05000277/LER-1998-002, Forwards Details of LER 98-002-00 Re 980505 Loss of Both Trains of Main CR Emergency Ventilation Sys,Per Requirements of 10CFR50.73(a)(2)(i)(B)

Forwards Details of LER 98-002-00 Re 980505 Loss of Both Trains of Main CR Emergency Ventilation Sys,Per Requirements of 10CFR50.73(a)(2)(i)(B)

ML20248M266
Person / Time
Site:	Peach Bottom
Issue date:	06/04/1998
From:	Warner M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9806150220
Download: ML20248M266 (5)

LER-2098-002, Forwards Details of LER 98-002-00 Re 980505 Loss of Both Trains of Main CR Emergency Ventilation Sys,Per Requirements of 10CFR50.73(a)(2)(i)(B)

Event date:
Report date:
2772098002R00 - NRC Website

text

_ _ _ _ _ _ _ _ _ _ _ _ _

• Mark E.W;rner

. Plant Manager

, _, i Peach Bottom Atomic Power Station v

PECO NUCLEAR ecco tee,ov c 1848 Lay Road emneev A Unit of PECO Energy Delta. PA 17314-9032 717 456 4244 June 4,1998 Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555 Docket No. 50-277 and 50-278

SUBJECT:

Licensee Event Report, Peach Bottom Atomic Power Station Unit 2 and Unit 3.

This LER reports the loss of both trains of the Main Control Room Emergency Ventilation (MCPEV) System and is being submitted pursuant to the requirements of 10 CFR 50.73 (a)(2)(i)(B).

Reference:

Docket No. 50-277 and 50-278 Report Number: 2-98-002 Revision Number: 00 Event Date: 5/5/98 Discovery Date: 5/5/98 Report Date: 6/4/98 Facility: Peach Bottom Atomic Power Station 1848 Lay Road, Delta, PA 17314 I[ l MEW /afp h & /7([

enclosure cc: N. J. Sproul, Public Service Electric & Gas  !

R. R. Janati, Commonwealth of Pennsylvania INPO Records Center )

H. J. Miller, US NRC, Administrator, Region l R. I. McLean, State of Maryland A. C. McMurtray, US NRC, Senior Resident Inspector A. F. Kirby Ill, DelMarVa Power l

CCN 98-14040

~

9906150220 990604 I

PDR ADOCK 05000277 g PM c - - - - - - - - - - - - - - - -

On Saturday, May 2,1998, the Main Control Room Emergency Ventilation (MCREV)

System was placed in service for the performance of a surveillance test (ST). The 'B' -

subsystem was in operation when the ST failed due to the flow rate not being within the allowable limits per Technical Specifications (TS). A Technical Specification Action (TSA) was entered and the 'B' MCREV subsystem was declared inoperable. An

, investigation to determine the cause of the low flow condition was initiated which

' included returning the normal control room ventilation system to service. During this evolution the 'B' fan control switch was repositioned from 'OFF' to ' AUTO' when the fan unexpectedly started and ran for approximately 15 seconds before its circuit breaker tripped due to an overcurrent condition. After maintenance was performed on the circuit breaker, the 'A' MCREV subsystem wa s placed in service to allow restoration of the 'B' MCREV subsystem. With 'A' MCREV subsystem in service, operators noticed that the flow rate was not within the allowable limits per TS. With both MCREV subsystems inoperable, LCO 3.0.3 was entered immediately for both units per the requirements of TS 3.7.4. 'A' MCREV flow was then adjusted to within TS limits, declared operable, and LCO 3.0.3 was exited. The 'B' MCREV subsystem was declared operable following replacement and testing of the failed fan circuit breaker and ;

adjustment of flow to within the TS limits.

l 1

l Requirements of the Report This LER is being submitted pursuant to 10 CFR 50.73 (a)(2)(i)(B) due to a condition prohibited by Technical Specifications. l Unit Conditions at Time of Discoverv  !

Units 2 and 3 were in the "RUN" mode at 100 percent of thermal reactor (Ells:RCT) power. There were no systems, structures nr components that were inoperable that contributed to the event.

