ML20095C130

Forwards Response to NRC Request for Addl Info Re GL 95-03, Circumferential Cracking of SG Tubes

ML20095C130
Person / Time
Site:	Sequoyah
Issue date:	12/06/1995
From:	Shell R TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-95-03, GL-95-3, TAC-M92274, TAC-M92275, NUDOCS 9512110377
Download: ML20095C130 (5)

Text

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i Tennessise Varley Authonty Post Omce Box 2000 Soddy Daisy. Tennessee 37379 i

December 6,1995 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:

In the Matter of

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Docket Nos. 50-327 Tenncssee Valley Authority

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50-328 SEQUOYAH NUCLEAR PLANT (SON)- UNITS 1 AND 2 - RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION REGARDING GENERIC LETTER (GL) 95-03

References:

1. NRC letter to TVA dated September 6,1995, " Request for Additional Information - Generic Letter 95-03, Circumferential Cracking of Steam Generator Tubes - Sequoyah Nuclear Plant Units 1 and 2 (TAC Nos. M92274 and M92275)"

2. NRC letter to TVA dated September 20,1995, " Supplemental Request for Additional Information-Generic Letter 95-03, Circumferential Cracking of Steam Generator Tubes - Sequoyah Nuclear Plant Units 1 and 2 (TAC Nos. M92274 and M92275)"

Enclosed is TVA's response to the NRC request for additionalinformation contained in the referenced letters. The enclosed information was verbally provided during a September 25,1995, teleconference between David Goetcheus of TVA and Ken Karwoski of NRC.

This information is being provided in writing within 90 days of your request as discussed during a subsequent phone call. If you have any questions concerning this issue, please telephone D. V. Goodin at (423) 843-7734.

Sincerely, Y-f R. H. Shell Man.ager SON Site Licensing Enclosure cc: See page 2 l

~ 9512110377 951206 PDR ADOCK 050003 7 p

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4 U.S. Nuclear Regulatory Commission Page 2.

t December 6,1995

- ccjEnclosure):

Mr. D. E. LaBarge, Project Manager ~

Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike l

Rockville, Maryland 20852-2739 NRC Resident inspector Sequoyah Nuclear Plant 2600 lgou Ferry Road Soddy-Daisy, Tennessee _37379-3624 i

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Regional Administrator U.S. Nuclear Regulatory Commission i

Region ll 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323-2711 l

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- ENCLOSURE i

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The following provides the TVA response to NRC's request for information as provided ~-

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in their September 6 and 20,1995, letters.

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i NRC Reauest

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t TVA reported that 16 expansion transition circumferentialindications.were j

detected in Unit 1 during the last steam generator (S/G) tube inspection outage

- and that over 50 percent of the tubes were inspected with a rotating pancake coil (RPC) probe ' Please discuss the expansion criteria used during these j

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examinations.

TVA indicated that the expansion criteria contained in the Westinghouse Owners' L

- Group WEXTEX Guidelines would be followed for indications detected at the expansion transition. Provide a summary of these expansion critena.

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TVA Resoonse The expansion criteria used during the last Unit 1 outage top-of-tubesheet l

- examinations was the Westinghouse Owners Group WEXTEX Guidelines, Revision 2, October 15,1991, and a copy was provided to the staff for their j

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- review of the expansion criteria.'

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NRC Reauest l

TVA indicated that dents greater than 5.0 volts were inspected with a RPC probe.

I Provide the procedures used for sizing the dents. If the procedure is identical to the procedure for the voltage-based repair criteria, a detailed description is not l

necessary.

I Future inspection plans for dented (greater than 5 volts) intersections concentrate l

at the lowest hot-leg tube support plates (TSPs). A large dent at an upper TSP t

may be more significant in terms of corrosion susceptibility as a result of higher stresses than a small dent at a lower TSP even though the temperature is lower at the upper TSP. Given this, discuss the basis for the proposed sample strategy

. given that cracking depends on many factors including temperature and stress levels.

i TVA Resoonse The procedure used for sizing dents is identical to the procedure for voltage-based

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- repair criteria. Sample strategy for dented TSP intersections was established as a

.part of Sequoyah Technical Specification Change 95-15, Revision 1 (Enclosure 4,

- Section 1.3.b.3), and TVA's letter to NRC dated September 15,1995, " Additional i

-'Information for Technical Specification (TS) Change 95-15, Revision 1."

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. 3. NRC Reaugal.

During the Unit 1 Cycle 6 outage, TVA indicated that one tube was conservatively plugged for a circumferentiat indication in a tube with a small radius U-bend and r

that the degradation mechanism is not active. Discuss the basis for these statements, particularly with respect to being conservatively plugged. For Units 1 and 2, clarify the extent of the RPC examinations performed in the U-bend region of Rows 1 and 2 (i.e., percentage of tubes inspected). Provide the expansion criteria implemented during the previous outage, if applicable.

. TVA Resoonse The one tube conservatively plugged for a circumferentialindication in a Row 1 U-bend was a preexisting indication in a previously heat-treated U-bend that had not significantly changed in service since the mid-1980's heat treatment. TVA elected to preventative!y plug the tube.

During the Unit 1 Cycle 6 outage,100 percent of Row 1 and the following percentages in Row 2 were RPC examined in the U-bend region.

S/G Nos.

Percentaaes S/G No.1 10 percent S/G No. 2 10 percent S/G No. 3 26 percent S/G No. 4 19 percent At the Unit 2 Cycle 6 outage, the Rows 1 and 2 U-bends were heat treated and 100 percent RPC examination of both Row 1 and Row 2 U-bends were performed after heat treatment.

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NRC Reauest Please provide the month and year for the completion of the last two R/G tube inspections at both Sequoyah Units 1 and 2.

TVA Resconse llL M2 Cycle 6 Completed inspections Completed inspections Refueling Outage on May 27,1993 on August 24,1994 i

Cycle 5 Completed inspections Completed inspections

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Refueling Outage on November 24,1991 on April 19,1992 i

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NRC Reauest

During the Maine Yankee outage in July / August 1994, several weaknesses ~were

' identified in its addy current program as detailed in NRC Information Notice 94-88, " Inservice inspection Deficiencies Result in Severely Degraded

' Steam Generator Tubes." In Information Notice 94-88, the staff observed that l

several circumferentialindications could be traced back to earlier inspections when the data was reanalyzed using terrain plots.- These terrain plots had not

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been generated as part of the original field' analysis for these. tubes.

l y-For the RPC examinations performed at your plant at locations susceptible to -

circumferential cracking during the previous inspection (i.e., previous inspection

, per your Generic Letter (GL] 95-03 response), discuss the extent to which terrain

. plots were used to analyze the eddy current data. If terrain plots were not routinely used at locations susceptible to circumferential cracking, discuss -

'j whether or not the RPC eddy current data has been reanalyzed using terrain i

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' mapping of the data, if terrain plots were not routinely used during the outage i

and your data has not been reanalyzed with terrain mapping of the data, discuss j

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your basis for not reanalyzing your' previous RPC data in light of the findings at Maine Yankee.

l Discuss.whether terrain plots will be used to analyze the RPC eddy current data at locations susceptible to circumferential cracking during your next S/G tube g

inspection (i.e., the next inspection per your GL 95-03 response).

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l TVA Resoonse I

In previous outages at Sequoyah Units 1 and 2 terrain plots were used and are

.j included in analysis of all RPC data. Sequoyah site specific analysis guidelines-l

, requir's terrain plots for analysis of RPC data and will be used at future S/G inspeetions.

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