ML112770203

South Texas Project, Units 1 and 2 - Licensee Slides from 10/3/11 Meeting LOCA Frequencies, Final Results (TAC Nos. ME5358 and ME5359)

ML112770203
Person / Time
Site:	South Texas
Issue date:	10/03/2011
From:	Kreslyon Fleming, Lydell B O South Texas
To:	Singal B K Plant Licensing Branch IV
Singal, B K, NRR/DORL, 301-415-301
Shared Package
ML112770162	List: ML112770170 ML112770176 ML112770203 ML112770230 ML112770237 ML112770246 ML112770251
References
TAC ME5358, TAC ME5359
Download: ML112770203 (59)

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LOCA Initiating Event Frequencies Final Results for 2011Risk Informed GSI-191 Resolution MdAt22201110/03/11 Pre-Licensing Meeting 1Monday, August 22, 20111:00 pm -4:30 p.m EDT Public Meeting with STP Nuclear Operating CompanyKarl N. FlemingKNF Consulting Services LLCBengt O. Y. Lydell Discussion Topics*Briefing on Final Results for 2011*Review of technical approach with focus on recent refinementsRisk Informed GSI-19110/03/11 Pre-Licensing Meeting 2*Highlights of Results-Component level for CASAGRANDE-Total LOCA frequencies for RISKMAN

-Comparison with NUREG-1829*Issues to Complete in 2012 LOCA Frequencies Objectives*Incorporate insights from previous work on LOCA frequencies*Characterize LOCA initiating events and their frequencies with respect to:-Specific components, materials, dimensions-Specific locations

-Range of break sizes

-Damage / Degradation mechanisms and mitigation effectivenessOtherbreakcharacteristicsegspeedRisk Informed GSI-191-Other break characteristics, e.g. speed*Quantify both aleatory and epistemic uncertainties; augment with sensitivity studies*Support interfaces with other parts of the GSI-191 evaluation-LOCA initiating event frequencies for PRA modeling-Break characterization for evaluation of debris formation*Participate in NRC workshops310/03/11 Pre-Licensing Meeting Current Status*Defined homogenous pipe failure rate categories*Refined method for deriving conditional rupture probabilities vs. break size*Obtainedfinal2011resultsforeachpipeObtained final 2011 results for each pipe category and provided to CASAGRANDE*Obtained final 2011 results for total LOCA frequencies from pipe failures with comparisons to NUREG-1829*Incorporated independent review comments and recommendations by MIT and Ali Mosleh10/03/11 Pre-Licensing Meeting 4 AcronymsASME American Society of Mechanical Engineers B-J ASME Section XI Similar Metal Weld B-F ASME Section XI Bimetallic Weld BC Branch Connection Weld CRP Conditional Rupture Probability CVCS Chemical Volume and Control SystemD&C Design and Construction Defects DEGBDblEddGilltiBkNPS Nominal Pipe Size PRAProbabilistic Risk Assessment PWR Pressurized Water Reactor PWSCC Primary Water Stress Corrosion Cracking PZR Pressurizer RCS Reactor Coolant System RI-ISIRisk Informed Inservice Inspection10/03/11 Pre-Licensing Meeting 5DEGB Double Ended Guillotine BreakDM Damage (Degradation)Mechanism ECCS Emergency Core Cooling System EPRI Electric Power Research Institute GM Geometric Mean GSI Generic Safety Issue HPI High Pressure Injection IGSCC Intergranular Stress Corrosion Cracking LOCA Loss of Coolant Accident SBSmall BoreSIRSafety Injection and Recirculation Systems TASCThermal StratificationTF Thermal Fatigue TTThermal TransientsSCStress Corrosion CrackingTGSCC Transgranular Stress Corrosion Cracking VF Vibration fatigue Pipe Rupture Model=iixixmLOCAF)( (2.1)ikikxkikixIFRP)(= (2.2)where: =)(xLOCAF Frequency of LOCA of size x, per reactor calendar-year, subject to epistemic uncertainty calculated via Monte Carlo =im Number of pipe welds of type i; each type determined by pipe size, weldtypeapplicabledamagemechanismsandinspectionstatus10/03/11 Pre-Licensing Meeting 6weld type, applicable damage mechanisms, and inspection status (leak test and NDE); no significant uncertainty =ix Frequency of rupture of component type iwith break size x, subject to epistemic uncertainty calculated via Monte Carlo or lognormal formulas =ik Failure rate per weld-year for pipe component type i due to failure mechanism k, subject to epistemic uncertainty determined by RI-ISI Bayes method and Eq. (2.3) below =)(ikxFRP Conditional probability of rupture of size xgiven failure of pipe component type i due to damage mechanism k, subject to epistemic uncertainty determined via expert elicitation using NUREG-1829 data =ikI Integrity management factor for weld type iand failure mechanism k,subject to epistemic uncertainty determined by Monte Carlo and Markov model Step-by-Step Procedure1 of 210/03/11 Pre-Licensing Meeting 7 Step-by-Step Procedure 2 of 210/03/11 Pre-Licensing Meeting 8 Step 1 Failure Rate Development1. Failure Rate Development 1.1 Determine component and weld types - i 1.2 Perform data query for failure counts - n 1.3 Estimate component exposure - T 1.4 Develop component failure rate prior distributions for each damage mechanism (DM) 15PerformBayes'updateforeachexposurecase(combinationofweldcountcaseandDM10/03/11 Pre-Licensing Meeting 91.5Perform Bayes update for each exposure case (combination of weld count case and DMsusceptibility [DMS] case) 1.6 Develop mixture distribution to combine results for different exposure hypotheses to yield conditional failure rate distributions ikgiven STP-specific applicable DMs1.7 Calculate total failure rate over all applicable damage mechanisms - ik Step 1.1 Definition of Component Types*Goal is to define homogeneous groups of components that may be characterized by a single failure rate estimate*Fundamental to any PRA data analysis

