ML13162A370

Applicant'S Environmental Report Operating License Renewal Stage, Byron Station, Units 1 and 2. Appendix F

ML13162A370
Person / Time
Site:	Byron
Issue date:	05/31/2013
From:	Exelon Generation Co
To:	Office of Nuclear Reactor Regulation
References
Download: ML13162A370 (314)

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Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Byron Station Environmental Report

This Page Intentionally Blank Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 TABLE OF CONTENTS Section Page F.1 METHODOLOGY ...........................................................................................................F-1 F.2 BYRON PRA MODEL ....................................................................................................F-3 F.2.1 PRA Model Changes Since the IPE/IPEEE ......................................................F-3 F.2.2 LEVEL 1 MODEL OVERVIEW ..........................................................................F-4 F.2.2.1 Contribution to CDF by Initiating Event ...........................................F-5 F.2.2.2 Top Ranking Accident Sequences ..................................................F-8 F.2.2.3 Risk Importance of Byron Systems .................................................F-8 F.2.2.4 Important Operator Actions .............................................................F-9 F.2.3 Level 2 Model Overview ....................................................................................F-9 F.2.3.1 level 1 to level 2 mapping ..............................................................F-10 F.2.3.2 Containment Event Tree Description ............................................F-12 F.2.3.3 Level 2 Release Category Definitions ...........................................F-20 F.2.3.4 Representative Sequences ...........................................................F-23 F.2.3.5 Source Term Results .....................................................................F-24 F.2.3.6 Level 2 Release Category Frequencies ........................................F-24 F.2.4 PRA Model Technical Adequacy for SAMA ....................................................F-24 F.3 LEVEL 3 RISK ANALYSIS ...........................................................................................F-32 F.3.1 Analysis ...........................................................................................................F-32 F.3.2 Population .......................................................................................................F-33 F.3.3 Economy .........................................................................................................F-33 F.3.4 Food and Agriculture .......................................................................................F-34 F.3.5 Nuclide Release ..............................................................................................F-34 F.3.6 Evacuation ......................................................................................................F-36 F.3.7 Meteorology ....................................................................................................F-37 F.3.8 MACCS2 Results ............................................................................................F-37 F.4 BASELINE RISK MONETIZATION ..............................................................................F-38 F.4.1 Off-Site Exposure Cost ...................................................................................F-38 F.4.2 Off-Site Economic Cost Risk ...........................................................................F-38 F.4.3 On-Site Exposure Cost Risk ...........................................................................F-39 F.4.4 On-Site Cleanup and Decontamination Cost ..................................................F-40 F.4.5 Replacement Power Cost ...............................................................................F-41 Byron and Braidwood Stations, Units 1 and 2 Page F-i License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.4.6 Maximum Averted Cost-Risk...........................................................................F-41 F.4.6.1 Internal Events Maximum Averted Cost-Risk ................................F-41 F.4.6.2 External Events Maximum Averted Cost-Risk ...............................F-42 F.4.6.3 Byron Maximum Averted Cost-Risk ..............................................F-44 F.5 PHASE 1 SAMA ANALYSIS ........................................................................................F-45 F.5.1 SAMA Identification .........................................................................................F-45 F.5.1.1 Level 1 Byron Importance List Review ..........................................F-46 F.5.1.2 Level 2 Byron Importance List Review ..........................................F-47 F.5.1.3 INDUSTRY SAMA REVIEW ..........................................................F-48 F.5.1.4 Byron IPE Plant Improvement Review ..........................................F-57 F.5.1.5 Byron IPEEE Plant Improvement Review .....................................F-58 F.5.1.6 External Events in the Byron SAMA Analysis ...............................F-58 F.5.2 Phase 1 Screening Process ............................................................................F-80 F.6 PHASE 2 SAMA ANALYSIS ........................................................................................F-82 F.6.1 SAMA 2: Replace the Positive Displacement Pump with a Self Cooled, Auto Start Pump ..............................................................................................F-83 F.6.2 SAMA 3: Auto Start of Standby SX Pump ......................................................F-86 F.6.3 SAMA 4: Install "No Leak" RCP Seals ............................................................F-88 F.6.4 SAMA 5: Modify the Startup Feedwater Pump to Start Using the AMSAC SG Low-Low-Low Level signal to Mitigate AFW Failure .................................F-90 F.6.5 SAMA 7: Establish Flow to the RH HX on RH Pump Start .............................F-92 F.6.6 SAMA 8: Install Kill Switches for the Fire Protection Pumps in the MCR........F-94 F.6.7 SAMA 9: Install Flow Restrictors in Fire Protection Pipes...............................F-96 F.6.8 SAMA 10: Alter Ductwork Between the Aux Bldg Sump Drain Room and the SX Pump Room ........................................................................................F-98 F.6.9 SAMA 11: Implement DMS ...........................................................................F-101 F.6.10 SAMA 13: Alternate AFW Cooling with Seal Protection................................F-104 F.6.11 SAMA 14 Automated RWST Makeup ...........................................................F-106 F.6.12 SAMA 15 Resolve Regulatory Issues and Complete Implementation of the Inter Unit AFW Cross-tie .........................................................................F-109 F.6.13 SAMA 16 Install High Flow Sensors On the Non-Essential Service Water System ..........................................................................................................F-111 F.6.14 SAMA 17 Use AMASC for Alternate LOW SG Level AFW Initiation .............F-113 F.6.15 SAMA 18 Automate Refill of the Diesel Driven AFW Pump Fuel Oil Day Tank ..............................................................................................................F-115 Byron and Braidwood Stations, Units 1 and 2 Page F-ii License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.6.16 SAMA 19 Replace MOVs in the RHR Discharge Line with Valves that Can Isolate an ISLOCA Event ......................................................................F-117 F.6.17 SAMA 21 Install an Emergency Isolation Valve in each of the RHR Suction Lines ................................................................................................F-119 F.6.18 SAMA 22 Install the Same High Flow Isolation Logic Used on Valve

_CC685 on Valve _CC9438 ..........................................................................F-121 F.6.19 SAMA 23 Install a Passive Hydrogen Ignition System ..................................F-123 F.6.20 SAMA 24 Provide a Reactor Vessel Exterior Cooling System ......................F-125 F.6.21 SAMA 25 Install a Filtered Containment Vent ...............................................F-127 F.6.22 SAMA 26 DMS Using a Dedicated Generator, Self Cooled Charging Pump, and a Portable AFW Pump ................................................................F-130 F.6.23 SAMA 27 Protect RH, SI, and CVCS Cubicle Cooling Fan Cables in Fire Zone 11.3-0 ...................................................................................................F-133 F.6.24 SAMA 28 Install Fire Barriers around MCC 134X .........................................F-133 F.6.25 SAMA 29 Automate Swap to Recirculation Mode .........................................F-134 F.6.26 SAMA 30 Protect AFW Cables in the Aux Building General Area, Elevation 383'................................................................................................F-136 F.6.27 SAMA 31 Unit 2 SAMA - Protect Cables for 2AF013A, B, and D in the Aux Building General Area, Elevation 426' ...................................................F-136 F.7 SENSITIVITY ANALYSIS ...........................................................................................F-138 F.7.1 Real Discount Rate .......................................................................................F-138 F.7.2 95th Percentile PRA Results .........................................................................F-139 F.7.2.1 Phase 1 Impact ...........................................................................F-141 F.7.2.2 Phase 2 Impact ...........................................................................F-144 F.7.2.3 95th Percentile Summary .............................................................F-144 F.7.3 MACCS2 Input Variations .............................................................................F-146 F.7.3.1 Meteorological Sensitivities .........................................................F-147 F.7.3.2 Evacuation Sensitivities ...............................................................F-147 F.7.3.3 Release Height & Heat Sensitivities ............................................F-148 F.7.3.4 Deposition Velocity ......................................................................F-149 F.7.3.5 Reactor Power .............................................................................F-149 F.7.3.6 Population Sensitivity ..................................................................F-149 F.7.3.7 Resettlement Planning Sensitivities ............................................F-150 F.7.3.8 Generic economic inputs sensitivity ............................................F-150 F.7.3.9 Rate of Return Sensitivities .........................................................F-151 F.7.3.10 Impact on SAMA Analysis ...........................................................F-151 Byron and Braidwood Stations, Units 1 and 2 Page F-iii License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.7.4 Inclusion of the AFW Cross-Tie in the Base Model.......................................F-152 F.8 CONCLUSIONS .........................................................................................................F-154 F.8.1 Optimal SAMA set .........................................................................................F-154 F.9 TABLES .....................................................................................................................F-158 F.10 FIGURES ...................................................................................................................F-293 F.11 REFERENCES ...........................................................................................................F-297 Byron and Braidwood Stations, Units 1 and 2 Page F-iv License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 LIST OF TABLES Table Page Table F.2-1 Byron/Braidwood PRA Model Update History ..................................................... F-158 Table F.2-2 Byron PRA Top Ranking Accident Sequences to CDF ....................................... F-165 Table F.2-3 Byron Important Operator Actions Based On CDF ............................................. F-167 Table F.2-4 Mapping of Level 1 Sequences to PDS .............................................................. F-168 Table F.2-5 Correlation of PDS to Sequences ....................................................................... F-170 Table F.2-6 Representative Sequences ................................................................................. F-172 Table F.2-7 Byron Source Term Summary............................................................................. F-176 Table F.2-8 Detailed Release Category Results .................................................................... F-185 Table F.3-1 County Growth Rates 2000 - 2030 ..................................................................... F-186 Table F.3-2 Estimated Population Distribution within a 10-Mile Radius of Byron, Year 2046 F-187 Table F.3-3 Estimated Population Distribution within a 50-Mile Radius of Byron, Year 2046 F-188 Table F.3-4 County Specific Land Use And Economic Parameters Inputs ............................ F-189 Table F.3-5 Byron MACCS2 Generic Economic Parameters ................................................. F-190 Table F.3-6 Byron MACCS2 End of Cycle Core Inventory ..................................................... F-191 Table F.3-7 MACCS2 Release Groups vs. Byron MAAP Release Groups ............................ F-192 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings ........ F-193 Table F.3-9 MACCS2 Base Case Mean Results Unit 1 ......................................................... F-203 Table F.5-1 Byron Level 1 IE Importance List Review ........................................................... F-204 Table F.5-2a Byron LERF FPIE Importance List Review ....................................................... F-242 Table F.5-2b Byron Late FPIE Importance List Review ......................................................... F-260 Table F.5-3 Byron Phase 1 SAMA List Summary .................................................................. F-270 Table F.6-1 Byron Phase 2 SAMA List Summary .................................................................. F-282 Table F.7-1 Generic Economic Sensitivity Case Values ........................................................ F-292 Byron and Braidwood Stations, Units 1 and 2 Page F-v License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 LIST OF FIGURES Figure Page Figure F.2-1 Byron Unit 1 Contribution to CDF by Initiating Event ....................................... F-293 Figure F.2-2 Byron Unit 2 Contribution to CDF by Initiating Event ....................................... F-294 Figure F.2-3 Unit 1 Fusell-Veselly by System based on CDF ............................................... F-295 Figure F.2-4 Containment Event Tree .................................................................................. F-296 Byron and Braidwood Stations, Units 1 and 2 Page F-vi License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Acronyms Used in Attachment F AF auxiliary feedwater AFW auxiliary feedwater AOT allowable outage time AMSAC anticipated transient without scram mitigating system actuation circuitry AP auxiliary power ASME American Society of Mechanical Engineers ATWS anticipated transient without scram CC component cooling water CCF common cause failure CCP centrifugal charging pump CCW component cooling water CDF core damage frequency CET containment event tree CF containment failure CHR containment heat removal CIS containment isolation system COP containment overpressurization CPI consumer price index CS containment spray CST condensate storage tank CV chemical and volume control system CVCS chemical and volume control system DCH direct containment heating DG diesel generator DMS diverse mitigation system DOE Department of Energy ECCS emergency core cooling system EDG emergency diesel generator EE external events EFPD effective full power days EPRI Electric Power Research Institute EPZ emergency planning zone ESF engineered safety features ESFAS engineered safety features actuation system Byron and Braidwood Stations, Units 1 and 2 Page F-vii License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Acronyms Used in Attachment F ETE evacuation time estimate F&O fact and observation FP fire protection FPIE full power internal events F-V Fussell-Vesely FW feedwater GE general emergency HCLPF high confidence of low probability of failure HEP human error probability HPI high pressure injection HRA human reliability analysis HVAC heating ventilation and air-conditioning HX heat exchanger IA instrument air IE initiating event IPE individual plant examination IPEEE individual plant examination - external events ISGTR induced steam generator tube rupture ISLOCA interfacing system LOCA JHEP joint human error probability LCO limiting conditions of operation LERF large early release frequency LMFW loss of main feedwater LOCA loss of coolant accident LOOP loss of off-site power MAAP modular accident analysis program MACCS2 MELCOR accident consequences code system, version 2 MACR maximum averted cost-risk MCC motor control center MCR main control room MDAFW motor-driven auxiliary feedwater MFW main feedwater MOV motor operated valve MSPI mitigating systems performance index Byron and Braidwood Stations, Units 1 and 2 Page F-viii License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Acronyms Used in Attachment F MUR measurement uncertainty recapture NEI Nuclear Energy Institute NRC U.S. Nuclear Regulatory Commission OECR off-site economic cost risk PDP positive displacement pump PDS plant damage state PGA peak ground acceleration PI-SGTR pressure induced steam generator tube rupture PMF probable maximum flooding PMP probable maximum precipitation PORV power operated relief valve PRA probabilistic risk analysis PSA probabilistic safety assessment PWR pressurized water reactor RAI request for additional information RCFC reactor containment fan coolers RCP reactor coolant pump RCS reactor coolant system RDR real discount rate RHR residual heat removal RLE review level earthquake RPS reactor protection system RPV reactor pressure vessel RRW risk reduction worth RWST refueling water storage tank SAMA severe accident mitigation alternative SAT system auxiliary transformer SBO station blackout SG steam generator SGTR steam generator tube rupture SI safety injection SLB steam line break SLOCA small loss of coolant accident SOARCA state of the art consequences analysis Byron and Braidwood Stations, Units 1 and 2 Page F-ix License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Acronyms Used in Attachment F SR supporting requirement SRP standard review plan SSPS solid state protection system SX essential service water TI-SGTR thermally induced steam generator tube rupture TS technical specification URE updating requirement evaluation VA auxiliary building HVAC VB vessel breach VCT volume control tank WS normal service water Byron and Braidwood Stations, Units 1 and 2 Page F-x License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 SEVERE ACCIDENT MITIGATION ALTERNATIVES The severe accident mitigation alternatives (SAMA) analysis discussed in Section 4.20 of the Environmental Report is presented below.

F.1 METHODOLOGY The methodology selected for this analysis is contained in NEI 05-01, Severe Accident Mitigation Alternatives (SAMA) Analysis Guidance Document (NEI 2005), which has been reviewed and endorsed by the U.S. Nuclear Regulator Commission (NRC). It involves identifying SAMA candidates that have potential for reducing plant risk and determining whether or not the implementation of those candidates is beneficial on a cost-risk reduction basis. The metrics chosen to represent plant risk include the core damage frequency (CDF), the dose-risk, and the offsite economic cost-risk. These values provide a measure of both the likelihood and consequences of a core damage event.

The SAMA process consists of the following steps:

• Byron Station (Byron) Probabilistic Risk Assessment (PRA) Model - Use the Byron Internal Events PRA model as the basis for the analysis (Section F.2). Incorporate External Events contributions as described in Section F.4.6.2.

• Level 3 PRA Analysis - Use the Byron Level 1 and 2 Internal Events PRA output and site-specific meteorology, demographic, land use, and emergency response data as input in performing a Level 3 PRA using the MELCOR Accident Consequences Code System Version 2 (MACCS2) (Section F.3). Incorporate External Events contributions as described in Section F.4.6.2.

• Baseline Risk Monetization - Use U.S. Nuclear Regulatory Commission (NRC) regulatory analysis techniques to calculate the monetary value of the unmitigated Byron severe accident risk. This becomes the maximum averted cost-risk that is possible (Section F.4).

• Phase 1 SAMA Analysis - Identify potential SAMA candidates based on the Byron Probabilistic Risk Assessment (PRA) (including the current fire model), Individual Plant Examination - External Events (IPEEE), and documentation from the industry and the NRC.

Screen out SAMA candidates that are not applicable to the Byron design or are of low benefit in pressurized (PWRs) such as Byron, candidates that have already been implemented at Byron or whose benefits have been achieved at Byron using other means, and candidates whose estimated cost exceeds the maximum possible averted cost-risk (Section F.5).

• Phase 2 SAMA Analysis - Calculate the risk reduction attributable to each of the remaining SAMA candidates and compare to the estimated cost of implementation to identify the net cost-benefit. PRA insights are also used to screen SAMA candidates in this phase (Section F.6).

• Sensitivity Analysis - Evaluate how changes in the SAMA analysis assumptions might affect the cost-benefit evaluation (Section F.7).

• Conclusions - Summarize results and identify conclusions (Section F.8).

Byron and Braidwood Stations, Units 1 and 2 Page F-1 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 The steps outlined above are described in more detail in the subsections of this appendix. The graphic below summarizes the high level steps of the SAMA process.

Is Does the Implementation Yes Implementation No Yes No Retain for Applicable to SAMA affect a cost greater Initial SAMA List cost greater potential Plant? risk significant than cost-risk than screening implementation system? reduction?

cost?

No Yes No Yes Phase I Screened Screened Screened Screened Phase II Analysis Analysis SAMA SCREENING PROCESS Byron and Braidwood Stations, Units 1 and 2 Page F-2 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.2 BYRON PRA MODEL The SAMA analysis is based upon Byron PRA model BB011b1, which includes an integrated internal flooding analysis, but not internal fires, seismic events, or other external events. The original Byron PRA was submitted to the NRC to satisfy the requirements of NRC Generic Letter 88-20 (NRC 1989). Since the original Individual Plant Examination (IPE) submittal to the NRC in April 1994 (ComEd 1994), a Modified IPE was submitted in March 1997 (ComEd 1997). The Modified IPE answered requests for additional information (RAI) from the NRC relative to the original IPE and incorporated plant procedure changes and modifications. The PRA was developed from the Modified IPE and since that time, it has been updated on numerous occasions to maintain consistency with the operating plant and to reflect the latest PRA technology.

The following subsections provide more detailed information related to the evolution of the Byron Internal Events PRA model and the current results. These topics include:

• PRA changes since the IPE / IPEEE

• Level 1 model overview

• Level 2 model overview

• PRA model review summary Sections F.4.6.2 and F.5.1.6 provide a description of the process used to integrate external events contributions into the Byron SAMA process.

F.2.1 PRA MODEL CHANGES SINCE THE IPE/IPEEE Compared with the IPE, the current PRA includes more current equipment availability and reliability data as well as any subsequent plant configuration changes that have had an impact on the risk profile. In addition to updating the data and plant and procedure changes, the model was converted from a support state model to a single top fault tree model. Over the course of multiple updates, there were many changes to PRA models and databases in each element of the PRA. These changes included:

• Revision of the definition of core damage and the success criteria

• Changes in the selection of initiating events and revision of initiating event frequencies

• Complete revisions to event tree analysis

• Enhancements and additions of system fault trees

• Enhanced treatment of offsite power recovery

• Upgraded PRA reliability database with plant-specific information

• Revision to common cause failures (CCFs) and the CCF data Byron and Braidwood Stations, Units 1 and 2 Page F-3 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2

• Revision to treatment of human actions

• Revised internal flooding analyses Table F.2-1 provides a summary of the model revision history, including a description of the major update issues for each revision.

F.2.2 LEVEL 1 MODEL OVERVIEW The Byron Level 1 PRA model includes a comprehensive treatment of accident sequences producing core damage from internal events at full power, including internal flooding. The frequency of all sequences for which reactor core cooling performance degrades beyond this point is defined as the Core Damage Frequency (CDF). The annual average CDF for each of the Byron units from the current analysis is shown in the following table.

CDF RESULTS FOR BYRON UNITS 1 AND 2 (BB011b1)

Unit CDF Truncation Limit Byron Unit 1 3.97E-5 1.0E-10 Byron Unit 2 3.82E-5 1.0E-10 The BB011b1 model, which was used to support the SAMA evaluation, was released to document the replacement of the LERF only model in the BB011b PRA with the WCAP-16341-P Level 2 model. The Level 1 portions of the BB011b and BB011b1 models are the same. The discussion in F.2.2 describes the Level 1 model that is common to both the BB011b and BB011b1 models.

The leading causes of core damage are described in the following sections.

The freeze date for the inclusion of plant specific date for the model was December 2010. A specific freeze date for physical changes is more difficult to establish given that issues are tracked in a database and addressed based on the priority of the change and the resources available. It is possible that recent risk significant changes have been incorporated in the BB011b/BB011b1 model while the incorporation of older, non-risk significant changes has been deferred until a later model update.

For internal events contributors, the differences between the units are minor and are documented in the PRA system notebook. For the purposes of the SAMA analysis, the Unit 1 model is used as the quantification basis and considered to be representative of both units. For the fire contributors, there are differences in the units which translate to measurable differences Byron and Braidwood Stations, Units 1 and 2 Page F-4 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 in plant risk. For the SAMA analysis, the SAMA identification process was performed separately for each unit (refer to section F.5.1.6.1) to account for the differences. For SAMA quantification, the external events multiplier was based on the larger of the two units CDF values (section F.4.6.2) and for quantification of fire specific SAMAs, the contributions from the unit specific fire zones were used (section F.6).

F.2.2.1 CONTRIBUTION TO CDF BY INITIATING EVENT Initiating event contributions to the CDF profile are shown in figures F.2-1 and F.2-2. Details of the highest ranking initiating event contributions are briefly described below. The equipment failures or failures of operator actions which would produce core damage are highlighted.

Loss of Essential Service Water: Loss of Essential Service Water (SX) contributes between 45% and 46% to the CDF.

One set of important cutsets includes a loss of SX (e.g., due to common cause failure of all SX pumps) with failure of the operators to execute main feedwater restoration. Previously, such events were addressed by use of the diesel-driven auxiliary feedwater (AFW) pump, but new restrictions that require a running SX pump to prevent unintended recirculation and overheating of the diesel AFW pump now fail the diesel AFW pump on loss of all SX pumps.

Another important set of cutsets also applies to loss of SX scenarios, but includes operator action dependencies. Loss of SX initiated by loss of a running pump requires operator actions to restore SX by starting the opposite SX pump, cross-tying to the opposite unit, or providing an alternate cooling and suction source to the chemical and volume control (CV) pumps in order to maintain reactor coolant pump (RCP) seal cooling. If the RCP seal loss of coolant accident (LOCA) occurs, the loss of SX also inhibits the ability to remove decay heat during eventual recirculation operations, leading to core damage. Modeling of these sequences includes dependencies among these operator actions and credit for delayed recovery of SX and/or seal cooling.

The contribution of Loss of SX events remains high due to the high probability of an RCP Seal LOCA following a loss of SX. Loss of SX remains a challenging event even if there is not an RCP Seal LOCA as it is vital support to numerous systems (e.g., AF and room cooling for CV, residual heat removal (RH), and the EDGs).

Loss of SX leads to a loss of both sources of RCP seal cooling. The RCP thermal barriers are cooled by the Component Cooling Water (CC) System, and RCP seal injection is provided by the CV pumps. SX serves as the ultimate heat sink for CC as well as providing oil and room Byron and Braidwood Stations, Units 1 and 2 Page F-5 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 cooling for the CV pumps. Without cooling, temperature-induced degradation of the RCP seals may lead to a Seal LOCA event (1 in 5 probability), which is then modeled as a Small LOCA.

Loss of SX also fails or degrades much of the key safety equipment needed to maintain primary inventory control. With CV and safety injection (SI) pumps failed due to cooling dependencies on SX, high-pressure primary makeup is unavailable. Continuing primary leakage leads to eventual core damage. The alternate means of cooling the CV pump lube oil coolers from the fire protection (FP) system and the switching of the CV pump intake to the cooler refueling water storage tank (RWST) are important actions in reducing the importance of loss of SX events.

Loss of Component Cooling Water: Loss of Component Cooling Water (CCW) contributes about 21% of CDF with this revision. Several of the minor model changes reduced the contribution of Loss of CCW events, including the modeling of recovery action to align and start the 0CC pump, removal of extraneous common cause failure terms, addition of Loss of CCW initiating events as exclusions to split CC train operation, and correction of some dependent human failure probabilities.

Internal Flooding: Internal Flooding sequences contribute 14-15% to CDF. Overall, the dominant internal flood scenario for CDF involves a rupture of the Fire Protection system within the common areas of the radiological controlled area of the Auxiliary Building. These particular flood scenarios account for about two-thirds of the total internal flood contribution to CDF.

Small LOCA: Small LOCA contributes about 4% to the CDF. Small LOCAs are leaks in the reactor coolant system pressure boundary into the containment with nominal leak rates that are equivalent to those which would be produced by ideal break sizes from about 1/2 inch to 2 inches in diameter. These include small pipe failures, failures in other pressure boundary components such as RCP seals, and leaks from the pressurizer relief, head vent, and pressurizer safety valves. These leak sources are generally separated into isolable and non-isolable sources.

Note that this section discusses the importance of LOCAs from an initiating event perspective.

Consequential RCP Seal LOCAs (i.e., failures due to a result of loss of seal injection and cooling) are not discussed in this category, since they are not Small LOCA initiating events, but are modeled as consequential Small LOCAs.

Small LOCAs, which are typically major contributors to PWR PRA results, have a high contribution to CDF due to the multiple mitigation systems required to function to prevent core damage. Since the leak size is not large enough to remove decay heat from the core, decay heat must be removed through the Steam Generators using the Auxiliary Feedwater Pumps, the Byron and Braidwood Stations, Units 1 and 2 Page F-6 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Startup Feedwater Pump, or Motor Driven Feedwater Pump. Reactor coolant system (RCS) inventory must also be maintained using emergency core cooling system (ECCS) Injection. Use of the Motor Driven and Startup Feedwater Pumps as a backup to the AF Pumps is hindered since the Safety Injection Signal isolates the Main Feedwater System. Small LOCAs are significantly more likely to occur than larger LOCAs.

The majority of the risk due to accident sequences initiated by small LOCAs is failure of the operator to secure the RH pumps in the mini-flow mode (to prevent their failure).

In Revision 6F, new cutsets included a LOCA with failure of the RH pumps and/or heat exchangers due to their dependence on CC. Small LOCAs are the most likely, so appear with the greatest frequency, but other LOCAs (including consequential LOCAs) also appear in the results.

Loss of Auxiliary Electric Power (AP): This initiating event category contributes approximately 5-6% of the total CDF. These initiating events represent failures of an AP power source to a running component, which then leads to a plant transient. The most important AP failures as initiating events lead to a Loss of SX or Loss of CCW, which are discussed above.

Steam Generator Tube Rupture: This initiating event category represents 3-4% of CDF. As with Small LOCAs, Steam Generator Tube Ruptures (SGTRs) require both Auxiliary Feedwater for Decay Heat Removal and ECCS Injection for RCS Inventory Control. Mitigation of this event is further complicated by the need to identify and isolate the ruptured Steam Generator. In the highest-ranking SGTR sequences, the operators fail to identify and isolate the ruptured steam generator and/or fail to depressurize and cooldown the RCS. If both actions fail, then core damage occurs due to the loss of RCS inventory from the affected steam generator (SG). If the ruptured SG is not isolated or the RCS depressurization / cooldown occurs late in the scenario, the steam generator is overfilled, the power operated relief valves (PORVs) are challenged, and pass liquid. The PORVs are then assumed to fail to fully close. In these scenarios, residual heat removal (RHR) is required for long term cooling, and its failure leads to core damage.

General Transients & LMFW: This initiating event category, which includes general reactor trips and losses of main feedwater (LMFW), accounts for approximately 2% of the total CDF.

The General Transient scenarios involve a failure of steam generator heat removal via auxiliary feedwater (AF system failures), followed by the operator failing to re-establish main feedwater using the startup or motor-driven feedwater pumps, followed by failure of bleed and feed Byron and Braidwood Stations, Units 1 and 2 Page F-7 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 cooling. The relatively high frequency of general transient initiating events (as compared to other initiating events) is the primary cause for the importance of this initiator.

Other Transients: This group of events contributes less than 5% of the CDF. The most significant events are Loss of Offsite Power, Loss of a 125V DC Bus, and interfacing system loss of coolant accident (ISLOCA). Each of the contributing events in this group comprises less than 2% of CDF.

RCP Seal LOCA: Also shown in Figure F.2-1 is the contribution of RCP Seal LOCA to the CDF results for Byron; RCP Seal LOCAs account for approximately two-thirds of the total CDF. A majority of the RCP Seal LOCA CDF originates from Loss of SX or Internal Flood initiating events. These initiators are described previously. Loss of Offsite Power and Loss of Component Cooling Water initiators also contribute to the importance of the RCP seals.

F.2.2.2 TOP RANKING ACCIDENT SEQUENCES The top ranked accident sequences are discussed in Table F.2-2. Examining the top accident sequences provides another perspective on the contributors to CDF. The Byron PRA consists of ten (10) event trees, which contain more than 100 accident sequences. About 10 sequences contribute to 99% of the total CDF. Table F.2-2 presents the significant accident sequences according the definition used in the American Society of Mechanical Engineers (ASME) PRA Standard, which includes all sequences in the top 95% of CDF and any individual sequences contributing more than 1%. The top 8 accident sequences comprise about 95% of the total CDF.

F.2.2.3 RISK IMPORTANCE OF BYRON SYSTEMS The Fussell-Vesely (F-V) importance measures evaluated from the Byron Unit 1 CDF model are used to evaluate one aspect of risk importance. F-V has been chosen to represent risk importance because it includes consideration of the impact of both initiating events and mitigation capability. Since failure or unavailability of a system may play a role in causing an initiating event or mitigating its consequences, the evaluation of system importance using F-V importance measures includes both aspects contributing to the risk of an accident. Figure F.2-3 shows the relative risk importance of systems at Byron Unit 1 from both initiating event causes and mitigation aspects, based on CDF. The Unit 2 results are very similar; the differences between the units have minor impacts on CDF. Note that basic events representing initiating event pipe rupture (LOCAs and internal floods) and operator actions are not included on the system importance figure since they do not directly relate to system component performance.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 As seen in Figure F.2-3, the Essential Service Water (SX) system is the most important system with about 50% contribution. Much of the SX system importance is due to its role as an initiator.

Very few options are available to prevent core damage after a total loss of SX.

The Component Cooling Water (CC) system is next most important at 21%. It also gets much of its importance due to its role as an initiating event.

The Auxiliary Electric Power (AP) system shows 16% contribution, a slight increase from the previous model. This contribution reflects both initiating events that can lead to Loss of SX or Loss of CC as well as AP component failures.

The Auxiliary Building Ventilation (VA) system, at 14%, reflects the need for room cooling for several key pumps, most notably the RH pumps. This shows more importance at Byron due to high VA plenum unavailability factors.

The Auxiliary Feedwater (AF) system is the next most important system at Byron from a CDF perspective (~3%). The contribution from AF reflects loss of the manual crosstie capability that was installed to allow the motor driven AF pumps to be used for either unit. This effectively decreased the available AF pumps per unit from 3 pumps to 2 pumps.

A similar effect results in normal Feedwater (FW) showing as next most important at 3%. This contribution includes both loss of feedwater as the initiating transient and loss of the pumps as a potential source of feedwater to the steam generators.

F.2.2.4 IMPORTANT OPERATOR ACTIONS During the course of an accident, significant benefit is gained from the correct performance of the operator crew in implementing the appropriate Emergency Operator Procedures as well as performing other actions to place the plant in a safe stable condition. Table F.2-3 lists actions that are significant contributors to CDF.

F.2.3 LEVEL 2 MODEL OVERVIEW The Byron Level 2 model is a state-of-the-art Level 2 analysis structure designed to address the Category II requirements of Regulatory Guide 1.200 and the ASME PRA Standard. The Level 2 analysis uses available technical work from the Byron Level 1 PRA and the Modular Accident Analysis Program (MAAP) results where appropriate, but applies the most recent accident progression research, current industry practices, and realistic plant-specific analyses. The Level 2 model is implemented in the CAFTA software package, which is consistent with the Level 1 PRA.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 The Level 2 model is generally consistent with the Simplified Level 2 Modeling Guidelines, WCAP-16341-P (WEST 2005), which many plants are currently using as a basis for updated Level 2 analyses. This WCAP provides a common, standardized method for PWRs with large dry containments to produce an analysis that generally meets capability category II of the ASME PRA standard. The guidance particularly addresses the latest understanding for induced steam generator tube ruptures, direct containment heating, and other important Level 2 phenomena.

While the WCAP is focused on modeling the large early release frequency (LERF) for the ASME standard, it includes guidance for including intact, small, and late releases to provide a more complete, though still standardized, Level 2 analysis. In addition to providing results at this level of detail, the Byron Level 2 model is structured to quantify contributions on a detailed release category level, which allows the assignment of source terms that are more representative of the sequences to which they are applied.

F.2.3.1 LEVEL 1 TO LEVEL 2 MAPPING Plant damage states (PDS) and their representative Level 1 accident scenarios provide an interface between the Level 1 and Level 2 analyses. Each Level 1 accident sequence that leads to core damage consists of a unique combination of an initiating event followed by the success or failure of various plant systems (including operator actions). Due to the large number of accident sequences created by the Level 1 PRA, the Level 1 sequences that result in core damage can be grouped into plant damage state bins. Each bin collects all of those sequences for which the progression of core damage, the release of fission products from the fuel, the status of the containment and its safeguards systems, and the potential for mitigating the potential radiological source terms are similar. The detailed containment event tree (CET) then analyzes each plant damage state bin as a group.

Plant damage state bins can be used as the entry states to the containment event tree quantification (similar to initiating events for the Level 1 PRA), or can be used to direct sequences onto specific containment event tree branches. The PDS bins for Byron are characterized by the status of containment bypass due to SGTR or ISLOCA, reactor coolant system pressure, and the availability of FW/AFW. A sequence by sequence classification was performed and documented as part of the Level 2 analysis.

F.2.3.1.1 Selection of Plant Damage State Parameters The definition of plant damage states incorporates information from the outcome of the Level 1 analysis that is important to the determination of containment response and the release of radioactive materials into the environment.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 The modeling approach for the current revision of the Level 2 PRA uses the CAFTA software package, which analyzes the Level 1 and Level 2 logic together in a single large fault tree.

Active systems such as containment coolers and containment spray are modeled in the Level 2 analysis alongside the Level 2 phenomenological events in order to accurately account for system dependencies with Level 1 systems, such as actuation signals, electrical power, and cooling water.

Along with containment systems performance, the CETs consider the influence that physical and chemical processes have on the integrity of the containment and on the release of fission products once core damage has occurred. The important physical conditions in the RCS and the containment include the pressure inside the reactor vessel at the onset of core damage, whether the reactor cavity is flooded, and the availability of cooling on the secondary side of the steam generators.

In the Level 2 analysis, the RCS pressure identified in the definition of PDSs is that which occurs at the onset of core damage. Events that could influence the change in pressure after the onset of core damage but prior to vessel breach are addressed in the CET. The two most important effects of high pressure for a Level 2 PRA are challenges to the steam generator tubes and direct containment heating. Because of this, two RCS pressure level categories are considered in the PRA: high and low. Pressure level assignment was based on the accident initiators (e.g., medium and large LOCAs result in low pressure) and the availability of feedwater (which results in pressure low enough to alleviate steam generator tube challenges). In general, either a medium/large LOCA, depressurization through the PORVs, or makeup to the steam generators is required to reach low pressure. Without secondary side cooling, smaller LOCAs (including seal LOCAs) and transients are modeled as high pressure scenarios.

AFW/FW availability is tracked separately from RCS pressure in the plant damage states because it is used in the scrubbing assessment for SGTR scenarios and because it impacts the timing of low pressure core damage scenarios.

Initiating events that bypass containment are treated separately in the Level 2 CET. As mentioned in the discussion of top events, containment bypass is identified by ISLOCA and SGTR events.

F.2.3.1.2 Plant Damage State Classifications The plant damage state, therefore, is a three character code that defines the important sequence characteristics for the Level 2 analysis (containment status, RCS pressure, AFW Byron and Braidwood Stations, Units 1 and 2 Page F-11 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Availability). The assignment of each individual Level 1 sequence is based on the following scheme:

• Containment Bypassed (by initiator, not containment isolation failure)

B: Bypass (ISLOCA or SGTR)

N: Not bypassed (all other events)

• RCS Pressure H: High Pressure (sequences without significant RCS leakage, anticipated transient without scram (ATWS) sequences)

L: Low Pressure (sequences that depressurize due to significant RCS leakage, such as large LOCA or medium LOCA).

-: Not Used (e.g., for containment bypass scenarios, RCS pressure is not asked)

• AFW/FW Available A: AFW or FW is available to provide makeup to the SGs (AFW is assumed to be available for pass through nodes. The exception is for secondary line break cases where AFW operability may be compromised).

N: AFW/FW is not available to provide makeup to the SGs.

-: Not Used (e.g., for containment isolation failure scenarios, AFW/FW availability is not asked)

Table F.2-4 provides the mapping of the Level 1 sequences to the Byron plant damage states.

Table F.2-5 documents the correlation between the Plant Damage States and the Level 2 sequences (i.e., defines which PDSs are used as initiators for the Level 2 sequence).

F.2.3.2 CONTAINMENT EVENT TREE DESCRIPTION To assess the accident progression following a core damage event, this Level 2 analysis uses the containment event tree shown in Figure F.2-4 based on the containment event trees (CETs) provided in WCAP-16341-P. While the function of the CET is essentially the same as the WCAP CETs, some changes were made to accommodate the capabilities and features of Byron PRA model. The event tree begins with one or more core damage sequences, and then asks a number of questions to determine the type of release, if any, that occurs. Each question is modeled as a top event in the event tree and the outcome is based on previous work for Byron (including logic taken from the existing model), recent accident progression research, and the guidance provided in the WCAP. Each top event in the event tree is discussed below.

Plant Damage States This first node of the containment event tree represents the collection of all core damage sequences from the Level 1 PRA into plant damage states. The assignment of core damage sequences to plant damage states provided in Table F.2-4.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Containment Bypass Level 1 PRA sequences with an initiating steam generator tube rupture or an un-isolated interfacing systems LOCA (ISLOCA) will bypass containment and are addressed by this node.

In the CET, the down branch on this node represents the bypassed condition while the up branch is used for non-bypassed scenarios.

The Byron-specific ISLOCA analysis does not explicitly show that the likely release paths from ISLOCAs would be submerged and no credit is taken for scrubbing by any potentially overlying pool of water. In addition, no credit is assumed to be available for scrubbing by the auxiliary building.

For SGTR core damage scenarios, the analysis assumes that the steam generator PORV will stick open once it passes water, providing a direct path to the atmosphere. While slightly conservative, this assumption is made because the SG PORVs are not designed to pass high pressure water and assuming the PORV sticks open simplifies the analysis. For steam generator tube rupture cases with AFW available, the Scrub node accounts for the potential of the operators to maintain water over the tubes to provide release scrubbing.

Containment Isolation For non-bypass scenarios, the possibility of containment isolation failure exists to provide a fission product release path through containment. The existing Byron PRA provides the associated containment isolation system (CIS) fault trees. The Level 2 model directly incorporates the CIS fault tree model into this top event. The containment isolation system includes all potential penetration locations with pipe sizes greater than 2 inches. Further details of the containment isolation system analysis are located in the Containment Isolation System Notebook.

Reactor Coolant System Pressure The next two top events are both used to characterize whether RCS pressure has been reduced enough to preclude induced SGTR events, but this node also considers if the degree of depressurization is large enough to preclude high pressure melt ejection events related to early containment failure (below about 200 psig based on WCAP 16341-P). A success (up path) on the RCS Pressure node represents core damage scenarios where the reactor coolant system is at low pressure due to a medium or large loss of coolant accident (identified by the plant damage state). Low pressure means that pressure is insufficient to challenge the steam Byron and Braidwood Stations, Units 1 and 2 Page F-13 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 generator tubes or result in direct containment heating later in the accident progression. The branch is determined by the initiating event from the Level 1 PRA.

AFW or FW Available Another method for reducing reactor pressure is through use of the steam generators. If steam generator makeup is available to the SGs as dictated by the Level 1 model logic, a decay heat removal path is available and the reactor can be reduced in pressure (to around 1000 psi). This pressure reduction will eliminate the challenge to the steam generator tubes, but it is not assumed to preclude the potential for direct containment heating (which is negligible for Byron).

In general, AFW/FW is considered available for heat removal if flow is available to 3 of 4 SGs or to 2 of 4 SGs in conjunction with operator action to manage the cooldown process. The Level 1 PRA is used to identify the availability of Feedwater and AFW, which is traced in the Level 2 PRA through the assignment of plant damage states.

Water Over SG Tubes For SGTR events, the magnitude of the release would be reduced if the radionuclides have to travel through a pool of water. This node is used for SGTR scenarios with AFW available and represents the probability that the operators will maintain about 10 feet (or more) of water over the top of the SG tubes (release scrubbing). Based on the guidance in WCAP-16341-P, the magnitude of the release can be reduced from Large to Small if the SG water level is maintained at least 10 feet above the top of the SG tubes. For Byron, a plant specific human reliability analysis (HRA) was performed to develop a probability of failing to perform this control task. The plant procedures instruct the operators to control level between 40% and 50% narrow range, which corresponds to between 7 and 8.8 feet above the top of the SG tubes. The procedure bases indicate this action is directed for the purpose of providing a scrubbing mechanism for any releases through the tubes and while the depth of water is less than the 10 feet described in the WCAP, it is considered to be adequate. The plant specific MAAP results demonstrate the large reduction in the source term resulting from a water depth of about 7 feet.

The up path in the CET represents the condition in which water level is successfully maintained above the SG tubes.

No Pressure-Induced Steam Generator Tube Rupture Core damage sequences that continue on the high pressure branch are assumed to be at or near the primary PORV/safety relief valve setpoint. Without water in the steam generators, there is a possibility of pressure-induced steam generator tube rupture early in the scenario.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Because the pressure is high from the beginning of the scenario, this question is asked prior to any operator actions or other reactor coolant system failures that could depressurize the RCS.

Details of this evaluation are based on WCAP-16341-P and are documented in the Byron Level 2 document. This event is modeled via basic event 1L2-SGT-VF-PISGR. The up path in the CET represents the condition in which no pressure induced steam generator tube rupture (PI-SGTR) occurs.

RCS Depressurization If the steam generator tubes survive the initial pressure differential, the operators could take action to depressurize the reactor coolant system in order to reduce the likelihood of tube rupture or direct containment heating. To do so, the operators would open a primary system PORV. If successful, the scenario transfers to a low-pressure accident progression. If the RCS is not depressurized, either due to human inaction or equipment failure, additional high-pressure failures are considered. This action appears in the plant Severe Accident Control Room Guideline Initial Response (SACRG-1) as well as in the emergency operating procedures (1BWFR-C.1, response to inadequate core cooling). This top event is modeled by gate 1HIGH-P and the HRA for the action is documented in the Byron Level 2 document, which includes consideration of human dependence factors. The gate couples the existing system fault tree with an operator action 1RY-DEPL2--HPVOA, OPS FAIL TO DEP RCS AFTER CD TO PREVENT INDUCED TUBE RUPTURE. The human error probability for this operator action is set to 2.5E-02 based on the HRA performed to support the Byron Level 2 analysis.

The up path in the CET represents the condition in which depressurization is successful.

No Thermally-Induced Steam Generator Tube Rupture With the reactor coolant system remaining at high pressure and without feedwater to enough steam generators to depressurize the reactor, the likelihood of thermally-induced creep rupture of steam generator tubes is addressed. As with pressure-induced tube rupture, the age and condition of the steam generator tubes must be considered. Failure probabilities for moderately-damaged tubes are used to account for plant aging during the license renewal term.

Details of this evaluation are in the Byron Level 2 document. Basic event 1L2-SGT-VF-TISGR represents the probability in the model. The up path in the CET represents the condition in which no thermally induced steam generator tube rupture (TI-SGTR) occurs.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Hot Leg Rupture During high-pressure core damage scenarios, a "race" occurs to determine where the RCS will first fail. While the reactor vessel will eventually fail as the molten core degrades the lower vessel head, failures may also occur in the steam generator tubes (discussed above) or in the hot leg or surge line of the reactor coolant system. For high-pressure, station-blackout-like scenarios which tend to occur on this branch, the likelihood of hot leg failure is very high. Based on the WCAP, this analysis uses a likelihood of 98% for hot leg failure (basic event 1L2-RCS-VF-DEP2 is used to represent the probability of vessel failure (0.02)). When hot leg failure occurs prior to vessel breach, the reactor coolant system depressurizes prior to failing the lower vessel head, thus eliminating the possibility of high-pressure core melt events leading to direct containment heating. This is generally a beneficial failure since it prevents direct containment heating. The up path in the CET represents the condition in which hot leg failure occurs before vessel breach.

For scenarios in which Hot Leg Rupture is asked after a thermally induced tube rupture, recent State of the Art Consequence Analysis (SOARCA) insights indicate that it is likely that the hot leg will fail at about the same time as the TI-SGTR event. If the hot leg fails shortly after the TI-SGTR, then the release pathway is essentially terminated. The radionuclides from the core are transferred into containment rather than to the secondary side through the broken SG tubes.

Event 1L2-NO-HLF-TISGTR (0.1) represents the probability that a hot leg failure does not occur at or shortly after the TI-SGTR such that the release continues through the broken SG tubes.

The event probability is based on NUREG/CR-7110 (NRC 2012) in which multiple sensitivity analyses indicate that the hot leg would fail within 10 minutes after TI-SGTR and that only 0.6%

of the iodine inventory would be released by the time of the hot leg failure. Based on the rapid increase in the creep rupture damage index at the time of TI-SGTR, it would be unlikely that the hot leg would remain intact for a period long enough for the release to transition to a point where it may be considered large (potentially 10% of the Iodine/Cesium based on WCAP-16341-P).

In this case, the 0.1 probability of the hot leg remaining intact was assigned based on judgment to enumerate an unlikely event (down branch in the CET). The up path in the CET represents the condition in which hot leg failure occurs at about the time of TI-SGTR to terminate the release through the tubes.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Containment Failure at Vessel Breach Three primary causes for containment failure at the time of reactor vessel breach apply to Byron

- steam explosion, hydrogen burn, and direct containment heating. The analysis of these containment challenges follows the guidance in WCAP-16341-P. Low pressure sequences (such as due to a LOCA) reduce reactor coolant system pressure to the point where containment is only subject to steam explosion and hydrogen burn challenges. Low pressure sequences due to steam generator cooling do not depressurize as far, and therefore consider steam explosion, hydrogen burn, and direct containment heating. High pressure sequences with depressurization after core damage due to operator action or hotleg failure are primarily subject to hydrogen burn challenges. High pressure scenarios at the time of vessel breach are primarily subject to direct containment heating challenges. Therefore, different branches through the event tree require different early containment failure probabilities. This model assigns probability CFE1 to the combination of steam explosion and hydrogen burn, CFE2 to hydrogen burn by itself, CFE3 to direct containment heating, CFE4 to the combination of all three effects. Recent research has provided an improved understanding of these phenomena and each is discussed below.

Ex-vessel steam explosions due to the pouring of the molten core into a pool of water can challenge the integrity of the containment via damage to the reactor cavity. Based on WCAP-16341-P, this is a greater issue for free-standing reactor cavities (as opposed to excavated cavities). Because Byron is an excavated cavity, steam explosions do not pose a failure mechanism for early containment failure.

Hydrogen burns can challenge the integrity of the containment by creating high pressure excursions. The amount of hydrogen released into containment depends upon the amount of core damage at the time of vessel failure. Scenarios that lead to hydrogen burns at plants like Byron are limited to about 50% zirconium oxidation (excluding in-vessel recovery cases).

Based on WCAP-16341-P, the plant-specific probability of early containment failure at Byron due to hydrogen burn is less than 0.001 at 40% oxidation and at 50% oxidation. To capture the possibility of containment failure due to hydrogen burn and/or steam explosion and maintain flexibility in the model, a probability of 0.001 will be used for both CFE1 and CFE2 in the model.

Direct containment heating (DCH) is also addressed by WCAP-16341-P. The WCAP reports plant-specific conditional containment failure probabilities due to direct containment heating for several plants, including Byron. The suggested probability is reported as 0.000 to cover all Byron and Braidwood Stations, Units 1 and 2 Page F-17 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 scenarios, and includes the effects of blowdown of the RCS, debris-to-gas heat transfer, exothermic metal/steam & metal/oxygen reactions, and hydrogen combustion that occur during a high-pressure melt ejection. To capture the possibility of DCH and maintain flexibility in the model, a CFE3 probability of 0.001 will be used in the model.

Note that previous Byron containment analyses have identified that the Unit 2 containment failure probabilities are slightly higher than the Unit 1 containment failure probabilities due to the existence of Bunker Ramo electrical penetrations in each Unit 2 containment. The containment failure probabilities due to DCH reported in the WCAP are copied from NUREG/CR-6338 (NRC 1996), which recognizes this difference between the Byron units (See Table 6.1 and Appendix D of NUREG/CR-6338). However, the strength of the unit 2 containments is sufficient to produce the same 0.000 failure probability for DCH, thereby removing the Unit 1/Unit 2 difference from the new Byron Level 2 model.

Based on the above assessments, the probability of early containment failure at Byron is negligible for any sequence. However, in order to maintain flexibility in the model for sensitivity analyses, all four early containment failure probabilities (CFE1, CFE2, CFE3, & CFE4) are maintained in the model and assigned a probability of 0.001.

Reactor Containment Fan Coolers Containment Heat Removal in the Byron Level 2 model can be accomplished only through the Reactor Containment Fan Coolers. The Containment Spray System, which is described separately, has no heat removal capability and RHR is not included given that core damage would generally have been avoided if it had been available. The Level 2 PRA models the containment heat removal function via gate 1CHR in the general event tree based on the WCAP, which is linked to the reactor containment fan cooler (RCFC) logic previously developed for the Byron model. One of the four RCFCs is required for success.

Note that for some Level 2 scenarios, this function may not be available due to power or cooling water failures; however, the fault tree models these support systems accordingly. Failure of containment heat removal will allow the containment to slowly pressurize until failure. The plant-specific MAAP calculations use a median failure pressure of 125 psig to define containment overpressure failure for Unit 1 (containment shell failure) and 98 psig for Unit 2 (Bunker Ramo Electrical Penetrations).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Containment Spray The Containment Spray (CS) system at Byron is not connected to a heat sink, cannot provide containment heat removal alone, and is considered separately in the CET for its ability to transfer water to the reactor cavity. The Byron Level 1 PRA does not include the containment spray system and the system model was developed to support the Level 2 analysis.

When containment heat removal is available to prevent long term containment overpressurization failures, consideration is given to the potential for basemat meltthrough. The basemat meltthrough probability in WCAP-16341-P is dependent on multiple variables, including whether or not there is water on the containment floor (i.e., in the reactor cavity). The simplifying assumption made in the WCAP Level 2 model related to the presence of water in the reactor cavity is that, if containment spray functions, the volume of the RWST is transferred to the cavity; otherwise, the cavity is assumed to be dry.

For cases in which containment heat removal fails, success of containment spray could reduce the magnitude of the release by providing a scrubbing mechanism within containment. For the Level 2 analysis, no credit is taken for the impact of scrubbing to reduce the magnitude of the late release. This is primarily because for the dominant scenarios, the containment spray pumps would be unavailable (loss of Service Water Events fail the Containment Spray pumps).

Basemat Meltthrough If no other containment failures occur during an accident scenario and containment heat removal exists, the last containment failure mode to examine is basemat meltthrough. If not cooled by an overlying water pool, the molten corium will begin to attack and erode the concrete basemat. Several beneficial factors at Byron make basemat meltthrough less severe than other plants. First, Byron has a "wet" containment design. If the RWST is injected into the primary system or containment via ECCS or containment spray, the water will drain to the reactor cavity and provide cooling of the molten corium, thus reducing the chance of basemat meltthrough.

Second, the Byron basemat is 9 feet thick under the reactor. Even without cooling of the molten corium, basemat meltthrough will require many hours to erode through this thickness of concrete. Third, Byron has a relatively large cavity floor area, meaning the molten corium will have more space to spread. This results in a shallow layer (about 8 inches thick) of corium which can be more easily cooled by overlying water (over 30 feet). For the containment event trees, sequences including injection of the RWST can avoid basemat meltthrough with a high probability of success, while sequences without injection are subject to eventual basemat Byron and Braidwood Stations, Units 1 and 2 Page F-19 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 meltthrough. Basemat meltthrough is only questioned if containment heat removal is successful and the status of the cavity (wet vs. dry) is determined based on the operation of the CS system. The probability of having basemat meltthrough with a shallow layer of corium and a deep water pool in the cavity is assigned a value of 0.05 (basic event 1L2-CNT-VF-BMMTW),

based on guidance in the WCAP. For scenarios where the cavity is dry, basic event 1L2-CNT-VF-BMMTD models eventual basemat meltthrough with a probability of 1.0.

F.2.3.3 LEVEL 2 RELEASE CATEGORY DEFINITIONS The Level 2 PRA containment event tree sequences are categorized into four general release categories, which are described below.

INTACT Containment structure and function succeed and prevent a substantial release of fission products. Source term calculations assume normal plant leakage to determine offsite consequences.

LATE Containment failure occurs, but is considered late because of a significant time delay between core damage and containment failure. Releases may be large or small, but offsite consequences are limited to latent health effects and contamination.

SERF Containment function is bypassed, but the radioactive release is scrubbed by an overlying water pool or limited by the size of the containment failure, reducing the offsite health effects.

LERF WCAP-16341-P identifies the types of sequences that should be defined as Large-Early evolutions based on a review of documented industry definitions for Large and Early. Byron uses the same classification scheme to identify the Large-Early sequences in the CET. In general, containment failure occurs early in the scenario. Early releases are defined as those releases that occur within a short time following core damage based on plant-specific source term calculations, such that adequate evacuation time is not available to protect the public from prompt health effects. Large releases are determined by plant-specific source term calculations for the sequences defined to be Large-Early (i.e., Large is not tied to a specific fraction of inventory for a given radionuclide), but it is generally greater than 4 percent of the CsI inventory for Byron.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.2.3.3.1 Detailed Level 2 Release Category Definitions A number of different Level 2 sequences contribute to each of the four general release categories above. Because the actual release characteristics will vary depending on how the containment event tree progresses, detailed release categories further define the Level 2 sequences. These detailed release categories consider the scenario characteristics and the ultimate containment failure mode. Each Level 2 sequence is mapped into one of these detailed release categories.

INTACT This release category captures all of the INTACT sequences. Because the containment is essentially intact, sequence variations have a negligible impact on the release characteristics.

INTACT-01, INTACT-02, INTACT-03, INTACT-04, and INTACT-05 contribute to this category.

Releases to the environment are via normal containment leakage.

LATE-BMT-AFW This release category captures sequences that result in basemat meltthrough with feedwater available to the steam generators. Because basemat meltthrough takes a significant amount of time to erode the thick basemat at Byron, the release is small and significantly delayed. LATE-01, LATE-02, LATE-04, and LATE-05.

LATE-BMT-NOAFW This release category captures sequences that result in basemat meltthrough without feedwater available to the steam generators. Because basemat meltthrough takes a significant amount of time to erode the thick basemat at Byron, the release is small and significantly delayed. LATE-07, LATE-08, LATE-10, and LATE-11 contribute to this category.

LATE-CHR-AFW This release category captures sequences that result in containment failure due to late overpressure with feedwater available to the steam generators. LATE-03 and LATE-06 contribute to this category.

LATE-CHR-NOAFW This release category captures sequences that result in containment failure due to late overpressure without feedwater available to the steam generators. LATE-09, LATE-12, LATE-13, and LATE-14 contribute to this category.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 LERF-ISLOCA This release category captures sequences caused by an un-isolated ISLOCA. Those sequences from LERF-11 with ISLOCA initiating events contribute to this category.

LERF-CI This release category captures sequences that result in containment isolation failure. LERF-09 contributes to this release category.

LERF-CFE This release category captures sequences that result in early containment failure due to steam explosion, hydrogen burn, and/or direct containment heating at the time of vessel breach.

LERF-01, LERF-02, LERF-03, LERF-04, LERF-05, AND LERF-06 contribute to this category.

LERF-SGTR-AFW This release category captures sequences caused by a steam generator tube rupture that have successful operation of auxiliary feedwater, but the operators fail to control SG level above 40%

narrow range level and the water inventory in the steam generators does not provide significant fission product scrubbing. With or without isolation of the ruptured steam generator, SGTR sequences with core damage provide a direct release path to the environment through the steam generator relief valves. Those sequences from LERF-10 with SGTR initiating events and successful AFW contribute to this category.

LERF-SGTR-NOAFW This release category captures sequences caused by a steam generator tube rupture that also have failed AFW. With or without isolation of the ruptured steam generator, SGTR sequences with core damage provide a direct release path to the environment through the steam generator relief valves. Those sequences from LERF-11 with SGTR initiating events and AFW failure contribute to this category.

LERF-ISGTR This release category captures sequences that result in either a pressure-induced or thermally-induced steam generator tube rupture that bypasses containment. LERF-07 and LERF-08 contribute to this category.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 SERF -TISGTR-HLF The sequences within this path are those that evolve into thermally induced steam generator tube ruptures, but are shortly followed by a hot leg failure, which effectively terminates the release from the ruptured steam generator. Basemat failure may or may not occur; however, the leakage from the ruptured SG tubes before hot leg failure results in a small/early release and this release is the dominant concern for this sequence. SERF-01 contributes to this category.

SERF-SGTR-AFW-SC Sequences within this path are bypass scenarios due to a steam generator tube rupture. The operators successfully maintain feedwater in the ruptured steam generator to scrub the radioactive release, resulting in a small, early release through the steam generator tube rupture.

SERF-02 contributes to this category.

F.2.3.4 REPRESENTATIVE SEQUENCES For each detailed release category defined above, accident progression calculations predict the timing and amount of release. Table F.2-6 describes the representative sequences for each detailed release category. The first column includes the dominant Level 2 sequence to each release category, with the percentage of that category that the sequence contributes. The representative sequences are selected considering both the likelihood of the scenario and its potential consequences. The potential consequences of the scenarios are based on judgment given that source terms are generally not available for a sequence unless it is identified as a representative sequence.

Because source terms are applied at the detailed release category level, however, the sequences within any given release category typically have very similar release characteristics.

The differences are often limited to whether feed and bleed or recirculation fails and in many cases, such a difference would have a minimal impact on the source term. The sequence that is judged to be associated with a higher potential source term is used as the representative sequence unless there is another sequence that accounts for a majority of the release category frequency and the sequence with the higher source term accounts for less than about 10 percent of the release category frequency. In those cases, the majority sequence would be chosen as representative.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.2.3.5 SOURCE TERM RESULTS The Byron MAAP (version 4.06) model was used to calculate source terms for each of the detailed release categories above. The timing of important events and the timing and magnitude of fission product releases for each representative sequence is documented in Table F.2-7.

F.2.3.6 LEVEL 2 RELEASE CATEGORY FREQUENCIES Table F.2-8 shows the calculated results for the detailed release categories.

F.2.4 PRA MODEL TECHNICAL ADEQUACY FOR SAMA As part of the PRA maintenance program, the Byron PRA model has been subjected to both internal and peer reviews since the submittal of the IPE, including the following:

• 1999 Westinghouse Owners Group Peer Review (performed on Revision 0 of the PRA)

• Standard Self Assessments - Several self-assessments have been performed on the PRA, the most recent of which was completed in June, 2012.

Performed on model of record BB011a, Evaluated against ASME/ANS RA-Sa-2009 (ASME 2009)

The 1999 Westinghouse Owners Group peer review resulted in a total of 27 Level A and B Findings and Observations, all of which have been closed out.

The 2012 self-assessment identified two (2) supporting requirements (SRs) that were classified as not being met and about twenty (20) that were considered to only meet the Capability Category I requirements.

The following table summarizes the issues related to the SRs that were not met and how this assessment could potentially impact the SAMA analysis. Note that the review was performed on the BB011a LERF only model that was replaced by the Byron 2012 Level 2 model (BB011b1) used to support the SAMA analysis.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of ASME Supporting Requirements Classified as Not Met in the BB011a Self-Assessment SR Assessment Comments Potential Impact on SAMA Since the NUREG/CR-6595 approach This SR is related to identifying and documenting has been used, the LERF analysis is potential limitations in the LERF analysis that would inherently structured to support impact applications. This is a documentation issue applications that do not require significant and would not directly impact the SAMA analysis.

LE-G5 capability for distinction among application-related changes to LERF In addition, the 2012 Level 2 model used to support contributors. the SAMA analysis includes an assessment of LE-G5-01 and URE BB-0966 model limitations and this SR is met.

BB-PRA-015 does not include a definition The Byron Level 2 model used to support the SAMA of significant accident progression analysis includes a definition of a significant sequence. Since the LERF methodology accident sequence and it is consistent with the follows the conservative NUREG/CR- definition provided in the ASME/ANS RA-Sa-2009.

6595 process, not meeting this This issue has been resolved.

LE-G6 requirement has no significant impact on risk-informed applications for which Capability Category I LERF is appropriate.

LE-G6-01 and URE BB-0967 The table below includes the original assessment comments associated with the SRs that only met Capability Category I in conjunction with an assessment of how the failure to meet Capability Category II could impact the SAMA analysis. Most of the SRs that were classified as only meeting the Capability Category I requirements were related to the BB011a LERF only model that was replaced by the Byron 2012 Level 2 model (BB011b1) used to support the SAMA analysis.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of ASME Supporting Requirements Classified as CC I in the BB011a Self-Assessment SR Assessment Comments Potential Impact on SAMA IE-A8 B/B PRA-001, Rev. 5, Initiating Event Capability Category II requires plant personnel Analysis, does not include a plant interviews as part of the initiating event identification personnel interview section or discussion. process. The existing list of initiating events is believed This gap is captured in fact and to be complete and while it is possible other events observation (F&O) IE-A8-001 and URE could exist, they would be small contributors and would BB-0958. not impact the SAMA analysis.

No meaningful impact on SAMA.

SC-A5 The mission time as used in the PRA For SR SC-A5, the Byron / Byron PRA model uses a 24-analysis is 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Refer to section hour mission time for most events. Core damage is 2.1.2 and Table 2-1 of BB PRA-003, assumed for scenarios that do not reach core damage in revision 2, Success Criteria Notebook. 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, but are not in safe/stable state. Additional SC-A5-01 and URE BB-0961 work could be performed to support redefining some sequences as non-core damage events.

For SAMA, the current modeling approach is conservative in that it increases the maximum averted cost risk (MACR) and adds potential sequences that could be recovered by a SAMA (increasing the averted cost benefit of a SAMA). Due to human dependence issues and limits on the ways recovery actions are credited in the PRA, the potential changes to mission time assessments to support alternate endstate classifications are likely limited.

No meaningful impact on SAMA.

HR-E3 While the HRA-related procedures were The incorporation of operator interview results into HRA discussed with Operations and Operations can impact the analysts understanding of the modeled training personnel, only a subset of the actions. For Byron, not all actions in the model or all entirety of procedure usage within the sequences in which the actions are used in the model modeled sequences were covered in were discussed in the interviews.

operator interviews and simulator The most important actions are well defined and are observations as documented in supported by interviews. No significant changes to the Appendices D, E, and F of the HRA PRA results would be expected as a result of performing Notebook (BB-PRA-004, VOLUME 1). interviews for the remaining actions.

Insights from the interviews and No meaningful impact on SAMA observations are factored into the associated HFE evaluations as documented in Appendices A and F of the HRA Notebook (BB-PRA-004, VOLUME 1).

Refer to Section 3 and Appendices A, D, E, and F of the HRA Notebook (BB-PRA-004, VOLUME 1).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of ASME Supporting Requirements Classified as CC I in the BB011a Self-Assessment SR Assessment Comments Potential Impact on SAMA HR-E4 Only a subset of the entirety of plant The incorporation of simulator observation data into response in the modeled scenarios were HRA can potentially provide more accurate timing covered in operator interviews and information and an enhanced understanding of the simulator observations as documented in modeled actions beyond what interviews alone can Appendices D, E, and F of the HRA provide. For Byron, not all actions in the model were Notebook (BB-PRA-004, VOLUME 1). observed in the simulator.

