ML15139A508

May 21, 2015, Public Meeting with Vogtle Regarding GSI-191 Resolution Plan and Current Status

ML15139A508
Person / Time
Site:	Vogtle
Issue date:	05/21/2015
From:	Southern Co
To:	Martin R Plant Licensing Branch II
Martin R
References
Download: ML15139A508 (62)

Text

VOGTLE GSI-191 RESOLUTION PLAN AND CURRENT STATUS NRC PUBLIC MEETING MAY 21, 2015

AGENDA

• Introductions

• Meeting Objectives

• Overview of Resolution Methodology

• Example Calculations

• Quality Assurance

• Conclusions

• Staff Questions and Concerns 2

MEETING OBJECTIVES

• Obtain staff feedback on the overall GSI-191 resolution path for Vogtle

• Describe change in strainer head loss strategy (currently planning to use 2009 head loss test results)

• Discuss use of deterministic vs. best estimate inputs in the evaluation

• Provide additional information on treatment of unqualified coatings (follow-up to November 2014 NRC meeting discussion) 3

OVERVIEW OF METHODOLOGY

• Resolution plan modified based on recent changes in South Texas Project (STP) pilot plant methodology

• No longer planning to perform head loss testing to develop a rule-based head loss model (as presented to the NRC in November 2014)

• Conventional and chemical head loss for break-specific debris loads will be determined based on 2009 Vogtle head loss testing

• Will continue to quantify risk by evaluating conditional probability of GSI-191 failures for different equipment configurations

• Will also continue to use best-estimate inputs for some parameters in the GSI-191 Risk-Informed Software 4

BEST-ESTIMATE INPUTS

• Containment temperature

• Pool temperature

• Containment Spray (CS) activation

• Pool volume/level

• Pool pH

• Emergency Core Cooling System (ECCS) flow rates

• Unqualified Coatings (UQC)failure

• Debris transport fractions

• Aluminum corrosion

• Calcium and aluminum precipitation

• Strainer geometry

• Net Positive Suction Head (NPSH) margin 5

VOGTLE PLANT LAYOUT

• Westinghouse 4-loop PWR (3,626 MWt per unit)

• Large dry containment

• Two redundant ECCS and CS trains

• Each train has an RHR pump, a high head pump, an intermediate head SI pump, and a CS pump

• SI and high head pumps piggyback off of the RHR pump

• Maximum (runout) flow rates:

• RHR 4,500 gpm/pump

• CS 3,200 gpm/pump

• Two redundant containment air cooling trains 6

STRAINER ARRANGEMENT

• Two RHR and CS pumps each with their own strainer

• Each strainer is similar with four stacks of disks

• RHR strainer: 18-disk tall, 765 ft2, height of 5.6 ft

• CS strainer: 14-disk tall, RHR B 590 ft2, height of 4.6 ft

• Perforated plate with CS B 3/32 diameter holes CS A RHR A 7

PLANT RESPONSE TO LOCAS

• Plant 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 pumps

• Containment spray is initiated from the RWST via CS pumps (hot leg breaks larger than 15 inches)

• RHR pumps switched to cold leg recirculation at RWST lo-lo alarm

• CS pumps switched to recirculation at RWST empty alarm

• CS pumps secured at least 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after start of recirculation

• RHR 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 />

• Containment conditions are break-specific

• Break flow rate

• Pool volume/level

• Pool temperature

• Containment pressure (Containment Spray Actuation Setpoint Reached?)

• Containment temperature

• Pool pH 8

BEST-ESTIMATE FLOW RATE

• Flow rates determined from best-estimate thermal-hydraulic modeling using RELAP5/MELCOR Break Size Injection CL Recirculation HL Recirculation (in) (gpm) (gpm) (gpm) 3 2,914 2,591 2,287 6 6,420 5,801 5,361 8 7,358 6,903 5,875 15 8,367 7,490 6,242 27.5 8,396 7,615 6,293 29 8,461 7,595 6,278 All flow rates based on two train operation 9

CONTAINMENT POOL WATER LEVEL

• Sump pool depth is evaluated on a break-specific basis

• The evaluation considers break location and size for the appropriate contribution of RWST, RCS and SI accumulators to pool level

• The resulting sump pool depth ranges between 3.5 ft and 9.1 ft during sump recirculation

• 3.5 ft - Minimum water level 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> after an SBLOCA

• 9.1 ft - Maximum water level at CS switchover to recirculation for an LBLOCA 10

