ML070050212

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Steam Generator Tube Inspection Discussion Points - Oconee Nuclear Station
ML070050212
Person / Time
Site: Oconee Duke Energy icon.png
Issue date: 10/26/2006
From: Olshan L
NRC/NRR/ADRO/DORL/LPLII-1
To: Brandi Hamilton
Duke Power Co
Olshan L N, NRR/DORL, 415-1419
Shared Package
ML070080336 List:
References
TAC MD3388
Download: ML070050212 (11)
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Text

INRC Conference Call (10/26106)

Steam Generator Tube Inspection Discussion Points Oconee Nuclear Station, Unit 1

Background

" The steam generators are of the once-through design type and were manufactured by Babcock & Wilcox - Canada

" The tubing is thermally treated Alloy 690

  • The SG has 15 support plates, the support plates are made of 410 SS, the support openings are of the trifoil broach design, with the exception of some drilled openings at the 1 4th TSP
  • The tubes are hydraulically expanded into the tubesheet to a depth of 13 inches
  • Widespread tube wear was discovered during the first inspection on the Oconee Unit 1 replacement steam generators; similar but less severe wear was observed on Units 2 and 3

" The second inspection on the Oconee Unit 1 steam generators provides the first opportunity to establish growth rates for the wear being experienced NRC Generic Questions

1. Discuss any trends in the amount of primary-to-secondary leakage observed during the recently completed operating cycle.

There has been no primary-to-secondary leakage during the recently completed operating cycle.

2. Discuss whether any secondary side pressure tests were performed during the outage and the associated results.

No secondary side pressure tests have been performed. None are planned.

3. Discuss any exceptions taken to the industry guidelines.

No exceptions have been taken to the EPRI PWR Steam Generator Examination Guidelines.

4. For each steam generator, provide a description of the inspections performed including the areas examined, the probes used, and the expansion criteria. Also, discuss the extent of rotating probe inspections performed in the portion of the tube below the expansi6n transition region.

A full length bobbin coil inspection was performed on all in-service tubing in both steam generators. A combination X-probe was used for approximately 60% of the inspection, and a standard bobbin probe was used for the remaining 40% of the inspection. Selected indications were further characterized with an array probe. The screening criteria used for Enclosure 2

array analysis was as follows: (1) all wear indication > 20% TW, (2) new wear indications

> 10% TW, and (3) existing wear indications that have grown by >~ 10% TW. No. rotating coil inspections are being performed.

5. For each area examined, provide a summary of the number of indications found to date for each degradation mode. For the most significant indications in each area, provide an estimate of the severity of the indication. In particular, address whether tube integrity was maintained during the previous operating cycle. In addition, discuss whether any location exhibited degradation mode that had not previously been observed at this location in this unit.

Wear is the only type of degradation that has been observed to date on the Oconee Unit 1 replacement steam generators. This type of degradation was also observed during the previous Unit 1 inspection in April, 2005. Similar wear was identified during the Unit 2 and Unit 3 inspections in October, 2005 and May, 2006, respectively.

SG A - The inspection on the 1A steam generator is 95% complete. See Attachment A for a sumnmary of results and comparison to previous Unit 1 inspection results.

SG B - The inspection on the lB steam generator is 99% complete. See Attachment A for a summary of results and comparison to previous Unit 1 inspection results.

A total of 15 tubes have been identified with tube wear of > 40% through-wall. See Attachment B for data associated with these indications.

None of the wear indications detected approach tube integrity limits. The maximum NDE wear depth observed during this inspection was 49% through-wall. This is well below the condition monitoring limit of 73% through-wall.

6. Describe repair/plugging plans.

Thirty-nine (3 9) tubes. have been identified for plugging so far based on a plugging criterion of>ý 35% through-wall. All tubes that are plugged will be stabilized full length.

7. Describe in-situ pressure test and tube pull plans and results.

No in-situ pressure testing or tube pulls are planned.

8. Provide the schedule for steam generator related activities during the remainder of the current outage.

The tentative schedule for remaining steam generator related activities is as follows:

- close out eddy current testing (Thursday-Friday)

- performn plugging and stabilization (Friday-Sunday)

- install primary manways (Monday-Tuesday)

-perform secondary side visual inspection. on A steam generator (Monday-Tuesday)

-install instrumented inspection port covers on A steam generator (Wednesday-Thursday)

9. Discuss the following regarding loose parts: What inspections are performed to detect loose parts, a description of loose parts identified and their location within the steam generator, if loose parts were removed, tube damage associated with loose parts, and the source or nature of the loose parts.

No visual inspections were performed for loose parts. No indications of loose parts have been identified via eddy current. Loose parts have not been a historical problem on once-through steam generators.

10. For OTSGs, if you have Babcock& Wilcox welded plugs installed in the steam generators, discuss the actions taken in response to Framatomne' s notification of the effect of tub esheet hole dilation on the service life of the welded plugs.

