ML15308A031

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NRC Public Meeting on November 5, 2015 Regarding GSI-191 Resolution Plan and Current Status
ML15308A031
Person / Time
Site: Vogtle  Southern Nuclear icon.png
Issue date: 11/05/2015
From:
Southern Nuclear Operating Co
To:
Office of Nuclear Reactor Regulation
References
Download: ML15308A031 (87)
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Text

VOGTLE GSI-191 RESOLUTION PLAN AND CURRENT STATUS NRC PUBLIC MEETING NOVEMBER 5, 2015

AGENDA

  • 8:30 - Introductions/Purpose of Meeting
  • What we have learned
  • 8:45 - High Level Overview of Vogtles Closure Strategy
  • 9:30 - Review of Inputs and Assumptions
  • 10:15 - Explanation of Modeling
  • 13:00 - Interface with PRA
  • 13:30 - Uncertainty Quantification
  • 14:00 - Submittal Documentation
  • 14:45 - Closing Remarks 2

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 3

INTRODUCTION 4

VOGTLE PLANT LAYOUT

  • 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, height of 5 ft RHR B
  • CS strainer: 14-disk tall, 590 ft2, height of 4 ft CS B
  • Perforated plate with CS A 3/32 diameter holes RHR A 6

PLANT RESPONSE TO LOCAS

  • Plant response includes the following general actions:
  • ECCS injection is initiated from the RWST to the cold legs via RHR, SI, and High Head 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
  • 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

WHAT WE HAVE LEARNED

  • Containment sprays only actuate for the largest hot leg breaks under best estimate conditions
  • This led to unsubmerged strainers for many breaks because RWST is left with unused water
  • Wide variation in post-LOCA water levels and sump chemistry
  • Planned modifications
  • Reduce height of RHR strainers by ~6 inches
  • Change procedures to continue RWST drain down to just below empty level set point
  • Allows reduction of Tech Spec min water level by ~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 8

RWST LEVELS AND ALARMS 9

SUBMERGED STRAINER RESULTS Before Modifications After Modifications LBLOCA LBLOCA Max = ~8.2 ft Max = ~8.7 ft LBLOCA Best LBLOCA Best Estimate = Estimate =

~6.6 ft ~7.9 ft

~5 ft SBLOCA SBLOCA minimum minimum

= ~4.75 ft = ~4.5 ft

~4.425 ft 10

HIGH LEVEL OVERVIEW OF VOGTLES CLOSURE STRATEGY 11

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 12

ANALYSIS FLOWCHART Strainer Head Strainer WCAP-17788 Loss Test Penetration Test NARWHAL Bounded Bounded NARWHAL Acceptable Break Analysis Break Analysis Mitigation (Strainers) (Core)

Not Bounded Not Bounded Acceptable RG 1.174 CDF Risk: Submit Acceptance LERF LAR Guidelines Unacceptable Risk: Implement Refinements or Modifications 13

REVIEW OF INPUTS AND ASSUMPTIONS 14

DEBRIS GENERATION

  • 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 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
  • BADGER is a computer program that automates break 15 ZOI debris generation calculations using CAD software

INSULATION AND QUALIFIED COATINGS QUANTITIES

  • BADGER database contains 28,434 breaks at 930 weld locations
  • Breaks evaluated at each weld inside 1st isolation valve
  • Partial breaks evaluated in 2 inch increments for smaller break sizes, 1 inch increments for larger break sizes, and 1/2 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 16

NUKON DEBRIS GENERATED 17

UNQUALIFIED COATINGS

  • Inorganic Zinc (IOZ)
  • Alkyd
  • Epoxy
  • IOZ, alkyd, and epoxy coatings were 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 18

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

Epoxy 1,602 1,127 Alkyd 0 59 IOZ 24 31 Total 1,626 1,217

  • Coatings that fail in upper containment would have a reduced transport fraction for breaks where containment sprays are not initiated 19

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
  • Continue injecting water to empty RWST
  • Strainers are submerged for all scenarios 20

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 21

TRANSPORT - WASHDOWN

  • 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
  • Assumed 10% washdown for fines due to condensation and 0% for small pieces 22

CONTAINMENT PRESSURE COMPARISON

  • 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 23

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% 2%

Large 6% 3% 7% 4%

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.

