ML112770203

Licensee Slides from 10/3/11 Meeting LOCA Frequencies, Final Results

ML112770203
Person / Time
Site:	South Texas
Issue date:	10/03/2011
From:	Kreslyon Fleming, Lydell B South Texas
To:	Balwant Singal 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 2011 Risk Informed GSI-191 Resolution M d Monday, A Augustt 22,22 2011 1:00 pm - 4:30 p.m EDT Public Meeting with STP Nuclear Operating Company Karl N. Fleming KNF Consulting Services LLC Bengt O. Y. Lydell 10/03/11 Pre-Licensing Meeting 1

Risk Informed GSI-191 Discussion Topics

• Briefing on Final Results for 2011

• Review of technical approach with focus on recent refinements

• Highlights of Results

- Component level for CASAGRANDE

- Total LOCA frequencies for RISKMAN

- Comparison with NUREG-1829

• Issues to Complete in 2012 10/03/11 Pre-Licensing Meeting 2

Risk Informed GSI-191 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 effectiveness

- Other break characteristics, characteristics e e.g.

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 workshops 3 10/03/11 Pre-Licensing Meeting

Current Status

• Defined homogenous pipe failure rate categories

• Refined method for deriving conditional rupture probabilities vs. break size

• Obtained 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 Mosleh 10/03/11 Pre-Licensing Meeting 4

Acronyms ASME American Society of Mechanical Engineers NPS Nominal Pipe Size B-J ASME Section XI Similar Metal Weld PRA Probabilistic Risk Assessment B-F ASME Section XI Bimetallic Weld PWR Pressurized Water Reactor BC Branch Connection Weld PWSCC Primary Water Stress Corrosion Cracking CRP Conditional Rupture Probability PZR Pressurizer CVCS Chemical Volume and Control System RCS Reactor Coolant System D&C Design and Construction Defects RI-ISI Risk Informed Inservice Inspection DEGB D bl EEnded Double d dGGuillotine ill ti BBreakk SB Small Bore DM Damage (Degradation)Mechanism SIR Safety Injection and Recirculation Systems ECCS Emergency Core Cooling System EPRI Electric Power Research Institute TASC Thermal Stratification GM Geometric Mean TF Thermal Fatigue GSI Generic Safety Issue TT Thermal Transients HPI High Pressure Injection SC Stress Corrosion Cracking IGSCC Intergranular Stress Corrosion Cracking TGSCC Transgranular Stress Corrosion Cracking LOCA Loss of Coolant Accident VF Vibration fatigue 10/03/11 Pre-Licensing Meeting 5

Pipe Rupture Model F ( LOCAx ) = mi ix (2.1) i ix = ik P( Rx Fik ) I ik (2.2) k where:

F ( LOCAx ) = Frequency of LOCA of size x, per reactor calendar-year, subject to epistemic uncertainty calculated via Monte Carlo mi = Number of pipe welds of type i; each type determined by pipe size, weld type, type applicable damage mechanisms, mechanisms and inspection status (leak test and NDE); no significant uncertainty ix = Frequency of rupture of component type i with 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 P( Rx Fik ) = Conditional probability of rupture of size x given failure of pipe component type i due to damage mechanism k, subject to epistemic uncertainty determined via expert elicitation using NUREG-1829 data I ik = Integrity management factor for weld type i and failure mechanism k, subject to epistemic uncertainty determined by Monte Carlo and Markov model 10/03/11 Pre-Licensing Meeting 6

Step-by-Step Procedure1 of 2 10/03/11 Pre-Licensing Meeting 7

Step-by-Step Procedure 2 of 2 10/03/11 Pre-Licensing Meeting 8

Step 1 Failure Rate Development

1. 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) 15 1.5 Perform Bayes Bayes update for each exposure case (combination of weld count case and DM susceptibility [DMS] case) 1.6 Develop mixture distribution to combine results for different exposure hypotheses to yield conditional failure rate distributions ik given STP-specific applicable DMs 1.7 Calculate total failure rate over all applicable damage mechanisms - ik 10/03/11 Pre-Licensing Meeting 9

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 STP 10/03/11 Pre-Licensing Meeting 10

