05000352/LER-1985-082

LER 85-082-02:on 851014,RWCU Isolated Due to High Differential Flow.Implemented Mod 86-933 in May 1987. W/930908 Ltr

ML20057A213
Person / Time
Site:	Limerick
Issue date:	09/08/1993
From:	Boyce R, Kantner J PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-85-082, LER-85-82, NUDOCS 9309130209
Download: ML20057A213 (4)

LER-2085-082,

Event date:
Report date:
3522085082R00 - NRC Website

text

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PIllLADELPIIIA ELECTRIC COMI%NY LIMERICK GENERATING STATION P. O. BOX 2300 ,

SANATOGA, PA 19464-2300  ;

I (215) 327-12fy) LXT. 2fkK) l ROBERT W. BOYCE  !

September 08, 1993 IiNEdicYr$INawa sanou i Docket No. 50-352  !

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U.S. Nitclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 l t

i SUBJ ECT: Licensee Event Report f LiTnerick Generatina Station - Unit 1 l This LER concerns two isolations of the Reactor Water Cleanup  ;

system on high differential flow.

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Reference:

Docket No. 50-352 Report Number: 85-082 i Revision Number: 02 l Event Date: October 14, 1985 j Report Date: September 08, 1993  ;

Facility: Limerick Generating Station j P.O. Box 2300, Sanatoga, PA 19464-2300 i

This LER is being revised to change the corrective actions based  ?

on operating experience. Changes are indicated by revision bar markers in the right hand margin. The original LER was submitted pursuant to the requirements of 10 CFR 50.73 (a) (2) (iv) .

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cc: T. T. Martin, Administrator Region I, USNRC l N. S. Perry, USNRC Senior Resident Inspector, LGS mnn e ,p, ' '

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On October 14, 1985 at 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> with Unit 1 at less than one percent power, the Reactor Water Cleanup (RWCU) system isolated due to high differential flow. The system isolated twice while placing the "A" RWCU pump in service. The isolation was reset and the system was restored to service by 1640 hours0.019 days <br />0.456 hours <br />0.00271 weeks <br />6.2402e-4 months <br />. The RWCU system isolations had no affect on reactor water level and chemistry. An investigation showed that with RWCU system dump flow to the condenser or RWCU system flow. returned to the vessel at rates of 55 gpm or less, the square root extractor (a component in the flow instrument loop) output would drop downscale. A voltage signal equal to zero gpm flow would then be transmitted to the RWCU differential flow circuit summer. The flow summer compared measured inlet and outlet flow and isolated the RWCU System because its inputs indicated high differential flow (Inlet flow - Outlet flow > 54.9 gpm for 45 seconds). Modification 86-933, which replaced the square root extractors with instruments that have low end cut-out adjustments was implemented in May 1987 and eliminated the problem.

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1 Description of the Event:

4 On October 14, 1985 at 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> with Unit 1 at less than one percent power, an isolation of the Reactor Water Cleanup (RWCU) i

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system occurred. The flow through the RWCU system to the condenser was driven by reactor vessel standing head without operating RWCU i pumps or domineralizers for approximately eight hours prior to the

. system isolation. At 1630, the gravity flow was secured by closing ,

j the RWCU system dump valve. While attempting to place the "A" RWCU (

pump in service in accordance with system procedure S44.1.A, "RWCU i Normal Startup," the system inlet valve isolated due to high system differential flow. The isolation was reset using General Procedure l GP-8, " Primary and Secondary Containment Isolation Verification and 8 Reset." The "A" RWCU pump was then re-started and the system's inlet flow remained high, resulting in another system isolation. The isolation was reset using GP-8 and the system was restored to service by 1640 hours0.019 days <br />0.456 hours <br />0.00271 weeks <br />6.2402e-4 months <br /> using system procedure S44.7.A, " Reactor Water Cleanup Restoration Following Group III Isolation."

4 The EIIS code for the affected system is CE and the code for the ,

defective component, voltage modifier, is EM.  ;

, CoDsecuences of the Event: l t

t The adverse consequences, as a result of this event, were raglit ible. f The RWCU system isolations and no affect on reactor water level and l chemistry. The possible consequences at a higher reactor power level l would be minimal because measured high differential flow initiates  !

i isolation of the RWCU system from the reactor vessel.

Cause of the_ Event: l l

The suspected cause of the RWCU system isolation on high differential  !

) flow was the presence of pressure surges in the RWCU system when the  ;

system flow is changed from tne letdown mode (gravity fed flow bypasses RWCU pumps and demineralizers and flows to the condenser) to  ;

the operating (vessel-to-vessel) mode where flow is pumped through  :

the domineralizers and returns to the Reactor Pressure Vessel (RPV). l However, the continued investigation discovered that the event was a  ;

] result of a component limitation. The square root extractors (Bailey  !

7500) in the RWCU differential flow control circuit would drive  :

downscale during RWCU flows of 55 gpm or less. The normal range is 0 }

to 500 gpm. The square root extractors modify voltage signals from  !

j the flow transmitters and transmit them to the RWCU differential flow l circuit summer. The flow summer compares measured inlet and outlet i I

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flow and generates a high differential flow signal if inlet flow exceeds outlet flows by greater than 54.9 gpm for 45 seconds. During this event, system inlet flow was 80 gpm. Outlet flow was divided approximately 1/2 dump to the condenser and 1/2 return to the vessel as determined by control valve position. The flow summer compared the square root extractors' indicated inlet flow of 80 gpm, dump flow of 0 gpm, return to vessel flow of 0 gpm, and generated a high differential flow signal. Upon examination, it was discovered that

the square out root extractor cards were not designed with a low end cut-out adjustment. Therefore, there is no way of adjusting when the -

square root extractor must transmit an output voltage equal to zero

, gpm.

Corrective Actions:

PECo requested the General Electric Company prepare a Field Deviation l

' Disposition Request (FDDR) to provide square root extractors (Bailey 7501) with low end cut-out adjustments for the RWCU system. Plant modification (86-993) was installed in May 1987. A precaution statement was also added to procedure S44.1.A, "RWCU Normal Startup," '

stating that the RWCU system may isolate on high differential flow during the normal start-up of the system. .

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Erevious Simi. Jar Ocqurrences: i i LERc 85-072 and 85-002 involve RWCU system isolations caused by high i differential flow between the inlet and the outlet of the system l

! resulting from different root causes. i i

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