ML19332D879

LER 89-008-00:on 891102,RWCU Sys Experienced Partial Primary Containment Isolation Sys Group 5 Isolation Involving Valve 2G31-F004.Caused by Component Failure of Relay 2G31-R616D. Relay replaced.W/891129 Ltr

ML19332D879
Person / Time
Site:	Hatch
Issue date:	11/29/1989
From:	Hairston W, Tipps S GEORGIA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
HL-852, LER-89-008-03, LER-89-8-3, NUDOCS 8912050380
Download: ML19332D879 (7)

Text

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the soottiern etnVe system W. G. Hairston, Ill

. Senior Vice President : ~*

Nuclear Operations .

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HL-852-0445V o ,

November. 29, 1989- ,

y .U.S., Nuclear Regulatory Commission

-ATTN: ' Document Control Desk

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JHashington, D.Cr ;20555

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" J PLANT HATCH - UNIT 2

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0PERATING LICENSE NPF-5 LICENSEE EVENT REPORT FAULTY TIME DELAY RELAY CAUSES TH0 PARTIAL REACTOR HATER CLEANUP ISOLATIONS Gentlemen::

. LIn7accordance with the requirementsL of 10 CFR 50.73(a)(2)(iv), Georgia

Power ; Company isf submitting the- enclosed Licensee Event Report- (LER) ,

, , . concerning" thel unanticipated actuation of 'an Engineered Safety Feature. The

, event occurred at Plant Hatch'-' Unit 2. .

,, t Sincerely.

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- H. G. Hairston, III SHR/ct~

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Enclosure:

LER 50-366/1989-008 1 5 c:: (See next:page.)

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U.S. Nuclear Regulatory Commission

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, November- 29, 1989 Page Two-

.c: Georoia Power Company .

s Mr. H.:C. Nix, General Manager - Nuclear Plant

.Mr. J. D.~ Heidt ; Manager Nuclear Engineering and Licensing - Hatch GO-NORMS _

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U.S. Nuclear'Reaulatory Commission. Washinoton. D.C.

Mr. L. P. Crocker, Licensing Project Manager - Hatch U.S. Nuclear Reculatory Commission. Reaion L1 Mr. S. D. Ehneter, Regional Administrator Mr. J. E. Henning, Senior Resident Inspector - Hatch

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TITLE ada FAULTY TIME DELAY RELAY CAUSES TWO PARTIAL REACTOR WATER CLEANUP ISOLATIONS EVSWT DATE ISI LER NUMBER ISI REPORT DATE (7) OTHER F ACILITIES INVOLVED IO)

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LICENSEE CONTACT FOR THl3 LER H2%

NAME TELEPHONE NUMSER ARE A COOE j Steven B. Tipps, Manager Nuclear Safety and Compliance, Hatch 91 li 2 31617I -l718i SI1

' COMPLETE ONE LINE FOR EACH COMPONENT FwLURE DESCRIBED IN THt$ REPORT H3)

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"[,ORiA COMP)NENT REPORTA E l l. U CAU!E SYSTEM COMPONENT' pp CAUS $YSTEM Mh$C-

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i On 11/02/89, at approximately 1355 CST, Unit 2 was in the Refuel mode at  ;

L an approximate power level of 0 MWt (approximately 0% of rated thermal -i power). At that time Operations personnel were placing a Reactor Water  !

Cleanup system (RWCU) filter /demineralizer (F/D) in service when they received annunciation of RWCU system high differential flow. The RWCU i system then experienced an immediate, partial Primary Containment

--Isolation System Group 5 isolation involving only the outboard isolation

- valve 2G31-F004. Normal system response should have been isolation of

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D both valves, 2G31-F001 (inboard isolation valve) and 2G31-F004, following i

a 45-second time delay. On 11/09/89, at approximately 1233 CST, Unit 2 was in the Refuel-mode at an approximate power level of 0 MWt

.(approximately 0% of rated thermal power). At that time Operations

-personnel were returning a RWCU pump to service when identical annunciations and system responses occurred, resulting in a second partial isol ation.

The root cause of this event was component failure. Time deley relay 2G31-R616D was found to have experienced intermittent contact failure.