Homogeneous Pipe Failure Case Description Rate Cases Weld Type Damage Mechanism (DM) Comment 1 RCS Hot Leg Excl. SG B-F PWSCC, D&C Design basis LOCA location; B-F weld has Inlet higher failure rate but located inside Rx B-J TF, D&C cavity 2 RCS Cold Leg B-F PWSCC, D&C Lower temperatures and different pipe sizes relative to hot leg B-J D&C 3 RCS Hot Leg SG Inlet B-F PWSCC, D&C This case defined to address S/G Inlet nozzle-to-safe-end weld that has unusual failure count distribution[1]

4 PZR Surge Line B-F PWSCC, TF, D&C Includes surge line from branch connections and nozzles to pressurizer safe end; entire B-J, BC TF, D&C surge line subjected to thermal transients during startup and shutdown 5 PZR Medium Bore Piping B-F PWSCC, TF, D&C This includes pressurizer spray, and relief valve piping excluding the pressurizer surge line; B-F welds at STP in this category have B-J, BC TF, D&C weld overlays[2]

6 Class 1 Small Bore Piping B-J TF, D&C, TGSCC, VF This is all the Class 1 piping of size 2" and less and inside isolation valves 7 Class 1 Medium Bore SIR B-J TF, D&C, IGSCC Safety injection and residual heat removal Piping (RHR) systems in standby during normal operation; Class 1 is inside the isolation valves 8 Class 1 Medium Bore B-J, BC TF, D&C, TGSCC, VF CVCS piping with injection and letdown flow CVCS Piping during normal operation 10/03/11 Pre-Licensing Meeting 11

Component Categories 1 of 3 STP System Component Weld Total Pipe Size DEGB System Applicable DM Case Case Type No. of (in.) Size (in.)

Welds 1A B-F SC, D&C 4 29 41.0 1 RC Hot Leg 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 3A B-F 4 27.5 38.9 SC, D&C 3B B-J 4 31 43.8 3 RC Cold Leg 3C B-J 12 27.5 38.9 D&C 3D B-J 24 31 43.8 4A B-F SC, TF, D&C 1 16 22.6 4B B-J 7 16 22.6 4 RC Surge 4C BC TF, D&C 2 16 22.6 4D B-J 6 2.5 3.5 10/03/11 Pre-Licensing Meeting 12

Component Categories 2 of 3 STP System Component Weld Total Pipe Size DEGB System Applicable DM Case Case Type No. of (in.) Size (in.)

Welds 5A B-J 29 6 8.5 TF, D&C 5B B-J 14 3 4.2 5C B-J 53 4 5.7 5D BJ B-J D&C 4 3 42 4.2 5E B-J 29 6 8.5 5 PZR 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 6A B-J 16 2 2.8 6 Small Bore VF, SC, D&C 6B B-J 193 1 1.4 10/03/11 Pre-Licensing Meeting 13

Component Categories 3 of 3 STP System Component Weld Total Pipe Size DEGB System Applicable DM Case Case Type No. of (in.) Size (in.)

Welds 7A B-J 21 12 17.0 TF, D&C 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 SIR Lines Excl. 7F B-J 30 10 14.1 Accumulator 7G B-J, BC 42 8 11.3 7 7H B-J 23 6 8.49 D&C 7I 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 7M B-J SC, D&C 0 12 17.0 Accumulator 7N B-J TF, D&C 35 12 17.0 Lines 7O B-J, BC D&C 15 12 17.0 8A B-J 10 2 2.8 TF, VF, D&C 8B B-J 19 4 5.7 8 CVCS 8C B-J 47 2 2.8 VF, D&C 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 10/03/11 Pre-Licensing Meeting 14

Step 1.2 Failure Data Query System Event Nominal Failure Count by DM - Weld Locations System Case Type Pipe Size Totals D&C SC PWSCC TF V-F RCS Hot Leg Crack 32" 5 5 1

