ML19351E595

Forwards LER 80-071/03L-0

ML19351E595
Person / Time
Site:	Fort Saint Vrain
Issue date:	12/05/1980
From:	Warembourg D PUBLIC SERVICE CO. OF COLORADO
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19351E596	List: ML19351E595 ML19351E601
References
P-80423, NUDOCS 8012100503
Download: ML19351E595 (5)

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public seMee company *2 ccacado 16805 ROAD 19%

PLATTEVILLE, COLOR ADO 80651 December 5, 1980 l'^ ,,

. Fort St'. Vrain Unit No. 1 P-80423 4

Mr. Karl V. Seyfrit, Director Nuclear Regulatory Commission 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/

80-71, Final, subM.tted per the requirements of Technical Specification AC 7.5.2(b)2.

Also, please find enclosed one copy of- the Licensee Event Report f or Reportable Occurrence Report No. 50-267/80-71.

Very truly yours, Y/lm A Don Warembourg Manager, Nuclear Pro uction DW/cis Enclosure

< cc: Director, MI?C

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l REPORT DATE: December 5. 1980 REPORTABLE OCCURRENCE 80-71 ISSUE O OCCURRENCE DATE: November 6. 1980 Page 1 of 4 l

FORT ST. VRAIN NUCLEAR GENERATING FTATION l PUBLIC SERVICE COMPANY OF COLORADO l 16305 WELD COUNTY ROAD 191/2 PLATTEVILLE, COLORADO 80651 REPORT No. 50-267/80-71/03-L-0 Final IDENTIFICATION OF OCCURRENCE:

A =alfunction of helium circulator 13 speed modifier caused loss of plant protective system function of high speed trips.

This resulted in operation under a degraded mode permitted by LCO 4.4.1, Table 4.4-3, and is reportable per Fort St. " rain Technical Specification AC 7.5.2(b)2.

EVENT D ESCRIPTION:

While operating at 60" thermal power and 166 mi electrical power, operations personnel observed that one of three channels for the 13 circulator speed protection tripped on low speed while the circulator was operating a ap-prox 1=ately 5,700 rpm.

This resulted in loss of the speed signal and trip capability in one of the three associated high speed trip channels for the 13 circulator. The two redundant channels were available and operable.

See Figure 1. The speed modifier (SM), ([) , is designed to measure the ro-tational speed and alignment wobble of the helium circulator shaf t. This is accomplished by the use of a reluctance type detector probe (SE), ([) ,

connected to a phase sensitive carrier type electronics system.

Precision =achined slots in the rotating shaf t of the helium circulator pro-vide timing pulses wt ae f requency is proportional to shaf t rotational speed.

The electronic syswem which produces this signal operates on the principle of a balanced bridge connected to probes consisting of two identical coils.

In normal operation, the bridge is nulled f or mini =um zero phase shif t out-put with the rotating shaf t centered in the bearing.

j[!.W't' REPORTABLE OCCURRENCE 80-71 ISSUE O Page 2 of 4 EVENT DESCRIPTION: (Cont'd)

Three separate channels monitor the speed of each helium circulator. The pulse s gnals are transmitted by the S?t's, ([) , to the speed transmitter (ST), 3 , which produces a O to 10 veit cutput signal proportional to shaf t RP:t f or use in the summer modifiers and process trip modules. The process trip modules are the speed switches low (SSL), ({},andspeed switcheshigh(SSH),(}). 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 shutdown via the special control relays (XCR's).

CAUSE D ESCRIPTION:

The speed modifier malfunction was due to a bridge unbalance caused by a change in resistance between the two leads of the cable f rom the speed ele-ment @ to the speed modifier h .

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 af-fected channel.

No further corrective action is anticipated or required.

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e' l REPORTABLE OCCURRENCE 80-71 -

- ISSUE O

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Prepared By:--

Asa B. Reed j Technical Services Technician-i 1

Reviewed By: 2

jf.W.Gahm

! V Technical Services Supervisor ,

r Reviewed By: N j Frank l1. :tathie l Operations : tanager

) Approved By: / _. ?Idv d w Don Ware:::bour;; &

j Manager, Nuclear Production

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