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 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 2
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 Guidance ffor ttubes b with ith potentially t ti ll elevated l t d stress t
- 3. Deposit Modeling Results (Cruas)
- 4. Vogtle Tube Pull Evaluation
- 5. Insights from Bugey 3 Operating Experience
- 7. NEI 97-06 Revision
- 8. Update/Closure of Divider Plate Cracking
- 9. Upcoming Changes to Industry Documents
- 10. Recent SG Operating Experience 3
Survey results for -2 sigma 600TT tubes with cracks Herm Lagally, g y Westinghouse g
4
Blairsville Partial Manufacturing Flow Diagram Approx. final tube diameter in Final Anneal Cold Worked condition Visu Hydro Test, Thermal al Straighten Polish NDT &
NDT, Treat E Exa Visual m Pass Fail This path is limited by cumulative time at temperature Stress relieve Form U-bends Low Row U-bends 5
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
- 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 6
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
- 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) 7
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
- 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 9
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-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.
10
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 and straight legs would be smaller compared to normally processed tubes because the straight leg and U-bend both contain residual stresses 11
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
- 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 12
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 onlyy a relative scale of the U-bend 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 13
Eddy Current Signature of High Stressed Higher Row Tube Normal Tube Abnormal Tube U-bend 14
Typical Bobbin Voltage U-bend Offset Distributions 9
Thermally Treated 8 Tubes 7
6 HL 5
CL Volts S G -A M e a n 4 S G -A ,-2 s MA 3
2 Mill Annealed 1
Tubes 0
0 5 10 15 20 25 30 35 40 45 50 Row 15
ODSCC vs PWSCC Pulled tube destructive examination indicated bulk residual stress; primarily OD tensile hoop stress Final polish affects OD only; increases surface stress A600TT is resistant to PWSCC No corrosive concentration mechanism on primary side 16
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 gpprocesses override ppotential tube 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.
17
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 flfleett January J 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 18
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 1.75 2.21 3.98 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 3.66 1.07 1.95 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 59 EOC 16 2009 TSP SAI/OD Catawba 2 D 41 59 EOC 16 2009 TSP 1.89 1.58 1.95 SAI/OD Catawba 2 D 41 59 EOC 16 2009 TSP SAI/OD 19
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 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 20
Interim Guidance to address/clarify certain issues Helen Cothron, EPRI 21
NRC Technical Issues with Industry Guidance 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 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 22
NRC Technical Issues with Industry Guidance 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
- 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."
23
NRC Technical Issues with Industry Guidance 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 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 24 for concluding the performance criteria have been met."
Additional Information in Interim Guidance 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.
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 25
Additional Information in Interim Guidance 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 This interim guidance makes the requirement to use the ETSSs immediate 26
Issues Addressed in Current Guidance 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
- 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.
27
Issues Addressed in Current Guidance
- 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 inspection, (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 28
Issues Addressed in Current Guidance 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 applicable li bl sections ti off th the six i EPRI guidelines id li
- Technical Specifications establish NEI 97-06 and its associated guidelines as the steam generator program 29
Issues Addressed in Current Guidance 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.
However, 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.
30
Deposit Modeling Results (Cruas)
Heather Feldman, EPRI 31
Specifics of Model 51B Design Tubes R8[C47/C48/C49]
Tube Locations Chimney (12 quatrefoil holes without tubes) 32
Thermal-Hydraulic Analysis HL CL HL CL No Chimney
- Velocity does not increase preferentially near generator centerline with TSP deposit build up No Chimney, No Deposit Build Up No Chimney, With Deposit Build Up HL CL HL CL With Chimney
- Velocity increases significantly near generator centerline &
impinges on small-radius tubes in U-bend With Chimney, No Deposit Build Up With Chimney, With Deposit Build Up 33
Flow Induced Vibration Analysis Fluid-elastic instability is considered the predominant mechanism Characterized by Critical Velocity Ratio (CVR)
Ve = Equivalent uniform crossflow gap velocity (average over tube length)
Vc = Critical velocity for onset of fluid - elastic instabilit y (for each mode of vibration)
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 34
Tube Locations and Anti-Vibration Bars C48 C94 Tube-free Lane R1 R6C48 No AVB (R1 to R10)
R8C48 R10C48 R10C71 R10C93 R11 One AVB (R11 & R12)
R13 Two AVB's (R13 to R46)
R46 35
Critical Velocity Ratio 1.2 No Chimney With Build Up 1.0 With Chimney Critical Velocity Ratio 0.8 0.6 0.4 0.2 00 0.0 R6C48 R8C48 R10C48 Tube 1.2 No Chimney No Build Up 1.0 With Chimney Critical Velocity Ratio 0.8 0.6 0.4 0.2 0.0 R6C48 R8C48 R10C48 36 Tube
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 Therefore, tendencies for fluid fluid-elastic 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 37
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 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 38
Vogtle 1 Tube Pull Evaluation Rick Mullins, Southern Company 39
Background - Tube removal Two tubes exhibiting TTS ODSCC indications were selected for removal during 1R14
- Tube R11C62 contained axial indications.
