ML120250105

Licensee Slides for 1/26/12 Meeting Three Mile Island, Unit 1 - Summary of Tube to Tube Wear Identified During T1R19 (Fall 2011)

ML120250105
Person / Time
Site:	Three Mile Island
Issue date:	01/25/2012
From:	Exelon Nuclear
To:	Bamford P J Plant Licensing Branch 1
Bamford, Peter J., NRR/DORL 415-2833
Shared Package
ML120250090	List: ML120250105 ML120250111
References
T1R19
Download: ML120250105 (32)

Text

Three Mile Island, Unit 1Summary of Tube-to-Tube

Wear Identified During

T1R19 (Fall 2011)

January 26, 2012 NRC Headquarters 2 IntroductionIntroductions and Opening RemarksBill Carsky, TMI-1 Site Engineering Director*Greg Ciraula, TMI-1 Engineering Programs Manager*Mark Torborg, TMI-1 Steam Generator (SG) Program Engineer*SteveQueen,DirectorCorporateEngineeringPrograms Steve Queen, Director Corporate Engineering Programs*Jay Smith, Corpor ate SG Program Manager*Wendi Croft, Senior Licensing Engineer 3 PurposeProvide information on tube-to-tube (T-T) wear*Inspection results*How the indications were identified

• Reporting Criteria

• Primary and secondary analysisHotheindicationseresied

• Ho w the indications w ere si z ed*Basis for sizing techniques

• Future planned actions 4 BackgroundTMI-1 installed AREVA, Enhanced Once Through Steam Generators (EOTSGs) during T1R18*Operated January 2010 -October 2011General design features of EOTSGs*15,597 tubes per EOTSG*Full depth hydraulic expansions in tubesheets

• 15 stainless steel tube support plates (TSP)

Trefoil broached holes, 1.18" thick Numbered 01S (bottom) -15S (top) 15S TSP has 1470 drill holes in peripheral tubesSibtTSPif35"464"S pac i ng b e tween TSPs var i es f rom 35" -46.4"Aspirating ports are in 10 th span *Nominal gap between tubes is 0.25"First inservice inspection performed in October 2011*24-month fuel cycles*1.72 effective full power years (EFPY) on EOTSGs

• Maintained hot conditions throughout operating cycle 5 T1R19 Inspection Overview100% full length bobbin coil inspections in each EOTSGX-Probe inspections of peripheral tubes (two tubes deep) in each EOTSG (Evaluated 1 st span for loose parts)Tube damage mechanisms found in each EOTSG Tb ttbtlt(TTSP)(td)*T u b e-t o-t u b e suppor t p l a t e wear (T-TSP) (expec t e d)*Tube-to-tube wear (T-T) (not expected)No evidence of tie rod bowing No tie rod to tube c ontact or proximity 6 EOTSG A, T-T Wear Map 7 EOTSG B, T-T Wear Map 8 T1R19 T-T Wear IdentificationReported as absolute drift indications (ADIs) during bobbin coil inspection with most indications located:*In mid-span*In the 9 th span*In a radial pattern 30" -45"

• In adjacent tubes (two or three)Performed X-Probe and +Point on ADI signals*Verified indications in adjacent tubes face each other *Symmetrically tapered to maximum depth in center

• In ad jacent tubes the indications are at same elevation and are same len g th/de p thjgp*Length and depth have a correlation that is consistent with wear*Good correlation of phase angles and voltages between channelsAnalysts, Exelon Engineering, and AREVA Engineering consensus is that these indications are T-T wear*Notified Steam Generator Management Program (SGMP) per the requirements of Nuclear Energy Institute (NEI) 97-06 *Notified NRC 9Process for Screening T-T WearIndications reported as ADIs Industry standard is to use I-Codes to identify (possible) flaw signals where no qualified sizing technique exists and supplemental testing is required.

Exelon guidelines require analysts to report all indications of suspected tube wall degradation.

