ML20011A860

LER 81-020/01T-0:on 811011,Westinghouse Nbfd Relays in Reactor Protection Sys for Units 1 & 2 Found to Have Failed Relay Coils.Caused by Failure of Solder Joint Pigtail Connection Coil to Lead Wire

ML20011A860
Person / Time
Site:	Prairie Island
Issue date:	10/26/1981
From:	Hunstad A NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20011A856	List: ML20011A855 ML20011A860
References
LER-81-020-01T, LER-81-20-1T, NUDOCS 8111030296
Download: ML20011A860 (1)

Text

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rm runm.m (7-77)

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EVENT DESCRIPTION AND PROB ABLE CONSEQUENCES gg,,, l Two Westinghouse type NBFD relays stalled in the Reactor Protection System _for j

. Unit 1 and five NBFD relays in the Reactor Protection System for Unit 2-were  ; ,

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_ 9 ,,, found to have failed relay coils. The failed relays in all cases were in normally_j yg,,, , energized (deenergize to td.p) circuits in parallel with another NBFD relay. The1.' J l 0 l6 l l y aNor k hn 'a . I J a....

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[Yj@ [N)@ lW l1 l2 10 jh 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS l7 l o l ] The failure mode identified by Westinghouse involves _ failure of the solder I ii li] l joint "pigteil" connecting the coil wfDding to the lead wir.c_during_the. voltage i spike which occurs when the relay is deenergized. See Attachment.  ;

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ACTIVITY CO TENT HELEASED OF RELEASE AMOUNT OF ACTIVtTV LOCATION OF pet Et EE I l 1 l 6 l l Z l @ [Zj@l NA l l NA  ! I 7 8 9 10 11 44 45 f. . .

PERSONNEt EXPOSURES NUMBE R TYPE DESCRIPTION NA l i 17 ] l 0 l 0 l 0 l@l Z l@l l

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NUueER oESCRiPTiON@ L NA li 181 7 8 9 lo 10 lo l@l12 11 20 l g LOSS OF OR DAMAGE TO FACILITY $

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......_;_- A. A. Hunstad ,.,_..e 612-388 1123 ,

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October 26, 1981 Attachment to LER 81-20 /0lT-0 NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT-Docket No. 50-282 Cause Description and Corrective Action Information received from Westinghouse after the initial notification of this occurrence indicates that the coli design was modified to preclude this failure mode. The modification applies to relays purchased after January 1, 1981.

Westinghouse has identified this failure as a potential substantial safety hazard because of the implication for normally deenergized relays where surveillance testing does not check coil continuity. Coil continuity is checked on normally deenergized relays in the safeguards systems.

The failurcs occurred only in circuits where parallel relays were employed.

In all cases the failure was in the conservative direction. If the parallel relay had also failed, the reactor would have tripped.

The immediate corrective action was to replace and retest the defective relays.

Further corrective action will check all normally energized relays before and after the preformance of surveillance testing. Normally deenergized relays in the safeguards racks will be checked by performance of monthly surveillance testing and surveillance testing after any initiation of the safeguards logic.

The ultimste corrective action recommended by Westinghouse is to replace all relay coils with coils purchased after January 1, 1981. This aptcoach will not be pursued until there is reason to believe that 1) a nonconservative failure is demonstrated for equipment installed at Prairie Island anc 2) the new re'ay coils are demonstrated to have no further problems.

The failed relays are Westinghouse type NBFD DC relays utilizing style #1271C50C01 coils manufactured prior to January 1, 1981.

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