-04 CCF of AFW pumps discharge line CKVs 001, 002, &

014 to open 1-AFW-CKV-CC-331358__-

CC 7

1.166E-07 3.57E-05 3.07E+02 1.000E+00 2.424E-04 CCF of AFW pumps suction CKVs 033, 013, 058 to open 1-ACP-CRB-CO-AY2A02__

17 5.400E-06 3.44E-05 7.37E+00 1.000E+00 5.038E-06 CRB 1AY2A02 between inverter 1AD1I11 & 1AY2A spuriously opens 1-DCP-CRB-CO-AD101___

17 5.400E-06 3.44E-05 7.37E+00 1.000E+00 5.038E-06 CRB from battery 1AD1B to bus 1AD1 spuriously opens 1-DCP-CRB-CO-AD104___

17 5.400E-06 3.44E-05 7.37E+00 1.000E+00 5.038E-06 CRB 1AD104 from inverter 1AD1I11 to 1AD1 spuriously opens 1-DCP-CRB-CO-AD1104__

17 5.400E-06 3.44E-05 7.37E+00 1.000E+00 5.038E-06 CRB AD1104 spuriously opens on load shed logic circuits 1-DCP-CRB-CO-AY2A08__

17 5.400E-06 3.44E-05 7.37E+00 1.000E+00 5.038E-06 CRB spuriously opens (AY2A08 to sequencer A) 1-HPI-MOV-CC-HV8801AB-CC 8

1.626E-05 3.28E-05 3.02E+00 1.000E+00 1.597E-06 Charging pump BIT injection MOVs HV8801A & B fail to open due to CCF 1-ACP-CRB-CO-BB1609__

10 5.400E-06 3.26E-05 7.03E+00 1.000E+00 4.771E-06 Feeder CRB 1BB16 spuriously opens - 1BB16 to 1BBB 1-DCP-CRB-CO-BD1101__

8 5.400E-06 2.95E-05 6.47E+00 1.000E+00 4.327E-06 CRB BD1101 spuriously opens on load shed logic circuits 1-DCP-CRB-CO-BD111024 8

5.400E-06 2.95E-05 6.47E+00 1.000E+00 4.327E-06 CRB BD1110 to fan control logic spuriously opens 1-SWS-MOV-CF-116-ABCDE 6

4.696E-07 2.87E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-ABCDF 6

4.696E-07 2.87E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-ABCEF 6

4.696E-07 2.87E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-ABDEF 6

4.696E-07 2.87E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-ACDEF 6

4.696E-07 2.87E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-BCDEF 6

4.696E-07 2.87E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MDP-CF-FS-AC 8

8.309E-06 2.72E-05 4.28E+00 1.000E+00 2.593E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS

B-46 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-SWS-MDP-CF-FS-AE 8

8.309E-06 2.72E-05 4.28E+00 1.000E+00 2.593E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-CE 8

8.309E-06 2.72E-05 4.28E+00 1.000E+00 2.593E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-AFW-CKV-CF-PDCV 7

8.753E-08 2.68E-05 3.07E+02 1.000E+00 2.424E-04 CCF of pump discharge CKVs 001, 002, & 014 1-AFW-CKV-CF-PSCV 7

8.753E-08 2.68E-05 3.07E+02 1.000E+00 2.424E-04 CCF of pump suction CKVs 033, 058, & 013 1-ACP-CRB-CO-BBB45___

8 5.400E-06 2.67E-05 5.95E+00 1.000E+00 3.912E-06 480V MCC CRB 1BBB45 spuriously opens 1-ACP-CRB-CO-BYB116__

8 5.400E-06 2.67E-05 5.95E+00 1.000E+00 3.912E-06 120/240V CRB 1BYB116 spuriously opens 1-ACP-CRB-CO-AA0221__

9 5.400E-06 2.51E-05 5.65E+00 1.000E+00 3.675E-06 Feeder CRB 1AA02 spuriously opens - 1AA02 to 1AB05X 1-ACP-CRB-CO-AB0501__

