ML20086D847

AO 73-04:on 730116,feedback Signal to Recirculation Pump a Decreased,Causing Momentary Increase in Pump Speed.Caused by High Resistance,Normally Open,Relay Contact in Circuit Board.Relay Located,Tested & Replaced

ML20086D847
Person / Time
Site:	Vermont Yankee
Issue date:	02/26/1973
From:	Riley B, Rileyy B VERMONT YANKEE NUCLEAR POWER CORP.
To:	US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086D841	List: ML20086D839 ML20086D847
References
AO-73-04, AO-73-4, VYV-2423, NUDOCS 8312050183
Download: ML20086D847 (2)

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VMRMONT YANKEM NUCLEAR POWER CORPORATION V'  %

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P. O. BOX 157 VERNON. VcRMONT 05354 -

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February 26, 1973 4

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Directorate of Licensing r' r U.S. Atomic Energy Commission g4 ,_

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REFERENCE:

Operating License DPR-28 h fc. Ea N L Docket No. 50-271 /g ,

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Abnormal Occurrence No. A0-73-04 O

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Dear Sir:

g As defined by Technical Specifications for the Vermont Yankee Nuclear ,

Powc c Station, Section 6.7.B.d, we are reporting the following Abnormal _i m e m w mx .n, ,u, ,3 v9.

At approximately 1120 on January 16, 1973, during calibration and  ;

adjustment of the recirc pump control loop to balance the jet pump loop " -

flows and pressures, the feedback signal to the A Recirc Pump vas decreased [

causing a momentary (approximately 3 minutes) increase in pump speed. F-

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This speed increase was caused, as shown by subsequent investigation, [

by a high resistance, normally open, relay contact in a circuit board. The' cffect that this added resistance had upon the control loop was to produce f

excessive drag which subsequently led to over compensation when it fully 1 opened. The ensuing pressure transient of 4 psi r2sulted in a stack-gas ,

release peak of 2.65 C1/sec which occurred at approximately 1252. This f release rate exceeded the noble gas release rate of .22 Ci/sec as specified [

in Section 3.8. A.2 of Technical Specifications for a period of twelve rainutes. g On the three days preceding the transient, and at approximately 100% power, -.

the release rate was approximately .071 Ci/see and it returned to this level -

subsequent to this transient. The reactor was at approximately 100% power at the time of this incident.

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The circuit board relay noted above was located, tested, and replaced 7' subsequent to the reactor shutdown on January 17. Emergency procedures a governing operation with failed fuel are currently under review. -

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O VERf/.ONT YANKEE. nUCLEAM POWER CORPORATION o Directorate of Licensing February '!2,1973 Page 2

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The total annual averr.ne st..ck release rate since the beginning of plant power operat.'ons oa ' 3 Septenber 1972 and including this transient is 10,511 pCi/sec. Analysin of the release was ende by our engineering group and resul ted in the deterrrination that the maxinan exposure that could have occurred of f-sita due to the incident was <2 mR.

The Plant Oc.erations Review Connittee concluded that the reactivity inpact of thic minor transient was minirni af ter consideration of the Mininun Critical lleat Flux Ratio calculations which showed little change before, during, or after the transient. The high tission gas release rate was apparently the concre,uence of degraded fuel cladding which is being located and replaced during the current reconstitution outage.

Very truly yours, VERMOST YANREE 1:UCLEAR POWER CORPORATIO':

D D< b B.W. Riley M~

'% Q(O Plant Superintendent DUE/rph

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