ML20210E407
| ML20210E407 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 07/22/1999 |
| From: | Dennis Morey SOUTHERN NUCLEAR OPERATING CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NEL-99-0273, NUDOCS 9907280215 | |
| Download: ML20210E407 (5) | |
Text
$.
Dava Mirey S:uth:rn Nucint Vice President Op: rating C:mp:ny, Inc.
' Farley Pmiect Post Office Bc;1295 Birmingham, Alabama 3520!
Tel 205 992 5131 SOUTHERN July 22, 1999 COMPANY Energy to Serve limr World" Docket No:
50-348 NEL-99-0273 U. S. Nuclear Regulatory Commission ATrN: Document Control Desk Washington, D. C. 20555-0001 Joseph M. Farley Nuclear Plant Response to Request for Additional Information Unit 1 Cvele 16 Extension Reauest Ladies and Gentlemen:
j By letter dated April 23,1999, Southern Nuclear Operating Company (SNC) submitted a Facility Operating License change request for Farley Nuclear Plant Unit 1. This change is to allow for a risk informed approach for the evaluation of steam generator tube structural integrity as described by NEl 97-06 " Steam Generator Program Guidelines." By letter dated July 2,1999 the NRC staff requested additional infonnation in order to complete the review of the SNC submittal. In
. Attachment 1, SNC provides the information requested or documents completion of the required action.
There are no new commitments in this response. If you have any questions, please advise.
Respectfully submitted, Dave Morey EWC/maf. nrc7299. doc Attachment Sworn to andsubscribed before me thisr$
o 1999 Q.)
1
( Notary Public # (/
g Y17l l, 50 l 1l My Commission Expires:
b 9907280215 990722 PDR ADOCK 05000348 P
L Page 2 U. S. Nuclear Regulatory Commission cc:
Southern Nuclear Operatina Comoany Mr. L. M. Stinson, General Manager - Farley U. S. Nuclear Regulatory Commission. Washinaton. D. C.
Mr. L. M. Padovan, Licensing Project Manager - Farley l
U. S. Nuclear Regulatory Commission. Reaion II Mr. L. A. Reyes, Regional Administrator Mr. T. P. Johnson, Senior Resident Inspector - Farley i
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Attachment Responses to Request for Additional Information Regarding Unit I Cycle 16 Extansion Request
q NRC Ouestion j
1
'l.
Please submit a list of all confirmed freespan tube flaws identified in the outage with their i
corresponding voltages and phase angle measurements recorded using a bobbin coil prohe. In addition, please submit bobbin coil cddy current data (Eddynet format) for a sample of at least 20 tubes removed from service for freespan cracking in the end of-cycle (EOC)-15 outage. Provide data for each tube obtained in the EOC-14 and EOC-15 refueling outages. Include with the tube data the calibration standard data appropriate for each indication (s) to permit proper set-up of the equipment. List the true depths of the reflectors for each calibration standard included on the data disk.
Please send the eddy current data disk and calibration standard information to the followmg address:
Caius V. Dodd i
11740 Williamsburg Drive, N.
Knoxville, TN 37922-3818 SNC Response The information requested has been provided.
NRC Ouestion 2.
NDE sizing uncertainties in Table 5-4 appears to have been developed using two analysts (i.e.,
D4536 and D9999). However, the majority of the calls considered for sizing were from one of the two analysts. The predominant use of one eddy current analyst may bias the results in that uncertainty distributions will be specific to the particular analyst. Describe how the use of a
)
limited number of data analysts in the sizing uncertainty assessment permits an accurate prediction of the EOC-16 flaw distribution.
l SNC Response l
The approach used to develop + 1 Nt depth profiles for the Farley-1 operational assessment was to use l
a single analyst, designated as D9999, for the structurally most limiting indications. This included the larger indications that were expected to have the greatest growth rates. Pulled tube destructive exam results were used for the depth profiles of tubes R25C51 in SG B and R6C10 in SG C which constitute 8% of the total indications. Due to the relatively large number ofindications requiring profiling for SGs B and C, four additional analysts including Analyst P4536 were used in the evaluations to develop the total population ofindications. Three analysts used for the Farley-1 evaluations were assigned to other field SG inspections at the time the Farley operational assessment was performed and were not available for analysis of the pulled tubes. The blind analyses done by Analyst D9999 for the sludge pile indications (Location SP in Table 5-4) had been performed prior to the destructive examination of these pulled tubes in 1996 and were included to enhance the database for the Table 5-4 uncertainty estimates.