Not applicable.

11. For OTSGs, discuss any actions taken in response to the severed tube issue during the outage (reference NRC IN 2002-02).

No actions taken. This problem not applicable to the Oconee replacement steam generators.

Attachments

1) Attachment A - Oconee Unit 1 Steam Generator Tube Wear Summary
2) Attachment B - Oconee Unit 1 Tube Wear Indications >_40% TW
3) Areva ECT Examination Status Report (10/25/06, p.m.)
4) Tube Wear Elevation Distribution (SG A)
5) Tube Wear Elevation Distribution (SG B)
6) Tubesheet Map (SG A)
7) Tubeshe~et Map (SG B)
8) Preliminary Operational Assessment Results

Attachment A Oconee Unit 1 EOC 23 Steam Generator Tube Wear Summary Unit 1 EOC 23 Unit 1 EOC 22 IA SG 1B SG IA SG 1BBSG

  1. of wear indications 6989 5181 2439 1769
  1. of tubes with indications 4424 3714 1798 1450

% tubes with indications 28% 24% 12% 9%

Average wear depth (all indications) 9% 9% 10% 10%

Average wear depth (new indications) 8% 7% 10% 10%

Maximum wear depth (all indications) 49% 41% 42% 42%

Maximum wear depth (new indications) 36% 40% 42% 42%

  1. indications Ž40%TW 10 5 3 2
  1. indications 30% <40% TW 48 40 17 13
  1. indications >20% <30%TW 211 182 71 64 EFPY per cycle 1.37 1.37 1.24 1.24 Average growth rate per EFPY 2% 3% 8% 8%

95/50 growth rate per EFPY 7% 8% 15% 15%

Maximum growth rate per EFPY 27 29 34% 34%

  1. tubes plugged 20* 19* 30 18
  • Tentative based on data analyzed to date

Attachment B Oconee Unit 1 EOC 23 Steam Generator Tube Wear Indications >: 40%

Oconee Unit 1 Steam Generator A Indications 40 %TW and Previous History_____

ROW COL 2006 %TW 2005 %TW Change %TW LOCATION ELEV FROM 11 59 49 12 37 10 -0.51 75 124 44 19 25 11 0.16 79 8 42 9 33 10 -0.48 82 7 44 24 20 10 -0.45 82 8 42 21 21 10 -0.47 83 7 48 16 32 10 -0.47 84 6 44 16 28 10 -0.44 131 82 41 20 21 10 1 -0.5 139 68 48 16 1 32 10 -0.45 140 61 41 19 22 10 -0.45 Oconee Unit I Steam Generator B Indications Ž40 %TWV and Previous History ROW COL 2006 %TN 2005 %TVV Change %TW LOCATION ELEV FROM 59 5 40 0 40 10 -0.43 67 10 40 21 19 11 -0.43 73 9 40 12 28 10 --0.45 83 15 40 16 .24 11 -0.55 145 38 41 26 15 10 _-0.37

Duke Power Oconee Unit I R E0C23 ECT Examination Status Report A AR EVA 10/25/2006 16:24 SCOPE DESCRIPTION SIG A SIG B Log Exam Description Extents AIcquired Analyzed _ Scope V.ceeme:.f Acquired Analyzed Scope V. Compscato Both XProbe Bobbin Exam UTE-LTE Both MULC Bobbin Exam UTE-LT .E EE EEjEý]E EE 3ý E Both Special Interest Array Bobbin Various [.2 IZE I IF] i 1YI JX IIX IF Both Special interest MULC Bobbin Acquisition & Analysis Various

_EEJJ F F F 1I7 ~

~ FjI F F~

Both Special Interest MULC Bobbin Acquisition Only Vros Vai -L 98

_ NA j 34 34JO 11 38.; 42T 424 IA NIA 4

1193 83

[Tubes with Wear Indicati~ons: 4431 Tubes with Wear Indications by Support: NOTE: Some 012 8.28 004 4 012 26 004 11 tubes may have multiple indications at different____

supports. 01l 1350 003 is 011 6.79 003 19 010 1622 002 15 010 1715 002 19 00 18 01 5 009 74 01 14 0-9% 3533 0-9% 3028 Tubes with Wear Indications by Size 20 -29% 198 20 -29% 174

ONS I A Fall 2006 Outage Summary - Partial PS PWS 120 102506 Indication Count Support

