ML19263C992

LER 79-004/03L-0 on 790130:reactor Protection Sys Reactor Coolant Loop Tests Exceeded Tech Spec Response Time.Cause Unknown.Resistance Temp Detector Will Be Replaced During Spring 1979 Outage

ML19263C992
Person / Time
Site:	Millstone
Issue date:	03/08/1979
From:	Crockett J NORTHEAST UTILITIES
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19263C988	List: ML19263C987 ML19263C992
References
LER-79-004-03L-01, LER-79-4-3L-1, NUDOCS 7903200404
Download: ML19263C992 (2)

Text

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ATTACHMENT LER 79-04/3L-0 tiillstone Unit 2 Docket t'o. 50-336 EyENT DESCRIPTION Technical Specification Table 3.3-2 requires that RPS RTD's have a response tir.e of less than or equal to 10.0 seconds. The testing program used by liillstone to satisfy this requirement included removal of the RTD's from their wells and subjecting them to a response time plunge test by the manufacturer, Rosemount, Inc.

Subsequent investigations of alternate test methods by Northeast Utilities led to an evaluation of in-situ testing of RID time response by the loop current step response (LCSR) tethod. The test results for al' bdor Coolant System RPS input RTD's were received for evaluation of the test method on 1/30/79. Testing was performed by Analysis and lleasurement Services, and the validity of the LCSR test method and results was accepted by Northeast Utilities on 2/28/79. Hence the LCSR test method and results will be utilized to determine RTD response times per Technical Specification Table 3.3-2.

The test results received on 1/30/79 indicated that the RCS loop 1 channel C hot leg RTD, TE-ll2HC, had a response time of 11.2 seconds.

All other RTD's were within specification, with the highest response time measurcd for any other RTD of 6.7 seconds. The TE-ll2HC RTD is a

< Rosemount Madel No. 104ADA.

CAUSE DESCRIPTION The cause of the increase in TE-ll2HC response time is unknown. The TE-112HC RTD instrument loop provides a loop 1 hot leg signal which is averaged with the corresponding loop 2 cl anel C signal. This average hot leg temperature is then input to the RPS for the calculation of thermal power level by development of a delta-T power signal. The resultant delta-T power signal is used for generation of the variable high power trip, thermal margin / low pressure trip and local power density trip. Since only one channel was affected and the RPS trip scheme relies on a 2 out of 4 logic, the safety significance was minimal with the higher response time measured for TE-ll2HC.

Upon receipt of the test results a design change was evaluated and implemented which deleted the TE-ll2HC temperature loop input to the channel C hot leg temperature averaging circuit. An evaluation by Combustion Engineering and Northeast Utilities confirmed the acceptability of this change.

RTD TE-ll2HC will be replaced during the spring 1979 refueling outage.

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[ y [The lE-ll2HC response time increase cause is unknown._ All other RTD's were in I

A temporary modi fication was implemented to delete the TE-112E_as g [ spc ,ification.

This j g [ an RPS input., using the loop 2 TH signal as the average channel C input. _

RTO will be replaced _J hul Ec nditi n was evaluated as acceptable by the flSSS vendor.

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