ML15320A087

GSI-191 Resolution Plan and Current Status, NRC Public Meeting, November 5, 2015, Revised Meeting Handouts

ML15320A087
Person / Time
Site:	Vogtle
Issue date:	11/05/2015
From:	Southern Nuclear Company
To:	Office of Nuclear Reactor Regulation
References
Download: ML15320A087 (94)

Text

N O V E M B E R 5, 2 0 1 5 VOGTLE GSI-191 RESOLUTION PLAN AND CURRENT STATUS NRC PUBLIC MEETING

2 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

3 PURPOSE OF MEETING

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

• Discuss proposed plant modifications

• Discuss use of design basis (vs. best estimate) inputs in the evaluation

4 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 discharge during recirculation.

• Maximum design flow rates:

• RHR 3,700 gpm/pump

• CS 2,600 gpm/pump

• Two independent and redundant containment air cooling trains

5 STRAINER ARRANGEMENT

• Two RHR and CS pumps each with their own strainer

• Each GE strainer is similar with four stacks of disks

• RHR strainer: 18-disk tall, 765 ft2, 5 ft tall

• CS strainer: 14-disk tall, 590 ft2, 4 ft tall

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

6 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

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

• CS pumps switched to recirculation at RWST empty alarm

• CS pumps secured no earlier than 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after start of recirculation, and probably before 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> depending on pressure and dose rate

• 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 />

7 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

8 SCHEDULE UPDATE MILESTONE EXPECTED COMPLETION DATE Current Status Develop containment CAD model to include pipe welds Complete Complete Conduct meeting with NRC 3rd Quarter 2013 Complete Modify probabilistic risk assessment (PRA) to include Strainer and Core Blockage events 4th Quarter 2013 Complete Perform Chemical Effects testing 1st Quarter 2014 Complete Perform thermal and hydraulic modeling of RCS, Core, and Containment conditions 1st Quarter 2014 Complete Perform Strainer Head Loss and Bypass testing to establish correlation for range of break sizes 2nd Quarter 2014 Strainer Bypass Testing - Complete Strainer Headloss Testing - Using 2009 Vogtle test Assemble base inputs for CASA Grande 2nd Quarter 2014 Complete - Using NARWHAL instead of CASA Grande Evaluate Boric Acid Precipitation impacts 3rd Quarter 2015 Plan on using PWROG WCAP-17788 Finalize inputs to CASA Grande 3rd Quarter 2015 In Progress, Using NARWHAL instead of CASA Grande Complete Sensitivity Analyses in/for CASA Grande 4th Quarter 2015 2nd Quarter 2016 Integrate CASA Grande results into PRA to determine CDF and LERF 1st Quarter 2016 3rd Quarter 2016 Licensing Submittal for VEGP To be established through discussions with NRC - tentatively September 2016 Projected 1st Quarter 2017, require input from:

SE on STP Pilot Project and SE on WCAP-17788; which are not yet available.

9 WHAT WE HAVE LEARNED

• Containment sprays only actuate for the largest hot leg breaks under best estimate conditions

• This results in unsubmerged strainers for many breaks because RWST is left with unused water

• Wide variation in post-LOCA water levels and sump chemistry

• Aluminum corrosion is greater with sprays operating

• Planned modifications

• Reduce height of RHR strainers by ~6 inches (remove 2 disks)

• Change procedures to continue RWST drain down to just below empty level set point when CS does not actuate

• Allows reduction of Tech Spec min water level by 2% (~1 ft)

(increased operating margin)

• Equivalent to ~2 inches in containment pool level

• Combination of these three modifications results in submerged strainers and reduces risk

10 RWST LEVELS AND ALARMS (ECCS to Recirculation)

(CS to Recirculation)

El. 220-0 Bottom of Tank El. 274 98%

93%

29%

8%

(Proposed Change) 51.45 (Existing)

11 SUBMERGED STRAINER RESULTS Before Modifications After Modifications

~4.97 ft SBLOCA Recirc Valves open =

~4.75 ft LBLOCA Best Estimate = ~6.6 ft LBLOCA Max =

~8.2 ft

~4.425 ft SBLOCA Recirc Valves open = ~4.5 ft LBLOCA Best Estimate = ~7.9 ft LBLOCA Max =

~8.7 ft All heights are measured from floor SBLOCA long term = ~5.3 ft SBLOCA long term = ~3.5 ft

12 OVERVIEW OF METHODOLOGY

• Resolution plan modified based on 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)

• 2009 Vogtle head loss testing will be used to determine which breaks contribute to risk quantification

• Breaks with debris quantities greater than tested (mass/SA)* will fail

• Breaks with debris quantities less than tested (mass/SA) will pass

• Will continue to quantify risk by evaluating GSI-191 failures for number of strainers in operation

• Will use consensus models/design basis inputs for parameters in the GSI-191 Risk-Informed Software

• Mass/SA = Mass of debris per unit strainer area

13 PILOT PLANT COMPARISON (STP VS.

VOGTLE)

Differences

• Physical

• ECCS trains

• Strainer configuration

• Containment Spray Setpoint

• Strainer design

• Strainer surface area

• Modeling

• Software

• Break size and orientation sampling

• Strainer head loss test protocol

• Chemical effects

• Core blockage

• Time-dependent comparison to failure criteria

• Method for calculating CDF and LERF Similarities

• Physical

• Large dry containment

• 4 Loop Westinghouse NSSS

• Low density fiberglass insulation

• Trisodium phosphate buffer

• Modeling

• Break-specific ZOI debris generation

• Unqualified coatings

• Debris transport

• Past head loss testing to establish debris limits

• Penetration testing

• Mass balance of debris on strainer and core

14 SOFTWARE

• BADGER (Break Accident Debris Generation Evaluator)

• A computer program that automates break ZOI debris generation calculations using CAD software

• NARWHAL (Nuclear Accident Risk Weighted Analysis)

• A computer program that evaluates the probability of GSI-191 failures by holistically analyzing the break-specific conditions in a time-dependent manner

15 ANALYSIS FLOWCHART NARWHAL Break Analysis (Strainers)

NARWHAL Break Analysis (Core)

Strainer Head Loss Test Acceptable Mitigation WCAP-17788 Strainer Penetration Test CDF LERF Acceptable Risk: Submit LAR Not Bounded Bounded Bounded Not Bounded RG 1.174 Acceptance Guidelines Unacceptable Risk: Implement Refinements or Modifications

16 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

17 DEBRIS GENERATION

• Insulation and qualified coatings

• Automated analysis with containment CAD model using a tool called BADGER

• 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

• Unqualified coatings and latent debris quantities are identical for all breaks Nukon 17D Qualified Epoxy & IOZ with Epoxy topcoat 4D Interam Fire Barrier Material 11.7D

18 INSULATION AND QUALIFIED COATINGS QUANTITIES

• BADGER database contains 28,434 breaks at 930 weld locations

• Breaks evaluated at each Class 1 ISI weld

• Partial breaks evaluated in 2 inch increments for smaller break sizes, 1 inch increments for larger break sizes, and 1/2 inch increments for largest break sizes

• Partial breaks evaluated in 45° increments around pipe

• DEGB evaluated at every weld

• 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

19 NUKON DEBRIS GENERATED

20 UNQUALIFIED COATINGS

• Types of Unqualified Coatings at Vogtle

• Inorganic Zinc (IOZ)

• Alkyd

• Epoxy

• IOZ, alkyd, and epoxy coatings are assumed to fail as 100% particulate

• Size distribution for degraded qualified coatings and failure timing no longer being utilized because of the reliance on 2009 head loss testing

21 UNQUALIFIED COATINGS LOCATIONS

• Coatings that fail in upper containment would have a reduced transport fraction for breaks where containment sprays are not initiated Coating Type Upper Containment Quantity (lbm)

Lower Containment Quantity (lbm)

Epoxy 1,602 1,127 Alkyd 0

59 IOZ 24 31 Total 1,626 1,217

22 CONTAINMENT POOL WATER LEVEL

• Sump pool depth is evaluated on a break-specific basis using conservative inputs to minimize water level

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

• Planning to remove 2 disks from each RHR strainer to reduce overall height

• Modifying procedures for breaks that dont activate containment spray

• Continue RWST drain down to just below empty level set point

• Allows reduction of Tech Spec RWST min water level by 2% (~1 ft) to increase operator margin