Insights from the interviews and There is no way to predict what changes, if any, to observations are factored into the timing or modeling assumptions would result from associated HFE evaluations as additional operator interviews. The availability of documented in Appendices A and F of the interview information for the most important actions at HRA Notebook (BB-PRA-004, VOLUME Byron limits the potential knowledge gaps that may 1). otherwise be filled by simulator observations.

Refer to Section 3 and Appendices A, D, E, No meaningful impact on SAMA and F of the HRA Notebook (BB-PRA-004, VOLUME 1).

LE-B1 The NUREG/CR-6595 methodology is The WCAP methodology was used to identify LERF used to identify LERF contributors. The contributors and this issue is considered to be set defined is consistent with the addressed by the Level 2 model used to support the contributors in Table 4.5.9-3 for large dry SAMA analysis.

containments. A search for unique plant No impact.

issues, required for Capability Category II, was not performed. Level 1 scenarios are grouped for analysis in the Level 2 event trees based on the methodology presented in NUREG/CR-6595. Plant damage states are used to maintain the link to the appropriate supporting MAAP runs.

LE-C1 The NUREG/CR-6595 methodology is WCAP methodology developed accident sequences used to assess containment challenges consistent with the failure modes identified and the plant resulting from the various LERF specific failure rates provided in that guidance were contributors. The LERF fault tree logic used in the Byron Level 2 model.

models the NUREG/CR-6595 CET logic, No impact.

and contributions are grouped by LERF event tree designator.

LE-C2 The NUREG/CR-6595 methodology is The Byron severe accident control room guidance was used to assess containment challenges reviewed to identify and incorporate actions that were resulting from the various LERF judged to have the potential to mitigate severe contributors. Treatment of operator actions accidents.

is therefore conservative. No impact.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of ASME Supporting Requirements Classified as CC I in the BB011a Self-Assessment SR Assessment Comments Potential Impact on SAMA LE-C3 Repair of equipment is not addressed in No credit was taken for any actions to repair equipment the LERF model. to mitigate the Level 2 accident sequences. AC power recovery is treated in the Level 1 model and no additional credit was applied for the Level 2 model. This is consistent with the general PRA practice of not modeling actions to repair failed equipment due to the uncertainties related to the causes of equipment failure and the availability of timely repair strategies. This is considered to meet the intent of LE-C3.

No impact.

LE-C4 The NUREG/CR-6595 methodology is This issue is addressed by the Level 2 model used to used to assess containment challenges support the SAMA analysis.

resulting from the various LERF SG flooding and post core damage RCS contributors. The LERF fault tree logic depressurization was incorporated into the Level 2 models the NUREG/CR-6595 CET logic, model based on a review of the severe accident control and contributions are grouped by LERF room guidance. In addition, State of the Art event tree designator. Consequence Analyses (SOARCA) insights were used to enhance the SGTR analysis.

No impact.

LE-C9 The NUREG/CR-6595 approach has been No operator actions that would be taken in adverse implemented, and credit for equipment environments or opportunities for continued equipment operation or operator actions in adverse operation in a harsh environment were identified that environments is not credited. would realistically mitigate LERF scenarios. Human actions potentially taken after core damage are credited, but they are not in hazardous environments. SOARCA insights were used to enhance the SGTR analysis, however. The Level 2 model used for the SAMA analysis is considered to meet capability category II for LE-C9.

No impact.

LE-C10 LE-C9 is Cat I so this SR is Cat I. The Byron severe accident control room guidance and sequences were reviewed to identify potential mitigating factors as part of the Level 2 model used to support the SAMA analysis. This issue is considered to be resolved.

No impact.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of ASME Supporting Requirements Classified as CC I in the BB011a Self-Assessment SR Assessment Comments Potential Impact on SAMA LE-C11 The NUREG/CR-6595 approach is No operator actions that would be taken after modeled; continued operation of containment failure or opportunities for continued equipment or operator actions affected by equipment operation after containment failure were containment failure is not credited. identified that would realistically mitigate LERF scenarios. Human actions potentially taken after core damage are credited, but they are not in hazardous environments. SOARCA insights were used to enhance the SGTR analysis, however. The Level 2 model used for the SAMA analysis is considered to meet capability category II for LE-C11.

No impact.

LE-C12 Cat I since LE-C11 is Cat I. SOARCA results for induced SGTR are supported by plant specific MAAP runs. The Level 2 model used for the SAMA analysis is considered to meet capability category II for LE-C12.

No impact.

LE-C13 The NUREG/CR-6595 approach has been SG flooding is credited in the Level 2 model and the implemented, and no credit is taken for impact is modeled by plant specific HRA and MAAP scrubbing of containment bypasses. runs. This issue is addressed by the Level 2 model used to support the SAMA analysis.

No impact.

LE-D2 The NUREG/CR-6595 approach has been A plant specific analysis was used to identify the used. weakest point in containment and used to define the failure pressure for the plant specific MAAP analysis, but no location specific impact is modeled.

Low potential impact.

LE-D3 The NUREG/CR-6595 approach has been A plant specific analysis was used to identify the used. weakest point in containment and used to define the failure pressure for the plant specific MAAP analysis, but no location specific impact is modeled.

Low potential impact.

LE-D5 Steam generator isolation is modeled in Plant specific, detailed HRA supports the operator action the SGTR fault tree logic. The modeling is to isolate the SG and the model includes the hardware generally conservative in that any failure of required to perform the isolation.

any line to isolate, regardless of size, is Additional enhancements to model treated as failure of SG isolation. temperature/pressure effects on hardware operation are expected to have a small impact on SAMA.

LE-D6 The NUREG/CR-6596 approach is used. The WCAP methodology, in conjunction with plant An induced steam generator tube rupture specific analysis of SG PORV response, is considered to (ISGTR) probability is assigned for the meet capability category II requirements.

possibility of induced SGTR for sequences No impact.

per the NUREG methodology.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of ASME Supporting Requirements Classified as CC I in the BB011a Self-Assessment SR Assessment Comments Potential Impact on SAMA LE-E2 Parameter estimates for accident Phenomena values are based on plant-specific values progression phenomena are selected in and industry calculations that match plant specific accordance with NUREG/CR-6595, and features based on guidance in the WCAP. This issue is are generally conservative. addressed by the Level 2 model used to support the SAMA analysis.

No impact.

LE-E3 The LERF model is based on NUREG/CR- This issue is addressed by the WCAP Level 2 model 6595. Early containment failures (e.g., used to support the SAMA analysis.

failure prior to recirc), bypass sequences No impact.

(e.g., SGTR, ISLOCA), and isolation failures following core damage are modeled as LERF.

LE-F1 The spreadsheet for BB-PRA-015 includes Documentation issue, which is considered to be an assessment of LERF contribution by resolved by the Level 2 document.

accident class, which is equivalent to No impact.

identification of the contributors to LERF.

Although an assessment by PDS is not currently provided, the information is available to do so. Since the SR wording for Cat I indicates "e.g., PDS" but the wording for Cat II/III does not include the "e.g.", the Category assignment for this SR is Cat I, even though more than an identification of significant contributors has been performed.

LE-G3 The spreadsheet for BB-PRA-015 includes Documentation issue, which is considered to be an assessment of LERF contribution by resolved by the Level 2 document.

accident class, which is equivalent to No impact.

identification of the contributors to LERF.

Although an assessment by PDS is not currently provided, the information is available to do so. Since the SR wording for Cat I indicates "e.g., PDS" but the wording for Cat II/III does not include the "e.g.", the Category assignment for this SR is Cat I, even though more than an identification of significant contributors has been performed.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 The Byron PRA model BB011b1 results are suitable for use as a resource in the SAMA identification process. This conclusion is based on:

• The PRA technical capability evaluations that have been performed to demonstrate technical adequacy of the PRA,

• The PRA maintenance and update processes that are in place to ensure that the model reflects the as-built, as operated plant.

Although there are some open items from the self assessment that will not be resolved until future model updates are performed, they have insignificant impact on the conclusions of the SAMA analysis.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.3 LEVEL 3 RISK ANALYSIS This section addresses the key input parameters and analysis of the Level 3 portion of the risk assessment. In addition, Section F.7.3 summarizes a series of sensitivity evaluations to potentially critical parameters.

F.3.1 ANALYSIS The MACCS2 code (NRC 1998), version 1.13.1, was used to perform the Level 3 probabilistic risk assessment (PRA) for Byron. The MACCS2 code was developed to support probabilistic risk assessments (NRC 1998) and is the code typically used to calculate off-site population dose and costs in support of a SAMA analysis, as recognized in NEI 05-01 (NEI 2005). The atmospheric transport and dispersion straight-line Gaussian modeling incorporated in MACCS2 has been compared against more complex modeling approaches, such as the three-dimensional ADAPT/LODI code, and shown to be acceptable for the purposes of the MACCS2 code (NRC 2004b).

For the Byron MACCS2 analysis, the input parameter values used in NUREG-1150 (NRC 1990a), as detailed in NUREG/CR-4551 (NRC 1990b) and reflected in the MACCS2 Sample Problem A, (NRC 1998) formed the initial bases. NUREG-1150 is a seminal work in PRA performed by the NRC and the national laboratories that includes a Level 3 PRA for five different reactor sites. It was subjected to extensive peer review and has been accepted by the NRC as a standard reference for MACCS2 inputs for SAMA analyses. Where applicable, these initial values were replaced with site specific values applicable to Byron and the surrounding region. Site-specific data included population distribution, regional economic parameters such as property value of farm and non-farm land, and meteorological data. Generic economic parameters from the NUREG-1150 study for the costs of evacuation, relocation and decontamination were escalated from the time of their formulation (1986) to more recent (July 2012) costs. Plant-specific release data included release frequencies and the time-dependent distribution of nuclide releases from 13 accident sequences at Byron. The behavior of the population during a release (evacuation parameters) was based on plant and site-specific set points (i.e., declaration of a General Emergency) and evacuation time estimates (ET 2003).

These data were used in combination with site specific meteorology to calculate risk impacts (exposure and economic) to the surrounding population within 50 miles.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.3.2 POPULATION The population surrounding the Byron site is estimated for the year 2046, the last year of projected operation for Unit 2 given a 20 year license extension.

The population distribution projection was based on year 2000 census data available via SECPOP2000 (NRC 2003). (Year 2010 census data has not yet been incorporated into the SECPOP code or incorporated into the state projection data used to estimate county growth rates at the time of the Level 3 analysis.) The baseline resident year 2000 population from SECPOP was determined for each of 160 grid elements of a polar coordinate grid consisting of sixteen directions (i.e., N, NNE, NE,NNW) for each of ten concentric distance rings with outer radii at 1, 2, 3, 4, 5, 10, 20, 30, 40 and 50 miles surrounding the site. Transient population data from the Byron Evacuation Time Estimate (ETE) study (ET 2003) for the approximate 10 mile radial area around the site was added to the SECPOP permanent population, consistent with the guidance of NEI 05-01 (NEI 2005), on a grid element basis. In addition to the ETE category of transient population, the ETE category special facilities population was also included in the initial year 2000 population estimate. To estimate growth rates, Illinois (IDOC 2012), Wisconsin (WDOA 2012), and Iowa (SDCI 2012) county population projection data from applicable state data sources for the year 2030 were used. Table F.3-1 presents the county growth rates for the years 2000 to 2030. Individual growth rates were calculated for each grid element based on the county growth rates and the proportion of land in each grid element associated with the applicable counties. The combined resident and transient data (including special facilities) were projected from year 2000 to 2030, and then from 2030 to 2046 (using the year 2000 to 2030 growth rate times a 0.53 factor, i.e., 16/30) to calculate the 2046 population distribution. If county growth rate data projected a declining population for 2000 to 2030 for a particular county, zero population growth was assumed for that county. This condition only existed for the two Iowa counties of Clinton and Jackson.

The total year 2046 population for the 160 grid elements in the 50-mile region is estimated at 1,734,765. The distribution of the population is given for the 10-mile radius and the 50-mile radius from Byron in Tables F.3-2 and F.3-3, respectively.

F.3.3 ECONOMY MACCS2 requires certain regional agricultural and land based economic data (e.g., fraction of land devoted to farming, annual farm sales, fraction of farm sales resulting from dairy production, and property value of farm and non-farm land) for each of the 160 grid elements.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 with the economic parameter processing portion of the SECPOP2000 code, SECPOP2000 was not utilized to develop the county specific economic values for the Byron analysis. Instead, the economic values were developed manually following the SECPOP calculation approach documented in NUREG/CR-6525 (NRC 2003) using data from the 2007 National Census of Agriculture (USDA 2009) and 2007 data (for consistency with the census of agricultural data) from the Bureau of Economic Analysis (BEA 2012) for each of the 21 counties surrounding the plant, to a distance of 50 miles. Economic values were updated to July 2012 using the consumer price index (CPI) from the Bureau of Labor Statistics (BLS 2012). The values used for each of the 160 grid elements were based on the data for each of the applicable counties multiplied by the fraction of that element composed of the applicable county. Region-wide wealth data (i.e., farm wealth and non-farm wealth) were based on county-weighted averages for the region within 50-miles of the site using the same economic data sources. The portion of each county within 50-miles of the site was accounted for in the calculation. County specific land use and related economic parameter values are summarized in Table F.3-4.

In addition, generic economic data that is applied to the region as a whole were revised from the NUREG-1150 based data in order to account for cost escalation since 1986, the year that input was first specified. A factor of 2.09, representing cost escalation from 1986 (CPI index of 109.6) to July 2012 (CPI index of 229.1) was applied to parameter values describing cost of evacuating and relocating people and decontamination activities.

MACCS2 generic economic parameter values utilized in the Byron analysis are summarized in Table F.3-5.

F.3.4 FOOD AND AGRICULTURE Food ingestion is modeled using the new MACCS2 ingestion pathway model COMIDA2, consistent with MACCS2 Users Guide (NRC 1998). The COMIDA2 model utilizes national based food production parameters derived from the annual food consumption of an average individual such that site specific food production values are not utilized. The fraction of population dose due to food ingestion is typically small compared to other population dose sources. For Byron, approximately 5.6% of the total population dose is due to food ingestion.

F.3.5 NUCLIDE RELEASE The core inventory at the time of the accident is based on a plant specific calculation (Exelon 2008b). The core inventory represents bounding isotopic values (i.e., largest) for 100 effective full power days (EFPD) or 542.9 EFPD (end of cycle) for the core operating at 3586.6 MWt, the Byron and Braidwood Stations, Units 1 and 2 Page F-34 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 current licensed power level. This calculation reflects the current fuel management / burnup approach. Table F.3-6 summarizes the estimated Byron core inventory used in the MACCS2 analysis. Exelon has submitted a license amendment request (Exelon 2011) for a Measurement Uncertainty Recapture (MUR) power uprate for Byron, of approximately 1.63%

(i.e., from 3586.6 MWt to 3645 MWt). This proposed power uprate is included in the MACCS2 basecase analysis by including a core inventory scaling factor of 1.0163. The assumption of no MUR power uprate (i.e., scaling factor of 1.0) is evaluated in the sensitivity analysis.

Byron nuclide release groups, as represented using the MAAP computer code, are related to the MACCS2 release groups as shown in Table F.3-7. Thirteen radiological release categories were modeled, each segmented into three plumes. Consistent with the guidance of NEI 05-01 (NEI 2005), a plume release height of 30.3 m (99.4 ft) above grade is used representing a release from the mid-height of the containment. Buoyant plume rise is modeled assuming a thermal plume heat content of 10 MW for all releases except intact containment (where zero heat content is assumed). A value of 10 MW bounds typical values in NUREG/CR-4551 (NRC 1990b). Assumptions associated with release height and plume heat content are considered in the sensitivity analyses, presented in Section F.7.3.

For each of the thirteen release categories, a representative MAAP case was chosen based on a review of the Level 2 model cutsets and the dominant types of scenarios that contribute to the release category. Brief descriptions of each release category, dominant Level 2 sequences, and the representative MAAP case are provided in Table F.3-8. Representative MAAP cases were run until a plateau of the CsI and CsOH release fractions were achieved. Experience has shown that CsI is a primary contributor to early dose, and CsOH is a primary contributor to late dose and cleanup costs. In some cases, the MAAP cases were run to times that exceeded the plume release times allowed by MACCS2. In such cases, plumes were moved forward in time in the modeling to meet MACCS2 limitations. These time adjustments are noted in Table F.2-7.

Multiple release duration periods (i.e., plume segments) were defined which represent the time distribution of each categorys releases. A summary of the release magnitude and timing for those cases is provided in Table F.2-7.

A dry deposition velocity of 0.01 m/sec is used for the MACCS2 analysis, consistent with NRC recommendation as documented in the MACCS2 Sample Problem A (NRC 1998). The dry deposition velocity is considered in the sensitivity analysis, presented in Section F.7.3.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.3.6 EVACUATION Reactor trip for each sequence was taken as time zero relative to the core containment response times. A General Emergency (GE) is declared when plant conditions degrade to the point where it is judged that there is a credible risk to the public. For the Byron analysis the time of the GE declaration was estimated based on the Byron emergency action levels (Exelon 2012). The declaration times are presented in Table F.2-7. For most release categories the GE time is established as the time of core damage. However, a minimum GE time of 30 minutes is used for release categories with core damage projected to occur in less than 30 minutes. For the LERF-SGTR-NOAFW, the GE is declared earlier than the time of core damage based on the known loss of AFW. For two release categories (i.e., LERF-SGTR-AFW and SERF-SGTR-AFW-SC), the GE times were moved forward in time (i.e., earlier) in association with moving the plume segments release time earlier to meet MACCS2 release delay limitations of a maximum of 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> following accident initiation. Because the GE time modeled was moved earlier the same amount as the plume segment release times, this earlier modeling of GE time does not impact evacuation related timing issues. The only impact is that there is less time incorporated in the MACCS2 calculation for natural decay thereby adding a slight conservatism to the modeling.

Ninety five percent of the population within 10 miles of the plant (Emergency Planning Zone, EPZ) is assumed to evacuate and 5 percent is assumed not to evacuate, consistent with the MACCS2 Users Guide (NRC 1998). These values are conservative relative to the NUREG-1150 study (NRC 1990a), which assumed evacuation of 99.5 percent of the population within the EPZ.

The evacuees are assumed to begin evacuation 115 minutes after a general emergency has been declared at a base evacuation radial speed of 4.4 m/sec. The time to begin evacuation and the base speed are derived from the site specific evacuation study (ET 2003). The evacuation speed is a time-weighted average value accounting for season, time of day, and weather conditions. It is noted that the longest evacuation time presented in the study (i.e., full 10 mile EPZ, winter daytime adverse weather conditions) is 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> 50 minutes (from the issuance of the advisory to evacuate). The evacuation parameters were considered further in the sensitivity analyses presented in Section F.7.3.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.3.7 METEOROLOGY Annual hourly meteorology Byron data sets from 2008 through 2010 were processed for use in the MACCS2 analysis. Of the hourly data of interest (10-meter wind speed, 10-meter wind direction, multi-level temperatures used to calculate stability class, and precipitation), less than 4% of the data were missing for each of the three years of data. Traditionally, up to 10% of missing data is considered acceptable. MACCS2 requires complete sequential hourly data for the full year, and therefore missing data must be estimated. The percentages of data hours that included estimated data for missing data for years 2008, 2009, and 2010 were 3.2%, 1.5%, and 1.6%, respectively. Data gaps were filled in the following manner (order of priority):

• Wind direction data gaps for the 30-foot (10-meter) sensor were filled by using wind direction data from the 250-foot sensor, if available. Wind speed data gaps resulting from calm winds were assigned a 0.5 mph wind speed.

• Data gaps of less than six consecutive hours were filled by interpolation.

• Wind speed data gaps of greater than six consecutive hours were filled using the power law and wind speed data from the 250-foot sensor, if available. This was only required for the 2008 dataset.

• Data gaps of six or more consecutive hours were filled by substitution from the same hour of a nearby day.

The 10-meter wind speed and direction were combined with precipitation and atmospheric stability (derived from the vertical temperature gradient) to create the hourly data file for each year for use by MACCS2.

The 2008 data set was found to result (see Section F.7.3 for discussion of sensitivity analysis) in the largest economic cost risk and dose risk compared to the 2009 and 2010 data sets.

Therefore, the 2008 hourly meteorology was selected as the base case.

Atmospheric mixing heights were specified for AM and PM hours for each season of the year.

These values ranged from 300 meters to 1600 meters, as documented in the Byron UFSAR (Exelon 2010), based on Holzworth data (EPA 1972).

F.3.8 MACCS2 RESULTS Table F.3-9 shows the mean off-site doses and economic impacts to the region within 50 miles of Byron for each of 13 release categories calculated using MACCS2. The mean off-site dose impacts are multiplied by the annual frequency for each release category and then summed to obtain the dose-risk and offsite economic cost-risk (OECR) for each unit.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.4 BASELINE RISK MONETIZATION This section explains how Byron calculated the monetary value of the status quo (i.e., accident consequences without SAMA implementation). Byron also used this analysis to establish the maximum benefit that could be achieved if all on-line Byron risk were eliminated, which is referred to as the Maximum Averted Cost-Risk (MACR). Per the site PRA model (designated BB011b1), the Unit 1 internal events CDF of 3.97E-05 (at a truncation of 1E-10/yr) was used for the calculations in the following sections. External risk is addressed in Section F.4.6.2.

F.4.1 OFF-SITE EXPOSURE COST The baseline annual off-site exposure risk was converted to dollars using the NRCs conversion factor of $2,000 per person-rem, and discounted to present value using NRC standard formula (NRC 1997):

Wpha = C x Zpha Where:

Wpha = monetary value of public health accident risk after discounting C = [1-exp(-rtf)]/r tf = years remaining until end of facility life = 20 years r = real discount rate (as fraction) = 0.03 per year Zpha = monetary value of public health (accident) risk per year before discounting ($ per year)

The Level 3 analysis showed an annual off-site population dose risk of 34.45 person-rem. The calculated value for C using 20 years and a 3 percent discount rate is approximately 15.04.

Therefore, calculating the discounted monetary equivalent of accident dose-risk involves multiplying the dose (person-rem per year) by $2,000 and by the C value (15.04). The calculated off-site exposure cost is $1,066,436.

F.4.2 OFF-SITE ECONOMIC COST RISK The Level 3 analysis showed an annual off-site economic risk of $254,593. Calculated values for off-site economic costs caused by severe accidents must be discounted to present value as well. This is performed in the same manner as for public health risks and uses the same C value. The resulting value is $3,828,979.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.4.3 ON-SITE EXPOSURE COST RISK Occupational health was evaluated using the NRC recommended methodology that involves separately evaluating immediate and long-term doses (NRC 1997).

For immediate dose, the NRC recommends using the following equation:

Equation 1:

WIO = R{(FDIO)S -(FDIO)A} {[1 - exp(-rtf)]/r}

Where:

WIO = monetary value of accident risk avoided due to immediate doses, after discounting R = monetary equivalent of unit dose ($2,000 per person-rem)

F = accident frequency (events per year) (3.97E-05 (internal events CDF)) at an average 1E-10/yr truncation DIO = immediate occupational dose [3,300 person-rem per accident (NRC estimate)]

S = subscript denoting status quo (current conditions)

A = subscript denoting after implementation of proposed action r = real discount rate (0.03 per year) tf = years remaining until end of facility life (20 years).

Assuming FA is zero, the best estimate of the immediate dose cost is:

WIO = R (FDIO)S {[1 - exp(-rtf)]/r}

= 2,0003.97E-05 3,300{[1 - exp(-0.0320)]/0.03}

= $3,941 For long-term dose, the NRC recommends using the following equation:

Equation 2:

WLTO = R{(FDLTO)S -(FDLTO)A} {[1 - exp(-rtf)]/r}{[1 - exp(-rm)]/rm}

Where:

WLTO = monetary value of accident risk avoided long-term doses, after discounting, $

DLTO = long-term dose [20,000 person-rem per accident (NRC estimate)]

m = years over which long-term doses accrue (as long as 10 years)

Using values defined for immediate dose and assuming FA is zero, the best estimate of the long-term dose is:

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 WLTO = R (FDLTO)S {[1 - exp(-rtf)]/r} {[1 - exp(-rm)]/rm}

= 2,0003.97E-05 20,000{[1 - exp(-0.0320)]/0.03} {[1 -exp(-

0.0310)]/0.0310}

= $20,633 The total occupational exposure is then calculated by combining Equations 1 and 2 above. The total accident related on-site (occupational) exposure risk (WO) is:

WO = WIO + WLTO = ($3,941+$20,633) = $24,574 F.4.4 ON-SITE CLEANUP AND DECONTAMINATION COST The total undiscounted cost of a single event in constant year dollars (CCD) that NRC provides for cleanup and decontamination is $1.5 billion (NRC 1997). The net present value of a single event is calculated as follows. NRC uses the following equation to integrate the net present value over the average number of remaining service years:

PVCD = [CCD/mr][1-exp(-rm)]

Where:

PVCD = net present value of a single event CCD = total undiscounted cost for a single accident in constant dollar years r = real discount rate (0.03) m = years required to return site to a pre-accident state The resulting net present value of a single event is $1.3E+09. The NRC uses the following equation to integrate the net present value over the average number of remaining service years:

UCD = [PVCD/r][1-exp(-rtf)]

Where:

PVCD = net present value of a single event ($1.3E+09) r = real discount rate (0.03) tf = 20 years (license renewal period)

The resulting net present value of cleanup integrated over the license renewal term, $1.95E+10, must be multiplied by the internal events CDF (3.97E-05) to determine the expected value of cleanup and decontamination costs. The resulting monetary equivalent is $773,752.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.4.5 REPLACEMENT POWER COST Long-term replacement power costs were determined following the NRC methodology in NRC 1997. The net present value of replacement power for a single event, PVRP, was determined using the following equation:

PVRP = [$1.2x108/r] * [1 - exp(-rtf)]2 Where:

PVRP = net present value of replacement power for a single event, ($)

r = 0.03 tf = 20 years (license renewal period)

To attain a summation of the single-event costs over the entire license renewal period, the following equation is used:

URP = [PVRP /r] * [1 - exp(-rtf)]2 Where:

URP = net present value of replacement power over life of facility ($-year)

After applying a correction factor to account for Byrons size relative to the generic reactor described in NUREG/BR-0184 (NRC 1997) (i.e., 1185 megawatt electric / 910 megawatt electric), the replacement power costs are determined to be 7.20E+09 ($-year). Multiplying 7.20E+09 ($-year) by the CDF (3.97E-05) results in a replacement power cost of $285,652.

F.4.6 MAXIMUM AVERTED COST-RISK The Byron MACR is the total averted cost-risk if all internal and external events risk associated with on-line operation were eliminated. This is calculated by summing the following components:

• Maximum Internal Events Averted Cost-Risk

• Maximum External Events Averted Cost-Risk As described in Section F.5.1, the MACR is used in the SAMA identification process to determine the depth of the importance list review. In addition, the MACR is used in the Phase I analysis as a means of screening SAMAs. The following subsections provide a description of how each of these components is calculated and used together to obtain the Byron MACR.

F.4.6.1 INTERNAL EVENTS MAXIMUM AVERTED COST-RISK The maximum internal events averted cost-risk is the sum of the contributors calculated in Sections F.4.1 through F.4.5:

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Maximum Averted Internal Events Cost-Risk Off-site exposure cost $1,066,436 Off-site economic cost $3,828,979 On-site exposure cost $24,574 On-site cleanup cost $773,752 Replacement power cost $285,652 Total cost (per unit) $5,979,393 This total represents the per unit monetary equivalent of the risk that could be eliminated if all risk associated with on-line internal event hazards (including internal floods) could be eliminated for Byron. The internal events MACR is rounded to next highest thousand ($5,980,000) for SAMA calculations. It should be noted that the Phase II cost benefit calculations account for the difference between the rounded MACR and the actual MACR by adding the difference to the averted cost-risk calculated for each SAMA.

F.4.6.2 EXTERNAL EVENTS MAXIMUM AVERTED COST-RISK The maximum averted cost-risk for external events must be quantified for the cost benefit calculations; however, this cost-risk must be estimated based on information in the IPEEE (ComEd 1996) given that complete, current, quantifiable external events models are not available for Byron (other than for fire, which is discussed further in section F.5.1.6). Resources have been committed to update the seismic model for the site and a fire model update is in progress, but those models are not developed to the point where they can be used for quantitative or qualitative input to the SAMA analysis. As a result, an alternate method of accounting for the external events contributions must be established.

The method chosen to account for external events contributions in the SAMA analysis is to use a multiplier on the internal events results. In previous SAMA analyses, it has been assumed that the risk posed by external events and internal events is approximately equal. This assumption is not unreasonable unless available analyses indicate that there are external events contributors that present a disproportionate risk to the site. Based on the magnitude of the Byron fire CDF relative to the internal events CDF, it was concluded that the development of an external events multiplier was warranted.

The external events multiplier is the ratio of the total CDF (including internal and external) to only the internal events CDF. The lack of detailed analyses makes it difficult to establish a meaningful CDF for the non-fire initiator groups; however, some assumptions can be made Byron and Braidwood Stations, Units 1 and 2 Page F-42 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 about the non-quantified initiator groups that could be used to further develop a total external events CDF.

The Byron IPEEE methodology implies that if the plant licensing bases are met, the plant and facilities design meets the 1981 Standard Review Plan (SRP) criteria, and the site walkdown does not reveal any potential vulnerability not already considered in the design basis analysis, then the CDF posed by an initiator is less than the 1.0E-06 per year screening criterion. As described in Section F.5.1.6, these conditions are met for Byron and no contributors greater than 1.0E-06 were expected for any of the external events excluding internal fires. Based on this condition, a CDF of 1.0E-06 per year could be assumed for each of the contributors for which no complete quantitative basis exists to obtain a more detailed estimate of the external events CDF.

The latest available fire results are from the 2009 revision of the Byron fire model (Exelon 2009).

While an update of that model was in progress at the time the SAMA analysis was performed, the process was in its infancy and no information was available that could have been used to provide qualitative or quantitative input to the SAMA analysis. However, the 2009 Byron fire model does use the latest fire ignition frequencies from EPRI 1016735 (EPRI 2008).

In the 2009 fire model, the Unit 2 model is not refined to the same degree as the Unit 1 model, so the Unit 1 model is used as the basis for fire quantification. For the purposes of establishing the Byron SAMA External Events multiplier, the larger of the two quantified configurations (Unit 0 component cooling HX aligned to Unit 1) is used as the CDF (5.39E-05/yr).

Assuming a CDF of 1.00E-06/yr for the non-fire external events contributors and using the Unit 1 Fire CDF of 5.39E-05/yr, the external events contributions could be summarized as follows:

Modified IPEEE Contributor Summary Fire 5.39E-05 Seismic 1.00E-06 High Winds 1.00E-06 Transportation & Nearby Facility Accidents 1.00E-06 External Flooding 1.00E-06 Total EE CDF 5.79E-05 Byron and Braidwood Stations, Units 1 and 2 Page F-43 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 The External Events multiplier is the ratio of the total CDF (including internal and external events) to the internal events CDF. Using the total external events of 5.79E-05 from above and the Unit 1 internal events CDF of 3.97E-05, the External Events multiplier is:

EE Multiplier = (3.97E-05 + 5.79E-05) / 3.97E-05 = 2.5 F.4.6.3 BYRON MAXIMUM AVERTED COST-RISK The total MACR can be obtained by multiplying the internal events cost-risk by the EE multiplier of 2.5:

Single Unit MACR = $5,980,000

• 2.5 = $14,950,000 Alternatively, as stated in Section F.4.6, the MACR can be represented by the internal and external events contributions (based on the relative contribution of the CDF values to the total CDF):

Internal Events = $5,980,000 External Events = $8,970,000 Single Unit Maximum Averted Cost-Risk = $14,950,000 The MACR and implementation costs are considered on a per-unit scale for consistency (unless otherwise noted).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.5 PHASE 1 SAMA ANALYSIS The Phase 1 SAMA analysis, as discussed in Section F.1, includes the development of the initial SAMA list and a coarse screening process. This screening process eliminated those candidates that are not applicable to the plants design or are too expensive to be cost beneficial even if the risk of on-line operations were completely eliminated. The following subsections provide additional details of the Phase 1 process.

F.5.1 SAMA IDENTIFICATION The initial list of SAMA candidates for Byron was developed from a combination of resources.

These include the following:

• Byron PRA results and PRA Group Insights

• Industry Phase 2 SAMAs (review of potentially cost effective Phase 2 SAMAs from selected plants, as documented in section F.5.1.3)

• Byron Individual Plant Examination IPE (ComEd 1994)

• Byron IPEEE (ComEd 1996)

These resources are judged to provide a list of potential plant changes that are most likely to reduce risk in a cost-effective manner for Byron.

In addition to the Industry Phase 2 SAMA review identified above, an industry based SAMA list was used in a different way to aid in the development of the Byron plant specific SAMA list.

While the industry Phase 2 SAMA review cited above was used to identify potential SAMAs from specific sites that might have been overlooked in the development of the Byron SAMA list due to PRA modeling issues, a generic SAMA list was used to help identify the types of changes that could be used to address the areas of concern identified through the Byron importance list review. For example, if Instrument Air availability was determined to be an important issue for Byron, the industry list would be reviewed to determine if a plant enhancement had already been conceived that would address Byrons needs. If an appropriate SAMA was found to exist, it would be used in the Byron list to address the Instrument Air issue; otherwise, a new SAMA would be developed that would meet the sites needs. This generic list was compiled as part of the development of multiple industry SAMA analyses and is available in NEI 05-01 (NEI 2005).

It should be noted that the process used to identify Byron SAMA candidates focuses on plant specific characteristics and is intended to address only those issues important to the site. An evaluation of the generic SAMAs in NEI 05-01, as they are written, provides little benefit because in most cases the systems are not exactly the same as those at Byron. Without Byron and Braidwood Stations, Units 1 and 2 Page F-45 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 modifying the NEI 05-01 SAMAs to match the systems at Byron, many would be screened as not applicable. Further, the scopes of the generic SAMAs are not tailored to match the needs of a specific plant such that the generic SAMAs may only address a fraction of the required functions. As a result, evaluation of the entire generic SAMA list would only be useful after each SAMA has been modified to address the plant specific risk profile. The processes used for Byron were more efficient than evaluating the entire generic SAMA list, as written.

F.5.1.1 LEVEL 1 BYRON IMPORTANCE LIST REVIEW The importance list review was performed to identify the failure scenarios most important to Byron risk and to develop methods to mitigate those scenarios. For each event on the importance list, the reasons for the events importance are determined through sequence and systems analysis. Strategies to mitigate the relevant failures are developed based on accident sequence review, plant knowledge, and industry insights. For Byron, importance lists were developed and reviewed for the internal events model while for the fire model, the top contributing fire zone results were reviewed to identify SAMAs.

The importance list itself was developed from the Byron PRA cutsets and is comprised of the models basic events sorted according to their risk reduction worth (RRW) values. The events with the largest RRW values in this list are those events that would provide the greatest reduction in the CDF if the failure probability were set to zero. Because a PRAs importance list can be extensive, it is desirable to limit the review to only those contributors that could yield potentially cost beneficial results. One method that can be used to limit the scope of the importance list review is to correlate the RRW value threshold to the lowest expected cost of implementation for a SAMA. Usually, operator action modifications in the form of procedure changes are among the least expensive enhancements that can be made at a site, so they are often used as the representative lowest cost SAMA. For Byron, operator actions were considered as potential SAMA candidates and documented in Tables F.5-1, F.5-2a, and F.5-2b.

The cost of a procedure change varies depending on the type of procedure that is being changed, the scope of the changes that are proposed, and the training program changes, but the lower end of the cost estimates range from $50,000 to $100,000 (CPL 2006). For Byron, the upper end of this range ($100,000) is used as the lowest cost SAMA to account for engineering analysis, the update of procedure text and supporting documentation, and training.

The cost is considered to be a per unit cost.

The RRW value corresponding to $100,000 was determined to be about 1.017 for the internal events model. In some SAMAs, the RRW correlation is based on the total MACR that accounts Byron and Braidwood Stations, Units 1 and 2 Page F-46 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 for all external events contributions. For Byron, this was not done because 1) the fire results were reviewed separately for the purposes of SAMA identification, 2) the fire model is in an interim state. If the surrogate CDF values identified in Section F.4.6.2 for the non-fire external events are considered, the review threshold would be lowered slightly, but the impending implementation of the AFW Cross-tie would conversely increase the threshold slightly. Based on these factors, the use of the current internal events CDF to establish the review threshold is considered to result in an adequate review of the risk contributors for Byron. However, because the importance review to an RRW value of 1.005 was performed for the Braidwood SAMA analysis, applicable review results were generally available for Byron to the 1.005 level and the Byron SAMA analysis extended the importance review to an RRW value of 1.005.

Table F.5-1 documents the disposition of each basic event in the Level 1 internal events model with an RRW value of 1.005 or greater. The depth of the RRW review is consistent with NEI 05-01 guidance as well as other SAMA analyses.

For the fire analysis, the review threshold was correlated to the IPEEE screening threshold of a 1.0E-06 CDF. A direct correlation of fire CDF to potential averted cost-risk could be performed, but given the interim state of the model, this was not considered to be the best approach. The fire results are likely overly conservative and are also likely to change as the model is refined, but a review of all contributors with CDFs above 1.0E-06 is considered to provide some assurance the important issues have been identified for the site. Because the units are different with regard to fire events, the review was performed separately for Units 1 and 2. Section F.5.1.6.1 includes the detailed results of the fire zone review.

F.5.1.2 LEVEL 2 BYRON IMPORTANCE LIST REVIEW A similar review was performed on the importance listings from the Level 2 results. In this case, two separate Level 2 importance lists were developed. The reviews were performed on composite importance files for the following release categories:

• Large Early (LERF-ISLOCA, LERF-CI, LERF-CFE, LERF-SGTR-AFW, LERF-SGTR-NOAFW, LERF-ISGTR )

• Late (LATE-CHR-AFW, LATE-CHR-NOAFW, LATE-BMMT-AFW, LATE-BMMT-NOAFW)

These groupings were developed to prevent high frequency-low consequence events (i.e., the Intact release category) from biasing the importance lists. The release categories included in the review account for over 91 percent of the dose-risk while accounting for only about 70 percent of the Level 2 frequency. Exclusion of the other results from the Level 2 review allows Byron and Braidwood Stations, Units 1 and 2 Page F-47 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 the contributors that are most important to dose-risk and cost-risk to rise to the top of the importance lists.

The Level 2 basic events were also reviewed down to the 1.005 level. As described for the Level 1 RRW list, the review threshold was based only on the internal events results given that a separate, explicit review of the fire results was performed for SAMA identification.

Tables F.5-2a and F.5-2b document the disposition of each basic event in the Level 2 RRW lists with RRW values greater than 1.005.

F.5.1.3 INDUSTRY SAMA REVIEW The SAMA identification process for Byron is primarily based on the PRA importance listings, the IPE, and the IPEEE. In addition to these plant-specific sources, selected industry SAMA submittals and the associated Generic Environmental Impact Statement documents were reviewed to identify any Phase II SAMAs that were determined to be potentially cost beneficial at other plants. These SAMAs were further analyzed and included in the Byron SAMA list if they were considered to address potential risks not identified by the Byron importance list review.

While many of the industry SAMAs reviewed are ultimately shown not to be cost beneficial, some are close contenders and a small number have been estimated to be potentially cost beneficial at other plants. Use of the Byron importance ranking should identify the types of changes that would most likely be potentially cost beneficial for Byron, but review of selected industry Phase II SAMAs may capture potentially important changes not identified for Byron due to PRA modeling differences or SAMAs that represent alternate methods of addressing risk.

Given this potential, it was considered prudent to include a review of selected industry Phase II SAMAs in the Byron SAMA identification process. In order to improve the likelihood generic Westinghouse issues would be captured and that the SAMAs reviewed would be relevant to the Braidwood design, six Westinghouse PWRs were used as the sources for the SAMAs:

• Vogtle (SNC 2007, NRC 2008a)

• Shearon Harris (CPL 2006, NRC 2008b)

• H.B. Robinson (NRC 2003a)

• Prairie Island (NMC 2008, NRC 2011)

• Wolf Creek (WCNOC 2006, NRC 2008c)

• Indian Point Unit 2 (Entergy 2007, NRC 2010)

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Six Westinghouse PWR sites were chosen from available documentation to serve as the potential Phase 2 SAMA sources. Many of the industry Phase 2 SAMAs were already represented by other SAMAs in the Byron list, were known not to impact important plant systems or be relevant to the Byron design, or were judged not to have the potential to be close contenders for Byron. As a result, they were not added to the Byron SAMA list. If there were any unique SAMAs that were considered to have the potential to be cost effective for Byron, they were added to the list. The cost effective SAMAs for each of the sites identified above are reviewed in the following subsections.

F.5.1.3.1 Vogtle Vogtle identified two SAMAs in the baseline analysis that were determined to be potentially cost beneficial. Two additional SAMAs were identified as potentially cost beneficial in the 95th percentile PRA results sensitivity analysis (SAMAs 6 and 16), but after more detailed assessments of the associated implementation costs, it was concluded that SAMAs 6 and 16 were not cost beneficial.

Review of Vogtle Potentially Cost Beneficial SAMAs Industry SAMA Description Discussion for Byron Disposition Site SAMA for Byron ID SAMA List 2 Maintain Full Time There is no local power station with the capability of Not required Black Start Capability providing power to the Byron switchyard for which for the SAMA of the Plant Wilson operational procedures could be modified to list Combustion Turbines maintain full time black start capability for station blackout (SBO) support. Not applicable.

4 Prepare Procedures Byron already has procedures for inter-unit cross- Not required and Operator Training tie of the emergency buses. for the SAMA for Cross-Tying an list Opposite Unit DG Byron and Braidwood Stations, Units 1 and 2 Page F-49 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.5.1.3.2 Shearon Harris Review of Shearon Harris Potentially Cost Beneficial SAMAs Industry SAMA Description Discussion for Byron Disposition Site SAMA for Byron ID SAMA List 9 Proceduralize Actions The EDG room cooling system, which is modeled Not required to Open emergency in the PRA, is not an important contributor to plant for the SAMA diesel generator (EDG) risk for Byron. No SAMA required. list Room Doors on Loss of heating ventilation and air-conditioning (HVAC) and Implement Portable Fans 6 Flood Mitigation for This is a plant specific internal flooding issue Not required Scenarios 6 and 7 related to valve qualification in flooding conditions; for the SAMA however, similar issues have not been identified in list the review of the Byron flooding contributors.

8 Alternate Seal Cooling This SAMA was developed to address loss of 4kV Not required and Direct Feed to bus events where power is available to the for the SAMA Transformer 1B3-SB opposite 4kV bus, but vital equipment has failed on list the powered bus. Specifically, it provides an alternate power feed to the bus supporting an available AFW pump and procedure changes to increase the CCW heatup time so that the swing charging pump can be aligned to the opposite power division for seal injection. This SAMA is specific to the Harris configuration where simple procedure changes could be made that would provide adequate time to allow operators to align the swing charging pump to the opposite division of power. There is no equivalent condition for Byron and this SAMA is not applicable.

F.5.1.3.3 H.B. Robinson The H.B. Robinson SAMA analysis used a generic SAMA list as its starting point and few plant specific insights were available that might pertain specifically to Westinghouse PWRs. While CP&L did not identify any potentially cost beneficial SAMAs, the NRC identified two potentially cost beneficial SAMAs as part of the external events risk review, which are discussed below.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of H.B. Robinson Potentially Cost Beneficial SAMAs Industry SAMA Description Discussion for Byron Disposition for Site Byron SAMA List SAMA ID 1437-13-1 Replace cast-iron This is a seismic vulnerability specific to the Not required for the yokes on RHR valves Robinson configuration. There are no Byron SAMA list RHR components with high confidence of low probability of failure (HCLPF) values below the 0.3g review threshold and the RHR valve yokes were not identified as a potential weakness at Byron.

1437-13-2 Install a radiant heat This is a fire vulnerability specific to the Not required for the shield on the electrical Robinson configuration. Byron does not have SAMA list conduit to the a shutdown DG and this enhancement is not shutdown DG applicable to the site.

F.5.1.3.4 Prairie Island Nuclear Generating Plant Review of Prairie Island Potentially Cost Beneficial SAMAs Industry SAMA Description Discussion for Byron Disposition for Site SAMA Byron SAMA List ID 3 Provide Alternate Failure of the RWST flowpath to the charging Not required for the Flowpath from pumps is not a significant contributor for Byron. SAMA list RWST to Charging SAMA not required.

Pump Suction 9 Analyze Room Heat- This SAMA was developed to support the use of Not required for the up for Natural/Forced alternate room cooling (via a heatup analysis) in SAMA list Circulation the plants screenhouse when normal cooling (Screenhouse fails. For Byron, the loss of screenhouse Ventilation) cooling is not required for any PRA systems.

SAMA not required.

19a Provide a Reliable A SAMA for automated RWST refill was Already included Backup Water developed for Byron based on the PRA Source for importance list review (SAMA 14).

Replenishing the RWST N/A Provide a Gagging Based on information in the DCPP RAI Not required for the Device for Closing a responses (PG&E 2010), gagging devices are SAMA list stuck-open SG installed for maintenance tasks and are useful Safety Valve in for preventing PORVs from opening, but are not SGTR Events designed to reclose a stuck open PORV. This SAMA is not considered to be viable and is not included in the Byron SAMA list.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of Prairie Island Potentially Cost Beneficial SAMAs Industry SAMA Description Discussion for Byron Disposition for Site SAMA Byron SAMA List ID 22 Provide Compressed Air systems are modeled for Byron, but system Not required for the Air Backup for failures are not significant contributors to risk. SAMA list Instrument Air to SAMA not required.

Containment Byron and Braidwood Stations, Units 1 and 2 Page F-52 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.5.1.3.5 Wolf Creek Generating Station Review of Wolf Creek Generating Station Potentially Cost Beneficial SAMAs Industry SAMA Description Discussion for Byron Disposition for Site SAMA Byron SAMA List ID 2 Modify the Controls There is no local power station with the Not required for the and Operating capability of providing power to the Byron SAMA list Procedures for switchyard for which operational procedures Sharpe Station to could be modified to provide rapid start Allow for Rapid capability for SBO support. Not applicable.

Response

4 (case 2) Update emergency This SAMA was developed to address questions Not required for the procedures to direct about the ability of motor operated valves SAMA list local, manual closure (MOVs) to close against the differential pressure of the RHR in a specific ISLOCA sequence for Wolf Creek.

EJHV8809A and Discussions with an Exelon MOV Program EJHV8809B valves if engineer indicate that local operation of the they fail to close valve may be successful depending on several remotely factors. For example, if the motor gearing is the limit, the handwheel may function if enough force could be applied to the handwheel. If other portions of the valve are not capable of withstanding the force required to close, then the isolation will fail. For Byron, general training would direct operators to attempt a local valve closure given remote operation failure, so the Wolf Creek SAMA would provide no tangible benefit. A different SAMA (SAMA 19) was developed for Byron to replace the 8809 valves (and others) with valves of a different design to ensure a success path is available in ISLOCA scenarios.

5 Enhance procedures The EDG room cooling system, which is Not required for the to direct operators to modeled in the PRA, is not an important SAMA list open EDG Room contributor to plant risk for Byron. No SAMA doors for alternate required.

room cooling 1 Permanent, This was designed to assist in an SBO that Not required for the Dedicated Generator included a seal LOCA. The design includes a SAMA list for the NCP with 4kV, 500kW EDG to power a charging pump Local Operation of and transformer to support the 125V battery Turbine Driven AFW chargers. Byron does not have a turbine driven After 125V Battery AFW pump and the diesel pump requires SX for Depletion lube oil cooling, so the SAMA is not applicable to the plant configuration.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of Wolf Creek Generating Station Potentially Cost Beneficial SAMAs Industry SAMA Description Discussion for Byron Disposition for Site SAMA Byron SAMA List ID 3 AC Cross-tie Byron already has 4KV AC cross-tie capability. Already Capability Implemented 13 Alternate Fuel Oil For Wolf Creek, fuel oil failures contributed Not required for the Tank with Gravity significantly to the CDF and an alternate method SAMA list Feed Capability to transfer fuel to the EDG day tank was determined to be cost effective. The Byron fuel oil transfer configuration includes redundant pump trains for each diesel and fuel oil transfer failures are not significant contributors to plant risk. SAMA not required.

14 Permanent, This was designed to assist in an SBO that Included as SAMA Dedicated Generator included a seal LOCA. The design includes a 26.

for the NCP, one 4kV, 500kW EDG to power a charging pump, an Motor Driven AFW AFW pump, and a transformer to support the Pump, and a Battery 125V battery chargers. For Byron, both the Charger charging pumps and the AFW pumps ultimately require SX for cooling and this SAMA would require additional changes to make it applicable to the site. The Diverse Mitigation System (DMS) is proposed as the full scope SBO mitigation enhancement (SAMA 11); however, an alternate design could be investigated that uses a dedicated generator/ seal injection system to prevent seal LOCAs in conjunction with a portable SG makeup pump.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.5.1.3.6 Indian Point Energy Center Unit 2 Review of Indian Point U2 Potentially Cost Beneficial SAMAs Industry SAMA Description Discussion for Byron Disposition for Site SAMA Byron SAMA List ID 028 Provide a Portable This SAMA was designed to prolong AFW Not required for the Diesel Driven Battery availability in an SBO by using a portable SAMA list Charger generator to provide alternate battery charging capability. No discussion is provided in the Indian Point U2 SAMA analysis about primary side makeup requirements.

The industry initiatives for SBO mitigation, which are commitments, are more comprehensive than this SAMA and are addressed by the DMS SAMAs for Byron. No additional SAMAs required.

044 Use Fire Water This enhancement was intended to provide Not required for the System as Backup alternate steam generator (SG) makeup SAMA list for Steam Generator capability and relies on Fire Water as a suction Inventory source, but includes a new, electric, 800 gpm pump to provide flow.

The Fire Water system is a low pressure system that does not address early losses of SG makeup. Byron includes a SAMA to complete the AFW X-tie, which addresses the loss of AFW scenarios in a more cost effective manner.

No additional SAMAs required.

054 Install Flood Alarm in Providing a water sensor in the 480V AC Not required for the the 480V AC Switchgear room would provide early warning of SAMA list Switchgear Room flood conditions and improve the probability isolation could occur before equipment damage.

Internal flooding events for the Switchgear Rooms are not significant contributors for Byron and are below the review threshold for SAMA identification.

056 Keep RHR Heat The intent of this SAMA is to reduce the Not required for the Exchanger contribution of failures of the RHR heat SAMA list Discharge MOVs exchanger (HX) valves to open on demand.

Normally Open The Byron RHR HX outlet valves are normally open/fail open valves.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of Indian Point U2 Potentially Cost Beneficial SAMAs Industry SAMA Description Discussion for Byron Disposition for Site SAMA Byron SAMA List ID 060 Provide Added This change addresses a plant specific internal Not required for the Protection Against flooding issue and includes changes to the SAMA list Flood Propagation swing direction of a door, addition of ductwork, from Stairwell 4 into and a check valve.

the 480V AC Internal flooding events for the Switchgear Switchgear Room Rooms are not significant contributors for Byron and are below the review threshold for SAMA identification.

061 Provide Added This change addresses a plant specific internal Not required for the Protection Against flooding issue and includes upgrading the SAMA list Flood Propagation deluge room to close off flood paths.

from the Deluge Internal flooding events for the Switchgear Room into the 480V Rooms are not significant contributors for Byron AC Switchgear and are below the review threshold for SAMA Room identification.

065 Upgrade the This SAMA involves providing a hardwired Already included Alternate Safe connection from the Alternate Safe Shutdown Shutdown System to System power supply to a safety injection (SI)

Allow Timely pump to improve the probability that the Restoration of Seal operators can restore RCP seal cooling in a Injection and Cooling timely manner.

Byron does not have a similar system that could be enhanced for this function and the SAMA is not applicable to the site as written. However, SAMA 2, which was identified based on the PRA results, involves replacing existing equipment to provide an alternate means of seal cooling on failure of the running systems.

F.5.1.3.7 Industry SAMA Identification Summary The important issues for Byron are generally considered to be addressed by the SAMAs developed through the PRA importance list review. The plant changes suggested as part of that review were developed to meet the specific needs of the plant such that those SAMAs are more likely to provide effective means of risk reduction than SAMAs taken from other sites. However, effort was made to review other industry SAMA analyses to determine if other sites identified plant changes that could be cost beneficial for Byron based on modeling differences or other factors. For Byron, the industry review identified a potential alternate design for the implementation of the DMS that has been included in the Phase 1 SAMA list for consideration:

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2

• DMS Using a Dedicated Generator, Self-Cooled Charging Pump, and a Portable AFW Pump (SAMA 26)

F.5.1.4 BYRON IPE PLANT IMPROVEMENT REVIEW The Byron IPE, unlike many industry IPEs, did not document a definitive list of proposed plant enhancements. Instead, the IPE describes the Commonwealth Edison (ComEd) accident management program and how it was used to assess the IPE and Accident Management insights from the Byron, Braidwood and other ComEd plant IPEs, which were assessed together given that the insights were generally considered to be applicable to both the Byron and Braidwood sites. The discussion indicates that over 220 IPE and Accident Management insights were developed that were potentially applicable to PWRs and that they were evaluated by the review team; however, these insights are not specifically provided. A plant enhancement that is described in the IPE, a procedure modification to direct inter-unit 4 kV AC emergency bus cross-tie in non-SBO scenarios, was evaluated as part of the IPE process. The IPE includes a section documenting the impact of implementing the procedure, which was subsequently implemented at the site. One additional procedure enhancement, which was grouped in the Accident Management Guidance category, is described in the IPE. The insight was to update the plant procedures to direct reactor cavity flooding in core damage scenarios to provide a means of exterior vessel cooling. The IPE states that this potential procedure change was to be evaluated as part of the implementation of the Westinghouse Owners Group Severe Accident Management Guidance. No other specific proposed plant changes were identified in the IPE.

The table below summarizes the status of these changes for Byron:

Status of IPE Plant Enhancements Description of Potential Status of Disposition Enhancement Implementation Modify plant procedures to allow Implemented No further evaluation required.

inter-unit cross-tie for non-SBO conditions Update severe accident Implemented No further evaluation required.

guidelines to direct reactor cavity flooding to prevent reactor vessel failure The limited number of plant changes explicitly suggested in the IPE has been implemented at Byron and therefore no further review of these items is required.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.5.1.5 BYRON IPEEE PLANT IMPROVEMENT REVIEW Similar to the IPE, any proposed plant changes that were previously rejected based on non-SAMA criteria should be re-examined as part of this SAMA analysis. In addition, any issues that are in the process of being resolved should be examined because their resolutions could be important to the disposition of some SAMAs. The IPEEE was used to identify these items.

The only potential plant improvements identified in the Byron IPEEE were related to seismic initiators. The following table summarizes the status of the potential plant enhancements resulting from the IPEEE processes and the treatment of each in the SAMA analysis.

Status of IPEEE Plant Enhancements Description of Potential Enhancement Status of Disposition Implementation Control room ceiling diffusers are made of aluminum Resolved. No SAMAs Required and, if dislodged by a seismic event, may pose a personnel hazard (seismic)

Valve operator on 1(2)CV112E in contact with adjacent Resolved. No SAMAs Required plat form/steel grating.

Unanchored heat trace cabinet located in vicinity of Resolved No SAMAs Required MCC 1AP32E Multiple MCCs, battery chargers, and breakers were Resolved. No SAMAs Required.

found not to be tied together posing an impact issue (seismic).

The above plant changes suggested in the IPEEE have been resolved by the site and no further review is required.

F.5.1.6 EXTERNAL EVENTS IN THE BYRON SAMA ANALYSIS The IPEEE was used in the Byron SAMA analysis primarily to identify the highest risk accident sequences and the potential means of reducing the risk posed by those sequences. The types of events considered in the Byron external events analysis were identified by NUREG-1470 (NRC 1991) and included:

• Internal Fires

• Seismic Events

• High Winds and Tornadoes

• External Flooding

• Transportation and Nearby Facility Accidents

• Rail Transportation Accidents (treated as part of transportation and nearby facility accidents)

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2

• Barge Transportation Accidents

• Pipeline Transportation Accidents

• Military Facilities

• On-site Hazardous Material Accidents

• Severe Temperature Transients

• Severe Weather Storms

• Lightning Strikes

• External Fires

• Extraterrestrial Activity

• Volcanic Activity

• Abrasive Windstorms These potential contributors were evaluated using a progressive screening approach, per NUREG-1407, which resulted in the screening of most initiator types, but designated five initiators for further analysis:

• Internal Fires (Section F.5.1.6.1)

• Seismic Events (Section F.5.1.6.2)

• High Wind Events (Section F.5.1.6.3)

• External Floods (Section F.5.1.6.4)

• Transportation and Nearby Facility Accidents (Section F.5.1.6.5)

The external event types that were not explicitly evaluated in the IPEEE for Byron are considered to be negligible contributors to risk and they are excluded from further consideration in the SAMA identification process.

The types of information available for the initiators that were evaluated by Byron varies based on the manner in which they were addressed in the IPEEE and the Fire model. For instance, core damage frequency information was developed as part of the fire risk analysis while the seismic margins analysis does not directly provide any core damage frequency estimates.

Finally, a progressive screening approach was employed to address the other external events contributors that were considered to be applicable to the site and no quantitative information is available for those events.

While CDF results are available for fire events, the results are not necessarily compatible with those of the internal events analysis. For example, the Fire model is based on the NUREG/CR-6850 (EPRI 2005) methodology, which includes conservative approaches to address areas of uncertainty. This model is also in the development stage and it is not considered to be mature enough to use as a quantitative basis for detailed risk assessments. Finally, the fire model is Byron and Braidwood Stations, Units 1 and 2 Page F-59 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 not linked to the Level 2 PRA model and the consequences of the corresponding core damage scenarios are not available.

Because of the differences in the methods used to evaluate the external events risks, each of the external event contributors must be considered in a manner suiting the type of analysis performed. A summary of the review process used to identify SAMAs is provided for each of the external event types listed above followed by a description of the method used to quantitatively incorporate external events contributions into the SAMA analysis.

F.5.1.6.1 Internal Fires As discussed above, the techniques used to model external events vary according to the type of initiator being analyzed. For Byron, the 2009 Byron Fire PRA (Exelon 2009) is available for use in the SAMA analysis, but the model is considered to be an interim implementation of NUREG/CR-6850 given that not all tasks identified in that document are completely addressed or implemented in model. This was due to the graded approached used to develop the analysis and to the changing state-of-the-art methodologies at the time the analysis was developed.

The approach taken for the SAMA analysis is to use the fire model results to develop potential SAMAs and to use risk insights from both the fire and internal events PRA models to approximate potential averted cost-risk for the SAMAs. Even if it was considered appropriate to use the fire results directly for SAMA quantification, the fire model is not integrated with the most recent Level 2 and 3 analyses that are available to support the SAMA analysis, which prevents the evaluation of accident consequences in a manner consistent with the process used for the internal events models. Finally, the fire model is based on a previous revision of the PRA (Revision 6C) rather than the current revision (BB011b1), which introduces additional area of inconsistency.

While the fire model results are not necessarily comparable to the current PRA results, the SAMA analysis directly uses the fire CDF to develop the external events multiplier, as described in Section F.4.6.2.

The SAMA identification process for the fire model uses an IPEEE screening criterion to identify those fire contributors that are potentially significant to risk. Specifically, any fire zone with a CDF greater than the IPEEE screening threshold of 1.0E-06/yr was reviewed to identify potential SAMAs. Review of additional fire scenarios is possible, but this approach was chosen to limit the review of the interim model results to the largest contributors (the top 12 fire zones for Unit 1 and the top 14 fire zones for Unit 2 (26 fire zones in all)).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 The fire CDFs used to identify the fire zones for review are based on the Byron fire PRA scenario results, which include the fire ignition frequencies from EPRI 1016735 (EPRI 2008).

The fire scenario results for each zone were reviewed and grouped together to help identify target equipment that is common to multiple scenarios in a given fire zone. The reviews were performed and documented separately for the two units given that there are differences between them. The following tables provide a list of the fire zones with CDFs greater than 1.0E-06/yr.

Major Byron Unit 1 Fire Contributors Major Fire Zone Zone Description CDF Scenarios 11.3-0 D AUXILIARY BUILDING GENERAL AREA, ELV. 364 1.38E-05 11.6-0 F AUXILIARY BUILDING GENERAL AREA, ELV. 426 6.00E-06 DIVISION 11 engineered safety feature (ESF) 5.2-1 B, D 4.19E-06 SWITCHGEAR ROOM 11.3-1 B UNIT 1 CONTAINMENT PIPE PENETRATION AREA 3.98E-06 11.4-0 F AUXILIARY BUILDING GENERAL AREA, ELV. 383 3.79E-06 RADWASTE AND REMOTE SHUTDOWN PANEL 11.4C-0 V 3.58E-06 CONTROL ROOM 11.6C-0 A AUXILIARY BUILDING LAUNDRY ROOM 1.81E-06 17.2-2 A SX COOLING TOWER-DIV. 11/21 (BYR) 1.57E-06 SX TOWER ELECTRICAL EQUIPMENT ROOM, DIV.

18.14A-1 C 1.49E-06 12 (BYR) 5.1-1 B,D DIVISION 12 ESF SWITCHGEAR ROOM 1.27E-06 3.4A-1 A UNIT 1 CABLE RISER AREA ELV. 451 1.18E-06 UNIT 1 MAIN STEAM AND AUXILIARY FEEDWATER 18.3-1 A 1.13E-06 PIPE TUNNEL Byron and Braidwood Stations, Units 1 and 2 Page F-61 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Major Byron Unit 2 Fire Contributors Major Fire Zone Zone Description CDF Scenarios Division 22 containment electrical penetrations 11.6-2 A 2.05E-05 area 11.4-0 E Auxiliary building general area, elv. 383 1.40E-05 11.6-0 L Auxiliary building general area, elv. 426 1.06E-05 5.2-2 B, D Division 21 ESF switchgear room 6.51E-06 Radwaste and remote shutdown panel control 11.4c-0 Z 3.62E-06 room 1-2 A Unit 2 Containment 2.01E-06 11.3f-2 A Safety injection pump 2b room 1.84E-06 11.3g-2 A Centrifugal charging pump 2b room 1.84E-06 17.2-2 A SX Cooling Tower-Div. 11/21 (Byr) 1.69E-06 11.3a-2 A Safety injection pump 2a room 1.69E-06 18.14A-1 C Fuel handling building 1.75E-06 5.1-2 B, D Division 22 ESF switchgear room 1.56E-06 3.2-0 T4 Auxiliary building elv. 439 1.17E-06 5.5-2 Z, P, Q Unit 2 auxiliary electric equipment room 1.49E-06 For each fire zone with a CDF greater than 1.0E-06/yr, the contributing risk factors were reviewed to determine what measures could be taken to mitigate the fire event and the corresponding core damage sequences. Further discussion is provided for each of these fire compartments below.

U1: 11.3-0 (Scenario D), Auxiliary building general area, elv. 364 This fire scenario fails the heat removal medium for recirculation mode and fails the alternate room cooling for the division 2 injection pumps. Enhancements that would reduce the risk of these scenarios include SAMAs that improve secondary side heat removal capability and those that prevent seal LOCAs. Potential SAMAs include replacing the positive displacement pump (PDP) with a self-cooled, auto start pump for alternate RCP seal cooling (SAMA 2), installation of no-leak RCP seals (SAMA 4), installing alternate AFW pump cooling in conjunction with Byron and Braidwood Stations, Units 1 and 2 Page F-62 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 alternate RCP seal cooling (SAMA 13), completing the AFW crosstie (SAMA 15), and automating refill of the diesel driven AFW fuel oil tank (SAMA 18).

Fire scenario D is caused by a fire in MCC 132X1, which does propagate to other equipment.

The cables for the RH, SI, and CVCS pump cubicle cooler fans could potentially be protected to improve the likelihood that they will be available for injection and seal cooling (SAMA 27).

U1: 11.6-0 (Scenario F), Aux Building General Area, Elevation 426 This scenario is initiated in 480V MCC 134X, which leads to failure of a wide range of division 1 equipment, including: AFW, head vent valves (small LOCA), CCW, CVCS, and seal LOCAs are top contributors.