The corrective action for this event was replacing the relay.

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PLANT 4 AND SYSTEM IDENTIFICATION

', ; s GeneralLElectric1- Boiling Water Reactor a

p TEnergy' Industry Identification System codes are identified in the text as:(EIIS Code XX).

SUMMARY

OF EVENT! <

0. OnJ11/02/89,f at approximately:1355 CST, Unit 2 was in the Refuel mode at

"'L% van approximate. power level of 0 MWt.(approximately-0% of rated thermal

' power) . At that time Operations personnel were placing a Reactor Water

- ~ Cleanup system (RWCU, EIIS Code CE) filter /demineralizer (F/D) in s service:when they, received' annunciation of RWCU system high differential "

' flow'. The RWCU system then experienced an immediate, partial Primary

, Containment Isolation System (PCIS, EIIS Code JM) Group 5 isolation-involving only the outboard isolation valve 2G31-F004. Normal : system response should' have been isolation. of both_ valves, 2G31-F001 -(inboard

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isolation valve) and 2G31-F004, following a' 45-second time delay. On 1_1/09/89, .at approximately 1233 CST, Unit 2 was in the Refuel mode at an approximate power level of 0 MWt (approximately 0% of rated thermal power) ; At that time Operations personnel were returning a RWCU pump to service when' identical annunciations and system responses. occurred,

, (resulting: inia'second partial isolation, k >

!The root cause of this event was component failure. Time delay relay l2G31-R616D was found'to have experienced intermittent contact failure.

The corrective action for this event was replacing the relay. '

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! DESCRIPTION OF EVENT 10n:ll/02/89 at approximately .1355 CST, Operations personnel were in the process of' returning'a RWCU F/D to service. When the isolation valve to

the F/D.was opened, operators in the main control room received

' annunciation that the Leak Detection System (LDS, EIIS Code 00) had sensed a!high differential flow condition between the RWCU lines

entering and leaving primary containment. This alarm is expected momentarily. during the return of a F/D to service because, as voids in

' the F/D fill, a difference between inlet and outlet flow results.

Therefore the high differential flow signal incorporates a 45-second Ltime delay prior to initiation of system isolation. The resulting

isolation-normally-includes both the inboard and outboard PCIS Group 5

<  ; valves, 2G31-F001 and 2G31-F004 respectively. Should the alaru clear lbefore the 45 seconds have elapsed, the LDS should reset without causing an isolation. In this event, the isolation occurred almost instantaneously upon receiving the LDS alarm, and it involved only the j outboard isolation valve. The closure of the valve tripped the RWCU i

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0l0 0l3 0F 0 l5 I t i An investigation by. Operations personnel showed that no leak sufficient l

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l to cause the LDS actuation existed. Since available evidence indicated 1

.a- problem existed in:the time delay relay for the outboard isolation

. valve, 2G31-R616D, Instrumentation and-Control (I&C) technicians 4

functionally. tested and calibrated. the. isolation logic which included .

the time delay relay : No problems were found, and relay 2G31-R6160 functioned normally- at that time. When no system malfunctions were

-identified, RWCU was returned to service at approximately 1720 CST on

-11/02/89.

On 11/09/89 at approximately 1233 CST, Operations personnel were in the process-of returning a RWCU pump to service when the RWCU high differe.ntial flow signal annunciated again. The annunciator was

< followed almost immediately by closure of the outboard isolation valve and tripping of the pump. The annunciations and system response were identical to those which were observed on 11/02/89. Since all evidence again indicated a' problem with relay 2G31-R616D, I&C technicians replaced the relay with a new one. The RWCU system isolation logic was then' functionally tested and calibrated, and the system was returned to

-service at_ approximately 1646 CST on 11/11/89.

