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:	Peter Bamford 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 1 Summary of Tube-to-Tube Wear Identified During T1R19 (Fall 2011)

January 26, 2012 NRC Headquarters

Introduction 2 Introductions and Opening Remarks Bill Carsky, TMI-1 Site Engineering Director

• Greg Ciraula, TMI-1 Engineering Programs Manager

• Mark Torborg, TMI-1 Steam Generator (SG) Program Engineer

• Steve Queen, Director Corporate Engineering Programs

• Jay Smith, Corporate SG Program Manager

• Wendi Croft, Senior Licensing Engineer

Purpose 3 9 Provide information on tube-to-tube (T-T) wear

• Inspection results

• How the indications were identified

• Reporting Criteria

• Primary and secondary analysis

• Ho the indications were How ere si sized ed

• Basis for sizing techniques

• Future planned actions

Background 4 9 TMI-1 installed AREVA, Enhanced Once Through Steam Generators (EOTSGs) during T1R18

• Operated January 2010 - October 2011 9 General 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 tubes S

Spacing i b between t TSP TSPs varies i from f 35 - 46.4 46 4 Aspirating ports are in 10 span th

• Nominal gap between tubes is 0.25 9 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

T1R19 Inspection Overview 5 9 100% full length bobbin coil inspections in each EOTSG 9 X-Probe inspections of peripheral tubes (two tubes deep) in each EOTSG (Evaluated 1st span for loose parts) 9 Tube damage mechanisms found in each EOTSG

• T Tube-to-tube b t t b supportt plate l t wear (T-TSP)

(T TSP) (expected)

( t d)

• Tube-to-tube wear (T-T) (not expected) 9 No evidence of tie rod bowing 9 No tie rod to tube contact or proximity

EOTSG A, T-T Wear Map 6 EOTSG B, T-T Wear Map 7 T1R19 T-T Wear Identification 8 9 Reported as absolute drift indications (ADIs) during bobbin coil inspection with most indications located:

• In mid-span

• In the 9th span

• In a radial pattern 30 - 45

• In adjacent tubes (two or three) 9 Performed X-Probe and +Point on ADI signals

• Verified indications in adjacent tubes face each other

• Symmetrically tapered to maximum depth in center

• In adjacent j tubes the indications are at same elevation and are same length/depth g p

• Length and depth have a correlation that is consistent with wear

• Good correlation of phase angles and voltages between channels 9 Analysts, 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

Process for Screening T-T Wear 9 9 Indications 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.

• 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

Example TMI-1 T-T Wear Bobbin Data 10 Example TMI-1 T-T Wear Bobbin Data 11 Example TMI-1 MBM Screened as ADI 12 Summary of ADI Indications (T-T Wear) 13 9 ADI Indications 0.5 volt

• A - 9 Tubes Primary = 9, Secondary = 7, Both = 7

• B - 19 Tubes Primary = 19, Secondary = 18, Both = 18 9 All ADIs including review for paired tubes

• A A - 74 Tubes with ADIs (0.08(0 08 - 1.62 1 62 volts)

Primary = 20, Secondary = 34, Both = 13 o Either Primary or Secondary = 41 o 74 of 74 confirmed by +Point or X-Probe

• B - 202* Tubes with ADIs (0.07 - 1.25 volts)

Primary = 145, Secondary = 95, Both = 71 o Either Primary or Secondary = 169 o *183 of 202 confirmed by X-Probe

Process for Screening T-T Wear 14 9 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-Probe obe qua qualified ed for o ssizingg T-TSP S wear ea ((EPRI ETSS SS 11956.3) 956 3)

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

+Point qualified for sizing various shapes of wear (EPRI ETSS 27901 - 27907) o EPRI ETSS 27905.3 Flat Wear was determined to be the correct technique for T-T wear in EOTSGs

Example TMI-1 T-T Wear +Point Data 15 NOTE: Graphic shows partial indication

Example TMI-1 T-T Wear X-Probe Data 16 Example Depth Profiles in Paired Tubes 17 T-T Wear Depth Profiles EOTSG A , Tubes R26-T36 AND R26-T37 22 20 18 R26 - T36 R26 - T37 16 14 DEPTH (%

%TW) 12 10 8

6 4

2 0

13 14 15 16 17 18 19 20 21 22 23 24 AXIAL LOCATION ABOVE TSP 08S (INCHES)

T-T Wear Length-Depth Correlation 18 EOTSG A/B T-T WEAR LENGTH/DEPTH CORRELATION 9

8 7

LENGTH (IN NCHES) 6 y = -0.0098x2 + 0.509x + 1.8162 5

4 3

2 1

0 0 5 10 15 20 25 DEPTH (%TW)

