ML20217A065
| ML20217A065 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 03/17/1998 |
| From: | Feigenbaum T NORTH ATLANTIC ENERGY SERVICE CORP. (NAESCO) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| AR#-97030283, GL-97-05, GL-97-5, NYN-98039, NUDOCS 9803240221 | |
| Download: ML20217A065 (6) | |
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" -- ~ North North Atlantic Energy Service Corporation P.O. Box 300
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The Northeast Utilities System March 17,1998 Docket No. 50-443 NYN-98039 AR# 97030283 United States Nuclear Regulatory Commission
-Attention: Document Control Desk Washington, DC 20555-0001 Seabrook Station 90-Day Resnonse to Ger.eric Letter 97-05 This letter provides North Atlantic Energy Service Corporation's (North Atlantic) 90-day response to Generic Letter (GL) 97-05, " Steam Generator Tube Inspection Techniques." The response discusses the technique used at Seabrook Station for leaving steam generator tubes with
' indications in~ service based on sizing. North Atlantic does leave steam generator tubes in service based on through-wall sizing. To date, the only active damage mechanism at Seabrook Station is anti-vibration bar (AVB) wear. The techniques used to size this type of wear have been qualified in accordance with Appendix H of the EPRI Steam Generator Eddy Current Data Analysis Guidelines.
Should'you have any questions regarding this response, please contact Mr. Terry L. Harpster, Director of Licensing Services, at (603) 773-7765.
Very truly yours, NORTH ATLANTIC ENERGY SERVICE CORP.
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' fed C. Feigenbauf Executive Vice President and Chief Nuclear Officer cc:
..H. J. Miller, NRC Regional Administrator g'
- C. _W. Smith, NRC Project Manager, Project Directorate 1-3
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R. K. Lorson, NRC Senior Resident Inspector ky t
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STATE OF NEW HAMPSHIRE.
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March 17,1998 Then personally appeared before me, the above-named Ted C. Feigenbaum, Executive Vice President and Chief Nuclear Officer, North Atlantic Energy Service Corporation, that he is duly authorized to execute and file the foregoing information in the name and on the behalf of North Atlantic Energy Service Corporation and that the statements therein are true to the best of
' his knowledge and belief.
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Susan J. Messer, Notary Public My Commission Expires: December 22,1998
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ENCLOSURE TO NYN-98032
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Response to USNRC Generic Letter 97-05
" Steam Generator Tube Inspection Techniques" Introduction Generic Letter 97-05 (GL), Steam Ger.erator Tube Inspection Techniques, emphasizes the importance of using qualified sizing techniques when sizing is used as the basis for leaving steam generator tubes in service. In general, plant technical specifications require the removal from service or the repair of those tubes with degradation exceeding 40 percent of the nominal tube wall thickness. Ilowever, GL 97-05 states that there are degradation types for which the variability of tube material properties and geometry, degradation morphology, etc., can significantly alter a depth estimation of tube degradation. If an unqualified sizing technique is used, tubes with wall thickness degradation exceeding 40% may be left in service.
GL 97-05 requests licensees to review the types of steam generator tube indications that are being left in service based on sizing, the inspection method being used to perform the sizing for each type ofindication, and the technical basis for the acceptability of each inspection method.
This response provides the requested information for Seabrook Station.
Response to Requested Information Item (1):
(1) whether it is their practice to leave steam generator tubes with indications in service based on si:ing, Resoonse:
It is North Atlantic's practice to leave steam generator tubes with wear indications in service based on sizing.
North Atlantic leaves steam generator tube indications in service which can be sized at less than the Technical Specification value of 40%. The plant steam generators are Westinghouse Model F with thermally treated tubing.
Response to Reauested Information item (2):
(2) of the respame to item (1) is afirmative, those licensees should submit a written report i
that includes, for each type ofindication, a description of the associated nondestructive examination method being used and the technical basis for the acceptability of the technique used.
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Remonee-The nuclear power industry recently voted to adopt an initiative requiring each utility to implement the guidance provided in NEI 97-06, Steam Generator Program Guidelines, no later than the first refueling outage starting after January 1,1999. 'As specified in NEI 97-06, each utility is' required to follow the inspection guidelines contained in the latest revision of the EPRI PWR Steam Generator Examination' Guidelines.
Appendix li, " Performance Demonstration for Eddy Current Examination," of the PWR Steam Generator Examination Guidelines, Revisions 3 through 5, provides guidance on ;the
" qualification of steam generator tubing examination techniques and equipment used to detect and size flaws. Damage mechanisms are divided into the following categories: thinning, pitting, wear, outside diameter intergranular attack / stress-corrosion cracking (IGA / SCC), primary-side
' SCC, and impingement damage for qualification.
For qualification purposes, test samples are used to evaluate detection and sizing capabilities.
While pulled tube samples are preferred, fabricated samples may be used. If fabricated test samples are used, the samples are verified to produce signals similar to those being observed in the field in terms of signal characteristics, signal amplitude, and signal-to-noise ratio. Samples l
are examined to determine the actual through wall defect measurements as part of the Appendix 11 qualification process.
The procedures developed in accordance with Appendix 11 specify the essential variables for each procedure. These essential variables are associated with an individual instmment, probe, cable, or particular on-site equipment configurations. Additionally, certain techniques have undergone testing and review to quantify sizing performance. The sizing data set includcs the detection data set for the technique with additional requirements for number and composition of
- the grading units.
Mirino Techninues North ' Atlantic uses the following sizing techniques during steam generator inspections to leave
' flaws in service. : The basis for application of these sizing techniques is the conduct of the examinations under the Seabrook Station Quality Assurance Program following the requirements of Section XI and V of the ASME Code,1983 Edition, Summer 1983 Addenda, and Regulatory
. Guide 1.83. Additional support for sizing degradation-specific mechanisms is provided by the EPRI Appendix li qualification data sets.
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e-Wear
. For wear at anti-vibration bars (AVB), sizing is accomplished using the 300/150 absolute mix of '
the bobbin probe.~ A calibration curve for amplitude vertical maximum is determined based on the applicable standards replicating the damage mechanism type and quantity. The calibration curve used is selected to represent the full range of expected depths.
This sizing qualification is based on 64 sample data points. The samples range in depth from 4%
to 78% through wall depth.
Other Indications Wear is the only active damage mechanism identified so far at Seabrook Station. However, there
. are other imperfections and signals that have been identified and recorded. The imperfections and signals ~ noted are manufacturing burnish marks, dents, dings, and tangential flag signals 1
_(believed to be dings that occur at the tube tangent point to the U-bend), non-quantifiable signals and distorted tube support signals.' These indications have been determined to be non-relevant in accordance with the Seabrook Station Steam Generator Eddy Current Data Analysis Guidelines' 1
using methods to discriminate true wall-loss related flaws from non-relevant signals. The EPRI PWR Steam Generator Examination Guidelines also describe these signals as non-relevant. This I
discrimination analysis is not a sizing technique and actual degradation from the above signals '
would be repaired upon detection.
In addition, loose parts have been identified in the Seabrook Station Steam Generators. Where there is wear associated with the loose part, it is North Atlantic's practice to repair those tubes. In other words, sizing techniques are not employed in conjunction with loose parts.
' Millstone Point Unit 3 and Seabrook Nuclear Power Stations Steam Generator Eddy Current Data Analysis Guidelines Manual, ES-WC-94-033 3
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