ML20028G921

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LER 90-012-00:on 900825,reactor Tripped Due to Lightning Strike.Station Mod Request Issued to Provide Uninterruptable Power Source for Steam Bypass Control sys.W/900924 Ltr
ML20028G921
Person / Time
Site: Waterford Entergy icon.png
Issue date: 09/24/1990
From: Mcgaha J, Tanya Smith
ENTERGY OPERATIONS, INC.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-012-01, LER-90-12-1, W3A90-0408, W3A90-408, NUDOCS 9010030251
Download: ML20028G921 (5)
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W3A90-0408 A4.05 QA September 24, 1990 U.S. Nuclear Regulatory Commiss k.

ATTENTION:- Document Control Desk

- Washington, D.C. 20555

Subject:

Waterford'3'SES

. Docket No. 50-382 License No. NPF-38 Anporting of Licensee Event Report Gentlemen:

Attachcdtis Licensee Event Report Number LER-90-012-00 for Waterford' Steam Electric Station Unit 3. This Licensee Event Report'is submitted 1 pursuant to 10CFR50.73 (a) (2) (iv) .

Very;truly yours;

'(i.'.

J_ McGaha bGeneral Manager - Plant Operations

JRM/JEF/rk l Attachment cc: Messrs. R.D.. Martin J.T. Wheelock - INPO Records Center E.L. Blake W.M. Stevenson 1 D.L. Wigginton

'NRC Resident Inspectors Office 1

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COMPLif t ONE LINE FOR I ACH COMPONENT F AILURE DESCRitt0 IN THIS REPORT (13)

"^ ' I COMPONENT ntPomTa e CAUSE SYSTEM COMPONINT U " o "'R S CAUSE SYSTEM "")N'AC g pq i I I I I I I I I I I I I I l l l I I l l .

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Ytt lif vos complete LKPECTEQ $J0M133 ION DA ril NO l l l AosTu.CT cu-a ,, o a ,m., n . . .w..~a., r,or P.. m. ,,n.,n. a o o e, At 1802 hours0.0209 days <br />0.501 hours <br />0.00298 weeks <br />6.85661e-4 months <br /> on August 25, 1990, with Waterford Steam Electric Station Unit 3 3 at 100% power, a severe voltage transient on the southeastern Louisiana 230 KV power transmission grid resulted in a reactor trip. The transient was initiated when a fault attributed to a lightning strike occurred-at the Waterford 230 KV switchyard. One circuit breaker exploded and burned. The rapid reduction in load on the main generator, combined with an inoperable steam bypass control '

system caused reactor coolant system temperature and pressure to increase. A reactor trip occurred due to high pressurizer pressure. This event .s reportable '

as an automatic reactor protection system actuation.

As a result of this system transient, voltage on the Waterford 230KV switchyard decayed to 33 KV over a two second period. An investigation concluded that the in-plant safety bus voltage level did not drop low enough for a sufficient duration to actuate the undervoltage relays associated with the emergency diesel generators.

The root cause of this event was the severe grid disturbance, which is attributed to a lightning strike. Because plant prctective features functioned as designed, this eve:nt did not threaten the health or safety of the general public or plant personnel.

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.1 PAPE O Rt N R A 604 ud 6C

- OF WANAGEwtWT AND tiVDGE1,W ASHINGTON,DC 20603.

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' Electric-Station Unit 3 0 l5 l0 l0 l0 l31812 91 0 Olll2' ~

Ol 0 012 0F 014 Tsc w = s,.a = o,= .an w une in., asn4 w nn At 1802 hours0.0209 days <br />0.501 hours <br />0.00298 weeks <br />6.85661e-4 months <br /> on August 25, 1990, with Waterford Steam Electric Station (WSES)

Unit 3 at 100% power, a severe voltage transient occurred on the southeastern Louisiana 230 KV transmission grid which resulted in a reactor trip. The transient began when a ground fault occurred at the Waterford 230 KV switchyard (EIIS Identifier-FK) during a severe thunderstorm. .The ground fault is attributed to a lightning strike. The initial fault was cleared; however, the fault was reinitiated when the switchyard breaker (EIIS Identifier FK-BKR) failed to maintain an open circuit. The local breaker failure relaying (EIIS Identifier - 50) did not operate to clear the fault after the fault was reinitiated. The breaker exploded after approximately .5 seconds. Debris from the breaker was thrown on neighboring equipment resulting in multiple faults in the Waterford 230 KV switchyard. These faults, along with the initial fault, isolated the switchyard from the southeastern Louisiana 230 KV transmission grid by tripping local and remote breakers.