• Strainers are submerged for all scenarios

23 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

24 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 10% washdown for fines due to condensation and 0% for small pieces

25 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 Assumption to use for containment spray actuation is not obvious for most breaks/sizes

26 FIBER TRANSPORT FRACTIONS TO ONE RHR STRAINER

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

Debris Type Size 1 Train w/

Spray 2 Train w/

Spray 1 Train w/o Spray 2 Train w/o Spray*

Nukon Fines 58%

29%

23%

12%

Small 48%

24%

5%

2%

Large 6%

3%

7%

4%

Intact 0%

0%

0%

0%

Latent Fines 58%

29%

28%

14%

Strainers in Operation 2

4 1

2

27 PARTICULATE TRANSPORT FRACTIONS TO ONE RHR STRAINER Debris Type Size 1 Train w/

Spray 2 Train w/

Spray 1 Train w/o Spray 2 Train w/o Spray Interam Fines, Smalls 58%

29%

47%

23%

Unqualified Epoxy Particulate 58%

29%

47%

23%

Unqualified IOZ Particulate 58%

29%

16%

8%

Unqualified Alkyd Particulate 58%

29%

100%

50%

Qualified Epoxy Particulate 58%

29%

23%

12%

Qualified IOZ Particulate 58%

29%

23%

12%

Latent dirt/dust Particulate 58%

29%

28%

14%

28 CONTAINMENT SPRAY AND POOL pH Combining conditions in a non-physical way to bound release and precipitation

• Containment spray from the RWST will use a maximum pH for acidic conditions associated with the minimum RWST boron concentration.

• The design basis maximum containment pool pH is used for the sprays during recirculation and the containment pool to calculate chemical release.

• Lower pH values/profiles are used for aluminum solubility to account for lower TSP concentrations, higher boric acid concentrations, and pH effects due to core release and radiolysis.

29 CHEMICAL EFFECTS

• Overview

• Chemical precipitate quantities are determined for each break

• Corrosion/Dissolution Model

• Dissolution from insulation and concrete is determined using the WCAP-16530 equations

• Corrosion, dissolution and passivation of aluminum metal is determined using the equations developed by Howe et al. (UNM)

• Solubility

• No credit will be taken for calcium solubility

• ANL solubility equation (ML091610696, Eq. 4) will be used to credit delayed aluminum precipitation

• Once temperature limit is reached, all aluminum will precipitate

• Aluminum is eventually "forced" to precipitate for all breaks

• Precipitate Surrogates

• WCAP-16530 Calcium Phosphate

• WCAP-16530 Sodium Aluminum Silicate

30 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 40 lbm 30% fiber and 70% particulate Qualified coatings 249 lbm IOZ and epoxy Unqualified coatings 2,843 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

31 DEBRIS QUANTITIES AT ONE RHR STRAINER Debris Type 2009 Test Quantity Bounding Hot Leg Break (two trains with CS)

Bounding Cold Leg Break (2 trains, with CS)

Bounding Cold Leg Break (single train with CS)

Nukon 106.1 ft3 337.3 ft3 333.6 ft3 667.3 ft3 Latent fiber 3.9 ft3*

1.2 ft3 1.2 ft3 2.32 ft3 Interam 290.3 lbm*

12.0 lbm 17.4 lbm 34.8 lbm Qualified coatings 696.8 lbm*

27.3 lbm 72.2 lbm 144.4 lbm Unqualified coatings 2874.1 lbm*

824.5 lbm 824.5 lbm 1648.9 lbm Latent particulate 52.7 lbm*

14.8 lbm 14.8 lbm 29.6 lbm Sodium aluminum silicate 89.1 lbm

~55 lbm

~55 lbm

~102 lbm Calcium phosphate 52.8 lbm

~53 lbm

~53 lbm

~108 lbm

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

32 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)

• 1 inch submergence for vortex observations Alion Test Facility

33 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 (4 to 20 micron)

• Latent particulate: Silica sand w/ size distribution consistent with NEI 04-07 Volume 2 (75 to 2000 microns)

• Interam fire barrier: Interam E-54A

34 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

35 2009 TEST RESULTS Debris Load Thin-bed test head loss (ft)

Full-load test 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

36 APPLICATION OF 2009 RESULTS

• Total conventional debris plus calcium phosphate head loss will be applied at the start of recirculation

• Total aluminum precipitate head loss will be applied when temperature decreases to solubility limit

• 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

37 STRAINER ACCEPTANCE CRITERIA

• RHR and CS Pump NPSH Margin

• 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 24.0 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

• Multiple 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 curve fit of the test data will be used to evaluate maximum fiber penetration for a 16 disk strainer (RHR) and 14 disk strainer (CS).

39 0

200 400 600 800 1000 1200 1400 1600 1800 0

5000 10000 15000 20000 Cumulative Fiber Penetration (g)

Cumulative Fiber Addition (g)

FIBER PENETRATION RESULTS

40 IN-VESSEL EFFECTS

• Transport/accumulation of fiber to the core that penetrates RHR strainers is dependent on break location and flow path and will be based on WCAP-17788

• Values for core blockage and boron precipitation acceptance criteria will be based on WCAP-17788

41 EX-VESSEL EFFECTS

• A bounding evaluation performed for all components

• Existing evaluations will be updated in accordance with WCAP-16406-P-A,Evaluation of Downstream Sump Debris Effects in Support of GSI-191 Revision 1 and the accompanying NRC SER

42 LOCADM

• A bounding calculation performed to cover all scenarios

• Existing evaluations will be updated in accordance with WCAP-16793-A,Evaluation of Long-Term Cooling Considering Particulate, Fibrous, and Chemical Debris in the Recirculating Fluid Revision 2 and the accompanying NRC SER

43 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

44 GSI-191 ACCEPTANCE CRITERIA Acceptance Criteria Method for Addressing Debris exceeds limits for upstream blockage, e.g. refueling canal drain Bounding analysis - part of transport calculation Strainer head loss exceeds pump NPSH margin or strainer structural margin Break-specific analysis based on tested debris limits and maximum tested head losses Gas voids from degasification or flashing exceed strainer/pump limits Break-specific analysis based on head loss, pool temperature, etc.

Pumps fail due to air intrusion from vortexing Bounding analysis Penetrated debris exceeds ex-vessel wear and blockage limits Bounding analysis Penetrated debris exceeds in-vessel fuel blockage and boron precipitation limits Break-specific analysis based on penetration testing and flow splits Debris accumulation on cladding prevents adequate heat transfer Bounding analysis

45 OVERVIEW OF MODELING

• GSI-191 phenomena evaluated in a holistic, time-dependent manner with an evaluation tool called NARWHAL

• Developed using object oriented design

• Tracks movement of water and debris

• Evaluates each break with incremental time steps up to 30 days

• Evaluates range of breaks to determine which ones pass/fail the strainer and core acceptance criteria

• Uses top-down LOCA frequencies to calculate conditional failure probabilities for small, medium, and large breaks

46 OVERVIEW OF MODELING

• NARWHAL prototype has been used for preliminary risk-informed evaluations by several plants

• Version 1.0 is currently under development

• Software requirements, design, implementation, V&V, and user documentation prepared under ENERCONs Appendix B QA program

• NARWHALs object oriented design allows users to model unique plant-specific geometry with a common executable file

• Simplifies software maintenance

• Significantly reduces potential for software errors

47 OVERVIEW OF MODELING RWST Reactor Vessel Break Core ECCS CS Spray Nozzles Containment Compartments Sump Pool ECCS Strainers

48 OVERVIEW OF MODELING

49 OVERVIEW OF MODELING

• NARWHAL integrates models and inputs from design basis calculations and GSI-191 tests/analyses:

• Water volumes, temperature profiles, and pH from design basis calculations

• Debris quantities from BADGER database

• Location-specific transport fractions from transport calculation

• Chemical effects calculated using WCAP-16530 and Howe model

• Conventional and chemical head loss from 2009 strainer testing (scaled for temperature and flow)

• NPSH and structural margin from design basis calculations

• Degasification calculated using standard physical models

• Time-dependent penetration using data fit from 2014 strainer testing

• Core failure calculated using WCAP-17788 model and limits

50 OVERVIEW OF MODELING

1. Select unique break location, size, and orientation

2. ZOI debris quantities from BADGER (insulation and qualified coatings)

3. Debris quantities outside ZOI (unqualified coatings, latent, miscellaneous)

4. Blowdown transport to containment compartments and sump pool

5. Washdown transport from containment compartments to sump pool

6. Pool fill transport from sump pool to strainers and inactive cavities

7. Recirculation transport from sump pool to strainers

8. Debris penetration through strainers

9. Debris accumulation on core

51 OVERVIEW OF MODELING

2. Corrosion/

dissolution of metals, concrete, and debris in sump pool

1. Corrosion/

dissolution of metals, concrete, and debris by CS

4. Formation of chemical precipitates

3. Precipitate solubility limit

5. Recirculation transport from sump pool to strainers

6. Debris penetration through strainers

7. Debris accumulation on core

52 OVERVIEW OF MODELING

1. Strainer Head Loss (CSHL +

Conventional HL

+ Chemical HL)

2. Degasification gas void fraction

3. Pump NPSH margin

4. Strainer structural margin 5a. Does HL Exceed NPSH or structural margin?

Yes 7a. Fail strainer criteria No 6a. Pass strainer criteria 5b. Does void fraction exceed strainer or pump limits?