BEST-ESTIMATE POOL TEMPERATURE 300 3" Break 3" Recirc Pool Temperature (°F) 6" Break 250 8" Break 15" Break DEGB of Primary Piping 200 DEGB Recirc 150 100 0 2 4 6 8 10 12 Time (hour)

Note that the 3 break temperature profile is artificially high because manual actions were not modeled, and the lower flow rates for a 3 11 break result in less energy transfer to the ultimate heat sink

BEST-ESTIMATE CONTAINMENT PRESSURE 25 3" Break Containment Pressure (psig) 3" Recirc 20 6" Break 8" Break 15" Break 15 DEGB of Primary Piping DEGB Recirc 10 5

0 0 2 4 6 8 10 12 Time (hour) 12

POOL TEMPERATURE COMPARISON 13

CONTAINMENT PRESSURE COMPARISON

• Curves illustrate the basis for containment spray actuation logic

• For 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 less 14

CONTAINMENT POOL pH

• Sump pool and spray pH is evaluated on a break-specific basis

• The evaluation considers the best-estimate, time-dependent addition of RCS, Accumulator, and RWST water volumes, best estimate boric acid concentrations, and the estimated TSP dissolution rate

• pH is calculated as a function of boric acid and TSP concentrations using Visual MINTEQ

• Best Estimate pH: ~7.2 @ room temperature 15

DEBRIS GENERATION

• Insulation and qualified coatings

• Automated analysis with containment CAD model

• Calculate quantity and size distribution for each type of debris

• Partial breaks from 1/2 inch to double-ended guillotine breaks (DEGBs) for all Class 1 welds in containment

• ZOIs consistent with deterministic approach Nukon 17D Qualified Epoxy & IOZ with Epoxy topcoat 4D Interam Fire Barrier Material 11.7D

• Unqualified coatings and latent debris quantities are identical for all breaks 16

INSULATION AND QUALIFIED COATINGS QUANTITIES

• Debris quantities vary significantly across the range of possible breaks, and are calculated for each break

• Nukon: 0 ft3 to 2,229 ft3

• Qualified epoxy: 0 lbm to 219 lbm

• Qualified IOZ: 0 lbm to 65 lbm

• Interam fire barrier: 0 lbm to 60 lbm 17

NUKON DEBRIS GENERATED 18

UNQUALIFIED COATINGS

• Types of Unqualified Coatings at Vogtle

• Inorganic Zinc (IOZ)

• Alkyd

• Epoxy

• IOZ and alkyd coatings were assumed to fail as 100%

particulate

• Types of unqualified epoxy coatings at Vogtle that have been DBA tested:

• Starglaze 2001

• Amerlock 400

• Keeler & Long 4129 / 5009 / 6129

• DBA testing shows that some unqualified coatings systems will not completely delaminate after exposure

• Some of the Vogtle qualified coating systems may have been applied correctly, but were listed as unqualified because quality control inspections were not completed 19

UNQUALIFIED EPOXY SIZE DISTRIBUTION

• Unqualified epoxy coatings without DBA testing are assumed to fail as particulate

• Unqualified epoxy coatings with DBA testing are assumed to fail as both particulate and chips

• Comanche Peak DBA testing showed that epoxy coatings failed as chips

• EPRI test report stated that the failure mode of the tested epoxy top coats is flaking (i.e., failure as chips)

• Diablo Canyon testing showed that epoxy debris formed inside containment is expected to remain in large pieces (1-2 in2 chips) as long as the debris stays moist and is exposed to wet heat

• Results of Comanche Peak paint chip characterization are applied to the size distribution of epoxy coatings at Vogtle

• 12% particulate

• 37% fine chips (15.6 mil)

• 9% small chips (0.125 - 0.5 inch)

• 21% large chips (0.5 - 2 inch)

• 21% large curled chips (0.5 - 2 inch) 20

UNQUALIFIED COATINGS LOCATIONS Coating Type Upper Lower Containment Containment Quantity (lbm) Quantity (lbm)

Epoxy 1,602 1,099 Alkyd 0 31 IOZ 24 3 Total 1,626 1,133

• Coatings that fail in upper containment would have a reduced transport fraction for breaks where containment sprays are not initiated 21

