ML11152A170

05/12/2011-Meeting Slides from Meeting with TVA on Their Proposed Response to a Request for Additional Information on Generic Letter 2004-02

ML11152A170
Person / Time
Site:	Watts Bar, Sequoyah
Issue date:	05/12/2011
From:	Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation
lingam s p
Shared Package
ML11152A171	List: ML11152A163 ML11152A170
References
TAC MC4717, TAC MC4718, TAC MC4730, GL-04-002
Download: ML11152A170 (33)

Text

TENNESSEE VALLEY AUTHORITYSEQUOYAH NUCLEAR PLANT, UNITS 1 AND 2WATTSBARNUCLEARPLANTUNIT1 WATTS BAR NUCLEAR PLANT , UNIT 1NRCMeeting NRC MeetingRegarding Generic Letter 2004-02 Responses Rockville, MarylandMay 12, 2011 Agenda*Introduction

• Review of TVA Small Break Loss-of-Coolant Rod KrichAccident Water Level Calculations

-Sequoyah Nuclear Plant (SQN)

Sump Strainer Submergence Chris Carey

-Watts Bar Nuclear Plant (WBN)

Sump Strainer Submergence

• ReviewofWBNSumpStrainerStructural Robert Kirkpatrick Robert Kirk p atrick Review of WBN Sump Strainer Structural Integrity Calculation

• Applicability of Sump Strainer Structural IntegrityCalculationtoSQN/Plansfor p Dave Lafever Integrity Calculation to SQN/Plans for Insulation Remediation

• Schedule for Final Request for Additional InformationResponseSubmittal Kara Stacy Information Response Submittal*Closing Remarks Rod Krich 2

SQN Sump Strainer Submergence

Background

• NRC Requested TVA Provide Additional Information for SQN

-Demonstrate Adequate Sump Performance during Small BreakLoss-of-Coolant Accident (SBLOCA)

• NRC Concern is Tall Sump Strainers will be Partially Submerged when Engineered Safety Features (ESF) Pumps begin to take Suction from

Sump *Condition could Result in Less Water Flowing through Strainers than being Drawn by ESF Pumps and Cause Loss of Emergency Core CoolingSystem(ECCS)and/orContainmentSpray(CS)

Cooling System (ECCS) and/or Containment Spray (CS)3 SQN Sump Strainer Submergence (continued)ESF Design

• ECCS and CS Pum p Suctions Initiall y Ali gned to Refuelin g Wate rpyggStorage Tank (RWST)

• ECCS Pumps Aligned to Sump on RWST Low Level and CS Pumps AlidtSRWSTLLLl Ali gne d t o S ump on RWST L ow-L ow L eve l*CS Actuates on High-High Containment Pressure (2 psig)

• Containment Air Return Fans Force Steam and Hot Air in Lower Compartment through Ice Condenser

-Steam is condensed

-Hot Air is cooled

-Melt Water from Ice is produced

• Containment Desi gn Channels All Water from CS and Steam 4 gCondensation/Ice Melt Back to Sump SQN Sump Strainer Submergence (continued)SBLOCA Characteristics

• Break Flow Small enough that High Head ECCS Pumps Maintain Pressurizer Level*ECCS Pumps Provide Additional Water to RCS to Maintain Constant RCS Water Volume as RCS Cools

-Requirement Identified by NRC in Discussions with TVA/WBN, Unit 1

• RCS Pressure Remains above Accumulator PressurePreentsAccmlatorandLoHeadSafetInjection

-Pre v ents Acc u m u lator and Lo w Head Safet y Injection*Break Could be Located Such that Liquid Portion of Break Flow is Contained Inside Reactor Cavity (does not Fill Sump)

-This Break Location is not a Design Basis Accident LocationNot in Hot or Cold Leg Pipe

-This Break would not Generate Debris that could be Transported to Sump 5*CS Actuates for Even Smallest Breaks due to Buildup of Steam and Hot Air in Lower Compartment of Containment SQN Sump Strainer Submergence (continued)Original SQN SBLOCA Sump Level Calculation

• UsedOnlyPortionofWaterAvailableinRWSTbetweenRWST Used Only Portion of Water Available in RWST between RWST Minimum Full Level and RWST Low Level

• AssumesReactorCavityFilledpriortoRWSTLowLevel Assumes Reactor Cavity Filled prior to RWST Low Level-Only Occurs if CS does not Actuate

