ML100570301
| ML100570301 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 02/25/2010 |
| From: | Nuclear Energy Institute |
| To: | NRC/NRR/DCI/CSGB |
| Johnson Andrew B., DCI/CSGB, 415-1475 | |
| References | |
| Download: ML100570301 (109) | |
Text
NEI Steam Generator Task Force Industry Update for NRC February 25th, 2010
Agenda 8:30 am
Introductions
NRC Opening Remarks NRC/Industry NEI Steam Generator Task Industry Force Update 12:00 pm Lunch 1:00 pm NEI Steam Generator Task Industry 2
1:00 pm NEI Steam Generator Task Industry Force Update (continued) 3:30 pm NRC feedback on various issues (e.g., TSTF-510)
NRC 3:45 pm Address Public Questions/
Comments NRC/Industry 4:00 pm Adjourn
NEI Steam Generator Task Force Update on Technical Issues 1.
Survey results for -2 sigma 600TT tubes with cracks 2.
Interim Guidance or Information Letter to address/clarify certain issues
Condition Monitoring of tubes that cannot be inspected
Comparison of Condition Monitoring results with prior Operational Assessment
SG Program Updates
Validation of repair limits
Large leaks (e.g., due to a wear scar) vs. tube burst G id f
t b ith t
ti ll l
t d t 3
Guidance for tubes with potentially elevated stress 3.
Deposit Modeling Results (Cruas) 4.
Vogtle Tube Pull Evaluation 5.
Insights from Bugey 3 Operating Experience 6.
Project Plans for Foreign Object (FO) Detection & FO Wear Detection/Sizing 7.
NEI 97-06 Revision 8.
Update/Closure of Divider Plate Cracking 9.
Upcoming Changes to Industry Documents 10.
Recent SG Operating Experience
Survey results for -2 sigma 600TT tubes with cracks Herm Lagally, Westinghouse 4
g y
g
Blairsville Partial Manufacturing Flow Diagram Approx. final tube diameter in Cold Worked condition Final Anneal Straighten Polish Hydro Test, NDT &
Thermal Visu al E
5 Straighten Polish NDT, &
Visual Treat Exa m
Pass Fail Form U-bends Stress relieve Low Row U-bends This path is limited by cumulative time at temperature
Background on Low Row
In Spring 2002, ODSCC at HL and CL TSP intersections identified
- Limited to a small number of tubes in short row tubes
- All tubes with ODSCC exhibited a unique eddy current offset signal 6
current offset signal
- Destructive examination of pulled tubes indicated an unexpected level of residual stress in the straight leg of the tubes
- Root Cause Analysis suggested that the EC signal was related to variation in material condition most likely related to manufacturing sequence
- Possible inadequate final stress relief or cold working after stress relief prior to bending
Low Row Screen
If final thermal treat is inadequate or tube is cold worked after final thermal treatment the entire length of the tube may exhibit residual stress
After forming, the short-row u-bends are thermally treated
- Thermal treatment includes a short section of the straight legs 7
legs
- The U-bends are essentially stress free
- The straight legs still exhibit the residual stress (cold worked material condition)
Results in a characteristic bobbin signal
- Eddy current probe does NOT measure stress
- Eddy current responds to a change in the material condition (strained vs. non-strained)
Eddy Current Signature of Low Row Tube Normal Tube Abnormal Tube U-bend 8
Background for -2 Sigma Tubes
The same suspected manufacturing variance could exist in the longer-row tubes
- Difficult to detect in long rows because the U-bends are not stress relieved after forming
- Forming the U-bends strains the material 9
- The tube will exhibit a bobbin voltage difference between the straight leg and the U-bend
- A normally processed tube exhibits a larger voltage difference -
straight leg to U-bend - than a tube assumed to have residual stress
- Established by comparing EC voltage for TT tubes to MA tubes
- Lower -2 sigma of population selected as a conservative basis
- ODSCC indications at TSPs in -2 sigma tubes have been identified
High Row Screening Normal Process - entire length of tubing is essentially stress free
- Forming the U-bend by cold working changes the material condition in the U-bends compared to the straight legs
- Opposite condition of the stressed relieved short-10 row U-bends.
- The bobbin probe provides a similar signal change between the straight leg and U-bend, but in the opposite direction.
- Similarly, other manufacturing cold working such as tube expansion will leave higher residual stresses than in the straight sections of tubing.