The + Poiut data for these sludge pile indications were not Farley SG da a and were not available for reanalysis as part of this uncertainty study.
It is recognized that the use of a limited number of data analysts for Table 5-4 would not be adequate for a " generic"NDE uncertainty study. However, the limited number of analysts is adequate for support of the plant specific, Farley-1 operational assessment since the analysts used to develop Table 5-4 also performed the + Point sizing analyses for the most significant indications supporting the operational assessment for structural integrity and large growth rates. In addition, pulled tube I
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l destructive exam crack profiles were used for about 8% of the total ir.dications in the tube integrity analyses to climinate the NDE uncertainty in sizing these indications.
NRC Ouestion 3.
Some flaws identified in the destructive examination were excluded from the development of the probability of detection (POD) curves due to close proximity to other cracks (e.g., R25C51 - 4, 5, 6).
In other cases (e.g., R25C51 - 9 and 2), two closed spaced cracks were retained for the development of the POD correlatica We are concerned that including closely spaced cracks in the POD correlation does not provide a representative correlation because each crack may not be detected i%tly. Describe the steps taken to ensure that each flaw considered for the POD correlation's was detected indamient of one another. Discuss whether detection calls were from the original field analyses completed prior to selecting tubes for removal from the steam generator.
SNC Response h NDE analyses used to develop the POD curves are identified in the "Farley - 1: Final Cycle 16 Freespan ODSCC Operational Assessment" Tables 5-lb,5-2b and 5-3b for each of the pulled tubes i
used in the POD assessments. The analyses include the original field bobbin and a field reevaluation of the data. In these tab'.es, the columns labeled " Field Bobbin" represent the original field analyses completed prior to selecting tubes for removal from the steam generator. Since the bobbin detection analysis techniques were revised over the time frame of the 8/98 leaker outage and the 11/981R15 outage, it was appropriate to include this detection experience in the POD assessments. Therefore, the i
field analysts reevaluated the pulled tube data at the end of the IRIS inspection. These results are given in the " Field Bobbin Reevaluation" cohians of the subject tables and were included in the POD evaluation together with the original field a'ialysis results. The conservatism of using the original field analyses, which did not use the updated NDE analysis techniquer, offsets any non-conservatism that i
might result in the IRIS reevaluation from the analyst's knowledge that the tubes being evaluated were pulled tubes.
The steps taken to ensure that each flaw used for the POD evaluation was detected independent of any other flaw included:
The destructive exam lengths were combined to a single flaw when the combined sections included a burst test so that only the burst profile was used for the POD analysis. For example, on tube R25C41 -
4,5, 6, the burst was in section 4 and the three subsections span 1.36 inches. The three subsections were too short to allow confidence that the bobbin response for one subsection was inde@nt of the adjacent subsection.
Tube R25C51 cracks 8,9 and 2 are the closest spaced cracks used in the POD analysis. The maximum depths for these indications are located above the sleeve at 4.35 inches *,5.89 and about 7.5 inches (large indication). The destructive exam data shcw physical separation (zero depths) between these three indications and the spans between maximum depths are about 1.5 inches. Although a minimum separation for distinct cracks was not developed, the closest 1.5 inches separation is adequate for
. distinct dew: tion of different flaws by bobbin and + Point coils.
The remaining destructive exam sections used for the POD analyses are widely separated (inches of separation) and detaction would be clearly independent between sections. Consequently, the separation of cracks used for the POD is adequate to represent independent detection.
Table 5-2a of"Faricy - 1: Final Cycle 16 Freespan ODSCC Operational Assessment" erroneously listed this as 2.55 inches.