.WSES Unit 3 continued to supply the rapidly reduced Waterford switchyard loads.

The main turbine (EIIS Identifier - TA) load drop anticipator (EIIS Identifier

- JJ) sensed a large mismatch between main generator (EIIS Identifier - TB) output and main turbine power. This mismatch initiated a "close" intercept vcive (EIIS Identifier JJ-V) signal resulting in a sudden reduction in steam flow. The steam bypass control system (SBCS) (EIIS Identifier - JI) was not available as a result of the grid voltage fluctuations and reactor coolant system (EIIS Identifier - AB) temperature and pressure increascJ. A reactor trip' occurred due to high pressurizer pressure. Reactor coolant system heat removal was accomplished by automatic operation of the atmospheric dump valves (EIIS Identifier SB-PCV) and the main steam safety valves (EIIS Identifier

.SB-RV).

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TEXT CONTINUATION ia'"J,Jf.'NdEf'.",1','c'"*,'!df L".'"MERL 1 P APE Rwo RE tion R l'3 04 IC Of MANAGEMEt(t AND .UDGET,VWASHINGTON, DC 20601 -

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Although the main turbine tripped concurrent with the reactor trip, the main generator continued to be the only source of power to the Waterford switchyard. .;

The main generator tripped, due to a voltage to frequency mismatch, approximately thirty four seconds after the initial fault. The in-plant power supply

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transferred from the main generator to the Waterford switchyard. The switchyard L was re-energized by an externa. source approximately two seconds later. Voltage decayed to 33 KV prior to re-energization.

Approximately thirty-seven minutes after the initial disturbance, power from  ;

one of the two 230 KV supply lines from the switchyard was lost whmi ihe supply breaker was incorrectly opened by LP&L Southern Control in an attempt to isolate the initial failed breaker. The incorrect breaker was opened when personnel misread the breaker number due to the heavy smoke at the scene. Emergency  ;

Diesel Generator (EDG) "A" (EIIS Identifier - EK) started and aligned to the 4.16 KV "A" safety train components as designed.

All safety systems operated as designed throughout this event. The 4.16 KV "A" safety bus (Ells Identifier - EB) v- restored to its normal off-site power supply at 2046 hours0.0237 days <br />0.568 hours <br />0.00338 weeks <br />7.78503e-4 months <br /> and EDG "A" was secured. This event is being reported as an automatic reactor protection system actuation.

6 The root cause of this_ event was the severe grid disturbance attributed to a .,

lightning strike. Contributing factors include the unavailability of the SBCS due to the voltage tran, mnt and the inability of the switching station to rapidly clear the initial fault. An investigation was conducted to determine t

if the EDGs should have started on the initial fault. The investigation con-cluded that the safety bus voltage levels did not drop low enough for a sufficient duration to actuate the undervoltage relays (EIIS Identifier - 27) associated with the EDCs. A station modification request has been issued to provide an un-interruptable power source for the SBCS.

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Because plant protective features functioned as designed, this event did not I

threaten the health or safety of the general public or plant personnel. j h

SIMILAR EVENTS A similar event occurred on March 29, 1990, and was reported as LT 00-003. A severe voltage transient on the 230 KV power transmission grid resu ed in a I reactor trip. The transient was initiated when an Occider.tal Chemical .. , ~

employee inadvertently opened a wrong switch and caused a fault in the 230 KV l Substatlon. -l l

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ptANT CONTACT r

T.ll. Smith, plant Engineering Superintendent, '04-464-3127.

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