PNO-I-97-017, on 970319,Units 1 & 2 Experienced Dual Unit Reactor Trip from Full Power Due to Electrical Fault Protection Signal from 345 Kv Bus in Onsite Switchyard. Signal Tripped Both Main Generators

PNO-I-97-017:on 970319,Units 1 & 2 Experienced Dual Unit Reactor Trip from Full Power Due to Electrical Fault Protection Signal from 345 Kv Bus in Onsite Switchyard. Signal Tripped Both Main Generators

ML20138G033
Person / Time
Site:	Beaver Valley
Issue date:	03/20/1997
From:	Eselgroth P, David Kern NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
To:
References
PNO-I-97-017, PNO-I-97-17, NUDOCS 9705060141
Download: ML20138G033 (2)

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a March 20,1997 PRELIMINARY NOTIFICATION OF EVENT OR g gggRENCE PN1-97-017 i

{ This preliminary notification constitutes EA r~ gegsg POSSIBLE safety or public interest significance. The information is as ao sved without verification or evaluation, j

and is basically all that is known by the Repggggtggepqt)(g (qqpH j Facility: Licensee Emergency Classification:

Duquesne Light Company -

j Notification of Unusual Event j Beaver Valley 1 and 2 Alert -i

Shippingport, Pennsylvania Site Area Emergency-

] General Emergency l X Not Applicable Docket No.: 050-00334/412 .

! License No.: DPR-66/NPF-73 ,

j Event No.: 31970 i Event Location Code:

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SUBJECT:

BEAVER VALLEY UNIT 1 AND UNIT 2 REACTOR TRIPS AND COLD SHUTDOWN  :

i l At 6:06 a.m., on March 19,1997, Beaver Valley Units 1 and 2 experienced a dual unit reactor trip from full power due to an electrical fault protection signal from a 345 kV bus in the onsite '

switchyard. - This signal tripped both main generators and all four generator output breakers. All

control rods for both units inserted completely. The auxiliary feedwater systems started on low '

steam generator level signal, as expected, and no safety injection occurred at either unit.

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l On Unit 1, the emergency diesel generator (EDG 1-1) started, as expected, due to undervoltage; ,

i however, the undervoltage cleared and the EDG did not load on the bus per design. EDG 1-2 did l i not start. The licensee has declared the EDG 1-2 inoperable pending further assessment to -i determine whether EDG 1-2 should have started. All other safety systems responded as l

!- designed. Containment walkdowns following the trip identified a smallleak on a handhole on the

'C' steam generator. The plant will be placed in cold shutdown to repair the leak.

On Unit 2, the auxiliary feedwater pumps started as designed; however, the flow rate to the 'B' {'

steam generator was lower than the other steam generator flowrates (150 gpm vs. 270 gpm).

i The licensee declared the 'B' AFW header flowpath inoperable pending further inspection to l resolve the issue. All other safety systems responded as designed. Three condensate relief

{ valves lifted and failed to reseat following the reactor trip; no abnormal primary plant cooldown i rates were experienced. The plant will be placed in cold shutdown to perform inspections and l repairs on the 'B' AFW header.

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l Duquesne Light Company is performing a root cause evaluation to determine the reason for the

electrical fault protection signal that led to the reactor trips. Preliminary reviews indicate that

stuck breaker protection circuitry malfunctioned, causing several breakers (including the main  !

generator output breakers) to open. A minor transmission grid disturbance occurred immediately

prior to the trip. However, the licensee believes this transmission grid transient was small and should not have caused the protective relay to actuate. Review of the safety system issues will j be completed prior to restart of the units. While the units are down, other maintenance work will be accomplished and the dual unit outage duration is expected to last approximately one week.

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-i i 9705060141 970320 i PDR I&E PNO-I-97-017 PDR gj I l - . . . . -- - .- -- .- - . _ _ _ _ -_

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• PN1-97-017 - i

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The contents of this PN have been communicated to the Pennsylvania, Ohio and West Virginia .

state governments. ,

I The resident inspectors responded to the control room to observe plant stabilization following the trip. The inspectors will continue to evaluate !icensee event assessment and corrective actions prior to restart. <

Contact:

Peter Eselgroth David Kern (610) 337-5234 (412) 643-2000 l

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