Site Qualified Sizing Technique for T-T Wear 19 9 X-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 Wear

• 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

Graphic of Flat Wear Standard X-Probe 20 Graphic of Flat Wear Standard +Point 21 X-Probe Calibration Curve 22 X-Probe Amplitude - Depth Calibration Curve 70 60 50 0.613 y = 13.151x MET %

%TW 40 2 R = 0.991 30 20 10 0

0 2 4 6 8 10 12 14 Amplitude (Voltage Vmx)

X-Probe Calibration Curve Validation 23 X-Probe 300 kHz Axial Sy.x = 2.09 70 N = 32 60 Structural Variiable (%TW) 50 40 30 y = 0.9603x + 1.4017 2

R = 0.9831 20 r= 0.9915 10 0

0 10 20 30 40 50 60 70 NDE %TW

Comparison of +Point and X-Probe 24 EOTSG A X-Probe vs. +Point - %TW Correlation 30 25 20 X-Probe (%

%TW) 15 y = 0.9832x + 0.3458 2

R = 0.932 10 N = 41 5

0 0 5 10 15 20 25 30

+Point (% TW)

T1R19 T-T Wear Summary 25 9 A total of 257 tubes were identified with T-T wear

• EOTSG A: 89 indications in 74 tubes

• EOTSG B: 206 indications in 183 tubes 9 Wear depths range from 1% to 21% through wall (TW) 9 Wear axial lengths range from 2 to 8 9 No proximity or tube contact detected

• TTubes b are in i tension t i att cold ld conditions diti and d iin compression i att h hott conditions 9 Sizing performed by +Point Technique 27905.3 and a site qualified X-Probe Technique

• Good correlation between Bobbin, +Point, and X-Probe techniques 9 All tubes met condition monitoring limits and in-situ pressure testing was not required

T-T Wear Depth Distribution 26 30 25 EOTSG A 20 No. INDICATIONS 15 10 5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 DEPTH (%TW) 45 40 35 30 EOTSG B No. INDICATIONS 25 20 15 10 5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 DEPTH (%TW)

T1R19 T-T Wear Summary 27 EOTSG A EOTSG B Total number of In-Service Tubes 15597 15597 Number of T-T Wear Indications 89 206 Number of Tubes T-T Wear 74 183 Average Depth of T-T Wear 5.8% 7.4%

Maximum Depth of T-T Wear 21% 19%

Number of T-T Wear Indications >40% TW 0 0 Average Growth Rate T-T Wear 3.4%/EFPY 4.3%/EFPY 95 th Percentile Growth Rate T-T Wear 9.3%/EFPY 7.6%/EFPY Maximum Growth Rate T-T Wear 12.2%/EFPY 11.1%/EFPY Number of Tubes Plugged for T-T Wear 4 3

Condition Monitoring Summary for T-T Wear 28 9 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

Condition Monitoring Assessment for T-T Wear 29 CM Results for Tube-to-Tube Wear for Both Array Coil and +Point Sizing 100 CM Limit for X-probe sizing 90 SGA X-probe Depths SGB X-probe Depths 80 CM Limit for +Point Sizing SGA +Point Depths Structural Depth in Percen nt Throughwall 70 60 Conservatively 50 Assumed Wear Scar Length was entire span 40 between TSPs (39")

Actual lengths < 9" 30 20 10 0

0 5 10 15 20 25 30 35 40 45 Structural Length in Inches

Operational Assessment for T-T Wear 30 9 Mixed arithmetic/Monte Carlo method utilized

• Cycle length 1.927 EFPY

• Addressed indications sized with +Point and X-Probe separately

• End of cycle (EOC) length conservatively assumed 39

• Used maximum growth over previous cycle Conservative relative to ANO experience 9 Significant margin to leakage and burst at EOC

• Margin ~17% for worst case flaw at EOC 9 LBLOCA evaluation also demonstrates significant margin

Planned Future Actions 31 9 Update Site Specific Performance Demonstration (SSPD) training to include T-T wear 9 Convert TMI-1, X-Probe site qualification to EPRI Appendix H, Qualified Technique 9 Provide raw data to EPRI 9 Perform 100% eddy current examinations during T1R20 (Fall 2013) 9 Support AREVA root cause analysis 9 Implement appropriate actions based on the results of the root cause

TMI-1 Tube-to-Tube Wear Conclusions 32 9 T-T wear was identified during the first inservice inspection of the TMI-1 EOTSGs 9 All T-T wear indications meet Condition Monitoring and Operational Assessment performance criteria 9 T-T wear does not impact inspection interval length for Cycle 19