ML20043C523

LER 90-003-01:on 900208,HPCI Sys Isolation Valve Inadvertently Isolated During Surveillance Test.Caused by Both Channels of Isolation Logic Being in Tripped Condition at Same Time.Isolation of HPCI Sys reset.W/900601 Ltr

ML20043C523
Person / Time
Site:	Limerick
Issue date:	06/01/1990
From:	Madsen G, Mccormick M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-003, LER-90-3, NUDOCS 9006050280
Download: ML20043C523 (5)

Text

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h , PHILADELPHIA ELECTRIC COMPANY LIMERICK GENER ATING STATION P. O. BOX A SAN ATOG A, PENNSYLV ANI A 19464 (2 5 5) 3171200 axv. 2000 s - m. 4 m.coamie n. a... e.e. June 1, 1990-B u. . . ./M"/. .".'.",'.* * ". . . ... Docket No. 50-352 License No. NPF-39

'U.S. Nuclear Regulatory Commission ,

Attn: Document Control Desk _l Washington, DC 20555

SUBJECT:

Licensee Event Report Limerick Generating Station - Unit 1 This LER reports an Engineered Safety Feature actuation which also resulted in a condition whi::h the High Pressure Coolant Injection (HPCI) system could have been prevented from performing its intended safety function. Specifically, the HPCI system inboard' isolation valve inadvertently isolated due to the failure of a Rosemount trip unit.

Reference:

Docket No. 50-352 Report Number: ' 1-90-003 Revision Number: 01 Event Date: February 8, 1990 Report Date: June 1, 1990 Facility: Limerick Generating Station P.O. Box A, Sanatoga, PA 19464 This revised LER is being submitted to provide an update on the root cause investigation. Changes are indichted by revision bar markers in the right hand- -

i margin. The original LER was submitted pursuant to the requirements of 10 CFR~ l 50.73(a)(2)(iv) and 50.73(a)(2)(v).

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On February 8, 1990 at 1745 hours0.0202 days <br />0.485 hours <br />0.00289 weeks <br />6.639725e-4 months <br />, a High Pressure Coolant injection (HPCI) system inboard isolation valve inadvertently isolated during the performance of the "NSSSS-HPCI Steam Supply Pressure-Low" Surveillance Test. This valve is

.part of the Primary Containment Reactor Vessel Isolation Control System which is an Engineered Safety Feature. The valve closed when the Instrumentation and Controls (I&C) technicians tripped one channel of the isolation logic as directed by the test procedure. Subsequent investigation into the cause of the event revealed that the other channel of the isolation logic had inadvertently tripped during the performance of the ST resulting in the isolation of the HPCI system valve. The logic on this channel was in a tripped condition due to equipment malfunction. A Rosemount trip unit, PIS-55-1N6580, intermittently failed in the energized tripped condition due to the degradation of the Darlington output transistor inside the trip unit. The isolation was reset on February 8, 1990 at 1957 hours0.0227 days <br />0.544 hours <br />0.00324 weeks <br />7.446385e-4 months <br /> and the trip unit was replaced on February 14, 1990. The HPCI system was isolated for approximately two hours and there were -

no adverse consequences as a result of this event. The manufacturer of the trip unit is continuing the investigation into the root cause of the transistor failure and a supplement to this LER will be provided when the root cause information is obtained.

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Operating Condition: 1(PowerOperation)

Power Level: 100% i Description of the Event:

On February 8, 1990, at 1745 hours0.0202 days <br />0.485 hours <br />0.00289 weeks <br />6.639725e-4 months <br />, the Unit 1 High Pressure Coolant Injection (HPCI) (Ells:BJ) system inboard Primary Containment isolation valve (HV  !

1F002) inadvertently isolated during the performance of Surveillance Test (ST) procedure ST-2-055-610-1, "NSSS-HPCI Steam Supply Pressure-Low." The valve j closed when the Instrumentation and Controls (l&C) Technicians tripped one channel of the HPCI system isolation logic as directed by the test procedure.

.This valve is part of the Primary Containment Reactor. Vessel isolation Control '

System (PCRVICS) (Ells:BJ) which is an Engineered Safety Feature (ESF).