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 PZR-PORV Crack 4" ø 10" 2 2 PZR-SPRAY Crack 4" ø 10" 2 2 5 PZR-SPRAY Leak 4" ø 10" 1 1 PZR-SRV Crack 4" ø 10" 6 1 5 PZR SRV PZR-SRV Leak 4" ø 10" 1 1 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 6 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 Safety Injection Crack 4" ø 12" 3 1 2 7 Safety Injection Leak 4" ø 12" 3 3 RHR Crack 4" ø 12" 1 1 CVCS Crack 2" ø 4" 1 1 8

CVCS Leak 2" ø 4" 6 1 5 Total 163 23 21 46 9 64 10/03/11 Pre-Licensing Meeting 15

PIPExp Database 10/03/11 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 Welds NPS29 Weld Population PWR Plant B-F B-J Type B-F Welds B-J Welds Welds/loop 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 10/03/11 Pre-Licensing Meeting 17

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 p category g y is susceptible to DMs (e.g. TF and SC)

• DM Assessment for Hot Leg Welds Calc. Confidence Weld Susceptibility Fractions System Location Case Level C-F D&C ECSCC Fretting IGSCC PWSCC TF TGSCC VF Low N/A 1 N/A N/A N/A 1 N/A N/A N/A B-F (Un-1A Medium N/A 1 N/A N/A N/A 1 N/A N/A N/A mitigated)

High N/A 1 N/A N/A N/A 1 N/A N/A N/A RC Hot Leg Low N/A 1 N/A N/A N/A N/A 0.01 N/A N/A 1B, 1C B-J 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 10/03/11 Pre-Licensing Meeting 18

Uncertainty Model for Hot Leg B-J Welds Subject to Thermal Fatigue 10/03/11 Pre-Licensing Meeting 19

Summary of Component Exposure Estimates System Component Weld Best Upper Lower System Case Case Type Estimate Bound Bound 1A B-F 21,732 24,147 12,074 1 RCS Hot Leg 1B, 1C B-J 32,297 36,221 24,147 2 RCS SG Inlet 2 B-F 12,074 12,074 12,074 3A B-F 22,315 24,794 12,397 3 RCS Cold Leg 3B B-J 123,764 177,279 99,177 4A B-FF B 3,914 3,914 3,914 4 RCS Surge 4B B-J 27,007 54,013 13,503 4C BC 7,828 7,828 7,828 5A-5D B-J 351,127 496,158 286,245 5 PZR 5E-5G B-F 19,083 19,083 19,083 6 SB 6A-6B B-J 744,237 1,144,980 366,394 SIR Lines Excl. Accumulator 7A-7L B-J 590,797 637,190 507,518 7

SIR Accumulator Lines 7M-7O B-J 175,067 277,693 132,810 8A-8D B-J 562,348 627,324 403,018 8 CVCS 8E, 8F BC 81,393 90,797 58,332 Total Estimated Weld-Yrs 2,774,983 3,633,494 1,958,513 10/03/11 Pre-Licensing Meeting 20

Steps 1.4 and 1.5 Select Priors and Perform Bayes Updates - Hot Leg Welds Weld Type and Weld Count DM Prior Distribution(1) Evidence(2) Bayes Posterior Distribution(1)

Susceptibility DM(3) Case Type Median RF Failures Exposure Mean 5%tile 50%tile 95%tile RF(4)

