ML20248L399
| ML20248L399 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 03/13/1998 |
| From: | Sorensen J NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-97-05, GL-97-5, NUDOCS 9803200165 | |
| Download: ML20248L399 (5) | |
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Northern States Power Company Prairie Island Nuclear Generating Plant 1717 Wakonade Dr. East
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Welch, Minnesota 55089 March 13,1998 10 CFR 50.54(f)
Generic Letter 97-05 U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Response to Generic Letter 97-05:
Steam Generator Tube inspection Techniques On December 17,1997, the Nuclear Regulatory Commission issued the referenced Generic Letter requesting information. By this letter, Northern States Power Co. is providing the required 90 day response for the Prairie Island Nuclear Generating Plant and is making no new NRC commitments. Please contact Richard Pearson (612-388-1121)if you have questions regarding this issue.
Joel P Sorensen
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Plant Manager
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Prairie Island Nuclear Generating Plant
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Regional Administrator - Region Ill, NRC g
NRR Project Manager, NRC Senior Resident inspector, NRC
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Kris Sanda, State of Minnesota
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Attachment:
RESPONSE TO NRC GENERIC LETTER 97-05 l
9803200165 980313 88R 11glytlll!Ilyt%Ill
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l UNITED STATES NUCLEAR REGULATORY COMMISSION NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT DOCKET NO.
50-282 50-306 GENERIC LETTER 97-05: Steam Generator Tube inspection Techniques Northern States Power Company, a Minnesota corporation, with this letter is submitting information requested by NRC Generic Letter 97-05.
This letter contains no restricted or other defense information.
NORTHERN STATES POWER COMPANY BY o
m goel P'Sorens(n
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Plant Manager Prairie Island Nuclear Generating Plant m
On this day of UL before me a notary public in r
and for said County, person eared Joel # Sorensen, Plant Manager, Prairie island Nuclear Generating Plant; and being first duly sworn acknowledged that he is authorized to execute this document on behalf of Northern States Power Company, that he knows the contents thereof, and that to the best of his lepowledge, information, and belief the statements made in it are t and that it is not i terposed for delay.
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RESPONSE TO NRC GENERIC LETTER 97-05 i
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Within 90 days of the date of this generic letter, addressees are required to submit a written response that includes the following information:
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(1) whether it is their practice to leave steam generator tubes with indications in service based on sizing, i
The Prairie Island Nuclear Generating Plant (PINGP) does leave steam generator tubes in service based on sizing. Of the available sizing techniques, l
the PINGP currently uses those techniques associated with thinning at non-dented cold leg tube support plates, wear at anti-vibration bars (AVBs), freespan wear associated with old AVB locations, and wear from loose parts.
l The PINGP Unit 1 and 2 steam generators are Westinghouse Model 51. Steam generator tube indications are left in service if they can be sized at less than the PINGP Technical Specification value of 50% (40% if significant general tube thinning occurs). In addition, indications in tubes are left in service in accordance with the F* and Voltage Based Tube Support Plate repair criteria as l
authorized by the PINGP Technical Specifications.
(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.
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Introduction l'
The nuclear power industry recently voted to adopt an initiative requiring each l
utility to implement the guidance provided in NEl 97-06, Steam Generator Program Guidelines, no later than the first refueling outage starting after January l
1,1999. As specified in NEl 97-06, each utility is required to follow the inspection guidelines contained in the latest revision of the EPRI PWR Steam GeneratorExamination Guidelines.
Appendix H," Performance Demonstration for Eddy Current Examination," of the PWR Steam Generator Examination Guidelines, Revisions 3 through 5, (hereafter referred to as Appendix H) 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
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R:sponse to GL 97-05 March 13,1998 Page 2 of 3 cracking (lGA/ 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 by the technique developer to produce signals similar to those being observed in the field in terms of signal characteristics, signal amplitude, and signal-to-noise ratio. Samples are examined to determine the actual through wall defect l
measurements as part of the Appendix H qualification process.
l The procedures developed in accordance with Appendix H specify the essential variables for each procedure. Thuse essential variables are associated with an individual instrument, probe, cable, or particular on-site equipraent configurations. Additionally, certain techniques have undergone testing and
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review to quantify sizing performance. The sizing data set includes the detection data set for the technique with additional requirements for number and composition of the grading units.
L Sizina Techniaues At the PINGP the following sizing techniques are used during steam generator inspections to leave degraded tubes in service. The basis for application of these sizing techniques is the conduct of the examinations under the PINGP Quality Assurance Program following the requirements of Sections XI and V of the ASME Code,1989 Edition and Regulatory Guide 1.83. Additional support for sizing degradation-specific mechanisms is provided by the Appendix H qualification data sets.
Thinnino For thinning at non-dented cold leg tube support plate locations, the 400/100 kHz differential mix of the bobbin probe is used to size the through wall extent of wall thinning. A phase calibration curve is established using the 20%,60% and 100% holes of the ASME calibration standard. The depth of the thinning is called from the 400/100 kHz differential mix using the volts peak to peak or maximum rate of change.
The Appendix H sizing procedure is based on the analysis of 32 sample data points. Of the 32 data points, five (5) are from pulled tubes. The l
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samples ranged in depth from 9% to 100%.
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R:sponsa to GL 97-05 l
March 13,1998 j
Page 3 of 3
. Wear at New AVBs and Freasoan Wear at Old AVB Locations For wear associated with AVBs, the 200/100 kHz absolute mix of the bobbin probe is used to size the through wall extent of wear. An amplitude calibration curve is established using the 0% (noise), 30% and 50% single-sided wear scar standard which replicates the damage mechanism type. The depth of the wear is called from the 200/100 kHz absolute mix using vertical maximum amplitude.
The Appendix H sizing qualification is based on 64 sample data points.
The samples ranged in depth from 4% to 78% through wall depth.
Wear from Loose Parts and Foreign Material (site soecific qualification)
For wear from loose parts such as the previously installed tube lane blocking devices or from foreign material, the 400/100 kHz mix of the bobbin probe is used to size the extent of the wall thinning. A phase calibration curve is established using the 20%,60% and 100% holes of 3
the ASME calibration standard. The depth of the thinning is called from
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the 400/100 kHz differential mix using the volts peak to peak or maximum rate of change.
This site specific sizing qualification is based on 5 sample data points.
The samples ranged in depth from 14% to 30% through wall depth and from 0.41 inches to 2.215 inches long. The qualification was done using in situ mold samples from the actual tube lane blocking device wear scars in the steam generator and demonstrated that the eddy current sizing was conservative for wear scars left in service.
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