ML20245H735
| ML20245H735 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 06/26/1989 |
| From: | Rebecca Barr PORTLAND GENERAL ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-009, IEB-88-9, NUDOCS 8906300073 | |
| Download: ML20245H735 (5) | |
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i' David W. Cockfield Vice President, Nuclear June 26, 1989 Trojan Nuclear Plant Docket 50-344 License NPF-1 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington DC 20555
Dear Sir:
Nuclear Regulatory Comission (NRC)Bulletin 88-09 Thimble Tube Thinning in Westinghouse Reactors NRC Bulletin 88-03 requested that licensees establish and implement an inspection program to monitor thimble tube wear and submit a written response confirming these actions within 30 days of completion of the thimble tube inspections.
Portland General Electric Company completed the thimble tube inspections scheduled during the 1989 Refueling Outage on May 26, 1989.
Attached is a report that includes a description of the inspection program, the results of the inspection, and corrective actions taken for thimble tubes that did rot meet the acceptance criteria.
Sincerely, i
Attachment c:
Mr. John B. Martin Mr. R. C. Barc Regional Administrator, Region V NRC Resident Inspector U.S. Nuclear Regulatory Commission Trojan Nuclear Plant Mr. William T. Dixon State of Oregon Department of Energy Subscribed and sworn to before me this 26th day of June 1989.
8906300070 190626 PDR ADOCK 05000344 7
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1 Notary Public of Oregon
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Trojan Nuclear Plant Document Control Desk Docket 50-344 June 26, 1989 License NPF-1 Attachment Page 1 of 4' i
TROJAN THIMBLE TUBE INSPECTION PROGRAM Description The Thimble Tube Inspection Program utilizes eddy current measurements on the thimble tubes to assess wall thinning and location of wear.
Measurements were taken by Universal Testing Laboratories (UTL) using state-of-the-art equipment (MIZ-18) and methods. UTL has experience in taking similar measurements at other plants. Westinghouse Electric Corporation provided an independent review of the results.
The thimble tube inspections were performed on May 25 and.26, 1989; these were the first such measurements ever taken at Trojan. A 65 percent wall thinning was established as the maximum allowable wear and was based on an analysis performed by Westinghouse. An allowance for 10 percent wall j
thickness measurement uncertainty was used, so the measurements are l
i compared to a 55 percent wall thinning criterion. A wall thinning of 20 percent is the minimum detectable wear.
The thimble tubes at Trojan were retracted in 1985 by approximately 3/4-inches to accommodate an improved seal table seal design. No thimble tube leaks have ever occurred at Trojan.
The next thimble tube inspection is scheduled for no later than the 1992
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Refueling Outage. This is based on the conservative assumption that all
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the wear experienced to date has occurred since the thimble tubes were repositioned in 1985, calculating a yearly wear rate for each tube and projecting the amount of wear to occur in this interval. This also considers the retubing that is planned, as discussed in the corrective action below.
Subsequent inspections are tentatively scheduled at three year intervals, depending on the results of the inspections.
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Results Nine tubes of a total of 58 were identified with wall thinning greater than 55 percent. A total of 20 tubes experienced wear greater than 40 percent, and a total of 28 tubes experienced wear greater than l
30 percent.
i The measurement results are shown in Table 1 and Figure 1.
The wear is occuring in the portion of the thimble tube at the bottom of the fuel assembly and is caused by flow induced vlbration of the tube against the l'
fuel assembly instrumentation thimble entrance wall.
Corrective Action The nine thimble tubes with wear greater than 55 percent have been isolated by capping them. All tubes with wear greater than 40 percent i
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' Trojan Nuclear Plant Document Control Desk Docket 50-344 June 26, 1989 l
License NPF-1 Attachment l
Page 2 of 4 (including the nine isolated tubes) were retracted approxitaately two inches to place a different segment of the tube at the axial location i
experiencing the wear. All 28 tubes with wear greater than 30 percent will be replaced with new tubes of slightly greater wall thickness (.0515 inches versus'.0495 inches currently). The retubing has not yet been definitively scheduled but will occur as soon as practicable.
The Trojan Technical Specifications (TTS) require' that at least 44 of the 58 flux, thimbles be operable (75 percent).
Plugging the nine tubes with wear greater than 55 percent will leave at most 49 available flux thimbles. A License Change Application (LCA) will be submitted to the Nuclear Regulatory Commission (NRC) to require at least 29 of the flux I
thimbles (50 percent) to be operable.
Portland General Electric Company is currently performing analyses in support of this reduction and will submit the results with the LCA.
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' Docket 50-344 June 26,L1989 License NPF-1 Attachment Page 3'of'4 TABLE'1 Thimble Tube Inspection Program Summary of Measured Wear Wear Ranne -
Number of Thimbles Core Location (% wear)-
Not' detectable 21 F1, N2,"K2, H2, H3, F3, P4, i.
'G5,'J7,lL8, F8, L10, J10..
D10,~Hil,-K12, L13.B13,.
N14.:J14, L15 20%-29%'
9 N4(28), R6(28), N6(24),
F7(25), J8(23). C8(28),
E9(24), G12(26). N13(27)-
30%-39%
8 D3(39)..L5(33), R8(39),,
N8(35), G9(39), D12(35)',.
D14(36), H15(34)-
p 40%-49%
5 H4(49). B6(43),'B8(44),
H13(47),'A11(42) 50%-55%
6 J1(52), ES(51), K6(54),
A9(55), R11(54), L11(53).
56%-59%
O None.
60%-69%
3 H6(67), D8(63), E11(64) 70%-79%
3 B3(74), C5(70), F14(78) 80%-100%
3 M7(82), C7(88), P9(91)
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Trojan Nuclear Plant Document Contrb1 Desk Docket 50-344 June 26. 1989 License NPF-1 Attachment Page 4 of 4 FIGURE 1 Flux Thimble Core Locations and Measured Wear (%)
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