9 5.400E-06 2.51E-05 5.65E+00 1.000E+00 3.675E-06 Supply CRB 1AB05 spuriously opens - 1AB05X to 1AB05 1-ACP-CRB-CO-AB0514__

9 5.400E-06 2.51E-05 5.65E+00 1.000E+00 3.675E-06 CRB from 480V switchgear 1AB05 to 480V MCC 1ABF spuriously opens 1-HPI-MOV-CF-0112DE 8

1.187E-05 2.40E-05 3.02E+00 1.000E+00 1.597E-06 CCP RWST suction isolation MOVS LV0112 D& E fail from common cause to open 1-HPI-MOV-CF-8801AB 8

1.187E-05 2.40E-05 3.02E+00 1.000E+00 1.597E-06 CHARGING pump BIT injection MOVs HV8801A & B fail from common cause to open 1-AFW-SCV-CC-037_____

2 1.260E-05 2.37E-05 2.88E+00 1.000E+00 1.488E-06 MDAFWP B flow distribution line to SG 2 STOP CKV 037 randomly fails to open 1-AFW-SCV-CC-040_____

2 1.260E-05 2.37E-05 2.88E+00 1.000E+00 1.488E-06 MDAFWP B flow distribution line to SG 3 STOP CKV 040 randomly fails to open 1-AFW-SCV-CC-114_____

2 1.260E-05 2.37E-05 2.88E+00 1.000E+00 1.488E-06 SG 2 AFW feed line stop CKV 114 randomly fails to open 1-AFW-SCV-CC-115_____

2 1.260E-05 2.37E-05 2.88E+00 1.000E+00 1.488E-06 SG 3 AFW feed line stop CKV 115 randomly fails to open 1-SWS-MOV-CF-116-ABDE 6

3.852E-07 2.35E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-ABDF 6

3.852E-07 2.35E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-ABEF 6

3.852E-07 2.35E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-ACDE 6

3.852E-07 2.35E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-ACDF 6

3.852E-07 2.35E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-ACEF 6

3.852E-07 2.35E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116

B-47 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-SWS-MOV-CF-116-BCDE 6

3.852E-07 2.35E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-BCDF 6

3.852E-07 2.35E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-BCEF 6

3.852E-07 2.35E-05 6.20E+01 1.000E+00 4.828E-05 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-HPI-CKV-CC-013_____

8 1.070E-05 2.16E-05 3.02E+00 1.000E+00 1.597E-06 CCP BIT injection CV 013 (downstream of BIT before cold legs) fail to open - random fault 1-HPI-CKV-CC-189_____

8 1.070E-05 2.16E-05 3.02E+00 1.000E+00 1.597E-06 CCP RWST suction CV 189 fails to open 1-AFW-CKV-CC-001_____

5 1.070E-05 2.07E-05 2.94E+00 1.000E+00 1.532E-06 MDAFWP A discharge line CKV 001 randomly fails 1-AFW-CKV-CC-033_____

5 1.070E-05 2.07E-05 2.94E+00 1.000E+00 1.532E-06 MDAFWP A suction CKV 033 randomly fails to open 1-SWS-MDP-CF-FR-ABD 6

5.730E-08 2.06E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-ABF 6

5.730E-08 2.06E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-ADF 6

5.730E-08 2.06E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BCD 6

5.730E-08 2.06E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BCF 6

5.730E-08 2.06E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BDE 6

5.730E-08 2.06E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BDF 6

5.730E-08 2.06E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BEF 6

5.730E-08 2.06E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-CDF 6

5.730E-08 2.06E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-DEF 6

5.730E-08 2.06E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-AFW-CKV-CC-126_____

2 1.070E-05 2.01E-05 2.88E+00 1.000E+00 1.488E-06 SG 2 AFW feed line CKV 126 randomly fails to open 1-AFW-CKV-CC-128_____

2 1.070E-05 2.01E-05 2.88E+00 1.000E+00 1.488E-06 SG 3 AFW feed line CKV 128 randomly fails to open 1-AFW-CKV-CC-001014__-