• PrimaryAnalysis(manual)

Primary Analysis (manual)0.5 volts & 90º channel 6 or%TW >0 on channels 4 & 6 *Secondary Analysis (auto) 0.5 volts & 30º -95º on channel 6

%TW >0 on channels 4 & 6 and 0.16 volts on channel 6 0.25 volts & 60º -120º on channel 6 10 Example TMI-1 T-T Wear Bobbin Data 11 Example TMI-1 T-T Wear Bobbin Data 12Example TMI-1 MBM Screened as ADI 13Summary of ADI Indications (T-T Wear) ADI Indications 0.5 volt*"A" -9 Tubes Primary = 9, Secondary = 7, Both = 7*"B" -19 Tubes Primary = 19, Secondary = 18, Both = 18All ADIs including review for paired tubes

• "A"74TubeswithADIs(008162volts)*A -74 Tubes with ADIs (0.08 -1.62 volts)Primary = 20, Secondary = 34, Both = 13oEither Primary or Secondary = 41o74 of 74 confirmed by +Point or X-Probe *"B" -202* Tubes with ADIs (0.07 -1.25 volts)

Primary = 145, Secondary = 95, Both = 71oEither Primary or Secondary = 169o*183 of 202 confirmed by X-Probe 14Process for Screening T-T Wear Per Exelon & SGMP PWR Steam Generator Examinations Guidelines, I-Code indications are "Category III: Supplemental Test Required"*Prior to T1R19, +Point and X-Probe identified as probes to be used for supplemental examinations X-Pr obe qua lifi ed f o r s izin g T-T S P w ea r (EPRI ET SS 11 956.3)obequaedosgSea(SS9563)

+Point qualified for sizing T-TSP wear (EPRI ETSS 96910.1)

+Point qualified for sizing various shapes of wear (EPRI ETSS 27901 -27907)oEPRI ETSS 27905.3 "Flat Wear" was determined to be the correct technique for T-T wear in EOTSGs 15 Example TMI-1 T-T Wear +Point DataNOTE: Graphic shows partial indication 16 Example TMI-1 T-T Wear X-Probe Data 17 Example Depth Profiles in Paired TubesT-T Wear Depth ProfilesEOTSG A , Tubes R26-T36 AND R26-T37 12 14 16 18 20 22%TW)R26 - T36R26 - T37 0 2 4 6 8 10 12131415161718192021222324AXIAL LOCATION ABOVE TSP 08S (INCHES)DEPTH (%

18T-T Wear Length-Depth CorrelationEOTSG A/B T-T WEAR LENGTH/DEPTH CORRELATIONy = -0.0098x 2 + 0.509x + 1.8162 5 6 7 8 9 NCHES)0 1 2 3 40510152025DEPTH (%TW)LENGTH (I N 19 Site Qualified Sizi ng Technique for T-T WearX-Probe T-T wear sizing technique developed in cooperation with EPRI*Used two of the same samples used to develop ETSS 27905.3 (+Point Flat Wear)*Developed "Power" trend line/regression curve using methodology used for other EPRI X-Probe techniques ETSS 11956.1

-11956.4, Broached TSP Wea r*"Power" trend line/regression scatter plot based on multiple examinations of 16 wear scars Wear scars ranged from 8% -60% TW*Analysis of standards performed by multiple analysts from three different vendor organizations*Accuracy validated through comparison of +Point and X-Probe results for EOTSG A 20 Graphic of Flat Wear Standard X-Probe 21 Graphic of Flat Wear Standard +Point 22 X-Probe Calibration CurveX-Probe Amplitude - Depth Calibration Curvey = 13.151x0.613 R 2= 0.991 40 50 60 70%TW 0 10 20 3002468101214Amplitude (Voltage Vmx)MET %

23 X-Probe Calibration Curve ValidationX-Probe 300 kHz Axial 40 50 60 70 iable (%TW)Sy.x = 2.09N = 32y = 0.9603x + 1.4017 R 2 = 0.9831r= 0.9915 0 10 20 30010203040506070NDE %TWStructural Var i