Yes 7b. Fail strainer criteria No 6b. Pass strainer criteria

53 OVERVIEW OF MODELING

1. Core debris accumulation 2b. Does quantity exceed blockage limits?

Yes

3. Fail core criteria No

4. Pass core criteria 2a.

Does quantity exceed boron limits?

Yes No

54 OVERVIEW OF MODELING

• 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:

• 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

• It is not always obvious what conditions are bounding

55 INPUTS Input Values Sensitivity LOCA Frequency Based on NUREG-1829/PRA Need to address uncertainty Debris Generation Based on consensus models None Debris Transport Based on consensus models None Containment Temp Design basis None Pool Temp Design basis None Containment Spray Activation and Duration Competing effects (e.g. washdown, strainer surface area, corrosion)

Need to run for activation and duration Pool Volume/Level Based on consensus models None Pool pH Design Basis maximum for corrosion, minimum for precipitation None ECCS Flow Rates Design basis (same for all breaks)

None Aluminum and Calcium Corrosion WCAP-16530 and UNM equations None Aluminum Precipitation ANL equation None Penetration 2014 testing Need to address uncertainty Head Loss Maximums Extrapolated and scaled from 2009 tests final values None

56 DIFFERENCES (STP VS. VOGTLE)

• Physical

• ECCS trains (3 vs 2)

• Strainer configuration (3 combined vs 4 separate)

• Containment Spray Setpoint

• Strainer design (flow control vs no flow control)

• Strainer surface area (~1800 ft2 vs 765 ft2)

57 DIFFERENCES (STP VS. VOGTLE)

• Modeling

• Risk Informed Software (CASA Grande/RUFF/FiDOE vs BADGER/NARWHAL)

• Break size and orientation sampling (Search algorithm vs uniform)

• Strainer head loss test protocol (flume vs tank)

• Aluminum and Calcium precipitate quantity (bounding test vs break-specific analysis)

• Aluminum passivation (not credited vs credited using Howe paper)

• Core blockage (RELAP5-3D vs WCAP-17788)

• Failure criteria (bounding analysis vs time-dependent comparison of head loss with NPSH, gas void, and flashing)

• GSI-191 risk quantification (critical break size frequency vs conditional failure probability entered into PRA)

58 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

59 INTERFACE WITH PRA

• The change in core damage frequency (CDF) and change in large early release frequency (LERF) due to issues related to GSI-191 will be determined using:

• LOCA frequencies from NUREG-1829 or the Vogtle PRA

• Equipment configuration logic from PRA model of record

• GSI-191 conditional failure probabilities from NARWHAL

• Final risk calculation will be performed using the Vogtle model of record with GSI-191 conditional failure probabilities

60 INTERFACE WITH PRA

1. PRA identification of accident scenarios and equipment configurations that are risk-significant to GSI-191

2. NARWHAL evaluation of GSI-191 phenomena for each risk-significant scenario/configuration to determine CFPs for each strainer/core failure basic event

3. PRA quantification of CDF & LERF with GSI-191 failures

4. PRA quantification of CDF & LERF with no GSI-191 failures Output to submittal documentation

5. Calculate CDF & LERF Yes

6.

Meets RG 1.174 Criteria

?

7a. Identification of analytical refinements to analysis No 7b. Identification of potential plant modifications (physical or procedural)

61 METHODOLOGY FOR USING LOCA FREQUENCY TO CALCULATE CONDITIONAL FAILURE PROBABILITY

• Partition PRA categories (Catk) into size ranges (SRi)

• Calculate probability of a LOCA occurring in each size range for every PRA category (P(SRilCatk))

• Calculate probability of a LOCA occurring at each weld (Weldj) within each size range (P(WeldjlSRi))

• Calculate probability estimate for success criteria failure (SCF) at each weld in each size range (P(SCFlWeldj,SRi))

• Calculate probability estimate for success criteria failure at every PRA category (P(SCFlCatk))

62 METHODOLOGY FOR USING LOCA FREQUENCY TO CALCULATE CONDITIONAL FAILURE PROBABILITY P SCF Catk =

i=1 Nk

j=1 Mi P SRilCatk P Weldj SRi P SCF Weldj, SRi From NUREG-1829 (or Vogtle PRA)

From NUREG-1829 (or Vogtle PRA) using top-down methodology From NARWHAL

63 ILLUSTRATION OF PRA CATEGORIES AND LOCA FREQUENCY SIZE RANGES

64 EQUIVALENT DEGB DIAMETER

• NUREG-1829, Section 3.7:

The correlations which relate flow rates and LOCA size categories to the effective break sizes in each PWR and BWR system are summarized in Table 3.8.

The break size corresponds to a

partial fracture for pipes with larger diameters than the break size, a complete single-ended rupture in pipes with the same inside diameter, or a DEGB in pipes having inside diameters 1/2 times the break size. All panelists used these correlations to relate their elicitation responses determined for the effective break sizes to the appropriate LOCA size category. It is important to stress that breaks can occur in either LOCA sensitivity piping or non-piping systems and components.

65 METHOD FOR ADDRESSING DEGB FREQUENCIES

• NUREG-1829 provides LOCA frequencies vs. break flow rates, which are converted to equivalent diameter break sizes

• Double ended guillotine breaks (DEGBs) have a flow rate (area) twice as large as the pipe cross-sectional area

• Equivalent diameter for DEBG is calculated using pipe inner diameter: DDEGB,Eq = 2

• Dpipe

• Breaks Dpipe assumed to progress to DEGB for debris generation (bounding debris quantities)

• Frequency associated with DEGB tail assigned to Dpipe break size to calculate conditional failure probability within each size range

• NUREG-1829 only provides frequencies up to 31 breaks, so frequencies corresponding to primary loop pipe DDEGB,Eq values is determined through log-log extrapolation

• 27.5 38.9

• 29 41.0

• 31 43.8

66 METHOD FOR ADDRESSING DEGB FREQUENCIES

67 EQUIPMENT CONFIGURATION

• 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 train failure

68 EQUIPMENT CONFIGURATION

• LBLOCA

• All equipment available bounding or reasonably representative for:

• No pump failures: ~79%

• 1 or 2 CS pump failures: ~18%

• 1 RHR pump failure bounding or reasonably representative for other equipment failure configurations: ~3%

• The values above are being used to determine which configurations to investigate with NARWHAL

• Conditional failure probabilities for GSI-191 basic events (strainer and core failure) will be manually entered into the PRA model of record to calculate CDF

~97%

69 CONDITIONAL FAILURE PROBABILITIES

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

• Strainer CFP higher with 1 train operating

• Additional scenarios will likely need to be evaluated (1 CS pump failure, 1 RHR pump failure, etc.)