For the cases in which AFW is successful, recirculation mode is ultimately required for success due to the fire induced small LOCA condition, but having the ability to perform cooldown using secondary side heat removal provides an additional path to success that does not require the pressurizer PORVs. As a result, improving AFW reliability, which could be accomplished by implementing the AFW cross-tie (SAMA 15), would significantly reduce the risk of these scenarios. Another potential means of reducing the risk of these scenarios would be to provide automated makeup capability to the RWST to increase the time available for system cooldown to be performed (SAMA 14).

In addition, a notable contributor for this scenario is the operator failure to stop the RH pump when it is running without CC flow to the heat exchanger. A potential means of reducing the risk of this scenario is to change the procedures to direct initiation of CC flow to the RH heat exchangers when the pumps start (SAMA 7).

There are targets both above and around the ignition source and the installation of fire barriers around MCC 134X could potentially reduce the risk of these scenarios (SAMA 28).

U1: 5.2-1 (Scenarios B, D), Division 11 ESF Switchgear Room The larger contributor, fire scenario B, is initiated in 4KV bus 141, which results in failure of bus 141 and essentially all division 1 equipment.

Scenario D is initiated in bus 131X and results in failure of division 1 safety related 480V AC power, which has a similar impact to scenario B.

In these cases, the SG makeup function is important and the AFW cross-tie (SAMA 15) is a means of improving the availability of this function. The DMS could provide SG makeup capability (SAMA 11).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 In these scenarios, loss of the equipment occurs due to failure of the ignition source and the means of preventing loss of the equipment is limited to enhancements that prevent the fire from developing. Incipient fire detectors are a potential means of accomplishing this goal; however, the reliability of incipient detectors to prevent fires has neither been established nor accepted in the industry, and this enhancement is not suggested as a SAMA.

U1: 11.3-1 (Scenario B), Unit 1 Containment Pipe Penetration Area Fires in this scenario essentially fail all high pressure injection (HPI), division 1 recirculation, division 1 secondary side heat removal, RCP seal cooling to 2 of 4 pumps directly and the remaining 2 by loss of RWST inventory to the sump (with failure of the volume control tank (VCT) path).

The fire ignition source for this scenario is MCC 131X1, the failure of which results in the loss of the equipment identified above. Because the fire induced failures identified above are the result of damage to the ignition source for the fire scenario, the means of preventing loss of the equipment is limited to enhancements that prevent the fire from developing. Incipient fire detectors are a potential means of accomplishing this goal; however, the reliability of incipient detectors to prevent fires has neither been established nor accepted in the industry, and this enhancement is not suggested as a SAMA.

Installation of no leak RCP seals (SAMA 4) would prevent primary side inventory loss and reduce the risk from these fire scenarios. Completing the implementation of the AFW cross-tie enhancement would provide an alternate means of secondary side heat removal (SAMA 15).

Implementation of the DMS may also provide a means of mitigating the scenarios (SAMA 11).

U1: 11.4-0 (Scenario F), Auxiliary Building General Area, Elevation 383 Fire scenario F is initiated in AFW pump 1A or 2A, which results in failure of the division 1 AFW pumps for both units and the Unit 1 division 2 AFW pump.

For cases with only one AFW pump in the opposite unit, the AFW cross-tie is assumed to be unavailable.

Primary system cooling is available for these fire scenarios, but the operator failures lead to core damage. The DMS could potentially provide alternate secondary side heat removal capability, but operator action dependence issues would limit its benefit for the largest contributors (e.g., with recirculation start or RH pump trip for pump operation without CC flow to the RH HX). SAMAs that could reduce the risk of these scenarios include a procedure change Byron and Braidwood Stations, Units 1 and 2 Page F-64 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 to align CCW flow to the RH Heat Exchanges on RH pump start (SAMA 7) and automating the swap to recirculation mode (SAMA 29).

Protecting the AFW 1B and 2A pumps and cables in the Aux Building General Area, Elevation 383, is a potential means of improving the probability that these pumps will remain available for SG makeup after these fires (SAMA 30).

U1: 11.4c-0 (Scenario V), Radwaste and Remote Shutdown Panel Control Room This fire scenario includes seal cooling failure (CCW and CVCS), AFW failure, high pressure injection failure (CVCS), and failure of the Unit 1 SX system (no containment heat removal).

These failures can potentially be mitigated by the DMS capabilities; the portable SG injection pump can be used to provide SG makeup (through the FW connection point to bypass the AFW valve failures, in this case) and the no leak seals would maintain primary side inventory with makeup from an alternate 480V pump (SAMA 11). Installation of a diesel driven SX pump could also provide a potential success path (SAMA 1).

For this scenario, the ignition sources are the Unit 1 remote shutdown control panels (1PL04J, 1PL05J and 1PL06J). Because the fire induced failures identified above are the result of damage to the ignition source for the fire scenario, the means of preventing loss of the equipment is limited to enhancements that prevent the fire from developing. Incipient fire detectors are a potential means of accomplishing this goal; however, the reliability of incipient detectors to prevent fires has neither been established nor accepted in the industry, and this enhancement is not suggested as a SAMA.

U1: 11.6c-0 (Scenario A), Auxiliary building laundry room This scenario is a bounding fire that is based on the total initiating event frequency for the zone, which in this zone consists of all transient initiators.

The consequences of the fire are fairly broad and include division 1 power (including the 141-241 4 kV X-tie) and multiple failures of division 1 equipment (which are already unavailable due to the power failure).

The largest contributors to the consequential CDF for this scenario are failures of the division 2 AFW pump, division 2 SX equipment failures, and division 2 RHR system failures.

These failures can potentially be mitigated by the DMS capabilities; the portable SG injection pump can be used to provide SG makeup and the no leak seals would maintain primary side inventory (SAMA 11).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 No practical SAMAs have been identified to prevent the transient fires in this fire zone and because the fire is a bounding fire, no specific information is available regarding fire propagation or ignition sources that would help identify effective equipment protection methods.

U1: 17.2-2 (Scenario A), SX Cooling Tower-Div. 11/21 In this bounding fire scenario, the fire induced failures include SX cooling tower cells A through D (for those that are in standby). Other random failures contribute to the loss of SX.

Loss of SX leads to RCP seal LOCAs in cases where alternate cooling to the charging pumps fails. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Instead of replacing the PDP to protect the RCP seals, a passive means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4). The DMS expands on the inclusion of the no-leak seals to include a portable, long term SG makeup capability and primary side makeup pump (SAMA 11).

Because the fire is a bounding scenario, fire scenarios are not developed for all of the specific ignition sources in the fire zone, which limits the potential for fire specific SAMA identification.

U1: 18.14A-1 (Scenario C), SX Tower Electrical Equipment Room In this scenario, the fire induced failures include SX cooling tower cells E and F as well as multiple SX basin makeup sources.

Loss of SX leads to RCP seal LOCAs in cases where alternate cooling to the charging pumps fails. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Instead of replacing the PDP to protect the RCP seals, a passive means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4). The DMS expands on the inclusion of the no-leak seals to include a portable, long term SG makeup capability and primary side makeup pump (SAMA 11).

In this scenario, loss of the equipment occurs due to failure of the ignition source and the means of preventing loss of the equipment is limited to enhancements that prevent the fire from developing. Incipient fire detectors are a potential means of accomplishing this goal; however, the reliability of incipient detectors to prevent fires has neither been established nor accepted in the industry, and this enhancement is not suggested as a SAMA.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 U1: 5.1-1 (Scenarios B, D), Division 12 ESF Switchgear Room These scenarios are the result of a fire initiating in the B 4KV ESF bus or the B 480V ESF bus. These fires essentially eliminate an entire division of equipment. The largest contributors to these fire scenarios are failures of the SX system, including operator failure to start the standby SX pump on loss of the running pump, A SX pump maintenance, and failure of the A SX pump min flow path. These failures could be mitigated by installing a diesel driven SX pump train (SAMA 1) or automating start of the standby SX pump on low pressure (SAMA 3).

Implementation of the DMS would also provide an alternate means of providing heat removal without SX (SAMA 11).

U1: 3.4A-1 (Scenario A), Unit 1 Cable Riser Area Elevation 451 In this bounding fire scenario, the fire induced failures include an extensive amount of equipment including thermal barrier cooling, both divisions of HPI, and division 1 of AFW, EDG, SX, CCW, SI, and division 1 emergency 480V AC power.

These scenarios lead to loss of RCP seal cooling and seal LOCAs are a considerable risk.

Installation of no leak RCP seals (SAMA 4) would prevent primary side inventory loss and reduce the risk from these fire scenarios. The PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2).

Completing the implementation of the AFW cross-tie enhancement would provide an alternate means of secondary side heat removal (SAMA 15). The DMS expands on the inclusion of the no-leak seals to include a portable, long term SG makeup capability and primary side makeup pump (SAMA 11).

Because the fire is a bounding scenario, fire scenarios are not developed for all of the specific ignition sources in the fire zone, which limits the potential for fire specific SAMA identification.

U1: 18.3-1 (Scenario A), Unit 1 Main Steam and Auxiliary Feedwater Pipe Tunnel In this bounding fire scenario, the fire induced failures include failure of the low steam line pressure signal, failure of the main steam isolation valve isolation capability, and failure of both divisions of AFW (due to closure of all AFW isolation valves, which precludes use of the AFW X-tie).

The existing procedures include guidance to locally open the AF013A-H valves when verifying AFW flow after a system start, but this action is not credited in the model. If this action were included and credited, the frequency of these scenarios would be reduced and SAMAs would not be required.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Enhancements could be performed that would further reduce risk, however. Given that Feedwater/Condensate system is not credited, heat removal must be performed through initiation of feed and bleed and recirculation cooling for heat removal. Improving the reliability of these functions would reduce the risk of these fire scenarios. SAMAs that could accomplish this include a procedure change to align CCW flow to the RH Heat Exchanges on RH pump start (SAMA 7) and automating the swap to recirculation mode (SAMA 29).

Because the fire is a bounding scenario, fire scenarios are not developed for all of the specific ignition sources in the fire zone, which limits the potential for fire specific SAMA identification.

UNIT 2 U2: 11.6-2 (Scenario A), Division 22 Containment Electrical Penetrations Area In this bounding fire scenario, the fire induced failures result in a loss of a wide range of division 2 equipment, including AFW, SI, RHR, the 2B EDG, and SX. Also, thermal barrier cooling and both charging pumps are failed in addition to MCC 231X4. These failures result in a loss of RCP seal cooling, which results in an RCP seal LOCA in most of the contributors.

Installing the no-leak seals is a potential means of addressing this fire scenario (SAMA 4).

The PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Implementation of the DMS would also address the cases in which the seals do not fail through the SG makeup capability, but the cost of the additional scope of the DMS for only 10% of this fire scenario would not be cost beneficial. A smaller portion of the contribution is associated with the failure to stop the RH pumps when CC is not flowing to the RH heat exchangers. A potential means of reducing the risk of this scenario is to change the procedures to direct initiation of CC flow to the RH heat exchangers when the pumps start (SAMA 7).

Because the fire is a bounding scenario, fire scenarios are not developed for all of the specific ignition sources in the fire zone, which limits the potential for fire specific SAMA identification.

U2: 11.4-0 (Scenario E), Auxiliary Building General Area, Elevation 383 Fire scenario E is initiated in 480V MCC 232X1, which results in failure of SX pump 2B, SX unit 2 CC HX outlet, AFW pump 2B, charging pump 2B, RH pump 2B, SI pump 2B, EDG 2B, and others. Most of the failures are related to loss of the ignition source.

In most scenario E cases, an additional SX hardware failure eliminates the last remaining heat sink, and core damage occurs. The AFW cross-tie would help mitigate these failures by providing a heat sink that is not dependent on the units SX system (SAMA 15). Seal LOCAs Byron and Braidwood Stations, Units 1 and 2 Page F-68 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 are also a contributor, which could be addressed by no-leak seals (SAMA 4). For scenario B, the largest contributors to the conditional core damage probability are failures of the B AFW pump, including the failure to refill the diesel fuel oil tank and multiple pump hardware failures.

Automating the refill function would reduce the contribution of these scenarios (SAMA 18).

AFW B hardware failures could be mitigated with the AFW cross-tie (SAMA 15).

In this scenario, the fire induced damage is primarily the result of the loss of the ignition source, so fire barriers would provide little benefit for this scenario. Because many of the fire induced failures identified above are the result of damage to the ignition source for the fire scenario, the means of preventing loss of the equipment is limited to enhancements that prevent the fire from developing. Incipient fire detectors are a potential means of accomplishing this goal; however, the reliability of incipient detectors to prevent fires has neither been established nor accepted in the industry, and this enhancement is not suggested as a SAMA.

U2: 11.6-0 (Scenario L), Aux Building General Area, Elevation 426 Scenario L is initiated in 480V MCC 234X, which results in the failure of essentially an entire division of safety equipment (division 1). Thermal barrier cooling is also failed and AFW B is failed due to loss of flow to 3 of 4 SGs due to AFW isolation valve closure (prevents all SG makeup through the AFW system).

Seal LOCAs are could be addressed by no-leak seals (SAMA 4). Alternatively, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2).

For cases such as these where AFW is not available, improving the reliability of recirculation mode and RH availability would reduce risk. SAMAs that could accomplish this include a procedure change to align CCW flow to the RH Heat Exchanges on RH pump start (SAMA 7) and automating the swap to recirculation mode (SAMA 29).

For scenario L, installing cable wrap to protect the 2AF013A, B, and D cables would help preserve the AFW function and reduce the risk of this scenario (SAMA 31).

U2: 5.2-2 (Scenarios B, D), Division 21 ESF Switchgear Room These fire scenarios result in wide range of failures that essentially eliminate an entire division (division 1) of equipment and the division 1 inter-unit 4kV cross-tie.

One of the larger contributors to the conditional core damage probability for the scenario is the operator failure to refill the DG B fuel oil tank. Automating the refill capability would help reduce the risk from these fires (SAMA 18). An additional contributor is failure to start the standby SX Byron and Braidwood Stations, Units 1 and 2 Page F-69 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 pump on loss of the initially running pump; this could be addressed by automating start of the standby pump (SAMA 3). Another contributor is the failure of the operators to establish a cool suction source for the charging pumps on loss of SX. Replacing the existing PDP with a self-cooled charging pump with auto start capability would mitigate these scenarios (SAMA 2).

Installation of no-leak RCP seals is another means of addressing the failure of seal cooling (SAMA 4).

Fire scenario B is caused by a fire in 4160V switchgear 241, which results in the loss of most of the critical loads for this scenario. Because the fire induced failures identified above are the result of damage to the ignition source for the fire scenario, the means of preventing loss of the equipment is limited to enhancements that prevent the fire from developing. Incipient fire detectors are a potential means of accomplishing this goal; however, the reliability of incipient detectors to prevent fires has neither been established nor accepted in the industry, and this enhancement is not suggested as a SAMA. Fire scenario D occurs in the 231X switchgear and similarly, the impact from this fire is mostly caused by loss of the ignition source.

U2: 11.4C-0 (Scenario Z), Radwaste and Remote Shutdown Panel Control Room This fire scenario includes CCW failure, AFW failure, high pressure injection failure (CVCS pumps), and failure of the Unit 2 SX system (no containment heat removal).

These failures can potentially be mitigated by the DMS capabilities; the portable SG injection pump can be used to provide SG makeup (through the FW connection point to bypass the AFW valve failures, in this case) and the no leak seals would maintain primary side inventory with makeup from an alternate 480V pump (SAMA 11). Installation of a diesel driven SX pump could also provide a potential success path (SAMA 1).

For this scenario, the ignition sources are the Unit 2 remote shutdown control panels (2PL04J, 2PL05J and 2PL06J). Because the fire induced failures identified above are the result of damage to the ignition source for the fire scenario, the means of preventing loss of the equipment is limited to enhancements that prevent the fire from developing. Incipient fire detectors are a potential means of accomplishing this goal; however, the reliability of incipient detectors to prevent fires has neither been established nor accepted in the industry, and this enhancement is not suggested as a SAMA.

U2: 1-2 (Scenario A), Unit 2 Containment In this bounding fire scenario, the fire induced failures include a LOCA through the reactor head vent, failure to re-seat of the PORVs, failure of the block valves to open (if they are initially Byron and Braidwood Stations, Units 1 and 2 Page F-70 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 closed), failure of the low pressurizer pressure signal for SI, and failure of the high pressure recirculation suction path for both divisions of the CV/SI pumps (through CV8804A and SI8804B), and loss of the RCFC low speed mode on all fans.

For the cases in which AFW is successful, recirculation mode is ultimately required for success due to the fire induced small LOCA condition, but having the ability to perform cooldown using secondary side heat removal provides an additional path to success that does not require the pressurizer PORVs. As a result, improving AFW reliability, which could be accomplished by implementing the AFW cross-tie (SAMA 15), would significantly reduce the risk of these scenarios. Another potential means of reducing the risk of these scenarios would be to provide makeup capability to the RWST to increase the time available for system cooldown to be performed (SAMA 14).

Because the fire is a bounding scenario, fire scenarios are not developed for all of the specific ignition sources in the fire zone, which limits the potential for fire specific SAMA identification.

Given that the RCPs are the largest contributors to the ignition frequency, a potential means of reducing the fire frequency would be through a mechanism to prevent the fire. Incipient fire detectors are a potential means of accomplishing this goal; however, the reliability of incipient detectors to prevent fires has neither been established nor accepted in the industry, and this enhancement is not suggested as a SAMA.

U2: 11.3F-2 (Scenario A), Safety Injection Pump 2B Room In this bounding fire scenario, the fire induced failures include failure of the division 1 RWST low-low level signal for auto opening of 2SI8811A, failure of the high pressure recirculation suction path for both divisions of the CV/SI pumps (through CV8804A and SI8804B), and loss of SI pump 2B.

Without high pressure recirculation capability, the importance of AFW for heat removal is high.

As a result, improving AFW reliability, which could be accomplished by implementing the AFW cross-tie (SAMA 15), would significantly reduce the risk of these scenarios. The impact of this fire is likely overstated given that the model does not credit existing procedures that direct the operators to locally open the valves if they do not open remotely (and at least the CV8804A valve would be accessible).

Because the fire is a bounding scenario, fire scenarios are not developed for all of the specific ignition sources in the fire zone, which limits the potential for fire specific SAMA identification.

U2: 11.3G-2 (Scenario A), Centrifugal Charging Pump 2B Room Byron and Braidwood Stations, Units 1 and 2 Page F-71 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 In this bounding fire scenario, the fire induced failures include failure of charging pump 2B and the high pressure recirculation suction path for both divisions of the CV/SI pumps (through CV8804A and SI8804B).

Without high pressure recirculation, the importance of AFW for heat removal is increased. As a result, improving AFW reliability, which could be accomplished by implementing the AFW cross-tie (SAMA 15), would significantly reduce the risk of these scenarios. Automating the refill function for the diesel driven AFW fuel oil tank would also reduce the contribution of these scenarios (SAMA 18). The impact of this fire is likely overstated given that the model does not credit existing procedures that direct the operators to locally open the valves if they do not open remotely (and at least the CV8804A valve would be accessible).

Because the fire is a bounding scenario, fire scenarios are not developed for all of the specific ignition sources in the fire zone, which limits the potential for fire specific SAMA identification.

U2: 17.2-2 (Scenario A), SX Cooling Tower-Div. 11/21 In this bounding fire scenario, the fire induced failures include SX cooling tower cells A through D (for those that are in standby). Other random failures contribute to the loss of SX.

Loss of SX leads to RCP seal LOCAs in cases where alternate cooling to the charging pumps fails. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Instead of replacing the PDP to protect the RCP seals, a passive means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4). The DMS expands on the inclusion of the no-leak seals to include a portable, long term SG makeup capability and primary side makeup pump (SAMA 11).

Because the fire is a bounding scenario, fire scenarios are not developed for all of the specific ignition sources in the fire zone, which limits the potential for fire specific SAMA identification.

U2: 11.3A-2 (Scenario A), Safety Injection Pump 2A Room In this bounding fire scenario, the fire induced failures include failure of failure of SI pump 2A, the high pressure recirculation suction path for both divisions of the CV/SI pumps (through CV8804A and SI8804B), and the CV/SI suction cross-tie valves.

Without high pressure recirculation capability, the importance of AFW for heat removal is high.

As a result, improving AFW reliability, which could be accomplished by implementing the AFW cross-tie (SAMA 15), would significantly reduce the risk of these scenarios. Automating the refill function for the diesel driven AFW fuel oil tank would also reduce the contribution of these Byron and Braidwood Stations, Units 1 and 2 Page F-72 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 scenarios (SAMA 18). The impact of this fire is likely overstated given that the model does not credit existing procedures that direct the operators to locally open the valves if they do not open remotely (and at least the CV8804A valve would be accessible).

Because the fire is a bounding scenario, fire scenarios are not developed for all of the specific ignition sources in the fire zone, which limits the potential for fire specific SAMA identification.

U2: 5.1-2 (Scenarios B, D), Division 22 ESF Switchgear Room These fire scenarios result in wide range of failures that essentially eliminate an entire division (division 2) of equipment and the division 2 inter-unit 4kV cross-tie.

One of the larger contributors to the conditional core damage probability for the scenario is the operator failure to refill the DG B fuel oil. Automating the refill capability would help reduce the risk from these fires (SAMA 18). A smaller contributor is failure to start the standby SX pump on loss of the initially running pump; this could be addressed by automating start of the standby pump (SAMA 3). Another contributor is the failure of the operators to establish a cool suction source for the charging pumps on loss of SX. Replacing the existing PDP with a self-cooled charging pump with auto start capability would mitigate these scenarios (SAMA 2). Installation of no-leak RCP seals is another means of addressing the failure of seal cooling (SAMA 4).

Fire scenario B is caused by a fire in 4160V switchgear 242, which results in the loss of most of the critical loads for this scenario. Because the fire induced failures identified above are the result of damage to the ignition source for the fire scenario, the means of preventing loss of the equipment is limited to enhancements that prevent the fire from developing. Incipient fire detectors are a potential means of accomplishing this goal; however, the reliability of incipient detectors to prevent fires has neither been established nor accepted in the industry, and this enhancement is not suggested as a SAMA. Fire scenario D occurs in the 232X switchgear and similarly, the impact from this fire is mostly caused by loss of the ignition source.

U2: 3.2-0 (Scenario T4), Auxiliary Building Elevation 439 In this transient fire scenario, the fire induced failures are widespread and include failure of AFW 2B, thermal barrier cooling, RCP seal injection path for pumps B and C, CCW 2B, the B CC to RH Heat exchanger path, charging pump 2B, DG 2B, SX pump 2B, Unit 2 SX heat exchanger outlet path (no flow), SX cross-tie line failure, and 2SX034 fails closed (fails all SX with other failures).

For these cases, there is a complete loss of RCP seal cooling for half of the pumps and seal LOCAs are a driving concern. Installation of no-leak RCP seals is the most means of Byron and Braidwood Stations, Units 1 and 2 Page F-73 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 addressing the failure of seal cooling, but because all SX is lost, an alternate SG makeup source is required. The DMS provides these capabilities (SAMA 11).

This areas is a frequently travelled area of the plant and completely eliminating work or transportation of potential ignition sources through the area is not likely feasible, but in without other alternatives, such measures could be considered. In this case, however, there are existing plant procedures to operate valves that are assumed to fail closed that are not credited in the PRA (for example, opening the SX cross-tie valve could be performed locally to restore SX). If these procedures were credited, the risk of this scenario would be reduced below the review threshold and no additional SAMAs are suggested.

U2: 5.5-2 (Scenarios Z, P, Q), Unit 2 Auxiliary Electric Equipment Room The Z scenario includes failure of both AFW pumps and a majority of the conditional core damage probability is associated with two operator actions: failure to align recirculation mode, and failure to stop the RHR pumps when they are running without CC cooling to the heat exchangers. SAMAs that could reduce the risk of these scenarios include a procedure change to align CCW flow to the RH Heat Exchanges on RH pump start (SAMA 7), and automating the swap to recirculation mode (SAMA 29).

The P scenario includes fire induced failures of AFW A, thermal barrier cooling, A division of CVCS RWST suction, sump suction valve 2SI8811A, and DG 2A. Larger contributors to the conditional core damage probability include operator failures to refill the B AFW fuel oil tank, align recirculation mode, and to stop the RHR pumps when they are running without CC cooling to the heat exchangers. SAMAs that could reduce the risk of these scenarios include automating the AFW diesel fuel oil refill function (SAMA 18), a procedure change to align CCW flow to the RH Heat Exchanges on RH pump start (SAMA 7), and automating the swap to recirculation mode (SAMA 29). Completing the AFW cross-tie would also impact some of the risk (SAMA 15). RCP seal LOCAs are additional contributors that could be addressed with no-leak RCP seals (SAMA 4) or DMS (SAMA 11).

Fire scenario Q is essentially the division 2 version of scenario P and the same SAMAs are applicable.

E.5.1.6.1.1 Fire SAMA Identification Summary Based on a review of the Byron fire area results, four (4) additional SAMAs have been identified for inclusion in the Phase 1 SAMA list:

• Protect RH, SI, and CVCS Cubicle Cooling Fan Cables in Fire Zone 11.3-0 (SAMA 27)

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2

• Install Fire Barriers around MCC 134X (SAMA 28)

• Protect AFW Cables in the Aux Building General Area, Elevation 383' (SAMA 30)

• Protect Cables for 2AF013A, B, and D in the Aux Building General Area, Elevation 426' (SAMA 31)

F.5.1.6.2 Seismic Events The IPEEE (ComEd 1996) indicates that the EPRI seismic margins methodology was used to identify the minimal set of equipment required to safely shut the reactor down and to determine if that equipment is capable of surviving the Review Level Earthquake (RLE). The RLE, which is generally larger than the design basis earthquake, is a seismic event determined by a combination of the sites seismic hazard and seismic design basis that is intended to challenge the plant and identify the weak links for seismic events that are larger than the RLE. Equipment that is not capable of withstanding the RLE, which at Byron is a 0.3g event that results in a peak acceleration value of 0.636g at 8 Hz, is identified and required to be addressed. While methods exist for using this information to develop a figure of merit, it is not technically equivalent to a core damage frequency and was not performed as part of the Byron IPEEE.

It should also be noted that even in a seismic probabilistic risk assessment, the pedigree of information is not equivalent to what is used in the internal events models. Given that there is a limited amount of seismic response information available for nuclear power plants, analysis techniques developed to model the plant response often compensate by ingraining a conservative bias in their methodologies to prevent overestimating the capabilities of the plants.

While seismic risk evaluations are helpful in the identification of potential plant weaknesses, the degree of uncertainty in the CDF and other results is likely significantly larger than for internal events. With these limitations in mind, the Byron IPEEE seismic results and history were reviewed in order to determine if there were any unresolved issues that could impact Byron risk.

The issues of potential interest included:

• Unfinished plant enhancements that were determined to be required to ensure the equipment on the Safe Shutdown List would be capable of withstanding the RLE.

• Additional plant enhancements that were identified as a means of reducing plant risk, but were not implemented at the plant.

An effort was also made to use the results of the equipment and structural screening documentation to determine if any outlier issues there were screened in the IPEEE could impact seismic risk at Byron.

The conclusion of the seismic analysis for Byron was that the plant HCLPF is greater than 0.30g peak ground acceleration (PGA) and no programmatic issues were identified. However, Table Byron and Braidwood Stations, Units 1 and 2 Page F-75 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 3.3 of the IPEEE documents the outliers that were identified as part of the seismic capacity assessments. These are generally items with potential seismically induced interaction issues for which it was difficult to calculate a High Confidence of Low Probability of Failure value.

Those that were not clearly identified as resolved in the IPEEE are identified below in conjunction with their dispositions for the SAMA analysis.

Summary of Seismic Outlier Resolutions Equipment ID # Outlier Finding 1 SAMA Disposition 1(2)CV112E Valve operator is in contact with Evaluations have determined that the adjacent platform steel/grating, affected piping systems and valve are which poses an impact hazard. adequate with the reduced clearance.

Also, for 2CV112E, the grating has been modified.

No SAMAs are considered to be required.

1(2)AP25E Seismic interaction concern. Not Bolted adjacent MCCs together as required.

bolted to adjacent MCC No SAMAs are considered to be required.

1(2)AP44E and may impact MCC during seismic event.

1(2)AP27E Seismic interaction concern. Not Bolted adjacent MCCs together as required.

bolted to adjacent MCC No SAMAs are considered to be required.

1(2)AP47E and may impact MCC during seismic event.

1AP11E, 1AP13E Shipping bolts securing internal Bolts tightened during B1R08.

Transformers coils to frame are not tight No SAMAs are considered to be required.

(approximate 1/4-1/2 gap as nut is backed off).

1AP10E Seismic interaction concern. Seismic interaction issues were addressed.

2AP06E Adjacent, unanchored spare No SAMAs are considered to be required.

breakers(s) poses an interaction 2AP10E hazard.

2AP12E Switchgear 1(2)DC03E Adjacent cabinets not bolted Evaluation has determined that 1(2)DC05E together. consequences of relay chatter can be resolved by a proceduralized operator action.

No SAMAs are considered to be required.

1 Plant resolutions are based on the information provided in the plant seismic walkdown reports (Exelon 2012a, Exelon 2012b) unless otherwise noted.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Summary of Seismic Outlier Resolutions Equipment ID # Outlier Finding 1 SAMA Disposition 1IP05E Interaction (impact) concern with Duct box was secured to fan cabinet during 1IP07E adjacent filter duct box which is B1R08. No SAMAs are considered to be unsecured. required.

1IP06E 1IP08E 2DC04E Adjacent cabinets not bolted Evaluation has determined that 2DC06E together. consequences of relay chatter can be resolved by a proceduralized operator action.

No SAMAs are considered to be required.

1RD05E Seismic interaction concern. Not A plant evaluation (NTS #454-240-96-146-2RD05E bolted to adjacent 1(2)RD03E. 11A) has determined that consequences of May impact during seismic event. relay chatter are either an annunciator in the MCR or a reactor trip signal, which are acceptable and desirable conditions for the plant after a seismic event..

No SAMAs are considered to be required.

1(2)AP92E Not tied to adjacent MCC. As indicated in plant drawings (6E-0-3502 1(2)AP93E (Note 10), 6E-0-3507 (Note 9), and 6E 3391BE), the cabinets have been tied together, which was confirmed by a plant walkdown. Breakers were relocated in designated areas where no interaction hazard exists.

No SAMAs are considered to be required.

2IP06E Interaction (impact) concern with Fire extinguisher brackets secured.

2IP08E adjacent fire extinguisher (A No SAMAs are considered to be required.

27) which has an open (unsecured) retaining bracket.

2AP98E One shipping bolt securing Bolts were tightened during B2R07.

internal coils to frame is not tight No SAMAs are considered to be required.

(approximate 1/4 gap as nut is backed off).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Summary of Seismic Outlier Resolutions Equipment ID # Outlier Finding 1 SAMA Disposition 0PM01J Unsecured aluminum diffusers in Analysis was performed which evaluated the 0PM02J suspended ceiling pose a diffusers capacity for withstanding a seismic personnel hazard to operators if event of a magnitude required by the IPEEE 1PM01J they are dislodged due to seismic without an adverse effect. Conclusively, the 1PM04J motion. ceiling diffusers are capable of withstanding 1PM05J a seismic event of a magnitude required by 1PM06J the IPEEE without adverse effect.

1PM07J 1PM11J 1PM12J 2PM01J 2PM04J 2PM05J 2PM06J 2PM07J 2PM11J 2PM12J 1(2)PA01J Adjacent cabinets not bolted Interactions were evaluated that addressed 1(2)PA02J together. the loads for panels and concluded that they were acceptable when linked together.

1(2)PA03J Vendor walkdown confirmed these cabinets 1(2)PA04J to be linked together.

1(2)PA06J No SAMAs are considered to be required.

1(2)PA07J 1(2)PA08J 1(2)PA09J 1(2)PA10J 1(2)PA11J 1(2)PA12J 1(2)PA13J 1(2)PA14J 1(2)PA27J 1(2)PA28J 1(2)PA33J 1(2)PA34J 1(2)PA51J 1PA52J Byron and Braidwood Stations, Units 1 and 2 Page F-78 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.5.1.6.3 High Winds and Tornadoes The approach taken to analyze the high wind, flood, transportation and nearby facility, and other external event risk in the Byron IPEEE was to implement a progressive screening approach. The first three steps included 1) a review of Byron specific hazard data and licensing basis, 2) identification of significant changes since Operating License issuance, and 3) verification that the Byron design met the 1981 Standard Review Plan (SRP) criteria (in NUREG-1407, the 1975 SRP criteria are specified, but the 1981 SRP was determined to be equivalent for use as an IPEEE screening tool). An affirmative determination that the 1981 SRP screening criteria were met resulted in the screening of the hazard on the basis that conformance to the SRP met the IPEEE screening criterion.

For the SAMA analysis, this process is considered adequate for screening events that do not pose a credible threat to plant operations. However, any issues that could impact plant safety are reconsidered to determine if the development of a SAMA is appropriate to address the risk.

For Byron, no high wind or tornado vulnerabilities were identified in the IPEEE and there are no relevant potential plant enhancements.

In conclusion, no high wind or tornado related SAMAs are required for Byron.

F.5.1.6.4 External Floods For external flooding events, Byron Station was determined to meet the NRCs SRP for external flooding and these types of events were screened from further review. The IPEEE indicates that roof loading and grade level effects were considered related to Probable Maximum Precipitation (PMP) or Probable Maximum Flooding (PMF) events.

For PMP events, the IPEEE indicated that even under the worst postulated conditions, the roof design loads were not exceeded.

Flooding as a result of PMP or PMF effects was determined to not challenge the plant.

Maximum Flood levels from the Rock River were determined to peak at 708.3 feet mean sea level while plant grade is 870 feet mean sea level. The river screen house would be flooded by the PMF and the essential service water makeup pumps would fail, but the deep well makeup pumps have been qualified to survive the design basis seismic event and would be available as a backup source.

For PMP events with short term pooling of water at plant grade, plant structures were found to be protected by curbed entries that would prevent water incursion.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 For Byron, no external flooding vulnerabilities were identified in the IPEEE and there are no relevant potential plant enhancements.

F.5.1.6.5 Transportation and Nearby Facility Accidents Transportation and nearby facility accidents were included in the Byron IPEEE to account for human errors or equipment failures that may occur in events not directly related to the power generation process at the plant. The types of hazards considered for analysis included:

• Ground Transportation Accidents

• Accidents at Nearby Facilities

• Aircraft Accidents Both road and rail shipments in the area of the plant were evaluated by the NRC using the criteria in the SRP. No conditions were identified that posed a significant risk to the site and these types of events were screened from further consideration in the IPEEE. No SAMAs, therefore, are required to address these types of events.

The potential for nearby facility accidents was reviewed in the IPEEE and it was determined that of the facilities located near the plant, none posed a significant risk to the plant. A number of nearby industries and facilities ranging from manufacturing facilities for building materials and parts for quarries were identified, no conditions were identified that posed a significant risk to the site and events at nearby facilities were screened from further consideration in the IPEEE.

No SAMAs, therefore, are required to address these types of events.

It is recognized that the types of credible threats to nuclear facilities by aircraft have changed since the time the IPEEE was published. While this is true, efforts are underway within the industry to address this issue in conjunction with other forms of sabotage. Based on the fact that this topic is currently being analyzed in another forum and due to the complexity of the issue, intentional aircraft impact events are considered to be out of the scope of the SAMA analysis. Accidental aircraft impact was reviewed in the IPEEE and while it was determined that 4 airports are located within 10 miles of the site, the centerline for the closest low altitude airway was 5 miles from the plant. The conclusion in the IPEEE was that the SRP acceptance criteria were met and accidental aircraft impact posed no significant threat to plant operations. No SAMAs, therefore, are required to address these types of events.

F.5.2 PHASE 1 SCREENING PROCESS The initial list of SAMA candidates is presented in Table F.5-3. The process used to develop the initial list is described in Section F.5.1.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 The purpose of the Phase 1 analysis is to use high-level knowledge of the plant and SAMAs to preclude the need to perform detailed cost-benefit analyses on them. The following screening criteria were used:

• Applicability to the Plant: If a proposed SAMA does not apply to the Byron design, it is not retained. Similarly, any SAMAs that have already been implemented by Exelon or achieve results that Exelon has achieved by other means can be screened as they are not applicable to the current plant design. These criteria are not often explicitly used in the Phase I analysis because the SAMA identification methodology generally excludes such SAMAs; however, they are listed as a possible screening method given that there may be circumstances in which a SAMA would be included in the list even if it is not relevant to the site. An example may be the inclusion of a high profile SAMA that is well known in the industry, but not applicable to the specific site design. Such a SAMA may be included for documentation purposes. Another example may be an unimplemented SAMA from the IPE that has been superseded by another plant enhancement.

• Implementation Cost Greater than Screening Cost: If the estimated cost of implementation is greater than the modified MACR (refer to Section F.4.6), the SAMA cannot be cost beneficial and is screened from further analysis.

Table F.5-3 provides a description of how each SAMA was dispositioned in Phase 1. Those SAMAs that required a more detailed cost-benefit analysis are passed to the Phase 2 analysis and evaluated in Section F.6. Table F.6-1 contains the Phase 2 SAMAs.

Byron and Braidwood Stations, Units 1 and 2 Page F-81 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.6 PHASE 2 SAMA ANALYSIS The SAMA candidates identified as part of the Phase 2 analysis are listed in Table F.6-1. The base PRA model was manipulated to simulate implementation of each of the proposed SAMAs and then quantified to determine the risk benefit. Truncation values and binning cutoffs are the same as used in the base PRA model (CDF, LERF, Seismic and Fire), including Level 2 endstates.

In general, in order to maximize the potential risk benefit due to implementation of each of the SAMAs, the failure probabilities assigned to new basic events, such as human error probabilities (HEPs), were optimistically chosen so as not to inadvertently screen out any potential cost-beneficial SAMAs. Also, any new model logic that was added to the PRA model in order to simulate SAMA implementation was also simplified and optimistically configured to achieve the same effect.

Determining whether or not any given Phase 2 SAMA is potentially cost beneficial involved calculating what is known as the averted cost-risk, which was obtained by a multi-step process that includes the use of the baseline MACR as well as the internal events PRA results and a multiplier to account for external events contributions.

• The averted cost-risk is the difference between the baseline MACR and the MACR for the configuration in which the SAMA has been implemented (MACRSAMA). The MACRSAMA is comprised of the internal events contribution and the external events contribution.

The internal events portion of the MACRSAMA is calculated in the same manner as for the baseline MACR using the CDF, Level 2 PRA results, etc., as shown in Sections F.4.1 through F.4.6.1.

The contribution from the external events to the MACRSAMA is accounted for by multiplying the internal events MACRSAMA by the External Events Multiplier (refer to section F.4.6.2).

For some SAMAs identified by the Fire results review, the internal events PRA does not provide a means of modeling the impact of the SAMA. In these cases, the averted cost-risk is estimated using fire model insights and information from the internal events MACR calculation. The averted cost-risk is obtained by multiplying the internal events contribution to the MACR by the ratio of the CDF eliminated by the SAMA to the base internal events CDF.

The assumption is that the fire CDF is proportional to the internal events MACR. For example, if the SAMA is assumed to eliminate the entire CDF associated with Unit 1 fire zone 5.1-1, the averted cost risk would be (1.27E-06 / 3.97E-05 * $5,979,393 =

$191,280)

Byron and Braidwood Stations, Units 1 and 2 Page F-82 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Finally, a SAMA is determined to be potentially cost beneficial if its net value is positive. The net value is determined by the following equation:

Net Value = averted cost-risk - cost of implementation The implementation costs used in the Phase 1 and 2 analyses consist of industry estimates, Byron specific estimates, or in some cases, combinations of these two sources. It should be noted that Byron specific implementation costs do include contingency costs for unforeseen difficulties, but do not account for any replacement power costs that may be incurred due to consequential shutdown time unless specifically noted. Table F.5-3 provides implementation costs for each Phase 1 and Phase 2 SAMA.

The following sections describe the cost-benefit analysis that was used for each of the Phase 2 SAMA candidates.

It should be noted that apart from fire considerations, Byron units 1 and 2 are essentially identical in design and operation. The differences associated with fire related issues have been addressed by performing unit specific fire SAMA identification tasks and by using unit specific risk insights for quantification, when relevant. SAMAs developed to prevent or mitigate fire damage or propagation in a specific fire scenario required a unit specific quantification using the method described above. Unit specific fire SAMAs are applicable only to the unit for which they were derived. SAMAs identified to mitigate the impact of fire damage (e.g., SAMA 11 -

Implement DMS) were all also applicable to the internal events model and the External Events Multiplier was used to account for any fire related benefits for those types of SAMAs.

For all non-fire based SAMAs, the unit 1 PRA model was employed to evaluate the risk benefits and averted costs for each of the SAMAs, and was viewed as also being applicable to Unit 2.

That is, if a particular SAMA proves potentially cost beneficial for Unit 1, it will likewise be potentially cost beneficial for Unit 2.

F.6.1 SAMA 2: REPLACE THE POSITIVE DISPLACEMENT PUMP WITH A SELF COOLED, AUTO START PUMP Loss of SX requires swap of the charging pump suction source to the RWST as well as alignment of an alternate lube oil cooling source to maintain RCP seal injection. Replacing the positive displacement pump with a self-cooled pump with the capability to auto start on loss of charging and SX flow would provide a means of seal cooling on loss of the normal pumps.

Providing an automatic transfer switch to allow power from either division would enhance the SAMA's capability.

Byron and Braidwood Stations, Units 1 and 2 Page F-83 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Assumptions:

The seal injection pump is assumed to have a failure probability of 1E-3. Division 1 and division 2 emergency 480V AC power are assumed to be available to the new seal injection pump with an automatic transfer switch that is 100% reliable.

PRA Model Changes to Model SAMA:

The fault tree was updated to incorporate the self-cooled pump and power supplies under the existing seal injection logic.

Model Change(s):

The following modeling changes were made:

• New OR gate 1SAMA2-SEAL-INJ: Include new event 1SAMA2 and new gate 1SAMA2-POWER.

• New AND gate 1SAMA2-POWER: Include existing gates 1AP-BUS131X4 and 1AP-BUS132X4.

• New event 1SAMA2: SAMA 2 SEAL INJECTION PUMP FAILS; 1.00E-03.

• Under existing gate 1CSLOCA: Added NEW gate 1SAMA2-SEAL-INJ.

• Under existing gate 1CSLOCA-IE: Added NEW gate 1SAMA2-SEAL-INJ.

• Under existing gate 1LOSC-141: Added NEW gate 1SAMA2-SEAL-INJ.

• Under existing gate 1LOSC-142: Added NEW gate 1SAMA2-SEAL-INJ.

• Under existing gate 1LOSC-LOOP: Added NEW gate 1SAMA2-SEAL-INJ.

• Under existing gate 1RCP-SEALLOCA-SLB: Added NEW gate 1SAMA2-SEAL-INJ.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 1.36E-05 24.90 $218,298 Percent Change 65.7% 29.8% 14.3%

Byron and Braidwood Stations, Units 1 and 2 Page F-84 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 3.35E-06 1.25E-01 3.62E-02 $118 $34 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 8.79E-08 1.63E-02 2.71E-03 $22 $4 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 6.13E-07 1.05E+01 3.41E-01 $35,721 $1,159 LATE-CHR-NOAFW 8.35E-06 8.34E-06 1.78E+01 1.78E+01 $187,040 $186,816 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 1.47E-07 3.41E-01 1.37E-01 $1,655 $663 LERF-CFE 3.55E-08 1.03E-08 8.88E-02 2.58E-02 $582 $169 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.69E-07 6.97E-01 6.97E-01 $8,205 $8,205 Total 4.19E-05 1.47E-05 3.55E+01 2.49E+01 $254,593 $218,298 Applying the process described in Section F.4 yields an internal events cost-risk of $4,403,284.

After accounting for round up of the base internal events cost-risk, this value is $4,403,891.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $4,403,891

• 2.5 = $11,009,728 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 2 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $11,009,728 $3,940,272 Byron and Braidwood Stations, Units 1 and 2 Page F-85 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Based on a $5,751,110 cost of implementation for Byron, the net value for this SAMA is

-$1,810,838 ($3,940,272 - $5,751,110), which indicates this SAMA is not cost beneficial.

F.6.2 SAMA 3: AUTO START OF STANDBY SX PUMP The SX system includes logic that starts the standby SX pump for initiating events that generate SI or bus under-voltage signals, but for events without these signals, manual start of the standby SX pump is required when the running pump fails.

Automating the start of the standby SX pump would help reduce the reliance of operators to maintain cooling to critical loads. Use of flooding interlocks could be used to prevent auto actuation in flooding scenarios.

Assumptions:

It is assumed that the auto start logic of the standby SX pump can represented by a lumped event accounting for hardware and support system dependencies. The failure probability of the event (1SX-AUTOSTART) is assumed to be 1E-04.

The new autostart function also serves as a backup to the SI and undervoltage start signals.

PRA Model Changes to Model SAMA:

The standby SX pump start logic has been modified to include the auto start event (1SX-AUTOSTART) such that a failure of the SX pump to start requires failure of both the automated start function and the manual operator action.

Model Change(s):

Event 1SX-AUTOSTART has been included under the following gates:

• 1SX-PUMP-1A-SIG1: SX PUMP IS NOT STARTED MANUALLY FOR OTHER INITIATORS

• 1SX-PM1A-DG-ACT: SX PUMP 1A FTS VIA SIGNAL FAULT (DG SUPPORT- IELOP CAN BE PRESUMD; DC

• 1SX-PM1A-LOOP: SX PUMP 1A IS NOT ACTIUATED FOR LOOP IE

• 1SX-PM1B-DG-ACTSX PUMP 1B FTS VIA SIGNAL FAULT (DG SUPPORT- IELOP CAN BE PRESUMD; DC

• 1SX-PM1B-LOOP: SX PUMP 1A IS NOT ACTIUATED FOR LOOP IE

• 1SX-PUMP-1B-SIG1: SX PUMP IS NOT STARTED MANUALLY FOR OTHER INITIATORS Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Byron and Braidwood Stations, Units 1 and 2 Page F-86 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.22E-05 30.57 $231,705 Percent Change 18.9% 13.8% 9.0%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.18E-05 1.05E+01 6.56E+00 $35,721 $22,302 LATE-CHR-NOAFW 8.35E-06 7.96E-06 1.78E+01 1.70E+01 $187,040 $178,304 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 2.98E-07 3.41E-01 2.77E-01 $1,655 $1,344 LERF-CFE 3.55E-08 2.84E-08 8.88E-02 7.10E-02 $582 $466 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.59E-07 6.97E-01 6.71E-01 $8,205 $7,900 Total 4.19E-05 3.43E-05 3.55E+01 3.06E+01 $254,593 $231,705 Applying the process described in Section F.4 yields an internal events cost-risk of $5,283,419.

After accounting for round up of the base internal events cost-risk, this value is $5,284,026.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,284,026

• 2.5 = $13,210,065 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

Byron and Braidwood Stations, Units 1 and 2 Page F-87 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 SAMA 3 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $13,210,065 $1,739,935 Based on a $1,130,300 cost of implementation for Byron, the net value for this SAMA is

$609,635 ($1,739,935 - $1,130,300), which indicates this SAMA is potentially cost beneficial.

F.6.3 SAMA 4: INSTALL "NO LEAK" RCP SEALS For loss of RCP seal cooling scenarios, a passive means of reducing the probability of an RCP seal LOCA is to replace the existing pump seals with "no leak" seals (e.g., Westinghouse "shield" seals) that are less likely to fail on loss of cooling.

Assumptions:

The no-leak seal capabilities are assumed to be represented by a lower RCP seal LOCA probability. The no leak seals are assumed to reduce the seal LOCA probability by a factor of 1000.

PRA Model Changes to Model SAMA:

The impact of implementing this SAMA has been estimated by modifying the base model cutset file. Using the cutset editor, the deleted flag FLAG-SEAL-LOCA is restored to the cutsets and assigned a value of 1E-3. Because the cutsets already include events that represent seal LOCA probabilities that are less than 1.0, this process ultimately reduces the probability that a seal LOCA occurs to less than the assumed value of 1E-3, but it conservatively shows an increased averted cost-risk for the SAMA.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 1.33E-05 24.54 $215,658 Percent Change 66.5% 30.8% 15.3%

Byron and Braidwood Stations, Units 1 and 2 Page F-88 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 3.21E-06 1.25E-01 3.47E-02 $118 $33 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 8.42E-08 1.63E-02 2.59E-03 $22 $4 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 3.35E-07 1.05E+01 1.86E-01 $35,721 $633 LATE-CHR-NOAFW 8.35E-06 8.25E-06 1.78E+01 1.76E+01 $187,040 $184,800 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 1.46E-07 3.41E-01 1.36E-01 $1,655 $658 LERF-CFE 3.55E-08 1.02E-08 8.88E-02 2.55E-02 $582 $167 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.66E-07 6.97E-01 6.89E-01 $8,205 $8,113 Total 4.19E-05 1.42E-05 3.55E+01 2.45E+01 $254,593 $215,658 Applying the process described in Section F.4 yields an internal events cost-risk of $4,344,644.

After accounting for round up of the base internal events cost-risk, this value is $4,345,251.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $4,345,251

• 2.5 = $10,863,128 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 4 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $10,863,128 $4,086,872 Byron and Braidwood Stations, Units 1 and 2 Page F-89 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Based on a $12,230,000 cost of implementation for Byron, the net value for this SAMA is

-$8,143,128 ($4,086,872 - $12,230,000), which indicates this SAMA is not cost beneficial.

F.6.4 SAMA 5: MODIFY THE STARTUP FEEDWATER PUMP TO START USING THE AMSAC SG LOW-LOW-LOW LEVEL SIGNAL TO MITIGATE AFW FAILURE For accident sequences in which main feedwater has tripped and AFW has failed to start, it is necessary to manually restart the FW system for continued SG makeup. By modifying the startup feedwater pump to auto start and align on low steam generator level, the need for operator intervention after AFW failure is essentially eliminated. Use of the anticipated transient without scram mitigating system actuation circuitry (AMSAC) low-low-low SG level signal is an additional benefit that mitigates start signal failures.

Assumptions:

The auto start logic is only applicable to the startup FW pump, but to simplify the modeling, the auto start logic is also assumed to be capable of starting the main FW pump. This conservatively increases the averted cost-risk for this SAMA.

PRA Model Changes to Model SAMA:

The startup FW pump start logic has been modified to include the auto start event (1SUFW-AUTOSTART) such that a failure of the FW pumps to start requires failure of both the automated start function and the manual operator action.

Model Change(s):

The following modeling changes were made:

• Under gates 1FWR-TRANS and 1ALTFW-SLOCA: Added new AND gate 1FW-FWR-START. Deleted 1FW-FWR-OA

• New AND gate 1FW-FWR-START: Included existing gate 1FW-FWR-OA and new event 1SUFW-AUTOSTART.

• New event 1SUFW-AUTOSTART: AUTO START LOGIC FOR ALT FW FUNCTION. Failure prob. = 1.00E-04

• Under gate 1ALTFW-SGTR: Added new AND gate 1FW-FWR-START-SGTR. Deleted 1FW-FWR-OA-SGTR.

• New AND gate 1FW-FWR-START-SGTR: Included existing gate 1FW-FWR-OA-SGTR and new event 1SUFW-AUTOSTART.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Byron and Braidwood Stations, Units 1 and 2 Page F-90 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.60E-05 28.00 $176,115 Percent Change 9.3% 21.0% 30.8%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.12E-05 1.25E-01 1.21E-01 $118 $114 SERF-TISGTR-HLF 6.49E-09 5.49E-09 6.17E-03 5.22E-03 $44 $37 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 6.04E-08 6.36E-03 4.83E-03 $14 $11 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 5.00E-06 1.78E+01 1.07E+01 $187,040 $112,000 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.34E-07 3.41E-01 3.11E-01 $1,655 $1,506 LERF-CFE 3.55E-08 3.14E-08 8.88E-02 7.85E-02 $582 $515 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 4.17E-11 6.68E-04 3.25E-05 $6 $0 LERF-ISGTR 2.69E-07 1.64E-07 6.97E-01 4.25E-01 $8,205 $5,002 Total 4.19E-05 3.80E-05 3.55E+01 2.80E+01 $254,593 $176,115 Applying the process described in Section F.4 yields an internal events cost-risk of $4,473,821.

After accounting for round up of the base internal events cost-risk, this value is $4,474,428.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $4,474,428

• 2.5 = $11,186,070 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

Byron and Braidwood Stations, Units 1 and 2 Page F-91 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 SAMA 5 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $11,186,070 $3,763,930 Based on a $657,200 cost of implementation for Byron, the net value for this SAMA is

$3,106,730 ($3,763,930 - $657,200), which indicates this SAMA is potentially cost beneficial.

F.6.5 SAMA 7: ESTABLISH FLOW TO THE RH HX ON RH PUMP START To prevent overheating the RH pumps when they are operating on min-flow without CC cooling to the heat exchangers, procedure EP-0 (and potentially others) could be changed to direct the operators to align CC to the RH HX when the RH pumps start. This precludes the need for the operators to rely on a continuous action statement to protect the RH pumps if secondary side cooling is not established.

Assumptions:

It is assumed that the procedures can be modified in a way such that the flow to the HX is started when the corresponding RHR pump is confirmed to be running and that the step is written distinct manner (potentially with the caution that exists in the current FR-H.1 procedure related to the limitations on the RH pump run time without flow to the HX). It is assumed the impact of these changes can be approximated by crediting graphically distinct procedures and a check cue in the HRA methodology for the HFE 1RH-SP-X---HPMOA. The result is a reduction in the HEP from 7.3E-04 to 1.4E-04.

Unless the HEP is the lead action in a joint human error probability (JHEP), the value of the independent HEP has a small impact on the JHEP value. No changes are made to the JHEPs unless the chronologically first action is 1RH-SP-X---HPMOA.

PRA Model Changes to Model SAMA:

The database and recovery files were changed to use the updated HEPs reflecting the procedure modification.

Model Change(s):

The following modeling changes were made:

• 1RH-SP-X---HPMOA: HEP changed from 7.3E-04 to 1.4E-04.

• 1RX-JHEP33-HOADA: Updated JHEP calc from 3.9E-05 to reflect modified independent HEP value: 1.4E-4 * ((1 + 19*2.7E-03) / 20) = 7.4E-06.

Byron and Braidwood Stations, Units 1 and 2 Page F-92 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2

• 1RX-JHEP42-HOADA: Updated JHEP calc from 3.7E-05 to reflect modified independent HEP value: 1.4E-4 * ((1 + 19*9.6E-04) / 20) = 7.1E-06 Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.88E-05 35.41 $254,363 Percent Change 2.3% 0.1% 0.1%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.07E-05 1.25E-01 1.16E-01 $118 $109 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.36E-06 1.33E+00 1.31E+00 $8,349 $8,228 LATE-BMMT-AFW 5.30E-07 4.87E-07 1.63E-02 1.50E-02 $22 $20 LATE-BMMT-NOAFW 7.95E-08 7.81E-08 6.36E-03 6.25E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.35E-06 1.78E+01 1.78E+01 $187,040 $187,040 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.59E-07 3.41E-01 3.34E-01 $1,655 $1,619 LERF-CFE 3.55E-08 3.46E-08 8.88E-02 8.65E-02 $582 $567 LERF-SGTR-AFW 5.49E-08 5.40E-08 1.31E-01 1.29E-01 $1,005 $988 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.68E-07 6.97E-01 6.94E-01 $8,205 $8,174 Total 4.19E-05 4.09E-05 3.55E+01 3.54E+01 $254,593 $254,363 Applying the process described in Section F.4 yields an internal events cost-risk of $5,950,012.

After accounting for round up of the base internal events cost-risk, this value is $5,950,619.

The external events contributions are accounted for by multiplying this value by 2.5:

Byron and Braidwood Stations, Units 1 and 2 Page F-93 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Total Cost-RiskSAMA = $5,950,619

• 2.5 = $14,876,548 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 7 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,876,548 $73,452 Based on a $100,000 cost of implementation for Byron, the net value for this SAMA is -$26,548

($73,452 - $100,000), which indicates this SAMA is not cost beneficial.

F.6.6 SAMA 8: INSTALL KILL SWITCHES FOR THE FIRE PROTECTION PUMPS IN THE MCR Currently, it is not possible to terminate all flow from the fire protection system in the main control room (MCR). In the event of a flood caused by a fire protection system break, the availability of controls in the MCR that would allow the operators to shut down the fire protection pumps would increase the likelihood that the flood could be terminated before critical equipment is damaged.

Assumptions:

Installation of kill switches in the MCR will reduce the time required to perform the action to terminate the flood and potentially in a simplification of the control scheme. Each pump is assumed to have a dedicated, two position control switch that is distinct from the other controls on the main control room fire protection control panel.

With the revised controls proposed for this SAMA, the manipulation time for this action is assumed to be 3 minutes (1 minute for each pump).

The flood mitigation factors include multiple actions, including the initial flood termination action, but are not wholly determined by the flood termination action HEP. The flood mitigation factors were recalculated using the above assumptions.

PRA Model Changes to Model SAMA:

A recovery file was developed to modify the cutsets to use the updated Fire Protection flood mitigation factors the Auxiliary Building Fire Protection floods.

Byron and Braidwood Stations, Units 1 and 2 Page F-94 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Model Change(s):

The following changes were made to the cutsets:

• FLMITIG--G-T1-FP: Probability changed from 2.23E-04 to 1.10E-04.

• FLMITIG-M1-T1-FP: Probability changed from 3.33E-04 to 1.66E-04.

• FLMITIG-M2-T1-FP: Probability changed from 2.19E-03 to 1.89E-03.

• FLMITIG-M3-T1-FP: Probability changed from 6.94E-03 to 3.88E-03 Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.83E-05 34.53 $250,489 Percent Change 3.5% 2.6% 1.6%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.75E-05 1.05E+01 9.73E+00 $35,721 $33,075 LATE-CHR-NOAFW 8.35E-06 8.29E-06 1.78E+01 1.77E+01 $187,040 $185,696 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.54E-07 3.41E-01 3.29E-01 $1,655 $1,597 LERF-CFE 3.55E-08 3.40E-08 8.88E-02 8.50E-02 $582 $558 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.68E-07 6.97E-01 6.94E-01 $8,205 $8,174 Total 4.19E-05 4.04E-05 3.55E+01 3.45E+01 $254,593 $250,489 Byron and Braidwood Stations, Units 1 and 2 Page F-95 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Applying the process described in Section F.4 yields an internal events cost-risk of $5,851,638.

After accounting for round up of the base internal events cost-risk, this value is $5,852,245.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,852,245

• 2.5 = $14,630,613 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 8 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,630,613 $319,387 Based on a $338,830 cost of implementation for Byron, the net value for this SAMA is -$19,443

($319,387 - $338,830), which indicates this SAMA is not cost beneficial.

F.6.7 SAMA 9: INSTALL FLOW RESTRICTORS IN FIRE PROTECTION PIPES Large breaks in the fire protection systems are significant contributors to plant risk. Installing flow restrictors in the auxiliary building piping would increase the time available to respond to these flooding events. Locating flow restrictors outside the auxiliary building upstream of valves 0FP209A, 0FP209B, and FP033 would provide adequate protection for auxiliary building floods.

Assumptions:

It is assumed that fire protection code will allow the installation of flow restrictors in the fire protection system lines. If this is not possible, it is assumed that a flow analysis can be performed that will allow the throttling of the 0FP209A, 0FP209B, and 0FP033 valves (which may need to be replaced by valves of a different type) to achieve similar results.

It is assumed that the flow restrictions will limit flow of Fire Protection breaks in the Auxiliary building to 1000 gpm and that 1000 gpm is adequate to meet fire suppression requirements.

The increase in the time available to terminate the fire protection flood reduces the flood mitigation factor to 1.2E-4. Because the flow restrictors would limit flow to 1000 gpm for all Auxiliary Building Fire Protection breaks, this flood mitigation factor is assumed to be applicable to all Auxiliary Building Fire Protection flooding scenarios.

Byron and Braidwood Stations, Units 1 and 2 Page F-96 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 PRA Model Changes to Model SAMA:

A recovery file was developed to modify the cutsets to use the updated Fire Protection flood mitigation factor for all Auxiliary Building Fire Protection floods.

Model Change(s):

The following changes were made to the cutsets:

• FLMITIG--G-T1-FP: Probability changed from 2.23E-04 to 1.2E-04.

• FLMITIG-M1-T1-FP: Probability changed from 3.33E-04 to 1.2E-04.

• FLMITIG-M2-T1-FP: Probability changed from 2.19E-03 to 1.2E-04.

• FLMITIG-M3-T1-FP: Probability changed from 6.94E-03 to 1.2E-04 Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.66E-05 33.49 $245,971 Percent Change 7.8% 5.5% 3.4%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.59E-05 1.05E+01 8.84E+00 $35,721 $30,051 LATE-CHR-NOAFW 8.35E-06 8.23E-06 1.78E+01 1.75E+01 $187,040 $184,352 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.40E-07 3.41E-01 3.16E-01 $1,655 $1,533 LERF-CFE 3.55E-08 3.24E-08 8.88E-02 8.10E-02 $582 $531 Byron and Braidwood Stations, Units 1 and 2 Page F-97 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.66E-07 6.97E-01 6.89E-01 $8,205 $8,113 Total 4.19E-05 3.88E-05 3.55E+01 3.35E+01 $254,593 $245,971 Applying the process described in Section F.4 yields an internal events cost-risk of $5,705,994.

After accounting for round up of the base internal events cost-risk, this value is $5,706,601.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,706,601

• 2.5 = $14,266,503 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 9 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,266,503 $683,497 Based on a $349,300 cost of implementation for Byron, the net value for this SAMA is $334,197

($683,497 - $349,300), which indicates this SAMA is potentially cost beneficial.

F.6.8 SAMA 10: ALTER DUCTWORK BETWEEN THE AUX BLDG SUMP DRAIN ROOM AND THE SX PUMP ROOM Currently, the ductwork between the Auxiliary Building Sump Drain Room and the SX Pump Rooms provides a flowpath for flood water when the Auxiliary Building Sump Drain Room fills with water (at a depth of about 12 feet). Water then flows through the ductwork to the SX pump room and damages the SX pumps. Eliminating this pathway will increase the time available to mitigate the flooding event by precluding SX pump damage from the flooding event.

Assumptions:

The ductwork modification prevents water intrusion into the SX pump room duct until water level reaches the 364 elevation. It is assumed that the actual failure level is the same as that for the Byron and Braidwood Stations, Units 1 and 2 Page F-98 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 other critical equipment located on that level such that the time available for flood termination is the same as what is currently used for the internal flooding assessment.

This SAMA eliminates the T1 flooding scenarios that are related to failing SX due to the existing duct connections between the SX pumps rooms and the Auxiliary Building Sump Drain Room.

The flood mitigation factors for the normal service water (WS) and SX floods are simplified to the HEPs for termination of the flood before the level reaches elevation 364.

PRA Model Changes to Model SAMA:

A recovery file was developed to modify the cutsets to use the updated Fire Protection flood mitigation factor for all Auxiliary Building floods.

Model Change(s):

The following changes were made to the cutsets:

• Set probability of the following T1 flood events to 0.0: FLMITIG-FPCVCOOL, FLMITIG--G-T1-FP, FLMITIG--G-T1-SX, FLMITIG--G-T1-WS, FLMITIG-M1-T1-FP, FLMITIG-M1-T1-WS, FLMITIG-M2-T1-FP, FLMITIG-M3-T1-FP, FLMITIG-M3-T1-WS, FLMITIG--M-T1-SX.

• FLMITIG-M3-T2-WS: Probability changed from 2.14E-04 to 1.8E-04.

• FLMITIG--M-T2-SX: Probability changed from 2.09E-03 to 1.4E-04 Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.50E-05 31.32 $227,001 Percent Change 11.8% 11.7% 10.8%

Byron and Braidwood Stations, Units 1 and 2 Page F-99 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.50E-05 1.05E+01 8.34E+00 $35,721 $28,350 LATE-CHR-NOAFW 8.35E-06 7.50E-06 1.78E+01 1.60E+01 $187,040 $168,000 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 2.77E-07 3.41E-01 2.58E-01 $1,655 $1,249 LERF-CFE 3.55E-08 3.10E-08 8.88E-02 7.75E-02 $582 $508 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.46E-07 6.97E-01 6.37E-01 $8,205 $7,503 Total 4.19E-05 3.70E-05 3.55E+01 3.13E+01 $254,593 $227,001 Applying the process described in Section F.4 yields an internal events cost-risk of $5,311,758.

