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Slides for Meeting - Duke Energy - Oconee Steam Generator Wear Root Cause Update with NRC
	ML061140370
Person / Time
Site:	Oconee
Issue date:	04/25/2006
From:	; Duke Energy Corp
To:	; Office of Nuclear Reactor Regulation
References
	Download: ML061140370 (48)
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. Ir Duke Energy - Oconee NIuclear Station Steam Generator Wear Root Cause Update with NRC April 10, 2006 A11 ENCLOSURE 2

raEnergy.

Topics ofdiscussion

Introductions

Review of Unit I and 2 ROTSG Wear

Preliminary Probable Causes

Alloy 690 / 410S Tube Support Plate (TSP) material couple and Increased Wear Coefficient Tube to TSP relative rotation and reduced contact area

Steam Nozzle Flow Restrictor Acoustic Excitation Low Frequency Pressure Pulse Hourglassed Broach Plate Annular Flow Instability

Preliminary Metallurgical Observations

Plan for Future Activities

Conclusions 2

ONS I Wear Distributions

'a-Duke re' Energy.

ONSI A Tube Support Plate__

2 "3: [4

]~5`

6 7

'9 10-1 213"'14~ 15. Total

%tw<=5 1

4 231 1 5 2 1 17 6

1 3 100 5<'%/tw<=10 4

5 2

946 3181 383 344 228 110 121 1

1576 10<%tw<=15 1

2 _

8 89j 157 102 83 49 50 5 548 1 5<%twv<=210 13~7T7 31 16 8 14 1

130 20<%tw<=25 i

1 9 1 5 3

2 40 25<%tw<=30

_1 5

31 19 30<%tw<=35

_8 4

1 2 35<%tw<=40 2

2

-4 40<%/ltw<=45

___2 2

50'<%tw<z=55

__J___

0 55% tw> 60

_0 Total/Suppor 51_ 7 ml3 01 9 581 444 648 522 348 173 200 7 2431 ONSI-B

____Tube Support Plate T1~-2 3

5.

)~678~IZ01112,i314i5Total

%w=3 2

15 12 191 311 5

1[

1 107 5<%tw<=I0 1

9 615_-2 1-.

-30 34 2.53 _402 174 4

55 174 10 1160 10<%tw<=15 1

II 281 130 80 2 5

68[

2 321 15<%tvv<=20

______I__-

-71 40 35 17 1

1001 20<%hv<=25 1_

21 15 11 1

3 __

331 25<"%'tw--=30

___12 4

16 30'<%tw-=35 I5 3

8 35<%t'dv<=410 l

1 2

40'<%tw'v<45

__2 2

45<%twv<=50

__0 50<%'tw<-55 j

0

%tw>60 I~

0a Total/Support 31 121 91 51 31 1 39 46 3091 6361 3211 81 661 2771 141 17491 4

ONS 1 Wear Distributions P Duke tSEnergy.

1 6 0 150 140 130 120 110 100 90 -

80 70 -

60 50 -

40 -

30 20 1 0 n

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Oconee 1-A TSP (All),X l 1-5%

D 6-10%

11-15%

16-20%

o 21-25%

26-30%

31-35%

36-40%

o 41-45%

45 X2 Y

2 Q

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ONS 1 Wear Distributions m Duke EEnergy.

Oconee 1-B 160 150 140 130 120 110 100 -

90 80 -

70 -

60 50 40 -

30 20 10 0

LV A

i

47 IVI,. I I

- I

.I 11 1: -..

. I I II

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0 9

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TSP (All)

I 1-5%

1 6-10%

0 11-15%

i 16-20%

o 21-25%

26-30%

31-35%

36-40%

o 41-45%

->45%

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m'Duke ONS 2 Wear Distributions OEnergy.

ONS2-A 11-01-05 160 150 140 130 120 110 100 90 -

80 -

70 60 50 40 30 20 -

10 -

0 9Z 9'>

2 o

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5 9*

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TSP (All) 5% 10%

11-15% 20%

o 21-25%

26-30%

31-35%

36-40%

o 41-45%

. >45%

9, 9 99 9

9 9

9

99 99 9'K 99

9:'

99j9,

9499, X2 Y2Q Yt xOi Orientation 7

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0 00 00 0 0

0 0

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N (N

N (N (N N

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ONS 2 Wear Distributions PDuke

rEEnergy, 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

ONS2-B 11-04-05

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o 11-15%

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36-40%

o 41-45%

>45%

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Wear Indications per Steam Generator Duke

[Eergye Original Replacement OTSG OTSG SGA 555 1797 Oconee UnitlSGB 1232 1450 SGA 428 498 Oconee Unit 2 SGB 566 699 SGA 350 Scheduled April/May 2006 Oconee Unit 3 Scheduled AprilM SGB 280 Sh l

Apr 9

ONS I & 2 TSP Wear Frequency Comparison mb Duke c 'Energy.