1 Description of the Event On Saturday, May 2,1998, at 16:00, the Main Control Room Emergency Ventilation (MCREV) System was in operation for the performance of a surveillance test (ST) which verifies the flow rate through the system. ST-O-40D-326-2, ' Control Room Emergency Ventilation Capability Test", placed the 'B' subsystem in service. Step 6.2.3 of the ST, which verifies. and records the flow rate, was signed off unsatisfactorily. The indicated i flow was oscillt.Sg between 0.145" and 0.16" H2O which was below the acmptance ciiteria of 0.16" to 0.19" H20. The ST was stopped, technical specification actions (TSA) were entered and the 'B' MCREV subsystem, was declared inoperable per TS 3.7.4. The flow controlloop was suspect and troubleshooting was initiated. During restoration of the romal control room ventilation system, the 'B' MCREV fan control switch was repositioned from *OFF" to " AUTO" when the fan unexpectedly started and ran for approximately 15 seconds before tripping due to an overcurrent condition. The fan breaker was reset and opened for investigation. ,

On Monday, May 4,1998, at 01:15 the 'B" MCREV subsystem was placed in service to correct the low flow condition. This was accomplished by adjusting the 'B' tan flow controller thus increasing the fiow to within the TS limits. A pneumatic jumper was also l installed during this evolution to allow maintenance to be perfonned on the 'B' faa circuit breaker. Once this was completed norme.1 control room ventilation was restored.

Electricians perfonned maintenance on the 'B' fan circuit breaker, replacing the molded case circuit Leaker and auxiliary contacts. The molded case circuit breaker and auxiliary contacts were sent to Valley Forge Labs for examination and testing.

i l

l L ------_ _____ ______ _.----- - - - - - - - - . - - . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - - - -- - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - . _ _ _ _ _ _ _ _ _ _ _

_ _ __ __ j

l

..'~ ..

On Tuesday, May 5,1998, at 02:26, riuring clearance and jumper removal from the 'B' fan, the.'A' subsystem was placed in service. The post-maintenance test (PMT) was not

. yet performed on the 'B' fan breaker and the breaker remained in the open position.

At 03:40 MCREV flow indication was noticed to be oscillating between 0.145" and 0.16" H20. With the 'B' fan inoperable and the 'A' fan in operation with a flow less than or equal to that required by TS 3.7.4, the 'A' MCREV subsystem was declared inoperable and LCO 3.0.3 was entered for Unit 2 and Unit 3. Troubleshooting was performed to adjust flow to within TS limits. At 04:21 the 'A' MCREV System was declared operable,

' LCO 3.0.3 was exited, and normal control room ventilation was restored.- At 13:35 the 'B' fan circuit breaker was closed and the 'B' MCREV subsystem was placed in service to .

perform ST-O-40D-326-2 and the PMT for the circuit breaker. At 14:22 the ST and PMT were completed satisfactorily and normal control room ventilation was restored. During discussions between Plant Management, Engineering, and Operations, it was determined that increased monitoring was needed to ensure MCREV system operability is maintained. This was accomplished through a revision to the monthly ST (ST-O-40D-

, . 320-2 and ST-O-40D-325-2) to verify MCREV system flow was within TS criteria.

On Wednesday, May 6,1998, failure analysis results from Valley Forge Labs for the 'B' fan circuit breaker and auxiliary contacts was received. A review of these results as well-as all troubleshooting by Engineering and Operations determined the most probable ,

1cause to be the auxiliary contacts for the auto-start seal-in circuit. The circuit breaker was '

deiermined to be operable and the 'B' MCREV subsystem was declared operable.

- Causes of the Event l

This avent resulted from both flow controllers failing to control flow within the TS band due j

to setpoint drift.- The root cause investigation continues to examine the flow control loops and associated hardware to improve system reliability.

Analysis of the circuit breaker from Valley Forge Labs confirmed the integrity of the -

breaker, however the laboratory did identify poor auxiliary contact quality. .These  !

contacts operate the coil of the contactor which controls power to the fan motor. The l auxiliary contacts exhibited heavw oxidation and showed evidence of burns and arcing

on the contact surface. We concluded the changing contact resistance caused the coil i L to change state. If the power contacts operated by the coil were opened.and closed  !

rapidly, large voltage spikes would be generated by the motor coils'which would create )

current surges of adequate magnitude ano duration to cause the breaker to trip. This _ i condition has not been' duplicated on the MCREV System fan circuit in subsequent operational tests.

.,?-

Analysis of Event No actual safety consequences or implications occurred as a result of this event and the condition did not adversely effect the safe operation of the plant. No power reduction was initiated since the low flow condition was corrected in less than one hour in accordance with the TS required actions. During power operations, the MCREV System is in the " Auto" mode and would initiate if high radiation levels were sensed in the supply duct or when low flow is detected from the normal control room ventilation system Corrective Actions The flow control loops have been tuned to restore flow within the TS band. As an interim corrective action the monthly surveillance tests for both MCREV subsystems have been revised to provide flow criteria to ensure operability is maintained. The MCREV System is being reviewed by engineering to identify potential design improvements.

f I

The 'B' fan breaker was replaced and tested to prove operability. This included replacement of the auxiliary contacts.

Previous Similar Events l l

There have not been any previous similar events. '

l 1

L L_ _ - -

-