• DidnotAccountforContributiontoSumpWaterVolumefromSteam

• Did not Account for Contribution to Sump Water Volume from Steam Condensing and Ice Melting 6

SQN Sump Strainer Submergence (continued)Revised SQN SBLOCA Sump Level Calculation

• AccratelDeterminesWaterAailableinRWSTbeteenRWST

• Acc u ratel y Determines Water A v ailable in RWST bet w een RWST Minimum Full and RWST Low Level

-Still includes Adverse Instrument Errors

-Change increases Water Volume in Containment by 35,000 gallons

• Accounts for Time Dependent Filling of Reactor Cavity, based on SizefSBLOCA o f SBLOCA-Change Results in Less Water in Reactor Cavity at RWST Low Leveland More Water in Sump 7

SQN Sump Strainer Submergence (continued)Revised SQN SBLOCA Sump Level CalculationClltiDtidLBdAtfIthtldb

• C a l cu l a ti on D e t erm i ne d L ower B oun d on A moun t o f I ce th a t wou ld b e Melted by Steam from Break

-Am ou n t o f Stea m R e l eased fr o m Br ea k based o n Satu r ated Co n d i t i o n s at outoSteaeeasedoeabasedoSatuatedCodtosatRCS Pressure of 600 psia, Accumulator Pressure

-Released Steam Assumed to Condense on Ice and Flow to Sump as SaturatedWateratContainmentPressureof164 psia Saturated Water at Containment Pressure of 16.4 psiaLowest Containment Pressure that CS would be in Operation

-M e l t W ate r fr o m I ce a l so A ssu m ed to Fl o w to Su m p as Satu r ated W ate r at etateoceasossuedtootoSupasSatuatedateatContainment Pressure of 16.4 psiaMinimizes Amount of Ice that is Melted

-Ice Melt Predicted by this Method is Low Compared to Better Estimate Modeling of Ice Condenser by TVA's version of CONTEMPT 8

SQN Sump Strainer Submergence (continued)Revised SQN SBLOCA Sump Level Calculation

• ExplicitlyEvaluatedfollowingBreaksinsideReactorCavity

• Explicitly Evaluated following Breaks inside Reactor Cavity-100 gpm -Just above Break Size that would be Considered LOCA (i.e., Greater than Normal Makeup Capability)

-1200 gpm -Bounding Flow Rate for One-Train of ECCS when RCS remains Pressurized above Accumulator Pressure2500gpmBoundingFlowRateforTwoTrainsofECCSwhenRCSremains

-2500 gpm -Bounding Flow Rate for Two-Trains of ECCS when RCS remains Pressurized above Accumulator Pressure

• Breaks Larger than 2500 gpm cannot be Maintained above Accumulator Injection Pressure

-Accumulator Injection increases Water Volume in Containment 9

SQN Sump Strainer Submergence (continued)Insights from Revised SQN SBLOCA Sump Level Calculation

• About112gallonofMeltWaterFlowstoSumpforeverygallonremoved

• About 1.12 gallon of Melt Water Flows to Sump for every gallon removed from RWST by ECCS

• One CS Pum p in O p eration Results in Hi gher Sum p Level than Two CS ppgp Pumps in Operation

-Two CS Pumps increase Holdup of RWST Water in Refueling Canal

-More Ice Melt due to Longer Time required to Drain RWST to Low Level 10 SQN Sump Strainer Submergence (continued)Revised SQN SBLOCA Sump Level Calculation Results

• SumpWaterLevelatRWSTLowLevel Sump Water Level at RWST Low Level-ECCS Pumps Aligned to Sump

• WhenTwoCSpumpsareinOperation

• When Two CS pumps are in Operation-100 gpm -5.73 feet (4.36 feet of strainer submerged)

-1200 gpm-5.83 feet (4.45 feet of strainer submerged)

-2500 gpm-594feet(457feetofstrainersubmerged) 2500 gpm-5.94 feet (4.57 feet of strainer submerged)

• Above Sump Water Level are Greater than Previously Determined SBLOCA Sum p Level of 2.5 feet at RWST Low Level p-Increase due toCrediting Additional Water Volume in RWSTAccounting for Melt Water Addition to SumpAddiSTiDdtClltihihdAddi ng S ome Ti me D epen d ency t o C a l cu l a tion, w hi c h re d uces Water Holdup in Reactor Cavity 11 SQN Sump Strainer Submergence (continued)Revised SQN SBLOCA Sump Level Calculation Results

