ML120250105
| ML120250105 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| 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: |
| 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
2 Introduction 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 Steve Queen, Director Corporate Engineering Programs
- Jay Smith, Corporate SG Program Manager
- Wendi Croft, Senior Licensing Engineer
3 Purpose 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 ere si ed
- How the indications were sized
- Basis for sizing techniques
- Future planned actions
4 Background
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
i b t TSP i
f 35 46 4 Spacing between TSPs varies from 35 - 46.4 Aspirating ports are in 10th span 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
5 T1R19 Inspection Overview 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 b t
t b t
l t (T TSP) (
t d)
- Tube-to-tube support plate wear (T-TSP) (expected)
- Tube-to-tube wear (T-T) (not expected) 9 No evidence of tie rod bowing 9 No tie rod to tube contact or proximity
6 EOTSG A, T-T Wear Map
7 EOTSG B, T-T Wear Map
8 T1R19 T-T Wear Identification 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 tubes the indications are at same elevation and are same length/depth j
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
9 Process for Screening T-T Wear 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)
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
12 Example TMI-1 MBM Screened as ADI
13 Summary of ADI Indications (T-T Wear) 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 74 Tubes with ADIs (0 08 1 62 volts)
A - 74 Tubes with ADIs (0.08 - 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
14 Process for Screening T-T Wear 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 qualified for sizing T-TSP wear (EPRI ETSS 11956.3) obe qua ed o s g
S ea (
SS 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
15 Example TMI-1 T-T Wear +Point Data NOTE: Graphic shows partial indication
16 Example TMI-1 T-T Wear X-Probe Data
17 Example Depth Profiles in Paired Tubes T-T Wear Depth Profiles EOTSG A, Tubes R26-T36 AND R26-T37 12 14 16 18 20 22
%TW)
R26 - T36 R26 - T37 0
2 4
6 8
10 12 13 14 15 16 17 18 19 20 21 22 23 24 AXIAL LOCATION ABOVE TSP 08S (INCHES)
DEPTH (%
18 T-T Wear Length-Depth Correlation EOTSG A/B T-T WEAR LENGTH/DEPTH CORRELATION y = -0.0098x2 + 0.509x + 1.8162 5
6 7
8 9
NCHES) 0 1
2 3
4 0
5 10 15 20 25 DEPTH (%TW)
LENGTH (IN
19 Site Qualified Sizing Technique for T-T Wear 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
20 Graphic of Flat Wear Standard X-Probe
21 Graphic of Flat Wear Standard +Point
22 X-Probe Calibration Curve X-Probe Amplitude - Depth Calibration Curve y = 13.151x0.613 R2 = 0.991 40 50 60 70
%TW 0
10 20 30 0
2 4
6 8
10 12 14 Amplitude (Voltage Vmx)
MET %
23 X-Probe Calibration Curve Validation X-Probe 300 kHz Axial 40 50 60 70 iable (%TW)
Sy.x = 2.09 N = 32 y = 0.9603x + 1.4017 R2 = 0.9831 r= 0.9915 0
10 20 30 0
10 20 30 40 50 60 70 NDE %TW Structural Vari
24 Comparison of +Point and X-Probe EOTSG A X-Probe vs. +Point - %TW Correlation 20 25 30
%TW) y = 0.9832x + 0.3458 R2 = 0.932 N = 41 0
5 10 15 0
5 10 15 20 25 30
+Point (%TW)
X-Probe (%
25 T1R19 T-T Wear Summary 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 T b i
t i
t ld diti d i i
t h t
- Tubes are in tension at cold conditions and in compression at hot 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
26 T-T Wear Depth Distribution 0
5 10 15 20 25 30 No. INDICATIONS EOTSG A 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) 0 5
10 15 20 25 30 35 40 45 1
2 3
4 5
6 7
8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 DEPTH (%TW)
No. INDICATIONS EOTSG B
27 T1R19 T-T Wear Summary 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
28 Condition Monitoring Summary for T-T Wear 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
29 Condition 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 Throughwall CM Limit for X-probe sizing SGA X-probe Depths SGB X-probe Depths CM Limit for +Point Sizing SGA +Point Depths 0
10 20 30 40 50 0
5 10 15 20 25 30 35 40 45 Structural Length in Inches Structural Depth in Percen Conservatively Assumed Wear Scar Length was entire span between TSPs (39")
Actual lengths < 9"
30 Operational Assessment for T-T Wear 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
- Used maximum growth over previous cycle Conservative relative to ANO experience 9 Significant margin to leakage and burst at EOC
31 Planned Future Actions 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
32 TMI-1 Tube-to-Tube Wear Conclusions 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