05000456/LER-1990-008

LER 90-008-00:on 900608,reactor Trip Occurred Due to High Flux Rate Signal from Power Range Nuclear Instrumentation. Caused by Voltage Transient,Resulting from Lightning Striking Containment.Power Supply reset.W/900629 Ltr

ML20055D627
Person / Time
Site:	Braidwood
Issue date:	07/02/1990
From:	Querio R, Zagrzebski R COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BW-90-0671, BW-90-671, LER-90-008-06, LER-90-8-6, NUDOCS 9007090202
Download: ML20055D627 (4)

LER-2090-008,

Event date:
Report date:
4562090008R00 - NRC Website

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..- L Commtnwocith Editin Braldwood Nucttar Power Station

.- Route #1, Box 84 sl j'.

Brueville, !!linois 60407 h . Telephone 815/458-2801.

June 29,1990 BW/90-0671 y

.n U.' S, Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

Dear Sir:

The enclosed Licensee Event Report from Braidwood Generating -

Station is being transmitted to you in accordance with the requirements of 10CFR50.73(a)(2)(iv) which requires a 30-day written report.

This report is number 90-008-00; Docket No. 50-456.

Very truly yours, R. E, Querto Station Manager-

- Braldwood Nuclear Station REQ /JDW/sjs

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Enclosure:

Licensee Event Report No. 90-008-00 cc: NRC Region Ill. Administrator NRC Resident inspector INPO Record Center CECO Distribution List

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Reactor Trip due to Lightning Induced Voltage Transient in the Rod Control System, t

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ABSTRACT (Limit to 1400 spaces, i.e. approximately fif teen single-space typewritten .Ilnes) (16) j

.On lune 8, 1990 there was heavy thunderstorm activity in the Braidwood Station area. At 0618 a reactor trip '

' occurred on Unit I due to a high flux rate trip signal f rom the Power Range Nuclear Instrumentation. - The ~

Reactor Operators verified all automatic actions. All systems functioned as designed. Stable plant '

f c:nditions,were immediately established. An examination of the Rod Drive (RD) Power Cabinets indicated the power supply over voltage protectors (P50VP) had tripped in three of the RD Cabinets. There were no blown fus:s identified in any of the; cabinets. The PSOVP's were reset and all voltages were checked.. The root [

cause of this event was a! voltage transient. It is believed that Ilghtning struck the Unit 1 Containment and

--caused a voltage surge in the station ground system. This caused the activation of PSOVPs in the three RD  !

" ' Pow:r Cabinets. This shut of f the current to the stationary gripper coils of the rods powered by the c binets, and caused them to drop, resulting in a negative flux rate. The negative flux rate was of-suf ficient magnitude to activate the reactor trip signal f rom the Power Range Nuclear Instrumentation. No i dtmage.; occurred to the RD system. A review of the station lightning protection system is being conducted.

Th2 Station had made modifications to the RD power supply system and the station grounding system as corrsctive measures from previous events.

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.A.~; PLANT CONU1110NS PRIOR TO EVENT:

EUnit:- Braldwood,1:- Event Date: June 8, 1990; Event Time. 618;.

, _ Hodeth: I f. Power Operation,-

Rx Powert 1007.; ,

RCS (AB). Temperature / Pressure: ;N01/NOP, e;L (8.'OESCRIPi!0NOF_ EVENT:

'There were no: systems or components' inoperable at the beginning of the event which contributed to the severityLof? N the event.' < y

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Thtre was heavy thunderstorm activity in the Draldwood Station area at the time of the event.

At. 0618'on June 8.1990 a ReactorL Trip occurred on Unit 1 due to a high flur rate signal f rom the Power RangeL Nuclear Instrumentation (NR) (IG).

hTheNc'learSta'tionOperators(LicensedReactorOperators)verifiedall'automaticactions..-'All. systems' functioned :I

'Jas: designed. : Stable plant conditions were isonediately established.

An' examination of the Rod Drive (RD) [AA) Power. Cabinets indicated the following:

J1RD02Jl(SCDE) .' L'rgent alarm SIRD03J (20D) - Urgent alarm

?tRD04J (2AC): . Nu alarms, both +24 VDC Power Supply (PS) Over Voltage Protectors (OVP) tripped

- 1RD05J (100)'- Non-urgent alarm, with one PS'0VP tripped

1RD06J (1AC)

. No alarms, both +24 VDC PS OVP's tripped .

There were no blown fuses identified'in any of the cabinets. The PS OVPs were reset aid all voltages were checked. ,j Ti$eUnit2R0=PowerCabinetswereInspected.' They were not affected by this event. :j E '

. . ~1 E ITh)' appropriate NRC notification vla the ENS phone system was made at 0815 pursuant to 10CFR50.72(b)(2)(li).

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.This event:is being: reported pursuant to 10CFR50.73 (a)(2)(lv) - any event or condition that resulted in manual or j automatic {actuationofanyEngineeredSafetyFeature,includingtheReactorProtection' System. j I

C[CAUSEOFEVENTI

[Tharoot'causeof.thiseventwasavoltagetransient. It is believed that lightning str the Unit 1 Containment Land-caused a voltage surge in the station ground system. This caused activation of the +d s PS OVPs in the 1AC andl2AC-'R0 Power Cabinets which shut of f the current to the stationary gripper coils of Sht. t .i Dank A and  !

.Centrol Dank A f. C. This caused -the control rods to drop which resulted in a negative ~ flor ue. The' negative fluxirate was of suf ficient magnitude to activate the reactor trip signal f rom the Power R .. ige Nuclear  ;,

Instrumentation, e ,

The exahl, location ~of the 11ghtning strikes and the dissipation path is still unknown. ,

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D. :$AFETY ANAL.Y$l$1 This event had no effect on the safety of the plant or the public. All systems operated as designed.

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V Both~ trains of Reactor protection and ESI were operable and perf ormed their functions as-designed.

1he' Unit =was operating at 100% power which is the worst case condition for this type of event. Tne RD system

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-is designed to be 1nherently safe as rod insertion results on loss of power as was the case in this event '

t. CORRECTIVE AC110N$1-1hiinviediate corrective actions were to reset the p$ OVPs and verify RD system operability. No damage occurred to the RD system.

Coamionwealth Edison Engineering, Sargent 8 Lundy, and Westinghouse are conducting a review of the station' lightning protection system. -Further investigation and implementation of a lightning protection system is in.

.pregress. The results of this investigation will be tracked to cornpletion by action item no.

! 456-200-90-0230).

FL PREVIOUS OCCURRENCES:

There have been *hree previous occurrences of a lightning induced voltage transient resulting in a reactor trip.;

DVR Nulnher Title 20-1-88-240/88-02's Instrument failures on Unit I and Reactor Trip on Unit 2 as a Result of lightning Induced Voltage Transients 20-1 89-104/C9-0 W Unit 'I and Unit 2 Reactor Trip as a Result of Lightning Induced Voltage Transients Affecting the Rod Control System 20-2-89-075/89-004 Reactor Trip as a Result of Lightning Induced Voltage Translents Af fecting' the Rod Control System.

(The' Station had increased the time delay on the pS OVps and inve roved the station grounding system as icorrective' actions from previous events.

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G. ' COMPONENT FAILURE DATA:

! This event was not the result of component failure, nor did any compenents f all as a result of this event.

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