High Row Screening Off-Normal Process - entire length of tubing initially has residual stresses
- Forming the U-bend increases the residual stress (material condition) in the U-bends compared to the straight legs
- The bobbin voltage difference between the u-bend 11 and straight legs would be smaller compared to normally processed tubes because the straight leg and U-bend both contain residual stresses
High Row Screening Bobbin voltage difference between the straight legs and the U-bend is less than the population -
2 sigma lower voltage difference
- Population is all of the tubes in the bundle on both HL and CL 12
- Both HL and CL must be involved because the tube processing includes the entire length of the tube
- Local buffing/polishing can cause local regions of residual stress
- Does not impact a -2 sigma tube unless it simultaneously occurred at the same location on the HL and CL at location of voltage measurement
High Row Screening
-2 Sigma chosen to provide 95th percentile of the tube bundle offset population (H/L and C/L).
- It has no physical significance.
- It provides only a relative scale of the U-bend 13 y
condition compared to the straight leg as a standard.
- Definition of -2 sigma is statistical based which means all steam generators will have -2 sigma tubes
Eddy Current Signature of High Stressed Higher Row Tube U-bend Normal Tube Abnormal Tube 14
Typical Bobbin Voltage U-bend Offset Distributions 6
7 8
9 Thermally Treated Tubes 15 0
1 2
3 4
5 0
5 10 15 20 25 30 35 40 45 50 R o w Volts H L C L S G -A M ean S G -A,-2s M A Mill Annealed Tubes
ODSCC vs PWSCC Pulled tube destructive examination indicated bulk residual stress; primarily OD tensile hoop stress Final polish affects OD only; increases 16 Final polish affects OD only; increases surface stress A600TT is resistant to PWSCC No corrosive concentration mechanism on primary side
Application of High Stress and -2 Sigma Knowledge of the manufacturing sequence is critical to the application of the screening process results
- The likely manufacturing deviation results in a primarily OD tensile residual stress SG manufacturing processes override potential tube 17 g p p
manufacturing residual stresses
- Forming the U-bends
- Tube in tubesheet expansions Applicability of screening intended only for ODSCC at tube support plates
- No technical basis considered or provided to address SCC at other locations on the tube.
SGMP Survey Results All plants have completed the screening as recommended in SGMP Information Letter 9/14/2004 SGMP requested screening results from Alloy 600TT fl t J 2010 18 600TT fleet January 2010
- All plants responded
- Investigate the continued applicability of the screening methodology Only 2 plants have identified tube support plate ODSCC in higher row tubes
Summary Results for Cracks at Tube Support Plates Plant Unit SG Row Column Outage Year Location HL Offset CL Offset
-2 Sigma Orientation Braidwood 2
A 25 42 A2R10 2003 TSP 0.81 1.3 3.10 SAI/OD Braidwood 2
C 38 20 A2R10 2003 TSP 0.52 2.18 2.40 SAI/OD Braidwood 2
C 21 50 A2R10 2003 TSP SAI/OD Braidwood 2
C 21 50 A2R10 2003 TSP SAI/OD Catawba 2
B 24 62 EOC16 2009 TSP 2.42 1.9 3.03 SAI/OD Catawba 2
D 41 55 EOC16 2009 TSP SAI/OD Catawba 2
D 41 55 EOC 16 2009 TSP SAI/OD Catawba 2
D 41 55 EOC 16 2009 TSP SAI/OD Catawba 2
D 41 55 EOC 16 2009 TSP SAI/OD 1.95 1.75 2.21 3.98 3.66 1.07 19 Catawba 2
D 41 59 EOC 16 2009 TSP SAI/OD Catawba 2
D 41 59 EOC 16 2009 TSP SAI/OD Catawba 2
D 41 59 EOC 16 2009 TSP SAI/OD 1.89 1.58 1.95
Conclusion
To date -2 sigma tubes correlate reasonably well with ODSCC reported at TSPs
- Application of the screening for -2 sigma tubes provides a broad indication of relative tube straight leg material condition compared to the U-bend material condition
- Application of the screening for -2 sigma tubes does NOT provide the residual stress level in the tube 20
Screening results are applicable only to straight length of tubes above the TTS
-2 sigma tubes are NOT good predictor of potential for ODSCC at the tubesheet
-2 sigma tubes are NOT intended to address PWSCC
The survey results will be reviewed by SGMP to determine appropriate action
Interim Guidance to address/clarify certain issues 21 Helen Cothron, EPRI
Definitions in NEI 97-06 and the Integrity Assessment Guidelines
- Appendix A of the Integrity Assessment Guidelines, Revision 3 defines accident induced leakage as:
The primary-to-secondary leakage occurring during NRC Technical Issues with Industry Guidance 22 postulated accidents other than a steam generator tube rupture when tube structural integrity is assumed.
