ML19325E830

LER 88-026-01:on 880717,main Control Room Ventilation Sys Isolation Occurred Due to Channels C & D High Chlorine Concentration Signal.Caused by Rainwater Coming in Contact W/Chlorine Analyzer Probes.Procedure SE-2 done.W/891031 Ltr

ML19325E830
Person / Time
Site:	Limerick
Issue date:	10/31/1989
From:	Endriss C, Mccormick M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-88-026, LER-88-26, NUDOCS 8911090115
Download: ML19325E830 (5)

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10 CFR 50.73

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PHILADELPHIA ELECTRIC COMPANY  :

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' LIMERICK GEk ER ATING ST ATION ,

P. O.BO X A ,

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Docket No. 50-352 f

Document Control Desk

.U.S. Nuclear. Regulatory. Commission

~ Washington,.DC 20555 -

Licensee Event Report. l

SUBJECT:

' Limerick Generating Station - Unit 1 }

i This LER reports an automatic actuation of the Control Room Emergency Presh Air Supply (CREPAS), an Engineered Safety Feature, resulting from a chlorine concentration' signal caused by rainwater contacting chlorina analyzer probes.  ;

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Reference:

Docket No. 50-352 I

. Report Numbert. 1-88-026 -

Revision' Number: 01  :

Event.Date: July 17, 1988 Report Date: October 31, 1989 3' Facility: Limerick Generating Station P.O. Box A, Sanatoga, PA 19464 This revised LER is.being submitted due to the the completion of the modification committed to in the original LER.

The original LER was submitted pursuant to the requirements of 10  ;

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.CPR 50.73(a)(2)(iv). Changes in the revised LER are indicated by j; revision-bar markers in the right hand margin.

1 L Very truly yours,

( [p jd I, G JKP:sc cc: W. T. Russell, Administrator, Region I, USNRC T. J. Kenny, USNRC Senior Resident Inspector bOC ,g2 i.

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On July 17, 1988 at 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br />, a main control room ventilation system isolation occurred due to a "C and "D" channel high chlorine concentration signal. The "A" and "B" trains of the Control Room Emergency Fresh Air Supply (CREFAS) system, an Engineered Safety Feature, initiated as designed. The event I

occurred during severe local thunderstorms. The high chlorine concentration signal was caused by rainwater coming in contact with the analyzer probes resulting in a chemical imbalance in the probes' electrolyte. The analyzer probes are located close to ,

the outside air intake plenum. After the "C" and "D" channels l spiked, control room operators implemented Special Event Procedure SE-2 (Toxic Gas Procedure) and manually tripped the "A" and "B" chlorine isolation channels in accordance with procedures. Proper control room isolation was verified.

Chemistry sampled the Control Enclosure HVAC intake plenum and no chlorine was detected. All chlorine channels were verified to be within normal levels (less than 0.1 ppm). The isolation was reset and normal control rocm ventilation was restored at 2036 hours0.0236 days <br />0.566 hours <br />0.00337 weeks <br />7.74698e-4 months <br />. There was no release of radioactive material to the environment as a result of this event. A modification to relocate the detectors was implemented on August 28, 1988 to mitigate false environmentally related control room ventilation system isolations. Additionally, a second modification designed to change the chlorine detection logic was completed on September 7,.1989.

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Unit Conditions Prior to the Event:

Operating Mode 1 (Power Operation)  ;

Reactor Power 79%

Descript' ion of the Event:

On July 17, 1988 at 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br />, the main control room ventilation  !

system isolated due to a "C" and "D" channel high chlorine i concentration signal. l Both the "A" and "B" trains of the Control Room Emergency Presh

