ST-HL-AE-5190, Forwards Addl Info Re NRC GL 95-03, Circumferential Cracking of SG Tubes

Forwards Addl Info Re NRC GL 95-03, Circumferential Cracking of SG Tubes

ML20098C534
Person / Time
Site:	South Texas
Issue date:	10/02/1995
From:	Cloninger T HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-95-03, GL-95-3, ST-HL-AE-5190, NUDOCS 9510100190
Download: ML20098C534 (6)

Text

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l The Light l c o mp a ny out h Texas Project Electric &nerating Station P. O. Box 289 Wsworth, Texas 77483 Houston Lighting & Power October 2, 1995 ST-HL-AE-5190 I

File No.: G03.08 10CFR50 U. S. Nuclear Regulatory Commission l Attention: Document Control Desk Washington, DC 20555-0001 South Texas Project Electric Generating Station Units I and 2 Docket Nos. STN 50-498, STN 50-499 Additional Information Regarding NRC Generic Letter 95-03:

"Circumferential Crackine of Steam Generator Tubes"

Reference:

Correspondence from T. W. Alexion, Nuclear Regulatory Commission to W. T. Cottle, South Texas Project dated September 8,1995 ,

(ST-AE-HL-94301)

Pursuant to the referenced correspondence, the attachment provides additional information and clarification regarding South Texas Project's response on June 27,1995 to NRC Generic Letter 95-03.

If there are any questions regarding this request, please contact Mr. S. E. Thomas at (512) 972-7162 or me at (512) 972-8787.

f. .

1. Clon' ger Vice Pre dent.

Nuclear :ngi e.dte KJT/lf

Attachment:

Additional Information Regarding NRC Generic Letter 95-03 4 ^An1O 9510100190 951002 PDR ADOCK 05000498 P PDR Gl.B-95\5190 Project Manager on Behalf of the Participants in the South Texas Project i

. d Houston Lighting & Power Company ST-HL-AE-5190

South Texas Project Electric Generating Station File No.

G03.08 Page 2 c:

Leonard J. Callan Rufus S. Scott

, Regional Administrator, Region IV Associate General Counsel

U. S. Nuclear Regulatory Commission . Houston Lighting & Power Company

- 611 Ryan Plaza Drive, Suite 400 P. O. Box 61067.  !

Arlington, TX 76011-8064 Houston, TX 77208 Thomas W. Alexion Institute of Nuclear Power

~ Project Manager Operations - Records Center U. S. Nuclear Regulatory Commission. '/00 Galleria Parkway Washington, DC 20555-0001 13H15 Atlanta, GA 30339-5957 David P. Loveless Dr. Joseph M. Hendrie Sr. Resident Inspector

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50 Bellport Lane j c/o U. S. Nuclear Regulatory Comm. Bellport, NY I1713 l P. O. Box 910

' Bay City, TX 77404-0910 Richard A. Ratliff Bureau of Radiation Control J. R. Newman, Esquire Texas Department of Health Morgan, Lewis & Bockius 1100 West 49th Street 1800 M Street, N.W. Austin, TX 78756-3189 Washington, DC 20036-5869 K. J. Fiedler/M T. Hardt Attn: Document Control Desk

City Public Service Washington, D. C. 20555-0001 i P. O. Box 1771 San Antonio, TX 78296 J. C. Lanier/M. B. Lee J. R. Egan, Esquire City of Austin Egan & Associates, P.C.

Electric Utility Department 2300 N Street, N.W.

721 Barton Springs Road Washington, D.C. 20037 Austin, TX 78704

- Central Power and Light Company J. W. Beck j A'ITN: G. E. Vaughn/C. A. Johnson Little Harbor Consultants, Inc.

P. O. Box 289, Mail Code: N5012 44 Nichols Road Wadsworth, TX 77483 Cohassett, MA 02025-1166 c.

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UNITED STATES OF AMERICA.

NUCLEAR' REGULATORY COMMISSION In the Matter of )

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Houston Lighting & Power ) Docket Nos. 50-498 Company, et al., ) 50-499

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South Texas Project )

Units l'and 2 )

AFFIDAVIT ,

I, T. H. Cloninger, being duly sworn, hereby depose and say that I am Vice President, Nuclear Engineering, of Houston Lighting & Power Company; that I am duly authorized to sign and file _with the Nuclear Regulatory Commission the attached additional information regarding NRC Generic Letter 95-03:

"Circumferential Cracking of Steam Generator Tubes"; that I am familiar with the content thereof; and that the matter- forth therein are true and correct to the best of my know e and belief.

V o M

. 3. C'lon' ger Vipe Pre ident Nuclear ng' eri g STATE OF TEXAS )

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COUNTY OF MATAGORDA ) i Subscribed and sworn to before me, a Notary Public in and for the State of Texas, this 4 day of OctolR>t./ , 1995.

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Notary Public in and"for the State of Texas c- nnwmsumssr.msw i/ EUIU1 l S/*RC[lef ,

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ST-HL-AE-5190 Page 1 of 3 Attachment ADDITIONAL INFORMATION REGARDING NRC GENERIC LETTER 95-03 SOUTil TEXAS PROJECT UNITS 1 AND 2 South Texas Project responded to NRC Generic Letter 95-03, "Circumferential

< Cracking of Steam Generator Tubes", on June 27,1995. This attachment provides additional information and clarification regarding that response.

