ML072750780
| ML072750780 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/05/2007 |
| From: | Moroney B NRC/NRR/ADRO/DORL/LPLII-2 |
| To: | Campbell W Tennessee Valley Authority |
| Moroney B, NRR/DORL, 415-3974 | |
| References | |
| TAC MD5142 | |
| Download: ML072750780 (5) | |
Text
October 5, 2007 Mr. William R. Campbell, Jr.
Chief Nuclear Officer and Executive Vice President Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801
SUBJECT:
SEQUOYAH NUCLEAR PLANT, UNIT 2 - REQUEST FOR ADDITIONAL INFORMATION REGARDING 2006 STEAM GENERATOR TUBE INSPECTIONS (TAC NOS. MD5142)
Dear Mr. Campbell:
By letters dated December 20, 2006, March 20, 2007, and March 21, 2007, Tennessee Valley Authority (TVA) submitted information summarizing the results of the 2006 steam generator tube inspections at Sequoyah Nuclear Plant Unit 2. These inspections were performed during the fourteenth refueling outage.
In order for the staff to complete its review of the information provided, we request that TVA provide responses to the enclosed request for additional information (RAI). Based on discussions with your staff, we understand that you plan to respond to the enclosed RAI by November 9, 2007. If you have any questions about this material, please contact me at (301) 415-3974.
Sincerely,
/RA/
Brendan T. Moroney, Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-328
Enclosure:
Request for Additional Information cc w/encl: See next page
ML072750780 NRR-088 OFFICE LPL2-2/PM LPL2-2/LA CSGB/BC LPL2-2/BC NAME BMoroney RSola AHiser By memo dtd TBoyce DATE 10/04/07 01/03/07 7/31/07 10/05/07
Enclosure REQUEST FOR ADDITIONAL INFORMATION SEQUOYAH NUCLEAR PLANT, UNITS 2 2006 STEAM GENERATOR TUBE INSPECTIONS DOCKET NO. 50-328 By letters dated December 20, 2006 (ML063620407 [Agencywide Documents Access and Management System Accession Number]), March 20, 2007 (ML070870118), and March 21, 2007 (ML070860384), Tennessee Valley Authority, the licensee, submitted information summarizing the results of the 2006 steam generator (SG) tube inspections at Sequoyah Nuclear Plant (Sequoyah)Unit 2. These inspections were performed during the fourteenth end-of-cycle (ECO-14) refueling outage. In addition to these reports, the U.S. Nuclear Regulatory Commission (NRC) staff summarized additional information concerning the 2006 SG tube inspections at Sequoyah Unit 2 in a letter dated February 6, 2007 (ML070320194).
In order for the staff to complete its review of the portions of the reports addressing implementation of the voltage-based and W* repair criteria, we request responses to the following questions:
W* Alternate Repair Criteria (ARC)
- 1. A leakage value was assigned to each indication located within the top 8 inches of the secondary face of the tubesheet (or the bottom of the Westinghouse explosive tube expansion transition). This leakage value was obtained from Figure 6.4-3 of WCAP-14797, Revision 2. Since indications in this region of the tubesheet are plugged on detection at Sequoyah Unit 2, please discuss whether the severity of this indication was such that it would be expected to leak. The NRC staff notes that for indications that are left in service in this region of the tubesheet (at another facility), the correlation used for assigning leakage to these indications is based on a constrained crack leakage model (i.e., it has not approved the correlation in Figure 6.4-3 of WCAP-14797, Revision 2).
- 2. Regarding the operational assessment for the flaws located within the top 8 inches of the tubesheet, it was indicated that the number of detected indications was divided by 0.6 and then the number of tubes plugged was subtracted from this quantity. Since all tubes with indications in this region of the tubesheet should be plugged on detection, it would be expected (based on this methodology) that the operational assessment leakage value for this region would be less than (or equal to) the condition monitoring leakage. However, your operational assessment indicates that the amount of leakage in this region of the tubesheet is more than that calculated during your condition monitoring assessment (i.e., 0.050 gallons per minute (gpm) for condition monitoring versus 0.146 gpm for the operational assessment). Please clarify.
- 3. Briefly discuss the sources of the all other sources of leakage in your operational assessment.