' Subsequent investigation into the cause of the event revealed that the other channel of the HPCI isolation' logic had inadvertently tripped during the .

performance of the ST resulting in the isolation of the HPCI system valve. . The  !

reason this channel was in the tripped condition was not identified at the time of the ST performance. The ST was successfully reperformed and the HPCI iso _lation was reset at 1957 hours0.0227 days <br />0.544 hours <br />0.00324 weeks <br />7.446385e-4 months <br /> on February 8, 1990. The HPCI system was.

unavailable for automatic operation for approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and 12 minutes.

A four hour notification to the NRC was made at 1745 hours0.0202 days <br />0.485 hours <br />0.00289 weeks <br />6.639725e-4 months <br /> on February 8,1990 inaccordancewiththerequirementsof10CFR50.72(b)(2)(ii)and10CFR 50.72(b)(2)(iii) since this event resulted in an ESF actuation and a condition in which the HPCI system could have been prevented from fulfilling its intended i safety function to mitigate the consequences of an accident. Accordingly, this L report is being submitted in accordance with 10 CFR 50.73(a)(2)(iv) and L 50.73(a)(2)(v).

Consequences of the Event:

The HPCI system isolated as designed based on both of the isolation logic channels being in the tripped condition at the same time. There were no adverse

- . consequences and no release of radioactive material as a result of this event, In the event of an accident requiring the use of the HPCI system during-the time period that it was isolated, operators could have unisolated the system and then manually initiated the HPCI system. In addition, the Automatic Depressurization System, the Low Pressure Emergency Core Cooling Systems, and the Reactor Core Isolation Cooling-System (EIIS:BN) were operable to respond to an accident condition in the event that the HPCI system could not be manually initiated, n toIM 3e44

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The cause of the HPCI system isolation was due to both channels of the isolation logic being in the tripped condition at the same time. One channel of the isolation logic was placed in the tripped condition by the I&C technicians asi directed by the ST. The logic on the other channel inadvertently tripped due'to.

-equipment malfunction while the ST was being performed and was undetected by the I&C technicians until the isolation occurred. To investigate the cause of the isolation, a strip chart recorder was used to monitor trip unit behavior. This investigation revealed that the Rosemount trip unit, PIS-55-1N6580, (model

1. 5100U137030A005) intermittently failed in the energized condition due to the gradual degradation of the Darlington output transistor inside of the trip unit.

The failure of the degraded Darlington transistor had been previously identified in other similar events. These failures were previously recognized during investigations of single channel trips which resulted in annunciator ala,rms in the Main Control Room. However, none of these events resulted in reportable

! events. Detailed information was provided to the manufacturer at the time of L the failures and we requested an investigation into the cause. The failed component was returned to the manufacturer who is continuing a detailed investigation to determine the root cause of the transistor failure. The manufacturer is working.with the transistor supplier to isolate the cause of the failure.

l Corrective Actions:

l The isolation of the HPCI system was reset by Main Control Room Operators at 1957.' hours on February 8, 1990. The cause of why the other logic was in the tripped condition was not known when the isolation was reset. The trip unit transistor failure is of an intermittent nature such that after a failure it can reset itself. As a result of this characteristic, this failure was not readily identifiable. Once identified the PIS-55-1N6580 trip unit was replaced on February 14, 1990.

This event was discussed at an all hands I&C meeting on February 23, 1990 to stress the importance of recognizing the state of alarms and logic status lights l when confronted with a problem while performing surveillance tests and/or when troubleshooting a problem. Although this action could not have prevented this particular event from occurring, it will aid in expediting the identification of any potential future problems that may occur.

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Actions Taken to Prevent Recurrence:

' Actions to prevent" recurrence will be determined 'as appropriate, based on the -

results of the root cause investigation _being performed by the manufacturer.' A supplement to this LER will be provided when the results ofithe' manufacturer's' investigation are available. We will continue to pursue this issue with the ' .

manufacturer until a resolution is obtained.

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Previous Similar Occurrences:

There have been other HPCI system isolations (LER is 1-85-013, 1-85-016, 1 077 and 1-85-037) but none have been attributed to a failing trip unit. The ,

corrective actions to prevent recurrence from these previous events coul'd not s have prevented this event.

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. Tracking Codes:

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! 'B17 - Deficient equipment.

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