ML20248L332
| ML20248L332 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 03/13/1998 |
| From: | Jeffery Wood CENTERIOR ENERGY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 2521, NUDOCS 9803190356 | |
| Download: ML20248L332 (2) | |
Text
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Daws-Besse Nuclear Pc>wer Station ERM 5501 North State Route 2 m Oak Harbor, Ohio 43449u9760 John K. M 419 249 2300 Vice President - Nuclear pg w 419 321.g337 ,
Docket Number 50-346 '
License Number NPF-3 Serial Number 2521 i
March 13, 1998 '
United States Nuclear Regulatory Commission i Document Control Desk Washington, D. C. 20555-0001
Subject:
Transmittal of a Non-Proprietary Version of B AW-2303, Revision 3, "OTSG Repair Roll Qualification Report" l
i Ladies and Gentlemen:
Toledo Edison submitted a License Amendment application (Letter Serial Number 2512, dated February 26,1998) that proposed an amendment to the Davis-Besse Nuclear Power Station (DBNPS) Unit Number 1, Facility Operating License NPF-3, Appendix A, Technical Specifications. The proposed changes involved a new repair process for the Once-Through Steam Generators (OTSG) called " repair roll." The repair roll process is used for the repair of steam generator tubes with defects within the upper tube sheet. The application additionally proposed a reduction in the primary to secondary steam generator leakage limit from 1 Gallon Per Minute, total primary to secondary leakage (1440 Gallons Per Day) to 150 Gallons Per Day, primary to secondary leakage through the tubes of any one steam generator. These proposed changes involved Technical Specification (TS) 3/4.4.5, Reactor Coolant System - Steam Generators, TS 3/4.4.6.2, Reactor Coolant System - Operational Leakage, and their associated Bases.
In Letter Serial Number 2512, Toledo Edison committed to transmit to the NRC a non-proprietary version of Framatome Technologies Incorporated Topical Report B AW-2303, Revision 3 "OTSG Repair Roll Qualification Report." The non-proprietary version of BAW.
2303 is attached.
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9003190356 980313 PDR P
ADOCK 05000346 PDR fklhllfllll(lfflll
- e L _ _ _ _______
Docket Number 50-346 .
License Number NPF-3
,. Serial Number 2521 l' Page 2 I
Should you have any questions or require additional information, please contact Mr. James L.
I Freels, Manager - Regulatory Affairs, at (419) 321-8466.
- Very truly yours, l
FWK/laj I Attachment cc: A. B. Beach, Regional Administrator, NRC Region III S. J. Campbell, DB-1 NRC Senior Resident Inspector A. G. Hansen, DB-1 NRC/NRR Project Manager ;
i J. R. Williams, Chief of Staff, Ohio Emergency Management Agency, !
State of Ohio (NRC Liaison)
Utility Radiological Safety Board i
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BAW-2303 REV 3 NOVEMBER 1997 OTSG REPAIR ROLL QUALIFICATION REPORT FTl NON-PROPRIETARY l
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FRAMATOME TECHNOLOGIES P.O. BOX 10935
- LYNCHBURG, VA 24506-0935 i COPY NO.
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This document is the non-proprietary version of the proprietary document BAW-2303P-03. In order for this document to meet the non-proprietary criteria, certain blocks of information were withheld. The basis for determining what information to withhold was based on the two criteria listed below. Depending upon the applicable criteria, the criteria code, (c) or (d), represents the withheld information.
l
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(c) - The use of the information by a competitor would decrease his expenditures, in time or resources, in designing, producing or marketing a similar product.
(d) - The information consists of test data or other similar data concerning a process, method or component, the application of which results in a competitive advantage to FTI.
TABLE OF COlm. ifs Page
1.0 INTRODUCTION
...............................1-1 1.1 Background ...............................1-1 '
1.2 Purpose ...............................1-1 2.0 EXECUTIVE
SUMMARY
...............................2-1 3.0 REPAIR ROLL DESCRIPTION ............................ 3-1 3.1 Design ...............................3-1 3.2 Installation ...............................3-1 3.3 Process Verification......................... 3-2 4.0 DESIGN REQUIREMENTS ............................... 4-1 4.1 General ............................... 4-1 4.2 Design and Operational Loading ConditionF.... .4-1 i 5.0 DESIGN VERIFICATION ........... ...................5-1 I 5.1 Calculation of Tube Loads ...................5-1 5.2 Design Verification Testing.................. 5-2 5.2.1 Mockup Preparation and ECT Testing... 5-4 5.2.2 Leak Testing......................... 5-6 5.2.3 Thermal and Fatigue Cycling.......... 5-8 5.2.4 Ultimate Load Test................... 5-8 5.3 Effect of Tube Hole Dilation on Joint ...... 5-10 Strength 5.4 NDE Examination Effects on Final Re-Roll Length.............................. 5-15 5.5 Re-Roll Effect on Axial Tube Load........... 5-16 6.0 EVALUATION OF REPAIR ROLL LIFE ..................... 6-1 6.1 Tube Integrity in Repair Roll................ 6-1 l 6.2 Tubesheet Corrosion Beyond Repair Roll....... 6-1
7.0 CONCLUSION
S .............................7-1
8.0 REFERENCES
...............................8-1 APPENDIX A: ETSS for Bobbin and MRPC Examination........... A-1 of OTSG Tube Rerolls APPENDIX B: Reroll Exclusion Zones ........................B-1 l
FRAMATOME TECHNOLOGIES i BAW.2303 REV 03 i
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.. i TABLE OF CGn2m.niS-CONTINUED LIST OF TABLES ^
