ML20066D720

Informs NRC of Decision to Withdraw Commitment to Replace Four 10CFR50.49 Coaxial Cables W/Double Jacketed Cable. Single Jacketed Coaxial Cables Will Not Be Replaced as Previously Committed

ML20066D720
Person / Time
Site:	Browns Ferry
Issue date:	01/14/1991
From:	Medford M TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TAC-00421, TAC-421, NUDOCS 9101150341
Download: ML20066D720 (3)

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'JAN 141991 U.S. Nuclear Regulatory Commission ATTN:

Document Control Desk Washington, D.C.

20555 Centlement In the Matter of

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Docket No. 50-250 Tennessee Valley Authority

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BROWNS FERRY NUCLEAR PLANT (BFN) - UNIT 2 - CABLE INSTALLATION ISSUES -

DISPOSITION OF 10 CFR.50.49 COAXIAL CABLES (TAC 00421)

Reference:

NRC letter to TVA dated December 22, 1989 - Summary of Meeting with TVA Held on December 22, 1989 to Discuss BFN's Unit 2 Cable' Installation Program The purpose of this letter is to inform NRC of TVA's decision to withdraw a commitment to replace four 10 CFR 50.49 coaxial cables with double jacketed coaxial cable. The commitment to replace these coaxial cables at BFN resulted from meetings with NRC on December L8, l989 (refer to TVA slides in referenced letter) and February 13, 1990.

This commitment stemmed from visual and laboratory inspection of cables removed from conduits at Watts Bar Nuclear Plant which revealed damage to the outer jacket of the coaxial cable. The damaged resulted in a reduction of the jacket thickness to a value which was less than 80 percent of the manufacturer's nominal thickness.

The concern from this type of damage is the potential moisture migration along the cables' braided shield to the connector. This moisture migration reduces the insulation resistance between the conductor and the coaxial shield.

This failure will not occur during normal operation, but could occur during accident conditions which create a harsh environment.

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-The four 10 CFR 50.49 coaxial cables which TVA had previously committed to' replace are associated with the Victoreen radiation monitors. These

. coaxial cables are-the only single jacketed coaxial cables located in 10 CFR-50.49l applications for Unit 2. 'The cables inside containment to the monitors were environmentally qualified and supplied with the monitors. The cables are enclosed in scaled stainless steel tubing-from the-containment penetration to the monitors ensuring that no moisture can reach'the cable. Additionally, the coaxial cable associated with the-Victoreen radiation monitors are comprised of short runs (less than 75 feet) and were installed by pushing the cable intn the tubing in accordance with Victoreen Technical Manual'for High Range Containment h

Monitors. Since no additional cables will be added to these sealed tubes because they are dedicated to the Victoreen radiation monitors and considering the installation method used, cabic pullby is not a concern.

Due to-these considerations, there is a low probability that the coaxial cables-jacket-incurred damage.

j The coaxial cables outside' containment for these monitors do not have to operate for :any _ accidents outside containment. They are only required to operate-during-. Loss of Coolant Accident (LOCA)/High Energy Line Break conditions inside containment'and would not be exposed to a' steam environment during-the accident 'in which they are required to remain -

functional.

The moisture' intrusion problem identifled-at WBN for 10 CFR 50.49 coaxial cable-does not exist for the radiation monitors at BFN. Existing design requirements prevent-future installation of.10 CFR 50.49 single jacketed

.1 coaxial cable'which is susceptible to the-WBN coaxial cable failure mechanism.

~ Based on1the reasons above and the specific applications at BEN, BFN has

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decided not to replace the. single jacketed coaxial cables as previously committed.

There are no commitments contained in this submittal.

If you have any

. questions, please telephone Patrick P. Carter, BFN, Site Licensing,

'(205) 729-2566.

Very.truly yours, TENNESSEE VALLEY AUTHORITY n??.4 Maes:

M. O. Medford cc: 'See page 3

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-U.S. Nuclear RegulatoryLCommission' JAN 141991 f,-;

-cc:- Ms'. S. C.2 Brack, Deputy Director Project Directorate:IT -U.S. Nuclear Regulatory Commission:

One' White Flint North' N

11555-Rockville Pike, Rockville. MarylandE20S52-

-NRC Resident Inspector Browns Ferry Nuclear-Plant

' Route 12, Box 637 Athens,-Alabama 35609-2000

'Mr. Thierry M.~.Ross, Project Manager U._S._-Nuclear l Regulatory Commission One White Flint, North.

11555_Rockville Piku Rockville, Maryland'20852'

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Mr. 'B.?AL Wilson, Project Chief

-U.S.fNuclear-Regulatory Commission RegionLII=

101-Marietta Street, NW, Suite 2900

! Atlanta, Georgia 30323--

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