CC 3

4.506E-07 2.01E-05 4.56E+01 1.000E+00 3.526E-05 CCF of AFW pumps discharge line CKVs 001 & 014 to open 1-AFW-CKV-CC-033013__-

CC 3

4.506E-07 2.01E-05 4.56E+01 1.000E+00 3.526E-05 CCF of AFW pumps suction CKVs 033 & 013 to open

B-48 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-AFW-CKV-CC-002014__-

CC 2

4.506E-07 1.85E-05 4.21E+01 1.000E+00 3.248E-05 CCF of AFW pumps discharge CKVs 002 & 014 1-AFW-CKV-CC-058013__-

CC 2

4.506E-07 1.85E-05 4.21E+01 1.000E+00 3.248E-05 CCF of AFW pumps suction CKVs 058 & 013 to open 1-ACP-CRB-CO-AB1509__

7 5.400E-06 1.67E-05 4.10E+00 1.000E+00 2.449E-06 Feeder CRB 1AB15 spuriously opens - 1AB15 to 1ABB 1-DCP-CRB-CO-AD1101__

7 5.400E-06 1.67E-05 4.10E+00 1.000E+00 2.449E-06 CRB AD1101 spuriously opens on load shed logic circuits 1-DCP-CRB-CO-AD111024 7

5.400E-06 1.67E-05 4.10E+00 1.000E+00 2.449E-06 CRB AD1110 to fan control logic spuriously opens 1-ACP-CRB-CO-AA0205__

6 5.400E-06 1.54E-05 3.85E+00 1.000E+00 2.251E-06 RAT A Supply CRB AA0205 to 4.16KV bus AA02 spuriously opens 1-ACP-CRB-CO-ABB02___

7 5.400E-06 1.51E-05 3.80E+00 1.000E+00 2.213E-06 480V MCC AC CRB 1ABB02 spuriously opens 1-ACP-CRB-CO-AYB116__

7 5.400E-06 1.51E-05 3.80E+00 1.000E+00 2.213E-06 120/240V CRB 1AYB116 spuriously opens 1-SWS-MDP-CF-FR-ABDF 6

3.967E-08 1.42E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BCDF 6

3.967E-08 1.42E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FR-BDEF 6

3.967E-08 1.42E-05 3.60E+02 1.000E+00 2.836E-04 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FR 1-SWS-MDP-CF-FS-ABD 4

2.907E-06 1.19E-05 5.08E+00 1.000E+00 3.223E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ABF 4

2.907E-06 1.19E-05 5.08E+00 1.000E+00 3.223E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ADF 4

2.907E-06 1.19E-05 5.08E+00 1.000E+00 3.223E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BCD 4

2.907E-06 1.19E-05 5.08E+00 1.000E+00 3.223E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BCF 4

2.907E-06 1.19E-05 5.08E+00 1.000E+00 3.223E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BDE 4

2.907E-06 1.19E-05 5.08E+00 1.000E+00 3.223E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BDF 4

2.907E-06 1.19E-05 5.08E+00 1.000E+00 3.223E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BEF 4

2.907E-06 1.19E-05 5.08E+00 1.000E+00 3.223E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-CDF 4

2.907E-06 1.19E-05 5.08E+00 1.000E+00 3.223E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS

B-49 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-SWS-MDP-CF-FS-DEF 4

2.907E-06 1.19E-05 5.08E+00 1.000E+00 3.223E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-AFW-CKV-CF-SGCV 2

4.762E-08 9.75E-06 2.06E+02 1.000E+00 1.619E-04 CCF of SG CKVs 125, 126, 127, & 128 1-AFW-SCV-CC-1131415_-

CC 2

4.234E-08 8.67E-06 2.06E+02 1.000E+00 1.619E-04 CCF of SG AFW feed line stop CKVs 113 1-AFW-SCV-CC-1161314_-

CC 2

4.234E-08 8.67E-06 2.06E+02 1.000E+00 1.619E-04 CCF of SG AFW feed line stop CKVs 116, 113, & 114 to open 1-AFW-SCV-CC-1161315_-

