05000278/LER-1993-004

LER 93-004-00:on 930730,simulated Low Steam Flow Signal to Recombiner Initiated Isolation Signal to Off Gas Recombiner, Causing Main Condenser Vacuum to Begin Decreasing.Special Procedure SP-1438 revised.W/930830 Ltr

ML20056H117
Person / Time
Site:	Peach Bottom
Issue date:	08/30/1993
From:	Geoffrey Edwards, Wasong A PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CCN9314114, LER-93-004-03, LER-93-4-3, NUDOCS 9309080247
Download: ML20056H117 (5)

LER-2093-004,

Event date:
Report date:
2782093004R00 - NRC Website

text

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CCN9314114

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. PIIILADELPHIA ELECTRIC COMPANY ps T i

e , PEACH BOTTOM ATOMIC POWER STATION Mjm R.D.1, Box 208 gf Delta. Pennsylvania 17314 GARRLTT D. EDWARDS (717) 456-4244 l PLAN 1 MAN 0la I

August 30, 1993 Docket No. 50-278 f l

Document Control Desk  ;

U. S. Nuclear Regulatory Commission  !

Washington, DC 20555

SUBJECT:

Licensee Event Reoort '

Peach Bottom Atomic Power Station - Unit 3 This LER concerns a Unit 3 Low Condenser Vacuum scram and Primary Containment Isolation System Group 11/111 isolations following a Recombiner Off Gas isolation. ,

Reference:

Docket No. 50-278 Report Number: 3-93-004 Revision Number: 00  !

Event Date: 07/30/93 Report Date:  !

4 Facility: Peach Bottom Atomic Power Station  ;

RD1, Box 208, Delta, PA 17314 r i

This LER is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(iv).  !

i Sincerely, ,

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' i cc: R. A. Burrice!!i, Public Service Electric & Gas W. P. Dornsife, Commonwealth of Pennsylvania l INPO Records Center T. T Martin, US NRC, Administrator, Region I i R.1. McLean, State of Maryland B. S. Norris, US NRC, Resident inspector C. D. Schaefer, DelMarVa Power H. C. Schwemm, VP - Atlantic Electric )

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NAME Y E L { PeONE NgvBt H A54Le CUD 1 Anthony J. Wasong, Manager - Experience Assessment 711l7 4 I 5;6 l-171 01 Q j COMPL{ T{ DN( L]N[ F Dft 4 ACH COMPONE NT F ALLURE DESCRISI D IN TMi$ flEPDR1 M31 CAvtf Sv57& v COMrONENT ((h Tg [f3d CAv51 Sv 5'E M COMPON E NT

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4 On 7/30/93, after venting the Off Gas Recombiner (OGR) steam flow condensing r chambers using a Special Prccedure (SP-1438), a simulated low steam flow signal to the  :

Recombiner initiated an isolation signal to the OGR. This caused Main Condenser l l' vacuum to begin decreasing. At 0327 hours0.00378 days <br />0.0908 hours <br />5.406746e-4 weeks <br />1.244235e-4 months <br />, with the Reactor at 72% power, a auto half l scram signal was received due to low main condenser vacuum. Therefore, the unit was  ;

manually scrammed. An investigation has determined that the cause of the OGR isolation l was the combination of a previously failed fuse from unknown causes in the "B" OGR steam flow isolation logic and the blowing of a fuse in the "A" OGR steam flow isolation j logic due to grounding of a jumper being removed during the performance of SP-1438.  ;

Following the event, the scram and isolation logics were reset. Affected systems were l j restored to appropriate conditions and the blown fuses were replaced. SP 1438 has been ,

, revised to ensure that fuse status is monitored. An investigation is currently underway l to identify the cause of the fuse failure in the "B" OGR logic and to determine if terminal  !

point modifications are necessary. Design changes and/or corrective actions will be l implemented as necessary. No actual safety consequences occurred as a result of this  !

event. No previous similar LERs have been identified.  :

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Reovirements for the Report I This report is submitted to satisfy the requirements of 10 CFR 50.73(a)(2)(iv) because of f unp!anned Engineered Safety Feature Actuations.  ;

I Unit Conditions at Time of Event Unit 3 was in the RUN mode at approximately 100% of rated thermal reactor (Ells:RPV) I power at the time of the Off Gas Recombiner isolation. Reactor power was reduced to l approximately 72% power at the time of the scram. There were no systems, structures, or components that were inoperable that contributed to the event. ,