• Criteria-Pipe materials-Pipe size-Applicable damage mechanisms (DMs)

-Unusual distribution of component failures

-In-service inspection program status*STP Class 1 Pipe Weld Categories -8 System Groups-25 Categories based on combinations of DMs

-45 Categories based on DMs and Pipe Sizes

-775 Total number of Class 1 pipe welds at STP10/03/11 Pre-Licensing Meeting 10 Homogeneous Pipe Failure Rate CasesCaseDescriptionWeld TypeDamage Mechanism (DM)Comment1RCS Hot Leg Excl. SG InletB-FPWSCC, D&CDesign basis LOCA location; B-F weld has higher failure rate but located inside Rx cavityB-JTF, D&C2RCS Cold LegB-FPWSCC, D&CLower temperatures and different pipe sizes relative to hot legB-JD&C3RCS Hot Leg SG InletB-FPWSCC, D&CThis case defined to address S/G Inlet nozzle-to-safe-end weld that has unusual failure count distribution[1]10/03/11 Pre-Licensing Meeting 114PZR Surge LineB-FPWSCC, TF, D&CIncludes surge line from branch connections and nozzles to pressurizer safe end; entire surge line subjected to thermal transients during startup and shutdownB-J, BCTF, D&C5PZR Medium Bore PipingB-FPWSCC, TF, D&CThis includes pressurizer spray, and relief valve piping excluding the pressurizer surge line; B-F welds at STP in this category have weld overlays[2]B-J, BCTF, D&C6Class 1 Small Bore PipingB-JTF, D&C, TGSCC, VFThis is all the Class 1 piping of size 2" and less and inside isolation valves7Class 1 Medium Bore SIR PipingB-JTF, D&C, IGSCCSafety injection and residual heat removal (RHR) systems in standby during normal operation; Class 1 is inside the isolation valves8Class 1 Medium Bore CVCS PipingB-J, BCTF, D&C, TGSCC, VFCVCS piping with injection and letdown flow during normal operation Component Categories1 of 3System Case System Component Case Weld Type Applicable DM STP Total No. of Welds Pipe Size (in.) DEGB Size (in.) 1 RC Hot Leg 1A B-F SC, D&C 4 29 41.0 1B B-J D&C 11 29 41.0 1C B-J TF, D&C 1 29 41.0 2 RC SG Inlet 2 B-F SC, D&C 4 29 41.0 10/03/11 Pre-Licensing Meeting 123 RC Cold Leg 3A B-F SC, D&C 4 27.5 38.9 3B B-J 4 31 43.8 3C B-J D&C 12 27.5 38.9 3D B-J 24 31 43.8 4 RC Surge 4A B-F SC, TF, D&C 1 16 22.6 4B B-J TF, D&C 7 16 22.6 4C BC 2 16 22.6 4D B-J 6 2.5 3.5 Component Categories2 of 3System Case System Component Case Weld Type Applicable DM STP Total No. of Welds Pipe Size (in.) DEGB Size (in.) 5A B-J TF, D&C 2968.55B B-J 14 3 4.2 5C B-J D&C53 4 5.7 5DBJ434210/03/11 Pre-Licensing Meeting 135 PZR D&C5DB-J434.25E B-J 29 6 8.5 5F B-F SC, TF, D&C 0 6 8.5 5G B-F SC, D&C 0 6 8.5 5H B-F D&C (Weld Overlay) 4 6 8.5 5I BC D&C 2 4 5.7 5J B-J TF, D&C 2 2 2.8 6 Small Bore 6A B-J VF, SC, D&C 16 2 2.8 6B B-J 193 1 1.4 Component Categories3 of 3System Case System Component Case Weld Type Applicable DM STP Total No. of Welds Pipe Size (in.) DEGB Size (in.) 7SIR Lines Excl. Accumulator 7A B-J TF, D&C 21 12 17.0 7B B-J 9 8 11.3 7C B-J SC, TF, D&C 3 8 11.31 7D B-J SC, D&C 3 12 17.0 7E B-J, BC 57 12 17.0 7F B-J 30 10 14.1 7G B-J, BC 42 8 11.3 7H10/03/11 Pre-Licensing Meeting 147 D&C 7HB-J2368.497I BC 5 4 5.7 7J BC 9 3 4.24 7K BC 10 2 2.8 7L B-J 0 1.5 2.1 SIR Accumulator Lines 7M B-JSC, D&C 01217.07N B-J TF, D&C 35 12 17.0 7O B-J, BC D&C 15 12 17.0 8 CVCS 8A B-J TF, VF, D&C 10 2 2.8 8B B-J 19 4 5.7 8C B-J VF, D&C 47 2 2.8 8D B-J 6 4 5.7 8E BC TF, D&C 4 4 5.7 8F BC D&C 1 4 5.7 Total 775 Step 1.2 Failure Data QuerySystem Case System Event Type Nominal Pipe Size Failure Count by DM - Weld Locations Totals D&C SC PWSCC TF V-F 1 RCS Hot Leg Crack 32" 5 5 RCS Hot Leg Leak 32" 1 1 2 RCS Cold Leg Crack 32" 3 3 3 S/G Inlet Crack 32" 19 1 18 4 PZR-Surge Crack 16" 3 3 5 PZR-PORV Crack 4" ø 10" 2 2 PZR-SPRAY Crack 4" ø 10" 2 2 PZR-SPRAY Leak 4" ø 10" 1 1 PZR-SRV Crack 4" ø 10" 6 1 5 PZRSRVLeak4"ø10"1110/03/11 Pre-Licensing Meeting 15PZR-SRVLeak4" ø 10"116 CVCS Crack 1" 1 1 CVCS Leak 1" 6 1 5 Safety Injection Leak 1" 2 2 PZR-Sample/Instr. Crack 2" 5 1 2 2 PZR-SPRAY Crack 1" 1 1 PZR-SPRAY Leak 1" 3 1 1 1 RCS Crack 2" 14 1 3 2 1 7 RCS Leak 2" 62 12 10 2 2 36 RHR Leak 1" 6 1 5 S/G System Crack 1" 2 1 1 S/G System Leak 1" 4 2 2 7 Safety Injection Crack 4" ø 12" 3 1 2 Safety Injection Leak 4" ø 12" 3 3 RHR Crack 4" ø 12" 1 1 8 CVCS Crack 2" ø 4" 1 1 CVCS Leak 2" ø 4" 6 1 5 Total 163 23 21 46 9 64 PIPExp Database10/03/11 Pre-Licensing Meeting 16 Step 1.3 Component Exposure*Component Exposure includes-Reactor-years of service data (little uncertainty)-Number of components per reactor (almost always uncertain)

