ML18065B186
| ML18065B186 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 03/17/1998 |
| From: | Haskell N CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-97-05, GL-97-5, NUDOCS 9803260049 | |
| Download: ML18065B186 (12) | |
Text
A CMS Energy Company March 17, 1998 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Palisades Nuclear Plant 27780 Blue Star Memorial Highway Covert, Ml 49043 DOCKET 50-255 - LICENSE DPR PALISADES PLANT Tel: 616 764 2276 Fax: 616 764 2490 Nathan L. Haskell Director. Licensing 90-DAY RESPONSE TO GENERIC LETTER 97-05, "STEAM GENERATOR TUBE INSPECTION TECHNIQUES" Generic Letter (GL) 97-05, "Steam Generator Tube Inspection Techniques,!'iss.ued:
December 17, 1997, requests that licensees provide certain information for their
. facilities. This information concerns the practices for leaving steam generator,tubes*in service based on sizing and the nondestructive examinations methods arid acceptance criteria being used.
The attachment to this letter provides the requested information.
SUMMARY
OF COMMITMENTS This letter contains no new commitments and no revisions to existing commitments..
-~~
athan L. Haskell irector, Licen*sing **--
CC Administrator, Region Ill, USNRC Project Manager, NRR, USNRC NRG Resident Inspector - Palisades Attachment
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y CONSUMERS ENERGY COMPANY To the best of my knowledge, the contents of this response providing requested information per Generic Letter 97-05, are truthful and complete.
By
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Sworn and subscribed to before me this ) 1 day of ~
1998.
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Alora M. Davis, Notary Public Berrien County, Michigan (Acting in Van Buren County, Michigan)
My commission expires August 26, 1999
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v ATTACHMENT CONSUMERS ENERGY COMPANY PALISADES PLANT DOCKET 50-255 90-DAY RESPONSE TO GENERIC LETTER 97-05 "STEAM GENERA TOR TUBE INSPECTION TECHNIQUES" 9 Pages
90-DAY RESPONSE TO GENERIC LETTER 97-05 "STEAM GENERA TOR TUBE INSPECTION TECHNIQUES" INTRODUCTION Generic Letter (GL) 97-05, "Steam Generator Tube Inspection Techniques," was issued to licensees to (1) emphasize the importance of performing steam generator tube inspections using qualified techniques in accordance with the requirements of Appendix B to 10 CFR Part 50, and (2) require certain information to determine compliance with the current licensing basis for steam generator tube inservice inspections practices.
Following is the information requested for the 90-day response to GL 97-05:
NRC REQUESTED INFORMATION. ITEM 1 Within 90 days of the date of this generic letter, addressees are required to submit a written response that includes the following information:
(1) whether it is their practice to leave steam generator tubes with indications in service based on sizing CONSUMERS ENERGY COMPANY RESPONSE. ITEM 1 Palisades has a practice of leaving steam generator tubes with indications in service. This decision is based on sizing technique qualifications performed in accordance with the Electric Research Power Institute (EPRI) document TR-107569-V1R5, "PWR Steam Generator Examination Guidelines, Revisions 3-5, Volume 1 ", (as found in EPRI Research Project S530-10). It is also based on previous sizing qualifications and equivalencies performed by both Consumers Energy and Westinghouse.
The plant steam generators are Combustion Engineering (CE) Model 2530 with lnconel 600 tube material. Palisades leaves steam generator tube indications in service only if the indications are sized by a qualified technique at less than the Technical Specification plugging limit value of 40% of the nominal tube wall thickness. Other than two tubes with indications that will be characterized in the 1998 refueling outage, the indications left in service are due to wear at the vertical straps and diagonal bars.
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90-DAY RESPONSE TO GENERIC LETTER 97-05 "STEAM GENERA TOR TUBE INSPECTION TECHNIQUES" NRC REQUESTED INFORMATION. ITEM 2 Within 90 days of the date of this generic letter, addressees are required to submit a written response that includes the following information:
(2)
If the response to item (1) is affirmative, those licensees should submit a written report that includes, for each type of indication, a description of the associated nondestructive examination method being used and the technical basis for the acceptability of the technique used.
CONSUMERS ENERGY COMPANY RESPONSE. ITEM 2 Palisades uses the requirements of the American Society of Mechanical Engineers (ASME)
Code, Sections V and XI, 1989 Edition, for the conduct of the steam generator tube examinations. NRC Regulatory Guide 1.83, "lnservice Inspection of Pressurized Water Reactor Steam Generator Tubes" is used as the basis for sizing techniques. EPRI Steam Generator Examination Guidelines: Revisions 3 through 5, Appendix H, "Qualification Data Sets" and qualifications completed by Consumers Energy provide support for sizing degradation specific mechanisms.