- The phrase when tube structural integrity is assumed is deleted by this interim guidance
- The definition will be incorporated into the next revision of NEI 97-06
Implementation Issues with the Integrity Assessment Guidelines
- Section 7.6 of the Integrity Assessment Guidelines, Revision 3 states that a comparison of the CM results to the previous cycle OA predictions shall be performed.
- This requirement is not being implemented consistently NRC Technical Issues with Industry Guidance 23
- The following requirement is being added to the Integrity Assessment Guidelines with this interim guidance:
"A comparison table or discussion shall be documented in the OA report, with conclusions regarding validity of the prior cycle OA methodology or needed changes implemented in the current cycle OA methodology."
Implementation Issues with the Integrity Assessment Guidelines
- The Integrity Assessment Guidelines do not address performing CM on tubes that are scheduled for inspection but are unable to be inspected and, as a result, may be plugged (e.g., obstructed tube, permeability variations).
Tech Specs require that CM be performed on all tubes inspected NRC Technical Issues with Industry Guidance 24
- Tech Specs require that CM be performed on all tubes inspected or plugged.
- The following statements are being added to the Integrity Assessment Guidelines with this interim guidance:
"When meeting the performance criteria cannot be demonstrated based on the results of qualified inspection techniques, an engineering analysis, augmented inspection method(s) (e.g., ET diagnostic techniques, UT, PT, video probe), or in situ pressure testing are acceptable alternatives. CM by engineering analysis or augmented inspections shall include a rational basis for concluding the performance criteria have been met."
Definitions in NEI 97-06 and the Integrity Assessment Guidelines
- Appendix A and Section 2.6 of the Integrity Assessment Guidelines, Revision 3, define normal steady state full power operation as:
The conditions existing during MODE 1 operation at the maximum steady state reactor power as defined in the design or equipment specification.
Additional Information in Interim Guidance 25 Changes in design parameters such as plugging or sleeving levels, primary or secondary modifications, or Thot should be assessed and their effects on differential pressure included if significant.
- The definition will be simplified and consistent with other terminology in the document The conditions existing during Mode 1 operation at normal steady state full power operation.
- The definition will be incorporated into the next revision of NEI 97-06
Revision 3 of the Integrity Assessment Guidelines includes a requirement to use the Appendix I ETSSs
- Implementation date is Sept. 1, 2010 Primary goal of the Appendix I ETSSs was to provide generic, system performance indices Additional Information in Interim Guidance 26 This interim guidance makes the requirement to use the ETSSs immediate
Validation of Repair Limits
- Integrity Assessment, R2 requires repair limit to be determined as part of the DA process
- No requirement to revisit after inspection results confirm growth rates
- Revision 3 deleted the requirement, made it a recommendation and added guidance throughout the document Issues Addressed in Current Guidance 27 added guidance throughout the document
- Chapter 3 states that the repair limit and OA limit are obtained by further modification to consider degradation growth, and require that flaws on tubes remaining in service at the BOC satisfy the SIPC over the next inspection interval.
- Revision 3 deleted the requirement, made it a recommendation and added guidance throughout the document
- Chapter 6 explains that preventive repair may be required based on OA considerations. Depending on the growth rate of the degradation mechanism that is identified from the inspection and the length of time between planned inspections Issues Addressed in Current Guidance 28 inspection, and the length of time between planned inspections (multi-cycle inspection intervals), it may be necessary to establish a lower through-wall limit for plugging to ensure tube integrity at the time of the next inspection.
- Chapter 7 and 8 includes statements that plugging at lower limits may be necessary due to growth rates and cycle lengths
SG Program Updates
- NEI 03-08 requires utilities to implement the industry Guidelines and requires INPO to evaluate plant activities against the guidelines
- NEI 97-06 requires all licensees to meet the li bl ti f th i EPRI id li Issues Addressed in Current Guidance 29 applicable sections of the six EPRI guidelines
- Technical Specifications establish NEI 97-06 and its associated guidelines as the steam generator program
Large leaks
- Revision 3 of the Integrity Assessment Guidelines includes the following requirement:
In some SG designs wear scars do not have a sufficient length to cause a true tube burst.
However a large leakage event is possible In Issues Addressed in Current Guidance 30 However, a large leakage event is possible. In these cases, if the possibility of a tube burst is discounted, then the probability of a large leakage event shall be calculated and the significance of this probability evaluated.