-Fraction of the components susceptible to a DM (sometimes uncertain)*Components per reactor for Hot Leg Welds10/03/11 Pre-Licensing Meeting 17Plant PWR Type NPS29 Weld Population B-F Welds B-J Welds B-F Welds/loop B-J Welds/loop Braidwood-1 4-Loop 8 12 2 3 Braidwood-2 4-Loop 8 12 2 3 Byron-1 4-Loop 8 12 2 3 Byron-2 4-Loop 8 11 2 2.75 Kewaunee 2-Loop 4 6 2 3 Koeberg-1 3-Loop 3 9 1 3 Koeberg-2 3-Loop 3 9 1 3 STP-1 4-Loop 8 8 2 2 STP-2 4-Loop 8 8 2 2 V.C. Summer 3-Loop 6 6 2 2 Average 1.8 2.68 Min 1 2 Max 2 3 Damage Mechanisms (DM)*Damage Mechanism Assessment-All welds susceptible to D&C-All BF welds susceptible to PWSCC

-Many DMs can be ruled out for certain categories-In some cases some unknown fraction of a component category pgyis susceptible to DMs (e.g. TF and SC)*DM Assessment for Hot Leg Welds10/03/11 Pre-Licensing Meeting 18Calc. Case System Location Confidence Level Weld Susceptibility Fractions C-F D&C ECSCC Fretting IGSCC PWSCC TF TGSCC VF 1A RC Hot Leg B-F (Un-mitigated) Low N/A 1 N/A N/A N/A 1 N/A N/A N/A Medium N/A 1 N/A N/A N/A 1 N/A N/A N/A High N/A 1 N/A N/A N/A 1 N/A N/A N/A 1B, 1C B-J Low N/A 1 N/A N/A N/A N/A 0.01 N/A N/A Medium N/A 1 N/A N/A N/A N/A 0.02 N/A N/A High N/A 1 N/A N/A N/A N/A 0.08 N/A N/A Uncertainty Model for Hot Leg B-J Welds Subject to Thermal Fatigue10/03/11 Pre-Licensing Meeting 19 Summary of Component Exposure EstimatesSystem Case System Component Case Weld Type Best Estimate Upper Bound Lower Bound 1 RCS Hot Leg 1A B-F 21,732 24,147 12,074 1B, 1C B-J 32,297 36,221 24,147 2 RCS SG Inlet 2 B-F 12,074 12,074 12,074 3 RCS Cold Leg 3A B-F 22,315 24,794 12,397 3B B-J 123,764 177,279 99,177 4AB-F3,9143,9143,91410/03/11 Pre-Licensing Meeting 204 RCS Surge 4ABF 3,9143,9143,9144B B-J 27,007 54,013 13,503 4C BC 7,828 7,828 7,828 5 PZR 5A-5D B-J 351,127 496,158 286,245 5E-5G B-F 19,083 19,083 19,083 6 SB 6A-6B B-J 744,237 1,144,980 366,394 7 SIR Lines Excl. Accumulator 7A-7L B-J 590,797 637,190 507,518 SIR Accumulator Lines 7M-7O B-J 175,067 277,693 132,810 8 CVCS 8A-8D B-J 562,348 627,324 403,018 8E, 8F BC 81,393 90,797 58,332 Total Estimated Weld-Yrs 2,774,983 3,633,494 1,958,513 Steps 1.4 and 1.5 Select Priors and Perform Bayes' Updates -Hot Leg WeldsWeld Type and DM(3) Weld Count Case DM Susceptibility Case Prior Distribution(1) Evidence(2) Bayes' Posterior Distribution(1) Type Median RF Failures Exposure Mean 5%tile 50%tile 95%tile RF(4) Hot Leg B-F SC Low Base Lognormal8.48E-07100612,074 4.32E-041.78E-044.05E-047.78E-042.1Medium Base Lognormal8.48E-07100621,732 2.43E-041.01E-042.29E-044.37E-042.1High Base Lognormal8.48E-07100624,147 2.20E-049.10E-052.06E-043.94E-042.1Hot Leg B-F DC Low Base Lognormal 5.46E-08 100 0 12,074 1.02E-06 5.34E-10 5.16E-08 4.05E-06 87.1 Medium Base Lognormal5.46E-08100021,732 8.31E-075.28E-105.01E-083.54E-0681.9High Base Lognormal5.46E-08100024,147 8.31E-075.28E-105.01E-083.54E-0681.9Low Low Lognormal2.66E-071000241 8.88E-062.65E-092.64E-072.53E-0597.6Medium Low Lognormal2.66E-071000323 8.41E-062.65E-092.63E-072.49E-0597.0High Low Lognormal2.66E-071000362 8.22E-062.65E-092.63E-072.47E-0596.710/03/11 Pre-Licensing Meeting 21Hot Leg B-J TF Low Medium Lognormal2.66E-071000483 7.74E-062.64E-092.62E-072.43E-0595.8Medium Medium Lognormal2.66E-071000646 7.25E-062.64E-092.61E-072.37E-0594.8High Medium Lognormal2.66E-071000724 7.05E-062.64E-092.60E-072.35E-0594.3Low High Lognormal2.66E-0710001,932 5.38E-062.61E-092.54E-072.06E-0588.9Medium High Lognormal2.66E-0710002,584 4.90E-062.60E-092.51E-071.96E-0586.7High High Lognormal 2.66E-07 100 0 2,898 4.72E-06 2.59E-09 2.50E-07 1.91E-05 85.8 Hot Leg B-J DC Low Base Lognormal5.46E-08100024,147 7.99E-075.26E-104.98E-083.45E-0680.9Medium Base Lognormal5.46E-08100032,297 7.14E-075.22E-104.87E-083.17E-0677.9High Base Lognormal5.46E-08100036,221 6.82E-075.20E-104.83E-083.06E-0676.7Notes: (1) Failure rates expressed in failures per weld-year. (2) Exposure expressed in weld-years. (3) DM = Damage Mechanism; SC = stress corrosion cracking; TF = thermal fatigue; DC = design and construction defects.