Within Table 1, "Palisades Steam Generator Possible Degradation Mechanisms," is a list of degradation mechanisms (indications) by examination type and location, the authorized probe (representing the examination method used), the Palisades qualified eddy current Acquisition Technique Sheets (ACTS), the EPRI qualified technique, and detection/sizing criteria. The technical bases for the examination methods used is summarized later in this response.
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90-DA Y RESPONSE TO GENERIC LETTER 97-05 "STEAM GENERATOR TUBE INSPECTION TECHNIQUES" Table 1: Palisades Steam Generator Possible Degradation Mechanisms Degradation Authorized Palisades EPRI Detection/
Mechanism I Probe ACTS Qualified Sizing Exam Type Number Techniques Wear At Anti-EC610LLMC PAL-01,02 ETSS#96004 Yes/Yes Vibration Bars, EC590LLMC Vertical Straps &
Flow Baffles I Bobbin Coil General Pitting I EC610LLMC PAL-01,02 ETSS#96005 Yes/Yes Bobbin Coil EC590 LLMC IGA/ODSCC Within EC610LLMC PAL-01,02 ETSS#96007 Yes/No The Free Span I EC590LLMC Bobbin Coil ODSCC Tubesheet
+ PT610-115-36-SBO PAL-03 ETSS#96404 Yes/No Expansion For ETSS#96904 Yes/No Dented & Nondented Support Plates I Plus Point Rotating Pancake Coil PWSCC Tubesheet
+PT610-115-36-SBO PAL-03 ETSS#96510 Yes/No Expansion For ETSS#96902 Yes/No Dented & Nondented Support Plates I Plus Point Rotating Pancake Coil PWSCC Within The M+PT-580-MRPC-FH PAL-04 ETSS#96511 Yes/No Short Radius B-580-MRPC/FH-52PH PAL-05 U Bends I Plus Point Rotating Pancake Coil
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90-DAY RESPONSE TO GENERIC LETTER 97-05 "STEAM GENERATOR TUBE INSPECTION TECHNIQUES" Palisades Acquisition Technique Sheets (ACTS) and Analysis Technique Sheets (ANTS) list all of the acquisition and analysis parameters to be used for the eddy current inspection. The following listing references the Palisades ACTS and ANTS numbers to be used for these probe types:
- 1.
Bobbin Probe - ACTS PAL-01-198 and PAL-02-198, ANTS PAL-A-198.
- 2.
3 Coil Plus Point Rotating Pancake Coil (RPC) (with 0.115" pancake and 0.080" HF pancake) -ACTS PAL-03-198, ANTS PAL-B-198.
- 3.
U Bend Single Mag-Bias Plus Point -ACTS PAL-04-198, ANTS PAL-C-198.
- 4.
U Bend Single 0.110" Pancake Coil -ACTS PAL-05-198, ANTS PAL-D-198.
Note: Other probes with corresponding ANTS and ACTS may be added as necessary with approval from the Palisades ECT Level Ill Analyst.
At Palisades, the following sizing techniques are used during steam generator inspections to determine the acceptable steam generator tube indication size for continuing service:
- 1.
Wear For wear at the anti-vibration bars, vertical and diagonal straps and flow baffles, sizing is accomplished using the 550/150 differential mix and 300/150 absolute mix of the bobbin probe. A calibration curve for amplitude vertical maximum is determined based on the applicable standards replicating the mechanism type and quantity. The calibration uses a three (3) point curve of 0%, 30% and 50% wear scars. To date, all wear scar indications have been reported within this range.
This EPRI sizing qualification is based on 64 sample data points. The sample indications ranged in depth from 4% to 78% through-wall depth.
Three tubes have been plugged at Palisades for wear indication. R 137 C94 was plugged during the 1993 refueling outage. This tube had an external wear scar measured at 41 % using bobbin coil on the lower edge of the diagonal bar cold side.
Tubes R128 C105 and R116 C125 were plugged due to volumetric indications resultingfrom loose part wear at the top of the tube sheet transition. Tube R128 C105 also had a stabilizer installed as a result or wear detected by eddy current examination.
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90-DA Y RESPONSE TO GENERIC LETTER 97-05 "STEAM GENERA TOR TUBE INSPECTION TECHNIQUES"
- 2.
lntergranular Attack/Outside Diameter Stress Corrosion Cracking (IGA/ODSCC)
When detected using the Plus Point RPC probe, Palisades plugs this tube degradation indication type and does not size.