After accounting for round up of the base internal events cost-risk, this value is $5,312,365.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,312,365

• 2.5 = $13,280,913 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 10 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $13,280,913 $1,669,087 Based on a $1,320,300 cost of implementation for Byron, the net value for this SAMA is

$348,787 ($1,669,087 - $1,320,300), which indicates this SAMA is potentially cost beneficial.

Byron and Braidwood Stations, Units 1 and 2 Page F-100 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.6.9 SAMA 11: IMPLEMENT DMS The diverse and flexible coping strategies (FLEX) guide identifies different means of addressing required plant functions, but for this SAMA a specific approach is proposed. A portable 480V AC generator is proposed as a means of supporting long term diesel driven AFW operation by means of maintaining instrumentation and control power for the system by energizing the buses used for the battery chargers. A portable, engine driven SG makeup pump would provide an alternate means of SG makeup, with injection connections available on different divisions. Fire protection should provide both condensate storage tank (CST) makeup and a suction source connection for the portable SG makeup pump. Use of high temperature RCP seals would limit primary system leakage and the positive displacement pump could be replaced by one that could be powered by the portable generator for long term RCS makeup. A means of providing borated makeup to the RWST is also required, which could potentially be performed using the fire protection system and an eductor. Finally, a connection point to an outside source would have to be provided for the containment spray system for long term spray capability in an SBO.

Assumptions:

SAMA 11 was generally identified as a means of mitigating scenarios in which loss of SG makeup is a slowly developing evolution, such as in SBO events where battery depletion eventually fails diesel driven AFW or in loss of SX cases in which the AFW pumps (motor or diesel driven) may be able to run for some time before failure. No credit is taken for the DMS in LOCA or ATWS scenarios. The DMS is credited in SGTR cases as most cases include success of injection where time would be available to recover steam generator makeup. Prior to core damage, activity levels are expected to be low enough to perform any alignment required.

The DMS capabilities are assumed to be represented by a lower RCP seal LOCA probability and indefinite steam generator makeup capability. The no leak seals are assumed to reduce the seal LOCA probability by a factor of 1000. The steam generator makeup capability includes alignment and control of a portable 480V generator to support diesel driven AFW makeup or alignment and control of a portable SG makeup pump. A new event with a failure probability of 1E-2 is used for this function.

It is assumed that the cognitive failure to diagnose the need for secondary cooling (1FW-FRH1--

-HSGOA), which is related to the AFW X-tie, FW restoration, and bleed and feed, will also fail the DMS. In addition, any dependent combinations are also assumed to fail the DMS.

Byron and Braidwood Stations, Units 1 and 2 Page F-101 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 PRA Model Changes to Model SAMA:

The fault tree was updated to incorporate the DMS event and cognitive failure logic. After quantification, the deleted flag FLAG-SEAL-LOCA is restored to the cutsets in the cutset editor and assigned a value of 1E-3. Because the cutsets already include events that represent seal LOCA probabilities that are less than 1.0, this process ultimately reduces the probability that a seal LOCA occurs to less than the assumed value of 1E-3, but it conservatively shows an increased averted cost-risk for the SAMA.

Model Change(s):

The following modeling changes were made:

• New event 1DMS: DMS - OPS FAIL TO ALIGN/USE 480V CHARGER OR PORTABLE SG MAKEUP PUMP, 1.0E-02

• New OR gate 1DMS-FAILS: Include new event 1DMS, 1FW-FRH1---HSGOA, 1RX-JHEP03-HOADA and similar events for the following JHEP combinations: 07, 09, 11, 12, 14, 17, 21, 24, 25, 27, 39, 49, 50, 54, 58, 64, 74, and 80.

• Under gate 1AFW: Added NEW gate 1DMS-FAILS.

• Under gate 1AFW-LOOP-3SG: Added NEW gate 1DMS-FAILS.

• Under gate 1AFW-LOOP-2SG: Added NEW gate 1DMS-FAILS.

• Under gate 1AFW-SBO-3SG: Added NEW gate 1DMS-FAILS.

• Under gate 1AFW-SBO-2SG: Added NEW gate 1DMS-FAILS.

• Under gate 1AFW-LOB-MDP-3SG: Added NEW gate 1DMS-FAILS.

• Under gate 1AFW-LOB-MDP-2SG: Added NEW gate 1DMS-FAILS.

• Under gate 1AFW-LOB-DDP-3SG: Added NEW gate 1DMS-FAILS.

• Under gate 1AFW-LOB-DDP-2SG: Added NEW gate 1DMS-FAILS.

• Under gate 1AF-UBR-LATE: Added NEW gate 1DMS-FAILS.

• Under gate 1AF-UBR-LATE: Added NEW gate 1DMS-FAILS.

• Under gate 1AF-DP-LATE: Added NEW gate 1DMS-FAILS.

Post quantification, set flag FLAG-SEAL-LOCA to a probability of 1E-3.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 4.66E-06 7.11 $32,430 Percent Change 88.3% 80.0% 87.3%

Byron and Braidwood Stations, Units 1 and 2 Page F-102 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Category Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA INTACT 1.16E-05 2.25E-06 1.25E-01 2.43E-02 $118 $23 SERF-TISGTR-HLF 6.49E-09 1.52E-09 6.17E-03 1.44E-03 $44 $10 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 8.41E-08 1.63E-02 2.59E-03 $22 $4 LATE-BMMT-NOAFW 7.95E-08 3.12E-08 6.36E-03 2.50E-03 $14 $6 LATE-CHR-AFW 1.89E-05 3.36E-07 1.05E+01 1.87E-01 $35,721 $635 LATE-CHR-NOAFW 8.35E-06 4.26E-07 1.78E+01 9.07E-01 $187,040 $9,542 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 2.49E-08 3.41E-01 2.32E-02 $1,655 $112 LERF-CFE 3.55E-08 2.81E-09 8.88E-02 7.03E-03 $582 $46 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.82E-08 6.97E-01 7.30E-02 $8,205 $860 Total 4.19E-05 4.96E-06 3.55E+01 7.11E+00 $254,593 $32,430 Applying the process described in Section F.4 yields an internal events cost-risk of $828,760.

After accounting for round up of the base internal events cost-risk, this value is $829,367. The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $829,367

• 2.5 = $2,073,418 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 11 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $2,073,418 $12,876,582 Based on a $13,030,000 cost of implementation for Byron, the net value for this SAMA is

-$153,418 ($12,876,582 - $13,030,000), which indicates this SAMA is not cost beneficial.

Byron and Braidwood Stations, Units 1 and 2 Page F-103 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.6.10 SAMA 13: ALTERNATE AFW COOLING WITH SEAL PROTECTION For loss of SX events with consequential loss of offsite power (LOOP), the AFW lube oil coolers are unavailable and the AFW pumps are assumed to fail. The motor driven AFW pump discharge flow could be routed back to the lube oil coolers to provide a self-cooling mechanism that would eliminate the SX dependence. The cooling water return flow could potentially be returned to the AFW pump discharge path. For RCP seal protection, replacing the positive displacement pump (PDP) with a self-cooled pump with the capability to auto start on loss of charging flow/and or high seal injection water temp would provide a success path.

Assumptions:

This SAMA is assumed to eliminate the SX dependence for motor driven AFW pump operation.

The diesel driven AFW pumps is not modified for this SAMA given that an additional change would be required to provide flow to the cubicle coolers and because power is available to the motor driven AFW pump for most of the scenarios this SAMA is intended to address.

The seal injection pump is assumed to have a failure probability of 1E-3. Division 1 and division 2 emergency 480V AC power are assumed to be available to the new seal injection pump with an automatic transfer switch that is 100% reliable.

The AFW cross-tie is assumed to be unavailable for dual unit LOSX events (even after implementation) because the A pump would be needed on the opposite unit.

PRA Model Changes to Model SAMA:

The fault tree was updated to incorporate the self-cooled pump and power supplies under the existing seal injection logic. In addition, the SX dependencies were removed for the motor driven AFW pump.

Model Change(s):

The following modeling changes were made:

• New OR gate 1SAMA13-SEAL-INJ: Include new event 1SAMA13 and new gate 1SAMA13-POWER.

• New AND gate 1SAMA13-POWER: Include existing gates 1AP-BUS131X4 and 1AP-BUS132X4.

• New event 1SAMA13: SAMA 13 SEAL INJECTION PUMP FAILS; 1.00E-03.

• Under existing gate 1CSLOCA: Added NEW gate 1SAMA13-SEAL-INJ.

• Under existing gate 1CSLOCA-IE: Added NEW gate 1SAMA13-SEAL-INJ.

• Under existing gate 1LOSC-141: Added NEW gate 1SAMA13-SEAL-INJ.

• Under existing gate 1LOSC-142: Added NEW gate 1SAMA13-SEAL-INJ.

Byron and Braidwood Stations, Units 1 and 2 Page F-104 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2

• Under existing gate 1LOSC-LOOP: Added NEW gate 1SAMA13-SEAL-INJ.

• Under existing gate 1RCP-SEALLOCA-SLB: Added NEW gate 1SAMA13-SEAL-INJ.

• Under existing gates 1AF-PUMP1A-FR-HW-X, 1AF-PUMP1A-FR-HW, and Removed gate 0SX-ALL----CSRPG-FT.

• Under existing gates 1AF-PUMP-1A-FTR-SUPPORT and 1AF-TRAIN-1A-X-ND: Removed gate 1AF-PUMP1A-OIL.

• Under existing gate 2AF-XTIE-AF1A-FTR: Removed gate 1AF-PUMP1A-OIL-XTIE.

• Under existing gate 1AFW-SBO-MDP: Removed gate 1AFW-MDP-ND-SX.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 5.66E-06 7.13 $31,120 Percent Change 85.7% 79.9% 87.8%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 3.35E-06 1.25E-01 3.62E-02 $118 $34 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 8.79E-08 1.63E-02 2.71E-03 $22 $4 LATE-BMMT-NOAFW 7.95E-08 7.93E-08 6.36E-03 6.34E-03 $14 $14 LATE-CHR-AFW 1.89E-05 6.16E-07 1.05E+01 3.42E-01 $35,721 $1,164 LATE-CHR-NOAFW 8.35E-06 3.06E-07 1.78E+01 6.52E-01 $187,040 $6,854 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 8.28E-08 3.41E-01 7.70E-02 $1,655 $373 LERF-CFE 3.55E-08 3.06E-09 8.88E-02 7.65E-03 $582 $50 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.15E-10 6.68E-04 6.35E-04 $6 $5 Byron and Braidwood Stations, Units 1 and 2 Page F-105 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category LERF-ISGTR 2.69E-07 4.56E-08 6.97E-01 1.18E-01 $8,205 $1,391 Total 4.19E-05 6.35E-06 3.55E+01 7.13E+00 $254,593 $31,120 Applying the process described in Section F.4 yields an internal events cost-risk of $836,976.

After accounting for round up of the base internal events cost-risk, this value is $837,583. The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $837,583

• 2.5 = $2,093,958 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 13 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $2,093,958 $12,856,042 Based on a $5,951,110 cost of implementation for Byron, the net value for this SAMA is

$6,904,932 ($12,856,042 - $5,951,110), which indicates this SAMA is potentially cost beneficial.

F.6.11 SAMA 14 AUTOMATED RWST MAKEUP For SGTR scenarios, in which cooldown has failed, installing an automated RWST makeup system could provide a means of maintaining injection indefinitely. The makeup pump should be powered from a diesel backed bus. A boron source is required to ensure criticality does not occur. Including an alarm that identifies system actuation would provide an additional cue to address plant issues that have led to RWST depletion.

For non-SGTR scenarios, the availability of automated RWST makeup would extend the time available to transition to recirculation mode.

Byron and Braidwood Stations, Units 1 and 2 Page F-106 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Assumptions:

The RWST makeup capability will extend the time available to perform required actions in SGTR scenarios and scenarios requiring transition to recirculation mode, but it is assumed that the actions to control injection and perform a cooldown will eventually have to be taken to reach a successful endstate (i.e., injection with RWST makeup alone is not a success state). For this evaluation, it is assumed that the HEPs for the following operator actions are reduced by a factor of 10:

• 1SI-HPR----HSYOA: OPERATORS FAIL TO ESTABLISH HIGH PRESSURE RECIRC (SLOW EVENT)

• 1RC-LCD----HSYOA: OPERATORS FAIL TO TERMINATE BREAK FLOW ON SGTR In addition, the JHEPs including those actions were reviewed to determine which of the dependent actions would be impacted by this SAMA. Most of the JHEPs were already set to the floor value of 1.0E-06, but 1RX-JHEP28-HOADA, 1RX-JHEP51-HOADA and 1RX-JHEP71-HOADA would be impacted. 1RX-JHEP51-HOADA and 1RX-JHEP71-HOADA, which are related to establishing recirculation, were set to 0.0 for simplicity. 1RX-JHEP28-HOADA, which is the dependent combination of 1RC-DS-SGTRHDVOA and 1RC-LCD----HSYOA, is impacted, but the impact is on the chronologically second, or dependent, action of the pair. The impact is limited in these cases, but the JHEP was revised to reflect a factor of 10 reduction in 1RC-LCD--

--HSYOA and a change in the assessed dependence level from MODERATE to LOW.

PRA Model Changes to Model SAMA:

The cutsets were updated to account for the changes to the HEPs and JHEPs due to the increased time available for action.

Model Change(s):

The following modeling changes were made to the results cutsets:

• Event 1SI-HPR----HSYOA: HEP changed from 6.8E-03 to 6.8E-04.

• Event 1RC-LCD----HSYOA: HEP changed from 3.2E-03 to 3.2E-04.

• Event 1RX-JHEP51-HOADA: Set to 0.0.

• Event 1RX-JHEP71-HOADA: Set to 0.0.

• 1RX-JHEP28-HOADA: Updated JHEP calc from 3.3E-04 to reflect modified independent HEP value: 6.3E-3 * ((1 + 19*3.2E-04) / 20) = 3.2E-04 Byron and Braidwood Stations, Units 1 and 2 Page F-107 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.93E-05 35.34 $253,720 Percent Change 1.0% 0.3% 0.3%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Category Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA INTACT 1.16E-05 1.12E-05 1.25E-01 1.21E-01 $118 $114 SERF-TISGTR-HLF 6.49E-09 6.12E-09 6.17E-03 5.81E-03 $44 $41 SERF-SGTR-AFW-SC 1.38E-06 1.32E-06 1.33E+00 1.27E+00 $8,349 $7,986 LATE-BMMT-AFW 5.30E-07 5.28E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 6.50E-08 6.36E-03 5.20E-03 $14 $12 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.34E-06 1.78E+01 1.78E+01 $187,040 $186,816 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.65E-07 3.41E-01 3.39E-01 $1,655 $1,646 LERF-CFE 3.55E-08 3.53E-08 8.88E-02 8.83E-02 $582 $579 LERF-SGTR-AFW 5.49E-08 5.21E-08 1.31E-01 1.25E-01 $1,005 $953 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.62E-07 6.97E-01 6.79E-01 $8,205 $7,991 Total 4.19E-05 4.14E-05 3.55E+01 3.53E+01 $254,593 $253,720 Applying the process described in Section F.4 yields an internal events cost-risk of $5,951,964.

After accounting for round up of the base internal events cost-risk, this value is $5,952,571.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,952,571

• 2.5 = $14,881,428 Byron and Braidwood Stations, Units 1 and 2 Page F-108 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 14 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,881,428 $68,572 Based on a $3,800,000 cost of implementation for Byron, the net value for this SAMA is

-$3,731,428 ($68,572 - $3,800,000), which indicates this SAMA is not cost beneficial.

F.6.12 SAMA 15 RESOLVE REGULATORY ISSUES AND COMPLETE IMPLEMENTATION OF THE INTER UNIT AFW CROSS-TIE The inter unit AFW cross-tie is in place at the site, but regulatory issues must be resolved before it can be considered "implemented". Once the process is complete, it will allow one unit to use the other unit's AFW system to provide SG makeup. The cross-tie valve requires local, manual action for operation.

Due to the timing of the submittal of the license renewal application, the official PRA model does not credit the AFW cross-tie action, but this SAMA documents the estimated impact of implementing the cross-tie in the existing model.

Section F.7.4 includes a sensitivity analysis that assesses the impact of implementing the AFW cross-tie on the cost benefit results of the remaining SAMAs.

Assumptions:

The AFW cross-tie action is currently included in the PRA model (1AF-XTIEEHXVOA) with the actions execution failure probability set to 1.0. The failure to diagnose the need to initiate the AFW cross-tie alignment is already included in the model with a non 1.0 probability. The diagnosis component of the action is represented by a common cognitive term that addresses the set of potential actions that are performed in response to loss of secondary side heat removal (for example, alignment of the startup FW pump for SG makeup). Because this event is already incorporated into the analysis in a way that includes use of the cross-tie, no changes are required to the cognitive term or the associated joint HEPs.

The execution failure probability was previously estimated to be 2.4E-2 and that estimate is used to represent the cross-tie alignment failure probability in this analysis.

Byron and Braidwood Stations, Units 1 and 2 Page F-109 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 PRA Model Changes to Model SAMA:

The cutsets were updated to account for the completion of the AFW cross-tie modification.

Model Change(s):

The following modeling changes were made to the results cutsets:

• Event 1AF-XTIE--EHXVOA: HEP changed from 1.0 to 2.4E-02.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.89E-05 34.71 $246,863 Percent Change 2.0% 2.1% 3.0%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.09E-05 1.25E-01 1.18E-01 $118 $111 SERF-TISGTR-HLF 6.49E-09 2.11E-09 6.17E-03 2.00E-03 $44 $14 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 4.44E-08 6.36E-03 3.55E-03 $14 $8 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.04E-06 1.78E+01 1.71E+01 $187,040 $180,096 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.60E-07 3.41E-01 3.35E-01 $1,655 $1,624 LERF-CFE 3.55E-08 3.49E-08 8.88E-02 8.73E-02 $582 $572 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.46E-07 6.97E-01 6.37E-01 $8,205 $7,503 Total 4.19E-05 4.08E-05 3.55E+01 3.47E+01 $254,593 $246,863 Byron and Braidwood Stations, Units 1 and 2 Page F-110 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Applying the process described in Section F.4 yields an internal events cost-risk of $5,818,963.

After accounting for round up of the base internal events cost-risk, this value is $5,819,570.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,819,570

• 2.5 = $14,548,925 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 15 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,548,925 $401,075 There are no significant costs associated with completing the implementation of this modification and because the decision has already been made implement this change, it is not considered to be a traditional SAMA. The results are provided to document and demonstrate the estimated impact of the AFW cross-tie. However, the averted cost-risk of $401,075 is treated as the net value of this SAMA for this portion of the analysis.

F.6.13 SAMA 16 INSTALL HIGH FLOW SENSORS ON THE NON-ESSENTIAL SERVICE WATER SYSTEM Installing flow sensors in the WS lines with logic to trip the pumps on high flow conditions is a potential means of terminating WS flood events before critical systems are damaged.

Assumptions:

It is assumed that this SAMA eliminates all risk associated with WS flooding scenarios.

PRA Model Changes to Model SAMA:

The cutsets were updated to delete the contributions from WS flood initiators.

Model Change(s):

The following modeling changes were made to the results cutsets:

• Event %FL1WS-GA0----T1: Event set to 0.0.

• Event %FL1WS-GT0----NA: Event set to 0.0.

• Event %FL1WSM1A0----T1: Event set to 0.0.

• Event %FL1WSM2A0----T1: Event set to 0.0.

• Event %FL1WSM3A0HVACT1: Event set to 0.0.

Byron and Braidwood Stations, Units 1 and 2 Page F-111 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2

• Event %FL1WSM3A0----T1: Event set to 0.0.

• Event %FL1WSM3A0----T2: Event set to 0.0.

• Event %FL1WSM3A1DAFPT1: Event set to 0.0.

• Event %FL1WSM3A2DAFPT1: Event set to 0.0.

• Event %FL1WSM3A2DAFPT2: Event set to 0.0.

• Event %FL1WS-MT0----NA: Event set to 0.0.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.90E-05 33.82 $238,089 Percent Change 1.8% 4.6% 6.5%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Category Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.88E-05 1.05E+01 1.05E+01 $35,721 $35,532 LATE-CHR-NOAFW 8.35E-06 7.66E-06 1.78E+01 1.63E+01 $187,040 $171,584 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.08E-07 3.41E-01 2.86E-01 $1,655 $1,389 LERF-CFE 3.55E-08 3.47E-08 8.88E-02 8.68E-02 $582 $569 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.50E-07 6.97E-01 6.48E-01 $8,205 $7,625 Total 4.19E-05 4.10E-05 3.55E+01 3.38E+01 $254,593 $238,089 Byron and Braidwood Stations, Units 1 and 2 Page F-112 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Applying the process described in Section F.4 yields an internal events cost-risk of $5,663,001.

After accounting for round up of the base internal events cost-risk, this value is $5,663,608.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,663,608

• 2.5 = $14,159,020 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 16 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,159,020 $790,980 Based on a $993,800 cost of implementation for Byron, the net value for this SAMA is

-$202,820 ($790,980 - $993,800), which indicates this SAMA is not cost beneficial.

F.6.14 SAMA 17 USE AMASC FOR ALTERNATE LOW SG LEVEL AFW INITIATION For non-ATWS, the AMSAC logic could be used to provide a backup initiation signal for AFW.

This would mitigate failures of the normal solid state protection system (SSPS) initiation system.

Assumptions:

For this analysis, it is assumed that the AMSAC logic is 100 percent reliable and that the implementation of the SAMA can be modeled by eliminating the independent manual AFW initiation HFE in conjunction with all associated JHEPs.

PRA Model Changes to Model SAMA:

The fault tree was updated to use the existing AMSAC logic as a backup initiation signal to the AFW initiation logic.

Model Change(s):

The following HFEs were set to 0.0:

• 1AF-STARTFWHPMOA: OPERATORS FAIL TO MANUALLY START AF PUMPS FROM CR (LOFW)

• 1AF-START-BHPMOA: OPERATORS FAIL TO LOCALLY START B AUXILIARY FEEDWATER PUMP

• 1AF-START--HPMOA: OPERATORS FAIL TO MANUALLY START AF PUMPS FROM CR (NON-LOFW EVENT)

Byron and Braidwood Stations, Units 1 and 2 Page F-113 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2

• Joint HEPs: 1RX-JHEP19-HOADA, 1RX-JHEP20-HOADA, 1RX-JHEP21-HOADA, 1RX-JHEP29-HOADA, 1RX-JHEP35-HOADA, 1RX-JHEP36-HOADA, 1RX-JHEP38-HOADA, 1RX-JHEP39-HOADA, 1RX-JHEP40-HOADA, 1RX-JHEP41-HOADA, 1RX-JHEP64-HOADA, 1RX-JHEP70-HOADA, 1RX-JHEP71-HOADA, 1RX-JHEP73-HOADA, 1RX-JHEP74-HOADA Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.96E-05 35.41 $254,210 Percent Change 0.3% 0.1% 0.2%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.15E-05 1.25E-01 1.24E-01 $118 $117 SERF-TISGTR-HLF 6.49E-09 5.77E-09 6.17E-03 5.48E-03 $44 $39 SERF-SGTR-AFW-1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 SC LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-7.95E-08 7.25E-08 6.36E-03 5.80E-03 $14 $13 NOAFW LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.34E-06 1.78E+01 1.78E+01 $187,040 $186,816 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.63E-07 3.41E-01 3.38E-01 $1,655 $1,637 LERF-CFE 3.55E-08 3.48E-08 8.88E-02 8.70E-02 $582 $571 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.65E-07 6.97E-01 6.86E-01 $8,205 $8,083 Total 4.19E-05 4.18E-05 3.55E+01 3.54E+01 $254,593 $254,210 Byron and Braidwood Stations, Units 1 and 2 Page F-114 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Applying the process described in Section F.4 yields an internal events cost-risk of $5,969,721.

After accounting for round up of the base internal events cost-risk, this value is $5,970,328.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,970,328

• 2.5 = $14,925,820 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 17 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,925,820 $24,180 Based on a $981,730 cost of implementation for Byron, the net value for this SAMA is

-$957,550 ($24,180 - $981,730), which indicates this SAMA is not cost beneficial.

F.6.15 SAMA 18 AUTOMATE REFILL OF THE DIESEL DRIVEN AFW PUMP FUEL OIL DAY TANK The action to refill the diesel driven AFW pump fuel oil day tank is currently a manual action.

Level sensors in the tank could be used to control a fill valve on the gravity feed line to automate the function, which would potentially improve system reliability.

Assumptions:

For this analysis, it is assumed that the action is 100 percent reliable. Implementation of this SAMA is assumed to eliminate the independent HFE and all dependent combinations that include the action.

PRA Model Changes to Model SAMA:

The cutsets were modified by setting the action representing the failure to refill the AFW diesel fuel oil, and all JHEPs including that event, to 0.0.

Model Change(s):

The following HFEs were set to 0.0:

• 1AF01PB-FO-HXVOA: OPERATORS FAIL TO REFILL DDAFP FUEL OIL DAY TANK FROM STORAGE TANK

• Joint HEPs: 1AF01PB-FO-HXVOA, 1RX-JHEP03-HOADA, 1RX-JHEP04-HOADA, 1RX-JHEP07-HOADA, 1RX-JHEP16-HOADA, 1RX-JHEP17-HOADA, 1RX-JHEP19-HOADA, 1RX-JHEP21-HOADA, 1RX-JHEP24-HOADA, 1RX-JHEP29-HOADA, 1RX-JHEP31-Byron and Braidwood Stations, Units 1 and 2 Page F-115 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 HOADA , 1RX-JHEP35-HOADA, 1RX-JHEP36-HOADA, 1RX-JHEP38-HOADA, 1RX-JHEP39-HOADA, 1RX-JHEP40-HOADA, 1RX-JHEP41-HOADA, 1RX-JHEP43-HOADA, 1RX-JHEP46-HOADA, 1RX-JHEP50-HOADA, 1RX-JHEP51-HOADA, 1RX-JHEP53-HOADA, 1RX-JHEP54-HOADA, 1RX-JHEP55-HOADA, 1RX-JHEP57-HOADA, 1RX-JHEP58-HOADA, 1RX-JHEP60-HOADA, 1RX-JHEP65-HOADA, 1RX-JHEP68-HOADA, 1RX-JHEP77-HOADA, 1RX-JHEP79-HOADA , 1RX-JHEP83-HOADA Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.95E-05 35.32 $253,239 Percent Change 0.5% 0.4% 0.5%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.13E-05 1.25E-01 1.22E-01 $118 $115 SERF-TISGTR-HLF 6.49E-09 6.07E-09 6.17E-03 5.77E-03 $44 $41 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 6.88E-08 6.36E-03 5.50E-03 $14 $13 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.30E-06 1.78E+01 1.77E+01 $187,040 $185,920 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.65E-07 3.41E-01 3.39E-01 $1,655 $1,646 LERF-CFE 3.55E-08 3.53E-08 8.88E-02 8.83E-02 $582 $579 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.62E-07 6.97E-01 6.79E-01 $8,205 $7,991 Total 4.19E-05 4.15E-05 3.55E+01 3.53E+01 $254,593 $253,239 Byron and Braidwood Stations, Units 1 and 2 Page F-116 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Applying the process described in Section F.4 yields an internal events cost-risk of $5,949,619.

After accounting for round up of the base internal events cost-risk, this value is $5,950,226.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,950,226

• 2.5 = $14,875,565 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 18 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,875,565 $74,435 Based on a $1,608,680 cost of implementation for Byron, the net value for this SAMA is

-$1,534,245 ($74,435 - $1,608,680), which indicates this SAMA is not cost beneficial.

F.6.16 SAMA 19 REPLACE MOVS IN THE RHR DISCHARGE LINE WITH VALVES THAT CAN ISOLATE AN ISLOCA EVENT For cases in which the check valves fail in the RHR discharge line and an ISLOCA occurs, the event could be terminated if the containment isolation valves were capable of closing after the ISLOCA has occurred. Replacing the existing valves (MOVs _SI8809A, _SI8809B, and

_SI8840) with an alternate design could provide this capability.

Assumptions:

It is assumed that implementation of this SAMA will eliminate all risk from the ISLOCA events occurring in the RHR discharge lines PRA Model Changes to Model SAMA:

The cutsets were modified by setting the events representing ISLOCAs in the RHR discharge line to 0.0.

Model Change(s):

The following event was set to 0.0:

• %RCS-RHR-DISCHIE: FREQ OF EXPOSING RHR PUMP DISCHARGE HEADERS TO RCS PRESSURE Results of SAMA Quantification:

Byron and Braidwood Stations, Units 1 and 2 Page F-117 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.95E-05 32.08 $245,394 Percent Change 0.5% 9.5% 3.6%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.34E-06 1.78E+01 1.78E+01 $187,040 $186,816 LERF-ISLOCA 3.40E-07 8.21E-08 4.42E+00 1.07E+00 $11,832 $2,857 LERF-CI 3.67E-07 3.67E-07 3.41E-01 3.41E-01 $1,655 $1,655 LERF-CFE 3.55E-08 3.55E-08 8.88E-02 8.88E-02 $582 $582 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.69E-07 6.97E-01 6.97E-01 $8,205 $8,205 Total 4.19E-05 4.16E-05 3.55E+01 3.21E+01 $254,593 $245,394 Applying the process described in Section F.4 yields an internal events cost-risk of $5,734,097.

After accounting for round up of the base internal events cost-risk, this value is $5,734,704.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,734,704

• 2.5 = $14,336,760 Byron and Braidwood Stations, Units 1 and 2 Page F-118 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 19 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,336,760 $613,240 Based on a $900,000 cost of implementation for Byron, the net value for this SAMA is

-$286,760 ($613,240 - $900,000), which indicates this SAMA is not cost beneficial F.6.17 SAMA 21 INSTALL AN EMERGENCY ISOLATION VALVE IN EACH OF THE RHR SUCTION LINES For cases in which the two motor operated isolation valves in the RHR suction line fail and result in the overpressurization of the low pressure RHR piping, a LOCA outside containment can occur if the RHR piping breaks. In the event of a piping break, having an additional, normally open MOV located on the high pressure piping capable of closing against RCS pressure would provide a means of terminating the ISLOCA event.

Assumptions:

It is assumed that implementation of this SAMA will eliminate all risk from the ISLOCA events occurring in the RHR suction lines PRA Model Changes to Model SAMA:

The cutsets were modified by setting the events representing ISLOCAs in the RHR suction lines to 0.0.

Model Change(s):

The following event was set to 0.0:

• %RCS-RHR-SUCT-IE: FREQUENCY OF HAVING RCS PRESSURE IN THE RHR SUCTION LINE Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Byron and Braidwood Stations, Units 1 and 2 Page F-119 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.97E-05 34.59 $252,107 Percent Change 0.0% 2.4% 1.0%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.34E-06 1.78E+01 1.78E+01 $187,040 $186,816 LERF-ISLOCA 3.40E-07 2.75E-07 4.42E+00 3.58E+00 $11,832 $9,570 LERF-CI 3.67E-07 3.67E-07 3.41E-01 3.41E-01 $1,655 $1,655 LERF-CFE 3.55E-08 3.55E-08 8.88E-02 8.88E-02 $582 $582 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.69E-07 6.97E-01 6.97E-01 $8,205 $8,205 Total 4.19E-05 4.18E-05 3.55E+01 3.46E+01 $254,593 $252,107 Applying the process described in Section F.4 yields an internal events cost-risk of $5,915,947.

After accounting for round up of the base internal events cost-risk, this value is $5,916,554.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,916,554

• 2.5 = $14,791,385 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

Byron and Braidwood Stations, Units 1 and 2 Page F-120 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 SAMA 21 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,791,385 $158,615 Based on an $1,600,000 cost of implementation for Byron, the net value for this SAMA is

-$1,441,385 ($158,615 - $1,600,000), which indicates this SAMA is not cost beneficial.

F.6.18 SAMA 22 INSTALL THE SAME HIGH FLOW ISOLATION LOGIC USED ON VALVE _CC685 ON VALVE _CC9438 In the event that an RCP Thermal Barrier Cooling heat exchangers breaks, the current in-containment relief valves are designed to relieve pressure at 2485 psig, which would be within the capacity of the piping up to the isolation boundary. However, if the Thermal Barrier Cooling Hx were to break and the isolation valve failed to close, the CC system could be over pressurized and inventory could be transferred outside containment through the 150 psid relief valves. A potential means of mitigating this event would be to install the same isolation logic used on valve _CC685 on valve_CC9438.

Assumptions:

It is assumed that implementation of this SAMA will eliminate all risk from the ISLOCA events occurring in the RCP thermal barrier cooling heat exchangers.

PRA Model Changes to Model SAMA:

The cutsets were modified by setting the events representing ISLOCAs in the RCP thermal barrier cooling heat exchangers to 0.0.

Model Change(s):

The following event was set to 0.0:

%RCP-HX-RUPT--IE: FREQUENCY OF RCP HEAT EXCHANGER RUPTURE Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Byron and Braidwood Stations, Units 1 and 2 Page F-121 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.97E-05 35.24 $253,847 Percent Change 0.0% 0.6% 0.3%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.34E-06 1.78E+01 1.78E+01 $187,040 $186,816 LERF-ISLOCA 3.40E-07 3.25E-07 4.42E+00 4.23E+00 $11,832 $11,310 LERF-CI 3.67E-07 3.67E-07 3.41E-01 3.41E-01 $1,655 $1,655 LERF-CFE 3.55E-08 3.55E-08 8.88E-02 8.88E-02 $582 $582 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.69E-07 6.97E-01 6.97E-01 $8,205 $8,205 Total 4.19E-05 4.19E-05 3.55E+01 3.52E+01 $254,593 $253,847 Applying the process described in Section F.4 yields an internal events cost-risk of $5,961,668.

After accounting for round up of the base internal events cost-risk, this value is $5,962,275.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,962,275

• 2.5 = $14,905,688 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

Byron and Braidwood Stations, Units 1 and 2 Page F-122 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 SAMA 22 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,905,688 $44,312 Based on a $250,000 cost of implementation for Byron, the net value for this SAMA is

-$205,688 ($44,312 - $250,000), which indicates this SAMA is not cost beneficial.

F.6.19 SAMA 23 INSTALL A PASSIVE HYDROGEN IGNITION SYSTEM For accident scenarios resulting in the generation of hydrogen in quantities sufficient to cause significant hydrogen detonations, containment failure is possible. A potential means of preventing these containment failure scenarios would be to install a passive hydrogen ignition system.

Assumptions:

It is assumed that implementation of this SAMA will eliminate all containment failures due to hydrogen detonation. Some of the Level 2 events that represent containment failure due to hydrogen detonations also include containment failure due to other phenomena, but no attempt is made to separate them from the hydrogen failures. This results in an increased averted cost-risk, which makes it more likely that the SAMA will be cost effective.

PRA Model Changes to Model SAMA:

The cutsets were modified by setting the events representing containment failure due to hydrogen detonation to 0.0.

Model Change(s):

The following events were set to 0.0:

• 1L2-CNT-VF-CFE1: Early Cont Failure due to Hydrogen Burn or Stm Expl

• 1L2-CNT-VF-CFE2: Early Cont Failure due to Hydrogen Burn

• 1L2-CNT-VF-CFE4: Early Cont Failure due to Direct Containment Heating, Hydrogen Burn, or Stm Expl Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Byron and Braidwood Stations, Units 1 and 2 Page F-123 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.97E-05 35.34 $253,787 Percent Change 0.0% 0.3% 0.3%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.34E-06 1.78E+01 1.78E+01 $187,040 $186,816 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.67E-07 3.41E-01 3.41E-01 $1,655 $1,655 LERF-CFE 3.55E-08 0.00E+00 8.88E-02 0.00E+00 $582 $0 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.69E-07 6.97E-01 6.97E-01 $8,205 $8,205 Total 4.19E-05 4.19E-05 3.55E+01 3.53E+01 $254,593 $253,787 Applying the process described in Section F.4 yields an internal events cost-risk of $5,963,958.

After accounting for round up of the base internal events cost-risk, this value is $5,964,565.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,964,565

• 2.5 = $14,911,413 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

Byron and Braidwood Stations, Units 1 and 2 Page F-124 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 SAMA 23 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,911,413 $38,587 Based on a $760,000 cost of implementation for Byron, the net value for this SAMA is

-$721,413 ($38,587 - $760,000), which indicates this SAMA is not cost beneficial.

F.6.20 SAMA 24 PROVIDE A REACTOR VESSEL EXTERIOR COOLING SYSTEM This SAMA would provide the potential to cool a molten core before it causes vessel failure, if the lower head can be submerged in water. For Byron, use of existing emergency power is adequate to address the highest contributors.

Assumptions:

It is assumed that the implementation of this SAMA is 100 percent effective at preventing relocation of the core to the containment floor. For cases in which containment heat removal is successful, this would result in the reclassification of the basemat melt through scenarios as intact cases.

For containment overpressure failure cases, this SAMA would result in the retention of the core in the vessel without an overlying pool of water. The dominant scenarios for the existing containment overpressure failure cases are those in which containment spray is available and water is transferred to the containment floor. In these scenarios, use of the exterior vessel cooling system could actually prevent scrubbing of the release; however, for simplicity, the benefit of this SAMA is not reduced to address the fact that this SAMA would eliminate the scrubbing mechanism for these scenarios. This assumption increases this SAMAs averted cost-risk.

With the exception of hydrogen detonation, the early containment failure modes are linked to reactor vessel failure such that early containment failure would likely be avoided if reactor vessel failure is prevented. For simplicity, it is assumed that this SAMA eliminates all early containment failures.

PRA Model Changes to Model SAMA:

The events in the PRA model associated with early containment failure and basemat failure have been set to 0.0.

Byron and Braidwood Stations, Units 1 and 2 Page F-125 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Model Change(s):

The following event probability changes were made to the PRA model:

• 1L2-CNT-VF-CFE1: Early Cont Failure due to Hydrogen Burn or Stm Expl, set to 0.0.

• 1L2-CNT-VF-CFE2: Early Cont Failure due to Hydrogen Burn, set to 0.0.

• 1L2-CNT-VF-CFE3: Early Cont Failure due to Direct Containment Heating, set to 0.0

• 1L2-CNT-VF-CFE4: Early Cont Failure due to Direct Containment Heating, Hydrogen Burn, or Stm Expl, set to 0.0.

• 1L2-CNT-VF-BMMTD: Probability of BMMT with a dry cavity, set to 0.0.

• 1L2-CNT-VF-BMMTW: Probability of BMMT with water in the cavity, set to 0.0.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.97E-05 35.34 $253,974 Percent Change 0.0% 0.3% 0.2%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 0.00E+00 1.63E-02 0.00E+00 $22 $0 LATE-BMMT-NOAFW 7.95E-08 0.00E+00 6.36E-03 0.00E+00 $14 $0 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.35E-06 1.78E+01 1.78E+01 $187,040 $187,040 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.67E-07 3.41E-01 3.41E-01 $1,655 $1,655 LERF-CFE 3.55E-08 0.00E+00 8.88E-02 0.00E+00 $582 $0 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 Byron and Braidwood Stations, Units 1 and 2 Page F-126 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.69E-07 6.97E-01 6.97E-01 $8,205 $8,205 Total 4.19E-05 4.13E-05 3.55E+01 3.53E+01 $254,593 $253,974 Applying the process described in Section F.4 yields an internal events cost-risk of $5,966,733.

After accounting for round up of the base internal events cost-risk, this value is $5,967,340.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,967,340

• 2.5 = $14,918,350 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 24 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,918,350 $31,650 Based on a $1,250,000 cost of implementation for Byron, the net value for this SAMA is

-$1,218,350 ($31,650 - $1,250,000), which indicates this SAMA is not cost beneficial.

F.6.21 SAMA 25 INSTALL A FILTERED CONTAINMENT VENT This SAMA would provide a means of preventing long term containment overpressure failures by relieving pressure through a scrubbed release path. While post core damage venting is undesirable, a controlled scrubbed release is preferable to an unscrubbed release through a containment break.

Assumptions:

It is assumed that this SAMA is 100 percent reliable in operation, but the effectiveness of the radionuclide scrubbing mechanism is not complete. For this analysis, it is assumed that the filtered vent reduces the consequential dose and offsite economic cost associated with containment overpressure failures by a factor of 10.

Byron and Braidwood Stations, Units 1 and 2 Page F-127 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 PRA Model Changes to Model SAMA:

The results of the Level 3 model (dose, offsite economic cost) for the LATE-CHR-AFW and LATE-CHR-NOAFW endstates are reduced by a factor of 10.

Model Change(s):

The following changes were made to the L3 results:

• LATE-CHR-AFW: Dose-risk and OECR multiplied by 0.1.

• LATE-CHR-NOAFW: Dose-risk and OECR multiplied by 0.1.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.97E-05 9.99 $54,108 Percent Change 0.0% 71.8% 78.7%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Category Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA INTACT 1.16E-05 1.16E-05 1.25E-01 1.25E-01 $118 $118 SERF-TISGTR-HLF 6.49E-09 6.49E-09 6.17E-03 6.17E-03 $44 $44 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.30E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.95E-08 6.36E-03 6.36E-03 $14 $14 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+00 $35,721 $3,572 LATE-CHR-NOAFW 8.35E-06 8.35E-06 1.78E+01 1.78E+00 $187,040 $18,704 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.67E-07 3.41E-01 3.41E-01 $1,655 $1,655 LERF-CFE 3.55E-08 3.55E-08 8.88E-02 8.88E-02 $582 $582 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 Byron and Braidwood Stations, Units 1 and 2 Page F-128 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Release Category Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA LERF-ISGTR 2.69E-07 2.69E-07 6.97E-01 6.97E-01 $8,205 $8,205 Total 4.19E-05 4.19E-05 3.55E+01 9.99E+00 $254,593 $54,108 Applying the process described in Section F.4 yields an internal events cost-risk of $2,198,225.

After accounting for round up of the base internal events cost-risk, this value is $2,198,832.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $2,198,832

• 2.5 = $5,497,080 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 25 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $5,497,080 $9,452,920 Based on a $5,700,000 cost of implementation for Byron, the net value for this SAMA is

$3,752,920 ($9,452,920 - $5,700,000), which indicates this SAMA is potentially cost beneficial.

Byron and Braidwood Stations, Units 1 and 2 Page F-129 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.6.22 SAMA 26 DMS USING A DEDICATED GENERATOR, SELF COOLED CHARGING PUMP, AND A PORTABLE AFW PUMP This SAMA represents an alternate configuration of the DMS in which seal LOCAs are prevented using a seal injection system rather than by no leak seals. A dedicated 480V AC generator is proposed as a means of supporting long term SG makeup by maintaining the buses used for the battery chargers for SG level instrumentation and for powering a self-cooled primary side seal injection pump. A portable, engine driven SG makeup pump would provide an alternate means of SG makeup, with injection connections available on different divisions. Fire protection should provide both CST makeup and a suction source connection for the portable SG makeup pump A means of providing borated makeup to the RWST is also required, which could potentially be performed using the fire protection system and an eductor. Finally, a connection point to an outside source would have to be provided for the containment spray system for long term spray capability in an SBO.

Assumptions:

SAMA 26 was generally identified as a means of mitigating scenarios in which loss of SG makeup is a slowly developing evolution, such as in SBO events where battery depletion eventually fails AFW or in loss of SX cases in which the AFW pumps may be able to run for some time before failure. No credit is taken for the DMS in LOCA (other than seal LOCA) or ATWS scenarios. The DMS is credited in SGTR initiators as most cases include success of injection where time would be available to recover secondary side heat removal in the event of an initial AFW failure. Prior to core damage, activity levels are expected to be low enough to perform any alignment required.

The DMS capabilities are assumed to be represented by indefinite AFW makeup capability and by an alternate high pressure injection function capable of providing alternate seal injection to prevent RCP seal LOCAs. The current PRA does not include credit for RWST refill, so the PRA is structured to require recirculation mode in seal LOCA evolutions even with AFW success.

This SAMA, however, includes an RWST makeup capability that is assumed to preclude the need for recirculation mode. Long term containment overfill is potentially an issue that could ultimately prevent success in these cases, but it is assumed that a success of DMS high pressure injection and SG makeup results in a successful endstate. In order to simplify the modeling process, the seal LOCA flag is used to model the impact of the DMS high pressure seal injection system. The self-cooled charging pump is assumed to reduce the frequency of seal LOCA sequences by a factor of 100.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 The AFW makeup capability includes alignment and control of a dedicated (permanently installed) 480V generator and alignment and control of a portable SG makeup pump. A new event with a failure probability of 1E-2 is used for this function.

It is assumed that the cognitive failure to diagnose the need for secondary cooling (1FW-FRH1--

-HSGOA), which is related to the AFW X-tie, FW restoration, and bleed and feed, will also fail the DMS. In addition, any dependent combinations are also assumed to fail the DMS.

PRA Model Changes to Model SAMA:

The capabilities of SAMA 26 are essentially the same as those for SAMA 11 with the exception that the seal LOCAs are mitigated by an injection capability rather than prevented by an alternate seal design. The impact of the seal injection system is modeled by manipulating the cutsets from SAMA 11.

Model Change(s):

The cutsets from SAMA 11 were modified to reflect the use of the DMS primary injection capability for Seal LOCA mitigation.

The following modeling changes were made to the SAMA 11 cutsets:

• The FLAG-SEAL-LOCA flag was replaced by event 1DMS (as defined in SAMA 11) to represent the use of the DMS to mitigate Seal LOCAs.

• To address potential dependency issues, the 1DMS event was replaced by event 1DMS-DEPENDENT (set to 1.0) for any cutsets including failure to diagnose the need for feed and bleed (represents complete cognitive dependence between feed and bleed and primary side injection with the DMS). The HFEs addressed included 1FW-FRH1---HSGOA, 1RX-JHEP03-HOADA and similar events for the following JHEP combinations: 07, 09, 11,12, 14, 17, 21, 24, 25, 27, 39, 49, 50, 54, 58, 64, 74, and 80.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 4.90E-06 7.21 $32,778 Percent Change 87.7% 79.7% 87.1%

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 2.33E-06 1.25E-01 2.52E-02 $118 $24 SERF-TISGTR-HLF 6.49E-09 1.52E-09 6.17E-03 1.44E-03 $44 $10 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 8.80E-08 1.63E-02 2.71E-03 $22 $4 LATE-BMMT-NOAFW 7.95E-08 3.12E-08 6.36E-03 2.50E-03 $14 $6 LATE-CHR-AFW 1.89E-05 5.04E-07 1.05E+01 2.80E-01 $35,721 $953 LATE-CHR-NOAFW 8.35E-06 4.27E-07 1.78E+01 9.10E-01 $187,040 $9,565 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 2.63E-08 3.41E-01 2.45E-02 $1,655 $119 LERF-CFE 3.55E-08 2.97E-09 8.88E-02 7.43E-03 $582 $49 LERF-SGTR-AFW 5.49E-08 5.48E-08 1.31E-01 1.31E-01 $1,005 $1,003 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.82E-08 6.97E-01 7.30E-02 $8,205 $860 Total 4.19E-05 5.21E-06 3.55E+01 7.21E+00 $254,593 $32,778 Applying the process described in Section F.4 yields an internal events cost-risk of $843,494.

After accounting for round up of the base internal events cost-risk, this value is $844,494. The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $844,494

• 2.5 = $2,110,253 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 26 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $2,110,253 $12,839,747 Based on a $2,400,000 cost of implementation for Byron, the net value for this SAMA is

$10,439,747 ($12,839,747 - $2,400,000), which indicates this SAMA is potentially cost beneficial.

Byron and Braidwood Stations, Units 1 and 2 Page F-132 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.6.23 SAMA 27 PROTECT RH, SI, AND CVCS CUBICLE COOLING FAN CABLES IN FIRE ZONE 11.3-0 While most of the equipment damage in the dominant fire scenario in zone 11.3-0 is related to the loss of MCC 132X1 (the ignition source), protecting the cables related to the RH, SI, and CVCS pump cubicle cooling fans may reduce the likelihood that room cooling will be failed for those pumps.

Assumptions:

This SAMA will eliminate all of the risk associated with fire zone 11.3-0.

The ratio of internal events cost-risk to internal events CDF is equal to the ratio of fire cost-risk to fire CDF.

PRA Model Changes to Model SAMA:

The CDF associated with fire zone 11.3-0 was changed from 1.38E-05 to 0.0 to model the installation of the cable protection.

Results of SAMA Quantification:

The averted cost-risk for this SAMA is the cost-risk associated with fire zone 11.3-0 because this SAMA is assumed to entirely eliminate it. Using the assumptions identified above, the result is as follows:

$5,979,393 / 3.97E-05

• 1.38E-05 = $2,078,479 Based on a $975,000 cost of implementation for Byron, the net value for this SAMA is

$1,103,479 ($2,078,479 - $975,000), which indicates this SAMA is potentially cost beneficial.

F.6.24 SAMA 28 INSTALL FIRE BARRIERS AROUND MCC 134X Fires that start in this MCC are exacerbated by the propagation of the fire to nearby equipment.

Installation of fire barriers to protect the equipment could mitigate the consequences of the fires.

Assumptions:

This SAMA will eliminate all of the risk associated with fire zone 11.6-0.

The ratio of internal events cost-risk to internal events CDF is equal to the ratio of fire cost-risk to fire CDF.

PRA Model Changes to Model SAMA:

The CDF associated with fire zone 11.6-0 was changed from 6.00E-06 to 0.0 to model the installation of the fire barriers.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Results of SAMA Quantification:

The averted cost-risk for this SAMA is the cost-risk associated with fire zone 11.6-0 because this SAMA is assumed to entirely eliminate it. Using the assumptions identified above, the result is as follows:

$5,979,393 / 3.97E-05

• 6.00E-06 = $903,687 Based on a $975,000 cost of implementation for Byron, the net value for this SAMA is -$71,313

($903,687 - $975,000), which indicates this SAMA is not cost beneficial.

F.6.25 SAMA 29 AUTOMATE SWAP TO RECIRCULATION MODE Fully automating the swap to recirculation mode and removing the operator from the process can improve the reliability of the action.

Assumptions:

It is assumed that this SAMA will eliminate the contributions from the failure to swap to recirculation mode.

PRA Model Changes to Model SAMA:

The independent and dependent operator action events associated with recirculation initiation are set to 0.0 to represent this SAMA.

Model Change(s):

The following events were set to 0.0:

• 1SI-HPR----HSYOA: OPERATORS FAIL TO ESTABLISH HIGH PRESSURE RECIRC (SLOW EVENT)

• 1RX-JHEP19-HOADA and similar events for the following JHEP combinations: 36, 51, 55, and 71.

Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.94E-05 35.40 $254,103 Percent Change 0.8% 0.1% 0.2%

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA Category INTACT 1.16E-05 1.12E-05 1.25E-01 1.21E-01 $118 $114 SERF-TISGTR-HLF 6.49E-09 6.12E-09 6.17E-03 5.81E-03 $44 $41 SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.28E-07 1.63E-02 1.63E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 6.38E-08 6.36E-03 5.10E-03 $14 $12 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.34E-06 1.78E+01 1.78E+01 $187,040 $186,816 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.65E-07 3.41E-01 3.39E-01 $1,655 $1,646 LERF-CFE 3.55E-08 3.53E-08 8.88E-02 8.83E-02 $582 $579 LERF-SGTR-AFW 5.49E-08 5.49E-08 1.31E-01 1.31E-01 $1,005 $1,005 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.61E-07 6.97E-01 6.76E-01 $8,205 $7,961 Total 4.19E-05 4.15E-05 3.55E+01 3.54E+01 $254,593 $254,103 Applying the process described in Section F.4 yields an internal events cost-risk of $5,962,320.

After accounting for round up of the base internal events cost-risk, this value is $5,962,927.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,962,927

• 2.5 = $14,907,318 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 29 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,907,318 $42,682 Based on a $1,225,000 cost of implementation for Byron, the net value for this SAMA is

-$1,182,318 ($42,682 - $1,225,000), which indicates this SAMA is not cost beneficial.

Byron and Braidwood Stations, Units 1 and 2 Page F-135 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.6.26 SAMA 30 PROTECT AFW CABLES IN THE AUX BUILDING GENERAL AREA, ELEVATION 383' Fires initiating in the AFW 1A pump result in damage to the AFW 1B and 2A pumps. Protecting the AFW cables in these areas will improve the potential for pumps 1B and 2A to remain available in these scenarios for SG makeup.

Assumptions:

This SAMA will eliminate all of the risk associated with fire zone 11.4-0.

The ratio of internal events cost-risk to internal events CDF is equal to the ratio of fire cost-risk to fire CDF.

PRA Model Changes to Model SAMA:

The CDF associated with fire zone 11.4-0 was changed from 3.79E-06 to 0.0 to model the installation of the fire barriers.

Results of SAMA Quantification:

The averted cost-risk for this SAMA is the cost-risk associated with fire zone 11.4-0 because this SAMA is assumed to entirely eliminate it. Using the assumptions identified above, the result is as follows:

$5,979,393 / 3.97E-05

• 3.79E-06 = $570,829 Based on a $975,000 cost of implementation for Byron, the net value for this SAMA is

-$404,171 ($570,829 - $975,500), which indicates this SAMA is not cost beneficial.

F.6.27 SAMA 31 UNIT 2 SAMA - PROTECT CABLES FOR 2AF013A, B, AND D IN THE AUX BUILDING GENERAL AREA, ELEVATION 426' Fires in this are (initiated in MCC 234X, for example) can fail both trains of AFW. Protecting the cables that are vulnerable (A, B, and D in the important scenario), would help preserve the AFW function.

Assumptions:

This SAMA will eliminate all of the risk associated with fire zone 11.6-0 (Unit 2).

The ratio of internal events cost-risk to internal events CDF is equal to the ratio of fire cost-risk to fire CDF.

PRA Model Changes to Model SAMA:

The CDF associated with fire zone 11.6-0 (Unit 2) was changed from 1.06E-05 to 0.0 to model the installation of the fire barriers.

Byron and Braidwood Stations, Units 1 and 2 Page F-136 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Results of SAMA Quantification:

The averted cost-risk for this SAMA is the cost-risk associated with fire zone 11.6-0 (Unit 2) because this SAMA is assumed to entirely eliminate it. Using the assumptions identified above, the result is as follows:

$5,979,393 / 3.97E-05

• 1.06E-05 = $1,596,513 Based on a $975,000 cost of implementation for Byron, the net value for this SAMA is $621,513

($1,596,513 - $975,000), which indicates this SAMA is potentially cost beneficial.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.7 SENSITIVITY ANALYSIS The following three uncertainties were further investigated as to their impact on the overall SAMA evaluation:

• Use a discount rate of 7 percent, instead of 3 percent used in the base case analysis.

• Use the 95th percentile PRA results in place of the point estimate PRA results.

• Selected MACCS2 input variables.

• Inclusion of the AFW Cross-tie modification as part of the base model F.7.1 REAL DISCOUNT RATE A sensitivity study has been performed in order to identify how the conclusions of the SAMA analysis might change based on the value assigned to the real discount rate (RDR). The original RDR of 3 percent, which could be viewed as conservative, has been changed to 7 percent and the maximum averted cost-risk was re-calculated using the methodology outlined in Section F.4.

Based on the reduction in the MACR to $10,970,000 (a 27 percent reduction of the baseline MACR), two additional SAMAs would be screened in Phase 1 that were not screened when the RDR of 3 percent was used (SAMAs 4 and 11).

The Phase 2 analysis was re-performed using the 7 percent RDR. As shown below, the determination of cost effectiveness changed for one of the Phase 2 SAMAs when the 7 percent RDR was used in lieu of 3 percent.

Summary of the Impact of the RDR Value on the Detailed SAMA Analyses Change Averted Averted in Net Value Net Value SAMA Implementation Cost Risk Cost Risk Cost (3 percent (7 percent ID Cost (per unit) (3 percent (7 percent Effective RDR) RDR)

RDR) RDR) -

ness?

SAMA 2 $5,751,110 $3,940,272 -$1,810,838 $2,997,670 -$2,753,440 No SAMA 3 $1,130,300 $1,739,935 $609,635 $1,296,275 $165,975 No SAMA 5 $657,200 $3,763,930 $3,106,730 $2,718,822 $2,061,622 No SAMA 7 $100,000 $73,452 -$26,548 $58,700 -$41,300 No SAMA 8 $338,830 $319,387 -$19,443 $238,110 -$100,720 No SAMA 9 $349,300 $683,497 $334,197 $510,260 $160,960 No SAMA 10 $1,320,300 $1,669,087 $348,787 $1,226,492 -$93,808 Yes Byron and Braidwood Stations, Units 1 and 2 Page F-138 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Summary of the Impact of the RDR Value on the Detailed SAMA Analyses Change Averted Averted in Net Value Net Value SAMA Implementation Cost Risk Cost Risk Cost (3 percent (7 percent ID Cost (per unit) (3 percent (7 percent Effective RDR) RDR)

RDR) RDR) -

ness?

SAMA 13 $5,951,110 $12,856,042 $6,904,932 $9,432,235 $3,481,125 No SAMA 14 $3,800,000 $68,572 -$3,731,428 $51,795 -$3,748,205 No SAMA 15 $0 $401,075 $401,075 $292,477 $292,477 No SAMA 16 $993,800 $790,980 -$202,820 $570,825 -$422,975 No SAMA 17 $981,730 $24,180 -$957,550 $17,985 -$963,745 No SAMA 18 $1,608,680 $74,435 -$1,534,245 $54,630 -$1,554,050 No SAMA 19 $900,000 $613,240 -$286,760 $440,220 -$459,780 No SAMA 21 $1,600,000 $158,615 -$1,441,385 $113,510 -$1,486,490 No SAMA 22 $250,000 $44,312 -$205,688 $31,712 -$218,288 No SAMA 23 $760,000 $38,587 -$721,413 $27,615 -$732,385 No SAMA 24 $1,250,000 $31,650 -$1,218,350 $22,650 -$1,227,350 No SAMA 25 $5,700,000 $9,452,920 $3,752,920 $6,764,857 $1,064,857 No SAMA 26 $2,400,000 $12,839,747 $10,439,747 $9,425,752 $7,025,752 No SAMA 27 $975,000 $2,078,479 $1,103,479 $1,525,054 $550,054 No SAMA 28 $975,000 $903,687 -$71,313 $663,067 -$311,933 No SAMA 29 $1,225,000 $42,682 -$1,182,318 $32,587 -$1,192,413 No SAMA 30 $975,000 $570,829 -$404,171 $418,837 -$556,163 No SAMA 31 $975,000 $1,596,513 $621,513 $1,171,418 $196,418 No F.7.2 95TH PERCENTILE PRA RESULTS The results of the SAMA analysis can be impacted by implementing conservative values from the PRAs uncertainty distribution. If the best estimate failure probability values were consistently lower than the actual failure probabilities, the PRA model would underestimate plant risk and yield lower than actual averted cost-risk values for potential SAMAs. Re-assessing the cost-benefit calculations using the high end of the failure probability distributions is a means of identifying the impact of having consistently underestimated failure probabilities for plant equipment and operator actions included in the PRA model.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 A Level 1 internal events model uncertainty analysis was not performed for Byron model BB011b1. However, an uncertainty analysis was performed on Byron model BB011a in 2012.

Since the 95th percentile assessment employs a ratio rather than individual values, a determination was made to use the BB011a uncertainty results. The basis for this decision is that the 95th to CDF point estimate ratio is not expected to vary significantly between the two models, and hence, should provide a representative value. The availability and use of Level 2 uncertainties is unique since most plants incorporate only Level 1 analyses in their SAMA reports. The reason Level 2 analyses are not typically used is due to the differing degree of development and uncertainties between the two models. Specifically, the Level 1 model tends to represent the plant in a more thorough and comprehensive manner as opposed to the Level 2 model. Furthermore, there are more release contributors beyond those captured by LERF. As such, for the purposes of the 95th percentile analysis, only Level 1 results are used in the uncertainty process. The results of the Level 1 calculation are provided below.

In performing the sensitivity analysis, only the base case was used in determining the appropriate value for the 95th percentile. For those SAMAs that required the addition of new basic events, no new uncertainty distributions were assigned since the design and implementation of each SAMA was arbitrary and was defined by the analysis assumptions. The results of this uncertainty analysis, therefore, show the expected statistical uncertainty of the CDF risk metrics under the assumption that each SAMA was designed and implemented as it was specified in this analysis. All calculations were performed using version 3.0 of the EPRI Uncert software package for the Byron Unit 1 model.

The results of the uncertainty calculation are shown in the table below. The term CDFpe refers to the nominal BB011a CDF point estimate of 4.26E-05.

Summary of Uncertainty Distribution (from BB011a)

Mean 5% 50% 95% Factor > CDFpe 3.95E-05 1.03E-05 2.78E-05 1.04E-04 2.49 The above table reveals a factor that is 2.49 greater than the respective point estimate CDF, which is in agreement with industry experience. Therefore, for this analysis, the 95th percentile multiplier derived from the base case is used to examine the change in the cost benefit for each SAMA.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.7.2.1 PHASE 1 IMPACT For Phase 1 screening, use of the 95th percentile PRA results will increase the MACR and may prevent the screening of some of the higher cost modifications. However, the impact on the overall SAMA results due to the retention of the higher cost SAMAs for Phase 2 analysis is typically small. This is due to the fact that the benefit obtained from the implementation of those SAMAs must be extremely large in order to be cost beneficial.

The impact of uncertainty in the PRA results on the Phase 1 SAMA analysis has been examined. The MACR is the primary Phase 1 criterion affected by PRA uncertainty. Thus, this portion of the sensitivity is focused on recalculating the MACR using the 95th percentile PRA results and re-performing the Phase 1 screening process. As discussed above, the 95th PRA results are a factor of 2.49 greater than the point estimate CDF.

In order to simulate the use of the 95th percentile PRA results on the cost benefit calculations, the same scaling factor calculated for the Level 1 results was assumed to apply to the Level 3 results. Because the MACR calculations scale linearly with the CDF, dose-risk, and off-site economic cost-risk, the 95th percentile MACR can be calculated by multiplying the base case MACR by 2.49. This results in a 95th percentile MACR of $37,225,500.

The initial SAMA list has been re-examined using the revised MACR to identify SAMAs that would have been retained for the Phase 2 analysis. Those SAMAs that were previously screened due to costs of implementation that exceeded $14.95 million are now retained if the costs of implementation are less than $37,225,500. For Byron, SAMAs 1, 12 and 20 were screened in the Phase 1 analysis based on excessive implementation cost. Because the th implementation cost of SAMA 20 is less than the 95 percentile MACR, it has been retained for Phase 2 analysis.

Based on a detailed quantification of SAMA 20, new averted cost risk and net values at the 95th percentile were generated. As shown below, the net value for SAMA 20 is negative.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.7.2.1.1 SAMA 20: Disallow On-Line RHR Maintenance For cases in which one train of RHR is out of service for maintenance in such a way that it cannot respond in an accident scenario, the plant is vulnerable to single failure events for certain initiating events that require heat removal (for example LOCAs). Preventing on-line maintenance of RHR would significantly reduce the frequency of the associated core damage scenarios.

Assumptions:

It is assumed that implementation of this SAMA will eliminate all risk associated with RHR maintenance (no assessment is made to account for any increase in shutdown risk related to performing the maintenance during an outage).

PRA Model Changes to Model SAMA:

The cutsets were modified by setting the events representing RHR maintenance line to 0.0.