TABLE TITLE PAGE 4.1 B&W OTSG (177FA) Performance Characteristics .......... 4-2 4.2 B&W (177FA) Steam Generator Tube Repair .............. 4-3 40 Year Design Loadings 5.1.1 Axial Tube Load Summary ............................... 5-2 5.2.1 Tube Installation Data ................................ 5-4 5.2.2 Tube Installation Torque and Roll Lengths ............. 5-5 5.2.3 - Leak Test Results ................................ 5-7 5.2.4 Fatigue Test Axial Load Cycles ........................ 5-8 5.2.5 Ultimate Load Test Results ............................ 5-9 5.3.1 Tube Hole Dilation Allowables ....................... 5-11 LIST OF FIGURES FIGURE TITLE PAGE 3.1 Tube Repair Roll Sketch ............................... 3-3 5.1 OTSG General Arrangement .............................. 5-3 5.2 OTSG Tube Repair Roll Limitations .................... 5-13 (All plants except Oconee 1,2,3) 5.3 OTSG Tube Repair Roll Limitations ................. .. 5-14 (Oconee Units 1,2,3) l l
I FRAMATOME TECHNOLOGIES il BAW-2303 REV 03 l
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- _ _ _ _ _ _ _ . _ _ _ _ . _ _ _ _ _ . _ _ _ _ _ _ _ . . . . _ _ _ . - _ _ . _ . _ _ _ _ _. _ _ _ _ . _ _ _ _ _ . _ _ _ _ _ . . _ _ _ _ _ _ _ _ _ _ . . . . _ _ _ _ _ ____._.___d
LIST OF ABBREVIATIONS ECT Eddy Current Testing EFPY Effective Full Power Year ETSS Examination Technique Specification Sheet F*' F Star ID Inside Diameter IGA Inter-granular Attack MAI Mult'iple Axial Indications MIC Micrometer NDE Nondestructive Examination OD Outside Diameter OTSG Once-Through Steam Generator PWSCC Primary Water Stress Corrosion Cracking RFO Refueling Outage RPC Rotating Pancake Coil RT Roll Transition SAI Single Axial Indications SCC. Stress Corrosion Cracking 2D Two Dimensional' l
3D Three Dimensional FRAMATOME TECHNOLOGIES ill BAW 2303 REV 03
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1.O INTRODUCTION 1.1 Backcround Eddy current inspection of OTSG tubes has resulted in the detection of indications within the tubesheet region. These indications have been identified as single or multiple axial indications (SAI or MAI) , or volumetric (VOL) indications which require repair or plugging per typical plant technical specifications.
The indications are generally characterized as ID stress corrosion cracks (IDSCC) in the existing tube roll transitions.
The (IGA) intergranular attack volumetric
. indications are believed to be Such indications represent well documented degradation mechanisms in steam generator tubing. IDSCC occurs in susceptible alloy 600 material under the combined action of primary water, elevated temperature, and sustained tensile stresses which exist in the roll transition region of the tubes.
Theisnumber but of tubes expected with indications to increase in time. detected in OTSG's is small If degradation continues then a repair method may either be desirable or necessary to I maximize the number of tubes left in service for continued operation. One such repair method is to perform a tube roll expansion (repair roll) within the tubesheet beyond the existing degraded location.
1.2 Purcose The purpose of this document is to provide a technical justification to implement a tubesheet region repair roll in degraded tubes in OTSG's. A repair roll which is installed beyond the degraded region of tubing provides a frictional joint of undegraded tubing within the tubesheet bore, creating a new primary pressure boundary within the tube. The structural l
l aspects of the repair must be demonstrated in accordance with NRC Regulatory Guide 1.121, by establishing an engagement distance sufficient to withstand the axial tube loadings imposed by. normal operating condition and worst case faulted condition differential pressures and thermal displacements. The repair roll leakage must meet requirements for maintaining plant leakage within technical specification limits.
I FRAMATOME TECHNOLOGIES 11 BAW-2303 REV03
l 2.O EXECUTIVE
SUMMARY
Eddy current inspection of OTSG tubes has revealed tubes with indications at the roll transition within the tubesheet region.
These indications have been characterized as either axial or volumetric defects which may exceed the current plugging limit for the tubes. The axial indications have been predominantly attributed to stress corrosion cracking of the tube roll transitions.
The volumetric indications are believed to be IGA.
A process has been developed to repair these tubes allowing them to remain in service. This tube repair roll process consists of creating a new mechanict.1 tube-to-tubesheet-structural joint below the region of tube defects. This type of repair has been previously qualified by FTI for Westinghouse Model 27 steam generators at Connecticut Yankee and Westinghouse Model 51 steam generators at Point Beach 2, DC Cook, and Indian Point 2.
The qualification of the mechanical joint is based on establishing a mechanical roll length which will carry all of the structural loads imposed on the tubes. A series of tests and analyses were performed to establish this length. Tests that were performed included leak, tensile, fatigue, ultimate load, and eddy current measurement uncertainty. The analyses j evaluated plant operating and faulted loads in addition to '
tubesheet bow effects. Testing and analysis evaluated the tube springback and radial contact stresses due to temperature, pressure, and tubesheet bow.
The repair roll is defined as a (d) long, defect free roll expansion beyond the original roll expansion. The repair roll can be accomplished by one of two processes:
- 1. The double repair roll method.
- 2. The singl'e repair roll method.
