ML061300443
| ML061300443 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 05/31/2006 |
| From: | General Electric Co |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| TS-418, TS-431, TVA-BFN-TS-418, TVA-BFN-TS-431 DRF 0000-0051-5975, Rev 0, GE-NE-0000-0053-7413-R0-NP | |
| Download: ML061300443 (85) | |
Text
ENCLOSURE 5 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNITS 1, 2, AND 3 TECHNICAL SPECIFICATIONS (TS) CHANGES TS-431 AND TS-418 -
EXTENDED POWER UPRATE (EPU) OPERATION - STEAM DRYER STRESS REPORT BROWNS FERRY NUCLEAR PLANT UNITS 1, 2, AND 3 STEAM DRYER STRESS, DYNAMIC AND FATIGUE ANALYSES FOR EPU CONDITIONS (NON-PROPRIETARY VERSION)
Attached is Non-Proprietary General Electric Report No.
GE-NE-0000-0053-7413-RO-NP, "Browns Ferry Nuclear Plant Units 1, 2 and 3 Steam Dryer Stress, Dynamic and Fatigue Analyses for EPU Conditions."
GE Nuclear Energy
[ir, aral Le Ct f j rO,,=13nV 1':- Lit t3 1 "4 r?:h r 't C-rse,r , I " '.4 9' Non Proprietary Version GE-NE-0000-0053 -7413 -RO-NP DRF 0000-0051-5975 Revision 0 Class I May 2006 Browns Ferry Nuclear Plant Units 1, 2 and 3 Steam Dryer Stress, Dynamic and Fatigue Analyses for EPU Conditions
GE-NE- 0000-0053-741 3-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION IMPORTANT NOTICE REGARDING THE CONTENTS OF THIS REPORT Please Read Carefully NON-PROPRIETARY NOTICE This is a non-proprietary version of the document GE-NE-0000-0053-7413-RO-P, which has the proprietary information removed. Portions of the document that have been removed are indicated by an open and closed bracket as shown here ((.
IMPORTANT NOTICE REGARDING CONTENTS OF THIS REPORT Please Read Carefully The only undertakings of the General Electric Company (GE) respecting information in this document are contained in the contract between Tennessee Valley Authority, Browns Ferry Nuclear Plant and GE, 00001704 Release 00248, effective February 5, 2003, as amended to the date of transmittal of this document, and nothing contained in this document shall be construed as changing the contract. The use of this infornation by anyone other than Tennessee Valley Authority, Browns Ferry Nuclear Plant, for any purpose other than that for which it is furnished by GE, is not authorized; and with respect to any unauthorized use, GE makes no representation or warranty, express or implied, and assumes no liability as to the completeness, accuracy, or usefulness of the information contained in this document, or that its use may not infringe privately owned rights.
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GE-NE- 0000-0053-741 3-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION TABLE OF CONTENTS Section Page ACRONYMS AND ABBREVIATIONS ................................................. vi
- 1. EXECUTIVE
SUMMARY
................................................ 1
- 2. INTRODUCTION AND BACKGROUND ................................................. 3 2.1 Dryer Design Bases and Historical Development ................................................ 3 2.2 Browns Ferry Dryer Experience ................................................. 4 2.3 Motivation for Additional FIV and Structural Analysis ........................................ 8
- 3. Dynamic Analysis Approach ................................................ 9 3.1 Dynamic Loading Pressure Time Histories ............................................... 9 3.2 Stress Recovery and Evaluation Methodology ................................................. 9
- 4. Material Properties ................................................. 10
- 5. Design Criteria ................................................ . 10 5.1 Fatigue Criteria ............. 0.............................
5.2 ASME Code Criteria for Load Combinations ................................................ 11
- 6. Fatigue Analysis ................................................ . 11 6.1 Full Dryer Shell Finite Element Model ................................................ 12 6.2 Dynamic Loads ................................................ 13 6.3 Frequency Content of Loads ................................................ 13 6.4 Modal Analysis ................................................ 13 6.5 Structural Response to Loads . ...................... . 13 6.6 Stress Results from Time History Analyses .................................. 14 6.7 Weld Factors .................................... 17 6.8 Fatigue Analysis Results .................................. . 20
- 7. ASME Code Loads ................................... 22 7.1 ASME Code Load Combinations .................................. 22 7.2 ASME Code Load Case Stress Results .. ................................ 26
- 8. Proposed Dryer Modifications .................................. . 29
- 9. Conclusions................ 29
- 10. References ............ .. 31 ii Rev. 0
GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION List of Tables Table 2-1: BFNP Unit I Steam Dryer Inspection Data and Disposition for EPU ........................... 5 Table 2-2: BFNP Unit 2 Steam Dryer Inspection Data and Disposition for EPU . 6 Table 2-3: BFNP Unit 3 Steam Dryer Inspection Data and Disposition for EPU . 7 Table 4-1 Properties of SS304 [Reference 6] .0 Table 5-1 ASME Code Stress Limits [Reference 7] .11 Table 6-1 Time History Analysis Results from ANSYS: OLTP .15 Table 6-2 Time History Analysis Results from ANSYS: EPU .16 1 Table 6-3 Time History Results with Weld factors: OLTP .18 Table 6-4 Time History Results with Weld factors: EPU .19 Table 6-5 Final Stress Results: Design Margins for OLTP and EPU .21 Table 7-1 ASME Load Combinations .25 Table 7-2 OLTP ASME Results for Normnal and Upset Conditions: Average Stresses .27 Table 7-3 OLTP ASME Results for Faulted Conditions: Average Stresses .28 iii Rev. 0