• FullSubmergenceofTallStrainersOccurs<47minutesafterRWST Full Submergence of Tall Strainers Occurs < 4.7 minutes after RWSTLow Level due to Continued Operation of CS Pumps with their Suctions Aligned to RWST

-Due to Low Sump Flow Rate (<

2,500 gpm) and Short Time Period, no Significant Debris Accumulation Occurs prior to Full Submergence

-Debris Load for SBLOCA is < 25 p ercent of Debris Load for LBLOC A pNo Potential for Significantly Loading Strainers

-When CS Pumps are aligned to Sump (at RWST Low-Low Level), Sump Water Level is 8.5 feet or 1 foot above top of Tall Strainers (sump flow

> 5,100 gpm and < 12,500 gpm)

• SumpPerformanceforSBLOCAis Acceptable Sump Performance for SBLOCA is Acceptable 12 WBN, Unit 1, Sump Strainer Submergence Overview*AllWaterLevelswillFullySubmergeStrainer

• All Water Levels will Fully Submerge Strainer*Minimum SBLOCA Water Level increased to 5.78 feet from 5.48 feet

• SBLOCA Water Level increases over Time

-With Minimum Level at ECCS Switchover

• Hold Up in RCS due to decreasing Temperature Accounted for in Calculation 13 WBN, Unit 1, Sump Strainer Submergence (continued)

Assumptions

• AllAssumptionsareConservativeandTakentoMinimizeSumpWater All Assumptions are Conservative and Taken to Minimize Sump Water Level*WBN , Unit 1 , Water Level Assum p tions Consistent with SQN Assum p tions,,pp-Minimum Injection from RWST

-No Accumulator Injection

-Reactor Coolant System (RCS) Break Location between Reactor Vessel and Biological Shield Wall

-Maximum RCS Makeu p due to Fluid Shrinka g e pg-Minimum Ice Melt 14 WBN, Unit 1, Sump Strainer Submergence (continued)

Assumptions

• MinimumInjectionfromRWST Minimum Injection from RWST-Fluid Assumed at Maximum Temperature of 105°F to Minimize Water Mass in Tank

-Beginning Water Level at Minimum Operating Level

-ECCS and CS Switchovers to Sump at Low and Low-Low Water Level Setpoint at Upper Analytical Limits

• No Accumulator Injection

-No Fluid from Accumulators Credited in SBLOCA Water Level Calculation

• RCS Break Location between Reactor Vessel and Biological Shield Wall

-Break Location Chosen so all ECCS Injection will be held up in Reactor Cavity 15 WBN, Unit 1, Sump Strainer Submergence (continued)

Assumptions

• MaximumRCSMakeupduetoFluidShrinkage Maximum RCS Makeup due to Fluid Shrinkage-RCS Pressure and Temperature Assumed to Decrease at (Bounding)

Rates Defined by 2-inch Line Break

-Long-Term Shrinkage Limited to Accumulator Check Valve Pressure of

600 psia*Minimum Ice Melt

-Ice Melt Previously Only included up to RHR Switchover

-Ice Melt Now included until CS Switchover to Sump

-Ice Melt Water and Vapor Exit Temperatures Conservatively taken to

minimiz e I ce M e l t a n d in c r ease Se n s i b l e H eat A dd i t i o neceetadceaseSesbeeatddto 16 WBN, Unit 1, Sump Strainer Submergence (continued)

Analysis*MethodologynotChangedbetweenRevisions

• Methodology not Changed between Revisions *RCS Holdup due to Fluid Shrinkage now Explicitly Calculated

• Calculation Accounts for Holdup Quantities in RCS, ECCS, and CS Piping, Containment Atmosphere, and Physical Locations in

Containment

• Fluid Volume Contributed from RCS Break and Ice Melt is Calculated using WBN Containment Dynamic Response Model based on WCAP 8282 WCAP-8282*Sump Water Volume then Calculated by Interpolation using Fluid VolumefromModel 17 Volume from Model WBN, Unit 1, Sump Strainer Submergence (continued)

Summary*WBNUnit1SumpStrainerwillRemainSubmergedforAllSBLOCA

• WBN , Unit 1 , Sump Strainer will Remain Submerged for All SBLOCA Accident Cases

