ML20154N876

Responds to NRC Bulletin 88-009, Thimble Tube Thinning in Westinghouse Reactors. Unit 2 Insp Will Be Performed During Refueling Outage 11 Scheduled for Apr 1990 to Comply W/ Bulletin

ML20154N876
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	09/23/1988
From:	Morgan W COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
5154K, IEB-88-009, IEB-88-9, NUDOCS 8809300029
Download: ML20154N876 (2)

Text

• O Commonwealth Edison One Rrst National Plaza, Chicago, Illinois j>

_v J Address Reply tg Post Omco Box 767

• (y Chica9o, Illinois 60690 0787 September 23, 1988 U.S. Fuclear Regulatory Commission Attre Document Control Desk Mr.shington, D.C. 20555

Subject:

Zion Station Units 1 and 2 Proposed Alternate Schedule for Compliance With NRC Bulletin 88-09 "Thimble Tube Thinning In Westinghouse Reactors" HJtC Dockpt No. 50/295 and 50/304

Reference:

NRC Bulletin No. 88-09: Dated July 26, 1988 Dear Sir The above referenced letter was issued to request that addressees establish and implement an inspection program to monitor incore thimble tube performance.

The bulletin stated that addressees that could not meet the inspection schedule described in Item 2 of Actions Raquestad submit to the NRC an alternative schedule with justification for the requested deviation.

Zion Station Unit 2, which is currently scheduled to enter its tenth l refueling outage on October 13, 1988, is proposing an alternative schedule for l establishing and implementing an inspection program as described in the l bulletin. Justification for the requested deviation is presented below In order to satisfy the schedule of actions requested in the Bttiletin, significant perturbations to the Unit 2 refueling outage schedule would be required. Based on the following technical justification, Zion Station proposes to perform the Unit 2 inspection during the eleventh refueling outage, which is currently scheduled for April of 1990. Zion Unit 1 will comply with the bulletin's requested schedule.

During the 10 cycles of operation on Unit 2 and the 10 cycles of operation on Unit 1, there have been no thimble leaks due to the phenomenon described in the bulletin. This would Indicate that the thimble wear mechanism at Zion is much less severe than that at other plants which have I experienced thimble feilures.

In addition, a modification to the high pressure sea 3s at the seal ,

table caused the thimbles to be withdrawn from their original position by 1 1/2 inches. The main purposes of withdrawing the thimbles were to 1) i establish a new sealing location for the Swage-Loc fittings that made up the seals and 2) accomode.to the size of the new seal design. The withdrawal also j had the effect of displacing the original wear location on thimbles. The wear  !

scar was moved to an area there it is not subjected to additional vibration-induced wear and it allowed for a different region of the thlmble to wear. This new waar location would not be expected to fail for at least eight operating cycles based on the previous thimble performance. The seal table modification was installed during the eighth refueling outage for both units. g 8009300029 880923 PDR ADOCK 05000295 8 0 0 PNU ,

Zion Station would also like to propose a post outage mini-inspection

'of up to ten thimbles that are to be removed from Unit 2 during the upcoming outage. The thimbles are being replaced due to blockage. Zion Station wauld most likely employ the eddy current method t.o determine the amount of wear on both the old and new wear locations. In this way, acceptance criteria for wear can be more thoroughly developed and plant specific wear rates may possibly be established, thus allowing the most appropriate inspection interval to be defined. Since the inspections will be performed in the spent fuel pool, there is also the possibility that more extensive testing, such as profilometry can be performed. This option could enhance the eddy current.

Inspection and may provide a more generic picture of the wear phenomenon.

In the unlikely event that a thimble or thimbles fall during operations, Zion Station is fully prepared to meet this occurrence. Leak detection is provided via a leak detection system attached to a common header to all six Incore ten path drives. In addition, a leak would be detected by the area radiation monitor located inside the seal table room. Other symptoms of leakage would include increased VCT make-up frequency, increased charging flows, a slow drop in pressurizer level, and increased containment or reactor cavity sump run times. A containment entry would be made at the sign of a leak to see if it would be possible to isolate the leak using the isolation valves at the seal table. If this were not possible, the unit would be brought to a safe condition per approved procedures and the manual isolation

! valve would be shut as soon as conditions would permit.

To the best of my knowledge and belief, the statements contained above are true and correct. In some respect these statements are not based on my personal knowledge, but obtained information furnished by other Commonwealth Edison employees, contractor employees, and consultants. Such information has been reviewed in accordance with company practice, and I believe it to be reliable.

Please address any questions that you or your staff may have concerning this response to this office.

Respectfully, W.E. H (L

an fdk [

I Huclear iconsing Admithstrator rf Attachments  ;

cc A.B. Davis Residert Inspector / Zion J. Ramsey HRR l Subscribed and (q p to beforA me thi W > day of DJ . (h W1___, 1988 l /,'ALC.2 0)b_

Not.sry Public I 5154K [

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