ML15308A031

NRC Public Meeting on November 5, 2015 Regarding GSI-191 Resolution Plan and Current Status

ML15308A031
Person / Time
Site:	Vogtle
Issue date:	11/05/2015
From:	Southern Nuclear Operating Co
To:	Office of Nuclear Reactor Regulation
References
Download: ML15308A031 (87)

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NOVEMBER 5, 2015VOGTLE GSI

-191 RESOLUTION PLAN AND CURRENT STATUSNRC PUBLIC MEETING AGENDA8:30 -Introductions/Purpose of MeetingWhat we have learned 8:45 -High Level Overview of Vogtle'sClosure Strategy9:30 -Review of Inputs and Assumptions10:15 -Explanation of Modeling13:00 -Interface with PRA13:30 -Uncertainty Quantification14:00 -Submittal Documentation14:45 -Closing Remarks 2 PURPOSE OF MEETINGObtain staff feedback on the overall GSI

-191 resolution path for VogtleDiscuss proposed plant modificationsDiscuss use of design basis vs. best estimate inputs in the evaluation 3

4INTRODUCTION VOGTLE PLANT LAYOUTWestinghouse 4

-loop PWR (3,626 MWt per unit)Large dry containmentTwo redundant ECCS and CS trainsEach train has an RHR pump, a high head pump, an intermediate head SI pump, and a CS pumpSI and high head pumps piggyback off of the RHR pump discharge during recirculation.Maximum design flow rates:RHR 3,700 gpm/pumpCS 2,600 gpm/pumpTwo independent and redundant containment air cooling trains 5

STRAINER ARRANGEMENTTwo RHR and CS pumps each with their own strainerEach GE strainer is similar with four stacks of disksRHR strainer:

18-disk tall, 765 ft 2, height of 5 ftCS strainer:

14-disk tall, 590 ft 2, height of 4 ftPerforated plate with 3/32" diameter holes 6RHR BCS BRHR ACS A PLANT RESPONSE TO LOCASPlant response includes the following general actions: Accumulators inject (breaks larger than 2 inches)ECCS injection is initiated from the RWST to the cold legs via RHR, SI, and High Head pumpsContainment spray is initiated from the RWST via CS pumps RHR pumps switched to cold leg recirculation at RWST lo-lo alarmCS pumps switched to recirculation at RWST empty alarmCS pumps secured no earlier than 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after start of recirculationRHR pumps switched to hot leg recirculation at 7.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> 7

WHAT WE HAVE LEARNEDContainment sprays only actuate for the largest hot leg breaks under best estimate conditionsThis led to unsubmerged strainers for many breaks because RWST is left with unused waterWide variation in post

-LOCA water levels and sump chemistryPlanned modificationsReduce height of RHR strainers by ~6 inchesChange procedures to continue RWST drain down to just below empty level set pointAllows reduction of Tech Spec min water level by ~1 ft(increased operating margin)Equivalent to ~2 inches in containment pool levelCombination of these three modifications results in submerged strainers and reduces risk 8

RWST LEVELS AND ALARMS 9

SUBMERGED STRAINER RESULTS 10Before ModificationsAfter Modifications~5 ftSBLOCA minimum

~4.75 ft LBLOCA Best Estimate = ~6.6 ft LBLOCA Max = ~8.2 ft~4.425 ftSBLOCA minimum = ~4.5 ft LBLOCA Best Estimate

~7.9 ft LBLOCA Max = ~8.7 ft 11HIGH LEVEL OVERVIEWOF VOGTLE'SCLOSURE STRATEGY OVERVIEW OF METHODOLOGY Resolution plan modified based on South Texas Project (STP) pilot plant methodologyNo longer planning to perform head loss testing to develop a rule-based head loss model (as presented to the NRC in November 2014)2009 Vogtlehead loss testing will be used to determine which breaks contribute to risk quantificationBreaks with debris quantities greater than tested (mass/SA)

• will "fail"Breaks with debris quantities less than tested (mass/SA) will "pass"Will continue to quantify risk by evaluating GSI

-191 failures for number of strainers in operationWill use consensus models/design basis inputs for parameters in the GSI

