ML20086L487

AO 74-14:on 740311,static Inverter for Reactor Core Isolation Cooling Sys Flow Controller Tripped Twice During Operation.Cause Unknown.Trip Points Reset & Voltage Recorder Installed on Inverter to Check Voltage Changes

ML20086L487
Person / Time
Site:	Peach Bottom
Issue date:	03/25/1974
From:	Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086L490	List: ML20086L487 ML20086L492
References
AO-74-14, NUDOCS 8402080262
Download: ML20086L487 (3)

Text

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. O fh U d PHILADELPHIA ELECTRIC COMPANY ,

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PHILADELPHIA. PA.19101 MAR 281974 _i

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March 25, 1974 VN W vM\ ./

U W Mr. A. Giambusso Deputy Director of Reactor Projects United States Atomic Energy Commission Directorate of Licensing Washington, DC 20545

Subject:

Abnormal Occurrence Notification The following occurrence was reported to Mr. R. Feil, A.E.C.

Region I Regulatory Operations Office on March 22, 1974. Written noti-fication was made to Mr. James P. O'Reilly,- Region I Regulatory Operations Office on the same date. In accordance with section 6 7 2.A of the Technical Specifications, Appendix A of DPR-44 for Unit 2 Peach Bottom Atomic Power Station, the following report is being submitted to the Directorate of Licensing as an Abnormal Occurrence.

This report covers an event which took place following a loss of outside power startup test during which the,RCIC system was operated to prove its operability during the loss of outside power condition.

The transient resulting from the loss of outside power did not produce conditions which required the automatic initiation of the RCIC system.

The RCIC system was successfully operated during this period to deliver water to the reactor vessel from.both the manual test potentiometer and _

the manual mode of the flow controller. However, during the operating period the static inverter tripped on two occasions. The system was re-established immediately after the inverter was reset.

Following the performance of the loss of outside power test, an investigation into the tripping of the-static inverter was initiated.

Other test data accumulated was also reviewed. Due to an oversight, the Abnormal Occurrence was not reported immediately af ter the test was completed. This f act was recognized during tne Plant Operations. and Review Committee review of the test report, and is hereby being reported at this time. ,

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Reference:

License Number DPR-44, Amendment Number 1 Technical Specification Reference 3 5 0 i i F /]

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Mr. A. Giambusso .

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Pcg2 2 Report No.: 50-277-74-14 Report Date: 3/ 22/74 Occurrence Date: 3/11/74 Facility: Peach Bottom Atomic Power Station - Unit 2 R. D. 1, Delta, Pennsylvania 17314 Identification of Occurrence:

The static inverter which supplies a.c. power for the reactor core isolation cooling system flow controller, tripped twice during operation of the system.

Conditions Prior to Occurrence:

Reactor shutdown - all rods inserted. Reactor had scrammed from approximately 22% power as part of startup program.

Description of Occurrence:

A startup test was being performed which initiated a loss of all offsite power to Unit 2. Following the subsequent scram, reactor level dropped to -4 inches and leveled out there. The high pressure coolant injection system was started manually by the control room operator to restore level to normal. Eight minutes after the scran the reactor core isolation cooling system was manually started on minimum flow recirculation flow path. Shortly thereafter, the static inverter tripped. Power was lost to the automatic flow controller, flow indicator, and all RCIC turbine and pump pressure indicators. The RCIC turbine was then manually tripped by the operator, the inverter trip was reset and the system was restarted immediately on the minimum flow recirculation flow path. Approximately thirty minutes following the scram the RCIC pump was injecting to the reactor vessel when the inverter tripped again. Once again the operator manually tripped the turbine and reset the inverter trip.

Designation of Apparent Cause of Occurrence:

No apparent cause of the tripping of the static inverter has been found. The three conditions which will trip the inverter are under-voltage (100 VDC) and overvoltage (147 VDC) at the inverter inputs and overcurrent in the output. At the time of the trip it was noted that a ground was on the 125 volt d.c. system and that larga motors in the plant were being started. It is thought that these two concurrent con-ditions may change d.c. voltage enough to cause a high voltage spike.

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Mr. A. Giambusso. .

Mrch25,1974() ()_ Paga 3

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Analysis of Occurrence:

Loss of the static inverter defeats the automatic flow control operation of the reactor core isolation cooling system. The flow con-troller will be demanding less than minimum flow, hence the system would not be capable of delivering water to the reactor vessel while in the automatic mode. Also, flow, pump suction and discharge pressure, and turbine steam supply and exhaust pressure,- indication is not available to the control room operator. However, turbine speed indication is still available and the operator can take manual control of the turbine by using the turbine test circuit. Turbine speed could then be in-creased and water injected to the reactor. Operating procedures are written to provide this type operation in the event that automatic operation is not available.

Corrective Action: .

Extensive testing of the static inverter proceeded following the failure. The high voltage trip setpoint was found to be 143 VDC instead of the 147 VDC. Under normal operating conditions, bus voltage is around 132 VDC. While the inverter was still in place, tripping of the inverter could not be repeated during testing. -The trip points have now been set properly and a voltage recorder is in-stalled on the inverter inputs to check line voltage changes.over a period of time and under dif ferent plant conditions.

Very truly yours,

,hll( . j u nj,<

M. J. Cooney Ass't Gen't Superintendent Generation Division l

cc: Mr. J. P. O'Rei lly i Director, Region 1 i United States Atomic Energy Commission ~

631 Park Avenue _

j King of Prussia, PA 19406 l

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