CL (1) 1--

15 1.1 13 12

=

6".

1 10 9 I 8-.

7 5

I p Indications per TSP ONS2-A i.

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15 14 13 1 2 I11 10 I-7 6

5 4

3 2

Indications per TSP ONS2-B

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Frequency 15 14' 13 12 I1 10 CL 9 a.

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Indications per TSP ONS 1 -A III C,0 0 C C)0 0

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Frequency 115 13 12 1 1 10 CL9 c0 8 6

J 4

3 1

Indications per Tsp ONSI -3 C)0C) 0 C)

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Frequency 10

Summary of Review of Eddy Current Data dr9nergy.

ONS 1 Summary ONSlA, 2431 indications were found on 1797 tubes i-ONSI-1B, 1749 indications were found on 1450 tubes Both ROTSGs 90% of the indications are less than or equal to 15%

of the through wall thickness t-50% of the indications are under 10% of the through wall thickness

< The vast majority of indications (095%)

are present in the superheated steam region on the 9th tube suppoIt plate and above All indication above the 9th support plate are predominately on the outer region of the bundle.

11

ONS1 Summary (cont'd)

fAnergy, The highest frequency of indications is at the 1Oth support plate, with the 1 1tI and 9VI showing the next highest population, The bleed port is located between the 9111 and IOt' ssupport plate the steam outlet nozzles are located at the elevation of the I itt' support plate.

Peripheral indications at the 1itO) TSP on both ROTSGs are more tightly distributed and show a tendency to form a "line" oriented relative to the steam nozzle orientation There is also a heavy defect concentration directly opposite the steam nozzles on the Y2 axis.

] The 1 5t1 support plate, which is directly below the high cross flow steam outlet region and has very few indications.

For SUppoiA plates 'I0 and above, there are very few indications in the interior with increasing occurrences towards the periphery t

The peak density of tube wear is typically a fen rows away from the periphery edge Support plate 9 has a significant percentage of indications in the interior of the bundle.

12

a~lDuke ONSI Summary (cont'd)

nEnergy, a-Virtually all indications are tapered wear marks with an angle nominally between 0.3 and 1.2 degrees.

Analysis of tube to TSP land clearances indicate no clear relationship between the size of the clearances and incidence of indications.

The original OTSGs tube wear is compared against the replacements in which the distribution of the tube wear in the upper TSPs is similar; although there are more indications for the replacements during the first fuel first cycle, than the life span of the original units.

JD The original OTSGs the 9VI and 10til TSP have the most indications followed by the 8th and the remainder in the upper TSPs.

The peak counts occur in the 1 Oth and 1 1itb TSP for the replacements followed by the remainder of the upper TSPs.

2 Only TSPs 7 and 8 differ with significantly more indications in the OTSGs than the ROTSGs.

13

ONS2 Summary All Enu F,;

ONS2-A, 633 indications were found on 498 tubes ONS2-B, 903 indications were found on 699 tubes Both ROTSGs 90% of the indications are less than or equal to 13% of the through wall thickness and 50% of the indications are under 8% of the through wall thickness lThere are significantly less indications than ONS1 with a less severe wear depth distribution.

'i The highest frequency of indications is at the 1 3t11 support plate for ONS2-A and the 12th1 support plate for ONS2-B. There is low incidence of indications on the 9t11, 101t, and 11 support plates when compared with ONS1.

Relative to ONSI there are an increased number of indications in the vicinity of the inspection ports in the lower bundle region below the 9th TSP.

Based on ECT, wear is predominately single lobe contact similar to ONS1 Preliminary review of X-Probe data shows no discemnable orientation pattern.

14

Oconee Tube Wear Probable Cause DEnUkegy.

IN To date, no singular technical root cause has been isolated, but five contributing causes have been identified by the Root Cause Team (BVVC and Duke Energy)

Probable Technical Causes:

Alloy 690 / 41 OS tube support plate (TSP) material couple and increased wear coefficient Tube to TSP relative rotation and reduced contact area Main steam nozzle flow restrictor acoustic excitation Low frequency pressure pulse Hourgiassed broach plate annular flow instability 15

mge'Duke rwEnergy.