CC 2

4.234E-08 8.67E-06 2.06E+02 1.000E+00 1.619E-04 CCF of SG AFW feed line stop CKVs 116, 113, & 115 to open 1-AFW-SCV-CC-1161415_-

CC 2

4.234E-08 8.67E-06 2.06E+02 1.000E+00 1.619E-04 CCF of SG AFW feed line stop CKVs 116, 114, & 115 to open 1-CVC-MDP-FR-CCPACCPB-CC 6

4.877E-06 8.55E-06 2.75E+00 1.000E+00 1.387E-06 CCF of CCP-A & CCP-B to run 1-AFW-TFF-FC-FT5154__

4 2.323E-06 8.00E-06 4.44E+00 1.000E+00 2.723E-06 MDAFWP B mini flow line flow transmitter FT-5154 randomly fails 1-SWS-MDP-CF-FS-ABDF 3

2.000E-06 7.20E-06 4.60E+00 1.000E+00 2.846E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BCDF 3

2.000E-06 7.20E-06 4.60E+00 1.000E+00 2.846E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BDEF 3

2.000E-06 7.20E-06 4.60E+00 1.000E+00 2.846E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-AFW-SCV-CC-16131415-CC 2

2.772E-08 5.68E-06 2.06E+02 1.000E+00 1.619E-04 CCF of SG AFW feed line stop CKVs 116, 113, 114, &

115 to open 1-RPS-TLC-CF-SSLAB 4

2.100E-06 5.61E-06 3.67E+00 1.000E+00 2.114E-06 CCF solid state logic in trains A and B (4 of 4) 1-SWS-MDP-CF-FS-ABC 3

2.907E-06 4.94E-06 2.70E+00 1.000E+00 1.345E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ABE 3

2.907E-06 4.94E-06 2.70E+00 1.000E+00 1.345E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ACD 3

2.907E-06 4.94E-06 2.70E+00 1.000E+00 1.345E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ACE 3

2.907E-06 4.94E-06 2.70E+00 1.000E+00 1.345E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ACF 3

2.907E-06 4.94E-06 2.70E+00 1.000E+00 1.345E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-ADE 3

2.907E-06 4.94E-06 2.70E+00 1.000E+00 1.345E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS

B-50 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-SWS-MDP-CF-FS-AEF 3

2.907E-06 4.94E-06 2.70E+00 1.000E+00 1.345E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-BCE 3

2.907E-06 4.94E-06 2.70E+00 1.000E+00 1.345E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-CDE 3

2.907E-06 4.94E-06 2.70E+00 1.000E+00 1.345E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-SWS-MDP-CF-FS-CEF 3

2.907E-06 4.94E-06 2.70E+00 1.000E+00 1.345E-06 System Generated Event based upon RASP CCF event :

1-SWS-MDP-CF-FS 1-AFW-SCV-CC-114115__-

CC 2

1.116E-07 4.58E-06 4.21E+01 1.000E+00 3.248E-05 CCF of SG AFW feed line stop CKVs 114 & 115 to open 1-AFW-SCV-CC-113114__-

CC 2

1.116E-07 4.57E-06 4.19E+01 1.000E+00 3.236E-05 CCF of SG AFW feed line stop CKVs 113 & 114 to open 1-AFW-SCV-CC-113115__-

CC 2

1.116E-07 4.57E-06 4.19E+01 1.000E+00 3.236E-05 CCF of SG AFW feed line stop CKVs 113 & 115 to open 1-AFW-SCV-CC-116114__-

CC 2

1.116E-07 4.57E-06 4.19E+01 1.000E+00 3.236E-05 CCF of SG AFW feed line stop CKVs 116 & 114 to open 1-AFW-SCV-CC-116115__-

CC 2

1.116E-07 4.57E-06 4.19E+01 1.000E+00 3.236E-05 CCF of SG AFW feed line stop CKVs 116 & 115 to open 1-AFW-SCV-CC-116113__-