70 PRA MODEL CHANGES

• Vogtle PRA model modified to incorporate conditional failure probabilities (CFPs) for GSI-191 strainer failures and core failures with associated initiating events and equipment configurations

• GSI-191 failure defined using PRA success criteria

• Strainer failure defined as failure of RHR pump/strainer

• CS strainer failures are calculated in NARWHAL, but not used in PRA

• GSI-191 failures binned into following CFP groups (separate CFPs defined for each LOCA category and each pump state)

• Core failures

• RHR Strainer A failures (without Strainer B or core failures)

• RHR Strainer B failures (without Strainer A or core failures)

• RHR Strainer A and B failures (without core failures)

• Each core and strainer CFP represented in PRA with a basic event that is combined with LOCA initiating event and pump failure logic to represent pump state associated with CFP

71 PRA MODEL CHANGES

72 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

73 UNCERTAINTY QUANTIFICATION

• Draft Reg Guide 1.229 requires uncertainty quantification for risk-informed GSI-191 evaluation

• Uncertainty quantification also required by Reg Guide 1.174

• Two different approaches that could be used to quantify uncertainty

• Simplified approach using sensitivity analysis

• Statistical sampling of input parameter distributions and propagating uncertainties

• Consensus inputs and models are considered to have no uncertainty

• Vogtle inputs that require uncertainty quantification

• LOCA frequency values

• Penetration model

• Containment spray activation and duration

• Possibly others

74 UNCERTAINTY QUANTIFICATION USING SENSITIVITY ANALYSIS

75 UNCERTAINTY QUANTIFICATION USING STATISTICAL SAMPLING

1. Select equipment failure configuration

2. Sample all random input values

3. Select break location, size, and orientation

5. Compare to GSI-191 acceptance criteria and PRA success criteria to identify strainer or core failures

9.

Output to PRA model

4. Evaluate GSI-191 phenomena at each time step for 30 days

6.

Sufficient breaks evaluated to estimate CFP?

No

7.

Sufficient random samples to estimate CFP PDF?

Yes No

8. All significant equipment configs.

evaluated?

Yes No Yes

76 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

77 SUBMITTAL DOCUMENTATION DISCUSSION Planning to follow the format, content, and depth of the August 2015 STP LAR

• GL 2004-02 Response following Staff Review Guidance (will have some pointers to risk informed summary)

• Risk Quantification and Summary

• Defense in Depth and safety margin

• Requests for exemptions (if 10CFR50.46(c) rule is not finalized)

• 10CFR50.46(d)

• GDC 19 (need being evaluated)

• GDC 35

• GDC 38

• GDC 41

• GDC 50.67 (need being evaluated)

• License amendment request

• Tech Spec markups

• Tech Spec Bases

• FSAR markups

• List of commitments

78 QUALITY ASSURANCE

• GSI-191 calculations are being revised to be safety related under vendor Appendix B QA programs

• Head loss testing in 2009 was conducted and documented as safety related under vendor Appendix B QA program

• Penetration testing was conducted and documented in 2014 as non-safety related following work practices established by vendor Appendix B QA program

• PRA has undergone an industry peer review per RG 1.200 and the ASME/ANS PRA Standard for CDF and LERF (RA-Sa-2009)

79 CONCLUSIONS

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

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

80 SCHEDULE UPDATE MILESTONE EXPECTED COMPLETION DATE Current Status Develop containment CAD model to include pipe welds Complete Complete Conduct meeting with NRC 3rd Quarter 2013 Complete Modify probabilistic risk assessment (PRA) to include Strainer and Core Blockage events 4th Quarter 2013 Complete Perform Chemical Effects testing 1st Quarter 2014 Complete Perform thermal and hydraulic modeling of RCS, Core, and Containment conditions 1st Quarter 2014 Complete Perform Strainer Head Loss and Bypass testing to establish correlation for range of break sizes 2nd Quarter 2014 Strainer Bypass Testing - Complete Strainer Headloss Testing - Using 2009 Vogtle test Assemble base inputs for CASA Grande 2nd Quarter 2014 Complete - Using NARWHAL instead of CASA Grande Evaluate Boric Acid Precipitation impacts 3rd Quarter 2015 Plan on using PWROG WCAP-17788 Finalize inputs to CASA Grande 3rd Quarter 2015 In Progress, Using NARWHAL instead of CASA Grande Complete Sensitivity Analyses in/for CASA Grande 4th Quarter 2015 2nd Quarter 2016 Integrate CASA Grande results into PRA to determine CDF and LERF 1st Quarter 2016 3rd Quarter 2016 Licensing Submittal for VEGP To be established through discussions with NRC - tentatively September 2016 Projected 1st Quarter 2017, require input from:

SE on STP Pilot Project and SE on WCAP-17788; which are not yet available.

81 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

82 BACKUP SLIDES

83 EXAMPLE CALCULATION

• Detailed physical calculations Break Location 11201-049-16-RB (10.5 DEG hot leg side break in annulus near surge line) 1 train operating with containment sprays activated Transport fractions: Maximum RHR flow rate: 3,700 gpm (design flow)

CS duration: 6 Hours Design basis temperature profile - Max Safeguards, with pool temperature drop to 90°F at Day 30 Minimum water level profile Sump pH used for corrosion: 8.1 Containment spray pH during Injection used for corrosion: 4.71 pH used for solubility: 7.6 Submerged Aluminum Area: 278.7 ft2 Unsubmerged Aluminum Area: 741.3 ft2 Submerged Concrete: 2,813 ft2 Aluminum Metal Release equations - WCAP 16530 Aluminum Solubility Equation - ANL Aluminum Solubility Equation Aluminum Solubility: Timing Only

84 BREAK LOCATION

85 POOL LEVEL

86 FIBER TRANSPORT TO ONE RHR STRAINER (1 TRAIN W/SPRAY)

• Transport fraction takes into account time-dependent transport (CS strainer active for 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />)

• • Combined fraction of fines due to erosion and intact pieces Debris Type Size DG Quantity (ft3)

Transport Fraction*

Quantity (ft3)

Nukon Fines 9.5 58%

6.1 Small 32.7 7%**

1.5**

Large 14.8 4%**

0.6**

Intact 15.9 0%

0.0 Total 72.9 8.2 Latent Fines 12.5 58%

7.8 Total 85.4 16.0

87 PARTICULATE TRANSPORT TO ONE RHR STRAINER (1 TRAIN W/SPRAY)

Debris Type Size DG Quantity (lbm)

Transport Fraction Quantity (lbm)

Interam Fines, Smalls 121.2 58%

70.3 Unqualified Epoxy Particulate 2,602.0 58%

1,509.2 Unqualified IOZ Particulate 25.0 58%

14.5 Unqualified Alkyd Particulate 32.0 58%

18.6 Qualified Epoxy Particulate 7.5 58%

4.4 Qualified IOZ Particulate 2.4 58%

1.4 Latent dirt/dust Particulate 170.0 58%

98.6 Total 2,960.1 1,717.0

88 CHEMICAL PRECIPITATE QUANTITIES

89 ALUMINUM CONCENTRATION AND SOLUBILITY

90 HEAD LOSS

• Clean strainer head loss: Bounding value of 0.162 ft at 4,500 gpm

• Conventional head loss

• Head loss due to chemical precipitates

• Values scaled to 16 disk RHR strainer area

• • Corrected to 3700 gpm and 90°F

• • • Applied at switchover to hot leg recirculation Head Loss Type Transported Quantity Max Tested Quantity*

Head Loss Corresponding to Max Tested Quantity (Unadjusted)

Head Loss with Flow and Temperature Correction**

Fiber 16.0 ft3 109.9 ft3 5.46 ft 4.41 ft Particulate 1,717.0 lbm 3,914.5 lbm Calcium Phosphate 9.6 lbm 52.8 lbm 1.11 ft 0.90 ft Sodium Aluminum Silicate 74.5 lbm 89.0 lbm 5.24 ft 4.23 ft Extrapolation to 30 days 2.13 ft***

1.72 ft

91 Short Term: Long Term:

VOID FRACTION AT RHR PUMP

92 DEBRIS TRACKING

• 100% capture of particulate and precipitate at strainer

• Penetration modeled based on test data curve fits

• All fiber is treated as fines

93 CORE ACCUMULATION

94

SUMMARY

Criteria Acceptance Criteria Example Results Example Pass/Fail NPSH Margin 16.6 ft 11.3 ft Pass Strainer Structural Margin 24.7 ft 11.3 ft Pass Partial Submergence Head loss less than 1/2 submerged height Fully submerged Pass Gas Void Fraction 2% at the pump 0.24% at the pump Pass Debris Limit Exceeds what was tested Not exceeded Pass Assumed core limits (to be replaced with WCAP-17788 criteria) 75 g/FA for Hot Leg Breaks 7.5 g/FA for Cold Leg Breaks 32 g/FA N/A Pass

N O V E M B E R 5, 2 0 1 5 VOGTLE GSI-191 RESOLUTION PLAN AND CURRENT STATUS NRC PUBLIC MEETING

2 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

3 PURPOSE OF MEETING

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

• Discuss proposed plant modifications

• Discuss use of design basis (vs. best estimate) inputs in the evaluation

4 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 discharge during recirculation.