Factors Investigated

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16

Factors Investigated M Duke PO'Energy.

Dynamic Pressure Induced Vibration

-Feedwater Spray Nozzle Dynamic Excitation of Lower Shroud

2Feedwater Spray Nozzle Dynamic Pressure Excitation of Tubes Acoustic Induced Vibration fAxial Acoustic Standing Waves between TSPs F4Acoustic Resonance with Cross Flow Voitex Shedding

.-;Steam Nozzle Flow Restrictor Acoustic Excitation of Tubes FI kIVVC;tLkpI NuJzIe I

AJoWJVUOL L..AUILCILII I U1 I UL)ua 17

D uke Factors Investigated (cont'd)

^

Dnuergy.

Structural Vibration Steam Nozzle Flow Restrictor Dynamic Excitation of Piping, Shell or Shroud Structural Vibration of Shell due to Mechanical Excitation of System including change in stiffness of ROTSG Structural Vibration of Shell due to Ineffective Upper Lateral Restraint Structural Vibration of Shell due to RCP excitation / unbalance S2 Structural Excitation of Hot Leg (1800 bend) due to RCS flow perturbations 18

Factors Investigated (cont'd)

V nergy.

Flow Induced Vibration

.-fHourglassed Broached Hole Annular Flow Instability O.D. Axial Flow Turbulence Induced Excitation

'Axial flow inside tube causing lateral vibration

,.Localized cross flow excitation at TSPs within a nominally axial flow field TuHigh Cross Flows and FIV loading in bleed port and steam exit region Localized 'jet pump' effect of feedwater spray nozzles uExcessive Bleed Flow attributed to steam carryunder in lower feedwater downcomer Downcomer flow leakage through lower inspection port sleeves DFiow Regime instability 19

Factors Investigated (cont'd)

VDnegy.

Flow Induced Vibration (cont'd)

-Porosity Related Flow Maldistribution at Tube Support Plates 2 Correctness of standard FIV analysis addressing fluid-elastic instability (FEI), random turbulence (RT) and voitex shedding L Effects of linear versus non-linear FIV analysis including clearance limited FEI' Unbalanced feedwater flow through spray nozzles Z 'U-tube' flow oscillations in lower bundle and downcomer 20

Factors Investigated (cont'd)

OFnry Mechanical I Material Interaction Effect of broached hole clearances Effect of tube tension including confir-mation of prestrain Effect of damping in Superheat region 2Relative mechanical interaction between tubes, TSPs, shroud and shell

~Effect of curved versus flat land

~Effect of improved tube I TSP alignment 2Material couple wear coefficient Plant O-perational Thermal Hydraulic Conditions and Geometry 21

PhDuke 0 Energy.

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. I..

-

I Discussion of Probable Causes 22

Alloy 690 1 410S TSP Wear Coefficient Energy.

>I A literature search of wear coefficients was conducted and found a wide variation of results for the same materials Comparison of the original material combination to the ROTSG material combination was initiated E Room temperature sliding tests in a dry environment have provided repeatable consistent results showing that the wear coefficient for Alloy 690 / 4 1 0S is about an order of magnitude higher than Alloy 600/ carbon steel Comparative simultaneous testing in autoclave fretting machines at Super heated conditions has been initiated to confirm the differences between the original material and ROTSG material combinations 23

Tube to TSP Relative Rotation and Reduced Contact Plkuke vnergy.

Volumnetric wear rate is proportional to work rate but through wall wear rate is related to the contacting surface area Dynam-ic contact between the tube and tube support 'land' should engage the full length of the land Relative angular rotation due to tube dynamic m-otion or rotation of -the TSPs can in crease the wear rate

-he Oconee ROTSGs TSPs are vertically positioned by both tie rod spacers starting from 'the lower tubeshe n b upr blocks around the outer edge of the TSPs which are welded to the shroud I.D.