GE-NE 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION List of Figures Figure 3-1 BFN Steam Dryer Finite Element Model with Boundary Conditions ......................... 32 Figure 3-2 BFN Steam Dryer Finite Element Model ............................................... ............ 33 Figure 3-3 BFN Steam Dryer Finite Element Model, con't .......................................................... 34 Figure 34 BFN Steam Dryer Finite Element Model, con't ................................. ........................ 35 Figure 3-5 EPU Applied Pressure Load to BFN Dryer .................................... ....................... 36 Figure 6-1 Frequency Content of Applied Load at EPU (Outer Hoods) ....................................... 37 Figure 6-2 Stress Time Histories for Several Dryer Components at EPU ..................................... 38 Figure 6-3 Outer Hood Pressure VS Stress Time Histories for EPU Nominal Case ..................... 39 Figure 6-4 Outer Hood FFT's for Nominal and +/-10% Cases at EPU ........ . ................. ............. 40 Figure 6-5 Inner Hood FFT's for Nominal and +/-10% Cases at EPU ......................................... 41 Figure 6-6 Cover Plate FFT's for Nominal and +/-10% Cases at EPU ........ ................................ 42 Figure 6-7 Trough FFT's for Nominal and +/-10% Cases at EPU ........... . ................................... 43 Figure 6-8 Skirt FFT's for Nominal and +/-10% Cases at EPU .................................................... 44 Figure 6-9 Modal Analysis Results: Outer Hoods ........................................................... 45 Figure 6-10 Modal Analysis Results: Inner Hoods ........................................................... 46 Figure 6-11 Modal Analysis Results: Skirt ........................................................... 47 Figure 6-12 Modal Analysis Results: Skirt, con't ........................................................... 48 Figure 6-13 Stress Intensity at EPU: Cover Plate ........................................................... 49 Figure 6-14 Stress Intensity at EPU: Manway Cover ............................................... ............ 50 Figure 6-15 Stress Intensity at EPU: Outer Hood..........................................................................51 Figure 6-16 Stress Intensity at EPU: Exterior Hood Plates - Outer Banks ................................... 52 Figure 6-17 Stress Intensity at EPU: Exterior Vane Bank End Plates - Outer Banks .................. 53 Figure 6-18 Stress Intensity at EPU: Hood Top Plates ........................................................... 54 Figure 6-19 Stress Intensity at EPU: Vane Bank Top Plates ......................................................... 55 Figure 6-20 Stress Intensity at EPU: Hood Stiffeners - Outer ....................................................... 56 Figure 6-21 Stress Intensity at EPU: Vane Bank Inner End Plates (2) ......................................... 57 Figure 6-22 Stress Intensity at EPU: Closure Plates - Outer Banks ........................................... 58 Figure 6-23 Stress Intensity at EPU: Inner Hoods......................................................................_59 Figure 6-24 Stress Intensity at EPU: Exterior Hood Plates - Inner Banks .......... ....................... 60 iv Rev. 0
GE-NE- 0000-0053-741 3-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Figure 6-25 Stress Intensity at EPU: Exterior Vane Bank End Plates - Inner Banks ................... 61 Figure 6-26 Stress Intensity at EPU: Hood Stiffeners - Inner (1) ................................................. 62 Figure 6-27 Stress Intensity at EPU: Hood Stiffeners - Inner (2) .............................. ................ 63 Figure 6-28 Stress Intensity at EPU: Vane Bank Inner End Plates (1) ......................................... 64 Figure 6-29 Stress Intensity at EPU: Vane Bank Inner End Plates (3) .... .................................... 65 Figure 6-30 Stress Intensity at EPU: Closure Plates - Inner Banks ................................. ............ 66 Figure 6-31 Stress Intensity at EPU: Steam Dams .......................................................... 67 Figure 6-32 Stress Intensity at EPU: Steam Dam Gussets .......................................................... 68 Figure 6-33 Stress Intensity at EPU: Baffle Plate .......................................................... 69 Figure 6-34 Stress Intensity at EPU: Trough .......................................................... 70 Figure 6-35 Stress Intensity at EPU: Base Plate ............................................ .............. 71 Figure 6-36 Stress Intensity at EPU: Support Ring .......................................................... 72 Figure 6-37 Stress Intensity at EPU: Skirt ........................................................... 73 Figure 6-38 Stress Intensity at EPU: Drain Pipes ........................................................... 74 Figure 6-39 Stress Intensity at EPU: Skirt Bottom Ring ........................................................... 75 Figure 6-40 Weld Factors ........................................................... 76 Figure 8-1 Proposed BFN Steam Dryer Modifications .......................................................... 77 v Rev. O
GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION ACRONYMS AND ABBREVIATIONS Item Short Form Description 1 ACM Acoustic Circuit Methodology used for predicting pressure loads on the dryer based on pressure measurements taken from main steam line sensors 2 ASME American Society of Mechanical Engineers 3 BWR Boiling Water Reactor 4 BFN Browns Ferry Nuclear Plant, Units 1, 2 and 3 5 CDI Continuum Dynamics, Inc.
6 EPU Extended Power Uprate 7 FEA Finite Element Analysis 8 FEM Finite Element Model 9 FFT Fast Fourier Transform 10 FIV Flow Induced Vibration 11 GE General Electric 12 GENE General Electric Nuclear Energy 13 Hz Hertz 14 IGSCC Intergranular Stress Corrosion Cracking 15 Mlbm/hr Million pounds mass per hour 16 MS Main Steam 17 MSL Main Steam Line 18 MWt Megawatt Thermal 19 NA Not Applicable 20 NRC Nuclear Regulatory Commission 21 OBE Operational Basis Earthquake 22 OLTP Original Licensed Thermal Power 23 Pb Primary Bending Stress 24 Pm Primary Membrane Stress 25 psi Pounds per square inch 26 Ref. Reference 27 RMS Root-Mean-Squared 28 RPV Reactor Pressure Vessel 29 SCF Stress Concentration Factor 30 SRSS Square Root Sum of Squares 31 SRV Safety Relief Valve 32 TVA Tennessee Valley Authority vi Rev. 0
GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION
- 1. EXECUTIVE
SUMMARY
Tennessee Valley Authority's Browns Ferry Nuclear Plant (BFN) Units 1, 2, and 3 are 251" diameter BWR/4 plants with the BWR/4 slant hood steam dryer. Structural analyses of the steam dryer were performed using a full three-dimensional finite element model of the BFNI dryer in support of the Unit I restart and Extended Power Uprate (EPU) programs for Units 1, 2, and 3. The analyses consisted of time history dynamic analyses, frequency calculations, and stress and fatigue evaluations.
