ML20006E011

LER 90-002-00:on 900114,RWCU Experienced High Differential Flow,Indicating Possibility of Leak in Sys.Caused by Component Failure & Less than Adequate Mounting for Relay. Relay Replaced W/Time Delay relay.W/900206 Ltr

ML20006E011
Person / Time
Site:	Hatch
Issue date:	02/06/1990
From:	Hairston W, Tipps S GEORGIA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
HL-961, LER-90-002, LER-90-2, NUDOCS 9002160009
Download: ML20006E011 (7)

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r. , , r r. 's r W. G. Hairston, lit i~ be'uor Vre- P'nde tt l wea, onmns J HL-961 i 000199 February 6, 1990 U.S. Nuclear Regulatory Commission L

ATTN: Document Control Desk Washington, D.C. 20555 1

PLANT HATCH - UNIT 2 NRC DOCKET 50-366 I

OPERATING LICENSE NPF-5 LICENSEE EVENT REPORT ,

FAULTY TIME DELAY RELAY AND INADEQUATE MOUNTING CAUSE PARTIAL REACTOR WATER CLEANUP ISOLATION Gentlemen:  !

In accordance with the requirements of 10 CFR 50.73(a)(2)(iv), Georgia Power Company is submitting the enclosed Licensee Event Report (LER) ,

concerning the unanticipated actuation of an Engineered Safety Feature.

This event occurred at Plant Hatch - Unit 2. .

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W. G. Hairston, III t

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Enclosure:

LER'50-366/1990-002 l c:- (See next page.)

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,- i Georgial\$wer etik l U.S. Nuclear Regulatory Commission February 6, 1990 Page Two c: Georaia Power Comoany Mr. H. C. Nix, General Manager - Nuclear Plant -

Mr. J. D. Heidt, Manager Engineering and Licensing - Hatch GO-NORMS U.S. Nuclear Reaulatory Commission. Washinoton. D.C.

Mr. L. P. Crocker, Licensing Project Manager - Hatch U.S. Nuclear Reaulatory Commission. Reaion II Mr. S. D. Ebneter, Regional Administrator Mr. J. E. Menning Senior Resident inspector - Hatch i

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On 1/14/90, at approximately 1700 CST, Unit 2 was in the Hot Shutdown mode at an approximate power level of 0 MWt (approximately 0% of rated thermal power). At that time, plant operators were opening High Pressure Coolant Injection (HPCI, E!!S Code

10) discharge valve 2E41-F006 when they received annunciation that the Reactor Water Cleanup (RWCU, E!!S Code CE) system was experiencing high dif ferential flow, indicating the possibility of a leak in the system. RWCU experienced an immediate, partial Primary Containment Isolation System (PCIS Ells Code JM) isolation l involving only the outboard isolation valve 2G31-F004 (E!!S Code ISV). Normal system response should have been isolation of both valves 2G31-F001 (inboard isolation valve) and 2G31-F004 following a 45-second time delay.

The root causes of this event were component failure and a less than adequate mounting for relay 2G31-R616D. Time delay relay 2G31-R6160 was found to have  ;

intermittent contact failure. '

Corrective action for this event will include replacing the relay with a time delay relay of a different design, and improving the relay mounting.

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. LICENSEE EVENT REPORT (LER) TEXT CONTINUATION s.*enovio oMe no Siso-oio.

EXPIREC. 8 '31/N FAC4LITY 4AME m DOCKET NUM86R 12) LER NUM8th 161 P&Of (31 vlam s Ak Rf N p g p PLANT HATCH, UNIT 2 o16l0l0l0l3l6l6 9 l0 -

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SUMMARY

OF EVENT On 1/14/90, at approximately 1700 CST, Unit 2 was in the Hot Shutdown mode at an approximate power level of 0 MWt (approximately 0% of rated thermal power). At that time, plant operators were opening High Pressure Coolant Injection (HPCI, Ells Code BJ) discharge valve 2E41-F006 when they received annunciation that the Reactor Water Cleanup (RWCU, Ells Code CE) system was experiencing high differential flow, indicating the possibility of a leak in the system. RWCU experienced an immediate, partial Primary Containment Isolation System (PCIS, Ells Code JM) isolation involving only the outboard isolation valve 2G31-F004 (Ells Code ISV). Normal system response should have been isolation of both valves 2G31-F001 (inboard isolation valve) and 2G31-F004 following a 45-second time delay.

