05000321/LER-1985-001, :on 850105,reactor Water Cleanup Sys Automatically Isolated Due to High Differential Flow Trip Signal.Caused by Air Trapped in Sensing Lines of Sys Inlet Flow Transmitter G31-N036

:on 850105,reactor Water Cleanup Sys Automatically Isolated Due to High Differential Flow Trip Signal.Caused by Air Trapped in Sensing Lines of Sys Inlet Flow Transmitter G31-N036

ML20101T891
Person / Time
Site:	Hatch
Issue date:	01/27/1985
From:	Elton T, Nix H GEORGIA POWER CO.
To:	NRC OFFICE OF ADMINISTRATION (ADM)
References
GM-84-041, GM-84-41, LER-85-001, LER-85-1, NUDOCS 8502060415
Download: ML20101T891 (3)

LER-1985-001, on 850105,reactor Water Cleanup Sys Automatically Isolated Due to High Differential Flow Trip Signal.Caused by Air Trapped in Sensing Lines of Sys Inlet Flow Transmitter G31-N036

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(1)
3211985001R00 - NRC Website

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488TR ACT (Limte se 7400 apsres. J.e., esereennetery arreen senere sesce tyneerrrfee hess# 1191 On 01/05/85, and on 01/10/85, the Reactor Water Cleanup (RWCU) system automatically leolated due to a high differential flow trip signal.

The outboard isolation valve (G31-F004) closed, and the running RWCU pump (G31-C001B) tripped.

The inboard icolation valve (G31-F001) did not shut as required by Tech. Specs section 3.7.D.1 and Tcble 3.7.1.

It was determined that the trips were caused by air trapped in the sensing lines of the system inlet flow transmitter (G31-NO36) and a leaking relief valve on the regenerative hrat exchanger (G31-B001).

The relief valve was replaced and the transmitter was vented.

The transmitter's proper operation was verified by observing its indicator, G31-R615, and it was returned to s::rvice.

An engineering evaluation was conducted, and it was determined that the RWCU system icolation logic would not allow a high differential flow trip to isolate both G31-F001 cnd G31-F004 unless both RWCU pumps were running.

There are, however, other signals which would have isolated both RWCU isolation valves regardless of pump status.

They l

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low reactor vessel water level

scram, high RWCU equipment room ambient l

temperature, and high differential temperature across the RWCU equipment room l

v:ntilation ducts.

l A DCR has been implemented which changed the isolation logic circuitry to allow a high I

differential flow trip to isolate both G31-F001 and G31-F004 with elther, both or n31ther RWCU pump running.

The changes were satisfactorily tested per the DCR functional test, and the system was returned to service on 01/12/85.

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ace asuwim This 30 day LER is required by 10CFR50.73(a)(2)(iv) because these events were tutomatic actuations of an ESF.

It is also required by 10CFR50.73(a)(2)(i) because sysluation of these events has shown that the unit has been operating contrary to the pesvisions of Tech. Specs. section 3.7.D.1, and Table 3.7.1.

On 01/05/85, at approximately 1824 CST with the reactor mode switch in the shutdown p sition and the unit shutdown, operations personnel were attempting to put the Ricctor Water Cleanup (RWCU) demineralizers in service with RWCU pump G31-C001B running and G31-C001A secured.

At this time, the Cleanup System Leak alarm ennunciaLed, the RWCU outboard isolation valve (G31-F004) closed and the "B" RWCU pump l

(G31-C001B) tripped. The inboard isolation valve (C31-F001) failed to close.

On 01/10/85, at approximately 1340 CST with the reactor mode switch in the startup and hat standby position and the unit at less than 1% thermal power, with G31-C001B running and G31-C001A secured, the Cleanup System Leak alarm again annunciated, G31-F004 closed and the "B" RWCU pump tripped.

The inboard isolation valve (G31-F001) failed to close.

C31-F001 was declared inoperable.

The RWCU system was removed from service, and G31-F001 and G31-F004 were closed as required by Tech. Specs. Table 3.2.1, reference no. 8, note C.

Eo actual or potential safety consequences resulted from these events nor was the hsolth and safety of the public affected.

Thsse are repetitive events as previously reported in LER 50-321/1984-29.

Investigation of the event on 01/10/85 revealed that a relief valve on the esgenerative heat exchanger (G31-B001) was leaking, and that the cleanup system inlet flow transmitter (G31-NO36) had air trapped in its sensing lines which was causing an seroneous signal to be sent to the differential flow network.

Tha relief valve was replaced and the transmitter was vented.

The transmitter's pecper operation was verified by observing its indicator, G31-R615, and it was esturned to service.

An engineering investigation was conducted to determine why G31-F001 had not shut when tha system isolated.

It was determined that the RWCU system isolation logic was such th:t it would not allow a high differential flow trip to isolate both G31-F001 and G31-F004 unless both RWCU pumps were running.

With G31-C001A running, G31-F001 would chut, G31-F004 would remain open.

With G31-C001B running, G31-F004 would shut, G31-F001 would remain open.

With no pumps running, neither valve would shut.

There cro, however, other signals which would have isolated both RWCU isolation valves regardless of pump status.

They are: low reactor vessel water level scram, high RWCU equipment room ambient temperature, and high differential temperature across the RWCU equipment room ventilation ducts.

A DCR has been implemented which changed the isolation logic circuitry to allow a high differential flow trip to isolate both G31-F001 and G31-F004 with either, both or noither RWCU pump running.

The changes were satisfactorily tested per the DCR functional test, and the system was returned to service on 01/12/85.

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. Edwin 1. Hatch Nuclear Plant January 27, 1985 i

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PLANT-E.

I.. HATCH Licensee Event Report

. Docket No. 50-321 1.

United States Nuclear Regulatory Commission Documer.t Control Desk l

Washington, D. C.

20555 Attached is Licensee Event Report No. 50-321/1985-001.

This report is required by 10CFR 50.73(a)(2)(1), and 10CFR 50.73(a)(2)(iv).

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