-191 Risk-Informed Software 12*Mass/SA = Mass of debris per unit strainer area ANALYSIS FLOWCHART 13NARWHAL Break Analysis(Strainers)NARWHAL Break Analysis(Core)Strainer Head Loss TestAcceptable MitigationWCAP-17788Strainer PenetrationTestCDFLERFAcceptable Risk: Submit LARNot BoundedBoundedBoundedNot BoundedRG 1.174 Acceptance GuidelinesUnacceptable Risk: Implement Refinements or Modifications 14REVIEW OF INPUTS AND ASSUMPTIONS DEBRIS GENERATIONInsulation and qualified coatingsAutomated analysis with containment CAD model using a tool called BADGER*Calculate quantity and size distribution for each type of debrisPartial breaks from 1/2 inch to double-ended guillotine breaks (DEGBs) for all Class 1 welds in containmentZOIs consistent with deterministic approachUnqualified coatings and latent debris quantities are identical for all breaks 15Nukon 17DQualified Epoxy

& IOZ with Epoxy topcoat 4DInteram Fire Barrier Material11.7D*BADGER is a computer program that automates breakZOI debris generation calculations using CAD software INSULATION AND QUALIFIED COATINGS QUANTITIESBADGER database contains 28,434 breaks at 930 weld locationsBreaks evaluated at each weld inside 1 stisolation valvePartial breaks evaluated in 2 inch increments for smaller break sizes, 1 inch increments for larger break sizes, and 1/2" increments for largest break sizesPartial breaks evaluated in 45°increments around pipeDEGB evaluated at every weldDebris quantities vary significantly across the range of possible breaks, and are calculated for each breakNukon: 0 ft 3to 2,229 ft 3Qualified epoxy:

0 lb mto 219 lb mQualified IOZ:

0 lb mto 65 lb mInteramfire barrier:

0 lb mto 60 lb m 16 NUKON DEBRIS GENERATED 17 UNQUALIFIED COATINGSTypes of Unqualified Coatings at VogtleInorganic Zinc (IOZ)AlkydEpoxyIOZ, alkyd, and epoxy coatings were assumed to fail as 100% particulateSize distribution for degraded qualified coatings and failure timing no longer being utilized because of the reliance on 2009 head loss testing 18 UNQUALIFIED COATINGS LOCATIONSCoatings that fail in upper containment would have a reduced transport fraction for breaks where containment sprays are not initiated 19Coating Type Upper Containment Quantity (lb m)Lower Containment Quantity (lb m)Epoxy1,6021,127Alkyd 0 59IOZ 24 31 Total 1,626 1,217 CONTAINMENT POOL WATER LEVELSump pool depth is evaluated on a break

-specific basis using conservative inputs to minimize water levelThe evaluation considers break location and size for the appropriate contribution of RWST, RCS and SI accumulators to pool levelPlanning to remove 2 disks from each RHR strainer to reduce overall heightModifying procedures for breaks that don't activate containment spray Continue injecting water to empty RWSTStrainers are submerged for all scenarios 20 DEBRIS TRANSPORTUsing logic tree approach defined in NEI 04

-07 consistent with industry developed methods for deterministic closureBlowdownWashdownPool fillRecirculationErosion 21 TRANSPORT

-WASHDOWNContainment Sprays OnAll fines (fiber and particulate) washed to lower containmentRetention of small and large pieces caught on gratings estimated based on Drywell Debris Transport StudyWashdownto various areas proportional to flow splitContainment Sprays OffAssumed 10% washdown for fines due to condensation and 0% for small pieces 22 CONTAINMENT PRESSURE COMPARISON 23Curves illustrate the basis for containment spray actuation logicFor analysis purposes (NPSH and gas voiding) containment pressure conservatively reduced to saturation pressure when pool temperature is >212 °F and atmospheric when pool temperature is 212

°F or lessAssumption to use for containment spray actuation is not obvious for most breaks/sizes FIBER TRANSPORT FRACTIONSTO ONE RHR STRAINER* This pump lineup was evaluated for different break locations. The transport fractions shown are the bounding values for an annulus break near the strainers.