These repair methods are shown in Figure 3.1. The double repair roll method consists of two overlapping roll expansions that also overlap the original roll. The first of the double rolls is made (d) inches beyond the original tube roll. The second of the double rolls is made between the first roll and the l original tube roll and overlapping both rolls. For this method, the repair roll length is (d) inches long. The extra (d) inch l
over the minimum (d) required length is used to cover the FRAMATOME TECHNOLOGIES 21 BAW-2303 REV 03 j
. \
uncertainty (d) of determining defect locations in the roll by EC testing methods, and to provide margin against the possibility of existing cracks migrating into the repair roll during the rolling process. -
The single repair roll method consists of one roll positioned approximately (d) inches (or greater) beyond the original j roll. This is the same location as the first roll of the double repair roll method.
The repair roll length is (d) as defined by the physical length of the roller pins used in the expander tool. Therefore, no extra roll length is provided in this method for EC measurement uncertainty. Likewise, no extra roll is needed to cover crack migration from the original roll, since '
the single repair roll does not overlap the original roll.
l The worst case operational leak rates for repairing all 15,531 i tubes in each OTSG (31,062 tubes total) will be less than (d)
GPD, assuming all tubes have-100% through wall defects.
The tubes which require repair are known to be susceptible to stress corrosion cracking. Therefore, the new roll transitions may eventually exhibit defects as the original roll transitions have. However, these defects are axial in nature, and are readily detected by eddy current inspection during normal refueling outage inspections. Similar future repair roll iterations are acceptable.
Based on the FTI qualification performed, as well as the history for similar industry repair rolls, there are no new safety issues associated with a re-roll repair.
FRAMATOME TECHNOLOGIES 2-2 BAW-2303 REV 03
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l 3.0 REPAIR ROLL DESCRIPTION 3.1 Desion The roll joint consists of installing either one roll expansion away from the original roll or two overlapping roll expansions in the region of unexpanded tubing beyond the degraded section within the tubesheet. The first roll is installed beyond the existing roll transition region. A second roll is installed which overlaps the first roll and the original roll. The roll expander used for re-roll qualification has a total roller length of [ (d) ] with an effective length of [ (d) ]
between the tapered ends. The second roll overlaps the effective region of the original roll by [ (d) ] and overlaps the first roll [ (d) ]. Figure 3.1 provides a sketch of the repair roll.
The objective of the two step roll is to achieve a [ (d) ]
minimum effective expansion beyond any defects to satisfy leakage and load capacity requirements. The two step roll conservatively produces a [ (d) ] expansion. A lubricant is used to lubricate the rollers and enhance the quality of the i rolls. The objective of the one step roll is to place the roll away from any existing tube defects.
3.2 Installation The repair roll is typically performed remotely using a manipulator and a DELTA plugging type tool head. A control system is used to position and install the new roll expansion.
The nominal required torque is [ (d) ]( [ (d) ] minimum) using the standard qualified tooling. Spacers between the tool and tubesheet or tube end are used to establish the amount of overlap and the proper roll depth for candidate tube locations.
The following is a summary of the tube repair roll installation process:
The DELTA tool is first calibrated to deliver a roll torque of (d) and to properly measure diameter. The target tubes are roll expanded to the torque setpoint, with torque and diametral expansion recorded onto disk.
FRAMATOME TECHNOLOGIES 3-1 BAW-2303 REV 03
'After [ (d) ] rolls are performed, the tool is removed and a calibration check is performed. The next group of tubes are then rolled.
After tube re-rolls are completed, performed.
post ECT examinatio'n is This ECT examination confirms the proper tubes were expanded, verifies proper diametral expansion, and verifies the new [ (d) ] roll expansion is free of degradation. )
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If any anomalies are noted at any time during the process, a Non- l Conformance Report (NCR) is written for disposition by Engineering.
i 3.3 Process Verification Standard pre-repair roll eddy current techniques are used to identify candidate tube locations for repair and determine where the lowermost defect is located. After repair roll installation, bobbin profilometry or equivalent techniques are used to generate a plot which identifies the new roll expansion length and relationship to the existing defect, and to verify that there are no defects in the required roll length region.
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i FRAMATOME TECHNOLOGIES 3-2 BAW-2303 REV 03
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Figure 3.1: Typical Tube Repair Roll Sketch (c) l FRAMATOME TECHNOLOGIES 3-3 BAW-2303 REV 03
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L 4.0 DESIGN REQUIREMENTS 4.1 General -
, The US NRC Regulatory Guide 1.121 [8.1) prescribes safety l
factors of 3 on normal operating and 1.43 on faulted condition differential pressure, respectively. These factors have been used as the basis for establishing a suitable repair roll length for recirculating steam generator tubes. [
(c)
]
The repair roll shall be of sufficient length such that the expansion alone (without any support from the original tube expansion and tube seal weld) provides the necessary structural strength to satisfy the normal and faulted tube loadings.
In addition, the roll shall provide a mechanical seal between the existing tube and tubesheet. The new joint shall provide leak limiting capability, assuming a full 360* circumferential sever immediately outboard of the new roll region. Leakage must be maintained well below the technical specification limits.
The repair roll becomes the new ASME Code pressure boundary.
The new roll carries the structural loadings and performs the function of isolating the primary water from the secondary water. The degraded tube between the minimum required repair roll length and the tube end can be excluded from future periodic inspection requirements because it is no longer part of the pressure boundary once the repair roll is installed.
I 4.2 Desian and Operational Loadino Conditions j
The design, operational, and accident temperatures and pressures for the Babcock & Wilcox 177 FA OTSG's are provided in Table 4.1. The resulting OTSG tube loads are summarized in Table 4.2.