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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 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%

25

CONTAINMENT POOL pH

  • The design basis maximum containment pool pH will be used for the sprays during recirculation and the containment pool to calculate chemical release.
  • Lower pH values/profiles will be considered for aluminum solubility to account for lower TSP concentrations, higher boric acid concentrations, and pH effects due to core release and radiolysis.

26

CHEMICAL EFFECTS

  • Overview
  • Chemical precipitate quantities are determined for each break
  • Corrosion/Dissolution Model
  • Corrosion and dissolution of aluminum 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

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 28

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, (single train with CS) with CS) 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 29

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 30

2009 TESTING DEBRIS LOADS

  • Nukon debris quantity based on 7D ZOI
  • The following debris surrogates used
  • Nukon and latent fiber: Nukon
  • Coatings: Silicon carbide (4 - 20 micron)
  • Latent particulate: Silica sand w/ size distribution consistent with NEI 04-07 Volume 2 (fine sand - < 2000 microns)
  • Interam fire barrier: Interam E-54A 31

2009 TEST 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 32

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 33

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 34

STRAINER ACCEPTANCE CRITERIA

  • 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 35

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).

36

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) 37

IN-VESSEL EFFECTS

  • Transport/accumulation of fiber to the core that penetrates RHR strainers is dependent on break location and flow path and will be based on WCAP-17788
  • Values for core blockage and boron precipitation acceptance criteria will be based on WCAP-17788 38

EX-VESSEL EFFECTS

  • A single bounding evaluation will be 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 39

LOCADM

  • A bounding calculation will be 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 40

EXPLANATION OF MODELING 41

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

Pumps fail due to air intrusion from vortexing Bounding analysis Penetrated debris exceeds ex-vessel wear Bounding analysis and blockage limits Penetrated debris exceeds in-vessel fuel Break-specific analysis based on blockage and boron precipitation limits penetration testing and flow splits Debris accumulation on cladding prevents Bounding analysis adequate heat transfer 42

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 43

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 44

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

  • RWST: Refueling Water Storage Tank 45

OVERVIEW OF MODELING 46

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 model
  • Conventional and chemical head loss from 2009 strainer testing
  • NPSH and structural margin from design basis calculations
  • Degasification calculated using standard physical models
  • Time-dependent penetration using data fit from strainer testing
  • Core failure calculated using WCAP-17788 model and limits 47

OVERVIEW OF MODELING

3. Debris quantities outside ZOI (unqualified coatings, latent, miscellaneous)
2. ZOI debris 4. Blowdown 5. Washdown
1. Select unique quantities from transport to transport from break location, BADGER (insulation containment containment size, and and qualified compartments compartments to orientation coatings) and sump pool sump pool
6. Pool fill transport 7. Recirculation from sump pool to transport from strainers and sump pool to inactive cavities strainers Acronyms:
  • ZOI: Zone of Influence

OVERVIEW OF MODELING

1. Corrosion/

dissolution of 3. Precipitate metals, concrete, solubility limit and debris by CS

2. Corrosion/

dissolution of 4. Formation of metals, concrete, chemical and debris in precipitates sump pool

5. Recirculation transport from sump pool to strainers
6. Debris 7. Debris Acronyms: penetration accumulation on

OVERVIEW OF MODELING 5b. Does

1. Strainer Head void fraction No 6b. Pass Loss (CSHL + 2. Degasification exceed strainer Conventional HL gas void fraction strainer or criteria

+ Chemical HL) pump limits?