Palisades has two tubes with indications found by the bobbin coil probe at the eggcrate support plates which may or may not be this type of degradation. The two tubes are R?O C53 in Steam Generator E-50A with an 8% indication at the third support cold leg and R135 C66 in Steam Generator E-50B with a 17% indication at the eighth support cold leg. These tubes are scheduled to be eddy current tested by Plus Point RPC during the upcoming 1998 refueling outage to better characterize the condition of the tube. No other possible degradation of this type has been reported.
The two indications were sized based on previous qualifications performed by Consumers Energy. These tubes were not rotating pancake coil (RPC) tested.
These two tubes were reported in the 1995 refueling outage and showed no significant change in the 1996 refueling outage. Although an EPRI sizing qualification does exist for the bobbin probe for ODSCC eggcrate support, Palisades will not size these indications with the bobbin probe in the future, due to Root Mean Square Error (RMSE) uncertainty. These indications detected with the bobbin probe will be reported and subsequently RPC tested for confirmation.
- 3.
Primary Water Side Stress Corrosion Cracking (PWSCC)
Palisades plugs this tube degradation indication type on Plus Point RPC detection and does not size.
Palisades has had two axial indications in Tubes R34 C51 at the top of the tube sheet and R1 C54 in the U bend region. Both axial indications appeared to be inner diameter (ID) initiated and both are in Steam Generator E-50A. Both of these tubes were plugged and a structural integrity assessment performed by Westinghouse Engineering determined that no stabilization or in-situ pressure testing was necessary for these two indications.
- 4.
Pitting This degradation has not been found at Palisades to date and correspondingly no calibration curve is necessary for sizing.
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90-DAY RESPONSE TO GENERIC LETTER 97-05 "STEAM GENERA TOR TUBE INSPECTION TECHNIQUES"
- 5.
Thinning This degradation has not been found at Palisades to date and correspondingly no calibration curve is necessary for sizing.
- 6.
Manufacturing Burnish Marks (MBM)
Palisades does have some MBMs which were confirmed with tube pulls at Palisades during preservice activities. The indications found during preservice were never sized. They are confirmed with a historical review when they are located with ECT.
If these MBM locations are not found during the historical review, the locations are Plus Point RPC tested which is capable of confirming the marks.
- 7.
Denting Denting is monitored during bobbin coil examination. If any bobbin coil indications are confirmed with Plus Point RPC testing as a degradation, then we will expand the denting scope to a 20% random sample of all dented tubes.
In the EPRI PWR Steam Generator Examination Guidelines, Revision 5 (Appendix F), denting is defined as "a local reduction (plastic deformation) in the tube diameter due to a buildup of corrosion products (magnetite)". Secondary side visual inspections to date have not identified any magnetite or scale buildup on the stainless steel eggcrate support plates or the steam generator tubes.
During the preservice inspection of the Palisades replacement steam generators, some minor indications which were characterized at that time as denting were found. These indications were identified in 294 tubes in Steam Generator E-SOA and 94 tubes in Steam Generator E-508 using bobbin coil examination. These indications are not denting indications as defined in the EPRI Guidelines. No significant changes have been observed with random sampling conducted on these indications during inservice baseline reviews.
Steam Generator Degradation Mechanisms The steam generators that are currently in use at Palisades Nuclear Plant, are replacement steam geoeratQrs and were installed in 1990-91. The preservice inspection indicated there were no active degradation mechanisms present within the steam generators prior to service. However, a large number of manufacturing-type indications were found in the free span of the tubing. To confirm these indications, several tubes were removed and evaluated to determine the cause of the eddy current responses. It was verified that these responses were caused by the manufacturing process of removing slight imperfections with 6
90-DAY RESPONSE TO GENERIC LETTER 97-05 "STEAM GENERA TOR TUBE INSPECTION TECHNIQUES" a buffing tool. This causes slight tube wall thinning in these areas. Of those identified, none exceeded the :.?:40% through-wall plugging criteria required by Palisades Technical Specifications.
Prior to the installation of these steam generators, CE advised Consumers Energy that the area around the center stay cylinder region was potentially susceptible to fretting wear at the bat wing locations. This region was preventatively plugged by CE prior to delivery of the steam generators. A total of 308 tubes were preventatively plugged in Steam Generator A and 309 tubes in Steam Generator 8. Each steam generator is designed with 8219 tubes.