FRAMATOME TECHNOLOGIES 4-1 BAW-2303 REV03
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TABLE 4.1: B&W OTSG (177FA) PERFORMANCE CHARACTERISTICS PRIMARY SECONDARY DESIGN CONDITIONS SIDE SIDE Design Pressure, psia [ (c) ]
Dssign Temperature, *F I (c) ]
Number of Tubes (DB-1) [ (c) ]
LEVEL A (NORMAL OPERATING) CONDITIONS (100% Full Power)
Pressure, psia [ (c) ]
Temperature, Inlet, 'F(DB-1) [ (c) ]
Temperature, Outlet,'F (DB-1) [ (c) ]
Flow Rate, Ibm /hr per generator (OCO-1,2,3) [ (c) ]
Flow Rate, Ibm /hr per generator (TMI-1) [ (c) ]
Flow Rate, Ibm /hr per generator (DB 1) [ (c) ]
Flow Rate, Ibm /hr per generator (CR-3) [ (c) ]
Flow Rate, Ibm /hr per generator (ANO-1) [ (c) ]
Heat Transferred, BTU /hr per generator (OCO-1,2,3) [ (c) ]
Heat Transferred, BTU /hr per generator (TMI-1) [ (c) ]
Heat Transferred, BTU /hr per generator (DB-1) [ (c) ]
Hsat Transferred, BTU /hr per generator (CR-3) [ (c) ]
Heat Transferred, BTU /hr per generator (ANO-1) [ (c) ]
Typical Full Load Pressure Drop (Max psi) [ (c) ]
LEVEL D (FAULTED) CONDITIONS Main Steam Line Break or Main Feedwater Line Break Maximum Pressure, psia [ (c) ]
(See additional loads in Table 2)
Loss of Coolant Accident Maximum Pressure, psia [ (c) ]
(See additionalloads in Table 2)
FRAMATOME TECHNOLOGIES 4-2 BAW-2303 REV 03
TABLE 4.2:B&W (177FA) STEAM GENERATOR TUBE REPAIR HARDWARE 40 YEAR DESIGN LOADINGS OTSG TUBE OPERATING LOADS LOAD SET TRANSIENT TRANSIENT TUBE NUMBER DESCRIPTION CYCLES LOAD (LBS) or (IN-LBS) 1 HEATUP (c) (c)
(Transients 1 A,18,1C,9 COOLDOWN 11,15,17A,178) 2 0% TO 15% PWR (c) (c)
(Transients 2A,28,14) 15% TO 0% PWR 3 REMAINING (c) (c)
(Transients 3,4,5,6,7,8) TRANSIENTS (c) (c)
Operating Basis Earthquake OBE (NORMAL) 1 (c)
SSE Safe Shutdown Earthquake l
l (FAULTED)
Main Steam Line Break 1 (c)
MSLB (Due to pressure and thermal differentials) l l (Due to Dynamic Tube Loading)
(FAULTED)
F = Force (LBS)
M = Moment (IN-LBS)
FRAMATOME TECHNOLOGIES 4-3 BAW-2303 REVE
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l 5.0 DESIGN VERIFICATION The design verification as described in this section develops the OTSG specific required length for the repair roll, This development begins by evaluating the design and operating conditions for OTSG plants. A summary of the analysis methodology and results is provided. Additionally, a summary of the repair roll testing is provided which supports the analysis in determining the final roll length. The process NDE requirements follow which describe the necessary post-repair roll verification actions and provide a review of previous testing methods and associated uncertainties. The following is a summary of the design verification methodology:
Determine tube loadings during normal and faulted conditions.
Perform design verification testing.
- Prepare rolled tube samples.
Perform leak tests.
Perform thermal and axial load cycling.
Perform final leak tests.
Perform ultimate load tests.
Determine exclusion zones for application of 1" actual reroll length based on tube hole dilation effects.
The effect of the re-roll process on the tube axial load is also evaluated.
5.1 Calculation of Tube Loads All of the critical physical design characteristics and materials of construction are equivalent to the original design and are summarized in Figure 5.1.
The performance characteristics of OTSG's are identified in Table 4.1. The following key factors affect the repair roll length as they [ (c) ]:
o Normal operating primary to secondary differential pressure o Faulted condition primary to secondary differential pressure
[ o Primary inlet and outlet temperatures '
i o Secondary outlet (steam) temperature o 100% Power temperatures of shell/ wrapper, tube, and tubesheet j f
i.
FRAMATOME TECHNOLOGIES 5-1 BAW-2303 REV 03 f
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The pressure and thermal differentials are used in the analysis to !
calculate the loads imposed on the tubes during normal and faulted conditions.
{
The primary inlet, outlet, and steam temperatures factor into the {
analysis by determining the effect on the preload strength as a l result of the expansion differences between the tube and tubesheet. The controlling required doint strength loads (from l Table 4.2) for Level A and Level D conditions are summarized below in Table 5.1.1. {
l Table 5.2.1: Axial Tube Load Summary Axial Average Primary i Tensile Tube Temp Pressure ;
Load (1bs) (*F ) (Dsi) l l
Level A: Cooldown [ (c) ]
Transient Level D: MSLB Accident ANO-1,CR-3,DB-1,TMI-1 [ (c) ]
ONS-1,0NS-2,0NS-3 [ (c) ]
5.2 Design Verification Testing Mechanical tests were performed during the qualification to evaluate various roll lengths at room temperature conditions. The l test data was then corrected by the analysis to obtain the final {
required length, as described in Section 5.4, for operating conditions. Tests performed consisted of leak testing, axial load l cycling, thermal cycling, and ultimate load tests. Normal operation and faulted' conditions were simulated during testing. A total of ( (d) ] were tested. Note that previous similar
! tube repair roll tests had been performed which produced acceptable results. Thus, this allowed focus on the anticipated required torque which minimized the sample size. Note also that test loads were increased per the ASME Code to accommodate the sample size.
