ML20064F165

/03L-0 on 781025:during Oper,Surveillance Test on Channel a Reactor Protec Sys Core Protec Calculator Reveated Sys Ground Traced to Signal for Pressurizer Pressure W/In Containment Boundary.Source Not Known at This Time

ML20064F165
Person / Time
Site:	Millstone
Issue date:	11/21/1978
From:	Bates R NORTHEAST UTILITIES
To:
Shared Package
ML20064F163	List: ML20064F157 ML20064F165
References
LER-78-029-03L, LER-78-29-3L, NUDOCS 7811280300
Download: ML20064F165 (2)

Text

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60 61 DOCK ET NUusER 68 69 EVENT DATE 74 7b REPORT DATE 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h I O I 21 1 Testing on the channel A reactor protection system (RPS) core protection i 10 :311 calculator indicated a grounded input that was traced to the signal for l F5T41 l Pressurizer Pressure within the containment boundary. The channel A trips l TTIT1 I for High Reactor Coolant System Pressure and Thermal Margin / Low Pressure O s I were bypassed and the grounded signal was isolated from the RPS. There  :

0 7 l are no consequences from this- event as the plant was operated in accord- l gf j i ance with Technical Specifications,'section 3.3.1.1, action 2-b. 80 l

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m1 The source of the ground is not known at this time. The grounded signal i i i was isolated from the reactor protection system with the temporary i ql addition of an isolation amplifier, and the channel restored to service. l At'the next available reactor shutdown, the ground will be cleared and 1 ml I

ml the isolation amplifier removed. 1 STA $  % POWER OTHE R STATUS DISCO RY OISCOVERY OESCRIPTION 37

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ATTACHf1ENT LER 78-29/3L-0 Millstone Unit 2 Docket No. 50-336 EVENT DESCRIPTION During steady state operation, surveillance testing on the channel A reactor protection systen (RPS) core protection calculator indicated a system ground.

Investigation showed the ground was on the signal for Pressurizer Pressure and was located within the containment boundary. -The channel A reactor trips for High Reactor Coolant System Pressure and Thermal Margin / Low Pressure were bypassed and the grounded signal was isolated from the RPS. ~ There are no probable consequences from this event since the plant was operated in accordance with action statement 2-b of section 3.3.1.1 of the Technical Specifications.

' CAUSE DESCRIPTION j

The source' of the ground is not known at this time, but is.either on the signal cable or .the channel A Pressurizer Pressure transmitter. The grounded signal was isolated from the reactor protection system with the-temporary addition of an isolation amplifier. Channel calibration checks showed the reactor protection system to be fully isolated from the grounded signal and the channel was restored to service. At the next available reactor shutdown, the ground will be cleared, the isolation amplifier removed and the channel restored to' norma 1 operation.

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