24 Debris Type Size1 Train w/

Spray2 Train w/

Spray1 Train w/o Spray2 Train w/o Spray*NukonFines 58%29%23%12%Small 48%24%5%2%Large 6%3%7%4%Intact 0%0%0%0%LatentFines 58%29%28%14%

PARTICULATE TRANSPORT FRACTIONSTO ONE RHR STRAINER 25Debris TypeSize1 Train w/ Spray2 Train w/ Spray1 Train w/o Spray2 Train w/oSprayInteramFines, Smalls 58%29%47%23%UnqualifiedEpoxyParticulate 58%29%47%23%UnqualifiedIOZParticulate 58%29%16%8%Unqualified AlkydParticulate 58%29%100%50%Qualified EpoxyParticulate 58%29%23%12%Qualified IOZParticulate 58%29%23%12%Latent dirt/dustParticulate 58%29%28%14%

CONTAINMENT POOL p HThe design basis maximum containment pool pH will be used for the sprays during recirculation and the containment pool to calculate chemical release. Lower pH values/profiles will be considered for aluminum solubility to account for lower TSP concentrations, higher boric acid concentrations, and pH effects due to core release and radiolysis.Containment spray from the RWST will use a maximum acidic pH associated with the minimum RWST boron concentration.

26 CHEMICAL EFFECTSOverviewChemical precipitate quantities are determined for each breakCorrosion/Dissolution ModelRelease and dissolution of calcium is determined using the WCAP-16530 equationsCorrosion and dissolutionof aluminum is determined using the equationsdeveloped by Howe et al. (UNM)SolubilityNo credit will be taken for calcium solubilityANL solubility equation (ML091610696, Eq. 4) will be used to credit delayed aluminum precipitation Once temperature limit is reached, all aluminum will precipitate Aluminum is eventually "forced" to precipitate for all breaksPrecipitate SurrogatesWCAP-16530 Calcium PhosphateWCAP-16530 Sodium Aluminum Silicate 27 MAXIMUM DEBRIS GENERATEDBounding quantities of Nukon, Interam and qualified coatings for DEGB in Loop 1&4 SG compartment 28Debris typeQuantityNotesNukon2,229 ft 3Including all size categoriesInteram 40 lb m 30% fiber and 70% particulateQualified coatings 249 lb mIOZ and epoxyUnqualified coatings2,843 lb mIOZ , alkyd, and epoxyLatent fiber 4 ft 315% of total latent debris; 2.4 lb m/ft 3Latent particulate 51 lb m85% of total latentdebrisMiscellaneous debris 2 ft 2Total surface area of tape and labels DEBRIS QUANTITIES AT ONE RHR STRAINER 29Debris Type2009 Test QuantityBounding Hot Leg Break(two trains with CS)Bounding Cold Leg Break(2 trains,with CS)Bounding Cold Leg Break (single trainwith CS)Nukon106.1 ft 3337.3 ft 3333.6 ft 3667.3 ft 3Latent fiber3.9 ft 3*1.2 ft 31.2 ft 32.32 ft 3Interam290.3 lb m*12.0 lb m17.4 lb m34.8 lb mQualified coatings696.8 lb m*27.3 lb m72.2 lb m144.4 lb mUnqualified coatings2874.1 lb m*824.5 lb m824.5 lb m1648.9 lb mLatent particulate52.7 lb m*14.8 lb m14.8 lb m29.6 lb mSodium aluminum silicate89.1 lb m~55 lb m~55 lb m~102 lb mCalcium phosphate52.8 lb m~53 lb m~53 lb m~108 lb m* These tested quantities exceed currently estimated values for all breaks under all equipment combinations at Vogtle 2009 STRAINER HEAD LOSS TESTINGTesting consistent with the NRC March 2008 GuidanceTank test with prototypical 7

-disk strainer moduleTotal area of 69 ft 2Walls and suction pipe arranged consistent with plant strainerBounding RHR strainer approach velocity for runout flow rate (4,500 gpm)1 inch submergence for vortex observations 30AlionTest Facility 2009 TESTING DEBRIS LOADS Nukondebris quantity based on 7D ZOIChemical precipitates quantity from WCAP-16530The following debris surrogates usedNukon and latent fiber: NukonCoatings: Silicon carbide (4 -20 micron)Latent particulate: Silica sand w/ size distribution consistent with NEI 04