CAUSE OF THE: EVENT- '

The root cause of this event was component failure.- Specifically, time delay relay 2G31-R616D experienced intermittent contact bounce when the relay deenergized.- Some relay activity is expected and normal during RWCU system work such as returning pumps to service, placing F/Ds in service,-etc. The pneumatic time delay mechanism is designed to hold the contacts closed for 45 seconds to prevent spurious actuation- of the

isolation logic.due to this' expected relay motion.. However, bench testing of. the relay by a Georgia Power Company' engineer showed the

. mechanical- shock of multiple and, occasionally, single relay actuations was sufficient to induce a short transient (80-milliseconds or less) in  !

the continuity of-the time delay relay contacts. Opening of the time delay contacts during the bench test was evidenced by deenergization of ia relay which was wired to remain deenergized once the time delay contacts opened. This time delay relay failure mode would have resulted in full actuation of one channel of the actual trip logic.

The contact bounce was intermittent, occurring in approximately one out

~o f. five actuations. The pneumatic time delay mechanism functioned

-normally .throughout the testing. This mechanism applies the motive force required to actuate a microswitch. The contacts in the microswitch were the specific source of failure because they exhibited <

transient discontinuity'even though the pneumatic time delay actuator was still attempting to hold the microswitch in the closed position.

The functional test performed by I&C technicians following the 11/02/89 l

- event required an ohmmeter to be placed across the closed contacts of  !

the time delay actuated microswitch. However, due to the reaction time '

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, lof> the ohmmeter,- the; transient'probably could not' have been observedL ,

even if. it had occurred during functional. testing. !Moreover, the intermittent character of the failure served to further reduce the.

p * :likelihoodiof- detecting the problem through in. situ functional . testing.-

-M REPORTABILITY ANALYSIS- AND= SAFETY- ASSESSMENT-This event.isireportable. per 10 CFR 50.73 (a)(2)(iv)'because an '

unplanned actuation of an Engineered Safety Feature occurred.

Specifically, the PCIS~ Group .5 outboard isolation valve, 2G31-F004, closed in response to.an--indication of high differential flow between the: RWCU system lines entering andsleaving primary containment.

The purp.ose of the RWCU LDS-is to detect leakage from the RWCU system outside primary containment and to. mitigate the consequences of that -

'," -leakage. This. system uses: leak detection-instrumentation which D

tinitiates closure of Primary Containment Isolation Valves (PCIVs) upon a

detecting 'a parameter' indicative of a leak. }

T :In the event addressed in this report, a momentary condition of high

-differential flow'was sensed. . Testing of the. time delay relay showed

' intermittent contact bounce when zthe relay deenergized. This resulted in the~-spurious; actuation of one channel of the trip logier and the

= closure of one'of' the isolation valves. The Group 5 PCIV closure logic channelsLare . independent so that the time delay relay'2G31-R616D only ihas thel capability to close the outboard valve, 2G31-R004.

Since-the actuation __was spurious, caused by a faulty relay, and no actual: system leak was observed by plant equipment operators, it is concluded. that this event had no adverse impact on nuclear- safety. This' analysis.is applicable to-:all~ power levels.

LCORRECTIVE ACTIONS Corrective actions for this event included replacing time delay relay

'2G31-R616D.with a new relay, and functionally testing and calibrating the newly; installed relay.

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~. ADDITIONAL INFORMATION s

fl. _No ~ plant systems other thanl the.'RWCU system and th.e Group 5'PCIVs.

were. affected by this event.

y7 l2. Pre'vious Similar Events:- >

Similar events in which the RWCU system isolated due_to high

< differential flow as 'a result of a component. failure wero f previously~ repor.ted in the following LER's:-

-i 50-366/1988-015, dated.08/26/88 50-366/1988-021, -dated 09/28/88 9 ;50-321/1989-012,-_ dated 10/31/89 '

The' corrective: actions: for these events included repairing or

-replacing valves, and counseling personnel involved in the previous

, i events.. These corrective actions would not have prevented the-event addressed in:this' report'because no valve failure caused this y c event,- and personnel error did not cause this event.

23.L Faile'd Co'mponent(s) Identification: .

E Ma' ster.. Parts List Number: - 2G31 -R616D H

~c LManufacturer: : General Electric Model Number: -CR2820c

_ Type: Pneumatic Time Delay Relay '

. Root ~ Cause Code: X-H' Manufacturer Code: G084

-EIIS Component-Code: 62-

, ' EIIS System. Code: CE '

"> . Reportable to NPRDS: Yes 3

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