FRAMATOME TECHNOLOGIES 5-2 BAW.2303 REV 03
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4
- Figure 5.1 OTSG General Arrangement (C) 4 FRAhiATOME TECHNOLOGIES 5-3 BAW-2303 REV03
- c .
'The tube to tubesheet crevice was clean when the test roll expansions were performed. Tube degradation is currently observed in the upper tubesheet roll transition. There is no evidence of significant crevice deposits in this region, therefore testing was performed without simulating deposits.
5.2.1 Mockup Preparation and ECT Testing The tubes were [ (d) ) nickel-chromium-iron alloy 600, heat 93452. This tubing possessed a yield strength of [ (d)
] and an ultimate strength [ (d) ). The mockup dimensions of tubesheet bore, surface roughness, and measured tube ID are recorded in Table 5.3.1. The tubesheet bore range tested was [
(d) ). This hole size is near the high end of the [ (d)
) range in operating OTSG's.
Table 5.2.1: Tube Installation Data BLOCK TS BORE (c) EXPANDED
-HOLE DIAMETER TUBE ID (INCH) (INCH) 1 ID MIC DELTA i
I (d)
ID MIC: Measured ID using micrometers.
DELTA: Tube ID as indicated by the DELTA installation tool.
The tube samples were roll expanded using a modified [ (c)
) roll expander on the DELTA tool.
The field expansions are performed with an [ (c) ]
expander mounted on the DELTA tool. The expanders used for qualification testing and field application have the same critical l l i I
FRAMATOME TECHNOLOGIES 5-4 BAW-2303 REV 03
, 1 dimensions. These expanders produce [ (c)
}. Both the qualification tool and the field tool are torque controlled. The primary difference between the qualification expander and the field tool is the length of the 1 expander cage. The qualification expander was modified in length to allow proper axial positioning in the test block.
The tube rolling maximum delivered torques and roll lengths are provided in Table 5.2.2. Roll lengths are shown for both physical measurements and eddy current test inspection measured values.
The tube rolling maximum delivered torques and roll lengths are '
provided in Table 5.3.2. Roll lengths are shown for both physical measurements and eddy current test inspection measured values. )
Table 5.2.2: Tube Installation Torque and Roll Lengths BLOCK ROLL CALC'D ECT ROLL ECT ERROR
-HOLE TORQUE ROLL LENGTH (INCH) (INCH) i ;
(IN-LBS) LENGTH RPC Bobbin RPC Bobbin (INCH) (d) kHz (d) kHz (d) kHz (d) kHz (d) (d) (d) (d) (d) (d) (d) l AVG. (d) (d) o l
FRAMATOME TECHNOLOGIES 5-5 BAW-2303 REV 03
(
r i l
i The roll length of (d) was measured following the ultimate load test by pulling the tube from the tubesheet. l l
The acquisition and analysis was performed in accordance. with 1 Examination Technique Specification Sheets in Appendix A. ( (c)
]ECT testing was acquired with [ (c) ]
probe. The [ (c) ] ECT testing was acquired with ( (c)
] probe. Refer to Appendix A for details on these probes.
Each sample was acquired (d) for both techniques, except for sample (c), which has only ( (c) ).
Tube expansion is a torque controlled process. To conservatively account for the torque required to expand the tube into contact with the tubesheet bore, a high yield strength tube was used.
Since less torque is required to expand lower yield strength tubing, tests performed using the high yield tubing are more conservative than tests performed with the low yield tubing.
The average error for the eddy current roll length is (d) inch at (d) kHz for a RPC probe with a standard deviation of (d) .
The average error was (d) inch at (d) kHz with a bobbin probe with a standard deviation of (d) .
5.2.2 Leak Testing Room temperature hydrostatic pressure tests were performed at (d) psi on the mockup samples. This value exceeds both 3 x normal operating pressure and 1.43 x MSLB pressure. The purpose of this test is to look for gross leakage or structural failure of the joints. No mechanical change er gross leakage in the samples were noted. Only one sample, ( (d) ].
The hydrostatic test was repeated after thermal and load cycles of the samples. Again, no mechanical change was noted in the joints.
There was no visible leakage in any sample during the second {
hydrostatic test. I Room temperature leak tests were performed on the samples at (d) psi. This was done both before and after thermal / load cycling was applied to the samples. Note that room temperature leak tests are conservative since higher temperatures increase the joint tightness due to thermal expansion differences between I600 tube and carbon steel tubesheet. The results of the leak tests are presented in Table 5.2.3. (
i FRAMATOME TECHNOLOGIES 5-6 BAW-2303 REV 03 I
1
'The leak testing at (d)' resulted in an average leak rate of
.[ (d) ] before-load testing. The final leak testing at [ (d)
] after thermal cycles and axial load cycles (cyclic tests discussed in 5.2.3). The average of initial and final leak rates [- (d) ]
Table 5.2.3: Leak Test Results BLOCK INITIAL FINAL. INITIAL FINAL
-HOLE PRESSURE PRESSURE LEAK LEAK DROP FROM DROP FROM RATE AT RATE AT .
(d) (d) (d) (d) ,
(IN'/HR) (IN'/HR)
(d) (d) (d) (d) (d)
AVG. (d) (d)
If all 15,531 tubes in each upper head of the two OTSG's are repaired by tube reroll, the worst case normal operational leakage is (d) .
This value is conservative due to:
It assumes all tubes have 100% through wall defects. l Operating differential pressure of (d) psi compared to the )
test pressure of (d) psi.