Model Change(s):

The following events were set to 0.0:

• 1RH01PA-----PMMM: RH PUMP 1RH01PA UNAVAILABLE DUE TO MAINTENANCE

• 1RH01PB-----PMMM: RH PUMP 1RH01PB UNAVAILABLE DUE TO MAINTENANCE Results of SAMA Quantification:

Implementation of this SAMA yielded a moderate reduction in internal CDF and similar reductions in Dose-Risk and Offsite Economic Cost-Risk. The results are summarized in the following table:

Internal CDF Dose-Risk OECR Base Value 3.97E-05 35.45 $254,593 SAMA Value 3.95E-05 35.42 $254,257 Percent Change 0.5% 0.1% 0.1%

A further breakdown of the Dose-Risk and OECR information is provided in the table below according to release category:

Release Category Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA INTACT 1.16E-05 1.13E-05 1.25E-01 1.22E-01 $118 $115 SERF-TISGTR-HLF 6.49E-09 6.31E-09 6.17E-03 5.99E-03 $44 $43 Byron and Braidwood Stations, Units 1 and 2 Page F-142 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Release Category Freq.BASE Freq.SAMA Dose-RiskBASE Dose-RiskSAMA OECRBASE OECRSAMA SERF-SGTR-AFW-SC 1.38E-06 1.38E-06 1.33E+00 1.33E+00 $8,349 $8,349 LATE-BMMT-AFW 5.30E-07 5.23E-07 1.63E-02 1.61E-02 $22 $22 LATE-BMMT-NOAFW 7.95E-08 7.22E-08 6.36E-03 5.78E-03 $14 $13 LATE-CHR-AFW 1.89E-05 1.89E-05 1.05E+01 1.05E+01 $35,721 $35,721 LATE-CHR-NOAFW 8.35E-06 8.34E-06 1.78E+01 1.78E+01 $187,040 $186,816 LERF-ISLOCA 3.40E-07 3.40E-07 4.42E+00 4.42E+00 $11,832 $11,832 LERF-CI 3.67E-07 3.65E-07 3.41E-01 3.39E-01 $1,655 $1,646 LERF-CFE 3.55E-08 3.53E-08 8.88E-02 8.83E-02 $582 $579 LERF-SGTR-AFW 5.49E-08 5.48E-08 1.31E-01 1.31E-01 $1,005 $1,003 LERF-SGTR-NOAFW 8.57E-10 8.57E-10 6.68E-04 6.68E-04 $6 $6 LERF-ISGTR 2.69E-07 2.66E-07 6.97E-01 6.89E-01 $8,205 $8,113 Total 4.19E-05 4.16E-05 3.55E+01 3.54E+01 $254,593 $254,257 Applying the process described in Section F.4 yields an internal events cost-risk of $5,967,807.

After accounting for round up of the base internal events cost-risk, this value is $5,968,414.

The external events contributions are accounted for by multiplying this value by 2.5:

Total Cost-RiskSAMA = $5,968,414

• 2.5 = $14,921,035 This information was used as input to the averted cost-risk calculation. The results of this calculation are provided in the following table:

SAMA 20 Averted Cost-Risk Unit Base Case Revised Averted Cost-Risk Cost-Risk Cost-Risk Byron Unit 1 $14,950,000 $14,921,035 $28,965 Based on a $20,000,000 cost of implementation for Byron, the net value for this SAMA is -

$19,971,035 ($28,965 - $20,000,000), which indicates this SAMA is not cost beneficial. When the 95th percentile PRA results are used, the averted cost-risk is increased by a factor of 2.49 to

$72,123, which still yields a negative net value ($72,123 - $20,000,000 = -$19,927,877). This SAMA is not cost beneficial.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.7.2.2 PHASE 2 IMPACT As discussed above, a single factor based on the 95th percentile for the base case is used to determine the impact of the cost-benefit analysis for the proposed SAMA candidates. The uncertainty analyses that are available for the Level 1 model are not available (or not used) for the Level 2 and 3 PRA models. In order to simulate the use of the 95th percentile results for the Level 2 and 3 models, the same scaling factor calculated for the Level 1 results was implicitly applied to the dose-risk and offsite economic cost-risk through the application of the multiplier to the base case averted cost-risk values.

The Phase 2 SAMA list was re-examined by multiplying the nominal averted cost risk by the ratio of the 95th percentile CDF to the point estimate CDF value (see Section F.7.2) to identify SAMAs that would be re-characterized as potentially cost beneficial, i.e., positive net value.

Those SAMAs that were previously determined to be not cost beneficial due to implementation costs exceeding their associated nominal averted cost risk may be potentially cost beneficial at the revised 95th percentile averted cost risk. In this case, eight additional Phase 2 SAMAs become potentially cost beneficial (SAMAs 2, 7, 8, 11, 17, 19, 28 and 30).

F.7.2.3 95TH PERCENTILE

SUMMARY

The following table provides a summary of the impact of using the 95th percentile PRA results on the detailed cost-benefit calculations that have been performed.

Summary of the Impact of Using the 95th Percentile PRA Results Change Averted Averted Net Value in SAMA Implementation Net Value Cost Risk Cost Risk (95th Cost ID Cost (per unit) (Base) (95th (Base) Percentile) Effective-Percentile) ness?

SAMA 2 $5,751,110 $3,940,272 -$1,810,838 $9,811,277 $4,060,167 Yes SAMA 3 $1,130,300 $1,739,935 $609,635 $4,332,438 $3,202,138 No SAMA 4 $12,230,000 $4,086,872 -$8,143,128 $10,176,311 -$2,053,689 No SAMA 5 $657,200 $3,763,930 $3,106,730 $9,372,186 $8,714,986 No SAMA 7 $100,000 $73,452 -$26,548 $182,895 $82,895 Yes SAMA 8 $338,830 $319,387 -$19,443 $795,274 $456,444 Yes SAMA 9 $349,300 $683,497 $334,197 $1,701,908 $1,352,608 No SAMA 10 $1,320,300 $1,669,087 $348,787 $4,156,027 $2,835,727 No SAMA 11 $13,030,000 $12,876,582 -$153,418 $32,062,689 $19,032,689 Yes SAMA 13 $5,951,110 $12,856,042 $6,904,932 $32,011,545 $26,060,435 No Byron and Braidwood Stations, Units 1 and 2 Page F-144 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Summary of the Impact of Using the 95th Percentile PRA Results Change Averted Averted Net Value in SAMA Implementation Net Value Cost Risk Cost Risk (95th Cost ID Cost (per unit) (Base) (95th (Base) Percentile) Effective-Percentile) ness?

SAMA 14 $3,800,000 $68,572 -$3,731,428 $170,744 -$3,629,256 No SAMA 15 $0 $401,075 $401,075 $998,677 $998,677 No SAMA 16 $993,800 $790,980 -$202,820 $1,969,540 $975,740 Yes SAMA 17 $981,730 $24,180 -$957,550 $60,208 -$921,522 No SAMA 18 $1,608,680 $74,435 -$1,534,245 $185,343 -$1,423,337 No SAMA 19 $900,000 $613,240 -$286,760 $1,526,968 $626,968 Yes SAMA 20 $20,000,000 $28,965 -$19,971,035 $72,123 -$19,927,877 No SAMA 21 $1,600,000 $158,615 -$1,441,385 $394,951 -$1,205,049 No SAMA 22 $250,000 $44,312 -$205,688 $110,337 -$139,663 No SAMA 23 $760,000 $38,587 -$721,413 $96,082 -$663,918 No SAMA 24 $1,250,000 $31,650 -$1,218,350 $78,809 -$1,171,192 No SAMA 25 $5,700,000 $9,452,920 $3,752,920 $23,537,771 $17,837,771 No SAMA 26 $2,400,000 $12,839,747 $10,439,747 $31,970,970 $29,570,970 No SAMA 27 $975,000 $2,078,479 $1,103,479 $5,175,413 $4,200,413 No SAMA 28 $975,000 $903,687 -$71,313 $2,250,181 $1,275,181 Yes SAMA 29 $1,225,000 $42,682 -$1,182,318 $106,278 -$1,118,722 No SAMA 30 $975,000 $570,829 -$404,171 $1,421,364 $446,364 Yes SAMA 31 $975,000 $1,596,513 $621,513 $3,975,317 $3,000,317 No When the 95th percentile PRA results were applied to the Phase 1 analysis, the increase in the MACR resulted in the retention of one SAMA that was screened in the baseline Phase 1 analysis (SAMA 20). The Phase 2 calculations performed for this SAMA using the 95th percentile PRA results indicate that SAMA 20 is not cost beneficial.

When the 95th percentile PRA results were applied to the original Phase 2 calculations, eight SAMAs (2, 7, 8, 11, 17, 19, 28 and 30) that were previously classified as not cost effective were determined to be potentially cost effective. The use of the 95th percentile PRA results is not considered to provide the best assessment of the cost effectiveness of a SAMA; however, these additional SAMAs should be considered for implementation to address the uncertainties inherent in the SAMA analysis.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.7.3 MACCS2 INPUT VARIATIONS The MACCS2 model was developed using the best information available for the Byron site; however, reasonable changes to modeling assumptions can lead to variations in the Level 3 results. In order to determine how certain assumptions could impact the SAMA results, a sensitivity analysis was performed on parameters that have previously been shown to impact the Level 3 results. These parameters include:

• Meteorological data

• Evacuation timing and speed

• Release height and heat

• Deposition velocity

• Reactor power level

• Population estimates

• Population resettlement planning

• Generic economic inputs

• Economic rate of return The risk metrics produced by MACCS2 that are evaluated in the sensitivity analyses are the 50 mile population dose risk and the 50 mile offsite economic cost risk. The subsections below discuss the changes in these results for each of the sensitivity parameters noted above. The final subsection, F.7.3.10, correlates the worst case changes identified in the sensitivity runs to a change in the sites averted cost-risk and discusses the implications of the sensitivity analysis on the SAMA analysis.

Sensitivity of Byron Baseline Risk to Parameter Changes Pop. Dose Risk Cost Risk Parameter Description Base (%) Base (%)

Meteorology Year 2009 Meteorology -4% -2%

Year 2010 Meteorology -1% -2%

Evacuation Evacuation delay time increased from 115 -0.1% 0%

Time minutes to 230 minutes (factor of 2)

Evacuation Average evacuation speed decreased 50% +2% 0%

Speed from 4.4 m/sec to 2.2 m/sec.

Release Release height set to ground level (in lieu of -1% -3%

Height mid-height of containment, 30.3 m).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Sensitivity of Byron Baseline Risk to Parameter Changes Pop. Dose Risk Cost Risk Parameter Description Base (%) Base (%)

Release height set to top of containment , +1% +3%

60.7m (in lieu of mid-height of containment, 30.3 m).

Release Heat No buoyant plume assumed (0 watts for -0.2% -3%

each plume segment).

Deposition Dry deposition velocity decreased from 0.01 -8% -19%

Velocity m/sec to 0.005 m/sec (factor of 2)

Reactor Power Reactor power decreased from 3645 MWt -1% -1%

to 3586.6 MWt, reflective of no MUR uprate Population Year 2046 population uniformly increased +28% +26%

30%

Resettlement No Intermediate Phase resettlement +17% -32%

Planning planning (in lieu of 6 months) 1 year Intermediate Phase resettlement -14% +35%

planning (in lieu of 6 months)

Economic Generic economic inputs increased (factor -6% +48%

Inputs of 2)

Rate of Return 3% expected rate of return (in lieu of 7%) +1% -9%

12% expected rate of return (in lieu of 7%) -2% +10%

F.7.3.1 METEOROLOGICAL SENSITIVITIES In addition to the year 2008 base case meteorological data, years 2009 and 2010 were also analyzed. Analysis of year 2009 and 2010 data sets yielded population dose-risks and cost risks that were 1% to 4% less than 2008 results. As no particular criteria have been defined by the industry related to determining which meteorological data set should be used as a base case for a site, the year 2008 data is chosen for Byron given that it represents site meteorological conditions and results in the highest dose risk and cost risk of the three data sets.

F.7.3.2 EVACUATION SENSITIVITIES The sensitivity of two evacuation parameters was assessed. The delay time to evacuation (increased from 115 minutes to 230 minutes) was found to have a negligible impact (approximately 0.1% decrease) on population dose risk. The dose impact of the increased delay time varied for the different release categories (i.e., some resulted in a dose increase, others in a dose decrease (notably LERF-ISLOCA), and some had no change). The differing Byron and Braidwood Stations, Units 1 and 2 Page F-147 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 impacts are attributed to the relationship between the start of evacuation movement and the time of the arrival of the risk significant plumes. The majority of the population dose risk is due to the long term dose associated with the late releases, notably the LATE-CHR-NOAFW and LATE-CHR-AFW release categories which contribute approximately 80% to the total population dose risk. The LERF-ISLOCA release category is the largest contributor (approximately 12%)

to population dose risk that occurs in the early time frame. The majority of LERF-ISLOCA release occurs during the first hour in the first plume, shortly after the GE declaration. With a longer delay time individuals are modeled to be located at home (which provides some radiological shielding) longer before beginning travel in their vehicles (which provides less radiological shielding). For individuals closer to the plant site, the longer delay time results in the fast release passing over them at their residence prior to the start of evacuation movement.

These individuals thus experience an early dose decrease (due to the shielding afforded by their residence as compared to their vehicles) for a longer delay time. This timing effect will vary across the analysis region based on the population distribution (e.g., distance from the site),

meteorological conditions (e.g., wind speed), and evacuation speed. The sensitivity case demonstrates that the overall impact is negligible for the values used.

The evacuation speed sensitivity which decreased the average radial evacuation speed by a factor of two (from 4.4 m/sec to 2.2 m/sec), bounding the longest evacuation time in the ETE study, demonstrates a small impact on population dose. The population dose risk increased approximately 2% using the slower evacuation speed. An increase in population dose is the generally expected result for a slower evacuation speed since evacuees would be expected to be exposed to radiological releases for a longer period of time. It is noted that while evacuation assumptions do impact the population dose-risk estimates, they do not impact MACCS2 offsite economic cost-risk estimates because MACCS2 calculated cost-risks are based on land contamination levels which remain unaffected by evacuation assumptions and the number of people evacuating.

F.7.3.3 RELEASE HEIGHT & HEAT SENSITIVITIES The release height sensitivity cases quantify the impact of the assumption related to the height of the release of the plumes. The baseline case assumes that the releases occur at approximately half the height of the containment building (30.3 m). Releases from higher heights tend to disperse material over a wider geographical region, generally impacting more people and creating larger long term dose and cleanup costs. A ground level release height (0 m) shows a decrease in dose risk and cost risk of 1% and 3%, respectively. A release from the Byron and Braidwood Stations, Units 1 and 2 Page F-148 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 top of containment (60.3 m) shows an increase in dose risk and cost risk of 1% and 3%,

respectively. The impacts of release height assumptions are small.

The release heat sensitivity case evaluates the impact of assumptions of thermal plume effects.

The base case assumed a heat content of 10 MW per plume segment, except for the intact containment release category where zero plume heat was assumed. The 10 MW per plume segment value is generally bounding for the values used in the NUREG-1150 (NRC 1990a) study as documented in NUREG/CR-4551 (NRC 1990b). Modeling plume heat increases the buoyancy effect of the released plumes and generally has similar impacts as modeling a higher release height. The sensitivity case assumed no thermal plume heat in the releases (i.e., no buoyant plumes). The impacts of assuming no plume heat are a dose risk and cost risk decrease of 0.2% and 3%, respectively.

F.7.3.4 DEPOSITION VELOCITY The dry deposition velocity sensitivity case evaluates the impact of the fission product particle size as reflected in the deposition velocity parameter. The base case assumes a deposition velocity of 0.01 m/sec, consistent with the NRC recommendation documented in MACCS2 Sample Problem A (NRC 1998). The sensitivity case uses a deposition velocity of 0.005 m/sec, reflective of a smaller particle size. Assuming a lower deposition velocity results in a decrease in the dose risk and cost risk of 8% and 19%, respectively. This decrease is attributed to smaller particles traveling further and exiting the 50 mile analysis region.

F.7.3.5 REACTOR POWER The reactor power sensitivity case evaluates the impact of not including the postulated measurement uncertainty recapture (MUR) power uprate. For this sensitivity case, the reactor power was decreased from 3645 MWt (assumes MUR implemented) to 3586.6 MWt (current licensed power level). Assuming the MUR power uprate is not implemented results in a very small decrease of dose risk and cost risk of 1%.

F.7.3.6 POPULATION SENSITIVITY A population sensitivity case assesses the impact of population assumptions. The base case year 2046 population is uniformly increased by 30% in all grid elements of the 50-mile radius.

This change has a significant impact on the dose risk and cost risk, increasing dose risk and cost risk by 28% and 26%, respectively. This sensitivity case demonstrates a significant dependence upon population estimates. This dependence is expected given that population dose and offsite economic costs are primarily driven by the regional population.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.7.3.7 RESETTLEMENT PLANNING SENSITIVITIES The MACCS2 consequence modeling incorporates an intermediate phase which depicts the time period following the release and immediate evacuation actions (termed the early phase) and extends to the time when recovery efforts such as decontamination and resettlement of people are begun (termed the long term phase). The intermediate phase thus models the time period when decontamination and resettlement plans are being developed. MACCS2 allows the habitation of land during the intermediate phase unless projected dose criteria is exceeded, in which case individuals are relocated. MACCS2 allows an intermediate phase ranging from no intermediate phase to a maximum of one year. The intermediate phase sensitivities show significant impacts and are therefore discussed further:

• The no intermediate phase resettlement planning case is developed based on the NUREG-1150 (NRC 1990a) modeling approach. The 32% reduction in cost risk seen in the sensitivity results, however, is judged too optimistic in that the land decontamination efforts are modeled as starting one week after the accident (i.e., directly after the early phase ends) such that a significant portion of population relocation costs are omitted. For instance, the costs associated with temporary housing of interdicted individuals while decontamination strategies are developed and decontamination teams are contracted are not accounted for without an intermediate phase. It is believed that the NUREG-1150 studies omitted the intermediate phase because the intermediate phase coding was not validated at that time (NRC 1998). A competing factor is that the population dose increases (17% increase over the base case) because people are allowed to re-occupy the decontaminated land sooner.

• The 1 year intermediate phase resettlement planning case is developed based on the maximum length of time allowed by MACCS2 for the intermediate phase. A long intermediate phase can be unrealistic in that re-occupation of contaminated land is not performed during this phase even if contamination levels decrease (by natural radioactive decay and weathering) to levels which would allow it (i.e., resettlement is evaluated as part of the long term phase, not the intermediate phase). Therefore population relocation costs may be over estimated using a long (i.e., one year) intermediate phase. An intermediate phase of one year shows a 35% increase in cost risk estimates compared with the base case selection of 6 months. The population dose decreased by 14% with a longer intermediate phase due to later resettlement on decontaminated land.

The six month intermediate phase (base case) is judged to be a best estimate approach in that it provides reasonable time for both decontamination and resettlement planning to be performed. The sensitivity cases demonstrate that the six month value used in the base case provides mid-range results for the modeling choices available.

F.7.3.8 GENERIC ECONOMIC INPUTS SENSITIVITY MACCS2 requires certain site specific economic data (e.g., fraction of land devoted to farming, annual farm sales, fraction of farm sales resulting from dairy production, and property value of Byron and Braidwood Stations, Units 1 and 2 Page F-150 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 farm and non-farm land) for each of the 160 spatial elements. The site specific base case values are calculated based on regional economic data.

In addition to these site specific values, generic economic data are utilized by MACCS2 to address costs associated with per diem living expenses (applied to owners of interdicted properties and relocated populations), relocation costs (for owners of interdicted properties),

and decontamination costs. For the Byron base case, these generic costs are based on values used in the NUREG-1150 study (NRC 1990a) as documented in the NUREG/CR-4551 (NRC 1990b) updated to July 2012 using the consumer price index.

This sensitivity case is performed to determine the variability in population dose risk and cost risk based on changes to these generic based values. The sensitivity case increases key generic based economic parameters as identified in Table F.7-1. In general, the inputs were arbitrarily increased by factor of 2.0. The increase in these economic parameters resulted in an increase in cost risk of 48% and a decrease in dose risk of about 6%. A significant increase in cost risk is expected since population relocation and decontamination costs are major contributors to total cost as calculated by MACCS2.

F.7.3.9 RATE OF RETURN SENSITIVITIES One of the economic cost components included in the MACCS2 calculated cost result is the financial loss associated with property and associated improvements (e.g., buildings) not achieving their expected annual rate of return during interdiction periods. A piece of land that is interdicted (i.e., not occupied) for a period of years will not achieve the historical rate of return or the rate of return achieved by other non-impacted properties during the interdiction period. This lack of expected return is an economic loss for the owner / society. The base case assumes a 7% expected rate of return, consistent with NRC guidance (NRC 2004a). A sensitivity case using a 3% expected rate of return shows a decrease in the expected cost risk of approximately 9%. This decrease in cost risk associated with the lower rate or return is expected since there is a lower expectation associated with the lands return on investment. A sensitivity case using a 12% expected rate of return, the value used in NUREG-1150 MACCS2 analyses (NRC 1990b), shows an increase cost risk of approximately 10%. For both sensitivity cases the dose risk changes are minor (1% to 2%).

F.7.3.10 IMPACT ON SAMA ANALYSIS Several different Level 3 input parameters are examined as part of the Byron MACCS2 sensitivity analysis. The primary reason for performing these sensitivity runs is to identify any Byron and Braidwood Stations, Units 1 and 2 Page F-151 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 reasonable changes that could be made to the Level 3 input parameters that would impact the conclusions of the SAMA analysis. While the table in Section F.7.3 summarizes the changes to the dose-risk and OECR estimates for each sensitivity case, it is prudent to consider if any of these changes would result in the retention of the SAMAs that were screened using the baseline results.

Of all the MACCS2 sensitivity cases, the largest dose-risk increase, 28%, occurred in the Population (Year 2046 population uniformly increased 30%) case. The largest OECR increase, 48%, occurred in the Generic Economic Input sensitivity case. While these changes are not insignificant, they are relatively small compared to the 95th percentile PRA results sensitivity in Section F.7.2, which increases the averted cost-risk values for the SAMAs by almost 250 percent. Therefore, the 95th percentile PRA results sensitivity is considered to bound this case and no SAMAs would be retained based on this sensitivity that were not already identified in Section F.7.2.

F.7.4 INCLUSION OF THE AFW CROSS-TIE IN THE BASE MODEL While the AFW Cross-tie modification is in the final stages of implementation for Byron, it was not officially implemented at the time the SAMA analysis was performed. Accordingly, the PRA model used for this analysis does not credit the AFW cross-tie. However, because the final implementation is imminent, a sensitivity analysis was performed to identify how the cross-tie capability would impact the SAMA analysis. In order to do this, the SAMA 15 (AFW Cross-tie) model was used as the new base model and the Phase 1 and 2 screening analyses were re-performed relative to that model.

Use of the SAMA 15 model as the base case resulted in a decrease in the MACR from

$14,950,000 to $14,547,500, which is based on the PRA results documented in Section F.6.12 and the rounding up of the internal events cost-risk in the same manner as the base case. This slight reduction did not result in the screening of any additional SAMAs in the Phase 1 analysis.

The impact on the Phase 2 analysis was determined by performing the calculation/model changes identified for each SAMA in conjunction with the changes identified for SAMA 15. The following table provides a comparison of the Phase 2 results for the nominal plant configuration to the configuration in which the AFW Cross-tie has been implemented. As documented in the Change in Cost Effectiveness? column, implementation of the AFW cross-tie is would not alter the conclusions of the cost-benefit analysis.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Impact of Assuming Implementation of AFW Cross-tie for the SAMA Base Case Change Averted Averted Net Value in SAMA Implementation Net Value Cost Risk Cost Risk (SAMA 15 Cost ID Cost (per unit) (Base) (SAMA 15 (Base) Base Case) Effective-Base Case) ness?

SAMA 2 $5,751,110 $3,940,272 -$1,810,838 $3,930,097 -$1,821,013 No SAMA 3 $1,130,300 $1,739,935 $609,635 $1,455,390 $325,090 No SAMA 4 $12,230,000 $4,086,872 -$8,143,128 $4,093,340 -$8,136,660 No SAMA 5 $657,200 $3,763,930 $3,106,730 $3,752,347 $3,095,147 No SAMA 7 $100,000 $73,452 -$26,548 $73,255 -$26,745 No SAMA 8 $338,830 $319,387 -$19,443 $327,560 -$11,270 No SAMA 9 $349,300 $683,497 $334,197 $690,325 $341,025 No SAMA 10 $1,320,300 $1,669,087 $348,787 $1,669,010 $348,710 No SAMA 11 $13,030,000 $12,876,582 -$153,418 $12,479,355 -$550,645 No SAMA 13 $5,951,110 $12,856,042 $6,904,932 $12,553,872 $6,602,762 No SAMA 14 $3,800,000 $68,572 -$3,731,428 $47,235 -$3,752,765 No SAMA 16 $993,800 $790,980 -$202,820 $799,070 -$194,730 No SAMA 17 $981,730 $24,180 -$957,550 $13,957 -$967,773 No SAMA 18 $1,608,680 $74,435 -$1,534,245 $79,665 -$1,529,015 No SAMA 19 $900,000 $613,240 -$286,760 $610,042 -$289,958 No SAMA 21 $1,600,000 $158,615 -$1,441,385 $155,417 -$1,444,583 No SAMA 22 $250,000 $44,312 -$205,688 $41,117 -$208,883 No SAMA 23 $760,000 $38,587 -$721,413 $28,082 -$731,918 No SAMA 24 $1,250,000 $31,650 -$1,218,350 $30,717 -$1,219,283 No SAMA 25 $5,700,000 $9,452,920 $3,752,920 $9,173,255 $3,473,255 No SAMA 26 $2,400,000 $12,839,747 $10,439,747 $12,442,435 $10,042,435 No SAMA27 $975,000 $2,078,479 $1,103,479 $2,064,311 $1,089,311 No SAMA28 $975,000 $903,687 -$71,313 $897,526 -$77,474 No SAMA29 $1,225,000 $42,682 -$1,182,318 $26,825 -$1,198,175 No SAMA30 $975,000 $570,829 -$404,171 $566,938 -$408,062 No SAMA31 $975,000 $1,596,513 $621,513 $1,585,630 $610,630 No Byron and Braidwood Stations, Units 1 and 2 Page F-153 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.8 CONCLUSIONS The benefits of revising the operational strategies in place at Byron and/or implementing hardware modifications can be evaluated without the insight from a risk-based analysis.

However, use of the PRA in conjunction with cost-benefit analysis methodologies provides an enhanced understanding of the effects of the proposed changes relative to the cost of implementation and projected impact on a larger future population. The results of this study indicate that many potential improvements were identified that warrant further review for potential implementation at Byron.

In summary, SAMAs 3, 5, 9, 10, 13, 15, 25, 26, 27, and 31 were found to be potentially cost beneficial in the baseline analysis.

When the 95th percentile PRA results are considered, SAMAs 2, 7, 8, 11, 16, 19, 28, and 30 are also potentially cost beneficial.

F.8.1 OPTIMAL SAMA SET While many SAMAs are potentially cost beneficial for Byron when considered independently, it should be noted that many SAMAs address similar areas of risk. Implementation of one SAMA may result in a change in the potential benefits of the remaining SAMAs such that they are no longer cost beneficial. Review of the potentially cost beneficial SAMAs can help identify an optimal set of SAMAs for implementation, that is, a reduced set of SAMAs that will address the largest risk contributors for the site. For example, the industry initiative to address Fukushima insights led to the development of a mitigation strategy with capabilities similar to SAMA 11 (DMS), which may be fully implemented or implemented in part by Byron for reasons outside of the SAMA analysis, but would mitigate many of the largest contributors to site risk. In addition, the AFW Cross-tie is in the final stages of implementation and should be considered as complete for any future considerations. Beginning with these plant enhancements, the remaining set of SAMAs can be reviewed to identify those that would mitigate the contributors not addressed by SAMAs 11 and 15. It is recognized that there are different combinations of SAMAs that could achieve similar results, but this is a demonstration of a potential approach to interpreting the results of the cost benefit analysis.

Assuming that the AFW Cross-tie and the DMS have been implemented, the SAMAs that were identified as potentially cost beneficial in the 95th percentile sensitivity analysis were assessed to determine if they would remain potentially cost beneficial. The following table summarizes the results of this review.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of Impact of the DMS and AFW Cross-Tie on Cost Benefit Analysis SAMA SAMA Title Discussion Number 2 Replace the Positive This SAMA is intended to prevent RCP seal LOCAs, Displacement Pump but the DMS virtually eliminates the RCP seal LOCA with a Self-Cooled, Auto contribution through the installation of no-leak seals.

Start Pump SAMA 2 would no longer be cost beneficial.

3 Auto Start of Standby Automating the start of the standby SX pump is SX Pump primarily used to prevent RCP seal LOCAs. The DMS virtually eliminates the RCP seal LOCA contribution through the installation of no-leak seals. SAMA 3 would no longer be cost beneficial.

5 Modify the Startup This SAMA addresses human errors associated with Feedwater Pump to initiation of secondary side heat removal, which would Start Using the AMSAC not be impacted by the DMS. SAMA 5 would remain a SG Low-Low-Low Level viable candidate for potential implementation.

signal to Mitigate AFW Failure 7 Establish Flow to the This SAMA helps reduce human errors after successful RH HX on RH Pump initiation of heat removal, which are dominated by Start small LOCA scenarios that the DMS would not mitigate. SAMA 7 would remain a viable candidate for potential implementation.

8 Install Kill Switches for This SAMA primarily protects the SX pumps, which in the Fire Protection turn helps prevent RCP seal LOCAs. The DMS Pumps in the MCR virtually eliminates the RCP seal LOCA contribution through the installation of no-leak seals. SAMA 8 would no longer be cost beneficial.

9 Install Flow Restrictors This SAMA primarily protects the SX pumps, which in in Fire Protection Pipes turn helps prevent RCP seal LOCAs. The DMS virtually eliminates the RCP seal LOCA contribution through the installation of no-leak seals. SAMA 9 would no longer be cost beneficial.

10 Alter Ductwork Between This SAMA primarily protects the SX pumps, which in the Aux Bldg Sump turn helps prevent RCP seal LOCAs. The DMS Drain Room and the SX virtually eliminates the RCP seal LOCA contribution Pump Room through the installation of no-leak seals. SAMA 10 would no longer be cost beneficial.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of Impact of the DMS and AFW Cross-Tie on Cost Benefit Analysis SAMA SAMA Title Discussion Number 13 Alternate AFW Cooling This SAMA provides a heat removal mechanism that is with Seal Protection not dependent on SX. The DMS provides the same capability. SAMA 13 would no longer be cost beneficial.

16 Install High Flow This SAMA primarily protects the SX pumps, which in Sensors On the Non- turn helps prevent RCP seal LOCAs. The DMS Essential Service Water virtually eliminates the RCP seal LOCA contribution System through the installation of no-leak seals. SAMA 16 would no longer be cost beneficial.

19 Replace MOVs in the The DMS would not impact ISLOCA risk. SAMA 19 RHR Discharge Line would remain a viable candidate for potential with Valves that Can implementation.

Isolate an ISLOCA Event 25 Install a Filtered After implementation of the DMS and SAMA 15, the Containment Vent MACR would only be $2,068,145. Even using the 95th percentile multiplier of 2.49, the 95th percentile MACR of $5,149,681 is less than the estimated implementation cost of $5,700,000. This SAMA would no longer be cost beneficial.

26 DMS Using a Dedicated This is an alternate approach to the DMS and it is Generator, Self-Cooled considered to be obviated by implementation of SAMA Charging Pump, and a 11.

Portable AFW Pump 27 Protect RH, SI, and This SAMA protects cables that are used to support CVCS Cubicle Cooling RCP seal cooling and heat removal via RH. The DMS Fan Cables in Fire Zone includes no-leak seals that would prevent most seal 11.3-0 LOCAs and preclude the need for RH while providing an alternate secondary side heat removal source.

SAMA 27 would no longer be cost beneficial.

28 Install Fire Barriers This SAMA addresses contributors related to RCP seal around MCC 134X LOCAs, which are addressed by the DMS, but also scenarios that include failure to restore FW, which would not be impacted by the DMS due to human dependence issues. SAMA 28 is considered to remain a viable candidate for potential implementation.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Review of Impact of the DMS and AFW Cross-Tie on Cost Benefit Analysis SAMA SAMA Title Discussion Number 30 Protect AFW Cables in This SAMA protects cables that are used to support the Aux Building AFW operation. While both the DMS and the AFW X-General Area, Elevation tie provide a means of SG makeup, an AFW pump is 383' failed in both units by the fire, which renders the AFW x-tie unavailable. In addition, human dependence issues would limit the credit for the DMS in the largest contributing scenarios. Finally, FW/Condenser is assumed to be lost in fire events, it is not clear there would be enough time to implement the DMS before core damage. This SAMA would remain potentially cost beneficial.

31 Unit 2 SAMA - Protect This SAMA protects cables that are used to support Cables for 2AF013A, B, AFW operation. While both the DMS and the AFW X-and D in the Aux tie provide a means of SG makeup, the AFW system Building General Area, injection path is failed by the fire and because Elevation 426' FW/Condenser is assumed to be lost in fire events, it is not clear there would be enough time to implement the DMS before core damage. This SAMA would remain potentially cost beneficial.

While a large number of SAMAs can be considered potentially cost beneficial for Byron when considered independently, there is a smaller subset of SAMAs that, if implemented, would render the remaining SAMAs not cost beneficial. This subset is SAMAs 5, 7, 11, 15, 19, 28, 2

30, and 31 .

2 Given that the fire model is in an interim state, the cost benefit analysis for SAMAs 28, 30, and 31 should also be considered interim until the associated fire scenarios are further refined.

Byron and Braidwood Stations, Units 1 and 2 Page F-157 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.9 TABLES Table F.2-1 Byron/Braidwood PRA Model Update History Model change Rev. Date CDF LERF Comments description Original IPE --- BY- 3.09E-05 2.73E-06 Initial IPE submittal, which was conducted to satisfy GL 88-20 04/1994 requirements. This study was based on the support-state BW- model methodology.

2.74E-05 2.62E-06 06/1994 Modified IPE --- IPE safety evaluation report was received on this study, which satisfied GL 88-20 requirements.

Changed PRA model 0 10/1999 BY1-4.98E-05 BY1-4.48E-06 PRA model was changed from the support state model to methodology and BY2-4.88E-05 BY2-4.35E-06 linked fault tree method. The changes involved extensive Updated all Data modifications to all event trees and fault trees.

BW1-4.86E-05 BW1-3.78E-06 All data, including initiating event frequencies, equipment BW2-4.86E-05 BW2-3.81E-06 failure data, common cause failure (CCF) data and human error probabilities were updated using most recent industry sources. Plant-specific data was also updated.

One SX pump criteria 1 10/2000 BY1-4.55E-05 BY1-5.41E-06 The SX pump success criterion was changed from two pumps incorporated BY2-4.45E-05 BY2-5.33E-06 to one pump.

BW1-4.61E-05 BW1-4.89E-06 BW2-4.60E-05 BW2-4.89E-06 LOOP/DLOOP Event 2 06/2001 BY1-4.81E-05 BY1-5.29E-06 The event tree was revised to remove extensive cutset Tree revised BY2-4.80E-05 BY2-5.27E-06 recoveries performed as post processing. Revision 2 of PRA model was documented as an interim model and was not BW1-4.60E-05 BW1-4.96E-06 released as a working model.

BW2-4.59E-05 BW2-4.96E-06 Byron and Braidwood Stations, Units 1 and 2 Page F-158 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-1 Byron/Braidwood PRA Model Update History Model change Rev. Date CDF LERF Comments description Internal flooding 3 06/2001 BY1-5.56E-05 BY1-6.26E-06 Previous revisions did not include the results of internal analysis revised and BY2-5.53E-05 BY2-6.24E-06 flooding analysis.

incorporation of plant A fire hose connection from FP system to the CV pump lube BW1-3.15E-05 BW1-4.65E-06 mods to CV pump oil cooler was made available as an alternate cooling water lube oil cooler BW2-3.14E-05 BW2-4.65E-06 source. This mod removed a complete dependency of CV pumps on SX system. FP and VA system models were added as a result of this change.

Incorporated a plant 3a 08/2001 BY1-5.50E-05 BY1-6.15E-06 This mod includes removal of automatic control of 1(2)SX173 mod at Byron (not BY2-5.48E-05 BY2-6.13E-06 and 1(2)SX178 air operated valves, which provide cooling applicable to Byron) water to AF pump 1B. This mod removed AF pump 1B BW1-3.15E-05 BW1-4.60E-06 dependency on Instrument Air.

BW2-3.14E-05 BW2-4.60E-06 RPS and CCW 3b Not Not Available Not Available The changes include system logic enhancements and system logic revised Available corrections identified during the previous PRA revision. The model revision was performed in support of Westinghouse Owners Group ATWS sensitivity study. This revision was not issued.

System Model and 4 02/2002 BY1-5.27E-05 BY1-5.41E-06 Made significant model enhancements to the following systems:

Containment Failure BY2-5.20E-05 BY2-6.15E-06 reactor protection system (RPS), engineered safety feature updates actuation system (ESFAS), CCW, PORVs, AFW and instrument BW1-3.12E-05 BW1-4.57E-06 power. The changes were system specific and included BW2-3.12E-05 BW2-4.93E-06 changes to address issues such as the need to remove instrument power for the PORVs for non-ATWS conditions, adding 3-of-4 common cause failure terms for the AF-005 valves, and the re-development of the RPS fault trees. Also, the Containment Failure likelihood was updated.

Byron and Braidwood Stations, Units 1 and 2 Page F-159 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-1 Byron/Braidwood PRA Model Update History Model change Rev. Date CDF LERF Comments description Inverter LCO AOT 4B 10/2002 BY1-5.36E-05 BY1-4.85E-06 Modifications to support more efficient model updates in the Extension BY2-5.26E-05 BY2-5.49E-06 future and other miscellaneous issues to support the 120VAC Inverter limiting condition for operation (LCO) AOT Extension BW1-3.26E-05 BW1-4.06E-06 Application. Multiple detailed modeling changes were BW2-3.24E-05 BW2-4.31E-06 performed to address known issues. For example, the small LOCA and transient accident modeling logic was changed, the pump signal modeling for CC, SX, and CV was changed, and the CCW fault tree was revised to update how the Unit 0 heat exchanger was credited.

Address 5 12/2002 BY1-4.91E-05 BY1-4.41E-06 Changed model to address several model issues and miscellaneous model BY2-4.68E-05 BY2-4.82E-06 incorporate values from updated failure and unavailability data, issues and updated operator action human error probabilities (HEPs), and support BW1-3.84E-05 BW1-4.20E-06 data. system initiating event frequencies.

BW2-3.83E-05 BW2-4.45E-06 New SX Success 5A 05/2003 BY1-6.43E-05 BY1-4.93E-06 Revised the model and data to address the PRA quality issues Criteria and Loss of BY2-6.34E-05 BY2-5.87E-06 raised by CR#00142080 (1/30/03) against Rev. 5 model. Re-SX frequency. evaluated the plant-specific data, performed full convergence BW1-5.78E-05 BW1-5.04E-06 Address quality issues analysis and a human failure dependency analysis.

for periodic update. BW2-5.75E-05 BW2-5.78E-06 Incorporated new SX success criteria. This model is used to support the SX technical specification (TS) CT (Completion Time) Extension (one-time relief) application.

Automatic 5B 06/2003 BY1-6.15E-05 BY1-4.65E-06 Revised the model so that automatic quantification can be Quantification using BY2-6.06E-05 BY2-5.52E-06 performed using ORAM-Sentinel and PSALINK program.

PSALink.

BW1-5.43E-05 BW1-4.74E-06 BW2-5.39E-05 BW2-5.39E-06 Byron and Braidwood Stations, Units 1 and 2 Page F-160 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-1 Byron/Braidwood PRA Model Update History Model change Rev. Date CDF LERF Comments description Conditional LOOP 5E Not BY1-5.79E-05 BY1-4,72E-06 Model revised to incorporate conditional dual unit LOOP for events Available BY2-5.72E-05 BY2-5.62E-06 most all initiators, updated some LERF binning, changed modeling of ESFAS testing, added RWST switchover channel BW1-5.46E-05 BW1-4.99E-06 testing and common cause. Other minor changes.

BW2-5.38E-05 BW2-5.75E-06 Incorporation of 5F 12/2006 BY1-5.75E-05 BY1-4.71E-06 Model revisions to the Byron/Byron PRA to deal with potential component spurious BY2-5.70E-05 BY2-5.62E-06 spurious operation of key components that were not operation accounted for in the full power internal events (FPIE) model in BW1-5.42E-05 BW1-4.98E-06 order to obtain more realistic results for the Byron Fire PRA BW2-5.36E-05 BW2-5.75E-06 activities.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-1 Byron/Braidwood PRA Model Update History Model change Rev. Date CDF LERF Comments description Periodic Update 6 07/2007 BY1-5.9E-05 BY1-3.2E-06 Periodic Model Update. Model revisions included changes to BY2-5.9E-05 BY2-4.4E-06 AFW success criteria based on new MAAP 4.0 analyses, revisions to HEPs to reflect new procedure changes and BW1-3.1E-05 BW1-2.9E-06 operator interviews, revision of the flooding analysis based on BW2-3.6E-05 BW2-3.9E-06 HEP changes, incorporation of updated data analyses, explicit modeling of ISLOCA sequences, expansion of CCF treatment for Byron SX tower modeling, incorporation of modeling changes to allow for multiple SX or CC pumps and/or heat exchangers to be out of service online, addition of ventilation modeling for motor-driven AF pumps, correction of emergency boration logic, incorporation of the new Byron air compressor configuration, accounting for instrument bus auto transfer features (both installed and future modifications), incorporation of logic to require operators to start another CC pump or reduce loads if a CC pump fails after two RH heat exchangers are in service on one CC pump, addition of normally open manual valve in the SX system that may be closed for system maintenance or repair online, changes to the RPS logic to better reflect the signals that cause a trip relative to the initiators, changed AF auto start logic to include AMSAC signals, removed credit for the diesel-driven AF pumps SX booster pump on loss of SX events (such as CCF of all four strainers) that would result in flow blockage, and other issues in the Updating Requirement Evaluation (URE) database. Due to issues identified with this model, it was not considered a model of record.

RPS/ESFAS 6A Not Not Available Not Available An application specific model for RPS/ESFAS TS Change RAI Application Available Responses.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-1 Byron/Braidwood PRA Model Update History Model change Rev. Date CDF LERF Comments description Error Correction 6B 02/2008 BY1-6.0E-05 BY1-3.1E-06 Addressed the issues identified in model revision 6 and other BY2-6.0E-05 BY2-4.3E-06 issues during review of the R6B model. Due to issues identified with merging the flood model with the base model, which were BW1-3.6E-05 BW1-2.9E-06 identified while incorporating new Byron flood mitigation BW2-3.6E-05 BW2-3.4E-06 procedures, this model was not considered a model of record.

Flood Procedures 6C 05/2008 BY1-3.6E-05 BY1-2.5E-06 Incorporated new Byron flood procedure in support of B/B BY2-3.6E-05 BY2-3.1E-06 RTS/ESFAS TS changes. Performed benchmark tests to switch over to CAFTA 5.3 and PRAQUANT 5.0a.

BW1-3.6E-05 BW1-2.9E-06 BW2-3.5E-05 BW2-3.4E-06 RCP Seal LOCA 6D 12/2008 BY1-2.2E-05 BY1-2.1E-06 Revised RCP seal LOCA model for nonLOOP sequences. Incorporated Model BY2-2.2E-05 BY2-2.3E-06 URE709 (Bleed & Feed Success Criteria), 711 (logic error correction),

712 (Revised BE name) and 715 (Correction of a logic issue in the BW1-2.3E-05 BW1-2.5E-06 MLOC05 sequence).

BW2-2.3E-05 BW2-2.7E-06 AF Crosstie 6E 06/2009 BY1-1.7E-05 BY1-1.2E-06 Incorporated AF Unit Crosstie Modification at Byron. The similar BY2-1.7E-05 BY2-1.5E-06 modification will be expected to be completed at Byron in October 2009. The HEP changes from HRA migration to HRA BW1-1.6E-05 BW1-1.4E-06 Calculator 4.0 were also implemented.

BW2-1.5E-05 BW2-1.6E-06 Software Revision 6E1 Not BY1-1.7E-05 BY1-1.1E-06 Re-quantified the results using FORTE 3.0c due to a memory Available BY2-1.7E-05 BY2-1.4E-06 error encountered with FORTE 2.2f at the truncation limits of 1E-11 for CDF and 1E-12 for LERF for some application cases. No BW1-1.6E-05 BW1-1.4E-06 modeling changes.

BW2-1.5E-05 BW2-1.6E-06 Addendum to identify 6E2 03/2010 BY1-1.7E-05 BY1-1.1E-06 Identified 12 operator actions as key assumptions to B/B PRA key operator actions BY2-1.7E-05 BY2-1.4E-06 R6E1 model, based on the BB HRA. This was an addition to the model documentation and did not change or supersede the BW1-1.6E-05 BW1-1.4E-06 R6E1 model.

BW2-1.5E-05 BW2-1.6E-06 Byron and Braidwood Stations, Units 1 and 2 Page F-163 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-1 Byron/Braidwood PRA Model Update History Model change Rev. Date CDF LERF Comments description Addendum to revise 6E3 05/2010 BY1-1.7E-05 BY1-1.1E-06 Document the B/B PRA results using FTREX 1.5 to enable the software quantification BY2-1.7E-05 BY2-1.4E-06 use of FTREX for Byron/Byron risk applications. The PRA model engine R6E was not changed, and the results from R6E1 and R6E3 are BW1-1.6E-05 BW1-1.4E-06 identical.

BW2-1.5E-05 BW2-1.6E-06 CC Split-train 6F 09/2011 BY1-2.53E-05 BY1-1.33E-06 Unscheduled update to incorporate operator actions to split operation and updated BY2-2.56E-05 BY2-1.83E-06 the CC trains under most conditions. This is expected to be a Internal Flooding temporary condition until plant modifications are completed BW1-4.02E-05 BW1-1.75E-06 Analysis that will support a return to the assumed conditions where the BW2-3.88E-05 BW2-2.22E-06 CC trains are not normally split. Also includes ongoing working model changes and the updated internal flooding model.

2011 Periodic Update BB011a 06/2012 BY1-4.17E-05 BY1-2.57E-06 Periodic Update, including new data analysis, new HRA BY2-4.03E-05 BY2-3.21E-06 dependency analysis, and new pre-initiator HRA. Nearly 400 UREs addressed. Model also removes credit for operator BW1-4.26E-05 BW1-2.67E-06 action to crosstie AFW. Model naming scheme modified to BW2-4.26E-05 BW2-3.28E-06 match new Exelon guidance.

2012 MSPI Update BB011b 11/2012 BY1-3.97E-05 BY1-2.55E-06 Emergent model update with improved modeling of CC and BY2-3.82E-05 BY2-3.19E-06 SX to support improved mitigating systems performance index (MSPI) calculations. Model includes credit for a new operator BW1-3.57E-05 BW1-2.52E-06 action to manipulate SX007 valves on loss of power and a BW2-3.51E-05 BW2-3.08E-06 new recovery action to use the 0CC pump to provide decay heat removal in key sequences.

2012 Level 2 Update BB011b1 12/2012 BY1-3.97E-05 BY1-1.07E-06 This is an application specific model that was developed to BY2-3.82E-05 BY2-1.02E-06 support the SAMA analysis. The LERF model was replaced with a Level 2 Model based on the methodology in WCAP-BW1-3.57E-05 BW1-1.05E-06 16341-P.

BW2-3.51E-05 BW2-1.04E-06 Byron and Braidwood Stations, Units 1 and 2 Page F-164 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-2 Byron PRA Top Ranking Accident Sequences to CDF Sequence ID Accident Sequence Description Contribution to CDF SLOC-18 Small LOCA with failure of High Pressure Injection via Charging Pumps 25-26%

and Safety Injection Pumps; AF fails, but Steam Generators are fed from the Motor Driven or Startup Feedwater Pump. LOCAs for this sequence are due to Loss of SX or internal flood initiators. Key operator actions that contribute to this sequence are failures to isolate internal floods in time to prevent failure of the SX pumps and failure to recover RCP seal cooling.

SLOC-06 Small LOCA with failure to establish ECCS recirculation cooling and 20-21%

successful cooldown and depressurization. Most of this sequence is due to RCP Seal LOCAs following a Loss of CCW. The dominant operator action which contributes to this sequence is failure to align the CV pump to a cool suction source.

SLOC-09 Small LOCA with failure of High Pressure Injection via Charging Pumps 20%

and Safety Injection Pumps. This sequence is dominated by induced RCP Seal LOCAs, primarily from Loss of SX and internal flood initiators.

Operator actions which contribute to this sequence are failure to open the SX crosstie valves, failure to align FP for CV pump cooling, and failure to isolate internal flood initiators. Dependent operator actions related to Loss of SX are key contributors.

TRAN-04 Transient with failure of all feed to the Steam Generators and failure to 17-20%

establish ECCS high pressure recirculation cooling after successful high pressure injection via the charging pumps. The dominant initiating events associated with this sequence are Loss of SX and internal flooding scenarios. The key operator actions which contribute to this sequence are failure to restore feedwater from the main feedwater pumps and failure to establish the AFW cross-tie.

SLOC-02 Small LOCA with failure to establish ECCS recirculation cooling and 4%

successful cooldown and depressurization. Essentially all of this sequence is due to random non-isolable small LOCAs. Induced RCP Seal LOCAs are negligible contributors. The dominant operator action which contributes to this sequence is failure to secure the RH pumps in the mini-flow mode (resulting in their failure).

SGTR-04 Steam Generator Tube Rupture with short term failure to depressurize the 3%

primary and long term failure to do the same. Risk from this sequence is dominated by the dependent human actions to cooldown the RCS and terminate the break flow.

TRAN-05 This is a transient with failure of Auxiliary Feedwater and failure of Motor 2%

Driven and Startup Feedwater Pumps. HPI is provided by the centrifugal charging pumps (CCPs), but feed and bleed fails due to failure of the PORVs to open due to operator failure.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-2 Byron PRA Top Ranking Accident Sequences to CDF Sequence ID Accident Sequence Description Contribution to CDF TRAN-09 This is a transient with failure of Auxiliary Feedwater, failure of Motor 2%

Driven and Startup Feedwater Pumps, and failure to establish Bleed and Feed using Charging Pumps and Safety Injection Pumps. The key initiating events associated with this sequence are Loss of SX and internal flooding. The SX pumps are the most risk significant components in this sequence. Operator actions which contribute to this sequence are failure to establish feedwater from the main feedwater system and failure to mitigate internal flooding events.

SLOC-25 Small LOCA with failure of all feedwater and high pressure injection. Key 2%

initiating events include Loss of SX and internal flooding. Key operator actions include recovery from the Loss of SX and mitigation of the flooding events.

LOOP-65 Station Blackout (SBO) with failure of all AFW. Offsite power is recovered 1%

prior to core damage and High Pressure Injection is established, but ECCS recirculation fails. The dominant initiating event is a Loss of SX followed by a consequential LOOP. Without SX cooling, there is no way to remove decay heat.

Total Contribution to CDF by Top 10 Sequences >99%

Byron and Braidwood Stations, Units 1 and 2 Page F-166 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-3 Byron Important Operator Actions Based On CDF Important Operator Actions Important Sequences/Scenarios Joint action to align cooling to the This is a joint event representing the failure of operators to first fail to 0CC HX and provide cooling to the align SX cooling water to the 0CC HX, followed by another CV pumps for loss of CC (16% of dependent failure to align FP cooling and a cool suction source to the CDF) CV pumps in order to maintain RCP seal cooling.

Joint action to start a standby This is a joint event representing the failure of operators to first fail to pump, establish an SX crosstie, start a standby pump (typically SX), followed by failure to crosstie SX.

and provide cooling to the CV Without SX, RCP seal cooling will be lost unless the CV pumps can pumps following loss of SX (14% of be provided with cooling from the FP system and a cool suction CDF) source. The third failure in this combination fails that cooling to the CV pumps.

Recover SX crosstie between units Upon Loss of SX, operators need to recover SX by establishing the (13% of CDF) SX crosstie to the opposite unit. If no RCP seal failure occurs, a later chance to recover the crosstie is credited, which is modeled by this action.

Recover FP cooling to CV pumps This action models the recovery of FP cooling to the CV pumps for for FP internal flood (9% of CDF) the purposes of high pressure injection following an FP internal flood where seal injection was previously lost. It is not credited if the FP piping break occurred in a location which prevent recovery or if the RCP seals fail and lead to a large Seal LOCA.

Restore feedwater as a source of Upon failure of AFW to provide cooling water to the steam secondary side cooling (8% of generators, operators have the opportunity to utilize the main CDF) feedwater or startup feedwater pumps to provide another source of feedwater. Failure results in a complete loss of feedwater to the steam generators. This is exacerbated by the current loss of credit for the AFW crosstie.

Mitigate FP Internal Flood Event Following a Fire Protection System rupture in the Aux Building, (7% of CDF) operators need to terminate the flooding event (requires turning off the Diesel Driven FP Pump at the Circ Water Pump House) to prevent flood damage to the SX system or need to align alternate cooling to the CV pumps to maintain RCS inventory control. Failure leads to a Loss of all RCP Seal Cooling and a high probability of an RCP Seal LOCA which cant be mitigated due to the loss of the SX pumps and other essential equipment in the Aux Building.

Align CV pump suction to RWST Upon loss of SX, cooling to the CV pumps must be established by upon loss of SX (5% of CDF) aligning FP and realigning the CV pump suction to use the RWST as a cool suction source. Failing to do so results in loss of seal injection to the RCP(s). Loss of SX also fails the CC system that fails RCP Thermal Barrier Cooling. This has a high probability of leading to an RCP Seal LOCA.

Byron and Braidwood Stations, Units 1 and 2 Page F-167 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-4 Mapping of Level 1 Sequences to PDS CDF Seq. ID PDS CDF Seq. ID PDS CDF Seq. ID PDS CDF Seq. ID PDS CDF Seq. ID PDS CDF Seq. ID PDS ATWS-02 NHA LODC-05 NHN LOOP-36 NHN LOOP-65 NHN SGTR-25 B-N SLOC-04 NHA ATWS-04 NHA LOOP-04 NHA LOOP-37 NHN LOOP-66 NHN SGTR-27 B-N SLOC-06 NHA ATWS-06 NHA LOOP-05 NHA LOOP-39 NHA LOOP-67 NHN SGTR-28 B-N SLOC-08 NHA ATWS-07 NHN LOOP-07 NHA LOOP-40 NHA LOOP-68 NHN SGTR-29 B-N SLOC-09 NHA ATWS-08 NHA LOOP-08 NHA LOOP-42 NHN LOOP-69 NHN SGTR-30 BHA SLOC-11 NHA ATWS-10 NHA LOOP-10 NHN LOOP-43 NHN MLOC-03 NLN SLBI-03 NHN SLOC-13 NHA ATWS-11 NHA LOOP-11 NHN LOOP-44 NHN MLOC-04 NLA SLBI-04 NHN SLOC-15 NHA ATWS-13 NHA LOOP-12 NHN LOOP-46 NHN SGTR-03 B-A SLBI-05 NHN SLOC-17 NHA ATWS-14 NHA LOOP-16 NHA LOOP-47 NHN SGTR-04 B-A SLBI-07 NHN SLOC-18 NHA ATWS-15 NHN LOOP-17 NHA LOOP-48 NHN SGTR-06 B-A SLBI-08 NHN SLOC-20 NHN ATWS-16 NHA LOOP-20 NHA LOOP-50 NHN SGTR-07 B-A SLBI-10 NHN SLOC-21 NHN 1ILOC-01 B-- LOOP-21 NHA LOOP-51 NHN SGTR-10 B-A SLBI-11 NHN SLOC-23 NHN 1ILOC-02 B-- LOOP-23 NHA LOOP-52 NHN SGTR-11 B-A SLBI-12 NHN SLOC-24 NHN 1ILOC-03 B-- LOOP-24 NHA LOOP-54 NHA SGTR-13 B-A SLBI-13 NHN SLOC-25 NHN 1ILOC-04 B-- LOOP-26 NHA LOOP-55 NHA SGTR-14 B-A SLBO-03 NHN SLOC-26 NHN 1ILOC-05 B-- LOOP-27 NHA LOOP-56 NHA SGTR-15 B-A SLBO-04 NHN TRAN-04 NHN LLOC-02 NLA LOOP-29 NHA LOOP-58 NHA SGTR-18 B-A SLBO-05 NHN TRAN-05 NHN LLOC-03 NLA LOOP-31 NHN LOOP-59 NHA SGTR-19 B-A SLBO-07 NHN TRAN-07 NHN LLOC-04 NLA LOOP-32 NHN LOOP-60 NHA SGTR-21 B-A SLBO-08 NHN TRAN-08 NHN Byron and Braidwood Stations, Units 1 and 2 Page F-168 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-4 Mapping of Level 1 Sequences to PDS CDF Seq. ID PDS CDF Seq. ID PDS CDF Seq. ID PDS CDF Seq. ID PDS CDF Seq. ID PDS CDF Seq. ID PDS LODC-03 NHN LOOP-33 NHN LOOP-62 NHA SGTR-22 B-A SLBO-09 NHN TRAN-09 NHN LODC-04 NHN LOOP-35 NHN LOOP-63 NHA SGTR-24 B-N SLOC-02 NHA XLOC-00 NLA Byron and Braidwood Stations, Units 1 and 2 Page F-169 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-5 Correlation of PDS to Sequences L2 Sequence NHA NHN NLA NLN B-- B-A BHA B-N Intact01 X X Intact02 X Intact03 X Intact04 X Intact05 X Late01 X X Late02 X X Late03 X X Late04 X Late05 X Late06 X Late07 X Late06 X Late07 X Late08 X Late09 X Late10 X Late11 X Late12 X Late13 X Late14 X Late15 X Late16 X LERF01 X X LERF02 X LERF03 X LERF04 X LERF05 X LERF06 X Byron and Braidwood Stations, Units 1 and 2 Page F-170 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-5 Correlation of PDS to Sequences L2 Sequence NHA NHN NLA NLN B-- B-A BHA B-N LERF07 X LERF08 X LERF09 X X X X LERF10 X X LERF11 X X SERF01 X SERF02 X X Byron and Braidwood Stations, Units 1 and 2 Page F-171 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-6 Representative Sequences Release Dominant Representative Sequence Discussion Category L2 Sequences LERF-ISLOCA LERF11-ISLOCA: 100% The Level 1 1ILOC-03 sequence is the dominant contributor and is used to characterize the release category. This sequence is a break in the RHR discharge line outside containment followed by successful injection, but core damage ensues as there is no water in the sump for recirculation mode.

ILOC-04, the other top contributor, is similar, but the break is in the RHR suction line.

ISLOCA in the RHR discharge line (800 gpm break), successful scram, successful injection, recirculation unavailable, core damage, containment bypass.

LERF-CI LERF09: 100% There are many different contributions to this release category due to its inclusive nature, but a vast majority includes failure of the recirculation mode after successful injection.

Approximately 60% of the total contribution comes from small LOCA scenarios (both small LOCA initiators and RCP seal LOCAs that evolve from other initiating events). The remaining 40% is comprised mostly of loss of SX and Flooding events. Medium LOCAs are small contributors and are almost all recirculation failures. A truly representative sequence for this release category would be a small LOCA with recirculation failure, but to address the faster evolving contributors with injection failures, the seal LOCA with F&B failure is used.

Loss of SX, successful scram, RCP seal LOCA, injection failure, core damage, containment isolation failure.

LERF-CFE LERF02: 75% The main difference between sequences LERF02 and LERF03 with respect to LERF03: 25% equipment availability is that AFW is available for LERF02 while it is not for LERF03. Both sequences include a mixture of injection and recirculation failures. Because LERF03 scenarios may evolve more quickly, they are used as the representative sequence as injection failure cases.

Loss of SX, successful scram, no AFW, FW not restored, seal cooling successful, operator fail to initiate feed and bleed injection, core damage, successful operator action to depressurize the RCS prior to vessel failure or tube rupture, vessel melt, and containment failure due to hydrogen burn.

Byron and Braidwood Stations, Units 1 and 2 Page F-172 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-6 Representative Sequences Release Dominant Representative Sequence Discussion Category L2 Sequences LERF-SGTR-AFW LERF10: 100% Over 80% of the contributors are the result of operator failure to cool down the RCS in time to prevent passing water through the SG PORVs followed by operator failure to cool down the RCS to terminate SGTR break flow before RWST depletion. An additional 3% of the contribution is from failure to cool down the RCS in time to prevent passing water through the SG PORVs followed by operator failure to establish shutdown cooling. The consequences of these scenarios are similar and the larger contributor is chose as representative.

SGTR, successful scram, SG isolation successful, failure to cool down RCS before passing water through the SG PORV, stuck open SG PORV, RCS injection successful, failure to cool down the RCS before RWST depletion, core damage, release through tubes.

LERF-SGTR-NOAFW LERF11: 100% The contributing scenarios are dominated by common cause failure of AFW followed by failure to restore main feedwater (MFW).

SGTR, scram successful, AFW fails, FW not restored, injection successful, RWST depletes, core damage, release through tubes.

LERF-ISGTR LERF08: ~99% Most of the induced tube rupture scenarios are pressure induced tube ruptures LERF07: ~1% (LERF08), but thermally induced ruptures (LEFF07) are also represented in the cutsets. The TI-SGTR contribution to LERF is small relative to the PI-SGTR due to likelihood of hot leg failure near the time of TI-SGTR (eliminates release pathway). Both scenarios, however, are dominated by transient initiators with AFW unavailability, most of which lead to recirculation failures.

Feed and Bleed failures are smaller contributors, but because of the potential impact on the source terms, the Feed and Bleed failure scenario is chosen as the representative case.

Loss of SX, successful scram, AFW unavailable, operators fail to align alt FW and fail to align F&B, core damage, pressure induced tube rupture occurs.

LATE-BMT-AFW LATE04: ~92% For both the LATE04 and LATE01 sequences, most of the contributors are LATE01: ~1% LOCA events (including seal LOCAs) with recirculation failures. The availability of water on the containment floor impacts the probability of the basemat meltthrough, but has a negligible impact on the source term itself.

For the basemat failure releases, the differences in LOCA size also have a minimal impact on the results. The largest frequency contributor is chosen as the representative sequence, which are the small LOCAs.

Small LOCA, successful scram, AFW available, injection successful, recirculation mode failure, core damage, containment heat removal success (RCFCs), CS success, basemat melt through.

Byron and Braidwood Stations, Units 1 and 2 Page F-173 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-6 Representative Sequences Release Dominant Representative Sequence Discussion Category L2 Sequences LATE-BMT-NOAFW LATE07: ~88% The difference in the two dominant Level 2 sequences is related to operation LATE08: ~12% of Containment Spray, which determines if there is a water pool in the reactor cavity when the core relocates to the containment. The scenarios for both sequences are essentially the same, most being transients with AFW failure followed by a mixture of either injection or recirculation mode failures. For this case, the scenarios with the feed and bleed failures are chosen as representative to capture any potential timing issues for evacuation.

General transient event, successful scram, AFW CCF to run, failure to restore FW, failure to initiate feed and bleed, core damage, no PI-SGTR, op depressurizes late, no early containment failure at vessel breach (VB),

containment heat removal (CHR) successful, CS successful, basemat failure.

LATE-CHR-AFW LATE06: >99.9% Late06 accounts for almost all of the contributions to this release category frequency. Over 95% of the contribution to the release category is from LOSW events or events that lead to SX failure, followed by a seal LOCA. The other contributions are almost all scenarios that result in a seal LOCA in a different manner. Recirculation and injection failures are both represented, but most are injection failures.

LOSW, successful scram, AFW failed, startup FW OK, failure to align alternate seal cooling, failure to align SX X-tie, seal LOCA, injection failure, core damage, no containment failure at VB, CHR fails with long term containment overpressurization (COP).

LATE-CHR-NOAFW LATE09: >99% Late09 accounts for almost all of the contributions to this release category frequency. Over 97% of the release category frequency is from LOSW events or events that lead to SX failure. These are generally followed by the unavailability of FW/Condensate and recirculation mode; injection failures contribute less than 10% of the frequency.

LOSW (all SX pumps CCF), successful scram, AFW failure from lack of SX cooling, failure to restore FW, SX X-tie not available, CHR not available for recirc, core damage, operator depressurizes late, no containment failure at VB, CHR fails with long term COP.

SERF-SGTR -TISGTR-HLF SERF01: 100% The SERF01 sequence is comprised of mostly feed and bleed failures with some recirculation failures after failure of AFW. The more rapidly evolving feed and bleed failures are chosen as the representative sequences.

Loss of 125 DC bus 111, successful scram, failure of AFW, failure of feed and bleed, core damage, late depressurization failure, TI-SGTR occurs, Hot leg fails at about the same time as TI-SGTR, no early containment failure, CHR success, CS success, no basemat failure.