UNQUALIFIED COATINGS FAILURE TIMING Coating Time-Dependent Failure Fraction Type 0 to 0.5 0.5 to 6 6 to 172 hours0.00199 days <br />0.0478 hours <br />2.843915e-4 weeks <br />6.5446e-5 months <br /> hours hours Epoxy 0 to 25% 0 to 25% 0 to 100%

Alkyd 0 to 25% 0 to 25% 0 to 100%

IOZ 0 to 25% 0 to 100% 0 to 100%

• Time-dependent failure based primarily on BWROG testing of various unqualified coatings systems and applications

• Coatings that fail in upper containment after sprays are secured would have a reduced transport fraction

• Any coatings that dont fail by 172 hours0.00199 days <br />0.0478 hours <br />2.843915e-4 weeks <br />6.5446e-5 months <br /> are assumed to fail by 14 days (100% total failure for all unqualified coatings) 22

DEBRIS TRANSPORT

• Using logic tree approach defined in NEI 04-07 consistent with industry developed methods for deterministic closure

• Blowdown

• Washdown

• Pool fill

• Recirculation

• Erosion 23

TRANSPORT - WASHDOWN

• Containment Sprays On

• All fines (fiber and particulate) washed to lower containment

• Retention of small and large pieces caught on gratings estimated based on Drywell Debris Transport Study

• Washdown to various areas proportional to flow split

• Containment Sprays Off

• Assumed 5% washdown for fines due to condensation and 0% for small pieces 24

FIBER TRANSPORT FRACTIONS TO ONE RHR STRAINER Debris 1 Train w/ 2 Train w/ 1 Train w/o 2 Train w/o Size Type Spray Spray Spray Spray*

Nukon Fines 58% 29% 23% 12%

Small 48% 24% 5% 6%

Large 6% 3% 7% 6%

Intact 0% 0% 0% 0%

Latent Fines 58% 29% 28% 14%

• This pump lineup was evaluated for different break locations. The transport fractions shown are the bounding values for an annulus break near the strainers.

25

PARTICULATE TRANSPORT FRACTIONS TO ONE RHR STRAINER 1 Train w/ 2 Train w/ 1 Train w/o 2 Train w/o Debris Type Size Spray Spray Spray Spray Unqualified Epoxy Fines 58% 29% 47% 23%

Fine Chips 0% 0% 0% 4%

Small Chips 0% 0% 0% 4%

Large Chips 0% 0% 0% 3%

Curled Chips 58% 29% 6% 9%

Unqualified IOZ Particulate 58% 29% 16% 8%

Unqualified Alkyd Particulate 58% 29% 100% 50%

Interam Fines 58% 29% 23% 12%

Qualified Epoxy Fines 58% 29% 23% 12%

Qualified IOZ Fines 58% 29% 23% 12%

Latent dirt/dust Fines 58% 29% 28% 14%

RCS Crud Fines 58% 29% 23% 12%

• Unqualified coatings transport fractions are preliminary and may change based on recent changes to the unqualified coatings calculation 26

CHEMICAL EFFECTS

• Overview

• Chemical precipitate quantities are determined for each break

• Corrosion/Dissolution Model

• Corrosion and dissolution of aluminum and calcium is determined primarily using the WCAP-16530 methodology with the following inputs:

• Best-estimate temperature profiles

• Best-estimate pH profile

• Break-specific debris quantities

• UNM release equations will be used for aluminum in TSP within the applicable temperature and pH limitations 27

CHEMICAL EFFECTS

• Solubility

• No credit will be taken for calcium solubility

• ANL solubility equation (ML091610696) will be used to credit aluminum solubility

• Aluminum will remain dissolved up to the calculated solubility limit

• Precipitate Type

• 2009 strainer head loss test results used calcium phosphate and sodium aluminum silicate (WCAP-16530 surrogates) 28

MAXIMUM DEBRIS GENERATED

• Bounding quantities of Nukon, Interam and qualified coatings for DEGB in Loop 1&4 SG compartment Debris type Quantity Notes Nukon 2,229 ft3 Including all size categories Interam 60 lbm 30% fiber and 70% particulate Qualified coatings 249 lbm IOZ and epoxy Unqualified coatings 2,759 lbm IOZ, alkyd, and epoxy Latent fiber 4 ft3 15% of total latent debris; 2.4 lbm/ft3 Latent particulate 51 lbm 85% of total latent debris Miscellaneous debris 2 ft2 Total surface area of tape and labels 29