Predictions of the fluctuating pressure loads on the dryer were developed in GE's scale model test (SMT) facility for use as input to the fatigue analysis. The scale model test loads were processed using an acoustic circuit model by Continuum Dynamics Inc. (CDI) to develop the detailed dryer pressure loads for the time history analyses. In addition, ASME Code based load combinations were also analyzed using the dryer finite element model. This report summarizes the dynamic, stress and fatigue analyses for the BFN Units 1, 2, and 3 steam dryer at original licensed thermal power (OLTP) and EPU conditions based on scale model test data.
The acceptance criterion used in the evaluation to predict fatigue susceptibility of the individual components was the ASME fatigue limit peak stress intensity greater than 13,600 psi. The load definitions based on the SMT methodology are conservative due to the nature of the boundary condition modeling in the test apparatus and due to the amplitude scaling used to bound the uncertainties in the SRV resonance frequency range. Due to the conservative nature of the SMT-based pressure loads, the analysis predicted that the majority of the steam dryer components are not vulnerable to fatigue at the OLTP conditions; however, there are a few locations that are at or near the fatigue stress limit. The 3/8-inch thick outer cover plate and manway cover are attached with 1/4/4-inch fillet welds. These welds are considered undersized and could lead to fatigue initiation at EPU conditions and will be reinforced as part of the EPU modifications. The results of the evaluation based on the ASME load combinations and associated stress acceptance criteria show acceptable stress margins for all operating conditions: normal, upset and faulted. The analyses show that the outer hood and cover plate locations are also regions of higher stress at EPU conditions.
Therefore, it is recommended that actions be taken to further evaluate the fluctuating stresses prior to extending power to 120% OLTP. Proposed modifications to improve the stress margins at these locations are identified in this report.
The stress analysis results for OLTP demonstrate that the BFN dryer stresses are generally below the fatigue endurance level screening criteria. When conservative stress concentration factors (SCF) are applied to address local stress intensification, a few dryer components are predicted to exceed the endurance level.
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION The Unit 1, 2, and 3 dryers have operated at OLTP for a period of eleven (I 1) to fifteen (15) years. Additionally the Unit 2 and 3 reactors have operated at 105%
OLTP for over six (6) years. Dryer inspections conducted throughout these operating periods have identified no unusual damage due to flow-induced vibration. Inspection has revealed some dryer tie-bar damage and drain channel cracking. Necessary modifications have been implemented to address these issues. The overall BFN dryer experience is representative of the fleet experience for BWR/4 slant hood dryers operating at stretch and EPU power levels.
The fact that no damage has been observed in dryer components predicted to have stresses exceeding the fatigue stress limit is an indication of conservatism in the BFN SMT-based load definition. This conservatism has been carried forward into the analysis for the stress predictions for EPU operating conditions. Carrying forward load-definition conservatism to EPU conditions assures conservative identification of dryer components that may require reinforcement modification, further analysis, or monitoring to assure that the endurance criteria are met under EPU conditions.
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION
- 2. INTRODUCTION AND BACKGROUND 2.1 Dryer Design Bases and Historical Development The function of the steam dryer is to remove any remaining liquid in the steam exiting from the array of axial flow steam separators. GE BWR steam dryers use commercially available modules of dryer vanes that are enclosed in a GE designed housing to make up the steam dryer assembly. The modules or subassemblies of dryer vanes, called dryer units, are arranged in parallel rows called banks. Six banks are used for the BFN dryers (BWR 4). Dryer banks are attached to an upper support ring, which is supported by four steam dryer support brackets that are welded attachments to the RPV. The steam dryer assembly does not physically connect to the shroud head and steam separator assembly and it has no direct connection with the core support or shroud. A cylindrical skirt attaches to the upper support ring and projects downward forming a water seal around the array of steam separators.
Normal operating water level is approximately at mid-height on the dryer skirt.
Wet steam flows upward from the steam separators into an inlet plenum, horizontally through the dryer vane banks, vertically in an outlet plenum and into the RPV dome.
Steam then exits the reactor pressure vessel (RPV) through steam outlet nozzles.
Moisture (liquid) is separated from the steam by the vane surface and the hooks attached to the vanes. The captured moisture flows downward under the force of gravity to a collection trough that carries the liquid flow to drain pipes and vertical drain channels. The liquid flows by gravity through the vertical drain channels to the lower end of the skirt where the flow exits below normal water level. The outlet of the drain channels is below the water surface in order to prevent reentrainment of the captured liquid.
GE BWR steam dryer technology evolved over many years and several product lines.
In earlier BWRI2 and BWR/3 dryers, the active height of the dryer vanes was set at 48 inches. In BWR/4 steam dryer designs like BFN the active vane height was increased to 72 inches. Perforated plates were included on the inlet and outlet sides of the vane banks of the 72-inch height units in order to distribute the steam flow uniformly through the bank. The addition of perforated plates resulted in a more uniform velocity over the height of the vanes. The performance for BWR/4 and dryer designs was established by testing in steam.
Most of the steam dryer is located in the steam space, with the lower half of the skirt extending below normal water level. These environments are highly oxidizing. All of the BWR/2-6 steam dryers are welded assemblies constructed from Type 304 stainless steel. The Type 304 stainless steel used in BWR/2-6 steam dryers was generally purchased with a maximum carbon content specification of 0.08% (typical 3 Rev. 0
GE-NE- 0000-0053-7413-RO-NP DRF 0000-005 1-5975 NON PROPRIETARY VERSION ASTM standard). Therefore, the weld heat affected zone material is likely to be sensitized during the fabrication process making the steam dryer susceptible to intergranular stress corrosion cracking (IGSCC). Temporary welded attachments may have also been made to the dryer material that could result in unexpected weld sensitized material. Steam dryer parts such as support rings and drain channels were frequently cold formed, also increasing IGSCC susceptibility. Many dryer assembly welds included crevice areas at the weld root, which were not sealed from the reactor environment. Cold formed 304 stainless steel dryer parts were generally not solution annealed after forming and welding. Because of the environment and material conditions, most steam dryers have exhibited IGSCC cracking.
Average steam flow velocities through the dryer vanes at OLTP conditions are relatively modest (2 to 4 feet per second). However, the outer hoods near the steam outlet nozzles are continuously exposed to steam flows in excess of 100 feet per second. These steam velocities have the potential for exciting acoustic resonances in the steam dome and steamlines, provided appropriate conditions exist, resulting in fluctuating pressure loads that act on the dryer.
