ML19332F775

LER 89-012-00:on 891110,RWCU Sys Differential Flow Oscillations Observed While Placing RWCU 2A Filter/ Demineralizer Into Svc.Caused by Leakage in Reactor HX Tube Side Safety Relief Valve.Valve removed.W/891211 Ltr

ML19332F775
Person / Time
Site:	Limerick
Issue date:	12/11/1989
From:	Endriss C, Mccormick M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-012-02, LER-89-12-2, NUDOCS 8912190003
Download: ML19332F775 (7)

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ra PHILADELPHIA ELECTRIC COMPANY i i

LIMERICK GENER ATING SYATION P.O. BOX A

5AN ATOG A. PENNSYLV ANI A 19464

. (215) 3271200 smt. 2000

u. s. u.co uicx. u., e.c. December 11, 1989 u-...7".'."."."',*,.".u,. Docket No. 50-353  :

License No. NPF-85

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U.S.. Nuclear Regulatory Commission Attn: Document Control ~ Desk- '

Washington, DC 20555

-SUBJFCT: Licensee Event Report Limerick Generating Station - Unit 2

..

This LER. reports the leakage of a Reactor Water Cleanup (RWCU) system safety relief valve which caused the Regenerative

' Heat Exchanger room temperature to increase. This resulted in an ,

isolation of the RWCU system due to a Nuclear Steam Supply l

-Shutoff System isolation actuation, an Engineered Safety Feature, l from a Steam Leakage Detection signal. i l:

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Reference:

Docket No. 50-353 a L .ReportLNumber: 2-89-012 j L Revision ~ Number: 00 g

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Event.Date: November 10, 1989 Report Date: December 11, 1989 Facility: Limerick Generating Station 1 P.O. Box A, Sanatoga, PA 19464 This LER is.being submitted pursuant to the requirements of

10 CFR 50.73(a)(2)(iv) . )

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Very truly yours,

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c CCE: kap cc: W. T. Russell, Administrator, Region I, USNRC T. J. Kenny, USNRC Senior Resident Inspector, LGS 8912190003 891211 PDR ADOCK 03000353 i 1

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ABSTRACT On November 10, 1989, while placing the 2A Reactor Water Cleanup (RWCU) Filter /Demineralizer (F/D) into service, RWCU system differential flow oscillations were observed by Operations personnel. At 0700, a Nuclear Steam Supply Shutoff System (NSSSS) isolation actuation, an Engineered Safety Feature (ESP),

from a Steam Leakage Detection (SLD) signal (from a high RWCU Regenerative Heat Exchanger (RHX) room temperature) resulted in the automatic isolation of the'RWCU Outboard Primary Containment Isolation Valve (PCIV), HV-44-2F004. The RWCU system isolation was per design. Operations personnel performed an investigation

-determining that the RWCU isolation was due to steam leakage from the RHX tube side safety relief valve (PSV-44-209 - Lonergan Model D72G). The RWCU system remained isolated following the investigation until PSV-44-209 was removed and a blank flange was installed under a temporary circuit alteration. The RWCU system was returned to service on November 12, at 1350 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.13675e-4 months <br />, after being isolated for approximately 55 hours6.365741e-4 days <br />0.0153 hours <br />9.093915e-5 weeks <br />2.09275e-5 months <br />. As a result of this event and other similar RWCU isolations, a re-evaluation of the potential failure mechanisms of the safety relief valve is being performed. As part of this evaluation, a different model relief valve has been installed on the RWCU system replacing PSV-44-209.

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Plant Conditions Prior to the Event:1

• 4 Operating Condition: 1 (Power Operation). ,

Power Level: 90%

Description of the Event:-

On November-10,'1989, at 0700-hours, the Reactor' Water Cleanup (RWCU).(EIIS:CE) Outboard Primary Containment Isolation Valve

_(PCIV) (EIIS:ISV), HV-44-2F004, automatically isolated. This isolation was due.to a-Nuclear Steam Supply Shutoff System

'(NSSSS)((EIIS:JM) isolation actuation, an Engineered Safety .

a Feature (ESP), from a Steam Leakage Detection (SLD) (EIIS IJ) . y' isolation signal.

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Operations personnel were placing the 2A RWCU Filter /Demineralizer (F/D) (EIIS FDM) into service per System '

Procedure-S45,l'.B " Placing RWCU Filter /Demineralizer in Service,"

.

