ML17333A529
| ML17333A529 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 07/30/1996 |
| From: | Fitzpatrick E AMERICAN ELECTRIC POWER CO., INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| AEP:NRC:1059F, NUDOCS 9608050250 | |
| Download: ML17333A529 (5) | |
Text
CATEGORY j.
REGULAT INFORMATION DISTRIBUTION ZSTEM (RIDS) j, ACCESSION NBR:9608050250 DOC.DATE: 96/07/30 NOTARIZED: NO DOCKET ¹ FACIL:50-315 Donald C.
Cook Nuclear Power Plant, Unit 1, Indiana M
05000315 50-316 Donald C.
Cook Nuclear Power Plant, Unit 2, Indiana M
05000316 AUTH.NAME AUTHOR AFFILIATION FITZPATRICK,E.E American Electric Power Co., Inc.
RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
SUBJECT:
Submits info re update on bottom mounted instrumentation thimble tubes.
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NOTES:
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American Electric P r
1 Riverside Plaza Columbus, OH 4321 373 614 223 1000 July 30, 1996 AEP:NRCr1059F Docket Nos.:
50-315 50-316 U. S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.
C.
20555 Gentlemen:
Donald C.
Cook Nuclear Plant Units 1 and 2
BOTTOM MOUNTED INSTRUMENTATION THIMBLE TUBE 1995-6 WEAR INSPECTION RESULTS AND COMMITMENT CHANGE The purpose of this letter is to provide the NRC with an updated status with regard to flow-induced vibrational wear of bottom mounted instrumentation thimble tubes.
Information on this topic was previously provided in our letter AEP:NRC:1059E, dated November 23, 1994.
During the 1992 refueling outages, 15 thimble tubes were replaced in Unit 1 and 22 thimble tubes were replaced in Unit 2.
The replacement thimble tubes were chrome plated at axial locations corresponding to the lower core plate and fuel assembly lower nozzle area.
During the 1995 Unit 1 and 1996 Unit 2 refueling
- outages, an eddy current inspection was performed on all thimble tube After two cycles of operation for each uni.t, the chrome plated thimble tubes show no indications of wear on the plated portions of the tubes.
Active indications of wear continued to be observed on the other thimble tubes.
These results reconfirm our conclusion based on the eddy current inspections during the 1994 refueling outages that the chrome plating is an effective engineered solution to vibration-induced thimble tube wear.
We informed the NRC staff in our November 23, 1994, letter that we intend to implement a design change to replace all present-design thimble tubes. with, chrome-plated tubes.
Although less severe, wear indications have also subsequently, been" observed, at, axial tube locations corresponding to the lower core support dome and diffuser plate in the lower internals.
The new thimble tubes will be chrome plated over a longer length to impede wear from occurring at these additional locations.
9608050250 960730
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U.
S. Nuclear Regulatory Commission Page 2
AEP:NRC:1059F We had anticipated that this design change will be implemented on both units during the refueling outages scheduled to occur in 1997.
However, it is now our plan to implement this change during the 1998 Unit 1 and 1999 Unit 2 refueling outages, thereby postponing implementation for one operating cycle.
The reasons for this scheduling change are 1) an analysis of thimble tube wear rates shows that one additional operating cycle may be achieved without significantly increasing the risk of a thimble tube failure =-and without significant loss of flux mapping locations, and 2) outage planning for other activities which require the lower internals to be removed during the 19>7 refueling outage" makes
-mpiementation of this change les.
desirable until a later date.
In the interim, we will continue to monitor thimble tube wear.
Eddy current inspections will be performed on every thimble tube during each refueling outage to continue to evaluate the effectiveness of the chrome plating and to continue to monitor the wear rates of the non-chrome plated tubes.
Until the present-design thimble tubes are replaced, wear indications on worn thimble tubes will be evaluated each refueling outage to determine if interim corrective actions (i.e.,
shortening of the tube to reposition the wear
- scar, isolating of the tube to contain a
potential through-wall
- leak, or thimble tube replacement),
are necessary.
We will continue to keep the NRC staff informed of developments in this area.
E.
E. Fitz atrick Vice President llg cc:
A. A. Blind W. Beach NFEM Section Chief NRC Resident Inspector
- Bridgman J.
R. Padgett