ML060110110

Letter Cycle 6 SG ISI Reports Review Summary Letter

ML060110110
Person / Time
Site:	Watts Bar
Issue date:	01/17/2006
From:	Pickett D Plant Licensing Branch III-2
To:	Singer K Tennessee Valley Authority
Pickett , NRR/DLPM, 415-1364
References
TAC MC7485
Download: ML060110110 (5)

Text

January 17, 2006 Mr. Karl W. Singer Chief Nuclear Officer and Executive Vice President Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801

SUBJECT:

WATTS BAR NUCLEAR PLANT, UNIT 1

SUMMARY

OF THE STAFFS REVIEW OF THE STEAM GENERATOR TUBE INSPECTION 15-DAY AND 90-DAY REPORTS FOR THE 2005 OUTAGE (TAC NO. MC7485)

Dear Mr. Singer:

In a letter dated March 23, 2005 (ADAMS Accession No. ML0508700458), Tennessee Valley Authority (TVA, the licensee) submitted the 15-day steam generator (SG) plugging and sleeving report in accordance with Technical Specification (TS) 5.9.9. In another letter dated March 23, 2005 (ML050870457), TVA submitted the F* (F-star) alternate repair criteria report in accordance with TS 5.9.9. By letter dated June 28, 2005 (ML051820267), TVA submitted the 90-day SG voltage-based alternate repair criteria report. By letter dated November 2, 2005 (ML053110148), TVA provided additional information concerning these reports. In addition to these reports, the U.S. Nuclear Regulatory Commission (NRC) staff summarized additional information concerning the 2005 SG tube inspection (i.e., end-of-cycle 6) in a letter dated June 20, 2005 (ML051510040).

As discussed in the enclosed evaluation, the NRC staff has completed its review of the above documents and concludes that the licensee provided the information required by their TSs. In addition, the staff did not identify any technical issues that warrant followup action at this time.

If you have any questions please contact me at (301) 415-1364.

Sincerely,

/RA/

Douglas V. Pickett, Senior Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-390

Enclosure:

As stated cc: see next page

ML0508700458), Tennessee Valley Authority (TVA, the licensee) submitted the 15-day steam generator (SG) plugging and sleeving report in accordance with Technical Specification (TS) 5.9.9. In another letter dated March 23, 2005 (ML050870457), TVA submitted the F* (F-star) alternate repair criteria report in accordance with TS 5.9.9. By letter dated June 28, 2005 (ML051820267), TVA submitted the 90-day SG voltage-based alternate repair criteria report. By letter dated November 2, 2005 (ML053110148), TVA provided additional information concerning these reports. In addition to these reports, the U.S. Nuclear Regulatory Commission (NRC) staff summarized additional information concerning the 2005 SG tube inspection (i.e., end-of-cycle 6) in a letter dated June 20, 2005 (ML051510040).

As discussed in the enclosed evaluation, the NRC staff has completed its review of the above documents and concludes that the licensee provided the information required by their TSs. In addition, the staff did not identify any technical issues that warrant followup action at this time.

If you have any questions please contact me at (301) 415-1364.

Sincerely,

/RA/

Douglas V. Pickett, Senior Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-390

Enclosure:

As stated cc: see next page DISTRIBUTION:

PUBLIC PLB II-2 r/f MMarshall RidsAcrsAcnwMailCenter MMurphy RidsOgcRp AHiser RSola (Hard Copy)

MVaaler RidsNrrPMDPickett MLesser RidsRgn2MailCenter (SCahill)

RidsNrrLACSola RidsNrrDorlPlbii2 KKarwoski ADAMS Accession No.: ML060110110 NRC-106 OFFICE PLBII-2 PLBII-2/LA PLBII-2/PM DCI/CSGB/BC PLBII-2/BC NAME MVaaler RSola DPickett AHiser MMarshall by memo dated DATE 1/13/06 1/13/06 1/13/06 1/17/06 11 / 29 / 05 Mr. Karl W. Singer Tennessee Valley Authority WATTS BAR NUCLEAR PLANT cc:

Mr. Ashok S. Bhatnagar, Senior Vice President Mr. Glenn W. Morris, Manager Nuclear Operations Corporate Nuclear Licensing Tennessee Valley Authority and Industry Affairs 6A Lookout Place Tennessee Valley Authority 1101 Market Street 4X Blue Ridge Chattanooga, TN 37402-2801 1101 Market Street Chattanooga, TN 37402-2801 Mr. Larry S. Bryant, Vice President Nuclear Engineering and Technical Services Mr. Paul L. Pace, Manager Tennessee Valley Authority Licensing and Industry Affairs 6A Lookout Place Watts Bar Nuclear Plant 1101 Market Street Tennessee Valley Authority Chattanooga, TN 37402-2801 P.O. Box 2000 Spring City, TN 37381 Mr. Robert J. Beecken, Vice President Nuclear Support Mr. Jay Laughlin, Plant Manager Tennessee Valley Authority Watts Bar Nuclear Plant 6A Lookout Place Tennessee Valley Authority 1101 Market Street P.O. Box 2000 Chattanooga, TN 37402-2801 Spring City, TN 37381 Mr. Michael D. Skaggs Senior Resident Inspector Site Vice President Watts Bar Nuclear Plant Watts Bar Nuclear Plant U.S. Nuclear Regulatory Commission Tennessee Valley Authority 1260 Nuclear Plant Road P.O. Box 2000 Spring City, TN 37381 Spring City, TN 37381 County Executive General Counsel 375 Church Street Tennessee Valley Authority Suite 215 ET 11A Dayton, TN 37321 400 West Summit Hill Drive Knoxville, TN 37902 County Mayor P. O. Box 156 Mr. John C. Fornicola, Manager Decatur, TN 37322 Nuclear Assurance and Licensing Tennessee Valley Authority Mr. Lawrence E. Nanney, Director 6A Lookout Place Division of Radiological Health 1101 Market Street Dept. of Environment & Conservation Chattanooga, TN 37402-2801 Third Floor, L and C Annex 401 Church Street Nashville, TN 37243-1532 Ms. Ann P. Harris 341 Swing Loop Road Rockwood, Tennessee 37854

EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION TENNESSEE VALLEY AUTHORITY STEAM GENERATOR TUBE INSPECTION REPORTS FOR THE 2005 OUTAGE WATTS BAR NUCLEAR PLANT, UNIT 1 DOCKET NO. 50-390 By letter dated March 23, 2005 (ADAMS Accession No. ML050870458), Tennessee Valley Authority (TVA, the licensee) submitted the 15-day steam generator (SG) plugging and sleeving report in accordance with Technical Specification (TS) 5.9.9. In another letter dated March 23, 2005 (ML050870457), TVA submitted the F* (F-star) alternate repair criteria report in accordance with TS 5.9.9. By letter dated June 28, 2005 (ML051820267), TVA submitted the 90-day SG voltage-based alternate repair criteria report. By letter dated November 2, 2005 (ML053110148), TVA provided additional information concerning these reports. In addition to these reports, the U.S. Nuclear Regulatory Commission (NRC) staff summarized additional information concerning the 2005 SG tube inspection (i.e., end-of-cycle 6) in a letter dated June 20, 2005 (ML051510040).

Watts Bar Unit 1 has four Westinghouse Model D3 SGs. Each SG contains 4674 mill annealed Alloy 600 tubes. Each tube has a nominal outside diameter of 0.75 inch and a nominal wall thickness of 0.043-inch. The tubes were hardroll expanded for the full length of the tubesheet.

The tubes are supported by a number of carbon steel support plates that have drilled holes through which the tubes pass. Below the tube supports is a flow distribution baffle.

The licensee implements alternate tube repair criteria for degradation within the tubesheet region (F-star) and for outside diameter stress corrosion cracking at the tube support plate elevations.

Tubes were repaired using Alloy 800 sleeves in both the end-of-cycle 5 (2003) and end-of-cycle 6 (2005) outages.

The licensee provided the scope, extent, methods, and results of their SG tube inspections for implementation of these alternate tube repair criteria in the documents referenced above.

The licensee also described corrective actions (e.g., tube plugging) taken in response to the inspection findings.

As a result of the review of the reports, the NRC staff has the following comment/observation:

One tube was identified with a 6.32 volt indication. The indication was located in a portion of the tube that passes through one of the tube support plates. The tube was removed from service. This indication was slightly greater than the structural limit

of 5.65 volts. Although the licensee did not assess the structural integrity of this single indication, they did perform an analysis of the probability of burst for the entire tube bundle which indicated that the tube bundle had adequate integrity. In addition, the licensee indicated that this indication would have adequate integrity with respect to main steam line break differential pressures with 95 percent probability using the 95/95 lower tolerance limit on material properties. The staff notes that maintaining tube structural integrity is important since an inherent assumption of the accident induced leakage model is that no tubes burst (rather they simply leak at a leak rate determined based on a correlation between leak rate and bobbin voltage).

The licensee underpredicted the maximum voltage observed during the end-of-cycle 6 inspections. Since the performance criteria were met during the end-of-cycle 6 inspection and predicted to be met for the end-of-cycle 7 inspections, no additional actions were taken during the end-of-cycle 6 inspections. The staff notes that although the performance criteria were met for the end-of-cycle 6, the underprediction in the maximum voltage can be used as an early predictor of a non-conservative methodology.

If the methodology is non-conservative, the projections for end-of-cycle 7 may be nonconservative. Given the margin to the acceptance limits (1 x 10-2 for probability of burst and 3 gallons per minute for accident induced leakage), the conservatism in the analysis methodologies (e.g., flaws are in the free span, the tube supports will deflect during a steam line break), and the planned replacement of the SGs at the end-of-cycle 7, the NRC staff has determined that no additional follow-up is required at this time.

Based on a review of the information provided (i.e., regarding implementation of the alternate tube repair criteria), the NRC staff concludes that the licensee provided the information required by their TSs. In addition, the staff concludes that there are no technical issues that warrant followup action at this time since the inspections appear to be consistent with the objective of detecting potential tube degradation and the inspection results appear to be consistent with industry operating experience at similarly designed and operated units.

Principal Contributor: Ken Karwoski Date: January 17, 2006