- 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
- 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) 100 90 80 70 60 Depth h (%TW) 50 40 30 20 10 0
0 20 40 60 80 100 120 140 Axial Position From Bottom (mils) 42
Met Depth Profile - R12C98 (circumferential crack) 100 90 80 70 60 Depth (%
%TW) 50 40 30 20 10 0
0 50 100 150 200 250 300 350 Azimuthal Location (Degrees) 43
In Situ Pressure Test Screening Data Field +Point Field Data Lab +Point Met Data Plant-Specific Review In Situ Parameters R12C98 SCI SCI MCI (138°) MCI Proof Test 0.44 v 0.39 v 3.09 v 31 cracks CA > 201° (OD) 54% TW OD 40% TW OD 70% TW OD 80% TW 7.3% PDA 0.16 in long 0.25 in long 21% PDA Leak Test 51° extent 38 ° extent 69° extent Longest crack 92° VCRIT = 3.9 v 0.39 v VTHR-L = 1.33 v 40% TW OD MDTHR-L = 75%
0.32 in long 27° extent R11C62 Damaged in pull SAI Unresolved MAI Unresolved MAI MAI Proof Test 0.71 v 0.71 v 6.14 v 100% TW (0.073 in) VM > 0.4 v and 88% TW OD 92% TW OD 96% TW OD 0.142 in long Length > 0.6 in 0.18 in long 0.29 in long 0.19 in long 100% TW (0.093 in) Leak Test 0.123 in long VCRIT = 2.4 v 100% TW (0.035 in) VTHR-L = 1.0 v 0.124 in long MDTHR-L = 75%
44
Burst Test
Purpose:
Confirm burst pressure exceeds 3xNODP
>4597 psig, includes factors for temperature, gage uncertainty R11C62 R11C62 R12C98 R12C98 Tube axial axial circ circ Region TTS freespan TTS freespan Burst Pressure (p (psig) g) 9700 12525 10725 11250 Burst Orientation axial axial circ axial Calculated Burst Pressure 6448 10926 10004 10926 (psig - from field ECT data)
Calculated Burst Pressure 9139 11347 9472 11347 (psig - from lab data) 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.
Note: Smaller Number=Larger L G Graini SiSize 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 boundaryy carbides for 600TT and a relatively y high g densityy of 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.
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 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 17-22 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 p
Microstructure indicates material did not respond as 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 Steve Swilley, EPRI 52
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 Steve Swilley, EPRI 57
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 distances ffrom structures t t and d tube t b surface f
researched for all three probe types
- Effects of Foreign Objects on wear sizing shows little impact in many cases (typically conservative) 58
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 ac e shop s op work o on o flaws a s in progress 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 59
NEI 97-06 Revision 3 Jim Riley, NEI 60
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 Revision process
- NRC review of draft?
Revision 3 will be issued this year 61
NEI 97-06 Revision 3 Team Gary Boyers, FPL Rick Mullins, SNC Dan Mayes, Duke Russ Lieder, NextEra Energy Scott Redner, Xcel Energy Helen Cothron, EPRI Jim Riley, NEI 62
Specific Revision Topics Definitions
- Accident induced leakage
- Normal steady state full power operation
- Operational p assessment
- SG tubing Performance of condition monitoring Accident leakage performance criteria 63
Additional Revision Topics Input requested 64
Revision Process Revision team develops draft SGTF review SGMP review NRC review?
PMMP approval No NSIAC approval required
- NSIAC will be informed of changes Implementation to be determined 65
Update/Closure of Divider Plate Cracking Chris Casino, Westinghouse Helen Cothron, EPRI 66
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 US plants.
- Model 51 is limiting case due to thinnest DP and greatest structural effect of degraded DP.
- Compares well with foreign OE.
67
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.
- Long, shallow cracks cannot rapidly propagate through the ductile weld material at high temperatures.
- Remaining weld ligaments in DP connections capable of bearing load.
68
Divider Plate Geometry Reference
>110 inches (Typical)
DP cracking limited to HAZ region of plate, SR and weld.
69
Divider Plate Geometry Reference Regions of Interest in Foreign OE 70
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.
initiation Domestic concerns led to proposing additional work.
Phase II of the program began 2007.
71
Divider Plate Project Update Key Issues in Phase II:
Analysis of Transients (LOCA and Non-LOCA).
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?
72
Divider Plate Project Update Phase II Analysis Details:
- Focused on fully degraded and more realistic conditions.
- 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.
73
Divider Plate Project Update Phase II Scope completed in 2008:
- Non-LOCA Transient Analysis Conclusions
- Worst case crack opening area (COA): 16 in2
- 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.
74
Divider Plate Project Update Phase II Scope completed in 2009:
- ARC Impact.
- SG Tube Plug and Sleeve Impact.
- Review if ASME Code Stress Reports are affected by degraded DP condition.