Deposit Modeling Results (Cruas) 31 Heather Feldman, EPRI
Specifics of Model 51B Design Tubes R8[C47/C48/C49]
32 Chimney (12 quatrefoil holes without tubes)
Tube Locations
No Chimney
- Velocity does not increase preferentially near generator centerline with TSP deposit build up HL CL HL CL Thermal-Hydraulic Analysis 33 No Chimney, No Deposit Build Up No Chimney, With Deposit Build Up With Chimney, No Deposit Build Up HL CL With Chimney, With Deposit Build Up HL CL With Chimney
- Velocity increases significantly near generator centerline &
impinges on small-radius tubes in U-bend
Fluid-elastic instability is considered the predominant mechanism
Characterized by Critical Velocity Ratio (CVR)
Flow Induced Vibration Analysis vibration) of mode each (for y
instabilit elastic fluid of onset for velocity Critical length) tube over (average velocity gap crossflow uniform Equivalent
=
=
c e
V V
34
CVR characterizes a margin for onset of fluid-elastic instability
- Values 1 imply a tube may be unstable
- Values < 1 imply a tube may be stable at the given conditions c
Tube Locations and Anti-Vibration Bars C48 C94 R1 R11 R13 No AVB (R1 to R10)
One AVB (R11 & R12)
Tube-free Lane R6C48 R8C48 R10C48 R10C71 R10C93 35 R46 Two AVB's (R13 to R46)
Critical Velocity Ratio 0 0 0.2 0.4 0.6 0.8 1.0 1.2 Critical Velocity Ratio No Chimney With Chimney With Build Up 36 0.0 R6C48 R8C48 R10C48 Tube 0.0 0.2 0.4 0.6 0.8 1.0 1.2 R6C48 R8C48 R10C48 Tube Critical Velocity Ratio No Chimney With Chimney No Build Up
Conclusions TSP build up has a detrimental effect on the FIV response of SGs with a chimney
- High velocities near the small radius tubes in the U-bend region Therefore tendencies for fluid elastic instability in this 37
- Therefore, tendencies for fluid-elastic instability in this region are higher than for neighboring tubes
- Velocity magnitude in this region is higher when there is TSP build up A SG with no chimney and with design and conditions analyzed in this study will not have FIV issues
SGMP Project Prediction of Steam Generator TSP Blockage Objective
- To develop a model to predict average blockage as a function of time for the top broached hole TSP Approach
- Model will be based on analysis of reported plant 38
- Model will be based on analysis of reported plant data supplemented by theoretical considerations
- Broached-hole design, TSP and tubing material, total operating time, secondary chemistry, rate of transport of secondary impurities, iron transport rate to the SGs, deposit characterization, blockage estimates from visual inspections and eddy current
- Statistical distributions, Monte Carlo approach
Vogtle 1 Tube Pull Evaluation 39 Rick Mullins, Southern Company
Background - Tube removal Two tubes exhibiting TTS ODSCC indications were selected for removal during 1R14
- Tube R11C62 contained axial indications.
40
- Damaged during the removal process.
- Loaded beyond the elastic limit during the removal and some test result data has been compromised.
- Tube R12C98 contained circumferential indications.
40
Lab Exam - Characterization of Cracks Both Tubes
- OD initiated stress corrosion cracks
- Within expansion transition (expansion transition and tube diameter typical)
R11C62 41
- Three distinct axial cracks, one small IGA patch
- All three ODSCC cracks were through wall R12C98
- Numerous circ cracks around circumference
- Not through wall 41
Met Depth Profile - R11C62 (160° axial crack) 50 60 70 80 90 100 h (%TW) 42 0
10 20 30 40 0
20 40 60 80 100 120 140 Axial Position From Bottom (mils)
Depth 42
Met Depth Profile - R12C98 (circumferential crack) 60 70 80 90 100
%TW) 43 0
10 20 30 40 50 0
50 100 150 200 250 300 350 Azimuthal Location (Degrees)
Depth (%
43
In Situ Pressure Test Screening Data Field +Point Field Data Review Lab +Point Met Data Plant-Specific In Situ Parameters R12C98 SCI 0.44 v 54% TW OD 7.3% PDA 51° extent SCI 0.39 v 40% TW OD 0.16 in long 38 ° extent MCI (138°)
3.09 v 70% TW OD 0.25 in long 69° extent 0.39 v 40% TW OD MCI 31 cracks 80% TW 21% PDA Longest crack 92° Proof Test CA > 201° (OD)
Leak Test VCRIT = 3.9 v VTHR-L = 1.33 v MDTHR-L = 75%
44 0.32 in long 27° extent R11C62 Damaged in pull SAI 0.71 v 88% TW OD 0.18 in long Unresolved MAI 0.71 v 92% TW OD 0.29 in long Unresolved MAI 6.14 v 96% TW OD 0.19 in long MAI 100% TW (0.073 in) 0.142 in long 100% TW (0.093 in) 0.123 in long 100% TW (0.035 in) 0.124 in long Proof Test VM > 0.4 v and Length > 0.6 in Leak Test VCRIT = 2.4 v VTHR-L = 1.0 v MDTHR-L = 75%
44
Burst Test
Purpose:
Confirm burst pressure exceeds 3xNODP
>4597 psig, includes factors for temperature, gage uncertainty Tube R11C62 axial R11C62 axial R12C98 circ R12C98 circ Region TTS freespan TTS freespan Burst Pressure (psig) 9700 12525 10725 11250 45 (p g)
Burst Orientation axial axial circ axial Calculated Burst Pressure (psig - from field ECT data) 6448 10926 10004 10926 Calculated Burst Pressure (psig - from lab data) 9139 11347 9472 11347 45
Microstructure
No significant difference in the microstructure was observed between regions near the cracks and remote from the cracks
The microstructure is characterized as having a fine grain size, in the range ASTM E112 size 9-10. The fine grain size suggests a lower temperature mill anneal.