4 RWCU' flow-oscillations occurred. The F/D inlet valve (EIIS:V) '

was open and the F/D was pressurized to approximately 1100 psig

((see Figure 1).- When the F/D discharge valve (EIIS:FCV) was

opened, to place the F/D in service, the "RWCU High Differential Flow Isolation Timer Initiated" annunciator (EIIS

ANN) alarmed,

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and' cleared, several times. A System Engineer (SE).was

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,  : dispatched-to the Auxiliary Equipment room to observe the RWCU differential flow instrumentation (EIIS:FFI).. The SE observed i flowloscillations on'the instrumentation from 30 gpm to 100 gpm.

Whil'e the SE was attempting to relay this information to the Main j Control Room operators, an isolation of the RWCU system occurred, -1

at 0700 hours0.0081 days <br />0.194 hours <br />0.00116 weeks <br />2.6635e-4 months <br />. The isolation occurred when the Regenerative Heat Exchanger.(RHX) (EIIS:HX) room temperature sensing element

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(TE-44-2N016D) of the SLD system sensed a room temperature above its 122 degree Fahrenheit setpoint initiating a NSSSS, Group III, Division 4 isolation actuation. The RWCU isolation signal caused l the RWCU Outboard'PCIV, HV-44-2F004, to close. The isolation was j accompanied by a "Div.4 Steam Leak Det. Sys Hi Temp" annunciator i and was immediately followed by an automatic fire alarm code for , a the-" Reactor Enclosure Elevation 283 feet -' North East Area / East Side," which is for the area of the RHX room.

1

Operations personnel conducted an investigation to determine the cause of the RWCU isolation and concluded that the RHX tube side Esafety relief valve, PSV-44-209 (Lonergan Model D72G) (EIIS

RV),

was' leaking. During the investigation, an expected second NSSSS isolation actuation, initiated from a high RWCU system differential flow condition occurred, closing the RWCU Inboard g.a.

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tnxrau nam .a m .m e cem w wIw (HV-44-2F001) and Outboard (HV-44-2P004) PCIVs, on November 10, at 1023 hour0.0118 days <br />0.284 hours <br />0.00169 weeks <br />3.892515e-4 months <br />.

The RWCU system remained isolated until PSV-44-209 was removed and a blank flange was installed using.a temporary circuit alteration. The RWCU system was returned to service on November 12, at 1350 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.13675e-4 months <br />. The RWCU system was out of service'for approximately 55 hours6.365741e-4 days <br />0.0153 hours <br />9.093915e-5 weeks <br />2.09275e-5 months <br />.

A four hour notification was made to the NRC on November 10, at 1057 hours0.0122 days <br />0.294 hours <br />0.00175 weeks <br />4.021885e-4 months <br />, in accordance with the requirements of 10 CFR 50.72(b)(2)(li) since the event resulted in the automatic actuation of an ESP. Accordingly, this event is being reported in accordance with the requirements of 10 CPR 50.73(a)(2)(iv).

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Consequences of the Event:

The consequences of this event were minimal. There was no release of radioactive material to the environment as a result of this event. The RWCU system isolated, as designed, when the RHX room temperature sensing element of the SLD system initiated a NSSSS Group III, Division 4 isolation signal. Had the RWCU Outboard isolation valve failed to close and steam continued to leak,-the redundant SLD/NSSSS channel (Inboard)_high temperature isolation signal would have initiated, isolating the RWCU system. -

The RWCU system was out of service for approximately 55 hours6.365741e-4 days <br />0.0153 hours <br />9.093915e-5 weeks <br />2.09275e-5 months <br />.

The Reactor Water purity remained within the limits specified by Technical Specifications. During that interval conductivity (an indicato' of Reactor Water purity) increased from a pre-event value of u.201 micro mhos per centimeter (cm) to a peak value of i 0.429 micro mhos per cm, on November 12. At 0100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />, on November 15, the conductivity value was 0.115 micro mhos per cm indicating the return of Reactor Water purity to conditions better than prior to the event.

Cause of the Event:

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The RWCU isolation was caused by the RHX tube side safety relief valve (PSV-44-209) leakage increasing the RHX room's temperature.

The RHX tube side safety relief valve leakage was possibly initiated by a pressure perturbation ~that occurred when the 2A RWCU F/D was placed in service. A root cause evaluation has determined the probable influences causing the valve leakage ga;,.a.M a...