(4) RF = Range Factor = SQRT (95%tile/5%tile).

Steps 1.6 and 1.7 Apply Mixture Distribution and Sum over applicable DMs*Hot Leg Weld CategoriesCalculation Case Weld Type DM Failure Rate Distribution (failures per weld-year) Mean 5%tile 50%tile 95%tile RF 10/03/11 Pre-Licensing Meeting 221A B-F SC + D&C 2.73E-04 1.04E-04 2.33E-04 5.78E-04 2.4 1B B-J D&C 1.44E-06 5.27E-10 4.12E-08 3.19E-06 77.8 1C TF + D&C 1.07E-05 1.79E-08 5.79E-07 2.83E-05 39.8 Mean Failure Rate Results for STP Class 1 Components10/03/11 Pre-Licensing Meeting 23 Step 2 CRP Development1. Conditional Rupture Probability (CRP) Development P(RxFik) 2.1Select components to define conditional rupture probability (CRP) model categories2.2Obtain expert reference LOCA distributions from NUREG-18292.3 Obtain expert multiplier distributions for 40-yr LOCA frequencies from NUREG-1829 2.4 Determine 40-yr LOCA distributions (product of Steps 2.2 and 2.3) for each expert, fit to lognormal 2.5Determine geometric mean of expert distributions from Step 2.4 (lognormal)10/03/11 Pre-Licensing Meeting 242.6a Benchmark Lydell Base Case Analysis for selected components2.6b Determine failure rate distribution for Lydell Base Case Analysis in NUREG-1829; fit to lognormal 2.6c Apply Lydell CRP model from Base Case Analysis 2.6d Determine LOCA frequency distribution from Lydell Base Case Analysis 2.7 Determine mixture distribution of NUREG-1829 GM (from Step 2.5) and Lydell LOCA frequency (from Step 2.6d to obtain Target LOCA frequency distribution for each CRP category component 2.8 Apply formulas to calculate CRP distributions to be used as prior distributions for each valid combination of CRP category and component 2.9 For each component in a given CRP category, perform Bayes' update with evidence of failure and rupture counts from service data Step-by-Step Procedure 2 of 210/03/11 Pre-Licensing Meeting 25 CRP Model Development*Goal is to make use of NUREG-1829 data in the characterization of epistemic uncertainty*Our technical approach is based on converting LOCA frequencies to CRPs to facilitate separate failure rate treatment-Our method is based on calculating LOCA frequency as the product of a failure rate and a CRP-Failure rate is established independent of NUREG-1829 data in Step 1 for all component ticategories-NUREG-1829 data is used to set target LOCA frequencies for each CRP model to be developed-CRP distributions are derived from target LOCA frequencies using formulas for the product of two lognormal distributions and the Lydell Base Case failure rate distributions *Two distinct sources of NUREG-1829 data-Base case analyses of specific PWR components (hot leg, surge line, HPI line for a specific 3-loop PWR design by Lydell using methodology similar to that being used for STP-Questionnaires provided by 9 experts with estimates of LOCA frequencies vs. break size for many PWR components for the entire fleet of U.S. PWRs10/03/11 Pre-Licensing Meeting 26 Step 2.1 Define CRP Model Categories*The following CRP models are used for all STP model CategoriesoHot Leg CRP modeloCold Leg CRP modeloSurge Line CRP modeloHigh Pressure Injection CRP model*This selection was based on the following considerations:SffiidiNUREG1829diidiifhCRPoSufficient data in NUREG-1829 and supporting input data to support estimation of the CRPsoCategories provide a unique model for all the categories with large pipe sizesoFurther detail in the treatment of smaller pipes is not warranted for this application, nor is it supported by sufficient pipe failure data.oThe SG Inlet categories are a special case of the welds in the hot leg and constitute a separate category solely to capture any "outliers" in the failure rate data. oThe High Pressure Injection CRP category is representative of the medium and small bore pipe with pipe diameter up to 12". They are all stainless steel lines connected to the larger pipe sizes and are subject to a similar range of DMs. Developing variants within this category would not be expected to have different results10/03/11 Pre-Licensing Meeting 27 Application of the CRP Models to the 8 System CategoriesCase Description Weld Type Damage Mechanism (DM) CRP Model and Bayes' Update Evidence 1 RCS Hot Leg Excl. SG Inlet B-F PWSCC, D&C Hot Leg CRP Model, updated with 0 ruptures in 6 failures B-J TF, D&C 2 RCS Cold Leg B-F PWSCC, D&C