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' PHILADELPHIA ELECTRIC COMPANY ;

LIMERICK GENEM ATING ST ATIONjP. O. BOX A1

. SAN ATOG A. PENNSYLV ANI A 19464October 131, 1989''

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(215) 3271200 sar 2000Docket No. 50-352u. 4. u. coa me n, e.., ex.

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Document Control Desk ,

iU.S. Nuclear Regulatory CommissionWashington, DC 20555

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SUBJECT: Licensee Event Report ,

L_imerick Generating Station - Unit 1 |

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This revised LER reports an automatic actuation of the |Control Room Emergency Air Supply (CREFAS), an Engineered Safety' Feature,'resulting from a chlorine concentration signal caused by

, rainwater contacting a chlorine analyzer probe.. , .

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Reference: Docket No. 50-352Report Number 1-88-027Revision. Number: 01Event Date: July 21, 1988 i

|j Report Date: October 31, 1989 l|

Facility: Limerick Generating Station!

| P.O. Box A',' Sanatoga, PA 19464l'

This revised LER is being submitted due to the completion of |

the modification committed to in the original LE,R. The original'LER was submitted pursuant to the requirements of 10 CFR J.:,

50.73(a)(2)(iv). Changes in this revised LER are indicated byrevision bar markers in the right hand margin.

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]Very truly yours, |

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cc: W. T. Russell, Administrator, Region I, USNRCT. J. Kenny, USNRC Senior Resident Inspector, LGS

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UCENSEE EVENT REPORT (LER) umt**nc, ,

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On July 21, 1988 at 1738 hours, the main control room ventilationsystem isolated on a "D" channel high chlorine concentrationsignal. The "B" train of the Control Room Emergency Presh AirSupply (CREFAS) system, an Engineered Safety Feature, initiated asdesigned. The' event occurred during heavy rain storms accompaniedby high winds. The high chlorine concentration signal'was causedby rainwater coming in contact wi.th the chlorine analyzer proberesulting in a chemical imbalance in the probe's electrolyte. Theanalyzer probes are located close tc the outside air intake plenum ;

' louvers. After the "D" chlorine detector spiked, operatorsimplemented Special Event Procedure SE-2 (Toxic Gas Procedure) andmanually tripped the "A", "B" and "C" chlorine isolation' channelsin accordance with procedures. Proper control room isolation wasverified. Following the storms, Instrument and Controls (I&C) ;

inspected the detector and ensured that the intake plenum area wasdry. All chlorine channels were verified to be within normal !

levels (less than 0.1 ppm). The isolation was reset at 2350 on ,

July 22, 1988, hours and normal control room ventilation was !

restored. There was no chlorine intake to the main control room.There was no release of radioactive material to the environment asa result of this event. A modification to move the chlorinedetector probes was implemented by August 28, 1988 to mitigatefalse, environmentally related, automatic control room ventilationsystem isolations. Additionally, a second modification designed tochange the chlorine detection logic was completed on September 7,1989.

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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION amovio ovs =o vio-o*. enems sm a !

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Limerick Cenerating Station, Unit 1

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Unit Conditions Prior to the Event:

Operating Mode 1 (Power Operation) j

Reactor Power 87%.

Description of the Event:

On July 21, 1988 at 1738 hours, the main control room ventilationsystem isolated on a "D" channel high chlorine concentration ::' signal. The "B" train of the Control Room Emergency Fresh Air *

Supply (CREFAS) system, an Engineered Safety Feature, started as1 designed when the chlorine analyzer momentarily spiked to'

approximately 1.5 ppm. The isolation occurred during heavy rainstorms which were accompanied by high winds. After,theisolation, control room operators implemented Special Event

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Procedure SE-2 (Toxic Gas Procedure). Operators verified thatthe "A", "B" and "C" chlorine detectors indicated normal levelsand the "D" channel isolation signal was determined to be false. ,

Operations personnel then manually tripped the "A", "B" and "C"chlorine isolation channels according to procedures'to ensure ,

