ML19325E831

LER 88-027-01:on 880721,main Control Room Ventilation Sys Isolated on Channel D High Chlorine Concentration Signal. Caused by Rainwater Coming in Contact W/Chlorine Analyzer Probe.Special Event Procedure SE-2 implemented.W/891031 Ltr

ML19325E831
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-88-027-01, LER-88-27-1, NUDOCS 8911090122
Download: ML19325E831 (5)

Text

i 10 CPR 50.73' e., ,

l PHILADELPHIA ELECTRIC COMPANY  ;

LIMERICK GENEM ATING ST ATION j

P. O. BOX A 1

. SAN ATOG A. PENNSYLV ANI A 19464

October 131, 1989 ,

(215) 3271200 sar 2000

u. 4. u. coa me n, e.., ex. Docket No. 50-352 a..,.......

Document Control Desk ,

U.S. Nuclear Regulatory Commission i Washington, DC 20555 j

SUBJECT:

Licensee Event Report ,

L_imerick Generating Station - Unit 1 l q

This revised LER reports an automatic actuation of the l Control Room Emergency Air Supply (CREFAS), an Engineered Safety

' Feature,'resulting from a chlorine concentration signal caused by rainwater contacting a chlorine analyzer probe.. , .

l l

Reference:

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

l Report Date: October 31, 1989 l l

Facility: Limerick Generating Station l P.O. Box A',' Sanatoga, PA 19464 l'

This revised LER is being submitted due to the completion of l 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 by revision bar markers in the right hand margin.

l Very truly yours, l

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O, JKP:sc cc: W. T. Russell, Administrator, Region I, USNRC T. J. Kenny, USNRC Senior Resident Inspector, LGS 8911090122 891031 ADOCK0500gg2 gff7,f ,

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On July 21, 1988 at 1738 hours0.0201 days <br />0.483 hours <br />0.00287 weeks <br />6.61309e-4 months <br />, the main control room ventilation system isolated on a "D" channel high chlorine concentration signal. The "B" train of the Control Room Emergency Presh Air Supply (CREFAS) system, an Engineered Safety Feature, initiated as designed. The' event occurred during heavy rain storms accompanied by high winds. The high chlorine concentration signal'was caused by rainwater coming in contact wi.th the chlorine analyzer probe resulting in a chemical imbalance in the probe's electrolyte. The analyzer probes are located close tc the outside air intake plenum  ;

' louvers. After the "D" chlorine detector spiked, operators implemented Special Event Procedure SE-2 (Toxic Gas Procedure) and manually tripped the "A", "B" and "C" chlorine isolation' channels in accordance with procedures. Proper control room isolation was verified. Following the storms, Instrument and Controls (I&C)  ;

inspected the detector and ensured that the intake plenum area was dry. 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 as a result of this event. A modification to move the chlorine detector probes was implemented by August 28, 1988 to mitigate false, environmentally related, automatic 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) j Reactor Power 87%

Description of the Event:

On July 21, 1988 at 1738 hours0.0201 days <br />0.483 hours <br />0.00287 weeks <br />6.61309e-4 months <br />, the main control room ventilation system 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 as 1

' designed when the chlorine analyzer momentarily spiked to approximately 1.5 ppm. The isolation occurred during heavy rain storms which were accompanied by high winds. After,the l

isolation, control room operators implemented Special Event Procedure SE-2 (Toxic Gas Procedure). Operators verified that the "A", "B" and "C" chlorine detectors indicated normal levels and 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 ,

. 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 the storms passed the area. Following the storms, Instrument and Controls (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 ,

I isolation was reset at 2350 hours0.0272 days <br />0.653 hours <br />0.00389 weeks <br />8.94175e-4 months <br /> on July 22, 1988, and normal control. room ventilation was restored. The duration of the l controlt room isolation was 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> and 12 minutes.

I:

Consequences of the Event:

The main control room ventilation system tripped and isolated. -

The."B" train of the CREFAS responded as designed. The "A" train m cf the CREPAS was in standby and available for operation. There was no chlorine intake to the main control room. If actual chlorine had been detected, as indicated by the redundant chlorine detectors, the chlorine detection system would have responded as designed and all control room personnel would have donned self contained breathing apparatus within two minutes as required by SE-2. There was no release of radioactive material as a result of this event, g< es.. us.

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r Cause of the Events The cause of the main control room ventilation system isolation

• and initiation of the "B" train of CREPAS was rainwater coming in contact with the chlorine analyzer probe during a heavy rain storm accompanied by high winds. This caused a chemical imbalance in the probe's electrolyte which simulated a high chlorine condition. The probe is located approximately one foot away from the outside air intake louvers of the Control Enclosure  :

intake plenum making it susceptible to moisture intrusion during inclement weather conditions. . .

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Corrective Actions: ,

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 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 (

l Isolation Signal", to ensure complete isolation of the main control room ventilation system as directed by SE-2. Following the storm, Instrument and Controls (I&C) inspected the detector and ensured that the air intake plenum was dry prior to resetting

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

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

reset and normal control room ventilation was restored at 2350 hours0.0272 days <br />0.653 hours <br />0.00389 weeks <br />8.94175e-4 months <br /> on July 22, 1988.

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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, 1988, there have been no spurious environmentally related chlorine detection system isolations of 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, a single spurious chlorine .

Isolation channel signal will not result in a MCR ventilation l syatem 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 l probe malfunction. This modification was completed on September 7, l 1989.

1 EIIS Codes:

I l

Control Room Ventilation - (VI)

Analyzer - (AE) l CREFAS - (VI) l 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 weather conditions.

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

,'Omas 3ese

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