The tubes tested were severed 360 degrees.
- The average tested roll length was (d) inch compared to a nominal reroll length of (d) inches. J i
An estimation of leakage at MSLB differential pressure ( (d)
, psi) is based on increasing the leak rate by the square of the l
pressure ratio, or [ (d) ). This results in a (d) higher l- - leak rai. . Therefore, the worst case MSLB leak rate at (d) psi is estimated to be (d) GPD for 15,531 tube ends per OTSG (31,062 total tube ends). This value is conservative for the same reasons mentioned above.
FRAMATOME TECHNOLOGIES 5-7 BAW-2303 REV 03
d.
5.2.3 Thermal and Fatigue Cycling The two mockup blocks were cycled 4
(
(d)
]
These thermal cycles were performed to. allow for any relaxation in. the tube to tubesheet joint due to differential thermal expansion of the Inconel and carbon steel.
t
')
Axial load cycling was performed to simulate the applied loads )
imposed on the OTSG tubes due to ( '
(d)
J' These loadings are based on normal operating i transients ' expected to occur over a 40 year design life of the OTSG's from Table 4.2.
The loadings from Table 4.2 are adjusted by increasing the
-number of cycles for the - first and second load sets and by increasing the applied force for the third load set. These adjustments are based on a quantity of (d) samples to conservatively envelope the testing of (d) samples. Table 5.2.4 summarizes the load sets for loading range and cycles developed from Table 4.2 data. No tube motions were observed during this test, thus all samples successfully passed. .l Table 5.2.4 Fatigue Test Axial-Load Cycles LOAD AXIAL TEST NUMBER OF SET LOADING RANGE CYCLES (LBS) 1 (d) (d) 2 (d) (d) 3 (d) (d) l 5.2.4 Ultimate Load Test An ultimate load test was performed to- axially load the tube joints until failure. This test was performed with ID gripper j fingers inside the tube pulled by a hydraulic jack using a manual pump. In each case the applied [ (d) ;
l FRAMATOME TECHNOLOGIES 5-8 BAW-2303 REV03
l I
]
The locids are summarized in Table 5.2.5. Tube movement was monitored by a dial indicator mounted on the mockup block and reacting off the mandrel of the ID gripper. (
(d)
] The final pullout loads were used to establish the required roll length in Section 5.3.
Table 5.2.5: Ultimate Load Test Results j BLOCK ROLL ROLL MAXIMUM MAXIMUM LOAD
-HOLE TORQUE LENGTH PULL LOAD CUMULATIVE (IN-LBS) (INCH) (LBS) TUBE MOVEMENT (INCH)
(d) (d) (d) (d) (d)
[
(d)
]
[
(d) ]
FRAMATOME TECHNOLOGIES 59 BAW-2303 REV 03
t
[
(d)
]
Applying a one-sided 95 percent tolerance limit factor of (d) l (reference 8.4) to the standard deviation of (d) results in a minimum joint load capacity of (d) .
This value exceeds the minimum required strength of (d) for an Oconee MSLB condition. Thus, all samples were acceptable. A (d) length will be conservatively assumed to correspond to this load of (d) .
This load will be used to determine the maximum tube hole dilation allowed due to tubesheet bow.
5.3 Effect of Tube Hole Dilation on Joint Strength The load testing summarized in Section 5.2 was performed in tubesheet mockups with as-fabricated bore diameters. In an operating OTSG, the tubesheet bore diameter can change during certain operating conditions due to the combined effects of primary to secondary pressure differential and thermal loads.
These loads cause the tubesheet to bow in one direction or the other, depending on the particular condition being evaluated. The bowing of the tubesheet will in turn cause the diameter of the tubesheet bore to increase or decrease, depending on its location.
The change in diameter is a maximum at the face of the tubesheet, ,
and decreases to zero at the neutral axis. An increase in l diameter will decrease the contact stress between the roll joint and the tubesheet, which reduces the pullout strength.
This effect on the strength of the re-rolled joint was evaluated analytically, and an exclusion zone was defined to ensure that the re-rolled joint is installed only in locations where the effects of tubesheet bow do not reduce the joint strength below what is required to sustain all required loads.
The largest amount of tubesheet bow is predicted to occur during a MSLB event, where the maximum primary to secondary pressure differential occurs in conjunction with the largest predicted tube tensile loads. Both tubesheets will bow inward (towards the i
secondary side) as a result of these loads. The tubesheet bore hole diameter on the primary side will increase near the periphery
! (where the tubesheet is in tension from the bow effect) and decrease near the center (where the tubesheet is in compression) .
FRAMATOME TECHNOLOGIES 5 10 BAW-2303 REV 03
i 4
l 1 On the secondary side the effect is reversed, i.e., the bore hole diameter will decrease on the periphery and increase in the !
l center.
l The initial preload of the re-rolled joint was estimated from measurements of tube diametral springback. Testing was performed by installing a re-rolled joint into a split tubesheet block, measuring the diameter at the joint location, and then removing the tubesheet block. The diameter of the tube in the joint region expands after removal of the block. The difference between the as-installed diameter and the " relaxed" diameter is the spring back, and is a representation of contact stress. (d) test samples were evaluated, resulting in an average spring back of (d) .
The room temperature radial (contact) stress was calculated from these results to be (d) psi.