Case Low Base Lognormal 8.48E-07 100 6 12,074 4.32E-04 1.78E-04 4.05E-04 7.78E-04 2.1 Hot Leg B-F SC Medium Base Lognormal 8.48E-07 100 6 21,732 2.43E-04 1.01E-04 2.29E-04 4.37E-04 2.1 High Base Lognormal 8.48E-07 100 6 24,147 2.20E-04 9.10E-05 2.06E-04 3.94E-04 2.1 Low Base Lognormal 5.46E-08 100 0 12,074 1.02E-06 5.34E-10 5.16E-08 4.05E-06 87.1 Hot Leg B-F DC Medium Base Lognormal 5.46E-08 100 0 21,732 8.31E-07 5.28E-10 5.01E-08 3.54E-06 81.9 High Base Lognormal 5.46E-08 100 0 24,147 8.31E-07 5.28E-10 5.01E-08 3.54E-06 81.9 Low Low Lognormal 2.66E-07 100 0 241 8.88E-06 2.65E-09 2.64E-07 2.53E-05 97.6 Medium Low Lognormal 2.66E-07 100 0 323 8.41E-06 2.65E-09 2.63E-07 2.49E-05 97.0 High Low Lognormal 2.66E-07 100 0 362 8.22E-06 2.65E-09 2.63E-07 2.47E-05 96.7 Low Medium Lognormal 2.66E-07 100 0 483 7.74E-06 2.64E-09 2.62E-07 2.43E-05 95.8 Hot Leg B-J TF Medium Medium Lognormal 2.66E-07 100 0 646 7.25E-06 2.64E-09 2.61E-07 2.37E-05 94.8 High Medium Lognormal 2.66E-07 100 0 724 7.05E-06 2.64E-09 2.60E-07 2.35E-05 94.3 Low High Lognormal 2.66E-07 100 0 1,932 5.38E-06 2.61E-09 2.54E-07 2.06E-05 88.9 Medium High Lognormal 2.66E-07 100 0 2,584 4.90E-06 2.60E-09 2.51E-07 1.96E-05 86.7 High High Lognormal 2.66E-07 100 0 2,898 4.72E-06 2.59E-09 2.50E-07 1.91E-05 85.8 Low Base Lognormal 5.46E-08 100 0 24,147 7.99E-07 5.26E-10 4.98E-08 3.45E-06 80.9 Hot Leg B-J DC Medium Base Lognormal 5.46E-08 100 0 32,297 7.14E-07 5.22E-10 4.87E-08 3.17E-06 77.9 High Base Lognormal 5.46E-08 100 0 36,221 6.82E-07 5.20E-10 4.83E-08 3.06E-06 76.7 Notes:

(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).

10/03/11 Pre-Licensing Meeting 21

Steps 1.6 and 1.7 Apply Mixture Distribution and Sum over applicable DMs

• Hot Leg Weld Categories Calculation Weld Failure Rate Distribution (failures per weld-year)

DM Case Type Mean 5%tile 50%tile 95%tile RF 1A B-F SC + D&C 2.73E-04 1.04E-04 2.33E-04 5.78E-04 2.4 1B D&C 1.44E-06 5.27E-10 4.12E-08 3.19E-06 77.8 B-J 1C TF + D&C 1.07E-05 1.79E-08 5.79E-07 2.83E-05 39.8 10/03/11 Pre-Licensing Meeting 22

Mean Failure Rate Results for STP Class 1 Components 10/03/11 Pre-Licensing Meeting 23

Step 2 CRP Development

1. Conditional Rupture Probability (CRP) Development P(RxFik) 2.1 Select components to define conditional rupture probability (CRP) model categories 2.2 Obtain expert reference LOCA distributions from NUREG-1829 2.3 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 2.5 Determine geometric mean of expert distributions from Step 2.4 (lognormal) 2.6a Benchmark Lydell Base Case Analysis for selected components 2.6b 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 10/03/11 Pre-Licensing Meeting 24

Step-by-Step Procedure 2 of 2 10/03/11 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 categories t i

- 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. PWRs 10/03/11 Pre-Licensing Meeting 26

Step 2.1 Define CRP Model Categories

• The following CRP models are used for all STP model Categories o Hot Leg CRP model o Cold Leg CRP model o Surge Line CRP model o High Pressure Injection CRP model

• This selection was based on the following considerations:

o Sufficient S ffi i d data iin NUREG NUREG-1829 1829 andd supporting i iinput ddata to support estimation i i off the h CRPs CRP o Categories provide a unique model for all the categories with large pipe sizes o Further detail in the treatment of smaller pipes is not warranted for this application, nor is it supported by sufficient pipe failure data.

o The 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.

o The 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 results 10/03/11 Pre-Licensing Meeting 27

Application of the CRP Models to the 8 System Categories Damage Case Description Weld Type CRP Model and Bayes Update Evidence Mechanism (DM)