-07 Volume 2 (fine sand

-< 2000 microns

)Interam fire barrier: Interam E-54A 31 2009 TEST PROCEDUREDebris introduction consistent with the NRC March 2008 GuidanceFor thin-bed testing, all particulate added first followed by small batches of fiber finesFor full-load testing, fiber and particulate mixture added in batches with constant particulate to fiber ratioChemical debris batched in lastHead loss allowed to stabilize after each chemical addition 32 2009 TEST RESULTS 33Debris LoadThin-bed test head loss (ft)Full-load test head loss (ft)Fiber + Particulate0.63 15.46 2After calcium phosphate 31.656.57After sodium aluminum silicate 32.6011.80Note: 1.Equivalent bed thickness of 0.625 inches, added in 5 fiber only batches, each 1/8" equivalent thickness 2.Equivalent bed thickness of 1.913 inches, added in 4 batches, each 0.478" equivalent thickness 3.Each chemical separately added in 3 equal batches APPLICATION OF 2009 RESULTSTotal conventional debris plus calcium phosphate head loss will be applied at the start of recirculationTotal aluminum precipitate head loss will be applied when temperature decreases to solubility limitHead loss will be scaled as a function of the average approach velocity and temperature based on the results of the flow sweeps performed at the end of the thin-bed and full

-load testsResults will be extrapolated to 30 daysBreaks that exceed the maximum tested fiber quantity, particulate quantity, or chemical precipitate quantity will be assigned a failing head loss value 34 STRAINER ACCEPTANCE CRITERIARHR and CS Pump NPSH MarginThe NPSH margin is calculated using break

-specific water level and flow ratesMinimum NPSH margin is 16.6 ft at 210.96F and acontainment pressure of

-0.3 psigStructuralStrainer stress analysis is based on a crush pressure of 24.7 ft for the RHR strainers and 23.0 ft for the CS strainersGas void2% void fraction at pump inlet 35 FIBER PENETRATION TESTINGMultiple tank tests were performed at Alden in 2014 for various strainer approach velocities, number of strainer disks and boron / buffer concentrationsNukon prepared into fines per latest NEI GuidanceA curve fit of the test data will be used to evaluate maximum fiber penetration for a 16 disk strainer (RHR) and 14 disk strainer (CS).

36 0 200 400 600 800 1000 1200 1400 1600 1800 0 5000 10000 15000 20000Cumulative Fiber Penetration (g)Cumulative Fiber Addition (g)FIBER PENETRATION RESULTS 37 IN-VESSEL EFFECTS Transport/accumulation of fiber to the core that penetrates RHR strainers is dependent on break location and flow path and will be based on WCAP-17788Values for core blockage and boron precipitation acceptance criteria will be based on WCAP

-17788 38 EX-VESSEL EFFECTSA single bounding evaluation will be performed for all componentsExisting evaluations will be updated in accordance with WCAP-16406-P-A ,"Evaluation of Downstream Sump Debris Effects in Support of GSI

-191" Revision 1 and the accompanying NRC SER 39 LOCADMA bounding calculation will be performed to cover all scenariosExisting evaluations will be updated in accordance with WCAP-16793-A,"Evaluation of Long-Term Cooling Considering Particulate, Fibrous, and Chemical Debris in the Recirculating Fluid" Revision 2 and the accompanying NRC SER 40 41EXPLANATION OF MODELING GSI-191 ACCEPTANCE CRITERIA Acceptance CriteriaMethod for AddressingDebris exceeds limits for upstream blockageBoundinganalysisStrainer head loss exceeds pump NPSH margin or strainer structural marginBreak-specific analysis based on tested debris limits and maximum tested head lossesGas voids from degasification or flashing exceed strainer/pump limitsBreak-specific analysis based on head loss, pool temperature, etc.Pumps fail due to air intrusion from vortexingBounding analysisPenetrated debris exceeds ex

-vessel wear and blockage limitsBounding analysisPenetrated debris exceeds in

-vessel fuel blockage and boron precipitation limitsBreak-specific analysis based on penetration testing and flow splitsDebris accumulation on cladding prevents adequate heat transfer Bounding analysis 42 OVERVIEW OF MODELINGGSI-191 phenomena evaluated in a holistic, time

-dependent manner with an evaluation tool called NARWHALDeveloped using object oriented designTracks movement of water and debrisEvaluates each break with incremental time steps up to 30 daysEvaluates range of breaks to determine which ones pass/fail the strainer and core acceptance criteria Uses top-down LOCA frequencies to calculate conditional failure probabilities for small, medium, and large breaks 43 OVERVIEW OF MODELINGNARWHAL prototype has been used for preliminary risk-informed evaluations by several plantsVersion 1.0 is currently under development Software requirements, design, implementation, V&V, and user documentation prepared under ENERCON's Appendix B QA programNARWHAL's object oriented design allows users to model unique plant