The root causes of this eve >re component failure and a less than adequate mounting for relay 2G31-R" Time delay relay 2G31-R616D was found to have intermittent contact faii.

Corrective action for th at will include replacing the relay with a time delay relay of a different de and improving the relay mounting.

DESCRIPTION OF EVENT On 1/14/90, at approximately 1700 CST, licensed plant operations personrel were performing 34SV-E41-001-2S, "HPCI Valve Operability," which required the opening of HPCI discharge valve 2E41-F006. Upon opening th'is valve, the RWCU leak detection system (LDS, Ells Code IJ ) annunciator sounded. Immediately the licensed operator observed that the RWCU pump trip light had illuminated and that isolation valve 2G31-F004 was moving to the closed position. The LDS alarm cleared within a few seconds. Plant equipment operators were dispatched to inspect the RWCU system for leaks. When no leaks were found, the system was returned to service at approximately 1748 CST.

Plant operations and mgineering personnel determined that the RWCU LDS had briefly sensed a high differential flow condition due to the brief flow transient which resulted from the opening of HPCI discharge valve 2E41-F006. Both the HPCI and RWCU systems discharge into the Feedwater (EIIS Code JB) system piping such that a brief pressure transient induced by the opening of 2E41-F006 could affect RWCU system discharge flow. Upon opening the HPCI discharge valve, RWCU discharge flow increased briefly due to the presence of lower pressure water in the HPCI piping.

Therefore, the brief receipt of a RWCU high differential pressure signal was not entirely unexpected. Momentary flow transients have been noted in the past when performing the same test.

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The RWCU LDS incorporates a time delay feature designed to prevent short transients from initiating an isolation. The fact that the isolation occurred in less' than the designed 45 seconds, and the fact that the isolation involved only the outboard isolation valve, 2G31-F004, indicated a problem existed with the time delay relay. Problems have been previously experienced with this, relay model.

Therefore, a new time delay relay was withdrawn from warehouse stock and tested in lieu of removing RWCU from service and removin0 the suspect relay from the circuit. Bench testing this new relay demonstrated that intermittent contact bounce occurred during relay chatter and occasionally during single actuations of the relay.

CAUSE OF THE EVENT The root causes of this event were component failure and a less than adequate mounting for time delay relay 2G31-R616D. Specifically, time delay relay 2G31-R616D experienced intermittent contact bounce when the relay was actuated by the flow transient. The relay is equipped with a pneumatic time delay mechanism designed to prevent spurious actuation of the isolation logic due to system transients or relay chatter. However, bench testing of a new relay (identical to the one installed) showed the mechanical shock of solenoid actuations was sufficient to induce a transient discontinuity in the time delay contacts. Thus the time delay contacts on 2G31-R616D apparently bounced during the flow transient due to actuation of the relay solenoid. This was sufficient to actuate the logic downstream of relay 2G31-R616D, which has a " seal in" function, resulting in full actuation of one channel of the trip logic. The bench test showed that mounting the relay more rigidly reduces, though it does not eliminate, the contact bounce problem. In this event, the subject relay was mounted to a steel plate inside a panel in the main control room. However, the mounting of the steel plate in the panel allowed more vibration than would be experienced with a typical wall '

mounting, making the relay more susceptible to contact bounce induced by repeated actuations of the solenoid. The time delay relay in the other channel of Group 5 PCIV- trip logic is mounted more stably, and thus did not experience contact bounce leading to a trip of the isolation logic.

