ML20004D655

Forwards LER 81-033/03L-0.Detailed Event Analysis Encl

ML20004D655
Person / Time
Site:	Fort Saint Vrain
Issue date:	05/27/1981
From:	Warembourg D PUBLIC SERVICE CO. OF COLORADO
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20004D656	List: ML20004D655 ML20004D666
References
P-81154, NUDOCS 8106090619
Download: ML20004D655 (5)

Text

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l pub [je Service Company #I CGIlOMdB n-:d if , 16805 ROAD 19%

idA - A PLATTEVILLE, COLOR ADO 80651 May 2 7, 1981 #

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Unit No. 1 G J W i 0 3 1981 * ~;i u.s. g ',,",@ ^ ***

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Mr. Karl V. Seyfrit, Director Nuclear Regulatory Com::tission Region IV Office of Inspection and Enforcement 611 Ryan Plaza Drive Suite 1000 Arlington, Texas 76012

Reference:

Facility Operating License No. DPR-34 Docket No. 50-267

Dear Mr. Seyfrit:

Enclosed please find a copy of Reportable Occurrence Report No. 50-267/

81-033, Final, submitted per the requirements of Technical Specification AC 7.5.2(b)2.

Also, please find enclosed one copy of the Licensae ~ ant Report for Repertable Occurrence Report No. 50-267/81-033.

Very truly yours, W

Don Warembourg Manager, Nuclear Production DW/cls Enclosure cc: Director, MIPC 001

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REPORT DATE: May 27, 1981 REPORTABLE OCCURRENCE S1-033 ISSUE O CCCURRENCE DATE: Acril 27, 1981 Page 1 of 4 FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO 16805 WELO COUNTY ROAD 19 1/2 -

PLATTEVILLE, COLORADO 80651 REPORT NO. 50-267/81-033/03-L-0 Final IDENTIFICATICN OF OCCURRENCE:

A malfunction of a helium circulator speed modifier caused loss of 1C helium circulator plant Protective System function of high speed trip. This resulted in operation under a degraded mode permittec by LCO A.4.1, Table 4.4-3, and is reportable per Fort St. Vrain  :

Technical Specification AC 7.5.2(b)2.

EVENT

. DESCRIPTION:

While operating at 30% thermal power and 70 MW electrical cower, Operations personnel coserved that one of three channels for the 1C circulator speed protection tripped on low speed while :he circulator was operating at approximately 4500 rpm.

This resulted in loss of the speed signal and trip capability in one of the three associated high speed trip channels for the IC circulator. The two redundant channels were available and operable.

See Figure 1. The speed modifier (SM), ([) , is cesigned to measure ,

the rotational speed and alignment wobble of the helium circulator shaft. This'is acccmplished by the use of a reluctance type detector i probe (SE),(]), connected to a phase sensitive carrier type electronics system. l t

Preci sion machined slots in ene rotating shaft of the helium  !

circulator provide timing pulses whose frequency is proportional to shaft rotational speec.  !

l The electronic system which produces tnis signal operates on the [

principle of a balanced bridge connectec to probes consistirig of two ,

identical coils. In normal operation, the bridge is nulled for l minimum zero phase shift outaut with the rotating shaft centered in the cearing.  ;

Three separate channels monitor the speed of each helium circulator.

The culse signals ara transmitted by the SM's. 2 , to the speed l transmitter ( S". ) , 3 , wnich produces a 0 to 1 volt output signal proportional to shaft RPM for use in the summer modifiers and process W .-- 9 7-<-m-yg-g , w a- ev7-+

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REPORTABLE OCCURRENCE 31-033 ISSUE O Page 2 of 4 trip mo ules. The procedure trip modules ara the speed switches low (SSL), 4 , and speed switches high (SSH), 5 . If the circulator speed reaches either the high or low trip setting, the SSL's or SSH's initiate trip signals to the two of three solid state logic, which produces a circulator shutcown via the special control relays (XCR's).

CAUSE DESCRIPTION:

The speed modifier malfunction was due to a bridge unbalance caused byachangein[-asistancebetweenthetwoleadsofthecablefromthe speed element ( ) to the speed modiff er (2) .

CORRECTIVE ACTION:

An installed spare speed element and cable were connected to the speed modifier, and the modifier was balanced, restoring the overspeed protection to the affected channel.

1 Nuclear Projects Department is analyzing the problem to determine if new cables should be run from the terminal box at the circulator to the Control Room.

No further corrective action is anticipated or required.

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REPORTABLE OCCURRENCE 81-033 ISSUE O l

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Prepared By: //L .

Asa B. Reec l Technical Services Technician  !

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1. -- I Reviewed By- -

W M anm Technical Services Supervisor f

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i Reviewed By: d.b.

Frank M/

Opera Mat.v.% p /

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Approved By: ) - WM, f Don Waremcourg #

Manager, Nuclear Production i

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