CC 2

1.116E-07 4.55E-06 4.18E+01 1.000E+00 3.225E-05 CCF of SG AFW feed line stop CKVs 116 & 113 to open 1-AFW-SCV-CC-HICCF___-

CC 1

2.570E-08 4.07E-06 1.59E+02 1.000E+00 1.253E-04 High order CCF comb. caused AFWS fail-stop CV FTO-AF flow distribution lines 1-SWS-MOV-OC-1668A___

2 7.008E-07 3.90E-06 6.57E+00 1.000E+00 4.404E-06 NSCW train A return isolation valve HV1668A spuriously closes 1-AFW-TFF-FC-FT5155__

2 2.323E-06 3.60E-06 2.55E+00 1.000E+00 1.226E-06 AFW MDP A mini flow line flow transmitter FT-5155 randomly fails 1-AFW-CKV-CC-001002__-

CC 1

4.506E-07 2.71E-06 7.02E+00 1.000E+00 4.763E-06 CCF of AFW pumps discharge line CKVs 001 & 002 to open 1-AFW-CKV-CC-033058__-

CC 1

4.506E-07 2.71E-06 7.02E+00 1.000E+00 4.763E-06 CCF of AFW pumps suction CKVS 033 & 058 to open 1-SWS-CTF-CF-S-ABCDEFGH 1

1.067E-07 1.54E-06 1.55E+01 1.000E+00 1.145E-05 System Generated Event based upon RASP CCF event :

1-SWS-FAN-CF-S 1-SWS-MOV-CF-116-DE 1

9.760E-07 1.47E-06 2.50E+00 1.000E+00 1.187E-06 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116 1-SWS-MOV-CF-116-DF 1

9.760E-07 1.47E-06 2.50E+00 1.000E+00 1.187E-06 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116

B-51 Table B-2 Internal Flooding Basic Event Importance Measures Name Count Prob FV RIR RRR Birnbaum Description 1-SWS-MOV-CF-116-EF 1

9.760E-07 1.47E-06 2.50E+00 1.000E+00 1.187E-06 System Generated Event based upon RASP CCF event :

1-SWS-MOV-CF-116

C-1 APPENDIX C:

INTERNAL FLOODING TOPICS FOR FUTURE WORK In developing the NRCs Level 1 internal flooding PRA (IFPRA), a number of topics were identified where additional study may be warranted. These topics were identified by the team developing the model, internal reviews, and the September 2017 review by the Level 3 PRA Technical Advisory Group.12F13 While further study of these topics were not completed as part of NRCs Level 1 IFPRA, the issues are documented here if future work on the topic is considered.

Each identified issue was assigned to the following categories for future consideration.

Potential Model Enhancement - The PRA could be enhanced with further analysis of the issue. However, the level of effort and resources required were not commensurate with improvement in study quality.

Consideration for Future Work - The issue would require more analysis and/or new method development. Further work in the area could represent an improvement to the current state of practice.

Candidate for Sensitivity Study - The issue could be adequately addressed by performing a sensitivity study on the baseline PRA model.

Out of Scope - An issue that may be related to the internal flooding analysis, but was considered out of scope for the current study.

Table C-1 Internal Flooding Topics for Future Work Topic Area Description Disposition Hydraulic analysis of postulated floods Documentation was not always available for the detailed hydraulic analysis of postulated floods including evaluation of flow rates, leakage through barriers and doors, effectiveness of drains, propagation pathways, and flood height with time. The PRA could be improved by a more thorough hydraulic evaluation, particularly for risk significant flood areas. For example, scenario 1-FLI-CB_A48_FP could benefit from additional evaluation of potential flood propagation from corridor A58 to room A48.

Potential Model Enhancement Flood impacts on essential switchgear rooms Given the importance of the essential switchgear rooms, additional evaluation of flood propagation that could impact essential switchgears for both safety-related trains may be warranted. If the assumptions and modeling approaches used in the hydraulic analyses were to be re-evaluated, then careful consideration should be given to any potential flood scenarios that could impact both essential switchgear rooms.