24

Tube to TSP Relative Rotation and Reduced Contact cont'd)

Lphuke

-2 Relative thermal expansion of the tie rods and the upper and lower shrouds, which are anchored at their bottom ends, cause vertical loads at the outer support blocks. These loads result in a dishing of the support plates k

The angular rotation of the support plate edge may be detrimental to wear due to the possibility of reduced contact area A relationship between the locations of the tapered wear marks and the angular rotation of the TSPs is still under review 25

Main Steam Nozzle Flow Restrictor Acoustic Excitation s Duke POEnergy.

~~~~~~~~~.

-..I

^...

Any sudden shock loss in a steam system is a potential source of acoustic energy X An illustration of acoustic energy generation and transmission in a piping system is shown in Figure 10-10 of Blevins (1994)

FB Force on bend Bend Area change Abrupt expansion Reservoir Fig. 10-1! A pipe run with an acoustical source at a valve.

3

Main Steam Nozzle Flow Restrictor Acoustics cont'd OrEnergy.

Analytical Acoustic Analysis Determined acoustic energy from steam nozzle flow restrictor pressure drop and velocity using conventional analytical analysis Lin Predicted ROTSG acoustic modes D From acoustic sound pressure levels and mode shapes determined magnitude and frequency of tube lateral loads Applied acoustic loading as forced vibration on tubes along with FIV loads and support contact forces

'Based on analysis, acoustic energy maybe significant, psfpfiaIIy in arpas MAwIa frnm Crmoss fInAXI Fadsk anrI nindr:A!i covers regions where wear was observed 27

PhDuke Main Steam Nozzle Flow Restrictor Acoustics cont'd OrEnergy.

Search for acoustics Original and Replacement OTSG Loose Part Monitoring System spectral content reviewed Steam line piping (outside of containment) instrumented to measure pipe wall accelerations at Units 1, 2 and 3 Microphone sound measurements taken around steam line Direct piessUre transducer measurements taken at ROTSG inspection ports during power escalation following Unit 2 outage More pressure transducer measurements planned for Unit 3 outage as well as containment microphone being installed 28

~Pkuke Main Steam Nozzle Flow Restrictor Acoustics cont'd dnergy.

Search for acoustics cont'd

Unit 2 pressure transducer acoustic frequencies were detected but the amplitudes were not as intense as those from predictive analysis

> Steam line piping acceleration measurements detected the same acoustic frequencies as those measured by the ROTSG pressure transducers. Steam line piping accelerations are largest at Unit 'I followed by Unit 2 followed by Unit 3 29

Dfuke Main Steam Nozzle Flow Restrictor Acoustics cont'd VEnergy.

Acoustic analysis conclusions

< Predictive analysis based on the pressure drop of the steam line flow restrictor and acoustic modal analysis indicates that the flow restrictor maybe an acoustic source that may explain the wear distribution within the bundle Field measurements and analysis of steam line accelerations indicate a potential that acoustic frequencies exists that may have potentially high energy levels PiPressure transducer measurements at ONS-2 detected acoustic frequencies at intensities less than expected from ONS-I investigations.

30

Low Frequency Pressure Pulse POAueZ.

Unexpected high pressure, low frequency signals were observed at the 9th and 1 0th TSP, especially at lower power during startup of unit #2 in the fall 2006 Signals still being evaluated. There is concern that they may not represent real pressure S:

Calculations by consultant indicate that energy is sufficient to cause damage if signals are real.

Signals at low power may be related to control valve operations.

31

Low Frequency Pressure Pulse PO~nergy.

Low Frequency Pressure Transients during Low Power Operations N ov 29 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> 18%

power G roup 2 T ransducers T S P9 3.

2.

1.

Pressure transients were Initiated at TSP9 but were detected also at the other TS P tra n sd u ce rs. N ote the magnitudes at the otherlocatlons were

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.1000 35I J.1 1 iJi 1

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.3000

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.000 100.00-1.00 200.00 250.00 XS.c

Low Frequency Pressure Pulse Low Frequency Pressure Transients during Low Power Operations P Duke r Energye

-AMS Press I-t-W FLONV A (SEL)TWaI Ilowik wbfr ICS FDW DE MAND A [k tb hr]

-ICS FDW ERROR A [k Iblhr]

Rx. PoAer

-SO STARTUP LEVEL A(sL)[in]

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-:--ICSMAIN FDW VALVE A [%DMD]

-CSSTARTUP FDW VALVEDENIAND A [%]

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Low Frequency Pressure Pulse hDuke rEnergya Low Frequency Pressure Transients during Low Power Operations

Annular Flow Instability of Hourglassed Broached Hole P'1Euey Annular flow instability, also known as 'leakage-flow-induced' vibration, typically occurs in cases where a flexible object is situated within an annular flow passage