The dryer is a passive, non-safety related component that was included in Class I seismic analyses. The steam dryer performs no safety functions. The steam dryer assembly is classified as an "internal structure" per ASME Boiler and Pressure Vessel Code,Section III, Subsection NG. Therefore the steam dryer needs only to be analyzed for those faulted load combinations for which loss of structural integrity of the steam dryer could interfere with the required performance of safety class equipment (i.e., generation of loose parts that may interfere with closure of the MSIVs) or affect the core support structure integrity (shroud, top guide, core support and shroud support).
2.2 Browns Ferry Dryer Experience The operating experience for the three Browns Ferry steam dryers has been typical of the overall BWR fleet experience with no unusual indications. The steam dryer inspection data and disposition of the indications for EPU is summarized in Tables 2-1 through 2-3 for each unit.
BFNI has been inactive since 1985 and is currently undergoing recovery and restart activities. BFNI operating experience has been limited to OLTP conditions. Dryer performance has been satisfactory. Limited drain channel weld cracks have been found similar to other BWR plants and will be repaired prior to renewed operations.
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GE-NE- 0000-0053-7413-R0-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION BFN2 and BFN3 were restarted at OLTP in 1992 and 1995, respectively. Both units were subsequently uprated to 105% OLTP in 1998. These dryers have operated satisfactorily at OLTP and 105% OLTP. Earlier drain channel cracking had been repaired and reinforced. Subsequent inspections have shown no recurrence of cracking in the repaired welds. BFN3 has experienced limited tie bar cracking.
These bars have been replaced with a modified design. The drain channel weld reinforcement and the modified tie-bar design will be implemented into the BFN1 dryer and the analysis of the BFNI dryer, as described in this report, has simulated this modified BFNI dryer condition.
Table 2-1: BFNP Unit 1 Steam Dryer Inspection Data and Disposition for EPU Location Year Indication Disposition for EPU Reason for Disposition Drain Apr-92 Indications reported in three Cause: Fatigue (drain Reinforcing the Channel vertical drain channel to skirt channel cracks): welds will reduce fillet welds (Channcl 2 right Installation or removal thc stress.
side approximately 12 in. (bent support bracket) long. Channel 3 Ilft side Welded repairs approximately 10 in. long. recommended for three Channel 4 right side drain channel weld approximately 14 in. long). cracks. It was also In Channel I right side a recommended that all small (less than I in. long) drain channel welds be indication transverse to the mitigated (increase weld. In addition, a broken 1/8" fillet welds size to locking fillet weld and bent 1/4" for at least lower support bracket were 76 inches. Transverse reported in the 184 degree indication on Channel leveling screw. I classified as a scratch.
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GE-NB- 0000-0053-741 3-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Table 2-2: BFNP Unit 2 Steam Dryer Inspection Data and Disposition for EPU Indication Disposition for Reason for EPU Disposition Guide Bracket May-93 Steam dryer lower guide Cause: Contact with Damage unrelated bracket damage at 180 deg guide rod during to fatigue or EPU.
installation.
Underwater welded repair by divers was done at next outage Support Ring Nov-88 Support ring cracks. Cause: IGSCC. None Damage unrelated required to fatigue or EPU.
Drain Nov-88 Cracks were reported in three Cause: Fatigue Reinforcing welds Channel of eight vertical drain channel Weld repair drain will reduce the welds. Cracking was located channel cracks. plus stress.
in throat of vertical drain mitigation of all drain channel to skirt 1/8-in. fillet channel welds welds. Two of the cracks (increase 1/8" fillet were approximately 12 weld size to 1/4" inches long and the third was minimum for at least approximately 24 inches lower 76" of each long. vertical drain channel
_weld).
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-005 1-5975 NON PROPRIETARY VERSION Table 2-3: BFNP Unit 3 Steam Dryer Inspection Data and Disposition for EPU Location Year Indication Disposition for Reason for EPU Disposition Drain Nov-91 Indications were reported in Cause: Fatigue Mitigation welds Channel three of eight vertical drain Underwater weld will reduce the channel to skirt welds (Channel I repair plus mitigation stress.
right side approximately 12 welds applied to all inches long. Channel 2 left side channels (1/8" fillet approximately 12 inches long. size increased to 1/4" Channel 3 right side for at least lower 76 approximately 10 inches long). inches of each Indications were located in throat vertical weld).
of the 1/8-inch fillet welds at the lower end of the welds.
Tie Bar Jun-03 During a mid-cycle outage Cause: Fatigue from Replaced with (Cycle 11). it was reported that an unknown cyclic bigger and all three of the center bank tic loading stronger tie bars.
bars were broken. These I" x 1" Divers removed the Failure of this x 3/16" angle cross section tie broken tic bars and component will bars provide lateral bracing welded three larger not result in a across the top of the center steam section (1.5" x 2.7") situation where dryer banks (banks 3 and 4 of 6 replacement tie bars steam could total banks). In each case. one adjacent to the bypass the dry er end of the tic bar had a fracture original tie bar and require an through the full bar cross section. locations. Outer unplanned plant A linear indication was reported bank hoods and cover shutdown to at the unbroken end of one lie plates were also repair.
bar. Although the bars were inspected and no bent. there was no evidence of indications were plastic deformation at the reported.
fracture surface. No indications were found as a result of visually examining the other 10 tie bars.
Support Mar-04 Number of gouges and contact Cause: Installation or Unrelated to bracket and marks removal EPU interfacing Take precautions dryer seismic during movement of block the dryer Note. Drain channels have cracked during normal operation and may crack at EPU.
Additional weld material will minimize the probability of cracking. Drain channel cracking has never led to an unplanned plant shutdown and can be repaired during an outage.
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GE-NE- 0000-0053-741 3-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION 2.3 Motivation for Additional FIV and Structural Analysis The dryer fatigue cracking experiences at Quad Cities and Dresden demonstrated the need to better understand the nature of the loading and the dynamic structural response of the steam dryers during normal operation. The expense involved with inspection and repair of the dryers for the extended life of the plants provide motivation for more accurately determining the plant-specific loads acting on the dryers and quantifying the stresses in the dryers at EPU conditions.
