ML20028B080

Revised Final Deficiency Rept Re Rockbestos Coaxial Cable Failure.Original Disposition Was to Replace Cable W/Cables Meeting Environ Requirements.Investigation Revealed Cable Not Available.Continued Use of Original Cables Recommended

ML20028B080
Person / Time
Site:	Fermi
Issue date:	11/16/1982
From:	Nells D DETROIT EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8211290433
Download: ML20028B080 (2)

Text

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Novenber 16, 1982 EF2-60507 Mr. Janes G. Keppler, Regional Administrator Region III U.S. Nuclear Regulatory Ccumission 799 Roosevelt Road Glen Ellyn, Illinois 60137

Subject:

Final Report of 10CFR50.55(e) Item on Rockbestos Coaxial Cable Problem (#45)

Dear Mr. Keppler:

This is an amendment to revise the disposition reported on the final report of this item suhttitted November 20, 1981, on Rockbestos Coaxial Cable short-ing the center conductor to the braided shield.

Rockbestos coaxial cable RSS-6 series 100 through 112 may be subject to failure at temperatures above 230 F according to the manufacturer.

The four cables (Rockbestos Catalogue "RSS-6-110") installed inside the primary containment were for Source Range Monitor (SRM) circuits. The original disposition was to replace these cables with cables meeting the environmental requirements. Further investigation by the Detroit Edison Environmental Qualification Group for an acceptable alternate triple shielded cable, required per GE for the SRM circuits to allow proper SRM cperation, revealed that acceptable replacement cable was not available.

Since the SRM circuits involved are nct safety related, continued use of these cables was recamended.

Ten additional cables (Rockbestos Catalogue "RSS-6-103") used for main steam line radiation monitors, were located in the steam tunnel area. The Environ-nental Qualification Group has recomnended the continued use of the existing cables inside the steam tunnel. The basis for retaining these cables was determined by the nature of the cable failure mechanism and the occurrence of the environmental conditions that caused the failure. The failure of the cable i

i involves a short circuit of the conductor to the shield during elevated tem-peratures. A failure of this type would cause the radiation monitor to trip, similar to a low level trip. The low level trip, however, dces not initiate reactor scram, but rather provides an alarm in th3 control room. The failure.

of the cable will not degrade nor inhibit other Reactor Protection System (RPS) functions.

The radiation monitors provide a reactor scram via RPS cn high-high radiation levels in the main steam lines. The accidents postulated to occur that cause high radiation lavels in the main steam lines are LOCA airl Control Rod Drop.

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Mr. Janes G. Kepplcr, Regional Administrator November 16, 1982 Page Two EF2-60407 Only in the case of Control Rod Drop is credit taken for MSIV closure initiated by the radiation nonitors. However, neither of these accidents cause a coincident increase in steam tunnel temperature sufficient to cause a failure of the cable.

The only postulated event that could cause temperatures in the steam 0

tunnel to approach 230 F would be a main steam line break. In this event, even if the radiation monitors failed, other trip functions am available to mitijate the break, namely flow and temperature, and again the failure of the cables will not degrade other RPS functions.

0 In sumnary, the two events, high temperature (230 F) and high radiation are not postulated to occur sinultaneously in the steam tunnel, and failure of the cable will not preclude the safety functions of the RPS.

If you have questions concerning this matter, please contact Mr. G.M. Trahey, Assistant Director-Project Quality Assurance.

Very truly yours, DAW /DF/cp cc: Mr. Richard DeYoung, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Camtission Washington, D.C. 20555 Mr. Bruce Little, Senior Resident Inspector U.S. Nuclear Regulatory Camtission 6450 North Dixie Highway Newport, Michigan 48166

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