DEBRIS QUANTITIES AT ONE RHR STRAINER Bounding Bounding Bounding Hot Leg Cold Leg Cold Leg 2009 Test Debris Type Break Break Break Quantity (two trains (2 trains, no (single train with CS) CS) no CS)

Nukon 119.8 ft3 337.4 ft3 72.7 ft3 145.5 ft3 Latent fiber 4.4 ft3* 1.1 ft3 0.5 ft3 1.1 ft3 Interam 327.8 lbm* 0 lbm 0 lbm 0 lbm Qualified coatings 786.7 lbm* 27.3 lbm 8.8 lbm 17.6 lbm Unqualified coatings 3,244.8 lbm* 575.3 lbm 458.8 lbm 917.5 lbm Latent particulate 59.5 lbm* 14.8 lbm 7.1 lbm 14.3 lbm Sodium aluminum silicate 100.6 lbm 17.8 lbm 8.5 lbm 17.0 lbm Calcium phosphate 59.6 lbm 57.4 lbm 56.0 lbm 112.1 lbm

• These tested quantities exceed currently estimated values for all breaks under all equipment combinations at Vogtle 30

2009 STRAINER HEAD LOSS TESTING

• Testing consistent with the NRC March 2008 Guidance

• Tank test with prototypical 7-disk strainer module

• Total area of 69 ft2

• Walls and suction pipe arranged consistent with plant strainer

• Bounding RHR strainer approach velocity for runout flow rate (4,500 gpm) 31

2009 TESTING DEBRIS LOADS

• Nukon debris quantity based on 7D ZOI

• Chemical precipitates quantity from WCAP-16530

• The following debris surrogates used

• Nukon and latent fiber: Nukon

• Coatings: Silicon carbide (1 - 100 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 32

2009 TEST PROCEDURE

• Debris introduction consistent with the NRC March 2008 Guidance

• For thin-bed testing, all particulate added first followed by small batches of fiber fines

• For full-load testing, fiber and particulate mixture added in batches with constant particulate to fiber ratio

• Chemical debris batched in last

• Head loss allowed to stabilize after each chemical addition 33

2009 TEST RESULTS Thin-bed test Full-load test Debris Load head loss (ft) head loss (ft)

Fiber + Particulate 0.631 5.462 After calcium phosphate3 1.65 6.57 After sodium aluminum silicate3 2.60 11.80 Note:

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 34

APPLICATION OF 2009 RESULTS

• Conventional debris head loss will be linearly interpolated between data points (debris was batched in)

• Chemical precipitate head loss will be based on a step function for intermediate loads

• Head 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 tests

• Results will be extrapolated to 30 days

• Breaks that exceed the maximum tested fiber quantity, particulate quantity, or chemical precipitate quantity will be assigned a failing head loss value 35

2009 TEST RESULTS - CONVENTIONAL HEAD LOSS 6

5 Head Loss (ft) 4 3

2 1

0 0 20 40 60 80 100 120 140 Fiber Load (ft3) 36 Interpolated head loss values between data points

2009 TEST RESULTS - CHEMICAL HEAD LOSS 1.2 1

Head Loss Change (ft) 0.8 0.6 0.4 0.2 0

0 20 40 60 80 Calcium Phosphate for One RHR Strainer (lbm)

• Chemical precipitates are assumed to pass through the strainer and not contribute to head loss when fiber load is less than 1/16 theoretical bed thickness

• Utilized step-wise head loss for both chemical types 37

STRAINER ACCEPTANCE CRITERIA

• RHR and CS Pump NPSH Margin

• Unsubmerged margin = half of submerged strainer height

• For fully submerged strainer, the NPSH margin is calculated using break-specific water level and flow rates

• Minimum NPSH margin is 16.6 ft at 210.96°F and a containment pressure of -0.3 psig

• Structural

• Strainer stress analysis is based on a crush pressure of 24.7 ft for the RHR strainers and 23.0 ft for the CS strainers

• Gas void

• 2% void fraction at pump inlet 38

FIBER PENETRATION TESTING

• Eleven tank tests were performed at Alden in 2014 for various strainer approach velocities, number of strainer disks and boron / buffer concentrations

• Nukon prepared into fines per latest NEI Guidance

• A bounding curve fit will be used to evaluate maximum fiber penetration 39

FIBER PENETRATION RESULTS 1800 1600 Cumulative Fiber Penetration (g) 1400 1200 1000 800 600 400 200 0