~ Eiherthe dynamics of the flow field or the varying position of the flexible object within the flow passage can cause a variation in the dynamnic pressure around the central object The difference in dynamic pressure around the perimeter of the central object causes a net lateral pressure force which may be destabilizing. The motion caused by the lateral force may increase the dynamic pressure imbalance and cause further lateral motion, hence creating instability.

35

D ukerg Annular Flow Instability of Hourglassed Broached Hole nVergyu Industry Experience with Annular Flow Instability Laboratory experiments of divergent nozzle annular flow instability show that a symmetric annular gap with divergent (expansion) angles of 5 to 150 can cause lateral vibration In some cases where the divergent profile had non-symmetric relief passages, annular flow instability was still observed

Some research has shown that inlet convergent profiles are a stable configuration The Oconee ROTSG configuration does not match the profile of a classic unstable profile but has some features that make it suspect and consequently a test program in air and water flows was initiated 36

Annular Flow Instability of Hourglassed Broached Hole Duke 4MVEnergy.

.-...-.

.

3. Laboir-atory experiments Water Angle=15° a) Gormian & al. 1987 (at EdF1in relation with PWR in-core)

J

/s grooves I

SaTong, vibratlions Vibrations No vibratiois 37

Annular Flow Instability of Hourglassed Broached Hole VDuke rdvEnergy.

Tube pitch

.875' Original Broached Hole Minimum tube Outside radius

.3125' Minimum Drill radius

.32' Note: Plate thickness 1.5' OTSG broached plate tube support

.Original TSP Design 58W Tube Support Plate Design 38

Annular Flow Instability of Hourglassed Broached Hole PVEnuergy.

ROTSG Broached Holed Hole 39

Annular Flow Instability of Hourglassed Broached Hole

OvEnkegy, Results of Analysis and Testing Air flow tests at hydraulic conditions equivalent to full power operation indicate that the hourglassed profile causes increased tube response relative to the original non-tapered flow passages The vibratory motions and frequencies measured do not result in an exceedingly high work rate at the support interface but are similar to those fromn cross flow FIV mechanisms Field data does not support annular flow instability as a singular root cause since axial flow is uniform at all radial positions while wear predominantly occurs around the periphery 40

ED Duke roEnergy.

Preliminary Metallurgical Studies 41

ONS 2 Tube Pulls FADuke Two full length tubes were removed from ONS 2 during outage for metallurgical analysis Westinghouse performing met exam Macro photography -complete Lab ECT - complete r:

SEM/EDX - ill progress Laser profilometry - in pi-ogress Meeting 4/11/05 to discuss results to date and future plans Wear tapered consistent with field ECT Sliding marks evident on upper bundle defects Preliminarv observations of wear surface suggest more than one mode of tube motion likely 42

ONS 2 Tube Pulls

", Duke rVEnergy.

1 in Top 53-114, Pce 32,TSP 14, 1 10 Deg.

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43

ONS 2 Tube Pulls OEnergy.

1 in Top 53-114, Pce 28,TSP 12, 120 Deg.

I} 111,11 cC 5aS0:iii S:i;f 44

D hDuke F'OEnergy.

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Future direction and conclusions

.1

-T-45

Status of ONS Steam Generator Root Cause Investigation O Energy, Install instrumentation package during spring 06 unit #3 outage, perform analysis of data and compare to unit #2, update root cause report/assumptions

i Install instrumentation package during fall 06 unit #1 outage, perform analysis of data and compare results of all testing update root cause report/assumptions Perform 1 00% eddy current inspection of unit #1, establish time rate of wear, validate models and assumptions used in operability assessments and evaluations, update root cause report/assumptions X Transition to corrective actions for probable causes 46

TEST INSPECTION PORT LOCATIONS I Duke rE'Energy.

-ACCELEROMETER LOCATION SEE DETAILVL l

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TSP 9 Inspection Port (Channel 25-100 uAlpC)

(Channel 26-100 uA(PC) 47

Concluding Remarks Vfnergy.

Root cause teams have been meeting on a regular basis and will continue through out the summer We now kiow more about what is not causing the wear scars and have 4-5 probable causes Testing and data analysis efforts will continue for units #3 this spring and unit #1 this fall X Eddy current results for the fall 2006 outage on unit #1 will give us our first clues as to the time rate of wear and the if new wear scars have initiated Root cause effort should come to some conclusions and begin winding down by the end of the year unless unexpected results are found during the unit H1 re-inspection ECT will continue on each unit for the foreseeable future 48

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