L G
i Si 46
Note: Smaller Number=Larger Grain Size
The microstructure exhibited some variety of grain sizes but did not exhibit any banding of small grains, which would be typical of low temperature mill annealed Alloy 600 (A600MA) with grains in the ASTM E112 size 10-12 range.
46
Microstructure (cont.)
The archive tubing has larger grains, ASTM size 8, which is more representative of A600TT tubing in Model F steam generators. The pulled Vogtle-2 tubes had grain sizes of 8 and 9
Both pulled tubes exhibit relatively low density of grain boundary carbides for 600TT and a relatively high density of 47 y
y g
y intragranular carbides
- The low density of intergranular carbide precipitation suggests that the mill annealed treatment was ineffective in dissolving sufficient carbon and carbides
- The fine grain size also suggests lower temperature mill anneal
- Without sufficient carbon in solution, intergranular carbides cannot precipitate during the thermal treatment
- Precipitation occurred on undissolved, intragranular carbides 47
Sensitization Test Sensitization tests performed and still under review Preliminary results suggest tubes were not sensitized The Vogtle 1 pulled tubes showed weight losses of 121-195 mg/dm2/day.
48
In contrast,
- Generic archived tubing showed a weight loss of 27 mg/dm2/day,
- The Vogtle 2 pulled tube ranged from 31-40 mg/dm2/day
- The Seabrook tube ranged from 32-87 mg/dm2/day.
48
Thermal Treatment Investigation A review of specific Vogtle-1 manufacturing records has been initiated.
The records are generally not detailed enough to 49 assign actual point specific heat treatment, furnace location, and other processing characteristics to a specific tube from a SG.
49
Comparison with Seabrook Pulled Tubes Orientation: Vogtle-1 mostly circ, Seabrook axial Location: Vogtle-1 at TTS, Seabrook at supports Freespan residual Stress: Vogtle-1 1 ksi, Seabrook 17-22 ksi 50 Seabrook 17 22 ksi Microhardness: Both low and even (~180 VHN)
Microstructure: Non-optimal microstructure in pulled tubes from Vogtle-1 and Seabrook.
50
Conclusions Vogtle-1 indications are ODSCC cracks within the expansion transition Cracks did not violate burst pressure criteria or exceed the in situ pressure test criteria Microstructure indicates material did not respond as 51 p
predicted to thermal treatment Vogtle-1 ODSCC dissimilar to Seabrook ODSCC Additional investigation is required No parameters identified outside manufacturing tolerances No method to identify susceptible tubes 51
Bugey 3 Operating Experience 52 Steve Swilley, EPRI
Bugey 3 Operating Experience 53
Bugey 3 Operating Experience 54
Bugey 3 Operating Experience 55
Bugey 3 Operating Experience 56
Project Plans for Foreign Object (FO) Detection
& FO Wear Detection/Sizing 57 Steve Swilley, EPRI
Detection of Foreign Objects Detection & Sizing of Foreign Object Wear Project update
- Report 1020631 Published January 2010
- Ability to detect foreign objects at varying di t f
t t
d t b f
58 distances from structures and tube surface researched for all three probe types
- Effects of Foreign Objects on wear sizing shows little impact in many cases (typically conservative)
Detection of Foreign Objects Detection & Sizing of Foreign Object Wear Project update (cont)
- Continuing research on effects of structure/transition on volumetric wear detection
- Sample fabrication
- Machine shop work on flaws in progress 59 ac e s op o
o a s p og ess
- Should lead to ETSS development for detection and sizing of loose part wear at TTS expansion transition
- 3 frequency bobbin mix will also be evaluated
- Developing detection and sizing ETSSs for array probes (Intelligent Probe and X Probe)
- Based upon existing EPRI loose part wear scar samples
NEI 97-06 Revision 3 60 60 Jim Riley, NEI
Overview NEI 97-06 revision 2 issued in 2005 Changes in SG program guidance and the SG tech specs have created inconsistencies Additional input requested today 61 61 Additional input requested today Revision process
- NRC review of draft?