Based on these needs, this evaluation was initiated to derive plant-specific loads and perform a comprehensive structural assessment for the BFN dryer design to assure that it could operate at EPU conditions. The loads affecting the steam dryer were determined by BFN plant-specific scale model testing, using the same SMT methodology benchmarked to the instrumented QC2 replacement dryer and used as input to a three-dimensional finite element model of the BFN steam dryer. Loads considered in the assessment included steady state pressure, fluctuating, and transient loads, with the primary interest in the steady state fluctuating loads that affect the fatigue life of the dryer. Additionally, ASME Code-based design load combinations for normal, upset and faulted service conditions were evaluated. Detailed finite element analyses using the dryer model, subjected to these design loads, were performned. The analytical results identified the peak stresses and their locations. The results of the analysis also included the analytically determined structural natural frequencies for the different key components and locations in the dryer. This report summarizes the dynamic, stress, and fatigue analyses performed based on the scale model load measurements and provides the basis for developing modifications that will increase stress margins and reduce the likelihood of fatigue cracking at EPU conditions.
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GE-NE- 0000-0053-7413-R0-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION
- 3. Dynamic Analysis Approach 3.1 Dynamic Loading Pressure Time Histories The primary dynamic loads of concern on the dryer are the fluctuating pressure loads during normal operation that may lead to fatigue damage. Scale model testing was performed using the BFN Unit I configuration in order to determine the fluctuating pressure loads. The overall scale model testing methodology is documented in Reference 1.
The BFN-specific testing is documented in Reference 2. Originally it was anticipated that a load definition would be developed based upon a load interpolation algorithm (LIA) that was being developed by GE. It was also anticipated that a load definition would be developed based using acoustic circuit methodology by CDI that has been previously reviewed by the NRC. The load interpolation algorithm is still being developed and validated. Therefore, it was decided to use the CDI Acoustic Circuit Model (ACM) in place of the LIA to develop the structural load definition.
Additional details on the CDI acoustic circuit model are provided in Reference 3.
Pressure measurements were taken from the steamlines in the SMT [Reference 2] and used as input to the ACM. The ACM was then used to predict the pressure loading on the steam dryer. This approach uses the ACM in the same manner as it would be used with in-situation plant data. Because this approach is a departure from the methodology described in References I and 2, a benchmark comparison was performed by CDI in order to demonstrate the validity of the approach. This benchmark is documented in Reference 3 and submitted separately by TVA. The pressure predicted from the scale model testing and CDI acoustic circuit model were applied as time history forcing functions to the structural finite element shell model of the dryer (Figures 3-1 through 3-4).
3.2 Stress Recovery and Evaluation Methodology The entire shell finite element model was divided into components with every element assigned to a component. An ANSYS [Reference 4] macro was written to sweep through each time step on every dryer model component to determine the time and location of the maximum stress intensity. The element stresses at all integration points (4 for quadrilateral and 3 for triangular elements) for the top and bottom element surfaces were surveyed. In addition, membrane stresses were extracted for use in the ASME load combination calculations. ANSYS maximum stress intensity results from this macro are presented in Tables 6-1 and 6-2.
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GE-NE- 0000-0053-74 13-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION
- 4. Material Properties The dryer assembly was manufactured from solution heat-treated Type 304 stainless steel conforming to the requirements of the material and fabrication specifications
[Reference 5]. ASME material properties were used in the ANSYS finite element model [Reference 6]. The applicable properties are shown in Table 4-1.
Table 4-1 Properties of SS304 [Reference 6]
Room temperature } Operating temperature Material Property 700F l 5450 F Sm, Stress Intensity Limit, psi 20000 16900 Sy, Yield strength, psi 30000 18900 Su, Ultimate strength, psi 75000 63400 E, Elastic modulus, psi 28000000 25600000
- 5. Design Criteria 5.1 Fatigue Criteria The fatigue evaluation consists of calculating the alternating stress intensity from flow induced vibration (FIV) loading at all locations in the steam dryer structure and comparing it to the allowable fatigue design threshold stress intensity. The fatigue threshold stress intensity from ASME Code Curve C is 13600 psi. The fatigue design criteria for the dryer is based on Figure 1-9.2.2 of ASME Section III [Reference 7],
which provides the fatigue threshold values for use in the evaluation of stainless steels. ASME Code fatigue Curve C assumes a mean stress equal to the material yield strength. The shell finite element model of the full dryer is not refined enough to predict the full stress concentrations in the welds. Therefore, additional weld factors are applied to the maximum stress intensities obtained from the shell finite element time history analyses at weld locations [Reference 8]. A key component of the fatigue alternating stress calculation at a location is the appropriate value of the stress concentration factor (SCF). The stress intensities with the applied weld factors are then compared to the fatigue criteria given above.
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GE-NE- 0000-0053-7413-R0-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION 5.2 ASME Code Criteria for Load Combinations The ASME Code stress limits used in the evaluation of the BFN dryer are listed in Table 5-1.
Table 5-1 ASME Code Stress Limits [Reference 71 Service level JStress J category Class I Components Stress limits (NB)
Stress Limit, ksi ]
Service levels A & B P, Sm 16.9 Pm+ Pb 1.5Sm 25.35 Service level D Pm Min(.7S, or 2.4 Sm) 40.56 Pm + Pb 1.5(Pm Allowable) 60.84 Legend:
Pm: General primary membrane stress intensity Pb: Pinaiy bending stress intensity S.: ASME Code stress intensity limit Su: Ultimate strength
- 6. Fatigue Analysis Time history analyses were performed using ANSYS Versions 8.1 and 9.0 [Reference 4]. The direct integration time history analysis method was used for all of the cases described in this report. ((
)) To account for dryer frequency uncertainty, the time step sizes were increased by plus 10%/o and minus 10% from the nominal case for the pressure loads. ((
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GE-NE- 00004-053-741 3-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION 6.1 Full Dryer Shell Finite Element Model The three-dimensional shell model of the BFN dryer is shown in Figures 3-1 through 3-4. The model incorporates distributed masses in the vane banks and submerged portion of the skirt. The steam dryer is built primarily of welded plates. ((
1]
The mass used on the skirt to represent the water was determined from a study using a detailed model of the skirt and water. ((
1]
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION 6.2 Dynamic Loads The primary dynamic loads of concern are the steam-flow induced fluctuating pressure loads during normal operation. These are the loads responsible for the fatigue damage experienced at EPU conditions by all four of the Dresden and Quad Cities steam dryers. As described in Section 3.1, BFN plant-specific scale model test loads were used as input to CDI's acoustic circuit model to predict the pressures acting on the dryer [Reference 3]. Figure 3-5 shows the applied load at the time when the pressure amplitude is a maximum for EPU operation.