Descriotion of Event 5 On 7/30/93 at 0320 hours0.0037 days <br />0.0889 hours <br />5.291005e-4 weeks <br />1.2176e-4 months <br />, after venting the Off Gas Recombiner (OGR) (Ells:WF) steam ,

flow condensing chambers using a Special Procedure (SP-1438) " PROCEDURE TO l PURGE AND VENT SENSING LINES, CONDENSING POTS AND FLOWTRANSMITTERS ,

FOR STEAM FLOW TO THE RECOMBINER", a simulated low steam flow signal to the j Recombiner initiated an isolation signal to the OGR. This caused Main Condenser l vacuum to begin decreasing. Several attempts were unsuccessfully made to restore tne OGR system to service. Condenser vacuum continued to decrease due to the isolation and a rapid reactor shutdown was commenced in accordance with General Procedure  ;

(GP-9-3) " FAST REACTOR POWER REDUCTION" and the " Condenser Low Vacuum"  ;

Operational Transient Procedure (OT-106). Reactor Pecirculation flow was reduced and Control Rod Drive (CRD) insertion was started. At 0327 hours0.00378 days <br />0.0908 hours <br />5.406746e-4 weeks <br />1.244235e-4 months <br />, with the Reactor at l

approximately 72% power, 3 reactor auto ha!f scram signal (Ells:JC) was received due i to the rapidly decreasing main condenser vacuum. Therefore, the unit was manually .

scrammed by placing the mode switch in the SHUTDOWN position. A Primary  :

Containment Isolation System (PCIS) (Ells:JM) Group 11/111 isolation occurred as expected  ;

due to Reactor water level dropping below 0" as a result of void collapse upon insertion  !

of the control rods. Reactor water level was maintained using the "C" Reactor Feed Pump i (RFP) (Ells:SK). Following the event, the scram and PCIS Group 11/111 isolation logics  !

were reset. Following receipt of the RFP low condenser vacuum alarm, the Reactor Core  !

Isolation Cooling (Ells:BN)(RCIC) system was placed in the Condensate Storage Tank l (CST) (Ells:KA) to CST mode. After the "C" RFP isolated on low condenser vacuum, the  ;

RCIC system was placed in the injection mode for reactor water level control. The High Pressure Coolant Injection System (Ells:BJ) was subsequently operated to assist in level recovery. Affected systems were restored to their appropriate conditions and the RCIC i system was used for level control. The NRC was notified of the event at 0539 hours0.00624 days <br />0.15 hours <br />8.912037e-4 weeks <br />2.050895e-4 months <br />. I i

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_Qagse of Event The cause of the PCIS isolations and scram was the loss of the OGR system which caused a Main Turbine Condenser low vacuum condition. An investigation has determined that the cause of the OGR isolation was the combination of a previously failed fuse from unknown causes in the *B" OGR steam flow isolation logic and the blowing of a fuse in the "A" OGR steam flow isolation logic due to grounding of a jumper being removed by a Shift Engineer (Utility ~ Non Licensed) during the performance of SP-1438.

Installation and removal of this jumper was difficult due to the physical layout of the terminal strip and the panel. In addition, no alarm or indicating light exists that would have alerted plant personnel to the condition of the fuse in the "B" OGR steam flow isolation logic prior to performing the procedure.

Analysis of Event No actual safety consequences occurred as a result of this event.

Although plant systems are designed to initigate a low condenser vacuum scram from 100% power, Operations personnel performed a fast power reduction to minimize the effect of a potential plant scram upon isolation of the GGR system. In addition, all automatic PCIS isolations and Reactor Protection System initiations functioned properly.

Corrective Action Following the event, the scram and PCIS Group 11/111 isolation logics were reset. Affected systems were restored to appropriate conditions and the blown fuses were replaced.

SP-1438 has been revised to ensure that fuse status is appropriately monitored prior to procedure start, periodically during performance, and after completion of the procedure.

An investigation is currently underway to identify the cause of the fuse failure in the *B" OGR logic. An evaluation will be performed to determine if terminal point modifications are necessary at the point where the jumper was installed or if a procedure revision can eliminate this difficult condition during jumper installation and removal. In addition, an evaluation will be performed to determine if there are other unmonitored fuses which could cause a plant transient under similar circumstances. Design changes and/or corrective actions will be implemented as necessary.

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Previous Similar Events -

No previous similar LERs have been identified which involved OGR isolation due to a blown fuse or a jumper being inadvedently grounded.

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l NRC f orm 3f4A [649)