Revision 3 will be issued this year
NEI 97-06 Revision 3 Team Gary Boyers, FPL Rick Mullins, SNC Dan Mayes, Duke 62 62 Russ Lieder, NextEra Energy Scott Redner, Xcel Energy Helen Cothron, EPRI Jim Riley, NEI
Specific Revision Topics Definitions
- Accident induced leakage
- Normal steady state full power operation
- Operational assessment 63 63 p
- SG tubing Performance of condition monitoring Accident leakage performance criteria
Additional Revision Topics Input requested 64 64
Revision Process Revision team develops draft SGTF review SGMP review NRC review?
65 65 PMMP approval No NSIAC approval required
- NSIAC will be informed of changes Implementation to be determined
Update/Closure of Divider Plate Cracking 66 Chris Casino, Westinghouse Helen Cothron, EPRI
Divider Plate Project Summary Phase I Results
- Cracks observed in divider plate (DP) welds, stub runner (SR) and heat affected zone (HAZ) in foreign fleet.
- Westinghouse Model 51 SG limiting case for 67 US plants.
- Model 51 is limiting case due to thinnest DP and greatest structural effect of degraded DP.
- Compares well with foreign OE.
Divider Plate Project Summary Phase I Results
- Degraded DP increases vertical tubesheet displacement.
- Observed cracks in foreign SGs not capable of causing the DP to fail suddenly.
68
- Long, shallow cracks cannot rapidly propagate through the ductile weld material at high temperatures.
- Remaining weld ligaments in DP connections capable of bearing load.
Divider Plate Geometry Reference
>110 inches (Typical) 69 DP cracking limited to HAZ region of plate, SR and weld.
Divider Plate Geometry Reference 70 Regions of Interest in Foreign OE
Divider Plate Project Update Foreign plants continue to inspect DP.
Cracks in the DP can increase in both length and depth during normal operations after initiation 71 after initiation.
Domestic concerns led to proposing additional work.
Phase II of the program began 2007.
Divider Plate Project Update Key Issues in Phase II:
Analysis of Transients (LOCA and Non-LOCA).
72 Analysis of Multiple Crack Geometries.
- Multiple and Combined origin sites.
Review if ASME Code Stress Reports are affected by degraded DP condition.
Are DP Cracks a safety concern?
Divider Plate Project Update Phase II Analysis Details:
- Focused on fully degraded and more realistic conditions.
A fully degraded divider plate has a crack 73
- A fully degraded divider plate has a crack that is 100% through wall and 100% of the length of the plate.
- More realistic conditions describes detailed 2D crack growth modeling in a 3D structure.
Divider Plate Project Update Phase II Scope completed in 2008:
- Non-LOCA Transient Analysis Conclusions Worst case crack opening area (COA): 16 in2 74
- Worst case crack opening area (COA): 16 in
- The bounding COA equals ~20 tubes.
- A fully degraded divider plate does NOT adversely affect SG performance during LOCA or non-LOCA events.
- A fully degraded divider plate is NOT a safety concern during plant operations.
Divider Plate Project Update Phase II Scope completed in 2009:
- ARC Impact.
- SG Tube Plug and Sleeve Impact.
75
- Review if ASME Code Stress Reports are affected by degraded DP condition.
Conclusions:
- No changes in current analyses would result from a degraded DP.
Divider Plate Program Documents Phase I Results:
- EPRI Final Report 1014982.
Phase II Results 76
- EPRI Technical Update 1016552.
- EPRI Technical Update 1019040.
- Final summary of Phase II scope to be published this year.
Divider Plate Project Update The following components were evaluated and are not affected by a degraded divider plate:
- Tubesheet
- Channel head 77
- The lower shell
- Tubesheet to channel head junctions
- Tubesheet to lower shell junctions
- Tube-to-tubesheet welds
Divider Plate Project Update The following analyses are not affected by a degraded divider plate:
- Supporting analysis and boundary conditions for lower SG complex.
Th f
f t f ti f th SG d
78
- The performance or safety function of the SG and the affected loop during a postulated accident condition.
- The supporting analysis basis for tube plugs installed prior to 1989.
- C* Alternate Repair Criteria.
- H* Alternate Repair Criteria.