Conclusions:
- No changes in current analyses would result from a degraded DP.
75
Divider Plate Program Documents Phase I Results:
- EPRI Final Report 1014982.
Phase II Results
- EPRI Technical Update 1016552.
- EPRI Technical Update 1019040.
- Final summary of Phase II scope to be published this year.
76
Divider Plate Project Update The following components were evaluated and are not affected by a degraded divider plate:
- Tubesheet
- Channel head
- The lower shell
- Tubesheet to channel head junctions
- Tubesheet to lower shell junctions
- Tube-to-tubesheet welds 77
Divider Plate Project Update The following analyses are not affected by a degraded divider plate:
- Supporting analysis and boundary conditions for lower SG complex.
- The Th performance f or safety f t function f ti off the th SG and d
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.
78
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.
- 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.
79
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.
- 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.
80
Recent Manufacturing OE SONGS replacement steam generator DP cracking.
- Manufacturing issue, not service induced.
- Significantly different design than existing fleet.
- DP in existing fleet are not intended to be structural components in lower SG complex.
81
Phase II Results Improved Crack Modeling Kinematic Modeling
- Based on Operating Experience
- Varying crack initiation sites
- Calculates Time to Failure Detailed FEA Studies D Crack Geometries
- Cold Leg or Hot Leg
- Varying crack initiation sites 82
Phase II Results Kinematic Modeling:
- Applies worst case observed crack growth rates.
- 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.
83
Phase II Crack Analysis INPUT OUTPUT DP Crack Indications Crack Analysis Results
- 1. Number of Crack Sites
- TS Displacement
- 2. Estimated Crack Length
- TS Mode Shape
- 3. Estimated Crack Depth
- Estimated Time to Failure MODEL Interlinked Beams Represent TS y(x,t)
Discrete Beam Model Discrete Plate Model Represented by Interlinked 1D Springs Cracked Regions of Plate 84
Phase II Results Several crack initiation patterns studied.
- Center of plate.
- Edges of plate.
- Center and edges g of pplate.
- Different lengths and depths.
Analysis predicts an increase in the time to propagate through-wall from 6 years to 60 years based on OE.
85
Phase II Results 0.60 Static Mode = 0 Hz Static Mode 0.50 Mode 1 Mode 1 = 28 Hz Mode 2 Mode 2 = 48 Hz Mode 3 0.40 Mode 4 Mode 3 = 85 Hz Norma alized Amplitude 0.30 Mode 4 = 136 Hz 0.20 0.10 0.00
-0.10
-0.20
-80 -60 -40 -20 0 20 40 60 80 Divider Plate Position, in
- Maximum Static Displacement at centerline ~ 0.35 inch.
- Frequencies above 7 Hz are very unlikely.
86
Phase II Results Detailed FEA Studies D Divider Plate D Crack Growth
- Varying V i L Length h anddDDepth h
- 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) 87
Phase II Results 62 in 25 in Final Mesh Solid Partitions
- Divider plate has a ~62 inch radius, 2 inches thick.
- 3-D Solid Finite Element Model.
88
Phase II Results Sub-Model Boundary Conditions Conservatively Applied to Maximize Crack Growth and Vertical Stresses Drawn from Bounding Normal and Upset Operational Conditions 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 89
Phase II Results Relative Vertical Displacement:
Uncracked Relative Vertical Displacement:
35x Magnification HL Face Crack, 50% Depth 35x Magnification 90
Phase II Results Cold Leg Hot Leg Face Crack Face Crack Relative Vertical Displacement Results (35x Magnification) 91
Phase II Results Stress Analysis Results
- Large Compressive Stresses develop ahead of crack edge.
- Magnitudes range from 3 ksi - 93 ksi.
- 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.
92
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.
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...
93
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 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.
94
Conclusion Cracks can grow in DP during normal operations, but, they are:
- Not a safety concern.
- Not a structural concern.
- 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 95
Upcoming Changes to Industry Documents Jim Benson, EPRI 96
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 y in revision
- Revision 4 to SG Primary-to-Secondary Leak Guidelines
- Revision 3 to SGMP Administrative Procedures
- Revision 4 to In Situ Pressure Test Guidelines 98
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 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 99
Recent SG Operating Experience June-December 2009 Russ Lieder, Nextera Energy Seabrook, LLC 100
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 Primary-to-Secondary 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 101
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
- 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.
102
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.
Entergy E t incorrectly i tl plugged l d a ttube b dduring i ththe 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 103
2009 Industry Operating Experience (June-December)
Salem Unit 2
- First ISI of replacement steam generators resulted in large population of AVB wear indications 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.
104
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
- PWSCC detected in cold leg tubesheets
- 3 tubes with indications below top of tubesheet
- In-situ testing not required
- No tubes pulled 105
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 p of tube sheet at bottom of expansion transition
- Length 0.12
- In-situ not required 106
NRC feedback on various issues (e g TSTF-510)
(e.g.,
107
Address Public Questions/Comments 108
Adjourn 109