Cold Leg CRP Model, updated with 0 ruptures in 3 failures B-J D&C 3 RCS Hot Leg SG Inlet B-F PWSCC, D&C Hot Leg CRP Model, updated with 0 ruptures in 19 failures 10/03/11 Pre-Licensing Meeting 284 PZR Surge Line B-F PWSCC, TF, D&C Surge Line CRP Model, updated with 0 ruptures in 3 failures B-J, BC TF, D&C 5 PZR Medium Bore Piping B-F PWSCC, TF, D&C HPI CRP Model, updated with 0 ruptures in 12 failures B-J, BC TF, D&C 6 Class 1 Small Bore Piping B-J TF, D&C, TGSCC, VF HPI CRP Model, updated with 0 ruptures in 106 failures 7 Class 1 Medium Bore SIR Piping B-J TF, D&C, IGSCC HPI CRP Model, updated with 0 ruptures in 14 failures 8 Class 1 Medium Bore CVCS Piping B-J, BC TF, D&C, TGSCC, VF HPI CRP Model Updated with 0 ruptures in 14 failures Steps 2.2 thru 2.5Expert Composite Distributions*Goal is to derive a single composite distribution that represents the inputs provided by 9 experts for LOCA frequencies for key components*Some experts provided asymmetric inputs but most provided symmetric inputs for lower, middle, and upper values*Weinvestigatedtwoapproachesforformingcompositedistributions*We investigated two approaches for forming composite distributions-Mixture Distribution Method; each expert is given equal weight in a sampling scheme in which an expert is selected and then a sample is randomly chosen from a lognormal distribution of LOCA frequency-Geometric Mean Method: a composite distribution is formed by taking the geometric means of two parameters of the experts lognormal distributions: the parameters chosen are the medians and range factors.-Both Methods require the combination of two distributions provided by each expert; one for a reference LOCA frequency and another for multipliers to reflect plant operation for 40 years10/03/11 Pre-Licensing Meeting 29 Treatment of Asymmetric Inputs*Raw data provided by the 9 experts is comprised of a lower value, mid value and upper value with understanding they are treated as the parameters of a lognormal distribution*In most cases the inputs are symmetric, i.e. Upper/Mid = Mid/Lower; in a few cases Mid/Lower > Upper/Mid*InNUREG1829splitlognormaldistributionswereusedtotreatthis*In NUREG-1829 split lognormal distributions were used to treat this asymmetry.*In this study we fit the asymmetric cases to lognormal using two methods: 1. RF = SQRT(Upper/Lower); 2. RF = Upper/Mid. We adopted 2 per recommendation from Dr. Mosleh*We rejected split lognormals as our tools do not support it and we adopted a different approach to treating the lower tails that is applied when we select our target LOCA frequencies10/03/11 Pre-Licensing Meeting 30 Comparison of Geometric Mean and Mixture Distributions for RCS Hot Leg10/03/11 Pre-Licensing Meeting 31 Comparison of Geometric Mean and Mixture Distributions for RCS Surge Line10/03/11 Pre-Licensing Meeting 32 Geometric Mean Composite Distributions Component LOCA Cat. Break Size (Inches) Geometric Mean Distribution ParametersEvents per Reactor-Calendar Year Mean 5%tile 50%tile 95%tile RF Hot Leg 1 0.5 4.08E-07 9.32E-09 1.21E-07 1.57E-06 13.0 2 1.5 1.28E-07 2.25E-09 3.34E-08 4.95E-07 14.8 3 3 6.51E-08 1.01E-09 1.59E-08 2.52E-07 15.8 4 6.75 2.59E-08 2.49E-10 4.96E-09 9.88E-08 19.9 5 14 1.50E-08 6.70E-11 1.90E-09 5.37E-08 28.3 6 31.5 3.16E-09 4.84E-12 2.18E-10 9.78E-09 45.0 1 0.5 1.47E-07 3.27E-09 4.30E-08 5.66E-07 13.2 2 1.55.20E-089.07E-101.35E-08 2.01E-0714.910/03/11 Pre-Licensing Meeting 33Cold Leg 3 3 2.19E-08 3.33E-10 5.31E-09 8.48E-08 16.0 4 6.75 7.85E-09 7.41E-11 1.49E-09 2.99E-08 20.1 5 14 4.54E-09 1.94E-11 5.60E-10 1.62E-08 28.9 6 31.5 1.10E-09 1.56E-12 7.23E-11 3.36E-09 46.4 Surge Line 1 0.5 3.60E-07 1.33E-08 1.34E-07 1.35E-06 10.1 2 1.5 1.26E-07 3.46E-09 4.09E-08 4.83E-07 11.8 3 3 6.45E-08 1.29E-09 1.79E-08 2.49E-07 13.9 4 6.75 1.92E-08 2.47E-10 4.28E-09 7.41E-08 17.3 5 14 2.72E-09 4.22E-11 6.66E-10 1.05E-08 15.8 HPI Line 1 0.5 1.27E-05 6.40E-07 5.45E-06 4.65E-05 8.5 2 1.5 4.58E-06 1.51E-07 1.62E-06 1.74E-05 10.7 3 3 7.21E-07 1.53E-08 2.06E-07 2.78E-06 13.5 4 6.75 1.29E-07 1.41E-09 2.64E-08 4.95E-07 18.8 5 14 3.03E-08 3.30E-10 6.20E-09 1.16E-07 18.8 Step 2.7 Selection of Target LOCA Frequencies*Four Options Considered-*Option 1: use only the Lydell Base Case results -*Option 2: use only the Experts' Mixture Distribution results-*Option 3: use only the Experts' Geometric Mean results