RCS Hot Leg Excl. B-F PWSCC, D&C Hot Leg CRP Model, 1

SG Inlet updated with 0 ruptures in 6 failures B-J TF, D&C B-F PWSCC, D&C Cold Leg CRP Model, 2 RCS Cold Leg updated with 0 ruptures in 3 failures B-J D&C RCS Hot Leg SG Hot Leg CRP Model, 3 B-F PWSCC, D&C Inlet updated with 0 ruptures in 19 failures B-F PWSCC, TF, D&C Surge Line CRP Model, 4 PZR Surge Line updated with 0 ruptures in 3 failures B-J, BC TF, D&C PZR Medium Bore B-F PWSCC, TF, D&C HPI CRP Model, 5

Piping updated with 0 ruptures in 12 failures B-J, BC TF, D&C Class 1 Small Bore HPI CRP Model, 6 B-J TF, D&C, TGSCC, VF Piping updated with 0 ruptures in 106 failures Class 1 Medium HPI CRP Model, 7 B-J TF, D&C, IGSCC Bore SIR Piping updated with 0 ruptures in 14 failures Class 1 Medium HPI CRP Model 8 B-J, BC TF, D&C, TGSCC, VF Bore CVCS Piping Updated with 0 ruptures in 14 failures 10/03/11 Pre-Licensing Meeting 28

Steps 2.2 thru 2.5 Expert 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

• 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 years 10/03/11 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

• In NUREG-1829 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 frequencies 10/03/11 Pre-Licensing Meeting 30

Comparison of Geometric Mean and Mixture Distributions for RCS Hot Leg 10/03/11 Pre-Licensing Meeting 31

Comparison of Geometric Mean and Mixture Distributions for RCS Surge Line 10/03/11 Pre-Licensing Meeting 32

Geometric Mean Composite Distributions LOCA Break Geometric Mean Distribution Parameters Component Size Events per Reactor-Calendar Year Cat.

(Inches) Mean 5%tile 50%tile 95%tile RF 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 Hot Leg 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 1.5 5.20E-08 9.07E-10 1.35E-08 2.01E-07 14.9 3 3 2.19E-08 3.33E-10 5.31E-09 8.48E-08 16.0 Cold Leg 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 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 Surge Line 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 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 HPI Line 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 10/03/11 Pre-Licensing Meeting 33

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 results

• O Option ti 1 rejected j t d as b based d on only l 1 expertt

• 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 Leg 10/03/11 Pre-Licensing Meeting 36

Comparison of GM and Mixture of GM and Lydell Base - Surge Line 10/03/11 Pre-Licensing Meeting 37

Comparison of GM and Mixture of GM and Lydell Base - HPI Line 10/03/11 Pre-Licensing Meeting 38

Comparison of Hybrid Methods STP Hot Leg Target LOCA Model - Worst Case 5%tile and 95%tile LOCA Cat. Break Size Mean 5%tile 50%tile 95%tile RF 1 0.5 5.79E-07 3.55E-09 8.72E-08 2.14E-06 24.6 2 1.5 1.95E-07 2.10E-10 1.09E-08 5.68E-07 52.0 3 3 1.05E-07 8.33E-11 4.89E-09 2.87E-07 58.7 4 6.76 3.75E-08 3.75 08 3.03E-11 3.03 1.77E-09

.77 09 1.03E-07

.03 07 58.3 5 14 2.02E-08 1.16E-11 7.75E-10 5.17E-08 66.8 6 31.5 2.41E-09 5.44E-12 2.08E-10 7.94E-09 38.2 STP Hot Leg Target LOCA Model - Probabilistic Mixture 1 0.5 5.08E-07 5.30E-09 1.05E-07 1.91E-06 19.0 2 1.5 9.32E-08 3.91E-10 1.46E-08 3.68E-07 30.7 3 3 4.54E-08 1.60E-10 6.39E-09 1.76E-07 33.1 4 6.76 1.64E-08 5.73E-11 2.05E-09 6.32E-08 33.2 5 14 8.37E-09 2.03E-11 7.64E-10 2.92E-08 37.9 6 31.5 1.80E-09 5.85E-12 1.80E-10 5.83E-09 31.6 10/03/11 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 distributions 10/03/11 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 distributions