The loads used in this analysis are based on measurements simulating Original Licensed Thermal Power (OLTP) of 3293 MWt and the EPU power level of 3952 MWt.
6.3 Frequency Content of Loads The frequency content of the BFN SMT loads is shown in Figure 6-1. The loading on the dryer is reasonably symmetric. ((
))
6.4 Modal Analysis Frequency calculations were performed with the dryer supported from the RPV dryer support brackets. The boundary conditions described in Section 6.1 were applied to the dryer finite element model for the modal analysis. The entire dryer was surveyed for the component natural frequencies. However, the focus of the assessment was on the outer dryer surfaces. Calculated component natural frequencies for the skirt are shown in Figures 6-11 and 6-12. ((
))
6.6 Structural Response to Loads Stress time histories for various components are plotted in Figure 6-2. A comparison of the pressure time history and resulting structural response for the outer hood is shown in Figure 6-3. The structural frequency responses for these components are 13 Rev. 0
GE-NE- 0000-0053-741 3-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION shown in Figures 6-4 through 6-8. ((
))
6.6 Stress Results from lime History Analyses Maximum stress intensity results from ANSYS for all components of the dryer are shown in Tables 6-1 and 6-2 (for OLTP and EPU, respectively) for three load cases (each power level evaluated at nominal, +10% and -10% frequency shifts ((
)) and plotted in Figures 6-13 through 6-39. These stresses are listed without the weld and weld undersize factors discussed in Section 6-7. Each component has the case that produced the highest stress intensity highlighted.
))
Design margins for both OLTP and EPU power levels are summarized in Table 6-5 and discussed in Section 6.8.
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Table 6-1 rime History Analysis Results from ANSYS: OLTP I]
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Table 6-2 Time History Analysis Results from ANSYS: EPU
((
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION 6.7 Weld Factors The calculation of fatigue alternating stress intensity using the prescribed stress concentration factors in ASME Code Subsection NG is straightforward when the nominal stress is calculated using the standard strength of material formulas.
However, when a finite element analysis (FEA) approach is used, the available stress component information is more detailed than that which would be obtained from the standard strength-of-materials formulas and requires added guidance for determining a fatigue stress intensity to be used in conjunction with the ASME Code S-N design curve. Reference 8 provides the basis for calculating the appropriate fatigue factors for use in the S-N evaluation to assess the adequacy of these welds based on the FEA results. Figure 6-40 summarizes the Reference 8 criteria. For the case of full penetration welds, the recommended SCF value is 1.4. In this case, the finite element stress is directly multiplied by the appropriate SCF to determine the fatigue stress.
The recommended SCF is 1.8 for a fillet weld when the FEA maximum stress intensity is used. In addition, some of the welds are undersized (weld leg length is less than the plate thickness) and the stresses are further adjusted based on the undersized weld factor shown below:
Undersized weldfactor = throat dimension for full sized weld/ throat dimension for undersized weld Note that the above discussion of stress concentration effects (SCF's, fatigue factors, weld factors) only applies to the fatigue evaluation. SCF, "fatigue factor," and "weld factor" are used interchangeably. For BFN dryer, the weld quality factor used was 1.0.
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GE-NE- 0000-0053-74 13-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Table 6-3 Time History Results with Weld factors: OLTP
((
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Table 6-4 Time History Results with Weld factors: EPU 11
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION 6.8 Fatigue Analysis Results The fatigue analysis results are from a shell finite element model used to assess the acceptability of the steam dryer against the fatigue design criteria. The maximum stresses directly from the ANSYS shell finite element analysis are summarized in Tables 6-1 and 6-2. The stresses with the appropriate weld factors applied are summarized in Tables 6-3 and 64. All nodes and elements in the steam dryer finite element model are included in one of the model components. Stress Intensity results and design margins for each of these dryer model components are presented in Tables 6-5 and 6-6 (for OLTP and EPU, respectively). The outer hood is the limiting component. The components with the lowest design margins are highlighted in the tables.
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Table 6-5 Final Stress Results: Design Margins for OLTP and EPU
((
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- 7. ASME Code Loads The BFN steam dryer was analyzed for the ASME Code load combinations (primary stresses) shown in Table 7-1. The acceptance criteria used for these evaluations are specified in Section 5.2 and are the same as those used for safety related components.
7.1 ASME Code Load Combinations Browns Ferry is not a "New Loads" plant; therefore, annulus pressurization and jet reaction loads are not part of the design and licensing basis for the plant and are not considered in these load combinations. The resulting load combinations for each of the service conditions are summarized in Table 7-1.
The steam dryer structural analyses consider the transient and accident events listed in Browns Ferry UFSAR Tables 14.4-1 and 14.4-2. The transient and accident events that are of particular interest for the evaluation of reactor internal pressure difference (RIPD) loading on vessel internals are events with one or more of the following characteristics: 1)pressurization, 2) depressurization, 3) core coolant flow increase, or 4) moderator temperature decrease. The load combinations for the limiting transient and accident events evaluated are listed in Table 7-1. The turbine stop valve closure transient (Upset I and Upset 2 in Table 7-1) is the limiting transient event for reverse pressure loading on the dryer. The Upset 3 load case bounds the remaining transient events. The Faulted I and Faulted 2 load cases address the main steamline break accident outside containment (the design basis event for the dryer). The Faulted 3 load cases address the remaining loss of coolant accidents Positive reactivity insertion events (e.g., rod withdrawal error, rod drop accident) do not result in a significant change in the reactor system pressure or steam flow rate and, therefore, are not significant with respect to the RIPD loading on the steam dryer.