-*Option 4: use a hybrid of the Experts' Geometric Mean and Lydell Base Case resultsOti1jtdbdl1t*Option 1 rejected as based on only 1 expert*Option 2 rejected as too sensitive to extreme values from 2 experts*Option 4 preferred over Option 3 as providing a more complete representation of both model and expert opinion aspects of epistemic Uncertainty*Two methods evaluated for Option 4-Worst case percentile method previously presented to the NRC-Mixture distribution method recommended by Dr. Mosleh as more consistent with established method for combining two distributions (selected)10/03/11 Pre-Licensing Meeting 34 Use of Worst-Case Percentiles from NUREG-1829 GM and Lydell Base Case 10/03/11 Pre-Licensing Meeting 35 Comparison of GM and Mixture of GM and Lydell Base -Hot Leg10/03/11 Pre-Licensing Meeting 36 Comparison of GM and Mixture of GM and Lydell Base -Surge Line10/03/11 Pre-Licensing Meeting 37 Comparison of GM and Mixture of GM and Lydell Base -HPI Line10/03/11 Pre-Licensing Meeting 38 Comparison of Hybrid MethodsSTP Hot Leg Target LOCA Model -Worst Case 5%tile and 95%tileLOCA Cat.Break SizeMean5%tile50%tile95%tileRF10.55.79E-073.55E-098.72E-082.14E-0624.6 21.51.95E-072.10E-101.09E-085.68E-0752.0 331.05E-078.33E-114.89E-092.87E-0758.746.763.75E-083.03E-111.77E-091.03E-0758.346.763.75083.03.7709.030758.35142.02E-081.16E-117.75E-105.17E-0866.8 631.52.41E-095.44E-122.08E-107.94E-0938.2STP Hot Leg Target LOCA Model -Probabilistic Mixture10.55.08E-075.30E-091.05E-071.91E-0619.0 21.59.32E-083.91E-101.46E-083.68E-0730.7 334.54E-081.60E-106.39E-091.76E-0733.1 46.761.64E-085.73E-112.05E-096.32E-0833.2 5148.37E-092.03E-117.64E-102.92E-0837.9 631.51.80E-095.85E-121.80E-105.83E-0931.610/03/11 Pre-Licensing Meeting 39 Selected Approach for Target LOCA Frequencies*Probabilistic mixture of two models-Model 1 Geometric mean of 9 expert distributions*Develop 40 year composite distribution of 9 experts using geometric mean method*Combined lognormal distribution for Current day and 40yr multipliers for each expert preserving median and RF=Upper/Mid*Developed composite distribution based on geometric means of each experts medians and range factors-Model 2 Bengt Lydell Base Case analysis-Results of Models 1 and 2 combined giving equal weight to each yielding a mixture distribution of the two models-This method produces somewhat greater uncertainties than using Model 1 by itself mostly by extending the lower tails of the distributions10/03/11 Pre-Licensing Meeting 40 Step 2.8 Develop CRP Distributions from Target LOCA Distributions*Target LOCA frequency distributions defined as lognormal distributions*CRP distributions assumed to be lognormal distributions10/03/11 Pre-Licensing Meeting 41*Lydell Base Case failure rate distributions fit to lognormal distributions*Formulas based on lognormal properties used to calculate CRP distribution parameters Step 2.8 CRP Distribution ParametersComponentLOCA Category Break Size (in.)Conditional Rupture ProbabilityDistribution ParametersMedian Mean 5th Percentile 95th Percentile Range Factor[1] Hot Leg 1 0.5 1.46E-03 1.84E-04 9.10E-04 4.50E-03 4.9 2 1.5 3.31E-04 1.35E-05 1.29E-04 1.23E-03 9.6 3 3 1.65E-04 5.01E-06 5.61E-05 6.28E-04 11.2 4 6.75 5.74E-05 1.49E-06 1.81E-05 2.20E-04 12.2 5 14 2.49E-05 4.54E-07 6.62E-06 9.65E-05 14.6 6 31.5 5.84E-06 1.06E-07 1.55E-06 2.26E-05 14.6[4]6D[2]44.5 3.20E-06 5.82E-08 8.49E-07 1.24E-05 14.6[4]1 0.5 1.20E-03 1.50E-04 7.48E-04 3.72E-03 5.0 2 1.5 2.74E-04 1.31E-05 1.15E-04 1.00E-03 8.7 3 3 1.13E-04 4.92E-06 4.54E-05 4.18E-04 9.2 10/03/11 Pre-Licensing Meeting 42Cold Leg4 6.753.58E-051.49E-06 1.41E-051.33E-049.55 14 1.59E-05 4.25E-07 5.09E-06 6.10E-05 12.0 6 31.5 4.48E-06 9.17E-08 1.26E-06 1.73E-05 13.7 6D[2]44.5 2.67E-06 4.88E-08 7.10E-07 1.03E-05 14.6 Surge Line 1 0.5 2.08E-02 2.42E-03 1.26E-02 6.53E-02 5.2 2 1.5 7.24E-03 1.40E-04 1.98E-03 2.80E-02 14.1 3 3 3.28E-03 4.68E-05 7.70E-04 1.27E-02 16.4 4 6.75 9.24E-04 1.32E-05 2.17E-04 3.57E-03 16.4[4]5 14 2.30E-04 3.29E-06 5.41E-05 8.90E-04 16.4[4]5D[3]19.81.19E-04 1.70E-06 2.80E-05 4.60E-04 16.4[4]HPI Line 1 0.5 1.08E-02 5.77E-03 1.02E-02 1.80E-02 1.8 2 1.5 3.00E-03 5.27E-04 2.10E-03 8.39E-03 4.0[4]3 3 6.45E-04 1.13E-04 4.53E-04 1.81E-03 4.0 4 6.75 9.67E-05 1.03E-05 5.67E-05 3.11E-04 5.5 5 14 2.27E-05 2.43E-06 1.33E-05 7.30E-05 5.5[4]Notes: [1] Range Factor = SQRT(95%tile/5%tile). [2] 6D corresponds to a double-ended break of a 31.5" pipe. [3] 5D corresponds to a double-ended break of a 14" pipe. [4] Range factors adjusted upwards to ensure no RF decrease with decreasing LOCA frequency.