Yes

3. Pump NPSH 7b. Fail strainer 5a. Does margin criteria 6a. Pass No HL Exceed strainer NPSH or 9b. Does criteria structural quantity No margin? 8. Core debris
4. Strainer exceed accumulation structural margin blockage Yes limits?

7a. Fail strainer 9a. Yes criteria Does quantity Yes 10. Fail core Acronyms: exceed criteria

  • HL: Head Loss core criteria
  • CSHL: Clean Strainer Head Loss
  • NPSH: Net Positive Suction Head 50

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 51

INPUTS Input Values Sensitivity 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 Competing effects (e.x. washdown, strainer surface Need to run for Activation and Duration area, corrosion) activation and duration Pool Volume/Level Based on consensus models None Pool pH Design Basis maximum for corrosion, design basis None minimum for precipitation ECCS Flow Rates Design basis (same for all breaks) None Aluminum and Calcium WCAP-16530 and UNM equations None Corrosion Aluminum Precipitation ANL equation None Penetration 2014 testing Need to address uncertainty Head Loss Maximums Extrapolated and scaled from 2009 tests None final values 52

INTERFACE WITH PRA 53

INTERFACE WITH PRA

  • Equipment configuration probabilities 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 54

INTERFACE WITH PRA

4. PRA quantification of CDF & LERF with no GSI-191 failures
2. NARWHAL
1. PRA identification evaluation of GSI-191 of accident scenarios phenomena for each 3. PRA and equipment risk-significant quantification of 5. Calculate configurations that scenario/configuration CDF & LERF with CDF & LERF are risk-significant to to determine CFPs for GSI-191 failures GSI-191 each strainer/core failure basic event 6.

Acronyms: 7a. Identification Meets No Yes Output to

  • GSI-191: Generic Safety Issue 191 refinements to 1.174 documentation
  • CFP: Conditional Failure Probability analysis Criteria
  • CDF: Core Damage Frequency  ?
  • CDF: Change in Core Damage Frequency 7b. Identification
  • LERF: Change in Large Early of potential plant Release Frequency modifications

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

56

METHODOLOGY FOR USING LOCA FREQUENCY TO CALCULATE CONDITIONAL FAILURE PROBABILITY Nk Mi SCF Cat k = P SR i lCat k P Weldj SR i P P SCF Weldj , SR i i=1 j=1 From NUREG-1829 From NUREG-1829 From NARWHAL using top-down methodology 57

ILLUSTRATION OF PRA CATEGORIES AND LOCA FREQUENCY SIZE RANGES 58

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 59

METHOD FOR ADDRESSING DEGB FREQUENCIES 60

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 train failure 61

EQUIPMENT CONFIGURATION PROBABILITY

  • All equipment available bounding or reasonably representative for:
  • No pump failures: ~79%
  • 1 or 2 CS pump failures: ~18% ~97%
  • 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 will be manually entering into the PRA model of record to calculate CDF 62

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.)

63

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 64

PRA MODEL CHANGES 65

UNCERTAINTY QUANTIFICATION 66

UNCERTAINTY QUANTIFICATION

  • Draft Reg Guide 1.229 requires uncertainty quantification for risk-informed GSI-191 evaluation
  • 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
  • Possibly others 67

UNCERTAINTY QUANTIFICATION USING SENSITIVITY ANALYSIS 68

UNCERTAINTY QUANTIFICATION USING STATISTICAL SAMPLING

1. Select 4. Evaluate GSI- 5. Compare to GSI-191
2. Sample all 3. Select break equipment 191 phenomena acceptance criteria and PRA random input location, size, failure at each time step success criteria to identify values and orientation configuration for 30 days strainer or core failures 6.

Sufficient No breaks evaluated to estimate CFP?

Yes 7.

Sufficient No random samples to estimate CFP PDF?