The minimum axial load capacity for a (d) rolled joint at room temperature conditions was, determined in Section 5.2.4 to be (d) lbs. The required strength of the joint for worst case normal operating and accident conditions are given in Table 5.3.1. Two bounding conditions were considered as discussed above, including l a normal operating cooldown transient and a MSLB. Two different !
load cases for the MSLB transient were evaluated, the first being l a bounding case for the non-Oconee plants, and the second being {
applicable for Oconee-1, 2, and 3. A finite element analysis was performed to determine the amount of tubesheet bow for each case, as well as the resulting hole dilation as a function of tube position and location within the tubesheet thickness. I For each of the three cases evaluated, an allowable tubesheet bore hole dilation was calculated such that the joint strength remained adequate to sustain the axial loads defined in Table 5.3.1. These calculations were based on the minimum joint strength of (d) lbs determined in Section 5.2.4, and the installed contact stress determined in the spring back testing discussed above.
Table 5.3.1: Tube Hole Dilation Allowables F,o F ,a F,,a,oco Max Tube Load (lbs) (d) (d) (d)
Roll Length Maximum Allowable Tube Hole Dilation (inch)
(d) (d) l (d) l (d) l FRAMATOME TECHNOLOGIES S 11 BAW-2303 REV 03
The calculated tube hole dilations due to thermal and pressure differentials were compared to the allowable dilations. The maximum tube hole dilations occur in the periphery of the tubesheet for rolls near the tube end for both upper and lower tubesheet. Maximum tube hole dilations occur near the center of the tubesheet at the secondary faces of the tubesheets. The application of a (d) roll expansion is limited to those portions of the tubesheet where the calculated dilation is less than the allowables.
Application of a longer reroll length (greater than (d) ) can be applied on a case by case analytical basis. In particular, if the roll length is increased from [ (d) ], then the roll may extend to (d) from the primary face for non-Oconee OTSG's. A roll length of (d) is used for the determination of exclusion zones presented in Figures 5.2 and 5.3.
Figure 5.2 graphically summarizes the tube reroll exclusion zones for all OTSG plants except Oconee 1, 2, and 3. Figure 5.3 graphically summarizes the tube reroll exclusion zones for OTSG's at Oconee 1, 2, and 3. Zones 3, 5, 8, and 11 are based on maintaining any roll transition (d) from the secondary face.
This (d) conservatively allows the tube to remain engaged in the tube hole in the unlikely event of a tube severance at the new roll transition. The exclusion zones are described in detail in Appendix B and the tubes in each zone are tabulated in Tables B.1 through B.6.
It should also be noted that so long as the structural margin is satisfied outside the exclusion regions, then any roll extending into those regions is conservative and will tend to strengthen the joint and improve leakage performance.
FRAMATOME TECHNOLOGIES 5-12 BAW-2303 REV 03 i
a FIGURE 5.2: OTSG TUBE REPAIR ROLL LIMITATIONS (All plants except Oconee 1,2,3)
I .
(d) i i
FRAMATOME TECHNOLOGIES 5 13 BAW-2303 REV03 j
FIGURE 5.3: OTSG TUBE REPAIR ROLL LIMITATIONS (Oconee Units 1,2,3)
I )
i f
(d) 1 1
l 1
FRAMATOME TECHNOLOGIES 5 14 BAW-2303 REV 03
~
'n 5.4 Non-Destructive Examination Ef fects on Final Re-roll Lencrth i
l A mimimum actual roll length of (d) is used to determine the areas that a repair roll can be performed. However, this length does not include ECT measurement uncertainty. Thus, the final acceptable re-roll length shall include an allowance for the uncertainty associated with the ECT measurement technique used to evaluate the installed roll.
The final roll length acceptance criteria .that is developed for OTSG's must be evaluated using standard steam generator eddy
- current techniques. Post-repair roll bobbin profiles are required l to verify expansion, show the new roll transition (s) , and provide measurements of the undegraded roll beyond the defect. j Measurement tolerances associated with remote eddy current measurements must be factored into the final value. Bobbin and RPC eddy current methods were both used to verify the accuracy and uncertainty in determining reroll lengths in 5/8" tubing. This testing was performed to determine the error associated with the NDE method that will be used in the steam generator to define the actual locations of the defect and the roll transition.
ECT analysis of rotating pancake coil (RPC) and bobbin coil data was performed to determine the distance from the bottom end of the roll transition to the simulated sever. Each eddy - current pull was analyzed (d) .
A total of [
(d) 1 The ECT errors were predominantly conservative, that is ECT underestimated the roll length. As a conservative practice, since i .
(d) I
] The factor for a 95% one-sided tolerance limit based on (d) samples (bobbin) is (d), reference 8.4. The additional roll length due to ECT uncertainty will be based on the error of ( (d)
) for bobbin and the factor of (d) times the standard deviation of ( (d) ] Therefore, the final length will be based on the necessary length for applied loads, L,,o =( (d) ), plus (d) times ;
the standard deviation of ECT error, plus the average error:
FRAMATOME TECHNOLOGIES 5-15 BAW-2303 REV03
~
i
~
L . L. + (d) *
[ (d) ]
l
+ ([ (d) ])
L= f(d) 1 i (Minimum Required Final Re-roll Length) -
5.5 Reroll Effect on Axial Tube Load Since.the will induce OTSG tubes ' are fixed on. each end, the re-roll process an axial load- into the tubes. This load was determined roll process.
by measuring how much the tube elongates due to the re-The expected elongation from the two step re-roll process is (d) inch.
This. elongation produces a compressive axial load of approximately (d) lbs and a stress of (d) psi'in the tube.
accidentThis ' axial stress would act to reduce che operating and tube loads. However, the benefit from conservatively neglected. this was 3
f I
i I FRAMATOME TECHNOLOGIES 5-16 BAW-2303 REV 03
6.0 EVALUATION OF REPAIR ROLL LIFE 6.1 Tube Integrity in Repair Roll .
The significant tube - degradation mechanisms 'in OTSG tubesheets have' been characterized as ID PWSCC and OD IGA. These degradation with mechanisms in:the elevated stress regions associated-a roll transition can potentially limit the life of the repair roll.