-specific geometry with a common executable fileSimplifies software maintenance Significantly reduces potential for software errors 44 OVERVIEW OF MODELING 45RWSTReactorVesselBreakCoreAcronyms:ECCS: Emergency Core Cooling SystemCS: Containment SprayRWST: Refueling Water Storage TankECCS CSSpray NozzlesContainmentCompartmentsSump PoolECCS Strainers OVERVIEW OF MODELING 46 OVERVIEW OF MODELINGNARWHAL integrates models and inputs from design basis calculations and GSI

-191 tests/analyses:Water volumes, temperature profiles, and pH from design basis calculationsDebris quantities from BADGER database Location-specific transport fractions from transport calculationChemical effects calculated using WCAP

-16530 modelConventional and chemical head loss from 2009 strainer testingNPSH and structural margin from design basis calculationsDegasification calculated using standard physical modelsTime-dependent penetration using data fit from strainer testingCore failure calculated using WCAP

-17788 model and limits 47 OVERVIEW OF MODELING 48Acronyms:ZOI: Zone of InfluenceCS: Containment SprayECCS: Emergency Core Cooling System1. Select unique break location, size, and orientation2. ZOI debris quantities from BADGER (insulation and qualified coatings)3. Debris quantities outside ZOI (unqualified coatings, latent, miscellaneous)4. Blowdown transport to containment compartments and sump pool5. Washdown transport from containment compartments to sump pool6. Pool fill transport from sump pool to strainers and inactive cavities

7. Recirculation transport from sump pool to strainers8. Debris penetration through strainers9. Debris accumulation on core OVERVIEW OF MODELING 49Acronyms:CS: Containment SprayECCS: Emergency Core Cooling System2. Corrosion/ dissolution of metals, concrete, and debris in sump pool1. Corrosion/ dissolution of metals, concrete, and debris by CS

4. Formation of chemical precipitates3. Precipitate solubility limit5. Recirculation transport from sump pool to strainers6. Debris penetration through strainers7. Debris accumulation on core OVERVIEW OF MODELING 501. Strainer Head Loss (CSHL + Conventional HL + Chemical HL)

2. Degasification gas void fractionAcronyms:ECCS: Emergency Core Cooling SystemCS: Containment SprayHL: Head LossCSHL: Clean Strainer Head LossNPSH: Net Positive Suction Head3. Pump NPSH margin4. Strainer structural margin5a. Does HL Exceed NPSH or structural margin?Yes7a. Fail strainer criteria No 6a. Pass strainer criteria5b. Does void fraction exceed strainer or pump limits?Yes7b. Fail strainer criteria No6b. Pass strainer criteria8. Core debris accumulation9b. Does quantity exceed blockage limits?Yes10. Fail core criteria No11. Pass core criteria9a. Does quantity exceed boron limits?Yes No OVERVIEW OF MODELINGAnalytical results showing whether a given break passes or fails are highly dependent on the assumptions and models used to evaluate the breakFor example, if sprays are not initiated for a given break: A smaller fraction of debris is washed down to the containment pool Corrosion/dissolution is reduced (unsubmerged materials)A larger fraction of debris in the pool is transported to the RHR strainersIt is not always obvious what conditions are bounding 51 INPUTS 52 Input Values SensitivityDebris GenerationBased on consensus modelsNoneDebris TransportBased on consensus modelsNoneContainment TempDesign basisNonePool TempDesign basisNoneContainment SprayActivation and DurationCompeting effects (e.x. washdown, strainer surface area, corrosion)Needto run for activation and durationPool Volume/LevelBased on consensus modelsNonePool pHDesign Basis maximum for corrosion, design basis minimumfor precipitationNoneECCS FlowRatesDesign basis (same for all breaks)NoneAluminum and Calcium CorrosionWCAP-16530 and UNM equationsNoneAluminum PrecipitationANL equationNonePenetration2014 testingNeedto address uncertaintyHead LossMaximums Extrapolated and scaled from 2009 tests final valuesNone 53INTERFACE WITH PRA INTERFACE WITH PRAThe change in core damage frequency (CDF) and change in large early release frequency (LERF) due to issues related to GSI-191 will be determined using:LOCA frequencies from NUREG

-1829 or the Vogtle PRAEquipment configuration probabilities from PRA model of recordGSI-191 conditional failure probabilities from NARWHALFinal risk calculation will be performed using the Vogtle model of record with GSI

