ML19263C381

LER 78-005/03X-2 on 781211: Malfunctions in 1A,1C & 1D Circulator Speed Measurement.Caused Loss of Circulator High Speed Signals.Caused by Loss of High Speed Circulator Trip. Redundant Sys Available

ML19263C381
Person / Time
Site:	Fort Saint Vrain
Issue date:	02/12/1979
From:	Gahm J PUBLIC SERVICE CO. OF COLORADO
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19263C376	List: ML19263C372 ML19263C381
References
LER-78-005-03X, LER-78-5-3X, NUDOCS 7902220047
Download: ML19263C381 (5)

Text

NRC FORM 3G6 U. S. NUCLEArt nEGULATORY COMMISSIOld (7 77) .

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LICENSEE EVENT REPORT

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CONT *iOL BLOCK: l l l l l (PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION) 1 f

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0 0 0 0 0 l- l0 0 @l4 1LICENSE 25 26 l1 l 2 0 @l TYPE 30 l@

57 C A T 58 7 8 9 . CENSEE CODE 14 15 uCENsE NUVBER CON'T 0 1 "E[p"C o l60L l@l610 l 5 l 0COCKET l 0 l NUM8 0 l ER 2 l 6 l 768l@l631 l 2 EVENT l 1 DATE 1 l 7 l 874 l@l75 01 REPORT 2 l ll CATE 21 7 l o80 @

7 3 VENT DESCRIPTION AND PROB ABLE CONSEQUENCES h a 2

' Operations persennel observed that malfuncticrns in lA. 1C. and 1D circulator speed I o 3i l measurement caused loss of circulator high speed signals. Problems occurred at I Reportable oer o 4 l different dates. All circulators not affected at the same time. 1 o 3 ] Technical Specification AC 7.5.2(b)2, operation under a degraded mode permitted by I o 6 lLCO 4.4.1. No ef fect on plant operation. Probable consequence was loss of high l ol7 l speed Circulator trip function. No af fect on public health or safety. Redundant l o aj l system available and operable for each circulator. 30

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7 8 3 SYSTEM CAUSE CAUSE COMP. VA LV E CODE CODE SUSCCOE COVPONENT CCDE SU8 CODE SU8 CODE o 9 lI lB @ El@ El @ lI N lS lT lR lU l@ l Tl@ 20 Z @

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_ SEQUENTI AL OCCURRENCE PEPCRT REVISICN LER RO EV ENT YE AR REPORT NO. CODE TYPE N O.

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_ l217 22l8 l 23 24 '6 27 28 23 30 31 32 ACTION FUTURE EFFECT SH UT DC'AN ATTACHVENT NPRC-4 PRlYE CCMP. CCMPCNENT TAKEN ACTICN ON PLANT YETHOD HOURS 44 SUBYiTTED FORU dub, SUPPLIER MANUFACTURER IXl@lXl@

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J3 34 3d 40 di 42 43 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS i o l General Atomic circulator speed / wobble modifiers caused a loss of clant orotective

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i l sys tem functions to high speed trio circuits due to electronic circuit unbalance l

, 7 l caused by signal cable resistance change. Modifiers adjusted, soare cable connected 1 3 3 las applicable. Adjustment of speed modifiers being checked weekly. Problem under l i .2 l investigation. l

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$A  % SCV.ER OTHER STATUS IS O RY DISCOVERY DESCRIPTION t 5 E l@ l0 l 5 l 0 l@ N/A l l A l@l Operator Observation l ACTIVITY CONTENT nELEASED OF RELEASE AMOUNT OF ACTIVITY LCCATION O': RELEASE 1 6 lZ l lZ N/A l l N/A l 7 a 9 10 11 44 45 SJ PERSONNEL EXPOSURES NUYBE R TYPE DESCRIPTICN

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REPORT DATE: Feb ruary 12, 1979 REPORTABLE OCCURRENCE 78-05 ISSUE 2 OCCURRENCE DATE: December ll,19 78 Page 1 of 4 FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 80651 REPORT No. 50- 26 7/ 78-05/03-X- 2 Supplemental Report: Additional Information IDENTIFICATION OF OCCURRENCE:

On twelve occasions between December 11, 1978, and February 1, 19 79, malf unc-tions of helium circulator speed modifiers caused loss of Plant Protective System function of high speed trips. Each of the twelve malfunctions resulted in operation under a degraded mode permitted by LCO 4.4.1 and are reparteble per Fo rt S t. Vrain Technical Specification AC 7.5.2(b)2.

This repcrt is sLbmitted as a supplement to Reportable Occurrence Report No.

50-267/ 78-05/03-L-0, Preliminary, ta provide additional information on the problems experienced since Mcvember 19, 1978.

EVENT DESCRIPTION:

Event 1 - Soeed Modifier, S5F21161 On December 11, 1978, while operating at 50% thermal power and 150 MW electrical power, operations personnel observed that one of three chan-nels for the LA circulator speed protection tripped on low speed while the circulator was operating at approximately 5,900 rpm. This resulted in loss of the speed signal and trip capability in one of the three as-sociated high speed t rip channels for the LA circulator. Two redundant channels were available and operable.

Event 2 - Speed Modiff er, S>b21161 On December 12, 1978, while operating at 69% thermal power and 210 MW electrical power, operations personnel observed that one of three chan-nels for the 1A circulator speed protection tripped on low speed while the circulator was operating at approxima tely 7,000 rpm. This resulted in loss of the speed signal and trip capability in one o f the three as-sociated high speed trip channels for the LA circulator. Two redundant channels were available and operable.