Divider Plate Project Update The following analyses were evaluated and determined to be sensitive to a degraded DP:
- SG mechanical tube plugs used after 1989.
- Laser welded and TIG welded sleeves.
- F* Alternate Repair Criteria.
79
- W* Alternate Repair Criteria.
DP factor of 0.76 was used in the analyses.
Conservative because 0.76 is less than the level of support in the case of a fully degraded divider plate.
Divider Plate Project Update The analyses for Leak Limiting Alloy 800 sleeves do not include a divider plate:
- It is unlikely that additional consideration of tubesheet deformation would invalidate the current design.
80
- The limiting cases for bending in the Alloy 800 sleeve design are in the free span and exceed any potential deformation that could be experienced by the tube to tubesheet portion of the tube.
Recent Manufacturing OE SONGS replacement steam generator DP cracking.
- Manufacturing issue, not service induced.
- Significantly different design than existing 81
- Significantly different design than existing fleet.
- DP in existing fleet are not intended to be structural components in lower SG complex.
Phase II Results Improved Crack Modeling Kinematic Modeling
- Based on Operating Experience
- Varying crack initiation sites 82
- Calculates Time to Failure Detailed FEA Studies D Crack Geometries
- Cold Leg or Hot Leg
- Varying crack initiation sites
Phase II Results Kinematic Modeling:
- Applies worst case observed crack growth rates.
Uses vibration models to estimate 83
- Uses vibration models to estimate displacement amplitudes per load cycle.
- Not a stress based analysis.
- Useful for estimating the effect of multiple cracks and multiple crack lengths at different locations.
Phase II Crack Analysis DP Crack Indications
- 1. Number of Crack Sites
- 2. Estimated Crack Length
- 3. Estimated Crack Depth INPUT Crack Analysis Results TS Displacement TS Mode Shape Estimated Time to Failure OUTPUT MODEL 84 Discrete Beam Model Discrete Plate Model Represented by Interlinked 1D Springs Cracked Regions of Plate y(x,t)
Interlinked Beams Represent TS MODEL
Phase II Results Several crack initiation patterns studied.
- Center of plate.
- Edges of plate.
- Center and edges of plate.
85 g
p
- Different lengths and depths.
Analysis predicts an increase in the time to propagate through-wall from 6 years to 60 years based on OE.
Phase II Results 0.20 0.30 0.40 0.50 0.60 alized Amplitude Static Mode Mode 1 Mode 2 Mode 3 Mode 4 Static Mode = 0 Hz Mode 1 = 28 Hz Mode 2 = 48 Hz Mode 3 = 85 Hz Mode 4 = 136 Hz 86
-0.20
-0.10 0.00 0.10
-80
-60
-40
-20 0
20 40 60 80 Divider Plate Position, in Norma
- Maximum Static Displacement at centerline ~ 0.35 inch.
- Frequencies above 7 Hz are very unlikely.
Phase II Results Detailed FEA Studies D Divider Plate D Crack Growth V
i L
h d D h
87
- Varying Length and Depth
- 10 Different Crack Patterns Analyzed
- Cold Leg and Hot Leg Cracks Studied
- Cracks can cross DP faces (e.g., hot leg face to cold leg face)
Phase II Results 62 in 25 in 88
- Divider plate has a ~62 inch radius, 2 inches thick.
- 3-D Solid Finite Element Model.
Final Mesh Solid Partitions
Phase II Results Sub-Model Boundary Conditions Conservatively Applied to Maximize Crack Growth and Vertical Stresses Drawn from Bounding Normal and Upset Operational Conditions 89 Limiting case in Original Design Basis for Model 51
- Hot Leg to Cold Leg Difference: 50 psi
- Primary to Secondary Difference: 1815 psi
- Temperature = 600 °F
Phase II Results 90 Relative Vertical Displacement:
Uncracked 35x Magnification Relative Vertical Displacement:
HL Face Crack, 50% Depth 35x Magnification
Phase II Results 91 Hot Leg Face Crack Cold Leg Face Crack Relative Vertical Displacement Results (35x Magnification)
Phase II Results Stress Analysis Results
- Large Compressive Stresses develop ahead of crack edge.
- Magnitudes range from 3 ksi - 93 ksi.
92
- It is not possible to grow a crack through the compressive stress field.
- In the worst case crack geometry, the compressive stresses range from 3 ksi to 60 ksi.
Phase II Results Divider Plate is not considered a part of the primary pressure boundary nor is it considered a significant part of the steam generator structure in the existing fleet.
93 Not classified as an ASME Structure.
WNEP 9106 Vol. 5, Page 6-1 (33/245): A rigid Section III analysis is therefore not required of the divider plate...