Byron and Braidwood Stations, Units 1 and 2 Page F-174 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-6 Representative Sequences Release Dominant Representative Sequence Discussion Category L2 Sequences SERF-SGTR-AFW-SC SERF02: 100% The SERF02 sequence is mostly comprised (72% based on the Unit 2 results that correctly include 2RX-JHEP33-HOADA) of SGTR events with failure the operators to cool down the RCS before overfilling the SG (opens a steam generator PORV for a LOCA) and subsequent operator error to cool down the RCS to terminate the break flow before depleting the RWST. The cases including 2RX-JHEP33-HOADA (about 8%) are SGTR events with operator failures to shut down dead headed RHR pumps (fails RH) and failure to reduce ECCS injection (to prevent lifting the SG safety valves).

SGTR, successful scram, operator fails to cool down the RCS, SG overfill causes stuck open PORV, operator fails to cool down the RCS to terminate break flow before the RWST is depleted, recirculation mode is unavailable, core damage, operators maintain SG level over the top of the SG tubes for release scrubbing.

INTACT INTACT02: ~85% Most of the intact contribution comes from small LOCA scenarios (including INTACT03: ~13% induced Small LOCAs) with recirculation failures. For intact containment scenarios, the path to core damage has a negligible impact on the source INTACT01: ~1%

term.

Small LOCA, successful scram, AFW available, injection successful, recirculation failure, core damage, containment intact.

Byron and Braidwood Stations, Units 1 and 2 Page F-175 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-7 Byron Source Term Summary LERF- LERF-CI LERF-CFE LERF- LERF- LERF- LATE-BMT- LATE-BMT- LATE- LATE-CHR- SERF- SERF-SGTR- INTACT ISLOCA SGTR- SGTR- ISGTR AFW(2) NOAFW CHR- NOAFW(4) SGTR- AFW-SC(5)

AFW(1) NOAFW AFW(3) TISGTR-HLF MAAP Case 1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 11a 12b 13a Run Duration 72 hr 72 hr 72 hr 200 hr 200 hr 800 hr 144 hr 144 hr 200 hrs 1600 hrs 72 hrs 200 hrs 72 hrs Time after Scram when GE is declared 6.91 5.93 3.16 87.00 0.50 3.16 12.17 3.14 5.93 3.14 3.17 84.60 12.17 Fission Product Group:

1) Noble Total Release Fraction 1.00E+00 9.80E-01 1.00E+00 8.10E-01 3.00E-01 1.00E+00 1.00E+00 1.00E+00 1.00E+00 1.00E+00 5.10E-01 7.90E-01 2.70E-03 Total Plume 1 Release Fraction 9.70E-1 4.30E-1 9.10E-1 4.40E-1 2.70E-1 5.00E-2 2.00E-4 4.00E-4 4.00E-3 7.00E-2 5.10E-1 4.20E-1 3.00E-4 Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 3.00E-2 5.00E-1 9.00E-2 8.00E-2 0.00E+0 9.50E-1 4.50E-3 3.90E-3 9.96E-1 9.30E-1 0.00E+0 1.30E-1 4.00E-4 Start of Plume 2 Release (hr) 8.00 11.00 8.00 89.00 25.00 17.00 17.00 13.00 60.75 36.50 4.00 87.00 18.00 End of Plume 2 Release (hr) 12.00 21.00 13.00 93.00 35.00 27.00 27.00 23.00 70.75 46.50 14.00 93.00 28.00 Total Plume 3 Release Fraction 0.00E+0 5.00E-2 0.00E+0 2.90E-1 3.00E-2 0.00E+0 9.95E-1 9.96E-1 0.00E+0 0.00E+0 0.00E+0 2.40E-1 2.00E-3 Start of Plume 3 Release (hr) 12.00 30.00 19.00 93.00 35.00 90.00 90.00 90.00 90.00 90.00 14.00 93.00 28.00 End of Plume 3 Release (hr) 22.00 40.00 29.00 98.00 45.00 100.00 100.00 95.00 100.00 100.00 24.00 95.00 38.00

2) CsI Total Release Fraction 7.80E-01 1.40E-02 3.00E-01 9.70E-02 4.10E-02 1.90E-01 6.80E-05 7.40E-04 1.40E-02 2.40E-01 5.80E-02 1.80E-02 3.20E-05 Total Plume 1 Release Fraction 7.10E-1 9.00E-3 1.40E-1 5.30E-2 3.80E-2 1.00E-3 2.70E-5 2.00E-5 2.00E-5 2.00E-4 5.80E-2 9.00E-3 2.70E-5 Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 Byron and Braidwood Stations, Units 1 and 2 Page F-176 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-7 Byron Source Term Summary LERF- LERF-CI LERF-CFE LERF- LERF- LERF- LATE-BMT- LATE-BMT- LATE- LATE-CHR- SERF- SERF-SGTR- INTACT ISLOCA SGTR- SGTR- ISGTR AFW(2) NOAFW CHR- NOAFW(4) SGTR- AFW-SC(5)

AFW(1) NOAFW AFW(3) TISGTR-HLF MAAP Case 1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 11a 12b 13a Run Duration 72 hr 72 hr 72 hr 200 hr 200 hr 800 hr 144 hr 144 hr 200 hrs 1600 hrs 72 hrs 200 hrs 72 hrs Time after Scram when GE is declared 6.91 5.93 3.16 87.00 0.50 3.16 12.17 3.14 5.93 3.14 3.17 84.60 12.17 Fission Product Group:

End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 2.00E-2 3.00E-3 1.30E-1 3.00E-3 2.00E-3 1.10E-1 7.00E-6 5.00E-5 7.00E-3 1.30E-1 0.00E+0 0.00E+0 2.00E-6 Start of Plume 2 Release (hr) 8.00 11.00 8.00 89.00 25.00 17.00 17.00 13.00 60.75 36.50 18.00 End of Plume 2 Release (hr) 12.00 21.00 13.00 93.00 35.00 27.00 27.00 23.00 70.75 46.50 28.00 Total Plume 3 Release Fraction 5.00E-2 2.00E-3 3.00E-2 4.10E-2 1.00E-3 7.90E-2 3.40E-5 6.70E-4 7.00E-3 1.10E-1 0.00E+0 9.00E-3 3.00E-6 Start of Plume 3 Release (hr) 12.00 30.00 19.00 93.00 35.00 90.00 90.00 90.00 90.00 90.00 93.00 28.00 End of Plume 3 Release (hr) 22.00 40.00 29.00 98.00 45.00 100.00 100.00 95.00 100.00 100.00 95.00 38.00

3) TeO2 Total Release Fraction 7.10E-01 1.90E-02 1.10E-01 6.30E-02 3.30E-02 2.00E-01 2.90E-05 1.10E-04 8.70E-05 1.10E-01 4.40E-02 9.50E-03 3.00E-05 Total Plume 1 Release Fraction 6.20E-1 1.60E-2 6.00E-2 3.80E-2 3.20E-2 1.00E-3 2.60E-5 2.00E-5 8.00E-6 1.00E-4 4.30E-2 5.40E-3 2.60E-5 Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 5.00E-2 2.00E-3 3.00E-2 1.00E-3 0.00E+0 1.19E-1 1.00E-6 1.00E-5 3.30E-5 1.30E-3 1.00E-3 2.00E-4 3.00E-6 Start of Plume 2 Release (hr) 8.00 11.00 8.00 89.00 17.00 17.00 13.00 60.75 36.50 4.00 87.00 18.00 End of Plume 2 Release (hr) 12.00 21.00 13.00 93.00 27.00 27.00 23.00 70.75 46.50 14.00 93.00 28.00 Total Plume 3 Release Fraction 4.00E-2 1.00E-3 2.00E-2 2.40E-2 1.00E-3 8.00E-2 2.00E-6 8.00E-5 4.60E-5 1.09E-1 0.00E+0 3.90E-3 1.00E-6 Byron and Braidwood Stations, Units 1 and 2 Page F-177 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-7 Byron Source Term Summary LERF- LERF-CI LERF-CFE LERF- LERF- LERF- LATE-BMT- LATE-BMT- LATE- LATE-CHR- SERF- SERF-SGTR- INTACT ISLOCA SGTR- SGTR- ISGTR AFW(2) NOAFW CHR- NOAFW(4) SGTR- AFW-SC(5)

AFW(1) NOAFW AFW(3) TISGTR-HLF MAAP Case 1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 11a 12b 13a Run Duration 72 hr 72 hr 72 hr 200 hr 200 hr 800 hr 144 hr 144 hr 200 hrs 1600 hrs 72 hrs 200 hrs 72 hrs Time after Scram when GE is declared 6.91 5.93 3.16 87.00 0.50 3.16 12.17 3.14 5.93 3.14 3.17 84.60 12.17 Fission Product Group:

Start of Plume 3 Release (hr) 12.00 30.00 19.00 93.00 35.00 90.00 90.00 90.00 90.00 90.00 93.00 28.00 End of Plume 3 Release (hr) 22.00 40.00 29.00 98.00 45.00 100.00 100.00 95.00 100.00 100.00 95.00 38.00

4) SrO Total Release Fraction 1.10E-01 3.00E-04 3.00E-03 9.90E-03 1.60E-04 7.90E-04 3.20E-06 2.90E-06 3.00E-05 2.60E-04 8.50E-05 8.00E-04 3.20E-07 Total Plume 1 Release Fraction 9.60E-02 2.30E-4 2.60E-3 1.00E-3 7.00E-5 1.00E-5 1.60E-6 2.20E-6 2.00E-8 2.00E-6 8.40E-5 1.50E-4 2.80E-7 Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 5.00E-03 3.00E-5 1.00E-4 2.10E-3 9.00E-5 7.80E-4 1.50E-6 1.00E-7 3.00E-8 5.00E-6 1.00E-6 1.70E-4 3.00E-8 Start of Plume 2 Release (hr) 8.00 11.00 8.00 89.00 25.00 17.00 17.00 13.00 60.75 36.50 4.00 87.00 18.00 End of Plume 2 Release (hr) 12.00 21.00 13.00 93.00 35.00 27.00 27.00 23.00 70.75 46.50 14.00 93.00 28.00 Total Plume 3 Release Fraction 0.00 4.00E-5 3.00E-4 6.80E-3 0.00E+0 0.00E+0 1.00E-7 6.00E-7 3.00E-5 2.53E-4 0.00E+0 4.80E-4 1.00E-8 Start of Plume 3 Release (hr) 30.00 19.00 93.00 90.00 90.00 90.00 90.00 93.00 28.00 End of Plume 3 Release (hr) 40.00 29.00 98.00 100.00 95.00 100.00 100.00 95.00 38.00

5) MoO2 Total Release Fraction 1.50E-01 1.70E-03 3.40E-02 4.60E-02 2.80E-03 3.30E-04 4.80E-06 1.20E-05 2.10E-06 1.20E-04 7.20E-03 4.60E-03 2.40E-06 Total Plume 1 Release Fraction 1.10E-1 1.60E-3 3.30E-2 2.10E-2 2.50E-3 4.00E-5 4.70E-6 1.20E-5 1.30E-6 4.00E-5 7.10E-3 3.10E-3 2.10E-6 Byron and Braidwood Stations, Units 1 and 2 Page F-178 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-7 Byron Source Term Summary LERF- LERF-CI LERF-CFE LERF- LERF- LERF- LATE-BMT- LATE-BMT- LATE- LATE-CHR- SERF- SERF-SGTR- INTACT ISLOCA SGTR- SGTR- ISGTR AFW(2) NOAFW CHR- NOAFW(4) SGTR- AFW-SC(5)

AFW(1) NOAFW AFW(3) TISGTR-HLF MAAP Case 1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 11a 12b 13a Run Duration 72 hr 72 hr 72 hr 200 hr 200 hr 800 hr 144 hr 144 hr 200 hrs 1600 hrs 72 hrs 200 hrs 72 hrs Time after Scram when GE is declared 6.91 5.93 3.16 87.00 0.50 3.16 12.17 3.14 5.93 3.14 3.17 84.60 12.17 Fission Product Group:

Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 4.00E-2 1.00E-4 1.00E-3 4.00E-3 3.00E-4 2.90E-4 1.00E-7 0.00E+0 8.00E-7 8.00E-5 1.00E-4 3.00E-4 2.00E-7 Start of Plume 2 Release (hr) 8.00 11.00 8.00 89.00 25.00 17.00 17.00 60.75 36.50 4.00 87.00 18.00 End of Plume 2 Release (hr) 12.00 21.00 13.00 93.00 35.00 27.00 27.00 70.75 46.50 14.00 93.00 28.00 Total Plume 3 Release Fraction 0.00E+0 0.00E+0 0.00E+0 2.10E-2 0.00E+0 0.00E+0 0.00E+0 0.00E+0 0.00E+0 0.00E+0 0.00E+0 1.20E-3 1.00E-7 Start of Plume 3 Release (hr) 93.00 93.00 28.00 End of Plume 3 Release (hr) 98.00 95.00 38.00

6) CsOH Total Release Fraction 7.70E-01 1.10E-02 6.10E-02 8.70E-02 2.70E-02 2.90E-01 5.00E-05 3.50E-04 4.50E-03 1.70E-01 3.10E-02 1.70E-02 2.90E-05 Total Plume 1 Release Fraction 7.00E-1 8.00E-3 3.40E-2 4.90E-2 2.60E-2 5.00E-4 2.60E-5 1.00E-5 7.00E-6 7.00E-5 3.10E-2 8.00E-3 2.60E-5 Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 2.00E-2 1.00E-4 1.20E-2 3.00E-3 1.00E-3 7.00E-2 2.00E-6 2.00E-5 2.20E-3 2.20E-2 0.00E+0 0.00E+0 2.00E-6 Start of Plume 2 Release (hr) 8.00 11.00 8.00 89.00 25.00 17.00 17.00 13.00 60.75 36.50 18.00 End of Plume 2 Release (hr) 12.00 21.00 13.00 93.00 35.00 27.00 27.00 23.00 70.75 46.50 28.00 Byron and Braidwood Stations, Units 1 and 2 Page F-179 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-7 Byron Source Term Summary LERF- LERF-CI LERF-CFE LERF- LERF- LERF- LATE-BMT- LATE-BMT- LATE- LATE-CHR- SERF- SERF-SGTR- INTACT ISLOCA SGTR- SGTR- ISGTR AFW(2) NOAFW CHR- NOAFW(4) SGTR- AFW-SC(5)

AFW(1) NOAFW AFW(3) TISGTR-HLF MAAP Case 1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 11a 12b 13a Run Duration 72 hr 72 hr 72 hr 200 hr 200 hr 800 hr 144 hr 144 hr 200 hrs 1600 hrs 72 hrs 200 hrs 72 hrs Time after Scram when GE is declared 6.91 5.93 3.16 87.00 0.50 3.16 12.17 3.14 5.93 3.14 3.17 84.60 12.17 Fission Product Group:

Total Plume 3 Release Fraction 5.00E-2 2.90E-3 1.50E-2 3.50E-2 0.00E+0 2.20E-1 2.20E-5 3.20E-4 2.30E-3 1.48E-1 0.00E+0 9.00E-3 1.00E-6 Start of Plume 3 Release (hr) 12.00 30.00 19.00 93.00 90.00 90.00 90.00 90.00 90.00 93.00 28.00 End of Plume 3 Release (hr) 22.00 40.00 29.00 98.00 100.00 100.00 95.00 100.00 100.00 95.00 38.00

7) BaO Total Release Fraction 1.20E-01 5.50E-04 1.10E-02 3.70E-02 2.30E-03 5.70E-04 3.00E-06 4.30E-06 1.40E-05 1.40E-04 3.10E-03 2.80E-03 1.50E-06 Total Plume 1 Release Fraction 1.20E-1 4.70E-4 1.10E-2 7.00E-3 2.00E-3 6.00E-5 2.10E-6 3.80E-6 9.00E-8 1.00E-5 3.10E-3 1.10E-3 1.40E-6 Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 0.00E+0 6.00E-5 0.00E+0 6.00E-3 3.00E-4 5.00E-4 7.00E-7 0.00E+0 1.00E-7 2.00E-5 0.00E+0 5.00E-4 1.00E-7 Start of Plume 2 Release (hr) 11.00 89.00 25.00 17.00 17.00 60.75 36.50 87.00 18.00 End of Plume 2 Release (hr) 21.00 93.00 35.00 27.00 27.00 70.75 46.50 93.00 28.00 Total Plume 3 Release Fraction 0.00E+0 2.00E-5 0.00E+0 2.40E-2 0.00E+0 1.00E-5 2.00E-7 5.00E-7 1.40E-5 1.10E-4 0.00E+0 1.20E-3 0.00E+0 Start of Plume 3 Release (hr) 30.00 93.00 90.00 90.00 90.00 90.00 90.00 93.00 End of Plume 3 Release (hr) 40.00 98.00 100.00 100.00 95.00 100.00 100.00 95.00

8) La2O3 Total Release Fraction 3.60E-03 1.90E-04 4.20E-04 4.50E-04 1.10E-05 8.00E-05 4.90E-07 4.00E-07 1.30E-06 7.30E-06 7.40E-06 4.10E-05 2.00E-08 Byron and Braidwood Stations, Units 1 and 2 Page F-180 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-7 Byron Source Term Summary LERF- LERF-CI LERF-CFE LERF- LERF- LERF- LATE-BMT- LATE-BMT- LATE- LATE-CHR- SERF- SERF-SGTR- INTACT ISLOCA SGTR- SGTR- ISGTR AFW(2) NOAFW CHR- NOAFW(4) SGTR- AFW-SC(5)

AFW(1) NOAFW AFW(3) TISGTR-HLF MAAP Case 1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 11a 12b 13a Run Duration 72 hr 72 hr 72 hr 200 hr 200 hr 800 hr 144 hr 144 hr 200 hrs 1600 hrs 72 hrs 200 hrs 72 hrs Time after Scram when GE is declared 6.91 5.93 3.16 87.00 0.50 3.16 12.17 3.14 5.93 3.14 3.17 84.60 12.17 Fission Product Group:

Total Plume 1 Release Fraction 1.60E-3 1.60E-4 3.70E-4 2.00E-5 7.00E-6 3.00E-7 1.40E-7 2.50E-7 1.00E-9 1.00E-7 7.30E-6 3.00E-6 1.80E-8 Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 1.90E-3 3.00E-5 1.00E-5 1.00E-5 4.00E-6 8.00E-5 3.40E-7 2.00E-8 1.00E-9 1.00E-7 1.00E-7 4.00E-6 2.00E-9 Start of Plume 2 Release (hr) 8.00 11.00 8.00 89.00 25.00 17.00 17.00 13.00 60.75 36.50 4.00 87.00 18.00 End of Plume 2 Release (hr) 12.00 21.00 13.00 93.00 35.00 27.00 27.00 23.00 70.75 46.50 14.00 93.00 28.00 Total Plume 3 Release Fraction 1.00E-4 0.00E+0 4.00E-5 4.20E-4 0.00E+0 0.00E+0 1.00E-8 1.30E-7 1.30E-6 7.10E-6 0.00E+0 3.40E-5 0.00E+0 Start of Plume 3 Release (hr) 12.00 19.00 93.00 90.00 90.00 90.00 90.00 93.00 End of Plume 3 Release (hr) 22.00 29.00 98.00 100.00 95.00 100.00 100.00 95.00

9) CeO2 Total Release Fraction 4.20E-02 3.30E-04 2.10E-03 3.10E-03 2.10E-05 1.80E-03 8.00E-06 7.40E-06 6.00E-05 3.20E-04 1.10E-05 2.50E-04 1.80E-07 Total Plume 1 Release Fraction 1.30E-2 1.80E-4 1.10E-3 2.00E-4 1.40E-5 1.00E-6 2.10E-6 4.60E-6 4.00E-9 1.00E-7 1.10E-5 2.00E-5 1.60E-7 Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 2.90E-2 4.00E-5 0.00E+0 1.00E-4 7.00E-6 1.80E-3 5.70E-6 5.00E-7 2.00E-9 2.00E-7 0.00E+0 2.00E-5 2.00E-8 Start of Plume 2 Release (hr) 8.00 11.00 89.00 25.00 17.00 17.00 13.00 60.75 36.50 87.00 18.00 Byron and Braidwood Stations, Units 1 and 2 Page F-181 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-7 Byron Source Term Summary LERF- LERF-CI LERF-CFE LERF- LERF- LERF- LATE-BMT- LATE-BMT- LATE- LATE-CHR- SERF- SERF-SGTR- INTACT ISLOCA SGTR- SGTR- ISGTR AFW(2) NOAFW CHR- NOAFW(4) SGTR- AFW-SC(5)

AFW(1) NOAFW AFW(3) TISGTR-HLF MAAP Case 1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 11a 12b 13a Run Duration 72 hr 72 hr 72 hr 200 hr 200 hr 800 hr 144 hr 144 hr 200 hrs 1600 hrs 72 hrs 200 hrs 72 hrs Time after Scram when GE is declared 6.91 5.93 3.16 87.00 0.50 3.16 12.17 3.14 5.93 3.14 3.17 84.60 12.17 Fission Product Group:

End of Plume 2 Release (hr) 12.00 21.00 93.00 35.00 27.00 27.00 23.00 70.75 46.50 93.00 28.00 Total Plume 3 Release Fraction 0.00E+0 1.10E-4 1.00E-3 2.80E-3 0.00E+0 0.00E+0 2.00E-7 2.30E-6 6.00E-5 3.20E-4 0.00E+0 2.10E-4 0.00E+0 Start of Plume 3 Release (hr) 30.00 19.00 93.00 90.00 90.00 90.00 90.00 93.00 End of Plume 3 Release (hr) 40.00 29.00 98.00 100.00 95.00 100.00 100.00 95.00

10) Sb (Grouped with TeO2)

Total Release Fraction 5.70E-01 3.10E-02 2.90E-01 6.10E-02 2.40E-02 2.50E-01 3.20E-03 2.10E-04 1.90E-02 2.00E-01 1.50E-02 8.00E-03 2.00E-05 Total Plume 1 Release Fraction 4.60E-01 4.00E-03 1.80E-01 3.10E-02 1.70E-02 2.00E-04 2.00E-05 4.00E-05 8.00E-06 1.00E-04 1.50E-02 4.40E-03 1.40E-05 Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 4.00E-02 0.00E+00 2.00E-02 5.00E-03 5.00E-03 5.00E-02 1.00E-05 1.00E-05 6.00E-03 3.00E-02 0.00E+00 4.00E-04 3.00E-06 Start of Plume 2 Release (hr) 8.00 8.00 89.00 25.00 17.00 17.00 13.00 60.75 36.50 87.00 18.00 End of Plume 2 Release (hr) 12.00 13.00 93.00 35.00 27.00 27.00 23.00 70.75 46.50 93.00 28.00 Total Plume 3 Release Fraction 7.00E-02 2.70E-02 9.00E-02 2.50E-02 2.00E-03 2.00E-01 3.17E-03 1.60E-04 1.30E-02 1.70E-01 0.00E+00 3.20E-03 3.00E-06 Start of Plume 3 Release (hr) 12.00 30.00 19.00 93.00 35.00 90.00 90.00 90.00 90.00 90.00 93.00 28.00 End of Plume 3 Release (hr) 22.00 40.00 29.00 98.00 45.00 100.00 100.00 95.00 100.00 100.00 95.00 38.00

11) Te2 (Grouped with TeO2)

Byron and Braidwood Stations, Units 1 and 2 Page F-182 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-7 Byron Source Term Summary LERF- LERF-CI LERF-CFE LERF- LERF- LERF- LATE-BMT- LATE-BMT- LATE- LATE-CHR- SERF- SERF-SGTR- INTACT ISLOCA SGTR- SGTR- ISGTR AFW(2) NOAFW CHR- NOAFW(4) SGTR- AFW-SC(5)

AFW(1) NOAFW AFW(3) TISGTR-HLF MAAP Case 1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 11a 12b 13a Run Duration 72 hr 72 hr 72 hr 200 hr 200 hr 800 hr 144 hr 144 hr 200 hrs 1600 hrs 72 hrs 200 hrs 72 hrs Time after Scram when GE is declared 6.91 5.93 3.16 87.00 0.50 3.16 12.17 3.14 5.93 3.14 3.17 84.60 12.17 Fission Product Group:

Total Release Fraction 2.00E-04 2.00E-06 8.00E-05 0.00E+00 1.40E-11 0.00E+00 8.80E-07 9.50E-09 2.50E-07 0.00E+00 0.00E+00 0.00E+00 0.00E+00 Total Plume 1 Release Fraction 0.00E+00 9.00E-07 1.00E-06 0.00E+00 0.00E+00 0.00E+00 3.00E-08 2.00E-11 2.00E-10 0.00E+00 0.00E+00 0.00E+00 0.00E+00 Start of Plume 1 Release (hr) 7.00 6.00 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 11.00 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 1.90E-04 8.00E-07 7.00E-06 0.00E+00 5.00E-12 0.00E+00 1.00E-08 1.00E-11 7.00E-08 0.00E+00 0.00E+00 0.00E+00 0.00E+00 Start of Plume 2 Release (hr) 8.00 11.00 8.00 25.00 17.00 13.00 60.75 End of Plume 2 Release (hr) 12.00 21.00 13.00 35.00 27.00 23.00 70.75 Total Plume 3 Release Fraction 1.00E-05 3.00E-07 7.20E-05 0.00E+00 9.00E-12 0.00E+00 8.40E-07 9.47E-09 1.80E-07 0.00E+00 0.00E+00 0.00E+00 0.00E+00 Start of Plume 3 Release (hr) 12.00 30.00 19.00 35.00 90.00 90.00 90.00 End of Plume 3 Release (hr) 22.00 40.00 29.00 45.00 100.00 95.00 100.00

12) UO2 (Grouped with CeO2)

Total Release Fraction 2.40E-04 8.70E-07 2.20E-05 0.00E+00 2.20E-14 2.50E-05 7.30E-08 1.50E-07 2.20E-07 4.10E-06 0.00E+00 0.00E+00 0.00E+00 Total Plume 1 Release Fraction 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 9.00E-09 4.00E-08 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 Start of Plume 1 Release (hr) 5.00 87.00 24.00 3.50 12.50 3.40 6.00 3.50 3.50 85.00 12.40 End of Plume 1 Release (hr) 8.00 89.00 25.00 4.50 17.00 13.00 9.00 13.50 4.00 87.00 18.00 Total Plume 2 Release Fraction 1.70E-04 3.00E-11 1.00E-07 0.00E+00 1.70E-14 2.50E-05 4.60E-08 1.00E-08 0.00E+00 1.00E-11 0.00E+00 0.00E+00 0.00E+00 Byron and Braidwood Stations, Units 1 and 2 Page F-183 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-7 Byron Source Term Summary LERF- LERF-CI LERF-CFE LERF- LERF- LERF- LATE-BMT- LATE-BMT- LATE- LATE-CHR- SERF- SERF-SGTR- INTACT ISLOCA SGTR- SGTR- ISGTR AFW(2) NOAFW CHR- NOAFW(4) SGTR- AFW-SC(5)

AFW(1) NOAFW AFW(3) TISGTR-HLF MAAP Case 1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 11a 12b 13a Run Duration 72 hr 72 hr 72 hr 200 hr 200 hr 800 hr 144 hr 144 hr 200 hrs 1600 hrs 72 hrs 200 hrs 72 hrs Time after Scram when GE is declared 6.91 5.93 3.16 87.00 0.50 3.16 12.17 3.14 5.93 3.14 3.17 84.60 12.17 Fission Product Group:

Start of Plume 2 Release (hr) 8.00 11.00 8.00 25.00 17.00 17.00 13.00 36.50 End of Plume 2 Release (hr) 12.00 21.00 13.00 35.00 27.00 27.00 23.00 46.50 Total Plume 3 Release Fraction 7.00E-05 8.70E-07 2.19E-05 0.00E+00 5.00E-15 0.00E+00 1.80E-08 1.00E-07 2.20E-07 4.10E-06 0.00E+00 0.00E+00 0.00E+00 Start of Plume 3 Release (hr) 12.00 30.00 19.00 35.00 90.00 90.00 90.00 90.00 End of Plume 3 Release (hr) 22.00 40.00 29.00 45.00 100.00 95.00 100.00 100.00 (1)

LERFSGTRAFW: All three plume start times and GE time were reduced by 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br /> to conform to MACCS2 input limits.

(2)

LATEBMTAFW: Plume 3 start time reduced from 107 hours0.00124 days <br />0.0297 hours <br />1.76918e-4 weeks <br />4.07135e-5 months <br /> to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> to conform to MACCS2 input limits.

(3)

LATECHRAFW: Plume 3 start time reduced from 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> to conform to MACCS2 input limits.

(4)

LATECHRNOAFW: Plume 3 start time reduced from 126 hours0.00146 days <br />0.035 hours <br />2.083333e-4 weeks <br />4.7943e-5 months <br /> to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> to conform to MACCS2 input limits.

(5)

SERFSGTRAFWSC: All three plume start times and GE time were reduced by 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> to conform to MACCS2 input limits.

Byron and Braidwood Stations, Units 1 and 2 Page F-184 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.2-8 Detailed Release Category Results BY Unit 1 BY Unit 2 Endstate Freq (/yr) Percent Freq (/yr) Percent INTACT 1.16E-05 27.6% 1.17E-05 29.1%

SERF-TISGTR-HLF 6.49E-09 0.0% 6.50E-09 0.0%

SERF-SGTR-AFW-SC 1.38E-06 3.3% 1.55E-06 3.8%

LATE-BMMT-AFW 5.30E-07 1.3% 5.14E-07 1.3%

LATE-BMMT-NOAFW 7.95E-08 0.2% 8.63E-08 0.2%

LATE-CHR-AFW 1.89E-05 45.1% 1.85E-05 45.8%

LATE-CHR-NOAFW 8.35E-06 19.9% 6.94E-06 17.2%

LERF-ISLOCA 3.40E-07 0.8% 3.40E-07 0.8%

LERF-CI 3.67E-07 0.9% 3.52E-07 0.9%

LERF-CFE 3.55E-08 0.1% 3.41E-08 0.1%

LERF-SGTR-AFW 5.49E-08 0.1% 6.18E-08 0.2%

LERF-SGTR-NOAFW 8.57E-10 0.0% 8.57E-10 0.0%

LERF-ISGTR 2.69E-07 0.6% 2.31E-07 0.6%

Total 4.19E-05 100.0% 4.03E-05 100.0%

Byron and Braidwood Stations, Units 1 and 2 Page F-185 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-1 County Growth Rates 2000 - 2030 Growth Rate County 2000 - 2030 Percentage Illinois Boone 24.6%

Bureau 14.8%

Carroll 6.1%

DeKalb 39.4%

Henry 6.3%

Jo Daviess 32.5%

Kane 67.8%

Kendall 55.7%

La Salle 26.8%

Lee 7.8%

McHenry 70.2%

Ogle 24.7%

Stephenson 5.5%

Whiteside 12.1%

Winnebago 29.0%

Iowa Clinton 0.0%(1)

Jackson 0.0%(2)

Wisconsin Green 33.4%

Lafayette 3.8%

Rock 18.4%

Walworth 39.8%

(1) Calculated Clinton County growth rate was -3.4%. Zero growth is assumed.

(2) Calculated Jackson County growth rate was -2.0%. Zero growth is assumed.

Byron and Braidwood Stations, Units 1 and 2 Page F-186 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-2 Estimated Population Distribution within a 10-Mile Radius of Byron, Year 2046 10-mile Sector 0-1 mile 1-2 miles 2-3 miles 3-4 miles 4-5 miles 5-10 miles Total(1)

N 0 2648 737 1010 1550 1231 5946 NNE 2 58 27 5533 3669 2323 9291 NE 0 8 36 1088 238 2043 1373 ENE 11 63 381 64 155 4270 678 E 0 0 0 97 53 1068 155 ESE 0 14 6 0 34 1140 60 SE 25 0 12 36 27 411 107 SSE 0 24 18 21 141 954 212 S 0 72 11 16 200 344 308 SSW 16 7 58 85 1362 4709 1538 SW 0 44 84 900 2076 7428 3115 WSW 0 8 532 1197 86 9791 1835 W 0 7 33 68 308 605 429 WNW 0 407 12 7 0 1362 440 NW 0 0 240 36 62 552 353 NNW 0 0 119 310 27 528 472 (1)

Total 54 3360 2306 10468 9988 38759 26312 (1) Population projections developed in electronic spreadsheet calculation and totals may differ slightly due to rounding of individual values.

Byron and Braidwood Stations, Units 1 and 2 Page F-187 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-3 Estimated Population Distribution within a 50-Mile Radius of Byron, Year 2046 50-mile Sector 0-10 miles 10-20 miles 20-30 miles 30-40 miles 40-50 miles Total(1)

N 5946 6308 5696 12283 16600 48063 NNE 9291 64680 57178 80691 89403 303564

-NE 1373 176552 90883 9505 45774 326127 ENE 678 8637 36188 26709 113802 190280 E 155 3768 10526 34756 234146 284414 ESE 60 1925 72838 28637 66464 171058 SE 107 17986 3397 4753 45592 72239 SSE 212 2094 1641 16079 5067 26039 S 308 2384 5172 2750 11763 22712 SSW 1538 11387 1635 3599 7251 30109 SW 3115 13937 35349 11918 6658 78394 WSW 1835 4647 3388 6658 26660 52967 W 429 1125 3042 4530 8257 17975 WNW 440 3603 3573 3645 6030 18639 NW 353 1583 34296 7950 6218 50937 NNW 472 4644 6399 8011 21210 41248 Total(1) 26312 325260 371201 262474 710895 1734765 (1) Population projections developed in electronic spreadsheet calculation and totals may differ slightly due to rounding of individual values.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-4 County Specific Land Use And Economic Parameters Inputs Farm Property Non-Farm Fraction Fraction Farm Sales Value Property Value County Farm Dairy ($/hectare) ($/hectare) ($/person)

Illinois Boone 0.76 0.074 1,466 13,492 211,408 Bureau 0.86 0.002 1,566 11,058 225,984 Carroll 0.93 0.062 1,929 10,042 213,874 DeKalb 0.92 0.013 2,013 12,637 203,355 Henry 0.93 0.002 1,497 10,768 219,909 Jo Daviess 0.73 0.174 1,199 10,927 253,565 Kane 0.58 0.018 2,544 13,291 246,480 Kendall 0.81 0.008 1,532 11,800 223,356 LaSalle 0.89 0.001 1,263 11,455 219,164 Lee 0.85 0.002 1,338 11,761 206,626 McHenry 0.56 0.067 1,793 13,774 268,236 Ogle 0.76 0.015 1,744 12,365 219,394 Stephenson 0.94 0.172 1,804 10,552 227,190 Whiteside 0.93 0.024 1,711 10,430 217,680 Winnebago 0.56 0.051 1,209 12,013 221,467 Iowa Clinton 0.89 0.046 1,434 9,300 220,742 Jackson 0.73 0.094 1,218 7,756 202,765 Wisconsin Green 0.82 0.557 1,514 9,749 235,318 Lafayette 0.85 0.459 1,581 9,619 198,295 Rock 0.75 0.223 1,403 11,010 213,731 Walworth 0.82 0.557 1,514 11,806 223,153 Byron and Braidwood Stations, Units 1 and 2 Page F-189 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-5 Byron MACCS2 Generic Economic Parameters Variable Description Value (1)

DPRATE Property depreciation rate (per yr) 0.20 DSRATE(2) Investment rate of return (per yr) 0.07 EVACST(3) Daily cost for a person who has been evacuated ($/person-day) 56.43 RELCST(3) Daily cost for a person who is relocated ($/person-day) 56.43 POPCST(3) Population relocation cost ($/person) 10,450 CDFRM0(3) Cost of farm decontamination for two levels of decontamination ($/hectare) (5) 1,176 2,613 CDNFRM(3) Cost of non-farm decontamination per resident person for various levels of 6,270 decontamination ($/person) (5) 16,720 TIMDEC(1) Decontamination time for each level(5) 2&4 months DLBCST(3) Average cost of decontamination labor 73,150

($/man-year)

(1)

TFWKF Time decontamination workers spend in farm land contaminated areas(5) 1/10 1/3 TWWNF(1) Time decontamination workers spend in non-farm land contaminated areas(5) 1/3 1/3 VALWF0(4) Value of farm wealth ($/hectare) 11,444 VALWNF(4) Value of non-farm wealth ($/person) 231,318 (1)

DPRATE uses NUREG/CR-4551 value (NRC 1990b).

(2)

DSRATE based on NUREG/BR-0058 (NRC 2004a).

(3)

These parameters use the NUREG/CR-4551 values (NRC 1990b), updated to July 2012 using the consumer price index.

(4)

VALWF0 and VALWNF are based on 2007 National Agriculture Census (USDA 2009) and Bureau of Economic Analysis 2007 data (BEA 2012), updated to the July 2012 using the consumer price index.

(5)

Two decontamination levels are modeled, consistent with NUREG/CR-4551 (NRC 1990b). The first value is associated with a dose reduction factor of 3. The second value is associated with a dose reduction factor of 15.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-6 Byron MACCS2 End of Cycle Core Inventory Entry Nuclide Activity Entry Nuclide Activity (Bq) (Bq) 1 Co-58 3.39E+16 31 Te-131m 5.09E+17 2 Co-60 2.59E+16 32 Te-132 5.05E+18 3 Kr-85 3.79E+16 33 I-131 3.55E+18 4 Kr-85m 1.14E+18 34 I-132 5.13E+18 5 Kr-87 2.25E+18 35 I-133 7.34E+18 6 Kr-88 3.18E+18 36 I-134 8.15E+18 7 Rb-86 8.60E+15 37 I-135 6.85E+18 8 Sr-89 3.86E+18 38 Xe-133 7.16E+18 9 Sr-90 2.98E+17 39 Xe-135 2.03E+18 10 Sr-91 5.22E+18 40 Cs-134 7.04E+17 11 Sr-92 5.49E+18 41 Cs-136 2.00E+17 12 Y-90 3.12E+17 42 Cs-137 4.08E+17 13 Y-91 4.72E+18 43 Ba-139 6.76E+18 14 Y-92 5.51E+18 44 Ba-140 6.53E+18 15 Y-93 6.14E+18 45 La-140 6.69E+18 16 Zr-95 6.05E+18 46 La-141 6.17E+18 17 Zr-97 6.19E+18 47 La-142 6.05E+18 18 Nb-95 6.10E+18 48 Ce-141 5.97E+18 19 Mo-99 6.72E+18 49 Ce-143 5.93E+18 20 Tc-99m 5.88E+18 50 Ce-144 4.53E+18 21 Ru-103 5.44E+18 51 Pr-143 5.78E+18 22 Ru-105 3.71E+18 52 Nd-147 2.44E+18 23 Ru-106 1.84E+18 53 Np-239 6.87E+19 24 Rh-105 3.39E+18 54 Pu-238 1.36E+16 25 Sb-127 3.78E+17 55 Pu-239 1.02E+15 26 Sb-129 1.13E+18 56 Pu-240 1.19E+15 27 Te-127 3.73E+17 57 Pu-241 4.71E+17 28 Te-127m 4.87E+16 58 Am-241 5.21E+14 29 Te-129 1.11E+18 59 Cm-242 1.47E+17 30 Te-129m 1.66E+17 60 Cm-244 1.61E+16 Byron and Braidwood Stations, Units 1 and 2 Page F-191 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-7 MACCS2 Release Groups vs. Byron MAAP Release Groups MACCS2 Release Groups Byron MAAP Release Groups Xe/Kr 1 - noble gases I 2 - CsI Cs 6 & 2 - CsOH and CsI(3)

Te 3, 10 & 11- TeO2, Sb(2) & Te2 (1)

Sr 4 - SrO Ru 5 - MoO2 (Mo is in Ru MACCS category)

La 8 - La2O3 Ce 9 & 12 - CeO2 & UO2 (1)

Ba 7 - BaO (1)

These release fractions are typically negligible compared to others in the group.

(2)

The mass of Sb in the core is typically much less than the mass of Te.

(3)

The mass of Cs contained in CsI is typically much less than the mass of Cs contained in CsOH, and is assumed to be negligible for this group.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings Source Release Category MAAP MAAP Case Justification and Description CsI RF(1) Tcd (2) Tvf (3) Tcf (4) Tend (5)

Term Case (Hrs) (Hrs) (Hrs)

(Hrs)

ST1 LERF-ISLOCA 1a Sequence Contributors: LERF11-ISLOCA (100%). The 0.78 6.91 9.65 Bypass 72 Level 1 1ILOC-03 sequence is the dominant contributor and is used to characterize the release category. This sequence is a break in the RHR discharge line outside containment followed by successful injection, but core damage ensues as there is no water in the sump for recirculation mode ILOC-04, the other top contributor, is similar, but the break is in the RHR suction line..

MAAP Case: ISLOCA in the RHR discharge line (800 gpm break), successful scram, successful injection, recirculation unavailable, core damage, containment bypass..

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings Source Release Category MAAP MAAP Case Justification and Description CsI RF(1) Tcd (2) Tvf (3) Tcf (4) Tend (5)

Term Case (Hrs) (Hrs) (Hrs)

(Hrs)

ST2 LERF-CI 2a Sequence Contributors: LERF09 (100%). There are 1.4E-2 5.93 8.67 ISLOCA 72 many different contributions to this release category due to its inclusive nature, but a vast majority include failure of the recirculation mode after successful injection.

Approximately 60% of the total contribution comes from small LOCA scenarios (both small LOCA initiators and RCP seal LOCAs that evolve from other initiating events). The remaining 40% is comprised mostly of loss of SX and Flooding events. Medium LOCAs are small contributors and are almost all recirculation failures. A truly representative sequence for this release category would be a small LOCA with recirculation failure, but to address the faster evolving contributors with injection failures, the seal LOCA with F&B failure is used.

MAAP Case: Loss of SX, successful scram, RCP seal LOCA, injection failure, core damage, containment isolation failure.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings Source Release Category MAAP MAAP Case Justification and Description CsI RF(1) Tcd (2) Tvf (3) Tcf (4) Tend (5)

Term Case (Hrs) (Hrs) (Hrs)

(Hrs)

ST3 LERF-CFE 3a Sequence Contributors: LERF02 (75%), LERF03 0.30 3.16 5.11 5.11 72 (25%). The main difference between sequences LERF02 and LERF03 with respect to equipment availability is that AFW is available for LERF02 while it is not for LERF03. Both sequences include a mixture of injection and recirculation failures. Because LERF03 scenarios may evolve more quickly, they are used as the representative sequence as injection failure cases.

MAAP Case: Loss of SX, successful scram, no AFW, FW not restored, seal cooling successful, operator fail to initiate feed and bleed injection, core damage, successful operator action to depressurize the RCS prior to vessel failure or tube rupture, vessel melt, and containment failure due to hydrogen burn.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings Source Release Category MAAP MAAP Case Justification and Description CsI RF(1) Tcd (2) Tvf (3) Tcf (4) Tend (5)

Term Case (Hrs) (Hrs) (Hrs)

(Hrs)

ST4 LERF-SGTR-AFW 4a Sequence Contributors: LERF10 (100%). Over 80% of 9.7E-2 137.0 155.19 NA 200 the contributors are the result of operator failure to cool down the RCS in time to prevent passing water through the SG PORVs followed by operator failure to cool down the RCS to terminate SGTR break flow before RWST depletion. An additional 3% of the contribution is from failure to cool down the RCS in time to prevent passing water through the SG PORVs followed by operator failure to establish shutdown cooling. The consequences of these scenarios are similar and the larger contributor is chose as representative..

MAAP Case: SGTR, successful scram, SG isolation successful, failure to cool down RCS before passing water through the SG PORV, stuck open SG PORV, RCS injection successful, failure to cool down the RCS before RWST depletion, core damage, release through tubes.

ST5 LERF-SGTR- 5a Sequence Contributors: LERF11(100%). The 4.1E-2 23.82 31.13 NA 200 NOAFW contributing scenarios are dominated by common cause failure of AFW followed by failure to restore MFW.

MAAP Case: SGTR, scram successful, AFW fails, FW not restored, injection successful, RWST depletes, core damage, release through tubes.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings Source Release Category MAAP MAAP Case Justification and Description CsI RF(1) Tcd (2) Tvf (3) Tcf (4) Tend (5)

Term Case (Hrs) (Hrs) (Hrs)

(Hrs)

ST6 LERF-ISGTR 6a Sequence Contributors: LERF08 (99%), LERF07 (1%). 0.19 3.16 7.39 17.23 800 Most of the induced tube rupture scenarios are pressure induced tube ruptures (LERF08), but thermally induced ruptures (LEFF07) are also represented in the cutsets.

The TI-SGTR contribution to LERF is small relative to the PI-SGTR due to likelihood of hot leg failure near the time of TI-SGTR (eliminates release pathway). Both scenarios, however, are dominated by transient initiators with AFW unavailability, most of which lead to recirculation failures. Feed and Bleed failures are smaller contributors, but because of the potential impact on the source terms, the Feed and Bleed failure scenario is chosen as the representative case.

MAAP Case: Loss of SX, successful scram, AFW unavailable, operators fail to align alt FW and fail to align F&B, core damage, pressure induced tube rupture occurs.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings Source Release Category MAAP MAAP Case Justification and Description CsI RF(1) Tcd (2) Tvf (3) Tcf (4) Tend (5)

Term Case (Hrs) (Hrs) (Hrs)

(Hrs)

ST7 LATE-BMT-AFW 7a Sequence Contributors: Late04 (92%), Late01 (1%). 6.8E-5 12.17 15.22 107.40 144 For both the LATE04 and LATE01 sequences, most of the contributors are LOCA events (including seal LOCAs) with recirculation failures. The availability of water on the containment floor impacts the probability of the basemat meltthrough, but has a negligible impact on the source term itself.

For the basemat failure releases, the differences in LOCA size also have a minimal impact on the results.

The largest frequency contributor is chosen as the representative sequence, which are the small LOCAs.

MAAP Case: Small LOCA, successful scram, AFW available, injection successful, recirculation mode failure, core damage, containment heat removal success (RCFCs), CS success, basemat melt through.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings Source Release Category MAAP MAAP Case Justification and Description CsI RF(1) Tcd (2) Tvf (3) Tcf (4) Tend (5)

Term Case (Hrs) (Hrs) (Hrs)

(Hrs)

ST8 LATE-BMT-NOAFW 8a Sequence Contributors: Late07 (88%), Late08 (12%). 7.4E-4 3.14 6.88 90.10 144 The difference in the two dominant Level 2 sequences is related to operation of Containment Spray, which determines if there is a water pool in the reactor cavity when the core relocates to the containment. The scenarios for both sequences are essentially the same, most being transients with AFW failure followed by a mixture of either injection or recirculation mode failures.

For this case, the scenarios with the feed and bleed failures are chosen as representative to capture any potential timing issues for evacuation..

MAAP Case: General transient event, successful scram, AFW CCF to run, failure to restore FW, failure to initiate feed and bleed, core damage, no PI-SGTR, op depressurizes late, no early containment failure at vessel breach, CHR successful, CS successful, basemat failure.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings Source Release Category MAAP MAAP Case Justification and Description CsI RF(1) Tcd (2) Tvf (3) Tcf (4) Tend (5)

Term Case (Hrs) (Hrs) (Hrs)

(Hrs)

ST9 LATE-CHR-AFW 9a Sequence Contributors: Late06 accounts for almost all 1.4E-2 5.93 8.88 60.78 200 of the contributions to this release category frequency.

Over 95% of the contribution to the release category is from LOSW events or events that lead to SX failure, followed by a seal LOCA. The other contributions are almost all scenarios that result in a seal LOCA in a different manner. Recirculation and injection failures are both represented, but most are injection failures.

MAAP Case: LOSW, successful scram, AFW failed, startup FW OK, failure to align alternate seal cooling, failure to align SX X-tie, seal LOCA, injection failure, core damage, no containment failure at VB, CHR fails with long term COP.

ST10 LATE-CHR-NOAFW 10a Sequence Contributors: Late09 accounts for almost all 0.24 3.14 10.12 36.50 1600 of the contributions to this release category frequency.

Over 97% of the release category frequency is from LOSW events or events that lead to SX failure. These are generally followed by the unavailability of FW/Condensate and recirculation mode; injection failures contribute less than 10% of the frequency.

MAAP Case: LOSW (all SX pumps CCF), successful scram, AFW failure from lack of SX cooling, failure to restore FW, SX X-tie not available, CHR not available for recirc, core damage, operator depressurizes late, no containment failure at VB, CHR fails with long term COP.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings Source Release Category MAAP MAAP Case Justification and Description CsI RF(1) Tcd (2) Tvf (3) Tcf (4) Tend (5)

Term Case (Hrs) (Hrs) (Hrs)

(Hrs)

ST11 SERF-SGTR - 11a The SERF01 sequence is comprised of mostly feed and 5.8E-2 3.17 6.69 NA 72 TISGTR-HLF bleed failures with some recirculation failures after failure of AFW. The more rapidly evolving feed and bleed failures are chosen as the representative sequences.

MAAP Case: Loss of 125 DC bus 111, successful scram, failure of AFW, failure of feed and bleed, core damage, late depressurization failure, TI-SGTR occurs, Hot leg fails at about the same time as TI-SGTR, no early containment failure, CHR success, CS success, no basemat failure.

ST12 SERF-SGTR-AFW- 12b Sequence Contributors: The SERF02 sequence is 1.8E-2 124.6 142.79 NA 200 SC mostly comprised (72% based on the Unit 2 results that correctly include 2RX-JHEP33-HOADA) of SGTR events with failure the operators to cool down the RCS before overfilling the SG (opens a steam generator PORV for a LOCA) and subsequent operator error to cool down the RCS to terminate the break flow before depleting the RWST. The cases including 2RX-JHEP33-HOADA (about 8%) are SGTR events with operator failures to shut down dead headed RHR pumps (fails RH) and failure to reduce ECCS injection (to prevent lifting the SG safety valves)..

MAAP Case: SGTR, successful scram, operator fails to cool down the RCS, SG overfill causes SO PORV, operator fails to cool down the RCS to terminate break flow before the RWST is depleted, recirculation mode is unavailable, core damage, operators maintain SG level over the top of the SG tubes for release scrubbing.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-8 Representative MAAP Level 2 Case Descriptions and Key Event Timings Source Release Category MAAP MAAP Case Justification and Description CsI RF(1) Tcd (2) Tvf (3) Tcf (4) Tend (5)

Term Case (Hrs) (Hrs) (Hrs)

(Hrs)

ST13 INTACT 13a Most of the intact contribution comes from small LOCA 3.2E-5 12.17 15.13 NA 72 scenarios (including induced Small LOCAs) with recirculation failures. For intact containment scenarios, the path to core damage has a negligible impact on the source term.

MAAP case: Small LOCA, successful scram, AFW available, injection successful, recirculation failure, core damage, containment intact.

Notes:

(1)

CsI RF - Cesium Iodide release fraction to the environment at the end of the run (2)

Tcd - Time of core damage (maximum core temperature >1800°F)

(3)

Tvf - Time of vessel breach (4)

Tcf - Time of containment failure (5)

Tend - Time at end of run. MAAP cases were run to achieve a plateau of the release fractions, with primary attention paid to CsI and CsOH release fractions.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.3-9 MACCS2 Base Case Mean Results Unit 1 Source Release Dose Offsite Freq. Dose-Risk OECR Term Category (p-rem) Economic (/yr) (p-rem/yr) ($/yr)

Cost ($)

ST1 LERF-ISLOCA 1.30E+07 3.48E+10 3.40E-07 4.42E+00 1.18E+04 ST2 LERF-CI 9.30E+05 4.51E+09 3.67E-07 3.41E-01 1.66E+03 ST3 LERF-CFE 2.50E+06 1.64E+10 3.55E-08 8.88E-02 5.82E+02 ST4 LERF-SGTR-AFW 2.39E+06 1.83E+10 5.49E-08 1.31E-01 1.00E+03 ST5 LERF-SGTR-NOAFW 7.79E+05 6.47E+09 8.57E-10 6.68E-04 5.54E+00 ST6 LERF-ISGTR 2.59E+06 3.05E+10 2.69E-07 6.97E-01 8.20E+03 ST7 LATE-BMT-AFW 3.08E+04 4.20E+07 5.30E-07 1.63E-02 2.23E+01 ST8 LATE-BMT-NOAFW 8.00E+04 1.82E+08 7.95E-08 6.36E-03 1.45E+01 ST9 LATE-CHR-AFW 5.56E+05 1.89E+09 1.89E-05 1.05E+01 3.57E+04 ST10 LATE-CHR-NOAFW 2.13E+06 2.24E+10 8.35E-06 1.78E+01 1.87E+05 ST11 SERF-SGTR-TISGTR-HLF 9.50E+05 6.75E+09 6.49E-09 6.17E-03 4.38E+01 ST12 SERF-SGTR-AFW-SC 9.62E+05 6.05E+09 1.38E-06 1.33E+00 8.35E+03 ST13 INTACT 1.08E+04 1.02E+07 1.16E-05 1.25E-01 1.18E+02 FREQUENCY WEIGHTED TOTALS 4.19E-05 3.55E+01 2.55E+05 Byron and Braidwood Stations, Units 1 and 2 Page F-203 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%SXIE 9.60E-01 1.852 Indicator for SX Initiating Event SX impacts several critical functions and systems and multiple SAMAs are potentially relevant. For failure of all SX pumps (both units) to run (a majority contributor), most contributors include operator failures such that additional actions would provide limited benefit. A diesel driven SX pump with an auto start function could be used to mitigate CCF failures of the SX pumps. To maximize benefit, backup manual controls would have to be included in the MCR (SAMA 1). For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). For the contributors in which the failure of SX is due to the failure to start the standby SX pump, automating the start of the standby SX pump on failure of the running pump is a potential solution (SAMA 3). Instead of replacing the PDP to protect the RCP seals, a passive means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4). Another potential means of mitigating this scenario would be to modify the Startup FW pump to auto start and align on low SG level (using the AMSAC SG level signal) (SAMA 5).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth FLAG-CCHTX0-U2 5.00E-01 1.476 CCW HTX 0 ALIGNED TO UNIT 2 This event is a plant configuration flag that represents conditions when the 0HX is aligned to the non-accident unit. Over 55% of the contributors including this flag are related to the operator actions linked with preventing seal LOCAs, such as starting the standby SX/CCW pump, providing alternate cooling to the charging pumps, performing the SX cross-tie. Loss of SX evolutions leading to seal LOCAs can be addressed by replacing the PDP with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4). Automating the start of the standby SX pump would also reduce some of these contributors and may be viable if combined with flooding sensors that would prevent auto start in flooding scenarios (SAMA 3). Fire protection system flooding in the Aux Building is another contributor, which could be mitigated by installing fire protection pump controls in the MCR (SAMA 8) or by installing flow restrictors in the fire protection lines (SAMA 9).

0SX01AB2AB-CPMFRIE 2.15E-04 1.45 FAILURE OF ALL SX PUMPS (1A/1B/2A/2B) These events represent a loss of all SX due to common cause pump failure. A TO RUN DUE TO CCF (4/4) diesel driven SX pump could be used to mitigate CCF failures of the SX pumps.

To maximize benefit, controls would have to be included in the MCR (SAMA 1).

For cases in which no seal LOCA occurs, secondary side heat removal can prevent core damage. The top contributor including SX pump CCF is the failure to recover FW for heat removal ( about 40%). A potential means of mitigating this scenario would be tomodify the Startup FW pump to auto start and align on low SG level (using the AMSAC SG level signal) (SAMA 5). For cases with seal LOCAS, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth FLAG-CCHTX0-U1 5.00E-01 1.425 CCW HTX 0 ALIGNED TO UNIT 1 This event is a plant configuration flag that represents conditions when the 0HX is aligned to the accident unit. Over 55% of the contributors including this flag are related to the operator actions linked with preventing seal LOCAs, such as starting the standby SX/CCW pump, providing alternate cooling to the charging pumps, performing the SX cross-tie. Loss of SX evolutions leading to seal LOCAs can be addressed by replacing the PDP with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4). Automating the start of the standby SX pump would also reduce some of these contributors and may be viable if combined with flooding sensors that would prevent auto start in flooding scenarios (SAMA 3). Fire protection system flooding in the Aux Building is another contributor, which could be mitigated by installing fire protection pump controls in the MCR (SAMA 8) or by installing flow restrictors in the fire protection lines (SAMA 9).

%CCIE 9.60E-01 1.257 Indicator for CCInitiating Event These initiating events essentially all lead to RCP seal LOCAs and over 99%

are related to the failure to establish a cool suction source for the charging pumps. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Installation of "no leak" RCP seals is another option (SAMA 4).

SEAL-U1-TRANS 2.10E-01 1.256 UNIT 1 SEAL LOCA OCCURRED - NON- Over 99% of the non-LOOP seal LOCA contributors include the failure to LOOP SEQUENCES establish a cool suction source for the charging pump for Loss of CCW initiating events. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Installation of "no leak" RCP seals is another option (SAMA 4).

Byron and Braidwood Stations, Units 1 and 2 Page F-206 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1RX-JHEP44-HOADA 5.00E-03 1.186 JOINT HEP FOR 1CV-ALL----HPMOA AND Over 99% of the contributors including this event are related to loss of 0CC-SXHTX0-HHXOA component cooling water initiators. The JHEP event represents the failure of the operators to align a cool suction source for the charging pumps in conjunction with a subsequent failure to align the 0 CC Hx to the accident unit.

These failures result in the loss of RCP seal cooling. These scenarios can be addressed by replacing the PDP with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4).

1CC01A------HXFFIE 5.34E-03 1.18 CCW HTX 1CC01A - LOSS OF FUNCTION Over 80% of the contribution for this event comes from its combination with 1RX-JHEP32-HOADA, which represents failure to align a cool suction source for the charging pumps and failure to align the "0" heat exchanger to the unit.

For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2).

Byron and Braidwood Stations, Units 1 and 2 Page F-207 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1RX-JHEP05-HOADA 3.30E-04 1.163 JHEP - 1RC-PUMPS--HPMOA/0SX-XTIE--- This JHEP represents the failure of 4 different actions: starting the standby HMVOA/(1FP-PRI-7X-HMVOA OR 1CV-ALL- CCW/CCP/SX pump (it is the SX pump for these contributors), aligning the

---HPMOA) inter-unit SX cross-tie, aligning fire protection water to charging pump lube oil cooling, and establishing a cool suction source for the charging pumps. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Automating the start of the standby SX pump would also reduce these contributors and may be viable if combined with flooding sensors that would prevent auto start in flooding scenarios (SAMA 3). Automating the SX X-tie is not suggested given that certain failures in the SX system could fail the non-accident unit if the X-tie is performed without consideration of the failure scenario. Installation of "no leak" RCP seals is another option (SAMA 4).

0VA1SUPP----PNMM 2.10E-02 1.147 UNIT 1 VA SUPPLY PLENUM For loss of SX scenarios, the Auxiliary Building HVAC system must be available MAINTENANCE to provide backup pump cubicle cooling even if fire protection is aligned as an alternte lube oil cooling supply. Installation of the "no-leak" RCP seals would prevent these scenarios (SAMA 4).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 0SX-XTIE-D-HMVRA 3.60E-01 1.146 RECOV OF LOSS OF SX SEAL LOCA This is a composite event that represents the probability that either the seal (COND PROB OF 0SX-XTIE-D-HMVRA + LOCA is too large for the CVCS to mitigate, or that the SX cross-tie is not 0.21 SEAL FAIL) performed in time to support injection with CVCS (to prevent core damage).

Main contributors include dependent operator action groups that include failures related to aligning alternate charging pump cooling, starting the standby SX pumps, and aligning the SX X-tie to prevent the seal LOCA. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Automating the start of the standby SX pump would also reduce these contributors and may be viable if combined with flooding sensors that would prevent auto start in flooding scenarios (SAMA 3).

An alternate means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4). Automating the SX X-tie is not suggested given that certain failures in the SX system could fail the non-accident unit if the X-tie is performed without consideration of the failure scenario.

1SX01PB-----PMFRIE 3.19E-02 1.129 FAILURE OF PUMP 1B TO RUN Over 85% of the contribution for this event comes from its combination with RANDOMLY JHEP 1RX-JHEP05-HOADA. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Automating the start of the standby SX pump would also reduce these contributors and may be viable if combined with flooding sensors that would prevent auto start in SX flooding scenarios (SAMA 3). Automating the SX X-tie is not suggested given that certain failures in the SX system could fail the non-accident unit if the X-tie is performed without consideration of the failure scenario. Installation of "no leak" RCP seals is another option (SAMA 4).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1FP-PRI-7F-HMVRA 4.50E-01 1.095 RECOV OF LOSS OF SX SEAL LOCA (1FP- These events represent a combination of conditions that preclude recovery of PRI-7D-HMVRA + 0.21 + 0.1 FP BREAK high pressure injection to prevent core damage in fire protection flooding events LOCATION) (alignment fails, break is too large, or break is in a location that precludes use of the FP system). Mitigation of the initiating event could be accomplished by providing shutdown switch for the fire protection pumps in the main control room, which would simplify the action and provide significant time margin for the operators to terminate the flood before critical equipment is lost (SAMA 8). An alternate strategy would be to place flow restrictors in the fire protection pipes to prevent high flow flooding events (SAMA 9). To prevent the seal LOCAs, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Installation of "no leak" RCP seals is another option (SAMA 4).

1FW-FWR---EHSYOA 1.40E-02 1.083 OPERATORS FAIL TO EXECUTE FW Over 95% of the contribution from this event is related to two cutsets, both of RESTORATION which are hardware failures that lead to loss of all SX. In these cases, there are no seal LOCAs, but lack of secondary side heat removal requires primary side makeup and when the RWST is depleted, recirc fails due to lack of SX/CC/RHR cooling. If the operators fail to restore feedwater after a loss of SX initiating event, CD ensues due to dependencies. In this case, they are longer term failures, but modifying the Startup FW pump to auto start and align on low SG level (using the AMSAC SG level signal) is a potential means of mitigating this scenario (SAMA 5). A diesel driven SX pump with an auto start function could be used to mitigate CCF failures of the SX pumps. To maximize benefit, backup manual controls would have to be included in the MCR (SAMA 1).

Byron and Braidwood Stations, Units 1 and 2 Page F-210 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth FLMITIG-M3-T1-FP 6.94E-03 1.069 FAILURE TO MITIGATE >3700 The events represent the failure to mitigate the fire protection flooding GPM FP FLOOD FOR T1 scenarios. Mitigation of the initiating event could be accomplished by providing shutdown switch for the fire protection pumps in the main control room, which SCENARIO would simplify the action and provide significant time margin for the operators to terminate the flood before critical equipment is lost (SAMA 8). An alternate strategy would be to place flow restrictors in the fire protection pipes to prevent high flow flooding events (SAMA 9). To prevent seal LOCAs, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Installation of "no leak" RCP seals is another option (SAMA 4). Floods that flow into the Aux Building impact the SX pump rooms via ductwork from the Aux Building drain sump room.

Altering the ductwork to eliminate communication between the rooms would help extend the time that is available to mitigate Aux Building flooding events (SAMA 10).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%FL1FPM3A0----T1 7.58E-04 1.065 UNIT 1 MAJOR FLOOD (>3,700GPM) The top 2 cutsets, only differentiated by the heat exchanger alignment, FROM FIRE PROTECTION INTO AUX contribute over 97% of the risk for this event. The scenarios include failure to BLDG - COMMON AREA mitigate the flooding event followed by the failure high pressure injection to provide makeup for the seal LOCA (1FP-PRI-7F-HMVRA). Mitigation of the initiating event could be accomplished by providing shutdown switch for the fire protection pumps in the main control room, which would simplify the action and provide significant time margin for the operators to terminate the flood before critical equipment is lost (SAMA 8). An alternate strategy would be to place flow restrictors in the fire protection pipes to prevent high flow flooding events (SAMA 9). To prevent seal LOCAs, which are a dominant consequence of the flood mitigation failure, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Installation of "no leak" RCP seals is another option (SAMA 4).

Floods that flow into the Aux Building impact the SX pump rooms via ductwork from the Aux Building drain sump room. Altering the ductwork to eliminate communication between the rooms would help extend the time that is available to mitigate Aux Building flooding events (SAMA 10).

Byron and Braidwood Stations, Units 1 and 2 Page F-212 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%APIE 9.60E-01 1.063 Indicator for AP Initiating Event About 75% of the contribution for this event comes from its combination with 1RX-JHEP05-HOADA or some combination of the events in this dependent action. This 1RX-JHEP05-HOADA represents the failure of 4 different actions:

starting the standby CCW/CCP/SX pump (it is the SX pump for these contributors), aligning the inter-unit SX cross-tie, aligning fire protection water to charging pump lube oil cooling, and establishing a cool suction source for the charging pumps. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2).