Voltage-Based ARC
- 1. An assessment of voltage-dependent growth was provided in Figure 3-18 of the March 20, 2007 letter. This assessment appears to be based on the composite number of indications from all four steam generators. Since operating experience indicates that voltage dependent growth can occur in a subset of the steam generators (i.e., not all of them), please discuss whether voltage dependent growth was observed in any of the steam generators. If so, discuss any planned corrective action.
- 2. In Table 4-4 of the March 20, 2007, letter, one indication measured 1.6 volts with a worn probe and when this indication was re-inspected with a non-worn probe there was no distorted support indication at this location. Please discuss any insights on why this indication was no longer present (given the original magnitude of the indication from the worn probe). In addition, discuss whether this area was inspected with a rotating probe to confirm the absence of degradation at this location.
- 3. In steam generator 1, the tube in row 3 column 15 had a 2.24 volt indication at the first hot-leg tube support plate elevation during the EOC-13 outage. During the EOC-14 outage, there was no bobbin indication at this location, but a rotating probe detected an indication and the inferred bobbin voltage was 1.57 volts. Please discuss why this indication was not plugged during the EOC-13 outage (i.e., was it not confirmed with a rotating probe). In addition, please discuss why there was no bobbin indication during the EOC-14 outage despite a relatively high inferred bobbin voltage of 1.57 volts.
- 4. In steam generator 2, two tubes (row 3, column 5; and row 7 column 20) had relatively high inferred bobbin voltages during the EOC-14 outage. These indications were detected with a bobbin coil during the EOC-13 outage. Please discuss why these indications were not detected with the bobbin coil during the EOC-14 outage given their relatively large inferred voltages and the past presence of indications at these locations. Please address the same question for the indication at the seventh hot-leg tube support in steam generator 3, row 42, column 53.
- 5. Table 4-4 of the March 20, 2007, letter indicates that a 1.03 volt indication was not detected with a worn probe and was only detected when re-inspected with a new probe (steam generator 3, row 44, column 59, first hot-leg tube support). Please discuss any insights on why this 1.03 volt indication was not detected even with the worn probe (i.e., were there any complicating factors associated with this signal or was this just a missed indication as a result of the probability of detection).
- 6. The March 20, 2007, letter indicates that when the final metallurgical examination from a tube removed from a steam generator during the EOC-14 outage is complete, the results will be provided to the NRC staff. Please discuss the schedule for submitting this report.
William R. Campbell, Jr.
SEQUOYAH NUCLEAR PLANT Tennessee Valley Authority cc:
Mr. Ashok S. Bhatnagar Senior Vice President Nuclear Generation Development and Construction Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Mr. James R. Douet Senior Vice President Nuclear Support Tennessee Valley Authority 3R Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Mr. Walter M. Justice II Interim Vice President Nuclear Engineering & Technical Services Tennessee Valley Authority 3R Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Mr. Timothy P. Cleary, Site Vice President Sequoyah Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Soddy Daisy, TN 37384-2000 General Counsel Tennessee Valley Authority 6A West Tower 400 West Summit Hill Drive Knoxville, TN 37902 Mr. John C. Fornicola, Manager Nuclear Assurance Tennessee Valley Authority 3R Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Ms. Ann P. Harris 341 Swing Loop Road Rockwood, TN 37854 Ms. Beth A. Wetzel, Manager Corporate Nuclear Licensing and Industry Affairs Tennessee Valley Authority 4X Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801 Mr. Glenn W. Morris, Manager Licensing and Industry Affairs Sequoyah Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Soddy Daisy, TN 37384-2000 Mr. Christopher R. Church, Plant Manager Sequoyah Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Soddy Daisy, TN 37384-2000 Senior Resident Inspector Sequoyah Nuclear Plant U.S. Nuclear Regulatory Commission 2600 Igou Ferry Road Soddy Daisy, TN 37379 Mr. Lawrence E. Nanney, Director Division of Radiological Health Dept. of Environment & Conservation Third Floor, L and C Annex 401 Church Street Nashville, TN 37243-1532 County Mayor Hamilton County Courthouse Chattanooga, TN 37402-2801 Mr. Robert H. Bryan, Jr., General Manager Licensing and Industry Affairs Tennessee Valley Authority 4X Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801