LIC-99-0029, Forwards Response to 990226 RAI for GL 97-05, SG Tube Insp Techniques

Forwards Response to 990226 RAI for GL 97-05, SG Tube Insp Techniques

ML20205G944
Person / Time
Site:	Fort Calhoun
Issue date:	03/30/1999
From:	Gambhir S OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-97-05, GL-97-5, LIC-99-0029, LIC-99-29, NUDOCS 9904070430
Download: ML20205G944 (3)

Text

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March 30,1999 LIC-99-0029 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Station PI-137 Washington, D.C. 20555-0001

References:

1. Docket No. 50-285

2. NRC Generic Letter 97-05, Steam Generator Tube Inspection Techniques, dated December 17,1997

3. Letter from OPPD (S. K. Gambhir) to NRC (Document Control Desk) dated ,

March 16,1998 (LIC-98-0031)

4. Letter from NRC (L. R. Wharton) to OPPD (S. K. Gambhir) dated February 26,1999

Subject:

Response to Request for Additional information (RAI) for Generic Letter (GL) 97-05, Steam Generator Tube Inspection Techniques in the Reference 4 RAI, the NRC requested additional clarifications of the Omaha Public Power District (OPPD) response to GL 97-05 (Reference 3). Accordingly, the OPPD response to the RAI is attached.

Please contact me if you have any questions.

Sincerely, l

r ,

i S. K. Gambhir

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Division Manager Nuclear Operations )  ;

JMC/TCM i

Attachment .

c: E. W. Merschoff, NRC Regional Administrator, Region IV L. R. Wharton, NRC Project Manager i W. C. Walker, NRC Senior Resident inspector bg Winston & Strawn )

9904070430 990330 #

lO PDR ADOCK 05000285 P PDR 45544 Employment with Equalopportunity

LIC-99-0029 Attachment .

. Page 1 of 2 Omaha Public Power District (OPPD) -

Response to Request for Additional Information dated February 26,1999, on Generic Letter 97-05, Steam Generator Tube inspection Techniques .

NRC Request No.1 Your response to GL 97-05 indicated that it is the practice at FCS to disposition tubes as acceptable for continued service with suspected pit indications. Provide the basis for confirming the indications dispositioned during inspections are pits and not volumetric intergranular attack l (IGA). If this determination was made by nondestructive examination techniques, describe the l

' mannerin which the technique was qualified to distinguish between the two damage modes. f Also, describe the assessment that was completed that evaluated the applicability of EPRI's qualification of the pitting sizing technique (ETSS 96005) to conditions at Fort Calhoun Station.

OPPD Response During the Fort Calhoun Station (FCS) 1996 Refueling Outage (RFO), and at the time of the

' OPPD response to GL 97-05, the EPRI PWR Steam Generator Examination Guidelines, Revision 4 document was used as guidance in performing steam generator tube examinations  ;

at FCS. It was the practice at that time to disposition tubes as acceptable for continued service with suspected pit indications utilizing a technique qualified for sizing as long as the measured -

depth was below the 40% through wall plugging limit defined in the Technical Specifications.

The qualification of the bobbin technique for sizing pit indications was documented under .

Revision 4 of the EPRI guidelines on Examination Technique Specification Sheet (ETSS) 96005, dated August 1996.

The indications were dispositioned as pits based on nondestructive examination techniques w using Plus Point

• rotating coil technology. There was no specific work performed to qualify this technique to distinguish between pits and nther types of volumetric indications. However, pits generally appear as' discreet, roundish signals which have relatively high signal amplitude when compared _to surface area. This is in contrast to other types of volumetric signals which generally _have lower signal amplitude when compared to surface area. The analysts made the judgement that the indications were pits based on this type of experience. It should be noted that the sizing technique used to size the pit indications was also qualified under the EPRI guidelines for sizing IGA indications. This qualification was documented on ETSS 96008, dated August 1996. Therefore, in the unlikely event that any of the indications dispositioned as pits -

were actually IGA, the technique used for sizing was still qualified under Revision 4 of the EPRI PWR Steam Generator Examination Guidelines. <

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In 1996, there were no specific recommendations in the EPRI guidelines that suggested a

/ technique _should be site qualified prior to use. Revision 4 of the guidelines contained acceptance criteria for which a probe could be qualified for sizing, and the bobbin probe met these criteria for sizing pit indications. The test application under the guidelines encompassed L pitting in the presence of copper. It is known that there is copper present in the FCS steam generators and that the potential _for copper presence in pit locations exists. Therefore, the m

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l LIC-99-0029 Attachment y Page 2 of 2 l

qualification was considered applicable to FCS. Differences in tester units, cable types and cable lengths between the as-qualified and field implementation configurations of the bobbin

' technique were evaluated through testing prior to the 1996 RFO. The field technique was considered acceptable for use at FCS based on this testing.

The EPRI PWR Steam Generator Examination Guidelines, Revision S document was issued subsequent to the 1996 RFO. Changes from Revision 4 to Revision 5 of the examination guidelines included removal of sizing qualification acceptance criteria and the addition of a requirement to perform a site qualification prior to using a technique for sizing. As a result of the changes in the guidelines, and in an effort to continue following the best industry guidance available, FCS conservatively implemented a plug-on-detection strategy for pit indications during the 1998 Refueling Outage. This was done in lieu of performing the additional site-qualification for sizing pit indications, which would have been required under Revision 5 of the EPRI guidelines. There war . no pit indications left in service based on size during the 1998 RFO, and all three of the tubes that were identified as containing pits in 1996 were plugged during the 1998 RFO.

The FCS data analysis procedure does not currently allow indications to be left in service based on sizing.

NRC Request No. 2 In your response to GL 97-05, you did not discuss yourpractice for addressing wearindications at tube supports. Discuss whether these indications are, or have been, identified during steam generator tube examinations at FCS, and provide the strategy for dispositioning tubes with these i indications. If these indications are dispositioned by sizing, submit a written report that describes l the nondestructive examination method being used and the technical basis for the acceptability l of the technique used. l OPPD Response l l

FCS has not identified wear indications at tube supports, and therefore is not currently leaving  !

wear indications in service based on size. The current method to disposition this type of indication would be to plug-on-detection. Should the need to size wear indications present itself in the future, appropriate industry guidance would be utilized to site qualify a technique prior to its use. l

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