REPORTABILITY ANALYSIS AND SAFETY AgESSMENT 1

This event is reportable under 10 CFR 50.73 (a)(2)(iv) because an unplanned -

actuation of an Engineered Safety Feature (ESF) occurred. Specifically, the PCIS l

' Group 5 outboard isolation valve, 2G31-F004, closed in response to an indication of high differential flow between the RWCU lines entering and leaving primary containment.

The purpose of the RWCU LDS is to detect leakage from the RWCU system outside  :

i primary containment and to mitigate the consequences of that leakage. This system uses leek detection instrumentation which initiates closure of Primary Containment Isolation Valves (PCIVs) upon detecting a parameter indicating a leak.

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"t!@,',' "?x',7 PLANT HATCH. UNIT 2 0151010 l o l 316 I 6 O b l2 014 0F Ol 8; 9 10 O l0 n m ~ nom a m ~ Nnc w m v<m In the event addressed in this report, a momentary condition of high differential flow was sensed, activating the time delay relay. Testing of a new time delay relay identical to the one installed in the RWCU system and mounted similarly to the actual field installation, showed intermittent contact bounce when the relay was actuated. This contact bounce is of sufficient duration to deenergize relays downstream of the time delay relay, which "scals in" an isolation, resulting in the full actuation of one channel of the isolation trip logic. The Group 5 PCIV closure logic channels are independent so that the time delay relay, 2G31-R616D, only has the capability to close the outboard isolation valve, 2G31-F004. Thus the other Group 5 PCIV, 2G31-F001, was unaffected by the event.

It should be noted that time delay relay 2G31-R6160 was mounted in compliance with applicable' seismic-related critoria. The architect / engineer was consulted during the course of the. event review to confirm seismic requirements were not violated by the installat'on.

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 level s.

CORRECTIVE ACTION Corrective actions for this event will include replacing time delay relays 2G31-R616C and 2G31-R616D with new relays of a different design. The new relays ,

will be installed in a rigid mounting. Design Change Request (DCR) 2H90-026 is '

under development to replace the relays and improve the relay mountings. The DCR will be reviewed by the Plant Review Board prior to DCR impler,catation to assure the design enhancement adequately addresses the event's root causes and meets all applicable regulatory criteria. The DCR will be implemented by 6/1/90.

ADDITIONAL INFORMATION

1. No plant systems other than the RWCU system and the Group 5 PCIVs were affected by this event.

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- 2. A similar event in which the RWCV system isolated due to a faulty time delay relay was reported in LER 50-366/1989-008, dated 11/29/89. The root cause for that event was reported to be component failure because bench testing identified a failed component whose symptoms duplicated those observed in Group 5 PCIV response during the event. Therefore, corrective action for that event was replacing the relay with a new relay of identical design. The '

component failure was believed at that time to be an isolated case based on information supplied by General- Electric representatives, Plant E. I. Hatch maintenance records and the Nuclear Plant Reliability Data System (NPRDS).

Therefore, it was not believed to be necessary to pursue the character of the mounting of the relay as a possible contributing factor or to search for ,

other anomalies in the performance of this relay model. Further bench-testing by Georgia Power Company following the subject event now indicates that other identical relays do exhibit the contact bounce phenomenon, but that increased rigidity in mounting the relay reduces the frequency of the ,

contact bounce, though it does not alleviate it. Since the corrective action '

for the previous event addressed neither the propensity for other relays of this design to exhibit contact bounce nor the issue of the rigidity of the relay mounting, the corrective actions for that event would not have prevented this event.

3. Upper level management personnel of Georgia Power Company recently convened a meeting of the Safety Review Board and were briefed on the issue of 1989 RWCU 1 isolations. ' ,

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FAILED COMPONENT IDENTIFICATION:

Master Parts List Number: 2G31 -R6160 Manufacturer: General Electric Type: Pneumatic Time Delay Relay Model Number: CR2820B128AA2

- Manufacturer Code: G080 EIIS System Code: .

CE EIIS Component Code: RLY Root Cause Code: X Reportable to NPRDS: Yes l

I NZC FQ8tM 366A *U.S. GPO: L998 S20-589 0004 n on .