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. complete.. isolation of the control room ventilation system. '

LProper control room isolation was verified and the control room i

remained in-an isolated mode, with.CREPAS operating, until thestorms passed the area. Following the storms, Instrument andControls (I&C) inspected the detector.and ensured that the air

! ' intake plenum was dry prior to resetting the isolation.t

L Operations personnel verified that all'four chlorine-isolation; channels were within normal range (less than 0.1 ppm). The

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I isolation was reset at 2350 hours on July 22, 1988, and normalcontrol. room ventilation was restored. The duration of the

| controlt room isolation was 30 hours and 12 minutes.I:.

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,,Consequences of the Event:

The main control room ventilation system tripped and isolated. -

The."B" train of the CREFAS responded as designed. The "A" traincf the CREPAS was in standby and available for operation. Theremwas no chlorine intake to the main control room. If actualchlorine had been detected, as indicated by the redundantchlorine detectors, the chlorine detection system would haveresponded as designed and all control room personnel would havedonned self contained breathing apparatus within two minutes asrequired by SE-2. There was no release of radioactive materialas a result of this event,

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Cause of the Events.

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The cause of the main control room ventilation system isolation *

and initiation of the "B" train of CREPAS was rainwater coming incontact with the chlorine analyzer probe during a heavy rainstorm accompanied by high winds. This caused a chemicalimbalance in the probe's electrolyte which simulated a highchlorine condition. The probe is located approximately one footaway from the outside air intake louvers of the Control Enclosure :intake plenum making it susceptible to moisture intrusion duringinclement weather conditions.

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Corrective Actions: ,

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Control Room personnel implemented Special Event Procedure SE-2(Toxic Gas Procedure) immediately following the isolation.Operations personnel then verified that the "A", "B" and "C" *

chlorine detectors indicated normal levels and the "D" channel,

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isolation signal was determined to be false. Operations'

personnel then manually tripped the "A", "B" and "C" chlorine "

isolation channels, in accordance with System Procedure S78.0.B -:" Verification of Control Room HVAC Response to a Control Room (

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| Isolation Signal", to ensure complete isolation of the maincontrol room ventilation system as directed by SE-2. Following

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the storm, Instrument and Controls (I&C) inspected the detectorand ensured that the air intake plenum was dry prior to resetting *

the isolation. Operations personnel verified that the chlorinedetector channels ("A", "B", "C" and "D") indicated ~ chlorine '

concentration levels were within normal levels (less than 0.1ppm). The main control room ventilation system isolation was ,

reset and normal control room ventilation was restored at 2350hours on July 22, 1988.

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Actions Taken to Prevent Recurrence:

Two modifications to CREFAS were implemented to prevent spuriousisolations of the Main Control Room (MCR) ventilation system. Thefirst modification consisted of moving the analyzer probes awayfrom the outside air louvers. This new location provides better'

protection for the analyzer probes from rainwater and dirt. Sincethe implementation of this modification on August 28, 1988, therehave been no spurious environmentally related chlorine detectionsystem isolations of the MCR ventilation system. The secondmodification changed the chlorine detection system logic from a"one out of one taken once" to a "two out of two taken once"configuration. With this change, a single spurious chlorine .

Isolation channel signal will not result in a MCR ventilation |

syatem isolation. This modification will prevent any spuriousenvironmentally related chlorine detection system isolations of the

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! MCR due to a single false isolation signal or a single detector

| probe malfunction. This modification was completed on September 7,| 1989.

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EIIS Codes:I

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Control Room Ventilation - (VI)Analyzer - (AE)

| CREFAS - (VI)

|Previous Similar Occurrences:

Limerick LERs 06-46, 87-03, 87-06, 87-09, 87-051, 88-014, 88-018,88-021 and 88-026 reported CREFAS actuations resulting from false-

"C" or "D" high chlorine concentration signal during rainy weatherconditions.

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Tracking Codes: (C) - Ext'ernal Cause(B99) - Design Deficiency

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