Yes

8. All 9.

No significant Yes Output equipment to PRA Acronyms: configs.

model

  • LOCA: Loss of Coolant Accident
  • GSI-191: Generic Safety Issue 191
  • CFP: Conditional Failure Probability 69
  • PDF: Probability Density Function

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 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) 70

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 71

SUBMITTAL DOCUMENTATION 72

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
  • License amendment request
  • Tech Spec markups
  • Tech Spec bases
  • List of commitments

UPDATED RESOLUTION SCHEDULE EXPECTED MILESTONE Current Status COMPLETION DATE Develop containment CAD model to include Complete Complete pipe welds Conduct meeting with NRC 3rd Quarter 2013 Complete Modify probabilistic risk assessment (PRA) to 4th Quarter 2013 Complete include Strainer and Core Blockage events

    • Perform Chemical Effects testing 1st Quarter 2014 Complete
    • Perform thermal and hydraulic modeling of 1st Quarter 2014 Complete RCS, Core, and Containment conditions
    • Perform Strainer Head Loss and Bypass testing Strainer Bypass Testing - Complete 2nd Quarter 2014 to establish correlation for range of break sizes 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 4th Quarter 2015 1st Quarter 2016 Grande Integrate CASA Grande results into PRA to 1st Quarter 2016 1st Quarter 2016 determine CDF and LERF To be established through Projected 1st Quarter 2017, require input from:

Licensing Submittal for VEGP discussions with SE on STP Pilot Project and SE on WCAP-17788; NRC - tentatively which are not yet available.

September 2016 74

CLOSING REMARKS 75

BACKUP SLIDES 76

EXAMPLE CALCULATION

  • Detailed physical calculations
  • Break Location 11201-049-16-RB (10.5 DEG hot leg side break in annulus near surge line)
  • Transport fractions: Maximum
  • Condensation washdown: 10%
  • RHR flow rate: 3,700 gpm (design flow)
  • CS timing: 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
  • pH used for solubility: 7.6
  • Submerged Concrete: 2,813 ft2

POOL LEVEL 78

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

Debris Type Size DG Quantity Transport Quantity (ft3) Fraction* (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

  • 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 79

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 80

CHEMICAL PRECIPITATE QUANTITIES 81

ALUMINUM CONCENTRATION AND SOLUBILITY 82

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 Max Head Loss Head Loss with Head Loss Transported Tested Corresponding to Flow and Type Quantity Quantity* Max Tested Quantity Temperature (Unadjusted) Correction**

Fiber 16.0 ft3 109.9 ft3 5.46 ft 4.41 ft Particulate 1,717.0 lbm 3,914.5 lbm Calcium 9.6 lbm 52.8 lbm 1.11 ft 0.90 ft Phosphate Sodium Aluminum 74.5 lbm 89.0 lbm 5.24 ft 4.23 ft Silicate Extrapolation 2.13 ft*** 1.72 ft Correction

  • Values scaled to 16 disk RHR strainer area
    • Corrected to 3700 gpm and 90°F
      • Applied to every break to correct chemical head loss 83

VOID FRACTION Short Term: Long Term:

84

DEBRIS PENETRATION

  • 100% capture of particulate and precipitate at strainer
  • Direct penetration curve fit (Placeholder) 0.44 4 , < 0.904

=

0.51%, 0.904 Where F = penetration fraction t = fiber bed thickness on strainer in inches

  • Captured fiber shedding
  • All fiber is treated as fines 85

DEBRIS PENETRATION (G/FA) 86

SUMMARY

Criteria Failure Example Results Example Pass/Fail NPSH Margin 16.6 ft 11.3 ft Pass Strainer Structural 24.7 ft 11.3 ft Pass Margin Partial 1/2 submerged Fully Pass Submergence height submerged Gas Void Fraction 2% at the pump 0.24% at the pump Pass Exceeds what was Debris Limit Not exceeded Pass tested 75 g/FA for Hot Assumed core limits Leg Breaks (to be replaced with 32 g/FA Pass WCAP-17788 criteria) 7.5 g/FA for Cold Leg Breaks 87

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