• Maximum design flow rates:

• RHR 3,700 gpm/pump

• CS 2,600 gpm/pump

• Two independent and redundant containment air cooling trains

5 STRAINER ARRANGEMENT

• Two RHR and CS pumps each with their own strainer

• Each GE strainer is similar with four stacks of disks

• RHR strainer: 18-disk tall, 765 ft2, 5 ft tall

• CS strainer: 14-disk tall, 590 ft2, 4 ft tall

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

6 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

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

• CS pumps switched to recirculation at RWST empty alarm

• CS pumps secured no earlier than 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after start of recirculation, and probably before 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> depending on pressure and dose rate

• 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 />

7 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

8 SCHEDULE UPDATE MILESTONE EXPECTED COMPLETION DATE Current Status Develop containment CAD model to include pipe welds Complete Complete Conduct meeting with NRC 3rd Quarter 2013 Complete Modify probabilistic risk assessment (PRA) to include Strainer and Core Blockage events 4th Quarter 2013 Complete Perform Chemical Effects testing 1st Quarter 2014 Complete Perform thermal and hydraulic modeling of RCS, Core, and Containment conditions 1st Quarter 2014 Complete Perform Strainer Head Loss and Bypass testing to establish correlation for range of break sizes 2nd Quarter 2014 Strainer Bypass Testing - Complete Strainer Headloss Testing - Using 2009 Vogtle test Assemble base inputs for CASA Grande 2nd Quarter 2014 Complete - Using NARWHAL instead of CASA Grande Evaluate Boric Acid Precipitation impacts 3rd Quarter 2015 Plan on using PWROG WCAP-17788 Finalize inputs to CASA Grande 3rd Quarter 2015 In Progress, Using NARWHAL instead of CASA Grande Complete Sensitivity Analyses in/for CASA Grande 4th Quarter 2015 2nd Quarter 2016 Integrate CASA Grande results into PRA to determine CDF and LERF 1st Quarter 2016 3rd Quarter 2016 Licensing Submittal for VEGP To be established through discussions with NRC - tentatively September 2016 Projected 1st Quarter 2017, require input from:

SE on STP Pilot Project and SE on WCAP-17788; which are not yet available.

9 WHAT WE HAVE LEARNED

• Containment sprays only actuate for the largest hot leg breaks under best estimate conditions

• This results in unsubmerged strainers for many breaks because RWST is left with unused water

• Wide variation in post-LOCA water levels and sump chemistry

• Aluminum corrosion is greater with sprays operating

• Planned modifications

• Reduce height of RHR strainers by ~6 inches (remove 2 disks)

• Change procedures to continue RWST drain down to just below empty level set point when CS does not actuate

• Allows reduction of Tech Spec min water level by 2% (~1 ft)

(increased operating margin)

• Equivalent to ~2 inches in containment pool level

• Combination of these three modifications results in submerged strainers and reduces risk

10 RWST LEVELS AND ALARMS (ECCS to Recirculation)

(CS to Recirculation)

El. 220-0 Bottom of Tank El. 274 98%

93%

29%

8%

(Proposed Change) 51.45 (Existing)

11 SUBMERGED STRAINER RESULTS Before Modifications After Modifications

~4.97 ft SBLOCA Recirc Valves open =

~4.75 ft LBLOCA Best Estimate = ~6.6 ft LBLOCA Max =

~8.2 ft

~4.425 ft SBLOCA Recirc Valves open = ~4.5 ft LBLOCA Best Estimate = ~7.9 ft LBLOCA Max =

~8.7 ft All heights are measured from floor SBLOCA long term = ~5.3 ft SBLOCA long term = ~3.5 ft

12 OVERVIEW OF METHODOLOGY

• Resolution plan modified based on 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)

• 2009 Vogtle head loss testing will be used to determine which breaks contribute to risk quantification

• Breaks with debris quantities greater than tested (mass/SA)* will fail

• Breaks with debris quantities less than tested (mass/SA) will pass

• Will continue to quantify risk by evaluating GSI-191 failures for number of strainers in operation

• Will use consensus models/design basis inputs for parameters in the GSI-191 Risk-Informed Software

• Mass/SA = Mass of debris per unit strainer area

13 PILOT PLANT COMPARISON (STP VS.

VOGTLE)

Differences

• Physical

• ECCS trains

• Strainer configuration

• Containment Spray Setpoint

• Strainer design

• Strainer surface area

• Modeling

• Software

• Break size and orientation sampling

• Strainer head loss test protocol

• Chemical effects

• Core blockage

• Time-dependent comparison to failure criteria

• Method for calculating CDF and LERF Similarities

• Physical

• Large dry containment

• 4 Loop Westinghouse NSSS

• Low density fiberglass insulation

• Trisodium phosphate buffer

• Modeling

• Break-specific ZOI debris generation

• Unqualified coatings

• Debris transport

• Past head loss testing to establish debris limits

• Penetration testing

• Mass balance of debris on strainer and core

14 SOFTWARE

• BADGER (Break Accident Debris Generation Evaluator)

• A computer program that automates break ZOI debris generation calculations using CAD software

• NARWHAL (Nuclear Accident Risk Weighted Analysis)

• A computer program that evaluates the probability of GSI-191 failures by holistically analyzing the break-specific conditions in a time-dependent manner

15 ANALYSIS FLOWCHART NARWHAL Break Analysis (Strainers)

NARWHAL Break Analysis (Core)

Strainer Head Loss Test Acceptable Mitigation WCAP-17788 Strainer Penetration Test CDF LERF Acceptable Risk: Submit LAR Not Bounded Bounded Bounded Not Bounded RG 1.174 Acceptance Guidelines Unacceptable Risk: Implement Refinements or Modifications

16 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

17 DEBRIS GENERATION

• Insulation and qualified coatings

• Automated analysis with containment CAD model using a tool called BADGER

• 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

• Unqualified coatings and latent debris quantities are identical for all breaks Nukon 17D Qualified Epoxy & IOZ with Epoxy topcoat 4D Interam Fire Barrier Material 11.7D

18 INSULATION AND QUALIFIED COATINGS QUANTITIES

• BADGER database contains 28,434 breaks at 930 weld locations

• Breaks evaluated at each Class 1 ISI weld

• Partial breaks evaluated in 2 inch increments for smaller break sizes, 1 inch increments for larger break sizes, and 1/2 inch increments for largest break sizes

• Partial breaks evaluated in 45° increments around pipe

• DEGB evaluated at every weld

• 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

19 NUKON DEBRIS GENERATED

20 UNQUALIFIED COATINGS

• Types of Unqualified Coatings at Vogtle

• Inorganic Zinc (IOZ)

• Alkyd

• Epoxy

• IOZ, alkyd, and epoxy coatings are assumed to fail as 100% particulate

• Size distribution for degraded qualified coatings and failure timing no longer being utilized because of the reliance on 2009 head loss testing

21 UNQUALIFIED COATINGS LOCATIONS

• Coatings that fail in upper containment would have a reduced transport fraction for breaks where containment sprays are not initiated Coating Type Upper Containment Quantity (lbm)

Lower Containment Quantity (lbm)

Epoxy 1,602 1,127 Alkyd 0

59 IOZ 24 31 Total 1,626 1,217

22 CONTAINMENT POOL WATER LEVEL

• Sump pool depth is evaluated on a break-specific basis using conservative inputs to minimize water level

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

• Planning to remove 2 disks from each RHR strainer to reduce overall height

• Modifying procedures for breaks that dont activate containment spray

• Continue RWST drain down to just below empty level set point

• Allows reduction of Tech Spec RWST min water level by 2% (~1 ft) to increase operator margin

• Strainers are submerged for all scenarios

23 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

24 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 10% washdown for fines due to condensation and 0% for small pieces

25 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 Assumption to use for containment spray actuation is not obvious for most breaks/sizes

26 FIBER TRANSPORT FRACTIONS TO ONE RHR STRAINER

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

Debris Type Size 1 Train w/

Spray 2 Train w/

Spray 1 Train w/o Spray 2 Train w/o Spray*

Nukon Fines 58%

29%

23%

12%

Small 48%

24%

5%

2%

Large 6%

3%

7%

4%

Intact 0%

0%

0%

0%

Latent Fines 58%

29%

28%

14%

Strainers in Operation 2

4 1

2

27 PARTICULATE TRANSPORT FRACTIONS TO ONE RHR STRAINER Debris Type Size 1 Train w/

Spray 2 Train w/

Spray 1 Train w/o Spray 2 Train w/o Spray Interam Fines, Smalls 58%

29%

47%

23%

Unqualified Epoxy Particulate 58%

29%

47%

23%

Unqualified IOZ Particulate 58%

29%

16%

8%

Unqualified Alkyd Particulate 58%

29%

100%

50%

Qualified Epoxy Particulate 58%

29%

23%

12%

Qualified IOZ Particulate 58%

29%

23%

12%

Latent dirt/dust Particulate 58%

29%

28%

14%

28 CONTAINMENT SPRAY AND POOL pH Combining conditions in a non-physical way to bound release and precipitation

• Containment spray from the RWST will use a maximum pH for acidic conditions associated with the minimum RWST boron concentration.

