ML081290185
| ML081290185 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/23/2008 |
| From: | James Smith Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML081290185 (8) | |
Text
Tennessee Valley Authority, Post Office Box 2000, Sodciy-Daisy, Tennessee 37384-2000 April 23, 2008 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:
In the Matter of ) Docket No. 50-327 Tennessee Valley Authority (TVA) )
SEQUOYAH NUCLEAR PLANT (SQN) - UNIT 1 CYCLE 15 (U1C15) - 180-DAY -
STEAM GENERATOR (SG) INSPECTION REPORT In accordance with the requirements of SQN Unit 1 Technical Specification 6.8.4.k, Steam Generator Program and Technical Specification 6.9.1.16, Steam Generator Inspection report, TVA is submitting the 180-day report that includes the results of inservice inspections performed on Unit 1 SGs during the U1C15 refueling outage.
There are no commitments contained in this letter.
Please direct questions concerning this issue to me at (423) 843-7170 or Russell R. Thompson at (423) 843-6672.
Sincerely, James D. Smith Manager, Site Licensing and Industry Affairs Enclosure cc: See page 2 Prinjec on recycled paper
U.S. Nuclear Regulatory Commission Page 2 April 23, 2008 cc (Enclosure):
Mr. Thomas H. Boyce, Senior Project Manager U.S. Nuclear Regulatory Commission Mail Stop 08G-9a One White Flint North 11555 Rockville Pike Rockville, Maryland 20852-2739
Tennessee Valley Authority Sequoyah Nuclear Plant Unit 1 Cycle 15 Refueling Outage October 2007 180 Day Steam Generator Inspection Report Prepared by:
Verified by:
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SQN Unit 1 Cycle 15 180-Day Report In accordance with Technical Specification 6.8.4.k, Steam Generator Program and Technical Specification 6.9.1.16, Steam Generator Tube Inspection Report, this report documents the results of the Unit 1 Cycle 15 (U1C15) steam generator (SG) tube inservice inspection. The following list is the required scope of the 180-day report.
- 1. The scope of inspections performed on each SG.
EDDY CURRENT EXAM TYPE (Exams) RSG 1 RSG 2 RSG 3 RSG 4 Total Full Length Bobbin (.610 coil) 2477 2481 2479 2480 9917 Full Length Bobbin (.590 coil) 42 42 42 42 168 Partial Length Bobbin (.570 coil HTE-VS3) 123 122 123 123 491 Expansion Full Length Bobbin (.610 coil) 479 286 116 0 881 Predetermined Diagnostic Plus Point 2 3 29 1 35 Diagnostic/PID Plus Point 0 1 1 1 3 Total Exams Completed 3123 2935 2790 2647 11495 Total Tubes Examined 3121 2933 2775 2645 11474 In accordance with the U1C15 Degradation Assessment, expansion sample examinations were performed in SGs 1, 2, and 3. No expansion sample was required in SG 4.
- 2. Active Degradation Mechanisms found.
INDICATIONS (Tubes) RSG 1 RSG 2 RSG 3 RSG 4 Total U-Bend Support Wear 32 2 11 2 47 Total 32 2 11 2 47
- 3. Nondestructive examination technique utilized for each degradation mechanism.
Bobbin coil examinations were utilized for the detection of U-bend Support Wear.
- 4. Location, orientation (linear), and measured sizes (if available) of service induced indications.
Refer to Table 1
SQN Unit 1 Cycle 15 180-Day Report
- 5. Number of tubes plugged during the inspection outage for each active degradation mechanism.
PLUGGING STATUS RSG 1 RSG 2 RSG 3 RSG 4 TOTAL Previously Plugged Tubes 14 6 6 5 31 Tubes Plugged by Damage Mechanism U-Bend Support Wear 0 0 0 0 0 Total Plugged Cycle 15 0 0 0 0 0 Total Tubes Plugged 14 6 6 5 31 Plugged Tube Percentage 0.28% 0.12% 0.12% 0.10% 0.16%
- 6. Total number and percentage of tubes plugged to date.
Refer to the response to Number 5 above. The U-bend Support Wear indications were tapered along the tube axially.
- 7. The results of condition monitoring, including the results of tubes pulls and in-situ testing.
No tube pulls or in-situ pressure tests were performed.
U-BEND SUPPORT WEAR Structural Integrity The SQN U1C15 degradation assessment predicted, based on past indications and growth rate data, that 25 tubes could be preventively plugged. A total of 51 indications in 47 tubes were detected. None exceeded the plugging limit of 40 percent. The U-bend Support Wear was assumed to have grown from 0 percent through wall over the last 2 fuel cycles. Using these growth rates, a repair limit of 30 percent was calculated which would ensure that a safety factor of 3 would be maintained (with a 95 percent probability) until the next planned inspection during the U1C18 refueling outage. Condition monitoring assumed the axial length of the U-bend Support Wear indication to be the width of the U-bend Support (i.e., 2 inches).