-&NISC1A 206 1 2 3 4.5 6 7-'7~ 10, 1:1 12' .1`,3. 14 :15' Total

%tw<=5 -3 1 3 5 6 122 1123 327 246 230 126 38 44 7 1181 5<%tW<1l0 7 13 14 4 12 3 31 253 811 933 894 546 328 282 19 4150 1O0<%tw<1l5 5 2 2 __2 __ 13 200 346 282 172 109 93 3 1229 15<%tw<=20 __2 74 122 95 57 45 32. 3 430 2O<%tw<=25 52 48 35 18 9 7 2 171 25<%tw<=30 - - - 39 30 25 5 _ 99 30<%tw<=35 25 25 11 1 _ 62 35<%tw<=40 __ 27 11 5 _ _ 43 40<%tw<=45 8 110 5 1_ _ 23 45<%tw<=50 6 ___ 6 50<%tw<=55 ___ 0 55<%tw<=60 0

%tw>60 Total/Support 15 16 19 4

19 9

53 391 11563,17771582 924 529 1459, 34 IAffec Tubes Tubes Analysed 7394 0

4424 157 157 ONSI-A Fall 2006 %tw TSP Distributions Saturtion Point 5 -Lower Shroud $UP." !Rl1 Upper Shroud 50 45-e 40 -

35 I-I S30 S25-20 15-10:...

0 1 2 3.4 5 6 7 8 9 1011 12 1314 15 TSP

ONS I B Fall 2006 Outage Summary - Partial PS PWS 120 102506 Indication Count

_____________Support___

ONSi B2'3 4 200 2 #7~ 66 0 i~ 21 14, 5 Total

%tw<=5 __ 6 1 3 163 194 215 383 1251 5 82 105 12 1294 5<%tw<=1O0 9 17 16 5 10 6 124 146 489 1053 329 18 201 391 26 2840 10<%tw<1l5 4 3 4 7 5 _ 7 7 146 278 138 5 34 155, 10 703 15<%tw<=20 2 2 1 7 105 73 1 5 54 4 254 20<%tw<=25 7 40 53 1 2 11 114 25<%tw<=30 1 33 3 2 2 68 30<%tw<=35 1 _ 14 13 1 129 35<%tw<=40 __6 8 _ 14 40<%tw<=45 1 _ 1 45<%tw<=50 0 50<%tw<=55 0 55<%tw<=60 ____ 0

%tw>60 - - - - - - - - - - - - - - - 0 Total/Support 16 28 22 12 15 9 294 347 765 1913 771 30 3241 7181 53 15317 Affected Tubes 3693 Tubes Analysed 15543 ONSI-B Fall 2006 %tw TSP Distributions Saturation Point Lower Shroud Superleot 0 Upper Shroud 55 50 45 40 35

  • 30

~25 N 20 15 10 t --

5 .

0 i 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TSP

W WINRoger Template #6036082.dwg ONSI Repi AX IS---- - - - - - - -W . ýý- l Outage

-W2 V__,n PAEVA-FDMSmapmodule S/G A PRIMARY FACE INLET A!; W~ wh W TOTAL TUBES: 15631 wwI TUBES SELECTED: 4424 OUT OF SERVICE (#): NA W_~ W~ Mw GROUP TUBES Wear 4424

-W W Ws W-~-wv vsW I wa  % w1MWW wwW W W W VIW I V4 _

SCALE: 0.067445 X Wed Oct 25 15:54:15 2006

W.

w Roger Template #6036082.dwg ONSI Repi VJAXIS -10 Outage AREVA-FOMSm~pmojeVoonaq50 S/G B PRIMARY FACE INLET TOTAL TUBES: 15631

.w TUBES SELECTED: 3714 OUT OF SERVICE (#): NA Mw w*ww . IN  % wWNw w -w IN .ý 1vw -w N w w w w Wo v.*... w h

-- 40 GROUP TUBES J5wvvw w w w w Wear 3714 IN IN w

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w VV w .'%IN Vi YAXIS SCALE: 0.067445 X Wed Oct 25 15:50:38 2006

Summary of Calculated Repair Limits J. A. Begley AREVA - NP Table I shows calculated repair limits for wear scars at Oconee Unit 1 using a variety of analysis methodologies with a 3AP value of 4050 psi. The repair limit is expressed in terms of an NDE %TW reading. Repair is required at or above the repair limit. Depth pro files are still consistent with a ratio of structural depth to maximum depth of 0.84 with a 0.40 inch structural length Table 1 Repair Limits for Tapered Wear Analysis Methodology Repair Limit NDE Reading, %TW Maximum Growth Rate and 95/5 0 NDE 2 Sizing Uncertainty, Monte Carlo Summation of Burst Equation and Material property uncertainties 95/50 Growth Rate from High Growth 42 Subset of Data, All Other Uncertainties at Worst Case 9-5/50 Levels____________________

95/50 Growth Rate from High Growth 54 Subset of Data with Monte Carlo Summation of All Other Uncertainties Maximum Growth Rate, All Other 24 Uncertainties at Worst Case 95/50 Levels Maximum Growth Rate, Monte Carlo 35 Summation of All Other Uncertainties

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