Each of the load combination cases is briefly discussed below:
Normal: The deadweight, normal differential pressure, and F1V loads are combined for the normal service condition. ((
)) There is a significant pressure variation across the outer vertical hood.
(( 3]
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Upset 1: This load combination represents the acoustic wave portion of the turbine stop valve closure transient (TSV1). ((
)) Deadweight and OBE seismic loads are also included.
Upset 2: This load combination represents the flow impingement portion of the turbine stop valve closure transient (TSV2). ((
I))
Deadweight and OBE seismic loads are also included.
Upset 3: This load combination bounds the other transient events. ((
Deadweight and OBE seismic loads are also included.
Faulted 1: This load combination is for the main steamline break outside containment accident with the reactor at full power. The faulted differential pressure load (DPf) represents the loading due to the two-phase level swell impacting the dryer. The interlock condition value of DPf ((( ))) was used for DPf because the vessel blowdown and level swell are more severe at the interlock condition. ((
)) Deadweight and SSE seismic loads are also included.
Faulted 2: This load combination is for the main steamline break outside containment accident with the reactor at low power/high core flow (interlock) conditions. The faulted differential pressure load (DPf) represents the loading due to the two-phase level swell impacting the dryer. ff
)) Deadweight loads are also included.
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Faulted 3: This load combination is for pipe breaks other than the main steamline break. ((
)) The normal operating differential pressure load (DPn) was conservatively assumed for the differential pressure load. Deadweight and SSE seismic loads are also included.
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Table 7-1 ASME Load Combinations Service Screening Fatigue Condition Load Combination Criteria(Note1) Acceptance Criteria Pm < 1.0 Sm FIVn <13,600 psi Normal DW + DPn + FIVn (Pm + Pb) c 1 5 Note 3 Sm DW + DPn + [ TSVI2 + OBE2 ]l/2 + Pm
- 1.0 Sm FIVn <13,600psi UpsetI F1Vn (Pm + Pb)
- 1.5 Notes2and3 Sm Note 5 Pm
__ Sm Note 5 Pm
- 2.4 Sm Not Applicable Faulted 2 DW + DPf2 (Pm + Pb) s 3.6 Sm Pm
- 1. These criteria are for screening purposes and are not requirements for the dryer components.
- 2. These transient events are of a short duration; therefore, fatigue is not a critical consideration.
- 3. The value of 13,600 psi is based on austenitic stainless steel.
- 4. ((
)), therefore, this load is not explicitly included in the dryer analysis
- 5. Upset Condition stress limits are increased by 10% above the limits shown in this table per NG-3223 (a) and NB-3223 (a)(1) 25 Rev. 0
GE-NE- 0000-0053-74 13-R0-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION 7.2 ASME Code Load Case Stress Results The maximum stresses reported from the ANSYS analysis runs are peak stresses and not general primary membrane or membrane plus bending stresses. In order to determine primary stress, contour plots were obtained for each of the components that do not meet the Code stress limits using the conservative peak stress intensity values.
The stress contour plots were evaluated, and a value of primary stress was determined by eliminating high peak stress areas resulting from discontinuities, badly shaped elements, etc. The primary stress values were then used in the calculation of total stress for the ASME load combination calculations. Tables 7-2 and 7-3 summarize the primary stresses for the OLTP cases for normal, upset, and faulted conditions.
From these results, the locations which do not meet the ASME limits (Table 5-1) using these very conservative maximum stresses are reviewed in more detail to obtain the average stresses required for compliance with the ASME Code stress limits.
Some of the stresses in Tables 7-2 and 7-3 are based on conservative peak stresses, which were not re-evaluated to obtain average stresses because they meet the stress limits. All of the stresses for the OLTP cases meet the ASME Code stress limits.
The ASME Code case evaluations at EPU will be performed with the final modified dryer configuration. For previous EPU dryer analyses, the ASME Code case evaluations have met the stress limits. Based on this experience, it is expected that the BFN dryer will meet the ASME Code stress limits for the modified dryer at EPU conditions.
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Table 7-2 OLTP ASME Results for Normal and Upset Conditions: Average Stresses
((
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Table 7-3 OLTP ASME Results for Faulted Conditions: Average Stresses
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- 8. Proposed Dryer Modifications Several dryer modifications are planned for the BFN I dryer as part of the restart program and Units 2 and 3 prior to extended power operation. These modifications are based on the previous BFN dryer operating experience and in response to the recommendations in SIL 644. The planned modifications are:
- 1. Manway cover weld reinforcement (SIL 644)
- 2. Cover plate weld reinforcement (SIL 644)
- 3. Tie bar replacement (BNF 3 experience)
- 4. Drain channel weld reinforcement (BNF 1, 2, 3 experience)
The stress analysis results show several components with potentially high stresses at EPU conditions. Additional dryer modifications are planned to address these high stress locations in order to increase the structural margin for EPU conditions. The modifications under detailed design analyses are:
- 1. Outer hood reinforcing panel (outer hood face plates and exterior hood plates)
- 2. Cover plate tip reinforcement
- 3. Outer hood top edge reinforcement Conceptual sketches of the proposed modifications are shown in Figure 8-1.
- 9. Conclusions The stress analysis results for OLTP demonstrate that the BFN dryer stresses are generally below the endurance level screening criteria. When conservative stress amplification factors are applied to address local stress intensification, a few dryer components are predicted to be at or near the endurance level.
The Unit 1, 2, and 3 dryers have operated at OLTP for a period of eleven (11) to fifteen (15) years. Additionally the Unit 2 and 3 reactors have operated at 105%
OLTP for over six (6) years. Dryer inspections conducted throughout these operating periods have identified no unusual damage due to flow-induced vibration. Inspection has revealed some dryer tie-bar damage and drain channel cracking. Necessary modifications have been implemented to address these issues. The overall BFN dryer experience is representative of the fleet experience for BXA tRI4 slant hood dryers operating at stretch and EPU power levels.
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GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Consequently, the analytical predictions of stresses exceeding the acceptance criteria for several dryer components are indicative of the conservatism that has been utilized in the BFN load definition. This conservative approach has been carried forward into the analysis for the stress predictions for EPU operating conditions. This approach will assure the conservative identification of components that may require reinforcement modification, further analysis, or monitoring to assure that the endurance criteria are met.
