ML20005G450
| ML20005G450 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 01/08/1990 |
| From: | Richter M COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 0034K:1, 34K:1, IEB-88-009, IEB-88-9, NUDOCS 9001190169 | |
| Download: ML20005G450 (2) | |
Text
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COIRIROR M N 4
Ora Fast MDonal Plaza. Chcago, liknois E
Kfdress Reply to. Post Offce Box 7C Chcago, hhnois 60690 0767 January 8, 1990 ti U.S. Nuclear Regulatory Comunission Attn Document Control Desk
. Washington, D.C.
20$55
Subject:
Braidwood Station Unit 1 Response to NRC Bulletin 88-09 NRC Docket No. 50-456 Reference NRC Bulletin 88-09, dated July 26, 1988.
Dear Sirt NRC Bulletin 88-09 (Bulletin) requested that addressees establish and implement an inspection program to periodically confirm incore neutron monitoring system thimble tube integrity at Westinghouse designed nuclear power reactors.
In accordance with the Bulletin, this letter presents the details of the incore thimble tube inspection program (Bulletin Action 1) and the results of the thimble tube inspections (Bulletin Action 2.a) performed during the first refueling outage for Braidwood Unit 1.
The thimble tube inspections are performed using eddy current testing. The inspections will be performed at every refueling outage until sufficient data has been accumulated to generate a baseline and correlation for thimble tube thinning. At that time, the inspection frequency will be evaluated and may be adjusted as applicable.
It is expected that at least two inspections will be necessary to accumulate sufficient data before considering any change in inspection frequency.
To establish the thimble tube wear acceptance criteria, a finite element structural analysis was utilized to evaluate the stresses in a worn bottom mounted instrumentation thimble tube. The wear scar geometry was assumed to be a flat bottom scar localized on one side of the thimble.
It was determined that a sixty percent (60%) maximum wall loss is acceptable in accordance with ASME Code material allowables, therefore, a wall loss criteria of 60% was adopted. This wall loss criteria (60%) is also applicable for Braidwood Unit 2 and Byron Station Units 1 and 2 since the analysis was bounding for all four units.
It should be noted that the wear scar calibration standard which was used for the Braidwood Unit 1 inspections varied from the wear scar standard assumed by the analysis, however, it was verified that the 60% wall loss criteria was still applicable.
All incore thimble tubes (50 total) for Braidwood Unit 1 were inspected from the seal table to the end of the thimble tubes.
Five (5) thimble tubes recorded evidence of degradation, as detailed in the following table.
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3001190169 900108 PDR ADOCK 05000456 o
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THIMBLE TUBE APPROX. WALL LOCATION OF THIMBLE' CDRE_ LOCATION LOSS INDICATION (1)
_WA1.1. LOSS -
TUBE STATUS All 18 TOP OF FUEL N0ZZLE INSTALLED g
B13 43 TOP OF VESSEL REPLACED PENETRATION SLEEVE
.D12 18 TOP OF VESSEL INSTALLED PENETRATION SLEEVE l
i E11 62 TOP OF LOWER CORE REPLACED SUPPORT PLATE J
H4 20 TOP OF FUEL N0ZZLE INSTALLED l
J The thimble tubes at core locations "B13" and " Ell", which exhibited wall loss 1
indications of approximately 43% and 62%, respectively, were replaced during the refueling outage. The thimble tubes at core locations "All", "D12" and i
"H4" exhibited wall loss indications of approximately 18% 18% and 20%,
1 respectively. These thimble tubes are not expected to exceed the acceptance i
criteria prior to the next refueling outage for Unit 1, and were not replaced. For these five (5) thimble tubes, the location of the thimble tube j
wear indicates that vibration induced fretting may have caused the wall loss.
This response completes the requirements of the Bulletin for Braidwood Unit 1.
Please direct any questions that you may have concerning
-l this response to this office.
j Respectfully, j
l e
M.H. Richter Generic Issues Administrator cci A.B. Davis - Regional Administrator, Region III Resident Inspector - Braidwood Station S. Sands - NRR Project Manager
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