0 5000 10000 15000 20000 Cumulative Fiber Addition (g) 40

IN-VESSEL EFFECTS

• Transport/accumulation of fiber to the core that penetrates RHR strainers is dependent on break location and flow path

• Hot leg break during cold leg recirculation: 100% accumulation on core

• Hot leg break during hot leg recirculation: 0% accumulation on core

• Cold leg break during cold leg recirculation: ratio of boiloff flow rate (time-dependent) divided by recirculation flow rate

• Cold leg break during hot leg recirculation: 0% accumulation on core

• Currently using placeholder values for core blockage and boron precipitation acceptance criteria

• 75 g/FA for hot leg breaks

• 7.5 g/FA for cold leg breaks

• Values will be modified as necessary based on results of PWROG testing 41

EXAMPLE CALCULATIONS

• Analytical results showing whether a given break passes or fails are highly dependent on the assumptions and models used to evaluate the break

• For example, if sprays are not initiated for a given break:

• Less water is injected from the RWST (potentially resulting in a partially submerged strainer)

• 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 strainers

• If the strainers are partially submerged:

• Effective strainer area is reduced giving a higher average approach velocity and a greater debris bed thickness

• Acceptance criterion is half the submerged strainer height

• Degasification does not occur

• It is not always obvious what conditions are bounding 42

BEST ESTIMATE VS. BOUNDING CONDITIONS

• Three sets of simulations were performed to evaluate the full range of breaks (over 28,000 breaks - from 1/2 to DEG breaks - on each Class 1 weld)

• Best-estimate conditions

• Bounding strainer conditions

• Bounding in-vessel conditions

• Each set of simulations included cases evaluating all equipment running and a single RHR pump failure

• Bounding simulations included both min and max input conditions for variables with competing effects (e.g., a higher pool temperature profile is conservative for NPSH margin and degasification, whereas a lower pool temperature profile is conservative for head loss) 43

KEY INPUT PARAMETER DIFFERENCES Input Parameter Base Case Bounding Strainer Bounding In-Vessel Conditions Conditions CS Termination Time Best-estimate Min/Max Minimum Hot Leg Switchover Time Best-estimate Best-estimate Maximum RWST Injection Volume Best-estimate Min/Max Best-estimate Pool Temperature Profile Best-estimate Best-estimate/Maximum Best-estimate as f(break size) with drop to 90 °F ECCS Flow Rate Best-estimate Maximum Min/Max as f(break size)

CS Flow Rate Best-estimate Minimum Minimum Pool pH Best-estimate Maximum with drop to 7 Maximum with drop to 7 Unqualified Coatings Failure Best-estimate 100% at Time 0 100% at Time 0 Unqualified Epoxy Size Best-estimate 100% particulate 100% particulate Miscellaneous Debris Area Best-estimate Best-estimate Minimum Debris Transport Best-estimate Maximum Maximum Debris Penetration Maximum Minimum Maximum 44

BASE CASE RESULTS

• The following slides show overall simulation results for all of the breaks evaluated under the base case conditions 45

BASE CASE RESULTS (ALL PUMPS RUNNING) 200 180 160 Fiber on RHR Strainer A (ft3) 140 120 100 80 60 40 20 0

0 500 1,000 1,500 2,000 2,500 Total Fiber Debris (ft3) 46

BASE CASE RESULTS (ALL PUMPS RUNNING) 140 Hot leg breaks where sprays are initiated (>15) 120 Fiber On the Core (g/FA) 100 80 Hot leg breaks where sprays are not initiated (15) 60 40 20 Cold leg breaks 0

0 500 1,000 1,500 2,000 2,500 Total Fiber Debris (ft3) 47

TIME-DEPENDENT RESULTS FOR SPECIFIC BREAKS

• The following slides show time-dependent results for the following individual breaks evaluated under base case conditions

• Hot leg break with max fiber generation (all pumps running)

• Cold leg break with max fiber generation (all pumps running)

• Hot leg break with max fiber generation (1 RHR failure) 48

FIBER ACCUMULATION FOR MAX FIBER HOT LEG BREAK (ALL PUMPS RUNNING)

Strainer Fiber Accumulation 200 180 160 RHR Strainer 140 CS Strainer Fiber Quantity (ft3) 120 100 80 60 40 20 0

0 50 100 150 200 250 300 350 400 450 500 Time (min) 49

COMPARISON OF FIBER ACCUMULATION ON RHR A STRAINER Fiber Accumulation on RHR A Strainer 350 300 Max HL Fiber Break (all pumps running) 250 Max HL Fiber Break (1 RHR Pump)