Phase II Results No identified need for US plants to inspect based on program results.
- Degraded DP is not a safety concern during operations.
- Degraded DP is not a structural concern during 94 Degraded DP is not a structural concern during operations.
- Degraded DP does not affect existing repair criteria or repair tools.
- DP Inspection not mandated by ASME Code.
No identified need to repair degraded DP.
Conclusion Cracks can grow in DP during normal operations, but, they are:
- Not a safety concern.
- Not a structural concern.
95
- Do not need to be inspected.
- Do not need to be repaired.
A Degraded DP is not considered to be a safety issue.
SGTF considers this issue closed
Upcoming Changes to Industry Documents 96 Documents Jim Benson, EPRI
SGMP Industry Document Status and Revision Schedule 97
SGMP Guidance Update Guideline revisions recently published
- Revision 3 to SG Integrity Assessment Guidelines
- Implementation required by September 1, 2010 Guidelines currently in revision 98 y
- Revision 4 to SG Primary-to-Secondary Leak Guidelines
- Revision 3 to SGMP Administrative Procedures
- Revision 4 to In Situ Pressure Test Guidelines
SGMP Guidance Update Guidelines recently reviewed
- Primary Chemistry - No revision required (June 2009).
Next annual review scheduled for June 2010.
- SG Exam Guidelines - Re-evaluate need for revision June 2010
- PWR Secondary Water Chemistry Guidelines Rev 7 -
99
- PWR Secondary Water Chemistry Guidelines, Rev 7 -
Review in late 2010 Interim Guidance Letters
- Draft IG Letter is in review to require the use of the new ETSSs developed under Appendix I of the SG Examination Guidelines Information Letters
- None
Recent SG Operating Experience 100 June-December 2009 Russ Lieder, Nextera Energy Seabrook, LLC
2009 Industry Operating Experience (June-December)
In situ pressure tests required at 2 stations in Fall 2009 to demonstrate tube performance criteria
- Vogtle 1 in-situ pressure tested a tube with a U-Bend axial indication
- Primary-to-Secondary leak identified during drain 101 Primary to Secondary leak identified during drain down (0.15 gpd)
- Negligible leakage during in-situ pressure test at normal operating differential pressure
- 0.002 gpm at accident differential pressure
- Waterford 3 in-situ tested a eggcrate axial indication
- No leakage or burst at 3P + 500 psi
2009 Industry Operating Experience (June-December)
Siemens SGs with Alloy 800 tubing reporting denting and OD circumferential crack-like indications at the top of the tubesheet
- Doel 3 increase in deposits at top of tubesheet and denting
- Asco 1 denting and OD circumferential cracking
- Asco 2 denting 102 Asco 2 denting
- Almaraz 1 denting
- Almaraz 2 denting and OD circumferential cracking
Belleville 2, Framatome SGs with Alloy 600TT tubing also reporting denting and OD circumferential cracking at the top of the tubesheet in the kiss roll area.
2009 Industry Operating Experience (June-December)
EDF continues to chemically clean all the SGs in their fleet to address the potentially adverse thermal/hydraulic effects of broach hole fouling. EdF will also employ the use of scale conditioning agents such as ASCA and DMT.
E t i
tl l
d t b d
i th ANO 103 Entergy incorrectly plugged a tube during the ANO Unit 2 outage in 2005. This missed plugged tube was identified during the 2009 outage.
- Incorrect measurement lengths from the robotic system which produced a slightly different location within the SG.
- Verification method determined to be inadequate
2009 Industry Operating Experience (June-December)
Salem Unit 2
- First ISI of replacement steam generators resulted in large population of AVB wear indications 104 indications.
- 1556 AVB wear indications in 584 tubes
- Quantity of wear impacts ability to skip the next cycle. Operational Assessment could only justify one cycle of operation.
2009 Industry Operating Experience (June-December)
Sequoyah 2 (Alloy 600 MA)
- CL Freespan crack indications detected by bobbin
- +point characterized the indication as 8 separate axial outer diameter crack like indications 105
- PWSCC detected in cold leg tubesheets
- 3 tubes with indications below top of tubesheet
- In-situ testing not required
- No tubes pulled
2009 Industry Operating Experience (June-December)
Seabrook
- Axial ODSCC at top of tubesheet hot leg
- Single indication in one steam generator
- Located 0.26 below top of tube sheet at 106 p
bottom of expansion transition
- Length 0.12
- In-situ not required
NRC feedback on various issues (e g TSTF-510) 107 (e.g., TSTF-510)
Address Public Questions/Comments 108 Questions/Comments
Adjourn 109