Automating the start of the standby SX pump would also reduce these contributors and may be viable if combined with flooding sensors that would prevent auto start in flooding scenarios (SAMA 3). Automating the SX X-tie is not suggested given that certain failures in the SX system could fail the non-accident unit if the X-tie is performed without consideration of the failure scenario. Installation of "no leak" RCP seals is another option (SAMA 4). For the SBO contributors, implementation of the DMS would proivide a means of maintaining heat removal and inventory control indefinitely (SAMA 11).

1CV-ALL----HPMOA 1.00E-02 1.056 OPERATORS FAIL TO ESTABLISH COOL This action represents failure to transfer charging pump suction to the RWST on SUCTION SOURCE FOR CHARGING loss of cooling to the letdown heat exchanger. It is mostly combined with CCW PUMP and SX pump failures and pump maintenance unavailabilities, which ultimately lead to seal LOCAs. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Installation of "no leak" RCP seals is another option (SAMA 4).

Byron and Braidwood Stations, Units 1 and 2 Page F-213 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1AP142------BSLPIE 2.12E-03 1.049 BUS 142 FAILS Over 97% of the contribution for this event comes from its combination with 1RX-JHEP05-HOADA or some combination of the events in this dependent action. This 1RX-JHEP05-HOADA represents the failure of 4 different actions:

starting the standby CCW/CCP/SX pump (it is the SX pump for these contributors), aligning the inter-unit SX cross-tie, aligning fire protection water to charging pump lube oil cooling, and establishing a cool suction source for the charging pumps. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2).

Automating the start of the standby SX pump would also reduce these contributors and may be viable if combined with flooding sensors that would prevent auto start in flooding scenarios (SAMA 3). Automating the SX X-tie is not suggested given that certain failures in the SX system could fail the non-accident unit if the X-tie is performed without consideration of the failure scenario. Installation of "no leak" RCP seals is another option (SAMA 4). In addition, failure of the AFW cross-tie is a minor contributor, which could be reduced by resolving the regulatory issues related to its use (SAMA 15).

%RC-SLOC1-N-PSIE 1.41E-03 1.037 SMALL LOCA INITIATING EVENT (NON- Over 73% of the contribution from the SLOCA initiating event is related to the ISOLABLE) failure to stop the RH pumps when they are on min-flow without CC cooling to the RH heat exchangers. A potential enhancement may be to establish CC to the RH heat exchanger when the RH pumps start (SAMA 7).

Byron and Braidwood Stations, Units 1 and 2 Page F-214 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1AP-BOTHSAT-TRMM 6.25E-03 1.036 BOTH U1 SAT OOS FOR TM - 141 PWR 1AP-BOTHSAT-TRMM represents the failure of the UAT to provide power to VIA 241; 142 PWR VIA 242; 156 - 159 ON the 143 bus when both U1 SATs are in maintenance. About 95% of the UAT contribution for this event comes from its combination with loss of service water events, which ultimately results in all SG makeup and RCS injection/heat removal capability. These contributors could be addressed by precluding simultaneous maintenance on both unit SATs or by providing contingency procedures to direct the power alignments required to operate the Startup Feedwater pump (SAMA 12). Alternatively, replacing the PDP with a self cooled high pressure injection pump with auto start capability would provide a means of maintaining RCP seal injection. For heat removal, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13).

1RX-JHEP28-HOADA 3.30E-04 1.029 JOINT HEP FOR 1RC-DS-SGTRHDVOA This event represents the dependent failure combination of performing RCS AND 1RC-LCD----HSYOA cooldown in time to prevent SG overfill (stuck open PORV) followed by failure to cool the RCS down in time to terminate break flow before the RWST is depleted. These events lead directly to core damage. Because of the operator dependence issues in the scenarios including this event, SAMAs requiring manual action would provide limited benefit. A potential means of mitigating these scenarios would be to provide an automated RWST makeup system to ensure injection can be maintained to the RCS for an indefinite period. A source of boration is assumed to be required to prevent recriticality, which could occur in some conditions if unborated water is used for RCS makeup (SAMA 14).

1RH-SP-X---HPMOA 7.30E-04 1.028 OPERATORS FAIL TO STOP RH PUMPS Over 94% of the contribution for this event comes from its combination with the small LOCA initiating event. This contribution is related to the failure to stop the RH pumps when they are on min-flow without CC cooling to the RH heat exchangers. A potential enhancement may be to establish CC to the RH heat exchanger when the RH pumps start (SAMA 7).

Byron and Braidwood Stations, Units 1 and 2 Page F-215 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1FP-PRI-7D-HMVRA 3.50E-01 1.026 RECOV OF LOSS OF SX SEAL LOCA This is a composite event that represents the probability that either the seal (COND PROB OF 1FP-PRI-7D-HMVRA + LOCA is too large for the CVCS to mitigate, or that the operators fail to align 0.21 SEAL FAIL) alternate cooling to the charging pumps in time to protect the RCP seals. Over 55% of the contribution is related to a fire protection system flood in the Aux Building common area. This event could be mitigated by installing fire protection pump controls in the MCR (SAMA 8) or by installing flow restrictors in the fire protection lines (SAMA 9). Another 30% of the contribution is associated with common cause failure of the SX pumps to run with a consequential seal LOCA. A diesel driven SX pump could be used to mitigate CCF failures of the SX pumps. To maximize benefit, controls would have to be included in the MCR (SAMA 1). For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Installation of "no leak" RCP seals is another means of preventing seal LOCAs (SAMA 4).

1AF-XTIE--EHXVOA 1.00E+00 1.023 OPERATORS FAIL TO EXECUTE AF This event represents failure of the AFW X-tie, which is assumed to always fail CROSSTIE FROM OPPOSITE UNIT due to regulatory issues. The AFW cross-tie is currently physically in place at the site, but credit cannot be taken for the x-tie capability until permission to fully implement it is granted. Competing the implementation of the AFW X-tie would address the contributors related to this event (SAMA 15).

Byron and Braidwood Stations, Units 1 and 2 Page F-216 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1SX01AB-----HXFFIE 5.65E-03 1.021 SX PUMP 1B OIL COOLER FAILS DURING Over 88% of the contribution for this event comes from its combination with the OPERATION dependent failure combination 1RX-JHEP05-HOADA. This JHEP represents the failure of 4 different actions: starting the standby CCW/CCP/SX pump (it is the SX pump for these contributors), aligning the inter-unit SX cross-tie, aligning fire protection water to charging pump lube oil cooling, and establishing a cool suction source for the charging pumps. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Automating the start of the standby SX pump would also reduce these contributors and may be viable if combined with flooding sensors that would prevent auto start in flooding scenarios (SAMA 3). Automating the SX X-tie is not suggested given that certain failures in the SX system could fail the non-accident unit if the X-tie is performed without consideration of the failure scenario. Installation of "no leak" RCP seals is another option (SAMA 4).

Byron and Braidwood Stations, Units 1 and 2 Page F-217 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1CV-ALL-D--HPMRA 3.60E-01 1.019 RECOV OF LOSS OF SX SEAL LOCA This event represents the probability that either the operators fail to swap the (COND PROB OF 1CV-ALL-D-HPMRA + charging pumps to a cool suction source in time to support CCP injection or that 0.21 SEAL FAIL) the resulting seal LOCA is too large for CCP makeup. Over 90% of the risk is related to scenarios in which all SX pumps fail due to common cause. For these cases, flow from another source needs to be established to the SX piping to cool the loads. A diesel driven SX pump could be used to mitigate CCF failures of the SX pumps. To maximize benefit, controls would have to be included in the MCR (SAMA 1). For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Automating the start of the standby SX pump would also reduce these contributors and may be viable if combined with flooding sensors that would prevent auto start in flooding scenarios (SAMA 3). Installation of "no leak" RCP seals is another means of preventing seal LOCAs (SAMA 4).

Byron and Braidwood Stations, Units 1 and 2 Page F-218 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 0AP-DLOOP-GT 2.40E-03 1.019 CONDITIONAL PROBABILITY OF DLOOP Over 75% of the contribution for this event comes from its combination with loss GIVEN GENERAL TRANSIENT of all SX events. A diesel driven SX pump could be used to mitigate CCF failures of the SX pumps. To maximize benefit, controls would have to be included in the MCR. There would be some dependence issues related to using this system, but starting a standby diesel SX pump may be faster and easier than restoring FW for heat removal (SAMA 1). For consequential LOOP paths, RCP seal protection can be pursued, but FW restoration in not available and an alternate form of heat removal is required. Replacinf the PDP with a self cooled high pressure injection pump with auto start capability would provide a means of maintaining RCP seal injection. For heat removal, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). For the SBO contributors, implementation of the DMS would proivide a means of maintaining heat removal and inventory control indefinitely (SAMA 11).

1RX-JHEP13-HOADA 6.50E-04 1.016 JOINT HEP FOR 1RC-PUMPS--HPMOA This event represents the failure of the operators to start the standby SX pump AND 0SX-XTIE---HMVOA after failure of the running pump and the dependent failure to subsequently align the SX cross-tie. A potential means of mitigating these events is automating the start of the standby SX pump on failure of the running pump (SAMA 3). Alternatively, installing "no leak" RCP seals would help ensure RCS inventory is maintained long enough for the operators to restore FW and perform a coodown (SAMA 4).

Byron and Braidwood Stations, Units 1 and 2 Page F-219 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth FLMITIG-M3-T1-WS 3.90E-03 1.016 FAILURE TO MITIGATE >3700 This event represents the failure to mitigate a flood in the non-essential service WS FLOOD FOR T1 SCENARIO water system (>3700 gpm), which includes flood termination before water damage to the SX pumps can occur and for aligning fire protection to the charging pumps for lube oil cooling. The short time frame available for flood termination precludes success of the manual action to shut the WS pumps off even though it is a 1 minute MCR action. Including logic to trip the WS pumps on high flow conditions is a potential means of mitigating the WS flood (SAMA 16). For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Floods that flow into the Aux Building impact the SX pump rooms via ductwork from the Aux Building drain sump room. Altering the ductwork to eliminate communication between the rooms would help extend the time that is available to mitigate Aux Building flooding events (SAMA 10).

1RX-JHEP32-HOADA 4.90E-04 1.016 JOINT HEP FOR 0CC-HTX0---HHXOA AND Over 85% of the contribution for this event comes from its combination with 1CV-ALL----HPMOA 1CC01A------HXFFIE, which is the loss of function of the 1CC01A HX. Failure to align the "0" HX in conjunction with failure to align a cool suction source to the charging pumps results in core damage. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Given that all scenarios including this JHEP are seal LOCA scenarios, installation of "no leak" RCP seals is another option to reduce the frequency of these contributors (SAMA 4).

Byron and Braidwood Stations, Units 1 and 2 Page F-220 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1RX-JHEP22-HOADA 2.40E-03 1.015 JOINT HEP FOR 0SX-XTIE---HMVOA AND This dependent failure combination represents the failure to align the SX cross-(1FP-PRI-7X-HMVOA OR 1CV-ALL---- tie and either the failure to align a cool suction source to the charging pumps or HPMOA) to align fire protection to the charging pump lube oil coolers. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). The top 50% of the contributors include evolutions in which SX is lost due to failure of the running pump and failure or maintenance unavailability of the remaining pump. A diesel driven SX pump could be used to mitigate CCF failures of the SX pumps. To maximize benefit, controls would have to be included in the MCR (SAMA 1).

%FL1WSM3A0----T1 4.23E-04 1.015 UNIT 1 MAJOR FLOOD (>3,700GPM) This event represents a flood in the non-essential service water system (>3700 FROM NORMAL SERVICE WATER INTO gpm). Over 96% of the contribution comes from a single cutset, which includes AUX BLDG - COMMON the event to mitigate the flood (FLMITIG-M3-T1-WS). Including logic to trip the WS pumps on high flow conditions is a potential means of terminating the WS flood before it damages critical equipment (SAMA 16). For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Floods that flow into the Aux Building impact the SX pump rooms via ductwork from the Aux Building drain sump room. Altering the ductwork to eliminate communication between the rooms would help extend the time that is available to mitigate Aux Building flooding events (SAMA 10).

Byron and Braidwood Stations, Units 1 and 2 Page F-221 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1AP-142-1---TRMM 2.76E-02 1.015 SAT 142-1 IS UNAVAILABLE DUE TO The unavailability of system auxiliary transformer (SAT) 142-1 fails the power MAINTENANCE (141 PWR SUPPLIED supply to the Startup Feedwater pump and also to the (2/4 condensate pumps FROM SAT 142-2) (A and C) (fast bus transfer inhibited). Failure of the remaining credited FW pump (FW01PA) or one additional condensate pump fails the Alternate FW function. Over 95% of the contributors including the 1AP-142-1---TRMM event also total loss of SX that leads to unavailability of AFW and another failure that leads to the unavaiability of Alternate FW (no heat removal). To mitigate these events, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). Currently, no credit is taken for manually aligning power to the non-Class 1E buses to restore power to the FW system, which is likely conservative.

1AP-142-2---TRMM 2.76E-02 1.015 SAT 142-2 IS UNAVAILABLE DUE TO The unavailability of SAT 142-2 fails the power supply to the Startup Feedwater MAINTENANCE pump and also to the (2/4 condensate pumps (A and C) (fast bus transfer inhibited). Failure of the remaining credited FW pump (FW01PA) or one additional condensate pump fails the Alternate FW function. Over 95% of the contributors including the 1AP-142-2---TRMM event also total loss of SX that leads to unavailability of AFW and another failure that leads to the unavaiability of Alternate FW (no heat removal). To mitigate these events, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). Currently, no credit is taken for manually aligning power to the non-Class 1E buses to restore power to the FW system, which is likely conservative.

Byron and Braidwood Stations, Units 1 and 2 Page F-222 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%FL1SX-MA0----T2 1.65E-04 1.013 UNIT 1 MAJOR FLOOD (>2000GPM) FROM This event represents a flood in the essential service water system (>2000 SX INTO AUX BLDG - COMMON AREA gpm) in the Auxiliary Building, which results in loss of SX and a seal LOCA.

Over 65% of the contribution is related to the failure to perform the flood mitigation task of terminating the event before the water level is high enough to fail the charging pumps (among other equipment). This task is for flood termination and alignment of alternate charging pump cooling, which is dominated by failure to align alternate charging pump cooling. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Floods that flow into the Aux Building impact the SX pump rooms via ductwork from the Aux Building drain sump room. Altering the ductwork to eliminate communication between the rooms would help extend the time that is available to mitigate Aux Building flooding events (SAMA 10).

Byron and Braidwood Stations, Units 1 and 2 Page F-223 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 0AP-DLOOP-SC 6.70E-01 1.013 FRACTION OF CONDITIONAL LOOPS The largest single contributor (about 40%) including this event is initiated by a THAT ARE SWITCHYARD-CENTERED CCF of all SX pumps. A diesel driven SX pump could be used to mitigate CCF failures of the SX pumps. To maximize benefit, controls would have to be included in the MCR (SAMA 1). There would be some dependence issues related to using this system, but starting a standby diesel SX pump may be faster and easier than restoring FW for heat removal. For consequential LOOP paths, RCP seal protection can be pursued, but FW restoration in not available and an alternate form of heat removal is required. Replacinf the PDP with a self cooled high pressure injection pump with auto start capability would provide a means of maintaining RCP seal injection. For heat removal, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). For the SBO contributors, implementation of the DMS would proivide a means of maintaining heat removal and inventory control indefinitely (SAMA 11).

%DC-LODC111-BSIE 5.39E-04 1.013 LOSS OF DC BUS 111 INITIATING EVENT Over 87% of the contribution for this event comes from its combination with the failure to perform the AFW X-tie. Loss of DC buss 111 in conjunction with maintenance of the AFW B pump is a dominant contributor to the loss of the AFW function. Competing the implementation of the AFW X-tie would address the contributors related to this event (SAMA 15).

%FW-GTR-1---HWIE 7.05E-01 1.012 GENERAL TRANSIENT INITIATING EVENT The largest contributor to the cutsets including this event (about 50%) is the failure to diagnose the need for seconday cooling (after failure of AFW). A potential means of mitigating this scenario would be to modify the Startup FW pump to auto start and align on low SG level (using the AMSAC SG level signal). Another 10% is related to the failure of the AFW cross-tie, which can be addressed by completing the modification (SAMA 15).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%SP-BB-A-SXPRB-1 1.21E-03 1.012 GLOBAL SPRAY SCENARIO UNIT 1 The "B" SX pump is failed by direct spray from a pipe break within the pump BYRON AND BRAIDWOOD IN AUX BLDG - room. Pump damage could potentially be prevented by installing spray shields SX PUMP ROOM B on the SX pump, but even if the pump is protected, the event would lead to a forced shutdown without the "B" SX pump when the break is discovered. A manual trip is preferable to an automatic trip, but the benefit of the spray shield is questionable. Over 84% of the contribution including this initiating event is associated with dependent failure event 1RX-JHEP05-HOADA. The PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Installation of "no leak" RCP seals is another option (SAMA 4). Automating the start of the standby SX pump (SAMA 3) would provide a means of supplying SX to required loads, but depending on where the pipe break is, the SX system may be shut down for evaluation and this capability would provide no benefit.

1AF01PB-----PDFR 9.58E-03 1.012 DIESEL-DRIVEN PUMP 1AF01PB About 60% of the contribution from this event includes failure of the AFW X-tie, RANDOM FAILURE TO RUN which is typically combined with loss of DC buss 111 (which fails the motor driven AFW (MDAFW) pump and FW condensate) or bus 141 (which also fails MDAFW and FW Condensate after div 1 battery depletion). The AFW cross-tie is currently physically in place at the site, but credit cannot be taken for the x-tie capability until regulatory issues are resolved and implementation is finalized.

Competing the implementation of the AFW X-tie would address the contributors related to this event (SAMA 15).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1FW-FRH1---HSGOA 1.10E-03 1.012 OPERATORS FAIL RECOGNIZE THE CUE These events represent the failure to recognize the need to align an alternate TO SECONDARY COOLING heat removal source (AFW X-tie, FW Restoration, or bleed and feed) after failure of AFW. The action itself is relatively reliable, has an alarmed cue, and clear procedure guidance. A larger contributor to the cognitive element is that the procedure step is not graphically distinct, but changing the procedure to include an emphasis on the step is not judged to provide more than an academic benefit. Nearly 50% of the contribution is related to total loss of SX due to pump CCF and strainer plugging. A diesel driven SX pump with suction from the WS forebay with an auto start function could be used to mitigate CCF failures of the SX pumps. To maximize benefit, backup manual controls would have to be included in the MCR and the pump discharge suction strainers would have to be replaced by suctions strainers of an alternate type (SAMA 1).

Accessibility of the strainers may allow manual clearing of debris in the event of a clogging event.

1CC01PA-B--CPMFRIE 2.18E-04 1.011 CCW PUMPS 1CC01PA & 1CC01PB FAIL Over 98% of the contribution for this event comes from a single cutset that TO RUN DUE TO CCF (2/4) includes the failure to establish a cool suction source for the charging pumps on loss of CC. The PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Installation of "no leak" RCP seals is another option (SAMA 4).

1SX004------MVOCIE 3.90E-04 1.011 1SX004 MOV TRANSFERS CLOSED 100% of the contributors including this event are related to loss of component cooling water initiators. The event represents the transfer closed of the Unit specific CC HX inlet valve, which then requires alignment of the 0 CC Hx to the accident unit. These failures result in the loss of RCP seal cooling and a subsequent seal LOCA. These scenarios can be addressed by replacing the PDP with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1SX007------MVOCIE 3.90E-04 1.011 1SX007 MOV TRANSFERS CLOSED 100% of the contributors including this event are related to loss of component cooling water initiators. The event represents the transfer closed of the Unit specific CC HX outlet valve, which then requires alignment of the 0 CC Hx to the accident unit. These failures result in the loss of RCP seal cooling and a subsequent seal LOCA. These scenarios can be addressed by replacing the PDP with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4).

FLMITIG--G-T1-FP 2.23E-04 1.011 The event represents failure to terminate the fire protection flood in the aux building. The scenarios including this event could be mitigated by installing fire protection pump controls in the MCR (SAMA 8) or by installing flow restrictors in the fire protection lines (SAMA 9). For fire protection breaks, there is a chance that the break is in an area that would preclude use of the fire protection system as an alternate cooling source for charging pump lube oil cooling, but for those cases in which the break does not prevent use of the system, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" seals (SAMA 4). Floods that flow into the Aux Building impact the SX pump rooms via ductwork from the Aux Building drain sump room. Altering the ductwork to eliminate communication between the rooms would help extend the time that is available to mitigate Aux Building flooding events (SAMA 10).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%FL1FP-GA0----T1 3.99E-03 1.01 UNIT 1 GENERAL FLOOD (100-2000GPM) The event represents failure to terminate the fire protection flood in the aux FROM FIRE PROTECTION INTO AUX building. The scenarios including this event could be mitigated by installing fire BLDG - COMMON A protection pump controls in the MCR (SAMA 8) or by installing flow restrictors in the fire protection lines (SAMA 9). For fire protection breaks, there is a chance that the break is in an area that would preclude use of the fire protection system as an alternate cooling source for charging pump lube oil cooling, but for those cases in which the break does not prevent use of the system, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" seals (SAMA 4). Floods that flow into the Aux Building impact the SX pump rooms via ductwork from the Aux Building drain sump room. Altering the ductwork to eliminate communication between the rooms would help extend the time that is available to mitigate Aux Building flooding events (SAMA 10).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth FLMITIG-M2-T1-FP 2.19E-03 1.01 The event represents failure to terminate the fire protection flood in the aux building. The scenarios including this event could be mitigated by installing fire protection pump controls in the MCR (SAMA 8) or by installing flow restrictors in the fire protection lines (SAMA 9). For fire protection breaks, there is a chance that the break is in an area that would preclude use of the fire protection system as an alternate cooling source for charging pump lube oil cooling, but for those cases in which the break does not prevent use of the system, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" seals (SAMA 4). Floods that flow into the Aux Building impact the SX pump rooms via ductwork from the Aux Building drain sump room. Altering the ductwork to eliminate communication between the rooms would help extend the time that is available to mitigate Aux Building flooding events (SAMA 10).

1CD05PD-----PMMM 2.87E-02 1.01 MAINTENANCE UNAVAILABILTY OF Over 80% of the contributors including this event are the result of two loss of SX CD/CB PUMP CD05PD/CB01PD cutsets, one with its combination with maintenance on the 141-1 SAT and the other with the 142-2 SAT. Each of the maintenance events prevents the fast transfer to the bus powering the "A" and "C" condensate/condensate booster pumps to the remaining SAT on a trip, which results in failure of the alternate FW capability. To mitigate these events, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13).

Currently, no credit is taken for manually aligning power to the non-Class 1E buses to restore power to the FW system, which is likely conservative.

Providing an alternate, diesel driven SX pump is another potential means of mitigating the events (SAMA 1).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%FL1FPM2A0----T1 3.77E-04 1.01 UNIT 1 MAJOR FLOOD M2 (3,700GPM) The event represents failure to terminate the fire protection flood in the aux FROM FIRE PROTECTION INTO AUX building. The scenarios including this event could be mitigated by installing fire BLDG - COMMON ARE protection pump controls in the MCR (SAMA 8) or by installing flow restrictors in the fire protection lines (SAMA 9). For fire protection breaks, there is a chance that the break is in an area that would preclude use of the fire protection system as an alternate cooling source for charging pump lube oil cooling, but for those cases in which the break does not prevent use of the system, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" seals (SAMA 4). Floods that flow into the Aux Building impact the SX pump rooms via ductwork from the Aux Building drain sump room. Altering the ductwork to eliminate communication between the rooms would help extend the time that is available to mitigate Aux Building flooding events (SAMA 10).

1FP-PRI-7X-HMVOA 4.60E-03 1.009 OPERATORS FAIL TO ALIGN FP SEAL Over 94% of the contribution for this event comes from its combination with the COOLING - SX NON-PIPE FAILURE Loss of SX initiating event, either all pumps on both units or al SX strainer on INITIATOR both units. A diesel driven SX pump with an auto start function could be used to mitigate CCF failures of the SX pumps. To maximize benefit, backup manual controls would have to be included in the MCR (SAMA 1). Another potential means of mitigating this scenario would be to modify the Startup FW pump to auto start and align on low SG level (using the AMSAC SG level signal) (SAMA 5). For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" seals (SAMA 4).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1RX-JHEP47-HOADA 3.30E-04 1.009 JOINT HEP FOR 1RC-PUMPS--HPMOA Over 85% of the contribution for this event comes from its combination with AND 0SX005-----HMVOA AND 1FP-PRI-7X- 1CC01A------HXFFIE, which is the loss of function of the 1CC01A HX. Failure HMVOA to align the "0" HX in conjunction with failure to align a cool suction source to the charging pumps results in core damage. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Given that all scenarios including this JHEP are seal LOCA scenarios, installation of "no leak" RCP seals is another option to reduce the frequency of these contributors (SAMA 4).

1RX-JHEP48-HOADA 3.30E-04 1.009 JOINT HEP FOR 1RC-PUMPS--HPMOA Over 85% of the contribution for this event comes from its combination with AND 0SX005-----HMVOA AND 1CV-ALL---- 1CC01A------HXFFIE, which is the loss of function of the 1CC01A HX. Failure HPMOA to align the "0" HX in conjunction with failure to align a cool suction source to the charging pumps results in core damage. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Given that all scenarios including this JHEP are seal LOCA scenarios, installation of "no leak" RCP seals is another option to reduce the frequency of these contributors (SAMA 4).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth FLMITIG--M-T2-SX 2.09E-03 1.009 FAILURE TO MITIGATE >2000 This event represents the failure to mitigate a flood in the essential service GPM SX FLOOD FOR T2 water system (>2000 gpm) in the Auxiliary Building, which results in loss of SX and a seal LOCA. The contribution is represented by a single cutset. Failure to SCENARIO perform the flood mitigation task of terminating the event before the water level is high enough to fail the charging pumps (among other equipment) or failure to align alternate charging pump lube oil cooling results in core damage. This task is for flood termination and alignment of alternate charging pump cooling, which is dominated by failure to align alternate charging pump cooling. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" seals (SAMA 4).

1SI-HPR----HSYOA 6.80E-03 1.009 OPERATORS FAIL TO ESTABLISH HIGH There is not a single dominant event related to the scenarios that include this PRESSURE RECIRC (SLOW EVENT) event, but failure of the AFW system is the condition that drives the need for recirculation mode. 38% of the contribution is directly tied to the failure of the AFW X-tie. Completing the implementation of the AFW X-tie would address the contributors related to this event (SAMA 15). Failure of the AFW system requires transition to an alternate method of heat removal, however, if the startup FW pump is enhanced to autostart on AFW failure, the importance of the action to manually align the startup feedwater would be reduced (SAMA 5).

The current configuration requires a manual restart of MFW as a backup heat removal source. Automating swap to recirculation mode is an additional potential enhancement (SAMA 29).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%RC-SGTR1-B-HXIE 8.44E-04 1.009 STEAM GENERATOR TUBE RUPTURE IN Over 70% of the contribution from this event is tied to the dependent human S/G 1B failure combination of failing to cool the RCS in time to prevent opening a SG PORV (lead to stuck open PORV) and the subsequent failure to cool the RCS to terminate flow from the break before RWST depletion. Installing an automated RWST makeup system that would extend the time available to perform the cooldown would provide additional time for action and, if the actuation is alarmed, it would provide an additional cue to perform the RCS cooldown (SAMA 14).

%RC-SGTR1-C-HXIE 8.44E-04 1.009 STEAM GENERATOR TUBE RUPTURE IN Over 70% of the contribution from this event is tied to the dependent human S/G 1C failure combination of failing to cool the RCS in time to prevent opening a SG PORV (lead to stuck open PORV) and the subsequent failure to cool the RCS to terminate flow from the break before RWST depletion. Installing an automated RWST makeup system that would extend the time available to perform the cooldown would provide additional time for action and, if the actuation is alarmed, it would provide an additional cue to perform the RCS cooldown (SAMA 14).

%RC-SGTR1-A-HXIE 8.44E-04 1.009 STEAM GENERATOR TUBE RUPTURE IN Over 70% of the contribution from this event is tied to the dependent human S/G 1A failure combination of failing to cool the RCS in time to prevent opening a SG PORV (lead to stuck open PORV) and the subsequent failure to cool the RCS to terminate flow from the break before RWST depletion. Installing an automated RWST makeup system that would extend the time available to perform the cooldown would provide additional time for action and, if the actuation is alarmed, it would provide an additional cue to perform the RCS cooldown (SAMA 14).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%RC-SGTR1-D-HXIE 8.44E-04 1.009 STEAM GENERATOR TUBE RUPTURE IN Over 70% of the contribution from this event is tied to the dependent human S/G 1D failure combination of failing to cool the RCS in time to prevent opening a SG PORV (lead to stuck open PORV) and the subsequent failure to cool the RCS to terminate flow from the break before RWST depletion. Installing an automated RWST makeup system that would extend the time available to perform the cooldown would provide additional time for action and, if the actuation is alarmed, it would provide an additional cue to perform the RCS cooldown (SAMA 14).

0SX-MU-LVL-HMVOA 5.30E-03 1.008 OPERATORS FAIL TO RESTORE LEVEL Normally, Circulating Water provides makeup to the SX basins, but on loss of TO SX TOWER BASIN offsite power, the Circ Water pumps are unavailable. The SX makeup pumps and Well Water pumps also provide automated basin makeup, but the Well Water level control system includes a non-emergency power dependence. For LOOP events in which the SX makeup pumps fail (essentially all the relevant contributors), the operators must manually control SX basin level. The action iteslf is relativley reliable with an alarmed cue and clear procedures. No procedure enhancements have been identified that would significatnly improve the reliabitlity of this action. For LOOP scenarios without SX, no heat removal mechanisms are available, but SAMAs that require additional opertor actions would have limited benefit due to human dependence issues. In order to provide heat removal capability for these conditions, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1SX01PA-----PMMM 5.90E-03 1.008 SX PUMP 1A UNAVAILABLE DUE TO About 70% of the contribution for this event comes from its combination with MAINTENANCE 1RX-JHEP22-HOADA or some combination of the events in this dependent failure combination. 1RX-JHEP22-HOADA represents the failure to align the SX cross-tie and either the failure to align a cool suction source to the charging pumps or to align fire protection to the charging pump lube oil coolers. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). A diesel driven SX pump could be used to mitigate CCF failures of the SX pumps. To maximize benefit, controls would have to be included in the MCR (SAMA 1).

1AP141------BSLPIE 2.12E-03 1.008 BUS 141 FAILS About 30% of the cases include unavailability of the "B" train AFW pump and failure of the AFW X-tie. Competing the implementation of the AFW X-tie would address these contributors (SAMA 15). About 65% of the contributors are cases in which seal cooling is lost followed by the on set of a seal LOCA. The DMS would provide a means of addressing these contributors (SAMA 11).

1AF01PB-----PDMM 7.12E-03 1.007 AF DIESEL-DRIVEN PUMP 1AF01PB About 45% of the contribution from this event includes failure of the AFW X-tie UNAVAILABLE DUE TO MAINTENANCE in conjunction with loss of DC buss 111 (which fails the MDAFWpump and FW condensate). The AFW cross-tie is currently physically in place at the site, but credit cannot be taken for the x-tie capability until regulatory issues are resolved and implementation is finalized. Competing the implementation of the AFW X-tie would address the contributors related to this event (SAMA 15).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1SX01A-1B--CPMFRIE 2.93E-04 1.007 FAILURE OF SX PUMPS 1A & 1B TO RUN Over 95% of the contribution for this event comes from its combination with DUE TO COMMON CAUSE 1RX-JHEP22-HOADA or some combination of the events in this dependent failure combination. 1RX-JHEP22-HOADA represents the failure to align the SX cross-tie and either the failure to align a cool suction source to the charging pumps or to align fire protection to the charging pump lube oil coolers. For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). A diesel driven SX pump could be used to mitigate CCF failures of the SX pumps. To maximize benefit, controls would have to be included in the MCR (SAMA 1).

1FW01PA-----PMMM 1.36E-02 1.007 MAINTENANCE UNAVAILABILITY OF Over 96% are initiated by common cause failure of all SX pumps followed by PUMP FW01PA failure of the MFW system to provide heat removal. Because most of those failures include unavailability of the startup feedwater pump, SAMA 2 is not an option. Providing an alternate, diesel driven SX pump is a potential means of reducing the risk of this scenario (SAMA 1). A potentially more cost effective solution would be to modify the AFW pumps to be self cooled in conjunction with the replacement of the PDP with a self cooled, auto start pump that would protect the RCP seals (SAMA 13). Implementation of the DMS is another potential means of addressing these scenarios (SAMA 11).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%FW-LMFW1---HWIE 6.90E-02 1.007 TOTAL LOSS OF MAIN FEEDWATER The failure evolutions initiated by the total loss of MFW initiator are diverse and there is no single dominant contributor to risk. One of the larger contributors is the a joint HEP representing the failure to manually initiate AFW and the subsequent failure to diagnose the need to align alternate heat removal. The independent action to align alternate heat removal is relatively reliable, has an alarmed cue, and clear procedure guidance. However, the dependent action chain begins with AFW start, which has a short available time for response and a relatively high HEP that drives the JHEP. Given the longer time frame available for starting Feed and Bleed, the importance of the action may be conservative. However, the AMSAC low level logic could be used to provide a backup start signal for AFW to mitigate these scenarios (SAMA 17).

Automating swap to recirculation mode is an additional potential enhancement (SAMA 29). Alternatively, installing an automated RWST makeup system that would extend the time available to perform the transition to recirculation. If the actuation is alarmed, it would provide an additional cue to perform the action (SAMA 14).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%RCS-RHR-DISCHIE 9.16E-07 1.007 FREQ OF EXPOSING RHR PUMP This event is a piping overpressurization event that leads to ISLOCA scenarios DISCHARGE HEADERS TO RCS and core damage (and containment bypass). Over 99% of the contribution is PRESSURE due to a single cutset that represents the conditional probability of a leak when the RHR line is subjected to high pressure. Potential enhancements include installing pressure monitoring instrumentation in the RHR lines or replacing the MOV in the suction line with a valve capable of closing against RCS pressure.

Success of the pressure monitoring instruments is predicted on a leak before break failure mode that would allow sufficient time to shut down the reactor and depressuirze the RCS before both check valves fail. For the large flow breaks represented by this event, it is not clear that pressure monitoring would provide adequate warning to mitigate the event and it is not consided to be a comprehensive means of reducing the frequency of these events. The ISLOCA analysis indicates that the isolation MOVs in the cold and hot legs are not designed to close against RCS pressure. A potential means of addressing these ISLOCA scenarios would be to replace MOVs _SI8809A, _SI8809B, and

_SI8840 with valves that could be used to terminate an ISLOCA event (SAMA 19).

LEAK-800-150 2.80E-01 1.006 CONDITIONAL PROB OF LEAK 800 GPM This event represent the probability that an ISLOCA occurs given exposure the GIVEN LEAK IS AT LEAST 150 GPM RHR line to overpressure conditions, 100% of which leads directly to core damage (and containment bypass). The ISLOCA analysis indicates that the isolation MOVs in the cold and hot legs are not designed to close against RCS pressure. A potential means of addressing these ISLOCA scenarios would be to replace MOVs _SI8809A, _SI8809B, and _SI8840 with valves that could be used to terminate an ISLOCA event (SAMA 19).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1AF01PA-B--CPMFR 8.20E-05 1.006 AF PUMPS FAIL TO RUN DUE TO CCF Over 35% of the contribution is related to the failure to recognize the need to (2/2) start an alternate heat removal system after AFW failure. Failure of the AFW system requires transition to an alternate method of heat removal, however, if the Startup FW pump is modified to auto start and align on low SG level (using the AMSAC SG level signal), the risk of this scenario could be reduced (SAMA 5). The current configuration requires a manual restart of MFW as a backup heat removal source. Other contributors include failure to perform the AFW X-tie and alignment of high pressure recirculation mode. The AFW X-tie is currently physically in place at the site, but credit cannot be taken for the x-tie capability until permission to fully implement it is granted. Completing the implementation of the AFW X-tie would address the contributors related to this event (SAMA 15). For the cases that include failure to swap to recirculation, this action is only required because of loss of AFW. Making the AFW X-tie available would also address most of these cases.

FLMITIG-FPCVCOOL 3.90E-03 1.006 FAILURE TO ALIGN FP This event represents the failure to align fire protection to alternate charging COOLING TO CV PUMP LUBE pump lube oil cooling for general flooding in the Auxiliary Building, many of which are SX system flood events. For these cases, the PDP could be OIL COOLER replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" seals (SAMA 4).

1CC01PAB2A-CPMFRIE 1.04E-04 1.005 CCW PUMPS Over 98% of the contribution for this event comes from its combination with the 1CC01PA/1CC01PB/2CC01PA FAIL TO failure to align a cool suction source to the charging pump. The PDP could be RUN DUE TO CCF (3/4) replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2).

Byron and Braidwood Stations, Units 1 and 2 Page F-239 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth 1CC01PAB2B-CPMFRIE 1.04E-04 1.005 CCW PUMPS Over 98% of the contribution for this event comes from its combination with the 1CC01PA/1CC01PB/2CC01PB FAIL TO failure to align a cool suction source to the charging pump. The PDP could be RUN DUE TO CCF (3/4) replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2).

1FWTRAIN-1AHOEXM 1.00E-02 1.005 1FW01PA PUMP TRAIN RESTORATION This event represents a pre-initiator restoration error of FW01PA pump when it FAILURE POST T/M is in standby mode. Most of the contributors are loss os SX scenarios that also include the failure or unavailability of the startup FW pump such that all primary and secondary side heat removal is failed. To mitigate these events, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13).

1RH01PB-----PMMM 8.79E-03 1.005 RH PUMP 1RH01PB UNAVAILABLE DUE One on the larger contributors (about 33%) is related to failure of the AFW X-tie.

TO MAINTENANCE Completing the implementation of the AFW X-tie would address the contributors related to this event (SAMA 15). Failure of the AFW system requires transition to an alternate method of heat removal, however, if the Startup FW pump is modified to auto start and align on low SG level (using the AMSAC SG level signal), the risk from this scenario could be reduced (SAMA 5). The current configuration requires a manual restart of MFW as a backup heat removal source. An additional 18% of the contributors are due to seal LOCAs caused by failure to align a cool suction source to the charging pumps on loss of CCW.

For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" seals (SAMA 4).

Byron and Braidwood Stations, Units 1 and 2 Page F-240 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-1 Byron Level 1 IE Importance List Review Event Name Probability Risk Description Potential SAMAS Reduction Worth

%SY-WRDLOOP-DLIE 2.87E-03 1.005 DUAL UNIT WEATHER-RELATED LOSS OF Many of these LOOP events include failures of the SX makeup system, which OFFSITE POWER (SUSTAINED) leads to loss of SX. In conjunction with the loop event, loss of SX fails all heat removal. To mitigate these events, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13).

Implementing the DMS would provide a means of mitigating these evens for cases when opertor failures do not fail the SX basin makeup function (benefit for about 75% of the cases).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth

%SXIE 9.60E-01 1.496 Indicator for SX Initiating Event Addressed in the Level 1 importance list.

0SX01AB2AB-CPMFRIE 2.15E-04 1.386 FAILURE OF ALL SX PUMPS (1A/1B/2A/2B) Addressed in the Level 1 importance list.

TO RUN DUE TO CCF (4/4) 1L2-SGT-VF-PISGR 2.80E-02 1.334 PRESSURE-INDUCED STEAM About 83% of the contributors are loss of SX initiators or events that lead to GENERATOR TUBE RUPTURE loss of SX followed by unavailability of main FW. A diesel driven SX pump with an auto start function could be used to mitigate CCF failures of the SX pumps. To maximize benefit, backup manual controls would have to be included in the MCR (SAMA 1). For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). For the contributors in which the failure of SX is due to the failure to start the standby SX pump, automating the start of the standby SX pump on failure of the running pump is a potential solution (SAMA 3). Instead of replacing the PDP to protect the RCP seals, a passive means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4). Another potential means of mitigating this scenario would be to modify the Startup FW pump to auto start and align on low SG level (using the AMSAC SG level signal) (SAMA 5). For the induced tube rupture event itself, the condition of the SG tubes does play a role in the determination of the failure probability, but SG replacement is already in progress at the site and no additional changes are suggested.

%RCS-RHR-DISCHIE 9.16E-07 1.319 FREQ OF EXPOSING RHR PUMP Addressed in the Level 1 importance list.

DISCHARGE HEADERS TO RCS PRESSURE LEAK-800-150 2.80E-01 1.316 CONDITIONAL PROB OF LEAK 800 GPM Addressed in the Level 1 importance list.

GIVEN LEAK IS AT LEAST 150 GPM Byron and Braidwood Stations, Units 1 and 2 Page F-242 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1RH-FAILS 1.00E+00 1.268 RH PUMPS FAIL DURING RECIRC MODE These failures are essentially all related to containment isolation failure (WITH CS IN RECIRCULATION MODE) scenarios. There are a number of isolation failure mechanisms, the largest of which is an operator error related to the failure to close the path between the RWST and the containment sump (1CI-RWST---HMVOA at 47%). The operator action evaluation is based on closing the required valves as part of the transition to recirculation mode and does not credit the additional isolation tasks that would close the relevant release pathway that are performed in the SACRG-1 procedure. The SACRG-1 isolation tasks, which are directed by a different procedure, based on different cues, and taken at a different time than the credited isolation actions could be credited to reduce the risk associated with this event. No additional procedural changes are considered to be required. The scenarios leading to the containment isolation failures include the same contributors reviewed in the Level 1 importance list (e.g., %SXIE 48%, %CCIE 22%, %APIE 9%,

%FL1FPM3A0----T1 7%) and the same SAMAs are applicable. No additional SAMAs are suggested.

FLAG-CCHTX0-U2 5.00E-01 1.134 CCW HTX 0 ALIGNED TO UNIT 2 Addressed in the Level 1 importance list.

1FW-FWR---EHSYOA 1.40E-02 1.12 OPERATORS FAIL TO EXECUTE FW Addressed in the Level 1 importance list.

RESTORATION FLAG-CCHTX0-U1 5.00E-01 1.12 CCW HTX 0 ALIGNED TO UNIT 1 Addressed in the Level 1 importance list.

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1CI-RWST---HMVOA 3.00E-03 1.111 OPERATORS FAIL TO CLOSE MOV SI8806 This event represents a containment isolation failure due to an operator OR CV112D/E OR SI8813/8920 OR 8814 error related to the failure to close the path between the RWST and the containment sump. The operator action evaluation is based on closing the required valves as part of the transition to recirculation mode and does not credit the additional isolation tasks that would close the relevant release pathway that are performed in the SACRG-1 procedure. The SACRG-1 isolation tasks, which are directed by a different procedure, based on different cues, and taken at a different time than the credited isolation actions could be credited to reduce the risk associated with this event. No additional procedural changes are considered to be required. The scenarios leading to the containment isolation failures include the same contributors reviewed in the Level 1 importance list (e.g., %SXIE 50%,

%CCIE 23%, %FL1FPM3A0----T1 7%, %APIE 6%) and the same SAMAs are applicable. No additional SAMAs are suggested.

1CI-CLASS-A-PNFF 2.30E-03 1.084 CLASS A PENTRATION FAILURE This event represents a containment isolation failure due to any/all penetration failures and is not associated with any specific penetration failure or weakness. This type of a general event does not provide meaningful insight into a specific enhancement that could be made to the penetration itself. The frequency of the scenarios that lead to core damage, however, can be reduced. All contributors above at least 2%of the portion of the CDF that includes this event are included in the L1 importance review, including %SXIE 49%, %CCIE 22%, %FL1FPM3A0----T1 7%,

%APIE 6%. SAMAs related to these events would be relevant to reducing the risk of the scenarios that include 1CI-CLASS-A-PNFF.

1FP-PRI-7D-HMVRA 3.50E-01 1.079 RECOV OF LOSS OF SX SEAL LOCA Addressed in the Level 1 importance list.

(COND PROB OF 1FP-PRI-7D-HMVRA +

0.21 SEAL FAIL)

%CCIE 9.60E-01 1.076 Indicator for CCInitiating Event Addressed in the Level 1 importance list.

Byron and Braidwood Stations, Units 1 and 2 Page F-244 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth SEAL-U1-TRANS 2.10E-01 1.076 UNIT 1 SEAL LOCA OCCURRED - NON- Addressed in the Level 1 importance list.

LOOP SEQUENCES FLMITIG-M3-T1-WS 3.90E-03 1.075 FAILURE TO MITIGATE >3700 Addressed in the Level 1 importance list.

WS FLOOD FOR T1 SCENARIO

%RCS-RHR-SUCT-IE 4.58E-07 1.065 FREQUENCY OF HAVING RCS This event is a piping overpressurization event that leads to ISLOCA PRESSURE IN THE RHR SUCTION LINE scenarios, core damage, and containment bypass. Over 98% of the contribution is due to a single cutset that represents the conditional probability of a leak that is at least 1700 gpm given a leak of 150 gpm when the RHR line is subjected to high pressure. The leak path is due to failure of two MOVs that are in series between the RHR pump suction and the RCS hot leg. There are currently no other valves in the suction path line that could be used to isolate flow. Potential enhancements include installing pressure monitoring instrumentation in the RHR lines or installing an emergency isolation valve in the suction line. Success of the pressure monitoring instruments is predicted on a leak before break failure mode that would allow sufficient time to shut down the reactor and depressurize the RCS before both isolation valves fail. For the large flow breaks represented by this event, it is not clear that pressure monitoring would provide adequate warning to mitigate the event and it is not considered to be a comprehensive means of reducing the frequency of these events. Therefore, installing an emergency isolation valve is suggested as a means of mitigating this sequence (SAMA 21).

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Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth LEAK-1700-150 1.40E-01 1.064 CONDITIONAL PROB OF LEAK 1700 GPM This event represents the conditional probability of a leak that is at least GIVEN LEAK IS AT LEAST 150 GPM 1700 gpm given a leak of 150 gpm when the RHR line is subjected to high pressure. The leak path is due to failure of two MOVs that are in series between the RHR pump suction and the RCS hot leg. There are currently no other valves in the suction path line that could be used to isolate flow.

Potential enhancements include installing pressure monitoring instrumentation in the RHR lines or installing an emergency isolation valve in the suction line. Success of the pressure monitoring instruments is predicted on a leak before break failure mode that would allow sufficient time to shut down the reactor and depressurize the RCS before both isolation valves fail. For the large flow breaks represented by this event, it is not clear that pressure monitoring would provide adequate warning to mitigate the event and it is not considered to be a comprehensive means of reducing the frequency of these events. Therefore, installing an emergency isolation valve is suggested as a means of mitigating this sequence (SAMA 21).

1RX-JHEP44-HOADA 5.00E-03 1.059 JOINT HEP FOR 1CV-ALL----HPMOA AND Addressed in the Level 1 importance list.

0CC-SXHTX0-HHXOA 1CC01A------HXFFIE 5.34E-03 1.056 CCW HTX 1CC01A - LOSS OF FUNCTION Addressed in the Level 1 importance list.

1RX-JHEP05-HOADA 3.30E-04 1.055 JHEP - 1RC-PUMPS--HPMOA/0SX-XTIE--- Addressed in the Level 1 importance list.

HMVOA/(1FP-PRI-7X-HMVOA OR 1CV-ALL----HPMOA)

Byron and Braidwood Stations, Units 1 and 2 Page F-246 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1AF-SGFLOODHPVOA 4.10E-02 1.054 Operator Maintains Faulted SG Full of Water This action is proceduralized, is based on appropriate and clear cues, is for Fission Product Scrubbing simple to perform, and the procedure includes a step that validates performance of the action. While the action is relatively reliable, it is influenced by the high stress of the scenario, which results in the HEP being dominated by a large execution failure term associated with a simple level adjustment action. No procedural changes have been identified that would significantly improve the assessed reliability of the action. Over 80% of the contributors including this action also include the joint HEP 1RX-JHEP28-HOADA. This event represents the dependent failure combination of performing RCS cooldown in time to prevent SG overfill (stuck open PORV) followed by failure to cool the RCS down in time to terminate break flow before the RWST is depleted. These events lead directly to core damage.

Because of the operator dependence issues in the scenarios including this event, SAMAs requiring manual action would provide limited benefit. A potential means of mitigating these scenarios would be to provide an automated RWST makeup system to ensure injection can be maintained to the RCS for an indefinite period. A source of boration is assumed to be required to prevent recriticality, which could occur in some conditions if unborated water is used for RCS makeup (SAMA 14).

Byron and Braidwood Stations, Units 1 and 2 Page F-247 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth

%FL1WSM3A0HVACT1 3.85E-05 1.052 UNIT 1 MAJOR FLOOD (>3,700GPM) This event is included in single cutset which is a normal service water FROM NORMAL SERVICE WATER INTO flooding scenario in the Aux Building with failure to provide alternate lube oil AUX BLDG - HVAC 45 cooling to the charging pumps. Including logic to trip the WS pumps on high flow conditions is a potential means of terminating the WS flood before it damages critical equipment (SAMA 16). For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Floods that flow into the Aux Building impact the SX pump rooms via ductwork from the Aux Building drain sump room. Altering the ductwork to eliminate communication between the rooms would help extend the time that is available to mitigate Aux Building flooding events (SAMA 10).

1AP-BOTHSAT-TRMM 6.25E-03 1.05 BOTH U1 SAT OOS FOR TM - 141 PWR Addressed in the Level 1 importance list.

VIA 241; 142 PWR VIA 242; 156 - 159 ON UAT 0VA1SUPP----PNMM 2.10E-02 1.046 UNIT 1 VA SUPPLY PLENUM Addressed in the Level 1 importance list.

MAINTENANCE 0SX-XTIE-D-HMVRA 3.60E-01 1.046 RECOV OF LOSS OF SX SEAL LOCA Addressed in the Level 1 importance list.

(COND PROB OF 0SX-XTIE-D-HMVRA +

0.21 SEAL FAIL) 1RX-JHEP28-HOADA 3.30E-04 1.045 JOINT HEP FOR 1RC-DS-SGTRHDVOA Addressed in the Level 1 importance list.

AND 1RC-LCD----HSYOA 1SX01PB-----PMFRIE 3.19E-02 1.042 FAILURE OF PUMP 1B TO RUN Addressed in the Level 1 importance list.

RANDOMLY

%APIE 9.60E-01 1.039 Indicator for AP Initiating Event Addressed in the Level 1 importance list.

Byron and Braidwood Stations, Units 1 and 2 Page F-248 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1CICS001AB-HMVOA 1.10E-03 1.037 OPERATORS FAIL TO CLOSE RWST This event represents a containment isolation failure due to an operator SUCTION MOV UPON SWITCH TO error related to the failure to close the path between the RWST and the RECIRC containment sump. The failure results in an open path between the RWST and the containment sump (from the sump through _SI8811A/B,

_CS009A/B, and _CS001A/B to the RWST). The containment isolation assessment does not credit the additional isolation tasks that would close the relevant release pathway (by closing _SI8811A/B) that are performed in the SACRG-1 procedure. If this action were credited, these contributors would be reduced. No additional procedural changes are considered to be required. The scenarios leading to the containment isolation failures include the same contributors reviewed in the Level 1 importance list (e.g., %SXIE 50%, %CCIE 23%, %FL1FPM3A0----T1 7%, %APIE 5%) and the same SAMAs are applicable. No additional SAMAs are suggested.

1FP-PRI-7F-HMVRA 4.50E-01 1.035 RECOV OF LOSS OF SX SEAL LOCA (1FP- Addressed in the Level 1 importance list.

PRI-7D-HMVRA + 0.21 + 0.1 FP BREAK LOCATION) 1CS001A-----MVOO 1.00E-03 1.033 CS PUMP RWST SUCTION MOV CS001A This event represents a containment isolation failure due to a valve failure.

FAILS TO CLOSE The failure results in an open path between the RWST and the containment sump (from the sump through _SI8811A, _CS009A, and _CS001A to the RWST). The containment isolation assessment does not credit the additional isolation tasks that would close the relevant release pathway (by closing _SI8811A) that are performed in the SACRG-1 procedure. If this action were credited, these contributors would be reduced. No additional procedural changes are considered to be required. The scenarios leading to the containment isolation failures include the same contributors reviewed in the Level 1 importance list (e.g., %SXIE 51%, %CCIE 23%,

%FL1FPM3A0----T1 7%, %APIE 5%) and the same SAMAs are applicable.

No additional SAMAs are suggested.

Byron and Braidwood Stations, Units 1 and 2 Page F-249 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1CS001B-----MVOO 1.00E-03 1.033 CS PUMP RWST SUCTION MOV CS001B This event represents a containment isolation failure due to a valve failure.

FAILS TO CLOSE The failure results in an open path between the RWST and the containment sump (from the sump through _SI8811B, _CS009B, and _CS001B to the RWST). The containment isolation assessment does not credit the additional isolation tasks that would close the relevant release pathway (by closing _SI8811B) that are performed in the SACRG-1 procedure. If this action were credited, these contributors would be reduced. No additional procedural changes are considered to be required. The scenarios leading to the containment isolation failures include the same contributors reviewed in the Level 1 importance list (e.g., %SXIE 51%, %CCIE 23%,

%FL1FPM3A0----T1 7%, %APIE 5%) and the same SAMAs are applicable.

No additional SAMAs are suggested.

1AP142------BSLPIE 2.12E-03 1.032 BUS 142 FAILS Addressed in the Level 1 importance list.

1AF-XTIE--EHXVOA 1.00E+00 1.03 OPERATORS FAIL TO EXECUTE AF Addressed in the Level 1 importance list.

CROSSTIE FROM OPPOSITE UNIT FLMITIG-M3-T1-FP 6.94E-03 1.026 FAILURE TO MITIGATE >3700 Addressed in the Level 1 importance list.

GPM FP FLOOD FOR T1 SCENARIO Byron and Braidwood Stations, Units 1 and 2 Page F-250 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1L2-CNT-VF-CFE4 1.00E-03 1.026 Early Cont Failure due to Direct Containment Over 99% of the contributors including this event are either small LOCAs or Heating, Hydrogen Burn, or Stm Expl RCP seal LOCAs with AFW available. The early containment failure mechanisms include direct containment heating (DCH), hydrogen burn, and ex-vessel steam explosion. DCH is included because in the scenarios where AFW is available (all cases with event 1L2-CNT-VF-CFE4), RCS pressure is assumed to be reduced to the point where ISGTR is avoided, but not below 200 psig where DCH could be avoided. The SARCG-1 procedure would direct depressurization, but this is not credited in the Level 2 model. Even if depressurization were credited and DCH could be avoided, the early containment failure probability for would remain the same for model as all early containment failure modes are assigned the same failure probability for Byron (based on the WCAP guidance). The most effective means of addressing the risk related to this event is to prevent core damage. The contributors are mainly seal LOCAs (95%). For cases in which aligning alternate cooling to the charging pump fails, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Installation of "no leak" RCP seals is another option (SAMA 4).

%FL1FPM3A0----T1 7.58E-04 1.024 UNIT 1 MAJOR FLOOD (>3,700GPM) Addressed in the Level 1 importance list.

FROM FIRE PROTECTION INTO AUX BLDG - COMMON AREA

%FL1WSM3A0----T1 4.23E-04 1.021 UNIT 1 MAJOR FLOOD (>3,700GPM) Addressed in the Level 1 importance list.

FROM NORMAL SERVICE WATER INTO AUX BLDG - COMMON 1AP-142-1---TRMM 2.76E-02 1.02 SAT 142-1 IS UNAVAILABLE DUE TO Addressed in the Level 1 importance list.

MAINTENANCE (141 PWR SUPPLIED FROM SAT 142-2)

Byron and Braidwood Stations, Units 1 and 2 Page F-251 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1AP-142-2---TRMM 2.76E-02 1.02 SAT 142-2 IS UNAVAILABLE DUE TO Addressed in the Level 1 importance list.

MAINTENANCE 0AP-DLOOP-GT 2.40E-03 1.019 CONDITIONAL PROBABILITY OF DLOOP Addressed in the Level 1 importance list.

GIVEN GENERAL TRANSIENT 1CV-ALL----HPMOA 1.00E-02 1.017 OPERATORS FAIL TO ESTABLISH COOL Addressed in the Level 1 importance list.

SUCTION SOURCE FOR CHARGING PUMP 1AF01PB-----PDFR 9.58E-03 1.016 DIESEL-DRIVEN PUMP 1AF01PB Addressed in the Level 1 importance list.

RANDOM FAILURE TO RUN

%DC-LODC111-BSIE 5.39E-04 1.015 LOSS OF DC BUS 111 INITIATING EVENT Addressed in the Level 1 importance list.

1FW-FRH1---HSGOA 1.10E-03 1.015 OPERATORS FAIL RECOGNIZE THE CUE Addressed in the Level 1 importance list.

TO SECONDARY COOLING

%FW-GTR-1---HWIE 7.05E-01 1.015 GENERAL TRANSIENT INITIATING EVENT Addressed in the Level 1 importance list.

%RCP-HX-RUPT--IE 1.22E-03 1.014 FREQUENCY OF RCP HEAT EXCHANGER This event represents in ISLOCA caused by failure of the RCP Thermal RUPTURE Barrier HX (tubes within the RCP rupture) and failure to isolate the component cooling return lines that can transport RCS inventory outside containment. The isolation failures include both a valve failure for the automatic isolation and failure of the manual backup isolation action.

Additional manual actions to mitigate the event are likely to provide limited benefit due to dependence issues. A potential means of mitigating this event would be to install the same isolation logic used on valve _CC685 on valve_CC9438 (SAMA 22).

1CD05PD-----PMMM 2.87E-02 1.013 MAINTENANCE UNAVAILABILTY OF Addressed in the Level 1 importance list.

CD/CB PUMP CD05PD/CB01PD Byron and Braidwood Stations, Units 1 and 2 Page F-252 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth

%RC-SGTR1-A-HXIE 8.44E-04 1.013 STEAM GENERATOR TUBE RUPTURE IN Addressed in the Level 1 importance list.

S/G 1A

%RC-SGTR1-B-HXIE 8.44E-04 1.013 STEAM GENERATOR TUBE RUPTURE IN Addressed in the Level 1 importance list.

S/G 1B

%RC-SGTR1-C-HXIE 8.44E-04 1.013 STEAM GENERATOR TUBE RUPTURE IN Addressed in the Level 1 importance list.

S/G 1C

%RC-SGTR1-D-HXIE 8.44E-04 1.013 STEAM GENERATOR TUBE RUPTURE IN Addressed in the Level 1 importance list.

S/G 1D 1CC685------MVOO 1.05E-03 1.013 MOV 1CC685 - FAILS TO CLOSE This event represents failure to close of the RCP Thermal Barrier Cooling return line isolation valve. The event is tied to the ISLOCA initiating event

%RCP-HX-RUPT--IE. The isolation failures include both a valve failure for the automatic isolation and failure of the manual backup isolation action.

Additional manual actions to mitigate the event are likely to provide limited benefit due to dependence issues. A potential means of mitigating this event would be to install the same isolation logic used on valve _CC685 on valve_CC9438 (SAMA 22).

1CC9519----HXVOA 1.00E-02 1.013 OPERATOR ACTION TO CLOSE MANUAL This action is tied to the ISLOCA initiating event %RCP-HX-RUPT--IE.

VALVE 1CC9519 Currently, this action is a screening value that represents failure to manually isolate the flow in the CC system coming from the thermal barrier HX break and details related to this action are limited. The isolation failures include both a valve failure for the automatic isolation and failure of the manual backup isolation action. Additional manual actions to mitigate the event are likely to provide limited benefit due to dependence issues. A potential means of mitigating this event would be to install the same isolation logic used on valve _CC685 on valve_CC9438 (SAMA 22).

0AP-DLOOP-SC 6.70E-01 1.013 FRACTION OF CONDITIONAL LOOPS Addressed in the Level 1 importance list.

THAT ARE SWITCHYARD-CENTERED Byron and Braidwood Stations, Units 1 and 2 Page F-253 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth

%RC-SLOC1-N-PSIE 1.41E-03 1.011 SMALL LOCA INITIATING EVENT (NON- Addressed in the Level 1 importance list.

ISOLABLE) 1RH-SP-X---HPMOA 7.30E-04 1.011 OPERATORS FAIL TO STOP RH PUMPS Addressed in the Level 1 importance list.

1AF01PB-----PDMM 7.12E-03 1.01 AF DIESEL-DRIVEN PUMP 1AF01PB Addressed in the Level 1 importance list.

UNAVAILABLE DUE TO MAINTENANCE 1SI-HPR----HSYOA 6.80E-03 1.009 OPERATORS FAIL TO ESTABLISH HIGH Addressed in the Level 1 importance list.

PRESSURE RECIRC (SLOW EVENT) 1FW01PA-----PMMM 1.36E-02 1.009 MAINTENANCE UNAVAILABILITY OF Addressed in the Level 1 importance list.

PUMP FW01PA 1AF01PA-B--CPMFR 8.20E-05 1.009 AF PUMPS FAIL TO RUN DUE TO CCF Addressed in the Level 1 importance list.

(2/2) 1L2-CNT-VF-CFE2 1.00E-03 1.008 Early Cont Failure due to Hydrogen Burn The scenarios that include this event are essentially all cases in which the operators successfully depressurize the RCS before TI-SGTR and RPV breach. The low pressure conditions preclude all early containment failure modes but hydrogen explosions. While this failure mode is considered to be highly unlikely for the Byron containment design, the event is included in the Level 2 model as a potentially conservative representation of the evolution.

A potential means of mitigating early containment failure due to hydrogen detonations would be to install a passive hydrogen ignition system (SAMA 23).

%FW-LMFW1---HWIE 6.90E-02 1.008 TOTAL LOSS OF MAIN FEEDWATER Addressed in the Level 1 importance list.

Byron and Braidwood Stations, Units 1 and 2 Page F-254 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1RX-JHEP64-HOADA 8.70E-03 1.008 JOINT HEP FOR 1AF-STARTFWHPMOA This dependent human failure event represents the failure to start AWF on AND 1FW-FRH1---HSGOA failure of the auto start function and subsequent failure to diagnose the need to align alt heat removal such as FW restoration, AFW X-tie, or B&F cooling.

The independent action to align alternate heat removal is relatively reliable, has an alarmed cue, and clear procedure guidance. However, the dependent action chain begins with AFW start, which has a short available time for response and a relatively high HEP that drives the JHEP. Given the longer time frame available for starting Feed and Bleed, the importance of the action may be conservative. However, the AMSAC low level logic could be used to provide a backup start signal for AFW to mitigate these scenarios (SAMA 17).

1SX01AB-----HXFFIE 5.65E-03 1.007 SX PUMP 1B OIL COOLER FAILS DURING Addressed in the Level 1 importance list.

OPERATION 1CV-ALL-D--HPMRA 3.60E-01 1.007 RECOV OF LOSS OF SX SEAL LOCA Addressed in the Level 1 importance list.

(COND PROB OF 1CV-ALL-D-HPMRA +

0.21 SEAL FAIL) 1FWTRAIN-1AHOEXM 1.00E-02 1.007 1FW01PA PUMP TRAIN RESTORATION Addressed in the Level 1 importance list.

FAILURE POST T/M 1RX-JHEP13-HOADA 6.50E-04 1.006 JOINT HEP FOR 1RC-PUMPS--HPMOA Addressed in the Level 1 importance list.

AND 0SX-XTIE---HMVOA 1AF01PA-----PMMM 2.12E-03 1.006 AF MOTOR-DRIVEN PUMP 1AF01PA Over 73% of the contributors include either the independent failure of 1FW-UNAVAILABLE DUE TO MAINTENANCE FRH1---HSGOA or a joint HEP that includes the action. A potential means of mitigating this scenario woudl be to modify the Startup FW pump to auto start and align on low SG level (using the AMSAC SG level signal) (SAMA 5). Another contributor in a dependent action chain (about 38%) is for the action to refill the diesel driven AFW pump fuel oil day tank. Automating the refuel function is a potential means of reducing the contribution of these events (SAMA 18).

Byron and Braidwood Stations, Units 1 and 2 Page F-255 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1AP141------BSLPIE 2.12E-03 1.006 BUS 141 FAILS Addressed in the Level 1 importance list.