• Lydell Base Case failure rate distributions fit to lognormal distributions

• Formulas based on lognormal properties used to calculate CRP distribution parameters 10/03/11 Pre-Licensing Meeting 41

Step 2.8 CRP Distribution Parameters Conditional Rupture Probability Distribution Parameters LOCA Break Component 5th 95th Range Category Size (in.) Median Mean Percentile Percentile Factor[1]

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 Hot Leg 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

[4]

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 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 Cold Leg 4 6.75 3.58E-05 1.49E-06 1.41E-05 1.33E-04 9.5 5 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 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]

Surge Line 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] 19.8 1.19E-04 1.70E-06 2.80E-05 4.60E-04 16.4 1 0.5 1.08E-02 5.77E-03 1.02E-02 1.80E-02 1.8

[4]

HPI Line 2 1.5 3.00E-03 5.27E-04 2.10E-03 8.39E-03 4.0 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

[4]

5 14 2.27E-05 2.43E-06 1.33E-05 7.30E-05 5.5 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.

10/03/11 Pre-Licensing Meeting 42

Comparison of CRP Models for Hot Leg -

STP vs. Lydell Base Case 10/03/11 Pre-Licensing Meeting 43

Comparison of CRP Models for Surge Line

- STP vs. Lydell Base Case 10/03/11 Pre-Licensing Meeting 44

Comparison of CRP Models for HPI Line

- STP vs. Lydell Base Case 10/03/11 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 Inlet Bayes Conditional Rupture Probability Distribution Parameters LOCA Break Component Update g y Category Size ((in.)) Mean 5%tile Median 95%tile RF

[1]

E id Evidence 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 0 Ruptures/ 3 3 1.64E-04 5.01E-06 5.60E-05 6.25E-04 11.2 6 Failures; Hot Leg 4 6.75 5.74E-05 1.48E-06 1.81E-05 2.20E-04 12.2 Hot Leg CRP Model 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

[2]

6D 44.5 3.20E-06 5.82E-08 8.49E-07 1.24E-05 14.6 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 0 Ruptures/ 3 3 1.61E-04 5.00E-06 5.58E-05 6.18E-04 11.1 Hot Leg at SG 19 Failures; 4 6.75 5.70E-05 1.48E-06 1.81E-05 2.19E-04 12.2 Inlet Hot Leg CRP Model 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

[2]

6D 44.5 3.20E-06 5.82E-08 8.49E-07 1.24E-05 14.6 10/03/11 Pre-Licensing Meeting 46

Step 3 STP-Specific LOCA Frequencies

1. STP-Specific LOCA Frequency Development 3.1 Determine weld counts and pipe sizes for each component - mi 3.2 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 3.4 Apply Markov model to specialize rupture frequencies for NDE or no NDE - Iik 3.5 3 5 Provide location by location LOCA frequencies vs. break size to CASAGRANDE - jx location-by-location 3.6 Provide Small, Medium, and Large LOCA frequencies to RISKMAN - F(LOCAx) 10/03/11 Pre-Licensing Meeting 47

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 di t ib ti distributions

• 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 Nozzle 10/03/11 Pre-Licensing Meeting 49

Comparison of Mean LOCA Frequencies for Hot Leg Weld Types 10/03/11 Pre-Licensing Meeting 50