-191 conditional failure probabilities 54 INTERFACE WITH PRA 551. PRA identification of accident scenarios and equipment configurations that are risk-significant to GSI-191 2. NARWHAL evaluation of GSI-191 phenomena for each risk-significant scenario/configuration to determine CFPs for each strainer/core failure basic event3. PRA quantification of CDF & LERF with GSI-191 failures4. PRA quantification of CDF & LERF with no GSI-191 failuresOutput to submittal documentation5. Calculate CDF & LERFAcronyms:PRA: Probabilistic Risk AssessmentGSI-191: Generic Safety Issue 191CFP: Conditional Failure ProbabilityCDF: Core Damage FrequencyLERF: Large Early Release Frequency Frequency Release FrequencyRG 1.174: Regulatory Guide 1.174Yes6. Meets RG 1.174 Criteria?7a. Identification of analytical refinements to analysis No7b. Identification of potential plant modifications (physical or procedural)

METHODOLOGY FOR USING LOCA FREQUENCY TO CALCULATE CONDITIONAL FAILURE PROBABILITYPartition PRA categories (Cat k) into size ranges (SR i)Calculate probability of a LOCA occurring in each size range for every PRA category (P(SR ilCat k))Calculate probability of a LOCA occurring at each weld (Weld j) within each size range (P(Weld jlSR i))Calculate probability estimate for success criteria failure (SCF) at each weld in each size range (P (SCFlWeld j, SR i))Calculate estimate for success criteria failure at every PRA category (P (SCFlCat k))56 METHODOLOGYFOR USING LOCA FREQUENCY TO CALCULATE CONDITIONAL FAILURE PROBABILITYPSCFCa t=P S RlCa t PWel d S RPSCFWel d , S R 57From NUREG-1829From NUREG

-1829 using top-down methodologyFrom NARWHAL ILLUSTRATION OF PRA CATEGORIES AND LOCA FREQUENCY SIZE RANGES 58 METHOD FOR ADDRESSING DEGB FREQUENCIESNUREG-1829 provides LOCA frequencies vs. break flow rates, which are converted to equivalent diameter break sizesDouble ended guillotine breaks (DEGBs) have a flow rate (area) twice as large as the pipe cross

-sectional areaEquivalent diameter for DEBG is calculated using pipe inner diameter:

DDEGB,EqDpipeDpipeassumed to progress to DEGB for debris generation (bounding debris quantities)Frequency associated with DEGB "tail" assigned to Dpipebreak size to calculate conditional failure probability within each size rangeNUREG-1829 only provides frequencies up to 31" breaks, so frequencies corresponding to primary loop pipe DDEGB,Eqvalues is determined through log

-log extrapolation29" 41.0"31"43.8"59 METHOD FOR ADDRESSING DEGB FREQUENCIES 60 EQUIPMENT CONFIGURATION PROBABILITYMost likely situation would be that all equipment is available and fully functionalEquipment failures due to non

-GSI-191 related issues can have a major effect on GSI

-191 phenomena (debris transport, flow splits, temperature and pressure profiles, etc.) There are many possible equipment failure combinations (RHR pumps, containment spray pumps, charging pumps, SI pumps, fan coolers, etc.)At Vogtle, GSI

-191 effects can be reasonably represented or bounded for most equipment failure combinations by the cases where all pumps are running or a single train failure 61 EQUIPMENT CONFIGURATION PROBABILITYLBLOCAAll equipment available bounding or reasonably representative for: No pump failures: ~79%1 or 2 CS pump failures: ~18%1 RHR pump failure bounding or reasonably representative for other equipment failure configurations: ~3%The values above are being used to determine which configurations to investigate with NARWHALConditional failure probabilities will be manually entering into the PRA model of record to calculate CDF 62~97%

CONDITIONAL FAILURE PROBABILITIES 63Coreconditional failure probability (CFP) higher when all pumps are operatingStrainerCFP higher with 1 train operatingAdditional scenarios will likely need to be evaluated (1 CS pump failure, 1 RHR pump failure, etc.)