Comparison of CRP Models for Hot Leg -STP vs. Lydell Base Case10/03/11 Pre-Licensing Meeting 43 Comparison of CRP Models for Surge Line -STP vs. Lydell Base Case10/03/11 Pre-Licensing Meeting 44 Comparison of CRP Models for HPI Line -STP vs. Lydell Base Case10/03/11 Pre-Licensing Meeting 45 Step 2.9 Bayes' Update of CRP Distributions*CRPs from Step 2.8 used as priors*Bayes' update for each of 8 systems using CRP models*Evidence is 0 LOCAs out of number of failures for system*Hot Leg CRP used for Hot leg and SG InletComponent Bayes' Update EidLOCA CategoryBreak Size (in.)Conditional Rupture Probability Distribution Parameters Mean5%tileMedian95%tileRF[1]10/03/11 Pre-Licensing Meeting 46Evidence gy()Mean5%tileMedian 95%tileRFHot Leg 0 Ruptures/ 6 Failures; Hot Leg CRP Model 1 0.5 1.43E-03 1.85E-04 9.04E-04 4.39E-03 4.9 2 1.5 3.28E-04 1.34E-05 1.29E-04 1.23E-03 9.6 3 3 1.64E-04 5.01E-06 5.60E-05 6.25E-04 11.2 4 6.75 5.74E-05 1.48E-06 1.81E-05 2.20E-04 12.2 5 14 2.49E-05 4.53E-07 6.62E-06 9.66E-05 14.6 6 31.5 5.85E-06 1.06E-07 1.55E-06 2.26E-05 14.6 6D[2] 44.5 3.20E-06 5.82E-08 8.49E-07 1.24E-05 14.6 Hot Leg at SG Inlet 0 Ruptures/ 19 Failures; Hot Leg CRP Model 1 0.5 1.39E-03 1.84E-04 8.91E-04 4.25E-03 4.8 2 1.5 3.22E-04 1.34E-05 1.28E-04 1.20E-03 9.5 3 3 1.61E-04 5.00E-06 5.58E-05 6.18E-04 11.1 4 6.75 5.70E-05 1.48E-06 1.81E-05 2.19E-04 12.2 5 14 2.35E-05 4.29E-07 6.26E-06 9.11E-05 14.6 6 31.5 5.84E-06 1.06E-07 1.55E-06 2.26E-05 14.6 6D[2] 44.5 3.20E-06 5.82E-08 8.49E-07 1.24E-05 14.6 Step 3 STP-Specific LOCA Frequencies1. STP-Specific LOCA Frequency Development 3.1 Determine weld counts and pipe sizes for each component - mi3.2 Identify which locations are in and out of the NDE program 3.3 Combine the results of Step 1 and Step 2 for component LOCA frequencies 3.4Apply Markov model to specialize rupture frequencies for NDE or no NDE-Iik3.5Providelocation-by-locationLOCAfrequenciesvs.breaksizetoCASAGRANDE-jx10/03/11 Pre-Licensing Meeting 4735Provide locationbylocation LOCA frequencies vs. break size to CASAGRANDEjx3.6 Provide Small, Medium, and Large LOCA frequencies to RISKMAN - F(LOCAx)