1RX-JHEP17-HOADA 3.60E-05 1.006 JOINT HEP FOR 1AF01PB-FO-HXVOA These are long term scenarios in which diesel driven AFW fuel oil refill fails AND 1FW-FRH1---HSGOA followed by failure to recognize the need for alternate heat removal.

Automating the refuel function is a potential means of reducing the contribution of these events (SAMA 18).

%CD-LCND1---HWIE 5.26E-02 1.005 LOSS OF CONDENSER HEAT SINK There is not a single dominant event related to the scenarios that include this event, but failure of the AFW system is the condition that drives the need for recirculation mode. Completing the implementation of the AFW X-tie would potentially address many of the contributors related to this event (SAMA 15); 34% alone are linked to CCF of the AFW pumps to run. Given the loss of the condenser initiating event, use of MFW is not an option for this scenario. Failure to swap to recirc mode is another contributor at about 37% of the total for this event. Installing an automated RWST makeup system that would extend the time available to perform the transition to recirculation and, if the actuation is alarmed, it would provide an additional cue to perform the action (SAMA 14).

1RX-JHEP32-HOADA 4.90E-04 1.005 JOINT HEP FOR 0CC-HTX0---HHXOA AND Addressed in the Level 1 importance list.

1CV-ALL----HPMOA 1AF01PA-----PMFS 1.28E-03 1.005 MOTOR-DRIVEN PUMP 1AF01PA About 60% of the contributors including this event result in PI-SGTR. A RANDOM FAILURE TO START large majority of those cases include the failure to restore FW to operation after AFW failure. If FW was restored, RCS pressure would be reduced to avoid the PI-SGTR event. A potential means of mitigating the PI-SGTR scenarios would be to modify the Startup FW pump to auto start and align on low SG level (using the AMSAC SG level signal) (SAMA 5). For the remaining contributors, which include containment isolation failures, SAMA 5 is also a means of avoiding core damage by restoring secondary side heat removal.

Byron and Braidwood Stations, Units 1 and 2 Page F-256 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1FW016------AVMM 7.61E-03 1.005 MAINTENANCE UNAVAILABILITY This event represents the maintenance unavailability of the motor driven CONTROL VALVE FW016 MFW pump flow control valve. All events are total loss of SX events (both units) so that the unavailability of the FW016 valve fails all heat removal capability when combined with a failure of the startup FW pump. Also, about 75% of the contributors including this event result in PI-SGTR. If FW was restored, RCS pressure would be reduced to avoid the PI-SGTR event.

For these scenarios, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13).

1FW02P------PMMM 1.36E-02 1.005 MFW MD START UP PUMP FW02P Over 99% of the contribution for this event comes from its combination with UNAVAILABLE DUE TO MAINTENANCE the Loss of SX initiating event, either all pumps on both units or al SX strainer on both units. A diesel driven SX pump with an auto start function could be used to mitigate CCF failures of the SX pumps. To maximize benefit, backup manual controls would have to be included in the MCR (SAMA 1). Also, about 79% of the contributors including this event result in PI-SGTR. If SG makeup was restored, RCS pressure would be reduced to avoid the PI-SGTR event. For these scenarios, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13).

Byron and Braidwood Stations, Units 1 and 2 Page F-257 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1AP131X1M2--CBOO 2.50E-03 1.005 FEED BREAKER 131X1M2 FROM MCC These failures, in combination with specific breaker failures, result in the 131X1 FAIL TO CLOSE loss of power to the Safety Injection minimum flow valves. For cases in which recirculation mode initiates successfully but subsequently fails due RHR pump failures, loss of power to the _SI8813, _SI8814, and SI8820 valves can result in a containment isolation failure. However, the current containment isolation analysis does not take credit for the additional isolation tasks that would close the relevant release pathway (by closing

_SI8811A/B) that are performed in the SACRG-1 procedure. If this action were credited, these contributors would be reduced. No additional procedural changes are considered to be required. The contributors that lead to core damage are those that have been treated in the level 1 importance, including the failure to align alternate cooling or a cool suction source for the charging pumps. Over 70% of the contributors are RCS Seal LOCAs, which could be addressed by providing a self cooled, auto start seal injection pump (SAMA 2) or by installing "no leak" RCP seals (SAMA 4).

1RX-JHEP22-HOADA 2.40E-03 1.005 JOINT HEP FOR 0SX-XTIE---HMVOA AND Addressed in the Level 1 importance list.

(1FP-PRI-7X-HMVOA OR 1CV-ALL----

HPMOA)

Byron and Braidwood Stations, Units 1 and 2 Page F-258 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2a Byron LERF FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1CD05PDCBPDHOEXM 1.00E-02 1.005 1CD05PD/1CB01PD PUMP TRAIN About 90% of the contributors including this event are related to the RESTORATION FAILURE POST T/M unavailability of either the 141-1 SAT or the 142-2 SAT. Each of the (STANDBY ONLY) maintenance events prevents the fast transfer to the bus powering the "A" and "C" condensate/condensate booster pumps to the remaining SAT on a trip, which results in failure of the alternate FW capability. To mitigate these events, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). Currently, no credit is taken for manually aligning power to the non-Class 1E buses to restore power to the FW system, which is likely conservative. Providing an alternate, diesel driven SX pump is another potential means of mitigating the events (SAMA 1).

1RX-JHEP47-HOADA 3.30E-04 1.005 JOINT HEP FOR 1RC-PUMPS--HPMOA Addressed in the Level 1 importance list.

AND 0SX005-----HMVOA AND 1FP-PRI-7X-HMVOA 1RX-JHEP48-HOADA 3.30E-04 1.005 JOINT HEP FOR 1RC-PUMPS--HPMOA Addressed in the Level 1 importance list.

AND 0SX005-----HMVOA AND 1CV-ALL----

HPMOA Byron and Braidwood Stations, Units 1 and 2 Page F-259 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2b Byron Late FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth

%SXIE 9.60E-01 2.994 Indicator for SX Initiating Event Addressed in the Level 1 importance list.

0SX01AB2AB-CPMFRIE 2.15E-04 1.814 FAILURE OF ALL SX PUMPS (1A/1B/2A/2B) Addressed in the Level 1 importance list.

TO RUN DUE TO CCF (4/4)

FLAG-CCHTX0-U2 5.00E-01 1.522 CCW HTX 0 ALIGNED TO UNIT 2 Addressed in the Level 1 importance list.

FLAG-CCHTX0-U1 5.00E-01 1.442 CCW HTX 0 ALIGNED TO UNIT 1 Addressed in the Level 1 importance list.

1RX-JHEP05-HOADA 3.30E-04 1.253 JHEP - 1RC-PUMPS--HPMOA/0SX-XTIE--- Addressed in the Level 1 importance list.

HMVOA/(1FP-PRI-7X-HMVOA OR 1CV-ALL----HPMOA) 0VA1SUPP----PNMM 2.10E-02 1.228 UNIT 1 VA SUPPLY PLENUM Addressed in the Level 1 importance list.

MAINTENANCE 0SX-XTIE-D-HMVRA 3.60E-01 1.226 RECOV OF LOSS OF SX SEAL LOCA Addressed in the Level 1 importance list.

(COND PROB OF 0SX-XTIE-D-HMVRA +

0.21 SEAL FAIL) 1SX01PB-----PMFRIE 3.19E-02 1.198 FAILURE OF PUMP 1B TO RUN Addressed in the Level 1 importance list.

RANDOMLY 1FP-PRI-7F-HMVRA 4.50E-01 1.143 RECOV OF LOSS OF SX SEAL LOCA (1FP- Addressed in the Level 1 importance list.

PRI-7D-HMVRA + 0.21 + 0.1 FP BREAK LOCATION) 1FW-FWR---EHSYOA 1.40E-02 1.124 OPERATORS FAIL TO EXECUTE FW Addressed in the Level 1 importance list.

RESTORATION FLMITIG-M3-T1-FP 6.94E-03 1.102 FAILURE TO MITIGATE >3700 Addressed in the Level 1 importance list.

GPM FP FLOOD FOR T1 SCENARIO Byron and Braidwood Stations, Units 1 and 2 Page F-260 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2b Byron Late FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth

%FL1FPM3A0----T1 7.58E-04 1.097 UNIT 1 MAJOR FLOOD (>3,700GPM) Addressed in the Level 1 importance list.

FROM FIRE PROTECTION INTO AUX BLDG - COMMON AREA

%APIE 9.60E-01 1.087 Indicator for AP Initiating Event Addressed in the Level 1 importance list.

1AP142------BSLPIE 2.12E-03 1.073 BUS 142 FAILS Addressed in the Level 1 importance list.

1AP-BOTHSAT-TRMM 6.25E-03 1.053 BOTH U1 SAT OOS FOR TM - 141 PWR Addressed in the Level 1 importance list.

VIA 241; 142 PWR VIA 242; 156 - 159 ON UAT 1FP-PRI-7D-HMVRA 3.50E-01 1.037 RECOV OF LOSS OF SX SEAL LOCA Addressed in the Level 1 importance list.

(COND PROB OF 1FP-PRI-7D-HMVRA +

0.21 SEAL FAIL) 1CV-ALL----HPMOA 1.00E-02 1.032 OPERATORS FAIL TO ESTABLISH COOL Addressed in the Level 1 importance list.

SUCTION SOURCE FOR CHARGING PUMP 1SX01AB-----HXFFIE 5.65E-03 1.03 SX PUMP 1B OIL COOLER FAILS DURING Addressed in the Level 1 importance list.

OPERATION 1CV-ALL-D--HPMRA 3.60E-01 1.028 RECOV OF LOSS OF SX SEAL LOCA Addressed in the Level 1 importance list.

(COND PROB OF 1CV-ALL-D-HPMRA +

0.21 SEAL FAIL) 0AP-DLOOP-GT 2.40E-03 1.025 CONDITIONAL PROBABILITY OF DLOOP Addressed in the Level 1 importance list.

GIVEN GENERAL TRANSIENT 1RX-JHEP13-HOADA 6.50E-04 1.024 JOINT HEP FOR 1RC-PUMPS--HPMOA Addressed in the Level 1 importance list.

AND 0SX-XTIE---HMVOA Byron and Braidwood Stations, Units 1 and 2 Page F-261 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2b Byron Late FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1RX-JHEP22-HOADA 2.40E-03 1.022 JOINT HEP FOR 0SX-XTIE---HMVOA AND Addressed in the Level 1 importance list.

(1FP-PRI-7X-HMVOA OR 1CV-ALL----

HPMOA)

FLMITIG-M3-T1-WS 3.90E-03 1.022 FAILURE TO MITIGATE >3700 Addressed in the Level 1 importance list.

WS FLOOD FOR T1 SCENARIO

%FL1WSM3A0----T1 4.23E-04 1.021 UNIT 1 MAJOR FLOOD (>3,700GPM) Addressed in the Level 1 importance list.

FROM NORMAL SERVICE WATER INTO AUX BLDG - COMMON 1AP-142-1---TRMM 2.76E-02 1.021 SAT 142-1 IS UNAVAILABLE DUE TO Addressed in the Level 1 importance list.

MAINTENANCE (141 PWR SUPPLIED FROM SAT 142-2) 1AP-142-2---TRMM 2.76E-02 1.021 SAT 142-2 IS UNAVAILABLE DUE TO Addressed in the Level 1 importance list.

MAINTENANCE 1L2-CNT-VF-BMMTW 5.00E-02 1.021 Probability of BMMT with water in the cavity These scenarios are those in which core damage has occurred, early containment failure has not occurred, the RCFS have provided containment heat removal, and containment spray has functioned to transfer water to the containment floor. Changes such as flooded rubble beds and core catchers are not suggested since they have been analyzed many times and determined not to be cost beneficial. A potential means of reducing these types of releases would be to install a reactor cavity flooding mechanism that could rapidly transfer water to the cavity at a depth that would provide adequate cooling for the lower part of the RPV (SAMA 24).

%FL1SX-MA0----T2 1.65E-04 1.019 UNIT 1 MAJOR FLOOD (>2000GPM) FROM Addressed in the Level 1 importance list.

SX INTO AUX BLDG - COMMON AREA Byron and Braidwood Stations, Units 1 and 2 Page F-262 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2b Byron Late FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth

%SP-BB-A-SXPRB-1 1.21E-03 1.017 GLOBAL SPRAY SCENARIO UNIT 1 Addressed in the Level 1 importance list.

BYRON AND BRAIDWOOD IN AUX BLDG -

SX PUMP ROOM B 0AP-DLOOP-SC 6.70E-01 1.017 FRACTION OF CONDITIONAL LOOPS Addressed in the Level 1 importance list.

THAT ARE SWITCHYARD-CENTERED FLMITIG--G-T1-FP 2.23E-04 1.016 FAILURE TO MITIGATE <2000 Addressed in the Level 1 importance list.

GPM FP FLOOD FOR T1 SCENARIO

%CCIE 9.60E-01 1.015 Indicator for CCInitiating Event Addressed in the Level 1 importance list.

SEAL-U1-TRANS 2.10E-01 1.015 UNIT 1 SEAL LOCA OCCURRED - NON- Addressed in the Level 1 importance list.

LOOP SEQUENCES

%FL1FP-GA0----T1 3.99E-03 1.015 UNIT 1 GENERAL FLOOD (100-2000GPM) Addressed in the Level 1 importance list.

FROM FIRE PROTECTION INTO AUX BLDG - COMMON A FLMITIG-M2-T1-FP 2.19E-03 1.015 FAILURE TO MITIGATE >2700 Addressed in the Level 1 importance list.

GPM FP FLOOD FOR T1 SCENARIO 1CD05PD-----PMMM 2.87E-02 1.014 MAINTENANCE UNAVAILABILTY OF Addressed in the Level 1 importance list.

CD/CB PUMP CD05PD/CB01PD

%FL1FPM2A0----T1 3.77E-04 1.014 UNIT 1 MAJOR FLOOD M2 (3,700GPM) Addressed in the Level 1 importance list.

FROM FIRE PROTECTION INTO AUX BLDG - COMMON ARE 1FP-PRI-7X-HMVOA 4.60E-03 1.013 OPERATORS FAIL TO ALIGN FP SEAL Addressed in the Level 1 importance list.

COOLING - SX NON-PIPE FAILURE INITIATOR Byron and Braidwood Stations, Units 1 and 2 Page F-263 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2b Byron Late FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1RX-JHEP47-HOADA 3.30E-04 1.013 JOINT HEP FOR 1RC-PUMPS--HPMOA Addressed in the Level 1 importance list.

AND 0SX005-----HMVOA AND 1FP-PRI-7X-HMVOA 1RX-JHEP48-HOADA 3.30E-04 1.013 JOINT HEP FOR 1RC-PUMPS--HPMOA Addressed in the Level 1 importance list.

AND 0SX005-----HMVOA AND 1CV-ALL----

HPMOA 1AF-XTIE--EHXVOA 1.00E+00 1.013 OPERATORS FAIL TO EXECUTE AF Addressed in the Level 1 importance list.

CROSSTIE FROM OPPOSITE UNIT FLMITIG--M-T2-SX 2.09E-03 1.013 FAILURE TO MITIGATE >2000 Addressed in the Level 1 importance list.

GPM SX FLOOD FOR T2 SCENARIO 0SX-MU-LVL-HMVOA 5.30E-03 1.012 OPERATORS FAIL TO RESTORE LEVEL Addressed in the Level 1 importance list.

TO SX TOWER BASIN 1SX01PA-----PMMM 5.90E-03 1.012 SX PUMP 1A UNAVAILABLE DUE TO Addressed in the Level 1 importance list.

MAINTENANCE 1RX-JHEP44-HOADA 5.00E-03 1.012 JOINT HEP FOR 1CV-ALL----HPMOA AND Addressed in the Level 1 importance list.

0CC-SXHTX0-HHXOA 1CC01A------HXFFIE 5.34E-03 1.011 CCW HTX 1CC01A - LOSS OF FUNCTION Addressed in the Level 1 importance list.

1SX01A-1B--CPMFRIE 2.93E-04 1.01 FAILURE OF SX PUMPS 1A & 1B TO RUN Addressed in the Level 1 importance list.

DUE TO COMMON CAUSE 1FW01PA-----PMMM 1.36E-02 1.01 MAINTENANCE UNAVAILABILITY OF Addressed in the Level 1 importance list.

PUMP FW01PA 1FW-FRH1---HSGOA 1.10E-03 1.009 OPERATORS FAIL RECOGNIZE THE CUE Addressed in the Level 1 importance list.

TO SECONDARY COOLING Byron and Braidwood Stations, Units 1 and 2 Page F-264 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2b Byron Late FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth FLMITIG-FPCVCOOL 3.90E-03 1.009 FAILURE TO ALIGN FP Addressed in the Level 1 importance list.

COOLING TO CV PUMP LUBE OIL COOLER

%SY-WRDLOOP-DLIE 2.87E-03 1.008 DUAL UNIT WEATHER-RELATED LOSS Addressed in the Level 1 importance list.

OF OFFSITE POWER (SUSTAINED) 1FWTRAIN-1AHOEXM 1.00E-02 1.007 1FW01PA PUMP TRAIN RESTORATION Addressed in the Level 1 importance list.

FAILURE POST T/M 0SX02PB-----PDFS 1.94E-02 1.006 SX MAKEUP PUMP-0B FAILS TO START Normally, Circulating Water provides makeup to the SX basins, but on loss RANDOMLY of offsite power, the Circ Water pumps are unavailable. The SX makeup pumps and Well Water pumps also provide automated basin makeup, but the Well Water level control system includes a non-emergency power dependence. For LOOP events in which the SX makeup pumps fail (over 70% of the contributors), the operators must manually control SX basin level. The action iteslf is relativley reliable with an alarmed cue and clear procedures. No procedure enhancements have been identified that would significatnly improve the reliabitlity of this action. For LOOP scenarios without SX, no heat removal mechanisms are available, but SAMAs that require additional opertor actions would have limited benefit due to human dependence issues. In order to provide heat removal capability for these conditions, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13).

%FW-GTR-1---HWIE 7.05E-01 1.006 GENERAL TRANSIENT INITIATING EVENT Addressed in the Level 1 importance list.

Byron and Braidwood Stations, Units 1 and 2 Page F-265 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2b Byron Late FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1FW02P------PMMM 1.36E-02 1.006 MFW MD START UP PUMP FW02P Over 97% of the contribution for this event comes from its combination with UNAVAILABLE DUE TO MAINTENANCE the Loss of SX initiating event, either all pumps on both units or al SX strainer on both units. A diesel driven SX pump with an auto start function could be used to mitigate CCF failures of the SX pumps. To maximize benefit, backup manual controls would have to be included in the MCR (SAMA 1). Alternatively, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). The DMS could also provide a means of alternate SG makeup and RCS seal protection, if required (SAMA 11).

1FW016------AVMM 7.61E-03 1.005 MAINTENANCE UNAVAILABILITY This event represents the maintenance unavailability of the motor driven CONTROL VALVE FW016 MFW pump flow control valve. Over 99% of the contributors including this event are total loss of SX events (both units) so that the unavailability of the FW016 valve fails all heat removal capability when combined with a failure of the startup FW pump. For these scenarios, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). The DMS could also provide a means of alternate SG makeup and RCS seal protection, if required (SAMA 11).

0AP-DLOOP-PC 2.20E-01 1.005 FRACTION OF CONDITIONAL LOOPS Over 75% of the contributors including this event are loss of SX event with THAT ARE PLANT-CENTERED consequential LOOP, which ultimately fails all heat removal capability. For these cases, RCP seal protection can be pursued, but FW restoration is not available and an alternate form of heat removal is required. Replacing the PDP with a self cooled high pressure injection pump with auto start capability would provide a means of maintaining RCP seal injection. For heat removal, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). For the SBO contributors, implementation of the DMS would proivide a means of maintaining heat removal and inventory control indefinitely (SAMA 11).

Byron and Braidwood Stations, Units 1 and 2 Page F-266 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2b Byron Late FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 0FP03PA-----PMMM 2.62E-02 1.005 FP MOTOR DRIVEN FIRE PUMP 0FP03PA These scenarios including this event are all seal LOCA events caused by

- UNAVAILABLE DUE TO MAINTENANCE loss of normal SX cooling and failure of the fire system to provide alternate seal cooling. A diesel driven SX pump with an auto start function could be used to mitigate CCF failures of the SX pumps. To maximize benefit, backup manual controls would have to be included in the MCR (SAMA 1).

Alternatively, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). Instead of replacing the PDP to protect the RCP seals, a passive means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4).

1AP141------BSLPIE 2.12E-03 1.005 BUS 141 FAILS Addressed in the Level 1 importance list.

0SX02PA-----PDFS 1.94E-02 1.005 SX MAKEUP PUMP-0A FAILS TO START Normally, Circulating Water provides makeup to the SX basins, but on loss RANDOMLY (DIESEL-DRIVEN) of offsite power, the Circ Water pumps are unavailable. The SX makeup pumps and Well Water pumps also provide automated basin makeup, but the Well Water level control system includes a non-emergency power dependence. For LOOP events in which the SX makeup pumps fail (over 78% of the contributors), the operators must manually control SX basin level. The action iteslf is relativley reliable with an alarmed cue and clear procedures. No procedure enhancements have been identified that would significatnly improve the reliabitlity of this action. For LOOP scenarios without SX, no heat removal mechanisms are available, but SAMAs that require additional opertor actions would have limited benefit due to human dependence issues. In order to provide heat removal capability for these conditions, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13).

Byron and Braidwood Stations, Units 1 and 2 Page F-267 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2b Byron Late FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 1RC-UBR2---2WRUB 1.52E-01 1.005 CORE UNCOVERY BEFORE POWER The scenatios including this event are essentially all SBOs with seal LOCA RECOVERY AFTER WEATHER-RELATED events. For these contributors, implementation of the DMS would proivide a LOOP OR DLOOP - UBR2 means of maintaining heat removal and inventory control indefinitely (SAMA 11).

1CD05PDCBPDHOEXM 1.00E-02 1.005 1CD05PD/1CB01PD PUMP TRAIN About 90% of the contributors including this event are related to the RESTORATION FAILURE POST T/M unavailability of either the 141-1 SAT or the 142-2 SAT. Each of the (STANDBY ONLY) maintenance events prevents the fast transfer to the bus powering the "A" and "C" condensate/condensate booster pumps to the remaining SAT on a trip, which results in failure of the alternate FW capability. To mitigate these events, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). Currently, no credit is taken for manually aligning power to the non-Class 1E buses to restore power to the FW system, which is likely conservative. Providing an alternate, diesel driven SX pump is another potential means of mitigating the events (SAMA 1).

0SX01AB2AB-CPMFR 5.89E-07 1.005 FAILURE OF ALL SX PUMPS (1A/1B/2A/2B) These events represent a loss of all SX due to common cause pump failure TO RUN DUE TO CCF (4/4) (but not as an initiating event). A diesel driven SX pump could be used to mitigate CCF failures of the SX pumps. To maximize benefit, controls would have to be included in the MCR (SAMA 1). For cases in which no seal LOCA occurs, secondary side heat removal can prevent core damage.

In order to provide heat removal capability for these conditions, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). For cases with seal LOCAS, the PDP could be replaced with a self-cooled high pressure injection pump with the capability to auto start on loss of charging flow (SAMA 2). An alternate means of preventing a seal LOCA would be to install "no leak" RCP seals (SAMA 4).

Byron and Braidwood Stations, Units 1 and 2 Page F-268 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-2b Byron Late FPIE Importance List Review Event Name Probability Risk Description Potential SAMAs Reduction Worth 0SX02PB-----PDMM 2.67E-02 1.005 SX MAKEUP PUMP-0B UNAVAILABLE DUE Normally, Circulating Water provides makeup to the SX basins, but on loss TO MAINTENANCE (BYRON) of offsite power, the Circ Water pumps are unavailable. The SX makeup pumps and Well Water pumps also provide automated basin makeup, but the Well Water level control system includes a non-emergency power dependence. For LOOP events in which the SX makeup pumps fail (about 65% of the contributors), the operators must manually control SX basin level. The action iteslf is relativley reliable with an alarmed cue and clear procedures. No procedure enhancements have been identified that would significatnly improve the reliabitlity of this action. For LOOP scenarios without SX, no heat removal mechanisms are available, but SAMAs that require additional opertor actions would have limited benefit due to human dependence issues. In order to provide heat removal capability for these conditions, the AFW output flow can be routed to the lube oil coolers to eliminate the SX cooling dependence (SAMA 13). For the loss of DC buss 111 initiating event (17%), the impact is similar and SAMA 13 is also applicable. The DMS could also mitigate these scenarios (SAMA 11).

Byron and Braidwood Stations, Units 1 and 2 Page F-269 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 1 Diesel Driven SX Pump In order to mitigate CCF failure of the SX pumps, a diesel driven Byron Level 1 Due to space and exhaust issues, a diesel As the implementation cost is pump could be installed in a flood safe location with suction from Importance driven system will require an additional greater than the MACR, this the WS forebay that includes a suction strainer of an alternate Review structure to house the pump and diesel SAMA has screened from design that is accessible for manual cleaning (in place of the pump engine combination. Limerick estimated the further analysis.

discharge strainers). Auto start capability would be required to cost of a diesel driven suppression pool increase the benefit of the SAMA, but water level interlocks for cooling system (housed in a dedicated critical rooms (e.g., SX pump rooms, Aux Building sump) may be building) to be $25,600,000 in 1989 (PECO required to prevent auto start in SX flooding evolutions. 1989). The Limerick enhancement is considered to be similar in scope to this SAMA and it is used as the basis for the cost estimate. Using the CPI to scale to cost to 2011 dollars, the result is $46,430,968 (224.9/124.0 *$25,600,000) (USDL 2012).

2 Replace the Positive Loss of SX requires swap of the charging pump suction source to Byron Level 1 Exelon estimates the cost of this SAMA to be As the implementation cost is Displacement Pump the RWST as well as alignment of an alternate lube oil cooling Importance $5,751,110. less than the MACR, this with a Self Cooled, Auto source to maintain RCP seal injection. Replacing the positive Review SAMA has been retained for Start Pump displacement pump with a self cooled pump with the capability to Phase 2 analysis.

auto start on loss of charging and SX flow would provide a means of seal cooling on loss of the normal pumps. Providing an automatic transfer switch to allow power from either division would enhance the SAMA's capability.

Byron and Braidwood Stations, Units 1 and 2 Page F-270 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 3 Auto Start of Standby Automating the start of the standby SX pump would help reduce Byron Level 1 Exelon estimates the cost of this SAMA to be As the implementation cost is SX Pump the reliance of operators to maintain cooling to critical loads. Use Importance $1,130,300. less than the MACR, this of flooding interlocks could be used to prevent auto actuation in Review SAMA has been retained for flooding scenarios. Phase 2 analysis.

4 Install "No Leak" RCP For loss of RCP seal cooling scenarios, a passive means of Byron Level 1 Exelon estimates the cost of this SAMA to be As the implementation cost is Seals reducing the probability of an RCP seal LOCA is to replace the Importance $12,230,000. less than the MACR, this existing pump seals with "no leak" seals (e.g., Westinghouse Review SAMA has been retained for "shield" seals) that are less likely to fail on loss of cooling. Phase 2 analysis.

5 Modify the Startup For accident sequences in which main feedwater has tripped and Byron Level 1 Exelon estimates the cost of this SAMA to be As the implementation cost is Feedwater Pump to AFW has failed to start, it is necessary to manually restart the FW Importance $657,200. less than the MACR, this Start Using the AMSAC system for continued SG makeup. By modifying the startup Review SAMA has been retained for SG Low-Low-Low Level feedwater pump to auto start and align on low steam generator Phase 2 analysis.

signal to Mitigate AFW level, the need for operator intervention after AFW failure is Failure essentially eliminated. Use of the AMSAC low-low-low SG level signal is an additional benefit that mitigate start signal failures.

6 Not Used.

7 Establish Flow to the To prevent overheating the RH pumps when they are operating on Byron Level 1 Procedure changes are estimated to cost As the implementation cost is RH HX on RH Pump min-flow without CC cooling to the heat exchangers, procedure EP- Importance $100,000 per site. less than the MACR, this Start 0 (and potentially others) could be changed to direct the operators Review SAMA has been retained for to align CC to the RH HX when the RH pumps start. This Phase 2 analysis.

precludes the need for the operators to rely on a continuous action statement to protect the RH pumps if secondary side cooling is not established.

8 Install Kill Switches for Currently, it is not possible to terminate all flow from the fire Byron Level 1 Exelon estimates the cost of this SAMA to be As the implementation cost is the Fire Protection protection system in the MCR. In the event of a flood caused by a Importance $338,830. less than the MACR, this Pumps in the MCR fire protection system break, the availability of controls in the MCR Review SAMA has been retained for that would allow the operators to shut down the fire protection Phase 2 analysis.

pumps would increase the likelihood that the flood could be terminated before critical equipment is damaged.

Byron and Braidwood Stations, Units 1 and 2 Page F-271 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 9 Install Flow Restrictors Large breaks in the fire protection systems are significant Byron Level 1 Exelon estimates the cost of this SAMA to be As the implementation cost is in Fire Protection Pipes contributors to plant risk. Installing flow restrictors in the auxiliary Importance $349,300. less than the MACR, this building piping would increase the time available to respond to Review SAMA has been retained for these flooding events. Locating flow restrictors outside the Phase 2 analysis.

auxiliary building upstream of valves 0FP209A, 0FP209B, and FP033 would provide adequate protection for auxiliary building floods.

10 Alter Ductwork Between Currently, the ductwork between the Auxiliary Building Sump Drain Byron Level 1 Exelon estimates the cost of this SAMA to be As the implementation cost is the Aux Bldg Sump Room and the SX Pump Rooms provides a flowpath for flood water Importance $1,320,300. less than the MACR, this Drain Room and the SX when the Auxiliary Building Sump Drain Room fills with water (at a Review SAMA has been retained for Pump Room depth of about 12 feet). Water then flows through the ductwork to Phase 2 analysis.

the SX pump room and damages the SX pumps. Eliminating this pathway will increase the time available to mitigate the flooding event by precluding SX pump damage from the flooding event.

Byron and Braidwood Stations, Units 1 and 2 Page F-272 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 11 Implement DMS The diverse and flexible coping strategies (FLEX) guide identifies Byron Level 1 For this application, the cost is based on a As the implementation cost is different means of addressing required plant functions in extreme Importance reduced scope of the DMS that accounts less than the MACR, this accident conditions, but for the SAMA analysis a specific approach, Review only for the alternate 480V AC power source, SAMA has been retained for called the Diverse Mitigation System (DMS), is proposed. A alternate SG makeup pump, and "no-leak" Phase 2 analysis.

portable 480V AC generator is proposed as a means of supporting RCP seals. Ginna estimated the cost of a long term AFW operation by means of maintaining instrumentation skid mounted 480V AC generator to be and control power for the system by energizing the buses used for $400,000 (RG&E 2002). An additional the battery chargers. A portable, engine driven SG makeup pump $400,000 is assumed for the cost of the would provide an alternate means of SG makeup, with injection portable, engine driven SG makeup pump to connections available on different divisions. Fire protection should address conditions where the AFW pumps provide both CST makeup and a suction source connection for the are unavailable. This is combined with the portable SG makeup pump. Use of high temperature RCP seals cost of SAMA 4 to yield a total of would limit primary system leakage and the positive displacement $13,030,000.

pump could be replaced by one that could be powered by the portable generator for long term RCS makeup. A means of providing borated makeup to the RWST is also required, which could potentially be performed using the fire protection system and an eductor. Finally, a connection point to an outside source would have to be provide for the containment spray system for long term spray capability in an SBO.

Byron and Braidwood Stations, Units 1 and 2 Page F-273 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 12 Modify Practices for For on-line SAT maintenance, a single SAT can provide power to Byron Level 1 Exelon plant personnel estimate that moving As the implementation cost is SAT Maintenance or the loads normally supplied by both SATs on a given unit. Importance the SAT maintenance to an outage would greater than the MACR, this Enhance Procedures However, in order to align this configuration, there is a transition Review require 1 week of additional time each SAMA has screened from period during which both SATs are unable to provide power to any outage at a cost of about $1 million a day. further analysis.

bus. For loss of SX events, this condition is critical because it For a two year cycle over 20 years, the total eliminates the ability to provide power to the Feedwater system for additional time would be 70 days for a total heat removal, which is the only heat removal mechanism available of $70 million.

without SX (due to system dependencies). Precluding on-line SAT maintenance is a potential means of reducing this on-line risk.

Alternatively, procedures from the Braidwood site that are no longer used at Byron could be modified to serve as contingency procedures for these maintenance evolutions. Braidwood has procedures to provide power to the buses required to power the Startup Feedwater pump, but they are not clearly linked to address the SAT maintenance scenario. Providing clear contingency procedures to perform the required power alignment could help reduce the risk of these scenarios.

13 Alternate AFW Cooling For loss of SX events with consequential LOOP, the AFW lube oil Byron Level 1 Ginna estimated the cost of the AFW change As the implementation cost is with Seal Protection coolers are unavailable and the AFW pumps are assumed to fail. Importance to be $200,000 (RG&E 2002). This is used less than the MACR, this The AFW discharge flow could be routed back to the lube oil Review with the cost of SAMA 2 to get a the total of SAMA has been retained for coolers to provide a self-cooling mechanism that would eliminate $5,951,110 for this SAMA. Phase 2 analysis.

the SX dependence. The cooling water return path could potentially be returned to the AFW pump discharge path. For RCP seal protection, replacing the positive displacement pump with a self cooled pump with the capability to auto start on loss of charging flow and/or high seal injection water temp would provide a success path.

Byron and Braidwood Stations, Units 1 and 2 Page F-274 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 14 Automated RWST For SGTR scenarios in which cooldown has failed, installing an Byron Level 1 TMI estimated the cost of a similar SAMA to As the implementation cost is Makeup automated RWST makeup system could provide an means of Importance be $3,800,000 (Exelon 2008a). less than the MACR, this maintaining injection indefinitely. The makeup pump should be Review SAMA has been retained for powered from a diesel backed bus. A boron source is required to Phase 2 analysis.

ensure criticality does not occur. Including an alarm that identifies system actuation would provide an additional cue to address plant issues that have led to RWST depletion.

15 Resolve Regulatory The inter unit AFW cross-tie is in place at the site, but regulatory Byron Level 1 Not Applicable No significant expenditures are Issues and Complete issues must be resolved before it can be considered Importance required to complete this Implementation of the "implemented". Once the process is complete, it will allow one unit Review enhancement, but the Inter Unit AFW Cross- to use the other unit's AFW system to provide SG makeup. The modification was not official at tie cross-tie valve requires local, manual action for operation. the time of the SAMA development and it is not credited in the PRA model of record. Retained for Phase 2 as a sensitivity analysis to demonstrate how crediting the cross-tie will impact the SAMA analysis.

16 Install High Flow Installing flow sensors in the WS lines with logic to trip the pumps Byron Level 1 Exelon estimates the cost of this SAMA to be As the implementation cost is Sensors On the Non- on high flow conditions is a potential means of terminating WS Importance $993,800. less than the MACR, this Essential Service Water flood events before critical systems are damaged. Review SAMA has been retained for System Phase 2 analysis.

17 Use AMASC for For non-ATWS, the AMSAC logic could be used to provide a Byron Level 1 Exelon estimates the cost of this SAMA to be As the implementation cost is Alternate LOW SG backup initiation signal for AFW. This would mitigate failures of the Importance $981,730. less than the MACR, this Level AFW Initiation normal SSPS initiation system. Review SAMA has been retained for Phase 2 analysis.

Byron and Braidwood Stations, Units 1 and 2 Page F-275 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 18 Automate Refill of the The action to refill the diesel driven AFW pump fuel oil day tank is Byron Level 1 Exelon estimates the cost of this SAMA to be As the implementation cost is Diesel Driven AFW currently a manual action. Level sensors in the tank could be used Importance $1,608,680. less than the MACR, this Pump Fuel Oil Day to control a fill valve on the gravity feed line to automate the Review SAMA has been retained for Tank function, which would potentially improve system reliability. Phase 2 analysis.

19 Replace MOVs in the For cases in which the check valves fail in the RHR discharge line Byron Level 1 Wolf Creek Estimated $600,000 for two As the implementation cost is RHR Discharge Line and an ISLOCA occurs, the event could be terminated if the Importance valves (WCNOC 2006), so $900,000 is less than the MACR, this with Valves that Can containment isolation valves were capable of closing after the Review assumed for the three valve change required SAMA has been retained for Isolate an ISLOCA ISLOCA has occurred. Replacing the existing valves (MOVs for Byron. Phase 2 analysis.

Event _SI8809A, _SI8809B, and _SI8840) with an alternate design could provide this capability.

20 Disallow On-Line RHR For cases in which one RHR HX is out of service for maintenance, Byron Level 1 Exelon plant personnel estimate that moving As the implementation cost is HX Maintenance the plant is vulnerable to single failure events for certain initiating Importance the RHR maintenance to an outage would greater than the MACR, this events that require heat removal (for example LOCAs). Preventing Review require 2-3 days of additional time each SAMA has screened from on-line maintenance of the RHR heat exchangers would prevent outage at a cost of about $1 million a day. further analysis.

the associated core damage scenarios. For a two year cycle over 20 years, the total additional time would be 20-30 days for a total of $20 million to $30 million. $20 million is used here.

Byron and Braidwood Stations, Units 1 and 2 Page F-276 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 21 Install an Emergency For cases in which the two motor operated isolation valves in the Byron LERF For installing four new MOVs in the high As the implementation cost is Isolation Valve in each RHR suction line fail and result in the overpressurization of the low Importance pressure injection system (rather than less than the MACR, this of the RHR Suction pressure RHR piping, a LOCA outside containment can occur if the Review replacing valves), TMI estimated a cost of SAMA has been retained for Lines RHR piping breaks. In the event of a piping break, having an $3,150,000 (Exelon 2008a). For the two Phase 2 analysis.

additional, normally open MOV located on the high pressure piping valves required by this SAMA, this cost is capable of closing against RCS pressure would provide a means of divided by two to yield about $1,600,000.

terminating the ISLOCA event.

22 Install the Same High In the event that an RCP Thermal Barrier Cooling heat exchangers Byron LERF A similar valve logic change was estimated As the implementation cost is Flow Isolation Logic breaks, the current in-containment relief valves are designed to Importance to be $250,000 in the Harris SAMA analysis less than the MACR, this Used on Valve _CC685 relieve pressure at 2485 psig, which would be within the capacity of Review (CPL 2006). SAMA has been retained for on Valve _CC9438 the piping up to the isolation boundary. However, if the Thermal Phase 2 analysis.

Barrier Cooling Hx were to break and the isolation valve failed to close, the CC system could be over pressurized and inventory could be transferred outside containment through the 150 psid relief valves. A potential means of mitigating this event would be to install the same isolation logic used on valve _CC685 on valve_CC9438.

23 Install a Passive For accident scenarios resulting in the generation of hydrogen in Byron LERF Calvert Cliffs estimated the cost of this As the implementation cost is Hydrogen Ignition quantities sufficient to cause significant hydrogen detonations, Importance enhancement to be $760,000 (BGE 1998). less than the MACR, this System containment failure is possible. A potential means of preventing Review SAMA has been retained for these containment failure scenarios would be to install a passive Phase 2 analysis.

hydrogen ignition system.

Byron and Braidwood Stations, Units 1 and 2 Page F-277 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 24 Provide a Reactor This SAMA would provide the potential to cool a molten core before Byron Late Calvert Cliffs estimated the cost of this As the implementation cost is Vessel Exterior Cooling it causes vessel failure, if the lower head can be submerged in Release enhancement to be $2,500,000 (BGE 1998), less than the MACR, this System water. For Byron, use of existing emergency power is adequate to Importance but it included its own power source. The SAMA has been retained for address the highest contributors. Review cost is reduced by a factor of 2 to account for Phase 2 analysis.

the use of existing power emergency power at Byron ($1,250,000).

25 Install a Filtered This SAMA would provide a means of preventing long term General Late Information for PWRs is limited, but the As the implementation cost is Containment Vent containment overpressure failures by relieving pressure through a Release Limerick SAMDA analysis provided costs less than the MACR, this scrubbed release path. While post core damage venting is Mitigation that ranged from $5.7 million to $11.3 million SAMA has been retained for undesirable, a controlled scrubbed release is preferable to an Method (PECO 1989). $5.7 million is used for this Phase 2 analysis.

unscrubbed release through a containment break. analysis.

Byron and Braidwood Stations, Units 1 and 2 Page F-278 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 26 DMS Using a Dedicated This SAMA represents an alternate configuration of the DMS in Industry SAMA For this application, the cost estimate is As the implementation cost is Generator, Self Cooled which seal LOCAs are prevented using a seal injection system Review derived from a reduced scope of equipment less than the MACR, this Charging Pump, and a rather than by no leak seals. A dedicated 480V AC generator is for simplicity. DC Cook estimated the cost of SAMA has been retained for Portable AFW Pump proposed as a means of supporting long term SG makeup by an RCP seal injection system with a Phase 2 analysis.

maintaining the buses used for the battery chargers for SG level dedicated deisel to be $2,000,000 (I&M instrumentation and for powering a self-cooled primary side seal 2003). The RCP seal injection DG is also injection pump. A portable, engine driven SG makeup pump would assumed to support SG level provide an alternate means of SG makeup, with injection instrumentation. To account for the cost of a connections available on different divisions. Fire protection should portable SG makeup pump, the cost of a provide both CST makeup and a suction source connection for the portable generator from Ginna (RG&E 2002) portable SG makeup pump A means of providing borated makeup is used as a surrogate ($400,000). The total to the RWST is also required, which could potentially be performed cost of the SAMA is $2,400,000.

using the fire protection system and an eductor. Finally, a connection point to an outside source would have to be provided for the containment spray system for long term spray capability in an SBO.

27 Protect RH, SI, and While most of the equipment damage in the dominant fire scenario Byron Fire Salem estimated the cost of installing cable As the implementation cost is CVCS Cubicle Cooling in zone 11.3-0 is related to the loss of MCC 132X1 (the ignition Results wrap and fire barriers to maintain divisional less than the MACR, this Fan Cables in Fire source), protecting the cables related to the RH, SI, and CVCS separation to be $975,000 (PSEG 2009). SAMA has been retained for Zone 11.3-0. pump cubicle cooling fans may reduce the likelihood that room While each fire barrier installation is unique, Phase 2 analysis.

cooling will be failed for those pumps. this is used as a rough estimate of the Byron cost.

Byron and Braidwood Stations, Units 1 and 2 Page F-279 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 28 Install Fire Barriers Fires that start in this MCC are exacerbated by the propagation of Byron Fire Salem estimated the cost of installing cable As the implementation cost is around MCC 134X the fire to nearby equipment. Installation of fire barriers to protect Results wrap and fire barriers to maintain divisional less than the MACR, this the equipment could mitigate the consequences of the fires. separation to be $975,000 (PSEG 2009). SAMA has been retained for While each fire barrier installation is unique, Phase 2 analysis.

this is used as a rough estimate of the Byron cost.

29 Automate Swap to Fully automating the swap to recirculation mode and removing the Byron Fire V.C. Summer estimated to cost of this As the implementation cost is Recirculation Mode operator from the process can improve the reliability of the action. Results and enhancement to be $1,225,000 (SCE&GC less than the MACR, this Level 1 2002). SAMA has been retained for Importance Phase 2 analysis.

Review 30 Protect AFW Cables in Fires initiating in the AFW 1A pump result in damage to the AFW Byron Fire Salem estimated the cost of installing cable As the implementation cost is the Aux Building 1B and 2A pumps. Protecting the AFW cables in these areas will Results wrap and fire barriers to maintain divisional less than the MACR, this General Area, Elevation improve the potential for pumps 1B and 2A to remain available in separation to be $975,000 (PSEG 2009). SAMA has been retained for 383' these scenarios for SG makeup. While each fire barrier installation is unique, Phase 2 analysis.

this is used as a rough estimate of the Byron cost.

Byron and Braidwood Stations, Units 1 and 2 Page F-280 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.5-3 Byron Phase 1 SAMA List Summary SAMA SAMA Title SAMA Description Source Cost Estimate Phase 1 Baseline Number Disposition 31 Protect Cables for Fires in this are (initiated in MCC 234X, for example) can fail both Byron Fire Salem estimated the cost of installing cable As the implementation cost is 2AF013A, B, and D in trains of AFW. Protecting the cables that are vulnerable (A, B, and Results wrap and fire barriers to maintain divisional less than the MACR, this the Aux Building D in the important scenario), would help preserve the AFW separation to be $975,000 (PSEG 2009). SAMA has been retained for General Area, Elevation function. While each fire barrier installation is unique, Phase 2 analysis.

426' this is used as a rough estimate of the Byron cost.

Byron and Braidwood Stations, Units 1 and 2 Page F-281 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.6-1 Byron Phase 2 SAMA List Summary SAMA SAMA Title SAMA Description Source Phase 2 Baseline Disposition Number 2 Replace the Positive Loss of SX requires swap of the charging pump suction source to the RWST as Byron Level 1 This SAMA's net value is negative and Displacement Pump well as alignment of an alternate lube oil cooling source to maintain RCP seal Importance is classified as not "cost beneficial".

with a Self Cooled, injection. Replacing the positive displacement pump with a self cooled pump Review Auto Start Pump with the capability to auto start on loss of charging and SX flow would provide a means of seal cooling on loss of the normal pumps. Providing an automatic transfer switch to allow power from either division would enhance the SAMA's capability.

3 Auto Start of Standby Automating the start of the standby SX pump would help reduce the reliance of Byron Level 1 This SAMA's net value is positive and is SX Pump operators to maintain cooling to critical loads. Use of flooding interlocks could Importance classified as potentially "cost be used to prevent auto actuation in flooding scenarios. Review beneficial".

4 Install "No Leak" RCP For loss of RCP seal cooling scenarios, a passive means of reducing the Byron Level 1 This SAMA's net value is negative and Seals probability of an RCP seal LOCA is to replace the existing pump seals with "no Importance is classified as not "cost beneficial".

leak" seals (e.g., Westinghouse "shield" seals) that are less likely to fail on loss Review of cooling.

Byron and Braidwood Stations, Units 1 and 2 Page F-282 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.6-1 Byron Phase 2 SAMA List Summary SAMA SAMA Title SAMA Description Source Phase 2 Baseline Disposition Number 5 Modify the Startup For accident sequences in which main feedwater has tripped and AFW has Byron Level 1 This SAMA's net value is positive and is Feedwater Pump to failed to start, it is necessary to manually restart the FW system for continued Importance classified as potentially "cost Start Using the SG makeup. By modifying the startup feedwater pump to auto start and align Review beneficial".

AMSAC SG Low- on low steam generator level, the need for operator intervention after AFW Low-Low Level signal failure is essentially eliminated. Use of the AMSAC low-low-low SG level signal to Mitigate AFW is an additional benefit that mitigate start signal failures.

Failure 6 Not Used.

7 Establish Flow to the To prevent overheating the RH pumps when they are operating on min-flow Byron Level 1 This SAMA's net value is negative and RH HX on RH Pump without CC cooling to the heat exchangers, procedure EP-0 (and potentially Importance is classified as not "cost beneficial".

Start others) could be changed to direct the operators to align CC to the RH HX when Review the RH pumps start. This precludes the need for the operators to rely on a continuous action statement to protect the RH pumps if secondary side cooling is not established.

Byron and Braidwood Stations, Units 1 and 2 Page F-283 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.6-1 Byron Phase 2 SAMA List Summary SAMA SAMA Title SAMA Description Source Phase 2 Baseline Disposition Number 8 Install Kill Switches Currently, it is not possible to terminate all flow from the fire protection system Byron Level 1 This SAMA's net value is negative and for the Fire Protection in the MCR. In the event of a flood caused by a fire protection system break, Importance is classified as not "cost beneficial".

Pumps in the MCR the availability of controls in the MCR that would allow the operators to shut Review down the fire protection pumps would increase the likelihood that the flood could be terminated before critical equipment is damaged.

9 Install Flow Large breaks in the fire protection systems are significant contributors to plant Byron Level 1 This SAMA's net value is positive and is Restrictors in Fire risk. Installing flow restrictors in the auxiliary building piping would increase the Importance classified as potentially "cost Protection Pipes time available to respond to these flooding events. Locating flow restrictors Review beneficial".

outside the auxiliary building upstream of valves 0FP209A, 0FP209B, and FP033 would provide adequate protection for auxiliary building floods.

10 Alter Ductwork Currently, the ductwork between the Auxiliary Building Sump Drain Room and Byron Level 1 This SAMA's net value is positive and is Between the Aux the SX Pump Rooms provides a flowpath for flood water when the Auxiliary Importance classified as potentially "cost Bldg Sump Drain Building Sump Drain Room fills with water (at a depth of about 12 feet). Water Review beneficial".

Room and the SX then flows through the ductwork to the SX pump room and damages the SX Pump Room pumps. Eliminating this pathway will increase the time available to mitigate the flooding event by precluding SX pump damage from the flooding event.

Byron and Braidwood Stations, Units 1 and 2 Page F-284 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.6-1 Byron Phase 2 SAMA List Summary SAMA SAMA Title SAMA Description Source Phase 2 Baseline Disposition Number 11 Implement DMS The diverse and flexible coping strategies (FLEX) guide identifies different Byron Level 1 This SAMA's net value is negative and means of addressing required plant functions in extreme accident conditions, Importance is classified as not "cost beneficial".

but for the SAMA analysis a specific approach, called the Diverse Mitigation Review System (DMS), is proposed. A portable 480V AC generator is proposed as a means of supporting long term AFW operation by means of maintaining instrumentation and control power for the system by energizing the buses used for the battery chargers. A portable, engine driven SG makeup pump would provide an alternate means of SG makeup, with injection connections available on different divisions. Fire protection should provide both CST makeup and a suction source connection for the portable SG makeup pump. Use of high temperature RCP seals would limit primary system leakage and the positive displacement pump could be replaced by one that could be powered by the portable generator for long term RCS makeup. A means of providing borated makeup to the RWST is also required, which could potentially be performed using the fire protection system and an eductor. Finally, a connection point to an outside source would have to be provide for the containment spray system for long term spray capability in an SBO.

13 Alternate AFW For loss of SX events with consequential LOOP, the AFW lube oil coolers are Byron Level 1 This SAMA's net value is positive and is Cooling with Seal unavailable and the AFW pumps are assumed to fail. The AFW discharge flow Importance classified as potentially "cost Protection could be routed back to the lube oil coolers to provide a self-cooling mechanism Review beneficial".

that would eliminate the SX dependence. The cooling water return path could potentially be returned to the AFW pump discharge path. For RCP seal protection, replacing the positive displacement pump with a self cooled pump with the capability to auto start on loss of charging flow and/or high seal injection water temp would provide a success path.

Byron and Braidwood Stations, Units 1 and 2 Page F-285 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.6-1 Byron Phase 2 SAMA List Summary SAMA SAMA Title SAMA Description Source Phase 2 Baseline Disposition Number 14 Automated RWST For SGTR scenarios in which cooldown has failed, installing an automated Byron Level 1 This SAMA's net value is negative and Makeup RWST makeup system could provide an means of maintaining injection Importance is classified as not "cost beneficial".

indefinitely. The makeup pump should be powered from a diesel backed bus. Review A boron source is required to ensure criticality does not occur. Including an alarm that identifies system actuation would provide an additional cue to address plant issues that have led to RWST depletion.

15 Resolve Regulatory The inter unit AFW cross-tie is in place at the site, but regulatory issues must be Byron Level 1 This SAMA's net value is positive and is Issues and Complete resolved before it can be considered "implemented". Once the process is Importance classified as potentially "cost Implementation of the complete, it will allow one unit to use the other unit's AFW system to provide SG Review beneficial".

Inter Unit AFW makeup. The cross-tie valve requires local, manual action for operation.

Cross-tie 16 Install High Flow Installing flow sensors in the WS lines with logic to trip the pumps on high flow Byron Level 1 This SAMA's net value is negative and Sensors On the Non- conditions is a potential means of terminating WS flood events before critical Importance is classified as not "cost beneficial".

Essential Service systems are damaged. Review Water System Byron and Braidwood Stations, Units 1 and 2 Page F-286 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.6-1 Byron Phase 2 SAMA List Summary SAMA SAMA Title SAMA Description Source Phase 2 Baseline Disposition Number 17 Use AMASC for For non-ATWS, the AMSAC logic could be used to provide a backup initiation Byron Level 1 This SAMA's net value is negative and Alternate LOW SG signal for AFW. This would mitigate failures of the normal SSPS initiation Importance is classified as not "cost beneficial".

Level AFW Initiation system. Review 18 Automate Refill of the The action to refill the diesel driven AFW pump fuel oil day tank is currently a Byron Level 1 This SAMA's net value is negative and Diesel Driven AFW manual action. Level sensors in the tank could be used to control a fill valve on Importance is classified as not "cost beneficial".

Pump Fuel Oil Day the gravity feed line to automate the function, which would potentially improve Review Tank system reliability.

19 Replace MOVs in the For cases in which the check valves fail in the RHR discharge line and an Byron Level 1 This SAMA's net value is negative and RHR Discharge Line ISLOCA occurs, the event could be terminated if the containment isolation Importance is classified as not "cost beneficial".

with Valves that Can valves were capable of closing after the ISLOCA has occurred. Replacing the Review Isolate an ISLOCA existing valves (MOVs _SI8809A, _SI8809B, and _SI8840) with an alternate Event design could provide this capability.

Byron and Braidwood Stations, Units 1 and 2 Page F-287 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.6-1 Byron Phase 2 SAMA List Summary SAMA SAMA Title SAMA Description Source Phase 2 Baseline Disposition Number 21 Install an Emergency For cases in which the two motor operated isolation valves in the RHR suction Byron LERF This SAMA's net value is negative and Isolation Valve in line fail and result in the overpressurization of the low pressure RHR piping, a Importance is classified as not "cost beneficial".

each of the RHR LOCA outside containment can occur if the RHR piping breaks. In the event of Review Suction Lines a piping break, having an additional, normally open MOV located on the high pressure piping capable of closing against RCS pressure would provide a means of terminating the ISLOCA event.

22 Install the Same High In the event that an RCP Thermal Barrier Cooling heat exchangers breaks, the Byron LERF This SAMA's net value is negative and Flow Isolation Logic current in-containment relief valves are designed to relieve pressure at 2485 Importance is classified as not "cost beneficial".

Used on Valve psig, which would be within the capacity of the piping up to the isolation Review

_CC685 on Valve boundary. However, if the Thermal Barrier Cooling Hx were to break and the

_CC9438 isolation valve failed to close, the CC system could be over pressurized and inventory could be transferred outside containment through the 150 psid relief valves. A potential means of mitigating this event would be to install the same isolation logic used on valve _CC685 on valve_CC9438.

23 Install a Passive For accident scenarios resulting in the generation of hydrogen in quantities Byron LERF This SAMA's net value is negative and Hydrogen Ignition sufficient to cause significant hydrogen detonations, containment failure is Importance is classified as not "cost beneficial".

System possible. A potential means of preventing these containment failure scenarios Review would be to install a passive hydrogen ignition system.

Byron and Braidwood Stations, Units 1 and 2 Page F-288 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.6-1 Byron Phase 2 SAMA List Summary SAMA SAMA Title SAMA Description Source Phase 2 Baseline Disposition Number 24 Provide a Reactor This SAMA would provide the potential to cool a molten core before it causes Byron Late This SAMA's net value is negative and Vessel Exterior vessel failure, if the lower head can be submerged in water. For Byron, use of Release is classified as not "cost beneficial".

Cooling System existing emergency power is adequate to address the highest contributors. Importance Review 25 Install a Filtered This SAMA would provide a means of preventing long term containment General Late This SAMA's net value is positive and is Containment Vent overpressure failures by relieving pressure through a scrubbed release path. Release classified as potentially "cost While post core damage venting is undesirable, a controlled scrubbed release Mitigation beneficial".

is preferable to an unscrubbed release through a containment break. Method 26 DMS Using a This SAMA represents an alternate configuration of the DMS in which seal Industry SAMA This SAMA's net value is positive and is Dedicated Generator, LOCAs are prevented using a seal injection system rather than by no-leak Review classified as potentially "cost Self Cooled Charging seals. A dedicated 480V AC generator is proposed as a means of supporting beneficial".

Pump, and a Portable long term SG makeup by maintaining the buses used for the battery chargers AFW Pump for SG level instrumentation and for powering a self-cooled primary side seal injection pump. A portable, engine driven SG makeup pump would provide an alternate means of SG makeup, with injection connections available on different divisions. Fire protection should provide both CST makeup and a suction source connection for the portable SG makeup pump. A means of providing borated makeup to the RWST is also required, which could potentially be performed using the fire protection system and an eductor. Finally, a connection point to an outside source would have to be provided for the containment spray system for long term spray capability in an SBO.

Byron and Braidwood Stations, Units 1 and 2 Page F-289 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.6-1 Byron Phase 2 SAMA List Summary SAMA SAMA Title SAMA Description Source Phase 2 Baseline Disposition Number 27 Protect RH, SI, and While most of the equipment damage in the dominant fire scenario in zone Byron Fire This SAMA's net value is positive and is CVCS Cubicle 11.3-0 is related to the loss of MCC 132X1 (the ignition source), protecting the Results classified as potentially "cost Cooling Fan Cables cables related to the RH, SI, and CVCS pump cubicle cooling fans may reduce beneficial".

in Fire Zone 11.3-0. the likelihood that room cooling will be failed for those pumps.

28 Install Fire Barriers Fires that start in this MCC are exacerbated by the propagation of the fire to Byron Fire This SAMA's net value is negative and around MCC 134X nearby equipment. Installation of fire barriers to protect the equipment could Results is classified as not "cost beneficial".

mitigate the consequences of the fires.

29 Automate Swap to Fully automating the swap to recirculation mode and removing the operator Byron Fire This SAMA's net value is negative and Recirculation Mode from the process can improve the reliability of the action. Results and is classified as not "cost beneficial".

Level 1 Importance Review Byron and Braidwood Stations, Units 1 and 2 Page F-290 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.6-1 Byron Phase 2 SAMA List Summary SAMA SAMA Title SAMA Description Source Phase 2 Baseline Disposition Number 30 Protect AFW Cables Fires initiating in the AFW 1A pump result in damage to the AFW 1B and 2A Byron Fire This SAMA's net value is negative and in the Aux Building pumps. Protecting the AFW cables in these areas will improve the potential for Results is classified as not "cost beneficial".

General Area, pumps 1B and 2A to remain available in these scenarios for SG makeup.

Elevation 383' 31 Protect Cables for Fires in this are (initiated in MCC 234X, for example) can fail both trains of Byron Fire This SAMA's net value is positive and is 2AF013A, B, and D in AFW. Protecting the cables that are vulnerable (A, B, and D in the important Results classified as potentially "cost the Aux Building scenario), would help preserve the AFW function. beneficial".

General Area, Elevation 426' Byron and Braidwood Stations, Units 1 and 2 Page F-291 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Table F.7-1 Generic Economic Sensitivity Case Values Variable Description Base Case Value Sensitivity Value DPRATE(1) Property depreciation rate (per yr) 0.20 0.20 (2)

DSRATE Investment rate of return (per yr) 0.07 0.07 (3)

EVACST Daily cost for a person who has been evacuated ($/person-day) 56.43 112.86 (3)

RELCST Daily cost for a person who is relocated ($/person-day) 56.43 112.86 (3)

POPCST Population relocation cost ($/person) 10,450 20,900 (3) (5)

CDFRM0 Cost of farm decontamination for two levels of decontamination ($/hectare) 1,176 2,352 2,613 5,226 CDNFRM(3) Cost of non-farm decontamination per resident person for various levels of 6,270 12,540 decontamination ($/person) (5) 16,720 33,440 TIMDEC(1) Decontamination time for each level(5) 2&4 2 & 12 months months DLBCST(3) Average cost of decontamination labor ($/man-year) 73,150 146,300 (1) (5)

TFWKF Time decontamination workers spend in farm land contaminated areas 1/10 1/4 1/3 1/4 TWWNF(1) Time decontamination workers spend in non-farm land contaminated areas(5) 1/3 1/4 1/3 1/4 VALWF0(4) Value of farm wealth ($/hectare) 11,444 11,444 (4)

VALWNF Value of non-farm wealth ($/person) 231,318 231,318 (1)

DPRATE uses NUREG/CR-4551 value (NRC 1990b).

(2)

DSRATE based on NUREG/BR-0058 (NRC 2004a).

(3)

These parameters use the NUREG/CR-4551 values (NRC 1990b), updated to July 2012 using the consumer price index for base case. They are increased by a factor of 2 for sensitivity.

(4)

VALWF0 and VALWNF are site specific values based on 2007 National Agriculture Census (USDA 2009) and Bureau of Economic Analysis 2007 data (BEA 2012), updated to the July 2012 using the consumer price index. They are not revised for the sensitivity case.

(5)

Two decontamination levels are modeled, consistent with NUREG/CR-4551 (NRC 1990b). The first value is associated with a dose reduction factor of 3. The second value is associated with a dose reduction factor of 15. The dose reduction factors of 3 and 15 are not revised for the sensitivity case.

Byron and Braidwood Stations, Units 1 and 2 Page F-292 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 F.10 FIGURES RCP Seal Loca Contribution: 67%

Inititiating Events SBO Contribution: 2.5%

ATWS Contribution: <1%

General Transient &

Other SGTR LMFW 4% Small LOCA 3% 2%

4%

Internal Flooding 14%

Loss of AP 6%

Loss of SX 46%

Loss of CCW 21%

3 CDF Contribution (based on Initiating event percent contribution)

LOSS OF SX 1.83E-05 LOSS OF CCW 8.34E-06 INTERNAL FLOODING 5.56E-06 LOSS OF AP 2.38E-06 SMALL LOCA 1.59E-06 OTHER 1.59E-06 SGTR 1.19E-06 GEN TRANSIENT &LMFW 7.94E-07 TOTAL 3.97E-05 Figure F.2-1 Byron Unit 1 Contribution to CDF by Initiating Event 3

The contributions from the consequential events are RCP seal LOCA: 2.66E-05, SBO: 9.93E-07, ATWS: <3.97E-07.

Byron and Braidwood Stations, Units 1 and 2 Page F-293 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 RCP Seal Loca Contribution: 69%

Inititiating Events SBO Contribution: 2.5%

ATWS Contribution: <1%

General Transient SGTR Other

& LMFW 4% 4% Small LOCA 2%

4%

Internal Flooding 15%

Loss of AP 5%

Loss of SX 45%

Loss of CCW 21%

4 INITIATING EVENT CDF CONTRIBUTION LOSS OF SX 1.72E-05 SMALL LOCA 8.02E-06 INTERNAL FLOODING 5.73E-06 LOSS OF CCW 1.91E-06 OTHER 1.53E-06 SGTR 1.53E-06 MEDIUM LOCA 1.53E-06 LOSS OF AP 7.64E-07 GEN TRANSIENT &LMFW 1.72E-05 TOTAL 3.82E-05 Figure F.2-2 Byron Unit 2 Contribution to CDF by Initiating Event 4

The contributions from the consequential events are RCP seal LOCA: 2.64E-05, SBO: 9.55E-07, ATWS: <3.82E-07.

Byron and Braidwood Stations, Units 1 and 2 Page F-294 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Key Equipment Contribution to CDF 60%

50%

% CDF Reduction 40%

30%

20%

10%

0%

Key Equipment Legend System Acronym System Name SX F.10.1.1 ESSENTIAL SERVICE WATER CC F.10.1.2 COMPONENT COOLING WATER AP F.10.1.3 AUXILIARY ELECTRIC POWER AF F.10.1.4 AUXILIARY FEEDWATER FW F.10.1.5 MAIN FEEDWATER DC F.10.1.6 DC POWER SY F.10.1.7 SWITCHYARD RH F.10.1.8 RESIDUAL HEAT REMOVAL VA F.10.1.9 AUXILIARY BUILDING HVAC DG F.10.1.10 DIESEL GENERATORS Figure F.2-3 Unit 1 Fusell-Veselly by System based on CDF Byron and Braidwood Stations, Units 1 and 2 Page F-295 License Renewal Application

Byron Station Environmental Report Appendix F Severe Accident Mitigation Alternatives Analysis Rev. 2 Figure F.2-4 Containment Event Tree Byron and Braidwood Stations, Units 1 and 2 Page F-296 License Renewal Application

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