All indications were a fraction of this length. The limiting indications were 16 percent maximum depth. The limiting tubes were in SG1, Row 76, Col 100 at VS2-0.97, Row 85, Col 67 at VS4+0.91, and Row 87, Col 73 at VS2+1.28. The EPRI, Steam Generator Degradation Specific Management Flaw Handbook, Section 5.3.3, Axial Thinning with Limited Circumferential Extent, equations were utilized to calculate the burst pressure. The calculated 95th percentile lower limit burst pressure was 6958 psig (3P is 4114 psig). The largest amplitude U-bend Support Wear indication was 0.58 volts, and therefore did not exceed the in-situ pressure testing leakage screening criteria of 7.9 volts. All U-bend Support Wear indications met condition monitoring performance criteria. Zero indications exceeded the 40 percent plugging limit and zero indications exceeded the 30 percent repair limit.
SQN Unit 1 Cycle 15 180-Day Report Leakage Integrity During the previous two fuel cycles, the Unit 1 operational primary to secondary leakage was below detection. The majority of the indications detected during U1C15 were less than 0.5 volts which in accordance with EPRI Steam Generator In-Situ Pressure Test Guidelines Revision 2 (TR-1007904), dated August 2003, Section B.3.4 is a quick screen for structural and leakage integrity, and therefore provides a 95 percent probability that none of the indications would leak should a postulated main steam line break have occurred. The greatest through wall was 16 percent.
The associated 95th percentile lower limit burst pressure was 6958 psig. The equations utilized for burst pressure determine the ligament tearing pressure or the pressure at which a partial through-wall indication goes through-wall (i.e., pop-through). If an indication has a 95 percent probability of not going through wall at 6958 psig, then it should not go through wall at the Main Steam Line Break pressure of 2405 psig. This provides additional confidence that no leakage would occur should a postulated main steam line break occur.
- 8. The effective plugging percentage of all plugging in each SG.
Refer to the response to Number 5 above.
SQN Unit 1 Cycle 15 180 Day Report Table 1 List of Indications The indications below were characterized as U-bend Support Wear. They were detected by bobbin coil. The associated maximum depth and voltage are included. The plugging limit at SQN Unit 1 is 40 percent through wall (TW).
SG ROW COL LOCATION %TW VOLTS CHARACTERIZATION RESOLUTION In service <30% Repair 1 68 76 VS2-.26 7 0.21 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 75 73 VS3+.80 9 0.28 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 78 78 VS2+.91 8 0.23 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 83 77 VS2+.91 10 0.32 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 87 73 VS2+1.28 16 0.58 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 87 73 VS3+1.00 15 0.51 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 87 75 VS2+1.14 13 0.4 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 87 81 VS4-1.11 15 0.53 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 88 70 VS4-1.11 13 0.39 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 90 70 VS4-1.00 13 0.37 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 92 70 VS2-.91 9 0.24 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 92 70 VS4+1.00 15 0.45 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 95 77 VS4-1.11 9 0.27 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 96 76 VS3+1.28 11 0.35 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 55 115 VS3-.91 15 0.47 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 61 85 VS2-1.09 8 0.21 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 67 87 VS3-.92 6 0.19 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 76 90 VS2+.86 9 0.26 U-BEND SUPPORT WEAR Limit In service <30% Repair 4 68 64 VS3-.83 10 0.37 U-BEND SUPPORT WEAR Limit In service <30% Repair 4 97 55 VS4-.83 8 0.29 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 69 59 VS3+.77 10 0.31 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 70 66 VS4-1.03 15 0.53 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 74 48 VS3-.88 6 0.17 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 83 45 VS4-.91 6 0.15 U-BEND SUPPORT WEAR Limit In service <30% Repair 2 20 80 VS3-.06 14 0.45 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 83 49 VS2+.77 7 0.2 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 84 64 VS4+1.03 11 0.31 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 85 65 VS4+.80 11 0.33 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 85 67 VS4+.91 16 0.54 U-BEND SUPPORT WEAR Limit 1 88 52 VS4-.91 8 0.22 U-BEND SUPPORT WEAR In service <30% Repair 1
SQN Unit 1 Cycle 15 180 Day Report Table 1 List of Indications SG ROW COL LOCATION %TW VOLTS CHARACTERIZATION RESOLUTION Limit In service <30% Repair 1 92 52 VS3+.83 6 0.17 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 92 68 VS4+.62 14 0.41 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 93 65 VS2+.85 9 0.25 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 95 63 VS3-.63 13 0.42 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 95 63 VS4-1.14 11 0.33 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 98 66 VS3+.82 8 0.24 U-BEND SUPPORT WEAR Limit In service <30% Repair 2 92 42 VS2-.74 8 0.23 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 62 112 VS3+.77 13 0.41 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 66 110 VS3+.80 11 0.34 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 76 100 VS2-.97 16 0.56 U-BEND SUPPORT WEAR Limit In service <30% Repair 1 92 88 VS4-.85 11 0.33 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 73 75 VS3+.74 7 0.23 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 79 79 VS2-.86 7 0.23 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 79 79 VS3+.86 8 0.27 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 80 72 VS4-.83 9 0.31 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 85 69 VS4+.83 10 0.35 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 87 63 VS2+1.07 9 0.28 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 87 65 VS3+.95 12 0.4 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 89 71 VS4+1.01 8 0.26 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 97 71 VS3+.74 8 0.26 U-BEND SUPPORT WEAR Limit In service <30% Repair 3 98 56 VS4-1.06 12 0.39 U-BEND SUPPORT WEAR Limit