Step 3.3 Combine Failure Rates and CRPs to Produce LOCA Frequencies*Two methods used:-Monte Carlo simulation integrated with failure rate analysis-Use of formulas for combining two lognormal ditibtidistributions*Calculation of total LOCA frequencies based on correlation of CRP model distributions (use of common CRP models)10/03/11 Pre-Licensing Meeting 48 Example Results -Hot Leg B-F Weld at RPV Nozzle10/03/11 Pre-Licensing Meeting 49 Comparison of Mean LOCA Frequencies for Hot Leg Weld Types10/03/11 Pre-Licensing Meeting 50 Form of LOCA Frequencies for CASAGRANDE*Different results for each of 45 component categories*Example results for large pipesCalc. CaseSystemSize Case (in.)DEGB (in.)Weld TypeDM1B1C3CCold Leg27.538.89B-JD&C3BCold LegHot LegHot Leg2941.01B-J1A2941.01B-F38.89B-FSC, D&C2SG Inlet2941.01B-FSC, D&CD&CSC, D&C3143.84B-FSC, D&CCold Leg3A27.5Cold Leg3143.84B-JD&C3DHot Leg2941.01B-JTF, D&C10/03/11 Pre-Licensing Meeting 51No. WeldsX, Break Size (in.)F(LOCA X)X, Break Size (in.)F(LOCA X)X, Break Size (in.)F(LOCA X)X, Break Size (in.)F(LOCA X)X, Break Size (in.)F(LOCA X)X, Break Size (in.)F(LOCA X)X, Break Size (in.)F(LOCA X)X, Break Size (in.)F(LOCA X)0.504.02E-070.501.95E-090.501.25E-080.501.98E-060.501.51E-070.501.51E-070.502.79E-090.502.79E-091.509.25E-081.504.49E-101.502.87E-091.504.59E-071.503.43E-081.503.43E-081.506.33E-101.506.33E-102.006.92E-082.003.36E-102.002.15E-092.003.45E-072.002.38E-082.002.38E-082.004.39E-102.004.39E-103.004.61E-083.002.24E-103.001.43E-093.002.31E-073.001.42E-083.001.42E-083.002.62E-103.002.62E-104.003.19E-084.001.55E-104.009.90E-104.001.60E-074.009.49E-094.009.49E-094.001.75E-104.001.75E-106.001.89E-086.009.19E-116.005.89E-106.009.52E-086.005.39E-096.005.39E-096.009.95E-116.009.95E-116.751.61E-086.757.83E-116.755.01E-106.758.12E-086.754.53E-096.754.53E-096.758.36E-116.758.36E-1114.007.01E-0914.003.40E-1114.002.18E-1014.003.35E-0814.002.01E-0914.002.01E-0914.003.70E-1114.003.70E-1120.003.70E-0920.001.80E-1120.001.15E-1020.001.81E-0820.001.15E-0920.001.15E-0920.002.11E-1120.002.11E-1129.001.90E-0929.009.24E-1229.005.92E-1129.009.57E-0927.506.96E-1027.506.96E-1027.501.28E-1127.501.28E-1131.501.64E-0931.507.97E-1231.505.11E-1131.508.30E-0931.505.63E-1031.505.63E-1031.501.04E-1131.501.04E-1141.011.04E-0941.015.03E-1241.013.22E-1141.015.24E-0938.894.12E-1043.803.38E-1038.897.60E-1243.806.23E-121224144411DEGB Frequency4 STP Results for Initiating Event Frequencies LOCAs from Pipe BreaksLOCA Category[1] Break Size (in.) Point Estimate[2] LOCA Frequency per Reactor-Calendar Year Range Factor[3] Mean 5%tile 50%tile 95%tile Small LOCA 0.5 to 2.0 3.59E-043.54E-041.42E-04 3.11E-047.03E-042.2Medium LOCA 2.0 to 6.0 2.01E-05 2.00E-05 1.44E-06 1.14E-05 6.53E-05 6.7 Large LOCA > 6.0 2.29E-06 2.09E-06 1.80E-07 9.53E-07 7.18E-06 6.3 Category 1 0.5 3.82E-04 3.76E-04 1.57E-04 3.30E-04 7.39E-04 2.2 10/03/11 Pre-Licensing Meeting 52Category 2 1.5 3.91E-05 3.90E-05 7.00E-06 2.37E-05 1.18E-04 4.1 Category 3 3 9.24E-069.09E-061.07E-06 5.04E-062.94E-055.2Category 4 6.75 1.84E-06 1.82E-06 2.00E-07 9.69E-07 5.83E-06 5.4 Category 5 14 4.40E-07 4.31E-07 4.45E-08 2.25E-07 1.39E-06 5.6 Category 6 0.5 4.48E-08 4.50E-08 1.61E-09 1.44E-08 1.65E-07 10.1 Notes: [1] Small, Medium, and Large LOCA categories consistent with STP PRA model; Categories 1-6 defined in NUREG-1829 (see Table 4-1). [2] Point estimate obtained with mean failure rate and CRP lognormal distributions and weld counts.

[3] Range Factor = SQRT(95%tile/5%tile).

Comparison STP Pipe Induced Mean LOCA Frequencies with NUREG-182910/03/11 Pre-Licensing Meeting 53 System Contributions to STP LOCA Category Frequency10/03/11 Pre-Licensing Meeting 54 System Contributions to STP LOCA Initiating Events10/03/11 Pre-Licensing Meeting 55 Contributions to LOCA Category 6 Frequency10/03/11 Pre-Licensing Meeting 56 Comparison of Uncertainties STP Pipe vs. NUREG-1829 Total LOCA Frequency10/03/11 Pre-Licensing Meeting 57 Key Results Demonstrated*The capability to estimate LOCA frequencies as a function of break size at each location.*The capability to utilize information from NUREG-1829 to characterize epistemic uncertainty associated with LOCA frequencies.*A method that incorporates via Bayes' uncertainty analysis the service data on pipe failures and component exposures.*A quantification of epistemic uncertainties associated with estimating the input parameters in the model equations, including both parametric and modeling sources of uncertainty.*The capability to quantify the impacts of information on degradation mechanism susceptibility at each location, based on insights from service data and results of RI-ISI evaluation.10/03/11 Pre-Licensing Meeting 58 Major Tasks for 2012*Non-isolatable LOCAs caused by failures of non-pipe components need to be addressed. These include control rod drive standpipes, instrument lines, and other components welded to the reactor pressure vessel, pump and valve bodies, pressurizer safety and relief valve leaks, and reactor coolant pump seals.*Isolatable LOCAs need to be addressed. These involve failures in Class 2 piping systems that can be isolated, including CVCS charging and letdown lines, RCP seal return lines, etc.*Pipebreaksinsteamandfeedwaterlinesinsidethecontainmentthatcouldgenerate*Pipe breaks in steam and feed-water lines inside the containment that could generate debris and lead to a need for recirculation cooling and/or containment spray actuation need to be addressed.*Execution of Step 3.4 to apply the Markov model to evaluate the impact of inspected and non-inspected NDE locations on the LOCA frequencies needs to be completed.*The current study is based on rough estimates of weld counts and pipe sizes for small bore pipes. If small bore pipes are found to contribute significantly to the risk of debris-induced ECCS failures, more detailed review of the small bore piping configurations needs to be completed.10/03/11 Pre-Licensing Meeting 59