, Air Supply-(CREFAS) system, an Engineered Safety Feature, started as designed when the "C" and "D" chlorine analyzers both spiked to approximately 3.0 ppm for approximately 90 seconds.~ The 3 isolation occurred during severe local thunderstorms.; After the 1 isolation, control room operators implemented Special Event i Procedure-SE-2 (Tnxic Gas Procedure). Operators. verified that j the "A" and "B". chlorine detectors indicated normal chlorine levels.and determined the "C" and "D" chlorine isolation signals  ;

were spurious. The "A" and'"B" channel chlorine detectors were then' tripped'by Operations personnel according to procedure te, ensure complete isolation of the Control Room-ventilation system. 1 Froper Control Room isolation was verified. Chemistry personnel  ;

I sampled the Control Enclosure HVAC intake plenum and verified '

that no chlorine was present. The isolation was reset and normal' control room ventilation was restored by 2036 hours0.0236 days <br />0.566 hours <br />0.00337 weeks <br />7.74698e-4 months <br />. The duration of the control room isolation was 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> and 6 minutes.

Consequences of the Event:

J The main control room ventilation system tripped and isolated. ,

The "A" and "B" trains of the'CREFAS responded as designed.

Chemistry took air samples and verified that there was no chlorine intake to the main control room. If actual chlorine had i been detected as indicated by redundant chlorine detectors, the chlorine detection system would have responded as designed and all personnel in the Contrdl Room would have donned self-contained breathing apparatus within two minutes of the isolation as required by Special Event Procedure SE-2 (Toxic Gas Procedure). There was no release of radioactive material as a result of this event.

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0 l2 l6 - 011 , 01 3 OF 0 l4 rext,, . ,. - =nce.,-m mi Cause of the Event:

i The cause of the main control room ventilation system isolation and initiation of.the "A" and "B" trains of CREFAS was caused by rainwater coming in contact with both the "C" and "D" chlorine analyzer probes during a severe local thunderstorm accompanied by high winds. This caused a chemical imbalance in the probes'  ;

electrolyte which simulated a high chlorine condition. The '

probes are located approximately one foot away from the outside air intake louvers of the Control Enclosure intake plenum making j them susceptible to moisture intrusion during inclement weather conditions.

Corrective Actions: I Control Room personnel implemented Special Event Procedure SE-2 1 (Toxic Gas Procedure) immediately following the isolation.

Operations personnel verified that the "A" and "B" chlorine detectors indicated normal levels and determined that the "C" and "D" chlorine isolation signals were spurious. The "A" and "B" channel chlorine detectors were then manually tripped by Operations personnel to ensure complete isolation of the Control ,

Room ventilation system. After the 90 second spike, Operations 1 personnel verified that all four chlorine detector channels ("A", I "B", "C" and "D") indicated chlorine concentration levels were within normal levels (less than 0.1 ppm). Chemistry personnel sampled the Control Enclosure HVAC intake plenum and verified that no chlorine was present. The main control room ventilation system isolation was reset at 2036 hours0.0236 days <br />0.566 hours <br />0.00337 weeks <br />7.74698e-4 months <br /> and normal control room ventilation restored.

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Actions Taken to Prevent Recurrence Two modifications to CREFAS were implemented to prevent spurious '

isolations of the Main Control Room (MCR) ventilation system.

The first modification consisted of moving the analyzer probes away from the outside air louvers. This new location provides better protection for the analyzer probes from rainwater and dirt. Since the implementation of this modification on August 28, 1989, there have been no spurious environmentally related chlorine detection system isolations for the MCR ventilation system. The second modification 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, & single spurious chlorine isolation channel signal will not result in a MCR ventilation system isolation. This modification'will prevent any spurious environmentally related chlorine detection system isolations of the MCR due to a single false isolation signal or a -

single detector-probe malfunction. This. modification was completed on September 7, 1989.

EIIS Codes:

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Control Room Ventilation - VI Analyzer - AE CREFAS - VI Previous Similar Occurrences:

Limerick LERs 86-46, 87-03, 87-06, 87-09,87-051, 88-014,88-018, and 88-021 reported CREFAS actuations resulting from false "C" or "D" channel high chlorine concentration signal during rainy ,

weather conditions.

Tracking Codes: (C) - External Cause (B99) - Design Deficiency ,

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