Form of LOCA Frequencies for CASAGRANDE

• Different results for each of 45 component categories

• Example results for large pipes Calc. Case 1A 1B 1C 2 3A 3B 3C 3D System Hot Leg Hot Leg Hot Leg SG Inlet Cold Leg Cold Leg Cold Leg Cold Leg Size Case (in.) 29 29 29 29 27.5 31 27.5 31 DEGB (in.) 41.01 41.01 41.01 41.01 38.89 43.84 38.89 43.84 Weld Type B-F B-J B-J B-F B-F B-F B-J B-J DM SC, D&C D&C TF, D&C SC, D&C SC, D&C SC, D&C D&C D&C No. Welds 4 11 1 4 4 4 12 24 X, Break Size X, Break Size X, Break Size X, Break Size X, Break Size X, Break Size X, Break X, Break (in.) F(LOCA X) (in.) F(LOCA X) (in.) F(LOCA X) (in.) F(LOCA X) (in.) F(LOCA X) (in.) F(LOCA X) Size (in.) F(LOCA X) Size (in.) F(LOCA X) 0.50 4.02E-07 0.50 1.95E-09 0.50 1.25E-08 0.50 1.98E-06 0.50 1.51E-07 0.50 1.51E-07 0.50 2.79E-09 0.50 2.79E-09 1.50 9.25E-08 1.50 4.49E-10 1.50 2.87E-09 1.50 4.59E-07 1.50 3.43E-08 1.50 3.43E-08 1.50 6.33E-10 1.50 6.33E-10 2.00 6.92E-08 2.00 3.36E-10 2.00 2.15E-09 2.00 3.45E-07 2.00 2.38E-08 2.00 2.38E-08 2.00 4.39E-10 2.00 4.39E-10 3.00 4.61E-08 3.00 2.24E-10 3.00 1.43E-09 3.00 2.31E-07 3.00 1.42E-08 3.00 1.42E-08 3.00 2.62E-10 3.00 2.62E-10 4.00 3.19E-08 4.00 1.55E-10 4.00 9.90E-10 4.00 1.60E-07 4.00 9.49E-09 4.00 9.49E-09 4.00 1.75E-10 4.00 1.75E-10 6.00 1.89E-08 6.00 9.19E-11 6.00 5.89E-10 6.00 9.52E-08 6.00 5.39E-09 6.00 5.39E-09 6.00 9.95E-11 6.00 9.95E-11 6.75 1.61E-08 6.75 7.83E-11 6.75 5.01E-10 6.75 8.12E-08 6.75 4.53E-09 6.75 4.53E-09 6.75 8.36E-11 6.75 8.36E-11 14.00 7.01E-09 14.00 3.40E-11 14.00 2.18E-10 14.00 3.35E-08 14.00 2.01E-09 14.00 2.01E-09 14.00 3.70E-11 14.00 3.70E-11 20.00 3.70E-09 20.00 1.80E-11 20.00 1.15E-10 20.00 1.81E-08 20.00 1.15E-09 20.00 1.15E-09 20.00 2.11E-11 20.00 2.11E-11 29.00 1.90E-09 29.00 9.24E-12 29.00 5.92E-11 29.00 9.57E-09 27.50 6.96E-10 27.50 6.96E-10 27.50 1.28E-11 27.50 1.28E-11 31.50 1.64E-09 31.50 7.97E-12 31.50 5.11E-11 31.50 8.30E-09 31.50 5.63E-10 31.50 5.63E-10 31.50 1.04E-11 31.50 1.04E-11 41.01 1.04E-09 41.01 5.03E-12 41.01 3.22E-11 41.01 5.24E-09 38.89 4.12E-10 43.80 3.38E-10 38.89 7.60E-12 43.80 6.23E-12 DEGB Frequency 10/03/11 Pre-Licensing Meeting 51

STP Results for Initiating Event Frequencies LOCAs from Pipe Breaks LOCA Break Point LOCA Frequency per Reactor-Calendar Year Range

[1] [2] [3]

Category Size (in.) Estimate Mean 5%tile 50%tile 95%tile Factor Small LOCA 0.5 to 2.0 3.59E-04 3.54E-04 1.42E-04 3.11E-04 7.03E-04 2.2 Medium 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 Category 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-06 9.09E-06 1.07E-06 5.04E-06 2.94E-05 5.2 Category 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).

10/03/11 Pre-Licensing Meeting 52

Comparison STP Pipe Induced Mean LOCA Frequencies with NUREG-1829 10/03/11 Pre-Licensing Meeting 53

System Contributions to STP LOCA Category Frequency 10/03/11 Pre-Licensing Meeting 54

System Contributions to STP LOCA Initiating Events 10/03/11 Pre-Licensing Meeting 55

Contributions to LOCA Category 6 Frequency 10/03/11 Pre-Licensing Meeting 56

Comparison of Uncertainties STP Pipe vs.

NUREG-1829 Total LOCA Frequency 10/03/11 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.

• Pipe breaks in steam and feed feed-water 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