After four cycles of operation, 5 additional tubes in Steam Generator E-50A have been plugged. One tube, R137 C94, was plugged during the 1993 refueling outage. This tube had an external wear scar measured at 41 % on bobbin on the lower edge of the diagonal bar cold side. Four tubes were plugged during the 1996 refueling outage. Tubes R 128 C105 and R116 C125 were plugged due to volumetric indications resulting from loose part wear at the top of the tube sheet transition. Tube R128 C105 also had a stabilizer installed as a result of wear detected by eddy current examination. Tube R34 C51 was plugged due to a single axial indication at the top of the tubesheet hot leg. Tube R1 C54 was plugged due to a single axial indication in the U bend. This brings the total of plugged tubes in Steam Generator E-50A to 313 tubes.
After four cycles of operation, no additional tubes in Steam Generator E-508 have been plugged.
Upon completion of the 1998 refueling outage, the Palisades replacement steam generators will have completed the initial 60 effective full power months of operation and 100% inservice eddy current testing.
Review of the indications in both steam generators show 8 tubes in Steam Generator E-50A and 5 tubes in Steam Generator E-508 (all indications of wear at vertical straps or diagonal bars) which met the following criteria:
- 1.
A new 20% or greater indication from the last inspection.
- 2.
A previous percent indication that shows 10% or greater growth in one cycle.
The number of Indications which meet this criteria do not constitute an Active Damage Mechanism in either steam generator when compared to the criteria set forth in the EPRI PWR Steam Generator Examination Guidelines: Revision 5.
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l Discussion 90-DA Y RESPONSE TO GENERIC LETTER 97-05 "STEAM GENERA TOR TUBE INSPECTION TECHNIQUES" Palisades uses a Palisades Steam Generator Procedure MRS 2.4.2 PAL-42, "Steam Generator Eddy Current Data Analysis Techniques," to control inspection analysis activities. This procedure was written to incorporate the EPRI PWR Steam Generator Examination Guidelines: Revision 5. The purpose of the procedure is to:
- 1.
Assure that the Nondestructive Examination (NOE) Data Analyst evaluates eddy current data accurately and consistently at Palisades.
- 2.
Provide a description of Palisades steam generators, a report on their operating history, an overview of their operating history, and an overview of the industry's operating experience with Combustion Engineering (CE) steam gener~tors.
- 3.
Provide information concerning EPRI Appendix H qualified eddy current techniques, wherein all inspection variables and reporting criteria are referenced in Palisades ACTS, Palisades ANTS, and in the Palisades Probe Authorization Letter.
Appendix C of MRS 2.4.2 PAL-42 refers to qualified techniques. Palisades Steam Generator procedure MRS 2.4.2 GEN-35, "Eddy Current Inspection of Preservice and lnservice Heat Exchanger Tubing," requires a Probe Authorization Letter from the vendor which must be approved by the Palisades Steam Generator Engineer. This letter:
- 1.
Lists all probes used for the inspection,
- 2.
States the status of Appendix H qualification for each probe or coil by each type of known degradation mechanism which occurred at Palisades, and
- 3.
States any known degradation mechanism which has occurred in similar steam generator types.
EPRI Steam Generator Examination Guidelines: Revision 5, is the basis for probe selection for degradation mechanisms.
Summary Palisades has a history of leaving tubes in service which have indications based on sizing only for the wear degradation mechanism. MBMs and denting indications are indications already identified during the preservice ECT examination and can be monitored during bobbin coil examination; confirmed and characterized by Plus Point RPC testing. Sizing guidelines are in accordance with EPRI PWR Steam Generator Examination Guidelines:
Revision 5.
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l 90-DA Y RESPONSE TO GENERIC LETTER 97-05 "STEAM GENERA TOR TUBE INSPECTION TECHNIQUES" Palisades uses documented NOE methods listed in Palisades ACTS and ANTS for possible degradations in steam generator examination regions. This documentation is referenced in Palisades procedure, "Steam Generator Eddy Current Data Analysis Technique". The technical basis for the acceptability of techniques used is provided by and modeled after EPRI Steam Generator Examination Guidelines: Revision 5, Appendix H, "Performance Demonstration For Eddy Current Examination".
The basis for application of the sizing techniques is the conduct of the examinations under the Palisades Quality Assurance Program following the requirements of Sections V and XI of the ASME Code, 1989 Edition, and of Regulatory Guide 1.83, "lnservice Inspection of Pressurized Water Reactor Steam Generator Tubes." Additional support for sizing degradation specific mechanisms is provided by EPRI Steam Generator Examination Guidelines: Revision 5, Appendix H, "Qualification Data Sets" and qualifications performed by Consumers Energy.
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