1. Additional Information Reauested by the NRC:

It was reported that the bend radii of the irmer row U-bend tubes are greater that those from other Westinghouse steam generators; however, no conclusions on the susceptibility of this region to circumferential cracking were provided. If this area is susceptible to circumferential cracking, submit the information requested in GL 95-03 per the guidance contained in the GL for this area (and any other area susceptible to circumferential cracking).

1. South Texas Proiect Response:

STP considers the stress relief process that was applied to the rows 1 & 2 U-bends to be effective to the extent that these areas are not susceptible to circumferential cracking.

As a conservative measure and to provide confirmation of the effectiveness of U-bend heat treatment, STP has monitored these inner row U-bends with a small sample of RPC examinations for cracking at the 1993 outages for both Units, at the 1995 outage for Unit I and plans to perform this inspection for Unit 2 in the upcoming outage planned for October of 1995.

2. Additional Information Reauested by the NRC:

In your response you indicated that no appreciable denting has been observed in either unit.

Does this imply that the dents are of such limited size that circumferential cracking could not occur at these locations? Provide the procedures used for sizing the dents. If a dent voltage threshold is used (e.g. 5.0 volts) for determining the size of the dents, provide the calibration procedure used. If the procedure is identical to the procedure for the voltage-based repair criteria, a detailed description is not necessary. If circumferential cracking could occur at these dented locations, submit the information requested in GL 95-03 per the guidance contained in the GL for this area.

O!,n 95\5190

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4 ST-HL-AE-5190 Page 2 of 3 l 1

Attachment

2. South Texas Proiect Response:

I STP Unit I has drilled carbon steel support plates and is, as such, susceptible to tube support plate denting which could lead to circumferential cracking. However, STP has monitored the condition of the tubing in this area since the baseline examination, recorded dents and noted no increase in denting beyond the manufacturing artifacts that were noted on the baseline examination. Successful chemistry control has precluded the occurrence of tube support plate 4 denting. STP plans to continue monitoring the tubing in the support plate area for

' degradation. At this time and in the absence of tube support plate denting STP does not consider the tube support plate area of the tubing susceptible to circumferential cracking.

A single exception to the above has been noted in one tube at a top support plate elevation.

i A tube support plate dent that is evident in the 1989,1993 and 1995 in-service examination-t data and was not apparent on the baseline examination has been recorded in tube IC-R36C34.

i At this time it is considered an anomalous condition. This condition is planned to be 4 examined with RPC at the next Unit 1 outage.

1 l STP guidelines for sizing dents are as follows:

Dent-like signals were reported using Mix 1.

. Mix 1 was a tube support plate suppression mix of the 550 kHz and 130 kHz differential signals.

I Support plate intersections were viewed at a span setting that provided at least a 3/4 i

full screen height for the 4 x 20% holes on the calibration standard.

A transfer / field standard was calibrated against a laboratory standard (which is the l- normalization the basis for the alternate plugging criteria for outer diameter stress j corrosion cracking at tube support plates) to establish voltages for the field standard

that was equivalent to the laboratory standard. The peak-to-peak response of the 4 x 20% holes was set to produce a field voltage equivalent to that obtained from the laboratory or trr.nsfer standard. This setting was saved and stored to all other ,

channels. Voltage normalization to the standard calibration voltages on Channel 1 (550 kHz differential) was the preferred normalization to minimize analyst sensitivity l 4

in establishing Mix 1. However, where the bobbin probes used result in a 550/130 kHz mix to 550 kHz voltages ratio which was not 0.66 - 0.72, then the 550/130 kHz ,

j mix field voltage equivalent was saved to Mix 1.

All dent signals greater than or equal to 3 volts on Mix 1 were reported.

GLB-95\5190 l

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ST-HL-AE-5190 '

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Page 3 of 3 f Attachment i

! STP Unit 2 has stainless steel support plates and STP considers this unit to be resistant to i denting and in turn non-susceptible to circumferential cracking in the tube support plate area.  ;

STP plans to monitor the tube support plate areas in Unit 2 for degradation using sampling methodology meeting or exceeding the Technical Specification requirements.  !

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i 3. Additional Information Reauested by the NRC:

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[ Several plants with preheater model steam generators have tubes expanded into the' tube

support plate in the preheater region to minimize the potential for vibration induced wear.

j Since these expansions contain similarities to other expanded regions which have experienced i circumferential cracking, discuss whether or not this area is susceptible to circumferential 4

cracking. If this area is susceptible to circumferential cracking, please submit the information

requested in GL 95-03 per the guidance contained in the GL.

3. South Texas Project Response:

! Preheater expansions have been performed at STP in nominally 160 tubes per steam generator p to minimize the potential for vibration induced wear. The original qualification program for the expansion process indicated that no definitive increase in O.D. or LD. stresses result from

the maximum expected field expansions. STP has examined process records from the field implementation of the process at STP and noted no examples of tubes that were over-i; expanded. Also, other operating Model E steam generators have been examined in these

! expansion for several cycles of operation in excess of STP's current operating age. No circumferential cracking has been noted. STP considers the tube areas expanded in the preheater to not be susceptible to circumferential cracking.

As a conservative measure to provide additional assurance of tube integrity STP has '

monitored preheater expansions with a small sample of RPC examinations for cracking of all types at the 1993 outages for both Units, for the 1995 outage for Unit I and plans to perform this inspection for Unit 2 in it's upcoming outage planned for October of 1995.

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GLB-95\$190

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