• RCSShrinkageNowExplicitlyCalculated RCS Shrinkage Now Explicitly Calculated

• Assumptions are Conservative and Documented in Calculation 18 WBN, Unit 1, Sump Strainer Structural Integrity Overview*InitialDesignBasisDebrisLoadedThinBedTestPerformedatAlden Initial Design Basis Debris Loaded Thin Bed Test Performed at Alden Laboratories, July 2010, resulted in Unacceptably High Head Loss

• Further Testin g Reduced Debris Head Loss g-But only by Removing Min-K Insulation

• As-TestedHeadLosshadNegativeImpactonStrainerAssembly As Tested Head Loss had Negative Impact on Strainer Assembly Structural Integrity

• Strainer Assembl y Structural Re quirement Bounds ECCS and CS Pum p yqpNet Positive Suction Head (NPSH) Requirements 19 WBN, Unit 1, Sump Strainer Structural Integrity (continued)

Overview*ReducingHeadLossandAcceptanceofWBNUnit1StrainerTesting Reducing Head Loss and Acceptance of WBN , Unit 1 , Strainer Testing Results Requires Additional Analysis and Modifications

• Three Approaches Considered for Addressing Test Results 1.Develop New Clean Strainer Head Loss (CSHL) Calculation using Computational Fluid Dynamics (CFD) Modeling of Strainer to Reduce CSHL 2.Determine Maximum Structural Qualification of Strainer Assembly 3.Modification to Reduce Debris Head Loss

• Pursuing Three Approaches Led to Following Solutions to increasedHeadLoss Head Loss 1.Replacement of Plenum Cover Plate with Larger Orifice Sizes to Reduce CSHL based on Results of New Calculation 2MiSttlQlifitifStiAbl 2.M ax i mum St ruc t ura l Q ua lifi ca ti on o f St ra i ner A ssem bl y 3.Removal of Min-K Insulation to Reduce Debris Head Loss 20 WBN, Unit 1, Sump Strainer Structural Integrity (continued)

CSHL Reduction

• CFDAnalysisPerformedtoEvaluateCSHL CFD Analysis Performed to Evaluate CSHL-Preliminary CFD Analysis Calculated CSHL of > 5 feet

• CSHLisaboveValueAllowedbyDesignSpecificationusedtoProcure

• CSHL is above Value Allowed by Design Specification used to Procure Strainer Assembly

• Hi gh CSHL Results from the existin g 5-inch and 5.5-inch Orifices used for ggFlow Balancing through 23 Strainer Modules 21 WBN, Unit 1, Sump Strainer Structural Integrity (continued)

CSHL Reduction

• OptimalOrificeSizeDeterminedUsingCFDMethodbyIncrementally Optimal Orifice Size Determined , Using CFD Method , by Incrementally Adjusting Orifice Diameter over Multiple Model Executions

• Optimal Orifice Sizes Reduce Head Loss while Maintaining Flow Balance

• New Orifice Diameters Range from 6.5 inches to 8 inches

• NewCleanStrainerHeadLossis

<2feet New Clean Strainer Head Loss is 2 feet*Since Orifices are Holes Cut in Plenum Top Cover Plates, Replacement of Orifices Requires Replacement of Cover Plates

• Design Change for Plenum Cover Plate Replacement will be Issued in Support of Implementation and Completion during Fall 2012 Outage 22 WBN, Unit 1, Sump Strainer Structural Integrity (continued)

CSHL Reduction

• PlenumCoverPlatesareshownbelow Plenum Cover Plates are shown below 23 WBN, Unit 1, Sump Strainer Structural Integrity (continued)

Structural Qualification

• WBN,Unit1,StructuralCalculationCurrentlyQualifiestheStrainer WBN, Unit 1, Structural Calculation Currently Qualifies the Strainer Assembly for a Debris-Laden Head Loss of 3.65 feet

• Additional Preliminary Study Calculation Confirms WBN, Unit 1, Strainer is Structurally Qualified Up to a Head Loss of 5.7 feet

• New Total Head Loss is 3.83 feet, including Debris Loading at 120°F

-After Modifications Implemented 24 WBN, Unit 1, Sump Strainer Structural Integrity (continued) Min-K Insulation Removal

• Min-KInsulationwasPrimarySourceofHeadLossduringRecent Min K Insulation was Primary Source of Head Loss during Recent Strainer Testing

-Test of Record, without Min-K, had Significantly Less Head Loss

• WBN will Remove All Min-K from Applicable Locations inside

Containment

-Min-K Insulation Currently used in Areas where Close Commodity Clearances Exist with Hot Piping 25 WBN, Unit 1, Sump Strainer Structural Integrity (continued) Min-K Insulation Removal