24 Comparison of +Point and X-ProbeEOTSG AX-Probe vs. +Point - %TW Correlation 20 25 30%TW)y = 0.9832x + 0.3458 R 2 = 0.932N = 41 0 5 10 15051015202530+Point (%TW)X-Probe (%

25 T1R19 T-T Wear SummaryA total of 257 tubes were identified with T-T wear*EOTSG A: 89 indications in 74 tubes*EOTSG B: 206 indications in 183 tubesWear depths range from 1% to 21% through wall (TW)Wear axial lengths range from 2" to 8" No proximity or t ube contact detectedTbititldditidiitht

• T u bes are i n t ens i on a t co ld con ditions an d i n compress i on a t h o t conditionsSizing performed by +Point Technique 27905.3 and a site qualified X-Probe Technique*Good correlation between Bobbin, +Point, and X-Probe techniquesAll tubes met condition monitori ng limits and in-situ pressure testing was not required 26 T-T Wear Depth Distribution 0 5 10 15 20 25 30No. INDICATION SEOTSG A 012345678910111213141516171819202122DEPTH (%TW) 0 5 10 15 20 25 30 35 40 4512345678910111213141516171819202122DEPTH (%TW)No. INDICATION SEOTSG B 27 T1R19 T-T Wear SummaryEOTSG AEOTSG BTotal number of In-Service Tubes1559715597Number of T-T Wear Indications89206Number of Tubes T-T Wear74183 Average Depth of T-T Wear5.8%7.4%Maximum Depth of T-T Wear21%19%Number of T-T Wear Indications >40% TW00 Average Growth Rate T-T Wear3.4%/EFPY4.3%/EFPY

95 thPercentile Growth Rate T-T Wear9.3%/EFPY7.6%/EFPYMaximum Growth Rate T-T Wear12.2%/EFPY11.1%/EFPYNumber of Tubes Plugged for T-T Wear43 28Condition Monitoring Su mmary for T-T Wear Condition Monitoring Satisfied*Utilized maximum depth and bounding length of 39" for 3 X normal operating pressure differential conditions

(3P)*Substantial margin against accident leakage and structural limits*Large break loss of coolant accident (LBLOCA) loading conditions evaluated and satisfied Assumed 180 degree circumferential extent of wear 29Condition Monitoring Assessment for T-T Wear CM Results for Tube-to-Tube Wear for Both Array Coil and +Point Sizing 60 70 80 90 100 nt ThroughwallCM Limit for X-probe sizingSGA X-probe DepthsSGB X-probe DepthsCM Limit for +Point SizingSGA +Point Depths 0 10 20 30 40 50051015202530354045Structural Length in InchesStructural Depth in Perce nConservatively Assumed Wear Scar Length was entire span between TSPs (39")

Actual lengths < 9" 30 Operational Assessment for T-T Wear Mixed arithmetic/Monte Carlo method utilized*Cycle length 1.927 EFPY*Addressed indications siz ed with +Point and X-Probe separately*End of cycle (EOC) length conservatively assumed 39"

• Usedmaximumgrowthoverpreviouscycle

• Used maximum growth over previous cycleConservative relative to ANO experienceSignificant margin to leakage and burst at EOC*Margin ~17% for worst case flaw at EOCLBLOCA evaluation also demonstrates significant margin 31 Planned Future Actions Update Site Specific Performance Demonstration (SSPD) training to include T-T wearConvert TMI-1, X-Probe site qualification to EPRI "Appendix H, Qualified Technique"Provide raw data to EPRI Perform 100% eddy current examinations during T1R20 (Fall 2013)Support AREVA root cause analysisImplement appropriate actions based on the results of the root cause 32TMI-1 Tube-to-Tube Wear Conclusions T-T wear was identified during the first inservice inspection of the TMI-1 EOTSGsAll T-T wear indications meet Condition Monitoring and Operational Assessment

performance criteria T-T wear does not impact inspection interval

length for Cycle 19