Fiber Volume (ft3)

Max CL Fiber Break (All Pumps Running) 200 150 100 50 0

0 200 400 600 800 1,000 1,200 1,400 1,600 Time (min) 50

DEBRIS ACCUMULATION FOR MAX FIBER COLD LEG BREAK (ALL PUMPS RUNNING)

RHR A Strainer Debris Accumulation 450 70 400 Quantity of fiber (ft3) and particulate (lbm) 60 Quantity of chemical precipitate (lbm) 350 50 300 Fiber Particulate 40 250 Aluminum Precipitate 200 Calcium Precipitate 30 150 20 100 10 50 0 0 0 5 10 15 20 25 30 Time (days) 51

RHR STRAINER HEAD LOSS FOR MAX FIBER COLD LEG BREAK (ALL PUMPS RUNNING)

RHR A Strainer Head Loss Calcium precipitation exceeds 2nd test batch 3

Calcium precipitation exceeds 1st test batch Clean Strainer Head Loss Conventional Debris Head Loss Chemical Head Loss 2.5 Total Strainer Head Loss HLSO: Reduced flow and 2

Head Loss (ft) 1.5 30 day test extrapolation 1

Start of recirc 0.5 CSHL set as a constant value 0

0 4 8 12 16 20 24 Time (hours) 52

RHR STRAINER HEAD LOSS FOR MAX FIBER COLD LEG BREAK (ALL PUMPS RUNNING)

RHR A Strainer Head Loss Aluminum precipitation due to decreased temp 3

Clean Strainer Head Loss Conventional Debris Head Loss Chemical Head Loss 2.5 Total Strainer Head Loss 2

Head Loss (ft) 1.5 1

0.5 0

0 5 10 15 20 25 30 Time (days) 53

CONDITIONAL FAILURE PROBABILITIES

• Base case preliminary results

• Core conditional failure probability (CFP) worse when all pumps are operating

• Strainer CFP worse with 1 RHR pump operating

• Bounding strainer conditions

• No core failures, but significantly more strainer failures than base case

• Bounding core conditions

• More core failures, but fewer strainer failures than base case 54

RISK QUANTIFICATION

• The change in core damage frequency (CDF) and change in large early release frequency (LERF) due to issues related to GSI-191 can be estimated based on:

• LOCA frequencies

• Equipment configuration probabilities

• GSI-191 conditional failure probabilities 55

LOCA FREQUENCY

• Break-specific LOCA frequencies (using the hybrid methodology developed by the STP pilot project) were used to determine the GSI-191 conditional failure probabilities for small, medium, and large breaks

• LOCA frequencies from PRA model of record were used to calculate risk

• Small (1/2-2) break frequency: 5.8E-04 yr-1

• Medium (2-6) break frequency: 4.9E-04 yr-1

• Large (6-31) break frequency: 1.2E-06 yr-1 56

EQUIPMENT CONFIGURATION PROBABILITY

• Most likely situation would be that all equipment is available and fully functional

• Equipment 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 RHR pump fails 57

EQUIPMENT CONFIGURATION PROBABILITY

• LBLOCA

• All equipment available bounding or reasonably representative for:

• No pump failures: 78.9%

96.6%

• 1 or 2 CS pump failures: 17.7%

• 1 RHR pump failure bounding or reasonably representative for other equipment failure configurations: 3.4%

• MBLOCA/SBLOCA

• All equipment available: 93.5%

• 1 RHR pump failure bounding or reasonably representative for other equipment failure configurations: 6.5%

58

GSI-191 RISK (BASE CASE)

Base case 59

QUALITY ASSURANCE

• Majority of GSI-191 calculations have been prepared as non-safety related under vendor Appendix B QA programs

• Additional GSI-191 calculations have been prepared as non-safety related following work practices established by vendor Appendix B QA program

• Head 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 program

• Chemical effects testing was conducted and documented as non-safety following a QA process consistent with the testing performed for the STP pilot project

• Thermal-hydraulic modeling was prepared and documented as non-safety following a QA process consistent with the modeling performed for the STP pilot project 60

CONCLUSIONS

• Models used to analyze GSI-191 phenomena at Vogtle are consistent with methods accepted for deterministic evaluations

• Preliminary results indicate that risk associated with GSI-191 is very low 61

QUESTIONS?

62