PRA MODEL CHANGESVogtle PRA model modified to incorporate conditional failure probabilities (CFPs) for GSI

-191 strainer failures and core failures with associated initiating events and equipment configurationsGSI-191 "failure" defined using PRA success criteriaStrainer failure defined as failure of RHR pump/strainerCS strainer failures are calculated in NARWHAL, but not used in PRAGSI-191 failures binned into following CFP groups (separate CFPs defined for each LOCA category and each pump state)Core failuresRHR Strainer A failures (without Strainer B or core failures)RHR Strainer B failures (without Strainer A or core failures)RHR Strainer A and B failures (without core failures)Each core and strainer CFP represented in PRA with a basic event that is combined with LOCA initiating event and pump failure logic to represent pump state associated with CFP 64 PRA MODEL CHANGES 65 66UNCERTAINTY QUANTIFICATION UNCERTAINTY QUANTIFICATIONDraft RegGuide 1.229 requires uncertainty quantification for risk-informed GSI-191 evaluationUncertainty quantification also required by RegGuide 1.174Two different approaches that could be used to quantify uncertaintySimplified approach using sensitivity analysisStatisticalsampling of input parameter distributions and propagating uncertainties Consensus inputsand models are considered to have no uncertaintyVogtle inputs that require uncertainty quantificationLOCA frequency valuesPenetration modelContainmentspray activation and durationPossibly others 67 UNCERTAINTY QUANTIFICATION USING SENSITIVITY ANALYSIS 68 UNCERTAINTY QUANTIFICATION USING STATISTICAL SAMPLING 69 1. Select equipment failure configuration

2. Sample all random input values3. Select break location, size, and orientation5. Compare to GSI

-191 acceptance criteria and PRA success criteria to identify strainer or core failures9. Output to PRA model4. Evaluate GSI

-191 phenomena at each time step for 30 days6. Sufficientbreaks evaluated to estimate CFP?No 7. Sufficient random samples to estimate CFP PDF?Acronyms:PRA: Probabilistic Risk AssessmentLOCA: Loss of Coolant AccidentGSI-191: Generic Safety Issue 191CFP: Conditional Failure ProbabilityPDF: Probability Density Function Yes No8. All significant equipment configs. evaluated?Yes NoYes QUALITY ASSURANCEGSI-191 calculations are being revised to be safety related under vendor Appendix B QA programsHead loss testing in 2009 was conducted and documented as safety related under vendor Appendix B QA program Penetration testing was conducted and documented as non-safety related following work practices established by vendor Appendix B QA programPRA has undergone an industry peer review per RG 1.200 and the ASME/ANS PRA Standard for CDF and LERF (RA-Sa-2009)70 CONCLUSIONSModels used to analyze GSI

-191 phenomena at Vogtle are consistent with methods accepted for design basis evaluationsPreliminary results indicate that risk associated with GSI-191 is very low 71 72SUBMITTAL DOCUMENTATION SUBMITTAL DOCUMENTATION DISCUSSIONPlanning to follow the format, content, and depth of the August 2015 STP LARGL 2004-02 Response following Staff Review Guidance (will have some pointers to risk informed summary)Risk Quantification and SummaryDefense in Depth and safety marginRequests for exemptions (if 10CFR50.46(c) rule is not finalized)10CFR50.46(d)GDC 19GDC 35GDC 38GDC 41GDC 50.67License amendment requestTech Spec markupsTech Spec basesFSAR markupsList of commitments 73 UPDATED RESOLUTION SCHEDULEMILESTONEEXPECTED COMPLETION DATECurrent StatusDevelop containment CAD model to include pipe weldsCompleteCompleteConduct meeting with NRC 3 rdQuarter 2013CompleteModify probabilistic risk assessment (PRA) to include Strainer and Core Blockage events 4 thQuarter 2013Complete**Perform Chemical Effects testing 1 stQuarter 2014Complete**Perform thermal and hydraulic modeling of RCS, Core, and Containment conditions 1 stQuarter 2014Complete**Perform Strainer Head Loss and Bypass testing to establish correlation for range of break sizes 2 ndQuarter 2014StrainerBypass Testing

-CompleteStrainer Headloss Testing

-Using 2009 Vogtle testAssemble base inputs for CASA Grande 2 ndQuarter 2014Complete -Using NARWHAL instead of CASAGrande**Evaluate Boric Acid Precipitation impacts 3 rdQuarter 2015Plan on using PWROG WCAP

-17788Finalize inputs to CASA Grande 3 rdQuarter 2015In Progress, Using NARWHAL instead of CASAGrandeComplete Sensitivity Analyses in/for CASA Grande 4 thQuarter 2015 1 stQuarter 2016Integrate CASA Grande results into PRA to 1 stQuarter 2016 1 stQuarter 2016Licensing Submittal for VEGPTo be established through discussions with NRC -tentatively September 2016Projected 1 stQuarter 2017, require input from: SE on STP Pilot Project and SE on WCAP

-17788; which are not yet available.