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- 10. References I GENE-0000-0045-9086-0l, "General Electric Boiling Water Reactor Steam Dryer Scale Model Test Based Fluctuating Load Definition Methodology - March 2006 Benchmark Report," March 2006.
- 2. GENE-0000-0052-3661-01, "Test Report # 1 Browns Ferry Nuclear Plant, Unit I Scale Model Test," April 2006.
- 3. C.D.I. Report No. 06-11, "Hydrodynamic Loads on Browns Ferry Unit I Steam Dryer to 200 Hz," April 2006.
- 4. ANSYS Release 8.1 and 9.0, ANSYS Incorporated, 2004.
- 5. Purchase Specification, "Standard Requirements for Steam Dryers" 21A3316 Rev. 1.
- 6. American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section 11, 1989 Edition with no Addenda.
- 7. American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section III, Appendix I, 1989 Edition with no Addenda
- 8. "Recommended Weld Quality and Stress Concentration Factors for use in the Structural Analysis of the Exelon Replacement Steam Dryer", GENE 0000-0034-6079, February 2005.
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Figure 3-1 BFN Steam Dryer Finite Element Model with Boundary Conditions 32 Rev. 0
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Figure 3-2 BFN Steam Dryer Finite Element Model 33 Rev. 0
GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION II Figure 3-3 BFN Steam Dryer Finite Element Model, con't 34 Rev. 0
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Figure 3-4 BFN Steam Dryer Finite Element Model, con't 35 Rev. 0
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Figure 3-5 EPU Applied Pressure Load to BFN Dryer 36 Rev. 0
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Figure 6-1 Frequency Content of Applied Load at EPU (Outer Hoods) 37 Rev. 0
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Figure 6-2 Stress Time Histories for Several Dryer Components at EPU 38 Rev. 0
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Figure 6-3 Outer Hood Pressure VS Stress Time Histories for EPU Nominal Case 39 Rev. 0
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Figure 6-4 Outer Hood FFTs for Nominal and +1-10% Cases at EPU 40 Rev. 0
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Figure 6-5 Inner Hood FFTs for Nominal and +1-10% Cases at EPU 41 Rev. 0
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((
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Figure 6-6 Cover Plate FFTs for Nominal and +/-10% Cases at EPU 42 Rev. 0
GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Figure 6-7 Trough FFT's for Nominal and +1-10% Cases at EPU 43 Rev. 0
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Figure 6-8 Skirt FFTs for Nominal and +1-10% Cases at EPU 44 Rev. 0
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Figure 6-9 Modal Analysis Results: Outer Hoods 45 Rev. 0
GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION Ii 11 Figure 6-10 Modal Analysis Results: Inner Hoods 46 Rev. 0
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Figure 6-11 Modal Analysis Results: Skirt 47 Rev. 0
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Figure 6-12 Modal Analysis Results: Skirt, con't 48 Rev. 0
GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION 11 Figure 6-13 Stress Intensity at EPU: Cover Plate 49 Rev. 0
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Figure 6-14 Stress Intensity at EPU: Manway Cover 50 Rev. 0
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Figure 6-16 Stress Intensity at EPU: Outer Hood 51 Rev. 0
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Figure 6-16 Stress Intensity at EPU: Exterior Hood Plates - Outer Banks 52 Rev. 0
GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION II Figure 6-17 Stress Intensity at EPU: Exterior Vane Bank End Plates - Outer Banks 53 Rev. 0
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Figure 6-18 Stress Intensity at EPU: Hood Top Plates 54 Rev. 0
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Figure 6-19 Stress Intensity at EPU: Vane Bank Top Plates 55 Rev. 0
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Figure 6-20 Stress Intensity at EPU: Hood Stiffeners - Outer 56 Rev. 0
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Figure 6-21 Stress Intensity at EPU: Vane Bank Inner End Plates (2) 57 Rev. 0
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Figure 6-22 Stress Intensity at EPU: Closure Plates - Outer Banks 58 Rev. 0
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Figure 6-23 Stress Intensity at EPU: Inner Hoods 59 Rev. 0
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Figure 6-24 Stress Intensity at EPU: Exterior Hood Plates - Inner Banks 60 Rev. 0
GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION TI Figure 6-25 Stress Intensity at EPU: Exterior Vane Bank End Plates - Inner Banks 61 Rev.0
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Figure 6-26 Stress Intensity at EPU: Hood Stiffeners - Inner (1) 62 Rev. 0
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Figure 6-27 Stress Intensity at EPU: Hood Stiffeners - Inner (2) 63 Rev. 0
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Figure 6-28 Stress Intensity at EPU: Vane Bank Inner End Plates (1) 64 Rev. 0
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Figure 6-29 Stress Intensity at EPU: Vane Bank Inner End Plates (3) 65 Rev. 0
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[l Figure 6-30 Stress Intensity at EPU: Closure Plates - Inner Banks 66 Rev. 0
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Figure 6-31 Stress Intensity at EPU: Steam Dams 67 Rev. 0
GE-NE- 0000-0053-7413-R0-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION 11 Figure 6-32 Stress Intensity at EPU: Steam Dam Gussets 68 Rev. 0
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Figure 6-33 Stress Intensity at EPU: Baffle Plate 69 Rev. 0
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]1 Figure 6-34 Stress Intensity at EPU: Trough 70 Rev. 0
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Figure 6-35 Stress Intensity at EPU: Base Plate 71 Rev.0
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]3 Figure 6-36 Stress Intensity at EPU: Support Ring 72 Rev. 0
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Figure 6-37 Stress Intensity at EPU: Skirt 73 Rev. 0
GE-NE- 0000-0053-7413-RO-NP DRF 0000-0051-5975 NON PROPRIETARY VERSION II Figure 6-38 Stress Intensity at EPU: Drain Pipes 74 Rev. 0
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Figure 6-39 Stress Intensity at EPU: Skirt Bottom Ring 75 Rev. 0
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11 Figure 8-1 Proposed BFN Steam Dryer Modifications 77 Rev. 0