• The design basis maximum containment pool pH is used for the sprays during recirculation and the containment pool to calculate chemical release.

• Lower pH values/profiles are used for aluminum solubility to account for lower TSP concentrations, higher boric acid concentrations, and pH effects due to core release and radiolysis.

29 CHEMICAL EFFECTS

• Overview

• Chemical precipitate quantities are determined for each break

• Corrosion/Dissolution Model

• Dissolution from insulation and concrete is determined using the WCAP-16530 equations

• Corrosion, dissolution and passivation of aluminum metal is determined using the equations developed by Howe et al. (UNM)

• Solubility

• No credit will be taken for calcium solubility

• ANL solubility equation (ML091610696, Eq. 4) will be used to credit delayed aluminum precipitation

• Once temperature limit is reached, all aluminum will precipitate

• Aluminum is eventually "forced" to precipitate for all breaks

• Precipitate Surrogates

• WCAP-16530 Calcium Phosphate

• WCAP-16530 Sodium Aluminum Silicate

30 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 40 lbm 30% fiber and 70% particulate Qualified coatings 249 lbm IOZ and epoxy Unqualified coatings 2,843 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

31 DEBRIS QUANTITIES AT ONE RHR STRAINER Debris Type 2009 Test Quantity Bounding Hot Leg Break (two trains with CS)

Bounding Cold Leg Break (2 trains, with CS)

Bounding Cold Leg Break (single train with CS)

Nukon 106.1 ft3 337.3 ft3 333.6 ft3 667.3 ft3 Latent fiber 3.9 ft3*

1.2 ft3 1.2 ft3 2.32 ft3 Interam 290.3 lbm*

12.0 lbm 17.4 lbm 34.8 lbm Qualified coatings 696.8 lbm*

27.3 lbm 72.2 lbm 144.4 lbm Unqualified coatings 2874.1 lbm*

824.5 lbm 824.5 lbm 1648.9 lbm Latent particulate 52.7 lbm*

14.8 lbm 14.8 lbm 29.6 lbm Sodium aluminum silicate 89.1 lbm

~55 lbm

~55 lbm

~102 lbm Calcium phosphate 52.8 lbm

~53 lbm

~53 lbm

~108 lbm

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

32 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)

• 1 inch submergence for vortex observations Alion Test Facility

33 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 (4 to 20 micron)

• Latent particulate: Silica sand w/ size distribution consistent with NEI 04-07 Volume 2 (75 to 2000 microns)

• Interam fire barrier: Interam E-54A

34 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

35 2009 TEST RESULTS Debris Load Thin-bed test head loss (ft)

Full-load test 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

36 APPLICATION OF 2009 RESULTS

• Total conventional debris plus calcium phosphate head loss will be applied at the start of recirculation

• Total aluminum precipitate head loss will be applied when temperature decreases to solubility limit

• 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

37 STRAINER ACCEPTANCE CRITERIA

• RHR and CS Pump NPSH Margin

• 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 24.0 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

• Multiple 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 curve fit of the test data will be used to evaluate maximum fiber penetration for a 16 disk strainer (RHR) and 14 disk strainer (CS).

39 0

200 400 600 800 1000 1200 1400 1600 1800 0

5000 10000 15000 20000 Cumulative Fiber Penetration (g)

Cumulative Fiber Addition (g)

FIBER PENETRATION RESULTS

40 IN-VESSEL EFFECTS

• Transport/accumulation of fiber to the core that penetrates RHR strainers is dependent on break location and flow path and will be based on WCAP-17788

• Values for core blockage and boron precipitation acceptance criteria will be based on WCAP-17788

41 EX-VESSEL EFFECTS

• A bounding evaluation performed for all components

• Existing evaluations will be updated in accordance with WCAP-16406-P-A,Evaluation of Downstream Sump Debris Effects in Support of GSI-191 Revision 1 and the accompanying NRC SER

42 LOCADM

• A bounding calculation performed to cover all scenarios

• Existing evaluations will be updated in accordance with WCAP-16793-A,Evaluation of Long-Term Cooling Considering Particulate, Fibrous, and Chemical Debris in the Recirculating Fluid Revision 2 and the accompanying NRC SER

43 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

44 GSI-191 ACCEPTANCE CRITERIA Acceptance Criteria Method for Addressing Debris exceeds limits for upstream blockage, e.g. refueling canal drain Bounding analysis - part of transport calculation Strainer head loss exceeds pump NPSH margin or strainer structural margin Break-specific analysis based on tested debris limits and maximum tested head losses Gas voids from degasification or flashing exceed strainer/pump limits Break-specific analysis based on head loss, pool temperature, etc.

Pumps fail due to air intrusion from vortexing Bounding analysis Penetrated debris exceeds ex-vessel wear and blockage limits Bounding analysis Penetrated debris exceeds in-vessel fuel blockage and boron precipitation limits Break-specific analysis based on penetration testing and flow splits Debris accumulation on cladding prevents adequate heat transfer Bounding analysis

45 OVERVIEW OF MODELING

• GSI-191 phenomena evaluated in a holistic, time-dependent manner with an evaluation tool called NARWHAL

• Developed using object oriented design

• Tracks movement of water and debris

• Evaluates each break with incremental time steps up to 30 days

• Evaluates range of breaks to determine which ones pass/fail the strainer and core acceptance criteria

• Uses top-down LOCA frequencies to calculate conditional failure probabilities for small, medium, and large breaks

46 OVERVIEW OF MODELING

• NARWHAL prototype has been used for preliminary risk-informed evaluations by several plants

• Version 1.0 is currently under development

• Software requirements, design, implementation, V&V, and user documentation prepared under ENERCONs Appendix B QA program

• NARWHALs object oriented design allows users to model unique plant-specific geometry with a common executable file

• Simplifies software maintenance

• Significantly reduces potential for software errors

47 OVERVIEW OF MODELING RWST Reactor Vessel Break Core ECCS CS Spray Nozzles Containment Compartments Sump Pool ECCS Strainers

48 OVERVIEW OF MODELING

49 OVERVIEW OF MODELING

• NARWHAL integrates models and inputs from design basis calculations and GSI-191 tests/analyses:

• Water volumes, temperature profiles, and pH from design basis calculations

• Debris quantities from BADGER database

• Location-specific transport fractions from transport calculation

• Chemical effects calculated using WCAP-16530 and Howe model

• Conventional and chemical head loss from 2009 strainer testing (scaled for temperature and flow)

• NPSH and structural margin from design basis calculations

• Degasification calculated using standard physical models

• Time-dependent penetration using data fit from 2014 strainer testing

• Core failure calculated using WCAP-17788 model and limits

50 OVERVIEW OF MODELING

1. Select unique break location, size, and orientation

2. ZOI debris quantities from BADGER (insulation and qualified coatings)

3. Debris quantities outside ZOI (unqualified coatings, latent, miscellaneous)

4. Blowdown transport to containment compartments and sump pool

5. Washdown transport from containment compartments to sump pool

6. Pool fill transport from sump pool to strainers and inactive cavities

7. Recirculation transport from sump pool to strainers

8. Debris penetration through strainers

9. Debris accumulation on core

51 OVERVIEW OF MODELING

2. Corrosion/

dissolution of metals, concrete, and debris in sump pool

1. Corrosion/

dissolution of metals, concrete, and debris by CS

4. Formation of chemical precipitates

3. Precipitate solubility limit

5. Recirculation transport from sump pool to strainers

6. Debris penetration through strainers

7. Debris accumulation on core

52 OVERVIEW OF MODELING

1. Strainer Head Loss (CSHL +

Conventional HL

+ Chemical HL)

2. Degasification gas void fraction

3. Pump NPSH margin

4. Strainer structural margin 5a. Does HL Exceed NPSH or structural margin?

Yes 7a. Fail strainer criteria No 6a. Pass strainer criteria 5b. Does void fraction exceed strainer or pump limits?