• 15LocationswhereMin

-Kwillberemoved 15 Locations where Min K will be removed*Locations Distributed throughout Lower ContainmentWBNMitiStitCtlfIltiiCtitthhf

• WBN M a i n t a i ns St r i c t C on t ro l o f I nsu l a ti on i n C on t a i nmen t th roug h use o f Design Drawings

-Therefore, All Min-K Locations are known

• Walkdowns Performed during recent Spring 2011 Outage to Confirm Information on Drawings

• Volume of Min-K Varies from 0.03ft 3 to 0.94ft 3depending on Location 26 WBN, Unit 1, Sump Strainer Structural Integrity (continued) Min-K Insulation Removal 27 WBN, Unit 1, Sump Strainer Structural Integrity (continued) Min-K Insulation Removal 28 WBN, Unit 1, Sump Strainer Structural Integrity (continued) Min-K Insulation Removal 29 WBN, Unit 1, Sump Strainer Structural Integrity (continued) Min-K Insulation Removal

• SomeLocationsmaybereplacedwithanIndustryApproved Some Locations may be replaced with an Industry Approved Non-Fibrous Type Insulation

-That does not Invalidate Sump Testing

• For Other Locations, if the Approved Material does not Provide Adequate Insulating Value, Modifications will be Required to Resolve Commodity ClearanceIssues Clearance Issues*Design Changes for Insulation Changes and Reroutes to Resolve Commodity Clearances will be issued in Support of Implementation and Completion during Fall 2012 Outage 30 WBN, Unit 1, Sump Strainer Structural Integrity (continued)

SummaryExistingConfigurationModifiedConfiguration Existing Configuration Modified ConfigurationOrifice Diameters (inches)5.0 and 5.56.5, 7.0, 7.5, and 8.0Debris Head Loss (feet)*0.031.88CleanStrainerHeadLoss(feet)362195 Clean Strainer Head Loss (feet)3.62 1.95Total StrainerHead Loss (feet)3.653.83 Structural Qualification (feet)3.655.7**RHRNPSHMargin(feet) 94110*For120°FconditionsTemperatureCorrected2010TestHeadLossis109feetat190

°FMaximum RHR NPSH Margin (feet)9.4 11.0CS NPSH Margin (feet)5.534.74 For 120 F conditions. Temperature Corrected 2010 Test Head Loss is 1.09 feet at 190 F MaximumSump Temperature.** Value will Change Slightly as it is based on 5.0-and 5.5-inch Or ifice Diameters. New Value will Support Modified Total Strainer Head Loss.

31 WBN, Unit 1, Sump Strainer Structural Integrity (continued)

Summary*InitialDesignBasisDebrisLoadedThinBedTestResultedin Initial Design Basis Debris Loaded Thin Bed Test Resulted in Unacceptably High Head Loss

• High Test Head Loss will be resolved by 1.Implementing Design Change to Replace Plenum Cover Plate with Larger Orifice Sizes in Fall 2012 Outage 2.Completing Reanalysis of Structural Qualification of Strainer Assembly

with New Orifices 3.Im p lementin g Desi g n Chan ge to Remove Min-K Insulation in Fall 2012 pggg Outage 32 Applicability of Sump Strainer Structural Integrity Calculation to SQN/Plans for Insulation Remediation

• SQN does not Contain Fibrous Insulation

-No Insulation Remediation Required

• SQNIndividualStrainerModulesareSimilartoWBNUnit1StrainerModules

• SQN Individual Strainer Modules are Similar to WBN , Unit 1 , Strainer Modules-Similar Structural Margin Results Expected for Basic Module Elements

• SQN Strainer Stacks are Taller than WBN, Unit 1, Stacks

-72 inches versus 55 inches*SQN Plenum Assemblies are More Compact with Different Plenum Support Arrangement than WBN Plenum Assemblies

-123 inches X 69 inches -SQN versus 304 inches X 130 inches -WBN, Unit 1

• SQN Stack/Plenum Differences Prevent Direct Extrapolation of WBN, Unit 1, Results *SQN Configuration Specific Evaluations Required

• SQN Maximum Differential Pressure Remains below Current Analyzed Limit of 35feet 3.5 feet-Therefore, no plans for additional SQN structural margin assessments 33