Potential Model Enhancement 13 The Level 3 PRA project Technical Advisory Group (TAG) consists of senior NRC technical staff in the area of PRA and in supporting technical areas (e.g., thermal hydraulics or seismic hazard), as well as one experienced PRA representative from the Electric Power Research Institute and one from Westinghouse. The TAG is tasked with providing insight, advice, and guidance to the Level 3 PRA project team on an ongoing basis, and reviewing all major project reports.

C-2 Table C-1 Internal Flooding Topics for Future Work Topic Area Description Disposition Floods impacting both Units In addressing the site level risk, additional consideration should be given to floods that could potentially impact both reactor units. The reference plant had very limited shared structures. One potential area that could be of concern was an area that includes the Unit 1 and Unit 2 control rooms. If a significant flood were to impact one control room, then the other control room would be impacted as well. While all flooding scenarios that could propagate to the control room were screened from further analysis, additional review and confirmation of the screening could be performed with consideration for impacts on both units.

Consideration for Future Work Large turbine building floods propagating to connected areas There were no direct connections from the turbine building to other buildings, such as the control building. So, there is limited potential for floods to propagate to other buildings. However, the modeled turbine building floods include very large capacity flood sources (e.g.,

circulating water), and these assume that all equipment on the lower level of the turbine building was failed due to the flood. Additional impacts outside the building could be considered, such as propagation to the transformer yard or switchyard.

Consideration for Future Work Steam line breaks The flooding analysis minimizes the contribution from steam line breaks. The internal events PRA does account for main steam (MS) and main feedwater (MFW) line breaks in the analysis. For the internal events analysis, the accident sequence modeling was focused on the plant response to the reactor transient, but does not account for possible local impacts on equipment near the break. It would be appropriate and consistent with EPRI flooding PRA guidance to consider multiple locations for MS/MFW breaks and incorporate the local impacts into the plant response model. This would be an improvement to the study. Another issue was that there were many steam lines identified as potential flooding sources, but they were not included in the estimation of flooding frequency. These were not necessarily the same lines that would be considered as high-energy line breaks in the internal events analysis. It was not until a detailed update of the flooding frequencies was performed that it was noticed that all steam lines were systematically ignored in the frequency estimation. These contributions to flooding frequency should be included.

Potential Model Enhancement Flooding impacts on turbine building non-safety batteries Insights from the internal events PRA identify the importance of non-safety related batteries located in the turbine building for restoring offsite power. None of the modeled turbine building floods included any impacts on these batteries. However, additional consideration should be given to the impacts of a large steam release in the turbine building (see description of Steam line breaks topic, above.) This could be a candidate for sensitivity study. It should be noted that the potential importance of these batteries depends on a consequential LOOP occurring. For a non-LOOP flood scenario, the loss of the batteries would have little impact on the accident response.

Candidate for Sensitivity Study Fire suppression system actuation The analysis does not address scenarios where a flood (a steam release) results in fire suppression system actuation in other parts of the plant. Water submergence and spray, other effects such as water/steam jet impingement, pipe whip, humidity, condensation and temperature were considered for equipment failure due to flood Potential Model Enhancement

C-3 Table C-1 Internal Flooding Topics for Future Work Topic Area Description Disposition events. However, this particular failure mode, where steam/humidity results in fire suppression actuation, was not considered in NRC's model development.

Flood impacts on SSCs The analysis assumes that flood waters reaching a zone will cause the loss of all equipment in that zone (regardless of flood height). Per operating experience, the number of flooding events failing large numbers of PRA-relevant components is much smaller than the number of flooding events. The assumption that flood water reaching a zone will cause loss of all equipment is potentially conservative and was identified as a modeling uncertainty in Table 4.5. Given the uncertainty in flood initiating event frequency, maximum flood height, susceptibility to other failure mechanisms (e.g., humidity), it was unclear if more optimistic assumptions would be appropriate. A more realistic modeling approach could be considered as a future enhancement.