74 75CLOSING REMARKS 76BACKUP SLIDES EXAMPLE CALCULATIONDetailed physical calculationsBreak Location 11201

-049-16-RB (10.5" DEG hot leg side break in annulus near surge line)1 train operating with containment sprays activatedTransport fractions: MaximumCondensation washdown: 10%RHR flow rate

3,700gpm (design flow)CS timing: 6 HoursDesign basis temperature profile

-Max Safeguards, with pool temperature drop to 90°F at Day 30Minimum water level profileSump pH used for corrosion: 8.1 Containment spray pH during Injection used for corrosion: 4.71pH used for solubility: 7.6Submerged Aluminum Area: 278.7 ft 2Exposed Aluminum Area: 741.3 ft 2Submerged Concrete: 2,813 ft 2Aluminum Metal Release equations

-WCAP 16530 Aluminum Solubility Equation

-ANL Aluminum Solubility EquationAluminum Solubility: Timing Only 77 POOL LEVEL 78 FIBER TRANSPORT TO ONE RHR STRAINER (1 TRAIN W/SPRAY)*Transport fraction takes into account time

-dependent transport (CS strainer active for 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />)**Combined fraction of fines due to erosion and intact pieces Debris Type Size DG Quantity (ft 3)Transport Fraction*Quantity (ft 3)NukonFines9.5 58%6.1Small32.77%**1.5**Large14.84%**0.6**Intact15.9 0%0.0Total72.98.2LatentFines12.5 58%7.8 Total 85.4 16.0 79 PARTICULATE TRANSPORT TO ONE RHR STRAINER (1 TRAIN W/SPRAY)Debris TypeSizeDG Quantity (lb m)TransportFractionQuantity (lb m)InteramFines, Smalls121.258%70.3UnqualifiedEpoxyParticulate2,602.058%1,509.2UnqualifiedIOZParticulate25.058%14.5Unqualified AlkydParticulate32.058%18.6Qualified EpoxyParticulate7.558%4.4Qualified IOZParticulate2.458%1.4Latent dirt/dustParticulate170.058%98.6Total2,960.11,717.0 80 CHEMICAL PRECIPITATE QUANTITIES 81 ALUMINUM CONCENTRATION AND SOLUBILITY 82 HEAD LOSSClean strainer head loss: Bounding value of 0.162 ftat 4,500 gpmConventional head loss Head loss due to chemical precipitates* Values scaled to 16 disk RHR strainer area** Corrected to 3700 gpmand 90°F*** Applied to every break to correct chemical head lossHead Loss TypeTransported QuantityMaxTested Quantity*Head LossCorresponding to Max Tested Quantity(Unadjusted)Head Losswith Flow and TemperatureCorrection**Fiber16.0 ft 3109.9 ft 35.46 ft4.41 ftParticulate1,717.0 lb m3,914.5 lb mCalcium Phosphate9.6 lb m52.8 lb m1.11 ft0.90 ftSodium Aluminum Silicate74.5 lb m89.0 lb m5.24 ft4.23 ftExtrapolation Correction2.13 ft***1.72 ft 83 Short Term: Long Term: VOID FRACTION 84 DEBRIS PENETRATION100% capture of particulate and precipitate at strainerDirect penetration curve fit (Placeholder)= 0.44,<0.904 0.51%, 0.904Where F = penetration fraction t= fiber bed thickness on strainer in inchesCaptured fiber sheddingAll fiber is treated as fines 85 DEBRIS PENETRATION (G/FA) 86

SUMMARY

Criteria Failure Example Results Example Pass/FailNPSH Margin16.6 ft11.3 ftPassStrainer Structural Margin24.7 ft11.3 ftPassPartial Submergence1/2 submerged heightFully submergedPassGas Void Fraction2% at the pump0.24% at the pumpPassDebris LimitExceeds what was testedNot exceededPassAssumed core limits (to be replaced with WCAP-17788 criteria)75 g/FA forHot Leg Breaks7.5 g/FA for Cold Leg Breaks32 g/FAPass 87