Yes 7b. Fail strainer criteria No 6b. Pass strainer criteria

53 OVERVIEW OF MODELING

1. Core debris accumulation 2b. Does quantity exceed blockage limits?

Yes

3. Fail core criteria No

4. Pass core criteria 2a.

Does quantity exceed boron limits?

Yes No

54 OVERVIEW OF MODELING

• 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:

• 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

• It is not always obvious what conditions are bounding

55 INPUTS Input Values Sensitivity LOCA Frequency Based on NUREG-1829/PRA Need to address uncertainty Debris Generation Based on consensus models None Debris Transport Based on consensus models None Containment Temp Design basis None Pool Temp Design basis None Containment Spray Activation and Duration Competing effects (e.g. washdown, strainer surface area, corrosion)

Need to run for activation and duration Pool Volume/Level Based on consensus models None Pool pH Design Basis maximum for corrosion, minimum for precipitation None ECCS Flow Rates Design basis (same for all breaks)

None Aluminum and Calcium Corrosion WCAP-16530 and UNM equations None Aluminum Precipitation ANL equation None Penetration 2014 testing Need to address uncertainty Head Loss Maximums Extrapolated and scaled from 2009 tests final values None

56 DIFFERENCES (STP VS. VOGTLE)

• Physical

• ECCS trains (3 vs 2)

• Strainer configuration (3 combined vs 4 separate)

• Containment Spray Setpoint

• Strainer design (flow control vs no flow control)

• Strainer surface area (~1800 ft2 vs 765 ft2)

57 DIFFERENCES (STP VS. VOGTLE)

• Modeling

• Risk Informed Software (CASA Grande/RUFF/FiDOE vs BADGER/NARWHAL)

• Break size and orientation sampling (Search algorithm vs uniform)

• Strainer head loss test protocol (flume vs tank)

• Aluminum and Calcium precipitate quantity (bounding test vs break-specific analysis)

• Aluminum passivation (not credited vs credited using Howe paper)

• Core blockage (RELAP5-3D vs WCAP-17788)

• Failure criteria (bounding analysis vs time-dependent comparison of head loss with NPSH, gas void, and flashing)

• GSI-191 risk quantification (critical break size frequency vs conditional failure probability entered into PRA)

58 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

59 INTERFACE WITH PRA

• The change in core damage frequency (CDF) and change in large early release frequency (LERF) due to issues related to GSI-191 will be determined using:

• LOCA frequencies from NUREG-1829 or the Vogtle PRA

• Equipment configuration logic from PRA model of record

• GSI-191 conditional failure probabilities from NARWHAL

• Final risk calculation will be performed using the Vogtle model of record with GSI-191 conditional failure probabilities

60 INTERFACE WITH PRA

1. PRA identification of accident scenarios and equipment configurations that are risk-significant to GSI-191

2. NARWHAL evaluation of GSI-191 phenomena for each risk-significant scenario/configuration to determine CFPs for each strainer/core failure basic event

3. PRA quantification of CDF & LERF with GSI-191 failures

4. PRA quantification of CDF & LERF with no GSI-191 failures Output to submittal documentation

5. Calculate CDF & LERF Yes

6.

Meets RG 1.174 Criteria

?

7a. Identification of analytical refinements to analysis No 7b. Identification of potential plant modifications (physical or procedural)

61 METHODOLOGY FOR USING LOCA FREQUENCY TO CALCULATE CONDITIONAL FAILURE PROBABILITY

• Partition PRA categories (Catk) into size ranges (SRi)

• Calculate probability of a LOCA occurring in each size range for every PRA category (P(SRilCatk))

• Calculate probability of a LOCA occurring at each weld (Weldj) within each size range (P(WeldjlSRi))

• Calculate probability estimate for success criteria failure (SCF) at each weld in each size range (P(SCFlWeldj,SRi))

• Calculate probability estimate for success criteria failure at every PRA category (P(SCFlCatk))

62 METHODOLOGY FOR USING LOCA FREQUENCY TO CALCULATE CONDITIONAL FAILURE PROBABILITY P SCF Catk =

i=1 Nk

j=1 Mi P SRilCatk P Weldj SRi P SCF Weldj, SRi From NUREG-1829 (or Vogtle PRA)

From NUREG-1829 (or Vogtle PRA) using top-down methodology From NARWHAL

63 ILLUSTRATION OF PRA CATEGORIES AND LOCA FREQUENCY SIZE RANGES

64 EQUIVALENT DEGB DIAMETER

• NUREG-1829, Section 3.7:

The correlations which relate flow rates and LOCA size categories to the effective break sizes in each PWR and BWR system are summarized in Table 3.8.

The break size corresponds to a

partial fracture for pipes with larger diameters than the break size, a complete single-ended rupture in pipes with the same inside diameter, or a DEGB in pipes having inside diameters 1/2 times the break size. All panelists used these correlations to relate their elicitation responses determined for the effective break sizes to the appropriate LOCA size category. It is important to stress that breaks can occur in either LOCA sensitivity piping or non-piping systems and components.

65 METHOD FOR ADDRESSING DEGB FREQUENCIES

• NUREG-1829 provides LOCA frequencies vs. break flow rates, which are converted to equivalent diameter break sizes

• Double ended guillotine breaks (DEGBs) have a flow rate (area) twice as large as the pipe cross-sectional area

• Equivalent diameter for DEBG is calculated using pipe inner diameter: DDEGB,Eq = 2

• Dpipe

• Breaks Dpipe assumed to progress to DEGB for debris generation (bounding debris quantities)

• Frequency associated with DEGB tail assigned to Dpipe break size to calculate conditional failure probability within each size range

• NUREG-1829 only provides frequencies up to 31 breaks, so frequencies corresponding to primary loop pipe DDEGB,Eq values is determined through log-log extrapolation

• 27.5 38.9

• 29 41.0

• 31 43.8

66 METHOD FOR ADDRESSING DEGB FREQUENCIES

67 EQUIPMENT CONFIGURATION

• 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 train failure

68 EQUIPMENT CONFIGURATION

• LBLOCA

• All equipment available bounding or reasonably representative for:

• No pump failures: ~79%

• 1 or 2 CS pump failures: ~18%

• 1 RHR pump failure bounding or reasonably representative for other equipment failure configurations: ~3%

• The values above are being used to determine which configurations to investigate with NARWHAL

• Conditional failure probabilities for GSI-191 basic events (strainer and core failure) will be manually entered into the PRA model of record to calculate CDF

~97%

69 CONDITIONAL FAILURE PROBABILITIES

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

• Strainer CFP higher with 1 train operating

• Additional scenarios will likely need to be evaluated (1 CS pump failure, 1 RHR pump failure, etc.)

70 PRA MODEL CHANGES

• Vogtle PRA model modified to incorporate conditional failure probabilities (CFPs) for GSI-191 strainer failures and core failures with associated initiating events and equipment configurations

• GSI-191 failure defined using PRA success criteria

• Strainer failure defined as failure of RHR pump/strainer

• CS strainer failures are calculated in NARWHAL, but not used in PRA

• GSI-191 failures binned into following CFP groups (separate CFPs defined for each LOCA category and each pump state)

• Core failures

• RHR Strainer A failures (without Strainer B or core failures)

• RHR Strainer B failures (without Strainer A or core failures)

• RHR Strainer A and B failures (without core failures)

• Each core and strainer CFP represented in PRA with a basic event that is combined with LOCA initiating event and pump failure logic to represent pump state associated with CFP

71 PRA MODEL CHANGES

72 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

73 UNCERTAINTY QUANTIFICATION

• Draft Reg Guide 1.229 requires uncertainty quantification for risk-informed GSI-191 evaluation

• Uncertainty quantification also required by Reg Guide 1.174

• Two different approaches that could be used to quantify uncertainty

• Simplified approach using sensitivity analysis

• Statistical sampling of input parameter distributions and propagating uncertainties

• Consensus inputs and models are considered to have no uncertainty

• Vogtle inputs that require uncertainty quantification

• LOCA frequency values

• Penetration model

• Containment spray activation and duration

• Possibly others

74 UNCERTAINTY QUANTIFICATION USING SENSITIVITY ANALYSIS

75 UNCERTAINTY QUANTIFICATION USING STATISTICAL SAMPLING

1. Select equipment failure configuration

2. Sample all random input values

3. Select break location, size, and orientation

5. Compare to GSI-191 acceptance criteria and PRA success criteria to identify strainer or core failures

9.