Consideration for Future Work Impact of NSCW pipe failures As discussed in 3.2.4, for the most important zone (AB_C113), the postulated failure of NSCW piping would not result in an immediate plant trip, but such a trip was assumed. The scenario could lead to a subsequent plant trip if required action and associated completion time are not met under LCO conditions. Other options could be to model repair/recovery action to prevent plant shutdown, or to model the impact of a controlled plant shutdown to meet the requirements of the LCO. Both of these alternative approaches were considered beyond the state of practice. The assumption of a plant trip was acknowledged as being potentially conservative. Other modeling alternatives could be considered in the future.

Consideration for Future Work Statistical model for initiating event frequencies Several modeling choices were made in the approach to estimating flooding initiating event frequencies. The choice of prior distribution can have a significant impact on the estimates. This project used constrained non-informative prior (CNIP) gamma distributions with mean values reported by EPRI. For this study, it was desired to use a gamma distribution for two reasons: (1) consistency with the other initiating event frequency distributions in the study, and (2) the choice of a conjugate prior for Poisson distributed data makes it easier for performing the updates. The use of the CNIP was selected because it provides a straightforward way to translate the EPRI data to a gamma prior distribution. Also, using the CNIP does not overwhelm the plant-specific data, as some other Bayesian update approaches are prone to do. The CNIP has been noted to introduce increased variance in the estimates, which may be appropriate given the uncertainty in the frequency estimate process. The CNIP may not always be the best choice, but it is often used in frequency estimates. The choice of total system feet of piping and the arbitrary pipe size category definitions can have a large impact on frequency estimate uncertainty, too. Other modeling choices could have been made, and could be considered as a model enhancement. Uncertainty in the frequency estimates can also be addressed through sensitivity studies.

Potential Model Enhancement and Candidate for Sensitivity Study

C-4 Table C-1 Internal Flooding Topics for Future Work Topic Area Description Disposition Heavy load drops resulting in floods The analysis does not explicitly discuss the possibility of heavy load drop accidents (especially in the turbine building), as exemplified by the 2013 event at Arkansas Nuclear One and discussed in NRC Information Notice 2016-11. Although such accidents may be less important to a single-unit, at-power analysis, they appear to be worth investigation in the multi-source analysis. A full PRA evaluation of heavy load drops could be an improvement to the study, but was considered to be out of the scope of the internal flooding PRA.

Additional information would have to be gathered to assess the types of heavy load lifts, probability of drop, impacts on the plant, etc.

Out of scope Post-flood human failure events The internal flooding analysis identified post-flood human failure events (HFEs) that were unrelated to flood mitigation. These HFEs can be influenced by stress and other factors related to the flooding scenarios. A set of human error probability (HEP) multiplier values could be developed to scale HEPs for flood scenarios. The HEP multipliers were not implemented in the NRC IFPRA model due to insignificant contribution from the post-flood HFEs that would be affected. A potential model enhancement could be considered to include the HEP multipliers and quantify the impact on internal flooding CDF results.

Potential Model Enhancement Impact of conditional pipe failures in response to a random initiating event The probability of a pipe failure in response to an initiating event is expected to be lower than the other component failures (e.g., pumps, valves) that can impact mitigating system reliability. The flooding operating experience considered by Reference IF-9 supports that such pipe failures would be rare. However, there appears to be a lack of systematic evaluations of conditional pipe failure probabilities that could contribute to mitigating system failures in response to the event. The demand of a piping system in response to an initiating event can involve stresses (e.g., water hammer, rapid pressurization) that can increase the failure probability. These types of conditions are not well captured in the operating experience data because demands in response to an initiating event are rare. Under some conditions the conditional failure probabilities may not be insignificant. For example, a piping system that is susceptible to aging related degradation effects and then is stressed due to a system demand in response to an initiating event could have a significantly increased conditional failure probability, and there could be multiple pipe segments susceptible to failure. Additional study is needed to fully characterize the issues and determine types of conditional pipe failures that could have risk significant impacts.

Consideration for Future Work