Event 3 - Speed Modifier, S5921161 on December 29, 1978, while operating at 64% thermal power and 200 MW electrical power, operations personnel observed that one of three chan-nels for the 1A circulator speed protection tripped on low speed while

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REPORTABLE OCCURRENCE 78-05 ISSUE 2 Page 2 of 4 EVENT DESCRIPTION (continued):

Event 3 - Speed Modifier, SM-21161 (continued) the circulator was operating at approximately 6,800 rpm. This resulted in loss of the speed signal and trip capability in one of the three as-sociated high speed trip channels for the lA circulator. Two redundant channels were available and operable.

Event 4 - Soeed Modifier, SM-21161 On January 1,1979, while operating at 64% thermal power and 200 MW electrical power, operations personnel observed that one of three chan-nels for the 1A circulator speed protection tripped on low speed while the circulator was operating at approximately 6,800 rpm. This resulted in loss of the speed signal and trip capability in one of the three as-sociated high speed trip ' channels for the 1A circulator. Two redundant channels were available and operable.

Event 5 - Speed Modifier, Sdb21162 On January 22, 1979, while operating at 28% thermal power and zero elec-trical power, operations personnel observed that one of three channels for the 1C circulator speed protection tripped on low speed while the circulator was operating at approximately 4,500 rpm. This resulted in loss of the speed signal and trip capability in one o f the three asso-ciated high speed trip channels for the 1C circulator. Two redundant channels were available and operable.

Event 6 - Soeed >bdifier, S$921162 On January 23, 1979, while operating at 60% thermal power and 185 MW electrical power, operations personnel observed that one of three chan-nels for the 1C circulator speed protection tripped on low speed while the circulator was operating at approximately 6,000 rpm. This resulted in loss of the speed signal and trip capability in one of the three as-sociated high speed trip channels for the 1C circulator. Two redundant channels were available and operable.

Event 7 - Soeed Modifier, S}b21172 On January 23, 1979, while operating at 33% thermal power and 80 MW electrical power, operations personnel observed that one of three chan-nels for the 1D circulator speed protection tripped on low speed while the circulator was operating at approximately 4,600 rpm. This resulted in loss of the speed signal and trip capability in one of the three as-sociated high speed trip channels for the ID circulator. Two redundant channels were available and operable.

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REPORTABLE OCCURRENCE 78-05 ISSUE 2 Page 3 of 4 EVENT DESCRIPTION (continued):

Events 8, 9, and 10 - Soeed Modifier, SM-21172 On January 28, 1977, while operating at 42% thermal power and 125 MW electrical power, operations personnel observed that one of three chan-nels for the 1D circulator speed protection tripped on low speed while the circulator was operating at approximately 5,200 rpm. These indivi-dual failures were experienced on the same channel. Each resulted in loss o f the speed signal and trip capability in one of the three asso-ciated high speed trip channels for the 1D circulator. The first failure occurred at approximately 0730 hours0.00845 days <br />0.203 hours <br />0.00121 weeks <br />2.77765e-4 months <br /> and was repaired at 0800 hours0.00926 days <br />0.222 hours <br />0.00132 weeks <br />3.044e-4 months <br />.

The second failure occurred at 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> and was repaired at 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br />.

The third failure occurred at 1640 hours0.019 days <br />0.456 hours <br />0.00271 weeks <br />6.2402e-4 months <br /> and was repaired at 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br />.

In each of the three cases, two redundant channels were available and o p e rab le .

Event 11 - Soeed Modifier, S}h21172 On January 30, 1979, while operating at 42% thermal power and 125 MM electrical power, operations personnel observed that one o f three chan-nels for the ID circulator speed protection tripped on low speed while the circulator was operating at approximately 5,200 rpm. This resulted in loss of the speed signal and trip capability in one of the three as-sociated high speed trip channels for the 1D circulator. Two redundant channels were available and operable.

Event 12 - Speed Modifier, SM-21172 On Feb ruary 1,1979, while operating at 28% thermal power and 44 MW electrical power, operations personnel observed that one of three chan-nels for the 1D circulator speed protection tripped on low speed while the circulator was operating at approximately 4,500 rpm. This resulted in loss of the speed signal and trip capability in one o f the three as-sociated high speed trip channels for the 1D circulator. Two redundant channels were available and operable.

CAUS E DES CRIPTION :

Instrument calibration drif t due to bridge unbalance.

The balancing problem is 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 te=perature and humidity of the ambient air.

CO RRECTIVE ACTION:

Events 1 and 2 Adjusting the 1A circulator speed modifier restored overspeed protec tion to the affected enannel.

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REPORTABLE OCCURRENCE 78-05 ISSUE 2 Page 4 of 4 CORRECTIVE ACTION (continued):

Events 3 and 4 Replacing the input cable with a spare and adjusting the 1A circulator speed modifier restored overspeed protection to the affected channel.

Event 5 No adjustments were made. Change in temperature from reactor power change altered cable tasistance and restored previous conditions of bridge balance and overspeed protection to the affected channel.

Event 6 Adjusting the 1C c _rculator speed modifier restored overspeed protection to the affected channel.

Events 7, 8, 9, 10, 11, and 12 Adjusting the 1D circulator speed modifier restored overspeed protection to the affected channel.

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

The problem is under investigation to determine what can be done to correct this situa tion. The results will be reported in a future supplemental report.

Prepared by: Ld_ L ' , -

MicPylel J. Ferris V Technical Services Engineer Reviewed by: j,Z d

//W.Gahm f'echnicalServicesSupervisor Reviewed by: / d4 d Frank M. Mathie Operations Manager Approved by: Y Don 'Jarembourg Manager, Nuclear Produ[ction