Information Notice 1985-86, Lightning Strikes at Nuclear Power Generating Stations

Lightning Strikes at Nuclear Power Generating Stations

ML031180204
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill
Issue date:	11/05/1985
From:	Jordan E NRC/IE
To:
References
IN-85-086, NUDOCS 8511010020
Download: ML031180204 (5)

SSINS No.: 6835 IN 85-86 UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, D.C. 20555 November 5, 1985 IE INFORMATION NOTICE NO. 85-86: LIGHTNING STRIKES AT NUCLEAR POWER

GENERATING STATIONS

Addressees

All nuclear power reactor facilities holding an operating license (OL) or a

construction permit (CP).

Purpose

This notice is provided to alert recipients of a potentially significant

problem of reactor trips and instrument damage caused by lightning strikes. It

is expected that recipients will review the information for applicability to

their facilities and consider actions, if appropriate, to preclude a similar

problem occurring at their facilities. However, suggestions contained in this

notice do not constitute NRC requirements; therefore, no specific action or

written response is required.

The NRC is continuing to evaluate pertinent information. Recipients of this

notice will be notified of additional information or if specific actions are

required.

Description of Circumstances

A number of plant trips and instrumentation problems attributable to lightning

have occurred over the past 6 years. Since solid state circuitry designs are

being increasingly employed in safety related systems, the impact of lightning

induced line surges on those circuits is emphasized in this notice. Descrip- tions of several of the more significant events are presented below. Events

involving lightning strikes of switchyards and the consequential impact on

power distribution systems are not covered by this notice. However. INPO SER

76-84 covers this latter subject as well as summarizing earlier INPO documents

dealing with lightning strikes at nuclear power plants.

Zion Power Station Units 1 and 2 On August 17, 1979, both units tripped simultaneously during a severe lightning

storm. Investigation indicated that a lightning strike in close proximity to

the plant caused either a momentary surge or interruption in the ac power

supply circuits to the rod control power supply cabinets. This transient

tripped the overload protection devices for the dc power supply cabinet, resulting in a power interruption to the control rod stationary gripper coils,

8511010020

IN 85-86 November 5, 1985 which caused the rods to drop into the core. The resulting high, negative flux

rate initiated the reactor trip signal. Tests verified that noise induced on

the ac input to one power supply would actuate the overvoltage protection trips

on the main and auxiliary power supplies. In addition to the noise spikes, one

Unit 2, 24-V positive power supply was' damaged by the lightning strike and had

to be replaced. The following corrective actions were initiated:

o The control rod system neutral was isolated from the station ground.

o The overvoltage protection trip setting was changed from 27 to 29 V.

o A low-pass filter was installed on the input to each 24-V positive power

supply, o A volt trap (a voltage suppressor'circuit designed to reduce large voltage

surges and noise induced by lightning strikes) was installed across the

50-ohm motor generator neutral resistor.

o A volt trap was installed across the power feed to the auxiliary power

supply.

The power feed for the auxiliary power supply was changed from the 480-V

system to'the control rod drive (CRD) motor generators.

Zion Unit Z experienced additional reactor-trips'attributed-to lightning-on

April 3 and July 16, 1980, before the above listed corrective actions were

implemented. In these cases it was determined that the transient tripped the

overload protection devices, as was the case in the trip of both units on

August 17, 1979. However, no power supplies or other equipment were damaged

during the latter two trips.

Again, on December 2, 1982, Zion Unit 2 reactor tripped from 100% power during

an electrical storm. It was concluded that lightning induced a disturbance in

the electrical system causing a reactor trip from a generator trip. Additional- lightning protection for the containment building was provided and the static

wire associated with the 345-kV line was isolated from the power station

structural 'steel.

Salem Power Station Unit 1 On June 8, 1980, the reactor tripped during an electrical storm. Lightning

struck at the south penetration area of reactor containment causing a transient

on seven main steam pressure transmitters. Two of these pressure transmitters

were damaged and had to be replaced. The transient caused a high steam line

pressure differential reactor trip signal and a safety injection signal. The

licensee believes the lightning strike hit main steam vent pipes which extend

above the penetration area roof and the surge was carried into the building via

piping connections.