Non-destructive ' eddy current. examinations, examinations of pulled tube samples, and acceleratedlaboratory. corrosion tests have all shown that PWSCC will occur in the roll transitions of alloy 600 tubing. Laboratory tests indicate that tensile stresses accelerate the rate of SCC and. moderately affect the rate of IGA. The operating temperature can also affect the corrosion rate in the roll- transitions. For example, intergranular corrosion tends to occur mainly in the elevated temperature r egion of the hot leg versus the cold leg. The presence of the high stress area in the new roll transition,
'along that with high hot leg temperature ((d) max. at DB-1) indicates the new roll transition will be susceptible to IDSCC as is the existing roll transtion.
The main difference between the original roll transition and the transition created by the repair roll is the full vessel stress relief performed during manufacture. Since the repair roll
-stresses may be higher than those in the steam generator af ter manufacture, the time to cracking for the .new transition is expected to be~less than the time for the original transition.
Whether the re-roll transitions last as long as the original tube roll transitions or not is uncertain. The re-rolls are expected
.to last a . minimum of a few . cycles before SCC occurs. Also, standard ECT inspection during normal refueling outage-activities j has proven successful in detecting these defects in the early ,i stages of progression to facilitate future repair or plugging. ;
6.2 Tubesheet Corrosion Beyond Repair Roll !I The tubesheet material is expected to be unaffected by corrosion ;
af ter installing a re-roll, even if defects currently exist in the original roll transition. {
The lack of concern for tubesheet l
FRAMATOME TECHNOLOGIES 61 BAW-2303P REV 03
- i. ?e l I
I corrosion is based on the restricted flow area for primary water to interact with the tubesheet and the lack of oxygen in the primary system during normal operating conditions.
The existing roll transition defects represent the only flow path that could initiate tubesheet corrosion. If the double repair roll method is used, these defects are expanded during the ' repair roll because.the repair roll overlaps the original tube roll.
The roll expansion will result in a tight contact between the. tube and the tubesheet in the defective portion of the original roll.
This tight contact will prevent primary water from flowing through the tube wall and past the tubesheet material.
If the single repair roll method is used, the defects will be unaffected by the repair roll. However, the flow path through these defects is not sufficient to initiate corrosion or transport any corrosion products in an oxygen free environment.
For . either repair method, the _ fluid flow between the tube and tubesheet 'is restricted by the repair roll. Therefore, crevice corrosion is not expected to affect the life of the repair roll.
FRAMATOME TECHNOLOGIES 6-2 BAW-2303P REV 03
7.0 ' CONCLUSIONS l
This repair evaluation has shown that application of a tubesheet region roll at OTSG plants is acceptable.
conclusions are provided. The foll'owing
- 1. \
A roll length of (d) is structurally adequate to satisfy all l j
of the loading requirements for the NRC Regulatory Guide (
1.121 and the leakage limits applicable to the OTSG plants technical specifications. This does not uncertainty include ECT of (d) for rolls which overlap ECT q
indications. {
2.
The qualification is valid for locating the roll expansion in the OTSG's with the exception of the exclusion zones identified in Appendix B.
- 3. If 15,531 tube ends per generator were repaired, conservative worst case leakage would be approximately (d)the GPD under normal operating conditions.
4.
A summary of the recommended design parameters for a field implemented repair roll joint is as follows:
(d) separated from existing defects and roll transitions, providing (d) of new effective roll, or (d) providing up to (d) of new ef fective roll, (d) inch minimum. The second repair roll will include a (d) overlap of the original roll to account for tolerances or defect length variations.
- (d) in-lbs nominal installation torque ((d) minimum)
Installation depth no closer than (d) from the secondary tubesheet face.
5.
The re-roll is applicable to repairing axial, volumetric, or circumferential defects. Testing was performed under the conservative assumption that the tube is severed.
l FRAMATOME TECHNOLOGIES 7-1 BAW-2303 REV 03 f
o .
8.0 ' REFERENCES 8.1 NRC Regulatory Guide 1.12.1 (Draft), " Bases for Plugging Degraded PWR' Steam Generator Tubes". ~
8.2 ASME Boiler and Pressure Vessel Code,.Section III, Subsection NB
.and Division I Appendices, 1989 Edition.
8.3 EPRI TR-103824, Steam Generator Reference Book, December 1994.
8.4 Natrella, Mary Gibbons, " Experimental Statistics", National Bureau of Standards, Handbook 91, page T-15.
i FRAMATOME TECHNOLOGIES 8-1 '
BAW-2303 REV 03
- s -
t . .
's APPENDIX A:
RTSS for Bobbin and MRPC Examination of OTSG Tube Rerolls I
(d) 1 l
FRAMATOME TECHNOLOGIES A-1
\ BAW-2303 REV 03
14
- l e . .
APPENDIX B: Raroll Exclusion Zones d Exclusion Zone Summary for Non-Oconee Plants (See Figure 5.2) -
[
(d) 1 i Exclusion Zone Summarv for Oconee Plants t (See Figure 5.3) l
[
(d)
)
]
Tables B.1 through B.6 summarize the tubes in the exclusion zones where a (d) reroll application is limited by tube hole dilation effects on joint strength.
I (d) 1
. 1 FRAMATOME TECHNOLOGIES B-1 BAW-2303 REV03