ML20065M797
| ML20065M797 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 12/06/1990 |
| From: | Tuckman M DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-009, IEB-88-9, NUDOCS 9012110212 | |
| Download: ML20065M797 (4) | |
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linke thirer Conspany J'S Ittntn Mulrar l'rt*du. tuat llrpt Ik e b estdtnt l'() lin.t 1007 Nuclear Operations Charinlic. N C 3 201-100?
(IOlll?%hil DUKEPOWER December 6, 1990 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C.
20555
Subject:
Catawba Nuclear Station, Unit 1 Docket No. 50-413 NRC Bulletin No. 88-09 Incore Instrument Guide Thimble Wear Examination in H. B. Tucker's retponse to NRC Bulletin 88-09 for Catawba Unit 1 nated March 16, 1989, it was stated that the next Incore Instrument Guide Thimble Wear Examination would take place at the End of-Cycle (EOC) 5.
At that time, Westinghouse had quoted a 10% uncertainty on the Eddy Current Testing Process. This 10% uncertainty was included in the decision to re-examine the thimble tubes at the EOC-5.
Westinghouse, through work on an Owners Group project, has determined that the 10%
uncertainty can be removed from the wear calculations.
Based on this information, Duke has re-calculated the Catawba Unit I wear predictior..
The new prediction shows that the thimbles should be re-examined at the EOC-6 in=tead of EOC-5.
This prediction may be updated again once the Westinghouse Owners Group Report is released.
Find attached the new wear calculations for Catawha Unit 1.
Very truly yours,
, Se M. S. Tuckman, Vice President l
Nuclear Operations l
CRL/7/lcs l
s 90.12110212 901206
<PDR ADOCK 05000413 O
PDC C2lf
///
U. S. Nuclear Regulatory Commission December 6, 1990 Page 2-cci Mr. W. T. Orders-NRC Resident Inspector Catawba Nuclear Station Mr. S. D. Ebneter
' I Regional Administrator, Region I"i O. S. Nuclear Regulatory Commission 101 Marietta Street, NW, Suite ?.900 t
Atlanta, Georgia 30323 Mr. R. E. Martin Office of Nuclear Reactor dagulations-U. S. Nuclear Reg'41atory Commission One White Flint borth, Mail Stop 9113 Washington, D.C.
20555 Mr, Stan Kirslis office of Nuclear Reactor Regulations U. S. Nuclear Regulatory Commission One White Flint Nortii. !iall Stop 9113 Washington, D.C.
20555 l
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Catawba Unit 1 Incore Instrument Guide Thimble Wear Examination The first Eddy Current Test-(ECT) occurred at the EOC-3 on Catawba 1.
The maximum wear detected was 55% through wall at location M-07.- This is the only location that showed any detectable wear. Wear occurs to the thimble tubes anytime the reactor coolant pumps are running (Modes 1-4).
Based on the data below, it is clear that the ratio of Mode 1-4 days to effective full power days (EFPD) is high for'the unit's initial cycle.
The average ratio for cycles 2-4 is 1.16.
This value will be used to estimate future cycles.
3 No. of Days In Cycle Modes 1-4 EFPD Ratio 1
594 336 1.77 2
351 275 1.28 3
313 300 1.04 4
370 320 1.16 Calculating the wear rate, WR, based on thimble M-07 results in the following:
WR = WL/ND Where:
WR = Wear rate WL = Maximum Indicated Wear. Loss from ECT Inspection ND = Number of Days in Modes.1 l l
A linear wear extrapolation for the numberf of additional days in Modes 1-4 before the thimble wall loss exceeds a 60% wall loss criterion is given by:
Where:
WLP = Predicted Wall Loss NDA = Number af Additional Days-in Modes 1-4 The calculated wear rate, WR, based on M-07 result is given by the-following:
WR = 55%/1258 days = 0.04372% per day in Modes 1-4 l
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Using this calculated ware rate, it is possible to estimate when other thimbles may reach the 60% wall loss criteria. This is then used to establish the thimble inspection interval.
NDA = (60% - WL)/WR-NDA = (60%-- 0%)/0.04372% per day in Modes 1-4 NDA = 1372 additional days in Modes 1-4 Note that a value of 0% was used for WL in the above equation.
This value was used since the wear prediction is on thimbles that have no wear. indicated-at the last inspection (it is not necessary'to predict wear on M-07 since it has been isolated).
Therefore, after 1372 additional days in Modes 1-4, Catawba 1 should be inspected. Using future estimates of Catawba 1 cycle lengths, the inspection time can be be determined.
Future. Catawba 1 "ycle Estimates EFPD No. of Days In Accumulative Including Modes'1-4
' Days In-Cycle
+10 Window (EFPD *1.16)
.Modos 1-4 4*
320 370
'370 5
310 360 730 l
6 360 418' 1148 7
360 418 1566
- Cycle 4 data is actual data.
Catawba 1 can operato to the EOC-6 before needing inspection.
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