IN 85-86 November 5, 1985 Kewaunee Power Station

On August 19, 1980, two of four instrument busses lost power during an electri- cal storm. This resulted in a spurious safety injection (SI) actuation signal, and the unit tripped from full power. In addition to inducing the instrumenta- tion transients, the inverter fuses were blown. These fuses were replaced, and

no other evidence of equipment failure was observed.

Byron Power Station Unit 1

On July 13, 1985, when lightning struck the Unit 1 containment, the reactor

tripped from approximately 11% power becauseiof induced voltage surges in

instrument and control cables in one of four containment penetration areas.

The induced voltage caused failure of four rod drive power supplies, including

1 redundant pair. The failure of the redundant supplies resulted in 10 control

rods dropping into the core. A power range negative-flux-rate reactor trip

resulted from the rod insertion. In addition to the reactor trip, damage

occurred to 30 plant instruments. The following systems were affected by the

damaged instrumentation: protection channel II, one train of the 48-volt power

supply for the solid state protection system, the meteorological tower, control

rod drive, and loose-parts monitoring.

A review of cable routings showed that a significant common denominator existed

in containment penetrations. All damaged instruments were associated with

cables passing through penetrations located in one containment region. In

addition to the damaged instrumentation, the lightning damaged a significant

amount of security equipment.

The licensee determined that an improved lightning protection system was

required to prevent recurrence of a similar incident. By installing copper

conductors, external to containment, from the roof mounted lightning rods

directly to ground rods in the earth, a low impedance path to ground was

provided for future lightning strikes. This modification is similar to the

Zion modification described above.

Arkansas Power Station Unit 2

On August 5, 1985, the reactor tripped from 100% power on a low departure-from- nucleate-boiling ratio (DNBR) signal as the result of a lightning strike

transient induced in two of the core protection system channels. The licensee's

followup investigation revealed no damage to the plant's electrical equipment

or instrumentation measuring systems.

IN 85-86 November 5, 1985 No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate regional office or this office.

£ ~rdact r

Division Emergency Preparedness

and Engineering Response

Office of Inspection and Enforcement

Technical Contacts: Ray S. Love, RIII

(312) 790-5593- Vincent 0. Thomas, IE

(301) 492-4755 RI N

Attachment: List of ~Recently Issued 1E Information Notices

I. f

. I

Attachment 1 IN 85-86 November 5, 1985 LIST OF RECENTLY ISSUED

IE INFORMATION NOTICES

Information Date of

Notice No. Subject Issue Issued to

85-85 Systems Interaction Event 10/31/85 All power reactor

Resulting In Reactor System facilities holding

Safety Relief Valve Opening an OL or CP

Following A Fire-Protection

Deluge System Malfunction

85-84 Inadequate Inservice Testing 10/30/85 All power reactor

Of Main Steam Isolation Valves facilities holding

an OL or CP

85-83 Potential Failures Of General 10/30/85 All power reactor

Electric PK-2 Test Blocks facilities holding

an OL or CP

85-82 Diesel Generator Differen- 10/18/85 All power reactor

tial Protection Relay Not facilities holding

Seismically Qualified an OL or CP

85-81 Problems Resulting In 10/17/85 All power reactor

Erroneously High Reading facilities holding

With Panasonic 800 Series an OL or CP and

Thermoluminescent Dosimeters certain material

and fuel cycle

licensees

85-80 Timely Declaration Of An 10/15/85 All power reactor

Emergency Class Implementa- facilities holding

tion Of An Emergency Plan, an OL or CP

And Emergency Notifications

85-17 Possible Sticking Of ASCO 10/1/85 All power reactor

Sup. 1 Solenoid Valves facilities holding

an OL or CP

85-79 Inadequate Communications 9/30/85 All power reactor

Between Maintenance, facilities holding

Operations, And Security an OL or CP; research

Personnel and nonpower reactor

facilities; fuel

fabrication and

processing facilities

OL = Operating License

CP = Construction Permit