ML20056A335
| ML20056A335 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 08/02/1990 |
| From: | Taylor D COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-009, IEB-88-9, NUDOCS 9008060402 | |
| Download: ML20056A335 (3) | |
Text
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1400 Opus Pirce Do:!ners Crove, Illinois 60515 August 2, 1990 1
U.S. Nuclear Regulatory Commission Attn: Document Control Desk Hashington, D.C.
20SSS
Subject:
Braldwood Station Unit 2 Response to NRC Bulletin 88-09 ffRC_00thet No. 50-457
Reference:
NRC Bulletin 88-09, dated July 26, 1988.
l
Dear Sir:
NRC Bulletin 88-09 (Bulletin) requested that addressees establish and implement an inspection program to periodically confirm incore neutron I
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 2.-
The thimble tube inspections are performed using eddy current l
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 1 and Byron Station Units 1 and 2 since the anelysis was bounding for all four units.
It should be noted that the wear scar t
calibration standard which was used for the Braidwood Unit 2 inspections varied from the wear scar standard assumed by the analysis, however, it was verified that the 60% wall loss criteria was still applicable, i
9008060402 900802 PDR:.ADOCK 05000457 4
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i US NRC August 2, 1990 0
i All incore thimble tubes (58 total) for Braidwood Unit 2 were inspected from the seal table to the end of the thimble tubes.
Eighteen (18) thimble tubes recorded evidence of degradation, as detailed in the attached table.
The thimble tube at core location "L13" exhibited a w611 loss indication of approximately 60% and was replaced.
The thimble tubes at locations "B13", "D3", "D12", "E9", "F8",
"H2", "Hil", "K6", "R6", and "R11",
exhibited wall loss indications of greater than 20% but less than 40%.
The thimble tubes at locations "All", "B0", "B8", "C8", "D14", "H13", and "K12" exhibited wall loss indications of less than 20%.
The seventeen (17) thliable tubes with wall loss indications of less than 40% were not expected to exceed the acceptance criteria prior to the next refueling outage for Unit 2 and were therefore not replaced.
For each of the eighteen (18) thlmble tubes exhibiting wall loss indic,tions, the locations of the thimble tube wear indicates that vibration induced fretting was the likely cause.
1 This response completes the reporting requirements of the Bulletin for Braldwood Unit 2.
Please direct any questions that you may have concerning this response to this office.
Respectfully, D.L. Taylor Generic Issues Administritor 1mw/ID129 cc:
A.B. Davis - Regional Administrator, Region III Resident Inspector - Braidwood Station l
S. Sands - NRR Project Manager SUBSCRIBED AND S N }0 ~ ~
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BE E E THIS Ap DAY 989.
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/LUACBMULL1 THIMBLE TUBE APPROX. HALL LOCATION OF THIMBLE CORE LOCATION LQ1S_IRQ1fATION ( U
_tLALL LQSS._
TUBE STATUS All
<20 TOP OF FUEL N0ZZLE INSTALLED B6
<20 TOP OF FUEL N0ZZLE INSTALLED B8
<20 TOP OF FUEL N0ZZLE INSTALLED B13 29 TOP OF LOWER CORE INSTALLED PLATE C8
<20 TOP OF FUEL N0ZZLE INSTALLED D3 29 TOP OF FUEL N0ZZLE INSTALLED D12 29 TOP OF VESSEL INSTALLED PENETRATION SLEEVE D14 (20 TOP OF VESSEL INSTALLED PENETRATION SLEEVE E9 30 TOP Of FUEL N0ZZLE INSTALLED F8 33 TOP 0F FUEL N0ZZLE INSTALLED H2 29 TOP Of FUEL N0ZZLE INSTALLED H11 25 TOP 0F VESSEL INSTALLED PENETRATION SLEEVE H13
<20 TOP Of VESSEL INSTALLED PENETRATION SLEEVE k6 30 TOP OF FUEL N0ZZLE INSTALLED K12
<20 TOP OF FUEL N0ZZEL INSTALLED L13 60 TOP Of VESSEL REPLACED PENETRATION SLEEVE R6 21 TOP OF FUEL N0ZZLE INSTALLED R11 27 TOP OF VESSEL INSTALLED PENETRATION SLEEVE I
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