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0l0 014 0F 0l6 to be a combination of trapped air, system evolutions and operations, piping induced loads / vibrations, and thermal effects associated with these evolutions. Major elerants of the investigation included design reviews for tne heat exchanger, its relief valves, and their installation cc.ifiguration. Also included was a review of maintenance history, examinations of the failed valve, and the results of differential seat leakage and set pressure tests on a. spare valve. When the RHX tube side safety relief valve passed water, the water flashed to steam as it encountered the lower room pressure. - The flashed steam vented to the room via an open funnel drain, and increased the room temperature. The increased temperature was sensed by the SLD room temperature sensor and triggered the NSSSS isolation actuation of the RWCU system. Additionally, the water that flashed to steam in the RHX room initiated the'ior'izing chamber type smoke detector in the room and caused the Reactor Enclosure

-fire alarm code to activate.

l Corrective Actions:

Operations personnel evaluated the high RHX room temperature I isolation of the RWCU system and the alarms and annunciators that ,

L were received and concluded that a RWCU steam leak caused by a l leaking RHX safety relief valve had occurred. To confirm this, Operations personnel reset the RWCU isolation, on November 10, at 1008 hours0.0117 days <br />0.28 hours <br />0.00167 weeks <br />3.83544e-4 months <br />, using General Plant (GP) procedure, GP-8, " Primary

[ and Secondary Containment Isolation Verification and Reset." A portion of the RWCU system was pressurized and included the tube side of the RHX. As a result, Operations personnel verified that the RHX tube side safety relief valve, PSV-44-209, was leaking.

I' Continuing the investigation to determine if the RHX shell side L safety relief valve, PSV-44-208, was leaking required

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pressurizing the Non-Regenerative Heat Exchanger (NRHX) and the shell side of the RHX. The possibility that the pressurization could initiate a high differential flow condition of sufficient duration to initiate a second SLD/NSSSS isolation signal was considered by Operations personnel. Upon pressurizing the NRHX and the shell side of the RHX, a RWCU Inboard (HV-44-2F001) and Outboard (HV-44-2F004) PCIVs isolation occurred on high RWCU system differential flow as expected, at 1023 hours0.0118 days <br />0.284 hours <br />0.00169 weeks <br />3.892515e-4 months <br />. During the pressurization and subsequent isolation of the RWCU system, no leakage was evident from PSV-44-208.

The RWCU system remained isolated following the above investigation until PSV-44-209 was removed and a blank flange was installed under a temporary circuit alteration. The RWCU system was returned to service on November 12, at 1350 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.13675e-4 months <br />.

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0l0 015 OF 0l6 wuu wa.v.es.nem.a mcinmaanm Actions'Taken to Prevent Recurrence: .

-As identified in LER 88-009, Revision 3, submitted to the NRC on March'7, 1989, a modification was generated to minimize the possibility of air entering the system during maintenance, thus reducing the potential for relief' valve lifting due to trapped air and the associated system transient. Currently, air entering the pump suction and discharge piping between the block valves during system maintenance cannot be completely vented before returning the pump to service. As a result, an air slug can make its way into the system. This modification adds high point vents and demineralizer water fill connections to the RWCU pumps, thereby limiting the amount of air entering the system. This l modification will be implemented during future RWCU pump outages initiated due to pump seal failures.

l As a result of this event and sther similar RWCU i.solations, a re-evaluation of the potential failure mechanisms of the safety  ;

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relief valve is being performed. As part of this evaluation, a

): different model relief valve has been installed on the RWCU L system replacing PSV-44-209. The operation of the new style valve will be monitored to determine whether it is suitable for

,

' permanent use in both Unit 1 and Unit 2 RWCU systems.

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Suitability will be determined based on the safety relief valve i

performance during RWCU system evolutions and operations, piping induced loads / vibrations and thermal effects associated.with

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these evolutions. If the new model valve is not suitable, ,

additional' actions will be taken until a suitable valve and ,

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system configuration are obtained.

l- Previous Similar Occurrences:

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LERs 1-86-040, 1-88-009, 1-89-033 and 1-89-055 reported isolations of the RWCU system due to leaking relief valves.

Previous evaluations of the relief valve failure mechanism were completed. In light of the new failures, the potential failure mechanisms are being re-evaluated for a more definitive cause and development of effective corrective actions.  !

Tracking Code: B2 - Failure due to Abo ^rmal Wear g.o- u..

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