ML19309A489

LER 79-041/03X-2 Final Supplement:On 791005,malfunctions in Circulator Speed Measurement Caused Loss of High Speed Signals.Caused by Signal Cable Connection Resistance Change. Modifiers Adjusted.New Connectors Installed.Circuits Tested

ML19309A489
Person / Time
Site:	Fort Saint Vrain
Issue date:	03/18/1980
From:	Gahm J PUBLIC SERVICE CO. OF COLORADO
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19309A483	List: ML19309A482 ML19309A489
References
LER-79-041-03X, LER-79-41-3X, NUDOCS 8003310357
Download: ML19309A489 (6)

Text

I NRC FOAM 384 U.S. NUCLEA3 REtutATOGY COMMissi!N (1 m .

LICENSEE EVENT REPORT CONTROL BLOCK: l l l l l l l (PLEASE PRINT OR TYPE ALL REQUIRED INPORMATION)

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Io I4l l AC 7.5.2(b)2, operation under a degraded mode permitted by LCO 4.4.1, Table 4.4-3. l

, IoIsl l No effect on plant operation. Probable consequence was loss of high soeed circulatori ioisl l trip function to one of three channels. No affect on public health or safety. I l o 12 l l Redundant system available and operable. Similar report RO 78-o5. I 101811 I

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l gl installed spare cable (s) as required to restore channel functions. New connectors l l

_mI were certified. installed. and circuits tested. I

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REPORT DATE: March 18. 1980 REPORTABLE OCCURRENCE 79-41 ISSUE 2 OCCURRENCE DATE: October 5.1979 Page 1 of 5 FORT ST. VRAIN NUCLEAR GE'IERATING STATION PUBLIC SERVICE COMPANY OF COLORADO 16805 WELD COUNTY ROAD 191/2 PLATIEVILLE, COLORADO 80651 REPORT NO. 50-267/79-41/03-X-2 FINAL SUPPLEMENT IDENTIFICATION OF OCCURRENCE:

A malfunction of helium circulator speed modifiers 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. Vrain Technical Specification AC 7.5.2(b)2.

This report is submitted as a Final Supplement to Reportable Occurrence Report No. 50-267/79-41/03-L-0, Preliminary and Supplemental report X-1.

EVENT DESCRIPTION:

See Figure 1. The speed measuring system (SM), O1 . i ae isaec o ure  ;

the rotational speed and alignment wobble of the helium circulator shaft.

TI is accomplished by the use of a reluctance type detector probe (SE),  !

, connected to a phase sensitive carrier type electronics system.

Precision machined slots in the rotating shaf t of the helium circulator provide timing pulses whose frequency is proportional to shaf t rotational speed.

The electronic system 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 for minimum zero phase shif t output with the rotating shaft centered in the bearing.

Three separate channels monitor the speed o ach helium circulator. The pulse si s are transmitted by the SM's, , to the speed transmitter (ST's), , which produces a 0 to 10 volt output signal proportional to shaft M for use in the summer modifiers and process t modules.

The p-- 'es trip mod are the speed switches low (9SL), , and speed swit et .4 high (SSH), . If the circulator speed reaches ther the high or low trip sett ng, the SS or SSH's initiate trip signals to the two of three solid state logic, ,w produces a circulator shutdown via the special control relays ( 's), .

l Table 1 summarizes the failures experienced and reported in the previous l two issues of this report.

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REPORTABLE OCCURRENCE 79-41 ISSUE 2 Page 2 of 5 EVENT DESCRIPTION: (Cont' d)

TABLE 1 Speed PPS Approximate Indicated Reactor Date Modifier Channel Circulator Speed Speed Power %

10- 5-79 21165 C 1A 4500 30 c) 10- 6-79 21165 C 1A 4500 29 s

m 10-6-79 21165 C 1A 4700 38 10- 8-79 21161 A 1A 5900 50

-4 10-26-79 21162 A 1C 4500 30 m

As an interim measure, the adjustment of the speed modifiers was checked on a weekly basis.

CAUSE DESCRIPTION:

Instrument calibration drif t due to bridge unbalance.

The balancing problem was caused by a change in resistance between the two leads of the speed element and ground at the circulator connection end.

The difference in resistance occurs over a period of time in the cable connectors as a result of the temperature and humidity of the ambient air.

CORRECTIVE ACTION:

Table 2 summarizes the corrective actions for the failures reported in the previous two issues of this report.

TABLE 2 Speed Date Mo difier Corrective Action c) 10- 5-79 21165 Balanced speed modifier.

g 10-6-79 21165 Balanced speed modifier.

m 10-6-79 21165 Balanced speed modifier.

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$ 10- 8-79 21161 Balanced speed modifier. '

-4 10-26-79 21162 Balanced speed modifier.

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. ,e REPORTABLE OCCURRENCE 79-41 ISSUE 2 Page 3 of 5 CORRECTIVE ACTION: (Cont'd)

New cable connectors were certified to conform with the requirements and specifications of the purchase order.

The new cable connectors have been installed and tested.

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No further correcE19e' action. is anticipated or required.

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REPORTABLE OCCURRENCE 79-41 ISSUE 2 Page 5 of 5 Prepared By: ch MicQelJ.Ferr$

Technical Services Engineer

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Reviewed By: / [

w.,cahm chnical Services Supervisor Reviewed By:

Frank M. Mathie Operations Manager 1

Approved By: lb /T _

Don Warembourg 47 Manager, Nuclear Production l

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