Output to PRA model

4. Evaluate GSI-191 phenomena at each time step for 30 days

6.

Sufficient breaks evaluated to estimate CFP?

No

7.

Sufficient random samples to estimate CFP PDF?

Yes No

8. All significant equipment configs.

evaluated?

Yes No Yes

76 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

77 SUBMITTAL DOCUMENTATION DISCUSSION Planning to follow the format, content, and depth of the August 2015 STP LAR

• GL 2004-02 Response following Staff Review Guidance (will have some pointers to risk informed summary)

• Risk Quantification and Summary

• Defense in Depth and safety margin

• Requests for exemptions (if 10CFR50.46(c) rule is not finalized)

• 10CFR50.46(d)

• GDC 19 (need being evaluated)

• GDC 35

• GDC 38

• GDC 41

• GDC 50.67 (need being evaluated)

• License amendment request

• Tech Spec markups

• Tech Spec Bases

• FSAR markups

• List of commitments

78 QUALITY ASSURANCE

• GSI-191 calculations are being revised to be safety related under vendor Appendix B QA programs

• Head loss testing in 2009 was conducted and documented as safety related under vendor Appendix B QA program

• Penetration testing was conducted and documented in 2014 as non-safety related following work practices established by vendor Appendix B QA program

• PRA has undergone an industry peer review per RG 1.200 and the ASME/ANS PRA Standard for CDF and LERF (RA-Sa-2009)

79 CONCLUSIONS

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

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

80 SCHEDULE UPDATE MILESTONE EXPECTED COMPLETION DATE Current Status Develop containment CAD model to include pipe welds Complete Complete Conduct meeting with NRC 3rd Quarter 2013 Complete Modify probabilistic risk assessment (PRA) to include Strainer and Core Blockage events 4th Quarter 2013 Complete Perform Chemical Effects testing 1st Quarter 2014 Complete Perform thermal and hydraulic modeling of RCS, Core, and Containment conditions 1st Quarter 2014 Complete Perform Strainer Head Loss and Bypass testing to establish correlation for range of break sizes 2nd Quarter 2014 Strainer Bypass Testing - Complete Strainer Headloss Testing - Using 2009 Vogtle test Assemble base inputs for CASA Grande 2nd Quarter 2014 Complete - Using NARWHAL instead of CASA Grande Evaluate Boric Acid Precipitation impacts 3rd Quarter 2015 Plan on using PWROG WCAP-17788 Finalize inputs to CASA Grande 3rd Quarter 2015 In Progress, Using NARWHAL instead of CASA Grande Complete Sensitivity Analyses in/for CASA Grande 4th Quarter 2015 2nd Quarter 2016 Integrate CASA Grande results into PRA to determine CDF and LERF 1st Quarter 2016 3rd Quarter 2016 Licensing Submittal for VEGP To be established through discussions with NRC - tentatively September 2016 Projected 1st Quarter 2017, require input from:

SE on STP Pilot Project and SE on WCAP-17788; which are not yet available.

81 AGENDA

• 8:30 - Introductions/Purpose of Meeting

• 8:45 - High Level Overview of Vogtle Closure Strategy &

What we have learned

• 9:00 - Review of Inputs and Assumptions

• 10:00 - Explanation of Modeling

• 11:30 - Interface with PRA

• 12:15 - Uncertainty Quantification

• 12:45 - Lunch

• 13:45 - Continued Discussion of Inputs and Assumptions

• 14:30 - Continued Discussion of PRA and Uncertainty

• 15:00 - Submittal Documentation

• 15:45 - Closing Remarks

82 BACKUP SLIDES

83 EXAMPLE CALCULATION

• Detailed physical calculations Break Location 11201-049-16-RB (10.5 DEG hot leg side break in annulus near surge line) 1 train operating with containment sprays activated Transport fractions: Maximum RHR flow rate: 3,700 gpm (design flow)

CS duration: 6 Hours Design basis temperature profile - Max Safeguards, with pool temperature drop to 90°F at Day 30 Minimum water level profile Sump pH used for corrosion: 8.1 Containment spray pH during Injection used for corrosion: 4.71 pH used for solubility: 7.6 Submerged Aluminum Area: 278.7 ft2 Unsubmerged Aluminum Area: 741.3 ft2 Submerged Concrete: 2,813 ft2 Aluminum Metal Release equations - WCAP 16530 Aluminum Solubility Equation - ANL Aluminum Solubility Equation Aluminum Solubility: Timing Only

84 BREAK LOCATION

85 POOL LEVEL

86 FIBER TRANSPORT TO ONE RHR STRAINER (1 TRAIN W/SPRAY)

• Transport fraction takes into account time-dependent transport (CS strainer active for 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />)

• • Combined fraction of fines due to erosion and intact pieces Debris Type Size DG Quantity (ft3)

Transport Fraction*

Quantity (ft3)

Nukon Fines 9.5 58%

6.1 Small 32.7 7%**

1.5**

Large 14.8 4%**

0.6**

Intact 15.9 0%

0.0 Total 72.9 8.2 Latent Fines 12.5 58%

7.8 Total 85.4 16.0

87 PARTICULATE TRANSPORT TO ONE RHR STRAINER (1 TRAIN W/SPRAY)

Debris Type Size DG Quantity (lbm)

Transport Fraction Quantity (lbm)

Interam Fines, Smalls 121.2 58%

70.3 Unqualified Epoxy Particulate 2,602.0 58%

1,509.2 Unqualified IOZ Particulate 25.0 58%

14.5 Unqualified Alkyd Particulate 32.0 58%

18.6 Qualified Epoxy Particulate 7.5 58%

4.4 Qualified IOZ Particulate 2.4 58%

1.4 Latent dirt/dust Particulate 170.0 58%

98.6 Total 2,960.1 1,717.0

88 CHEMICAL PRECIPITATE QUANTITIES

89 ALUMINUM CONCENTRATION AND SOLUBILITY

90 HEAD LOSS

• Clean strainer head loss: Bounding value of 0.162 ft at 4,500 gpm

• Conventional head loss

• Head loss due to chemical precipitates

• Values scaled to 16 disk RHR strainer area

• • Corrected to 3700 gpm and 90°F

• • • Applied at switchover to hot leg recirculation Head Loss Type Transported Quantity Max Tested Quantity*

Head Loss Corresponding to Max Tested Quantity (Unadjusted)

Head Loss with Flow and Temperature Correction**

Fiber 16.0 ft3 109.9 ft3 5.46 ft 4.41 ft Particulate 1,717.0 lbm 3,914.5 lbm Calcium Phosphate 9.6 lbm 52.8 lbm 1.11 ft 0.90 ft Sodium Aluminum Silicate 74.5 lbm 89.0 lbm 5.24 ft 4.23 ft Extrapolation to 30 days 2.13 ft***

1.72 ft

91 Short Term: Long Term:

VOID FRACTION AT RHR PUMP

92 DEBRIS TRACKING

• 100% capture of particulate and precipitate at strainer

• Penetration modeled based on test data curve fits

• All fiber is treated as fines

93 CORE ACCUMULATION

94

SUMMARY

Criteria Acceptance Criteria Example Results Example Pass/Fail NPSH Margin 16.6 ft 11.3 ft Pass Strainer Structural Margin 24.7 ft 11.3 ft Pass Partial Submergence Head loss less than 1/2 submerged height Fully submerged Pass Gas Void Fraction 2% at the pump 0.24% at the pump Pass Debris Limit Exceeds what was tested Not exceeded Pass Assumed core limits (to be replaced with WCAP-17788 criteria) 75 g/FA for Hot Leg Breaks 7.5 g/FA for Cold Leg Breaks 32 g/FA N/A Pass