Information Notice 1992-40, Inadequate Testing of Emergency Bus Undervoltage Logic Circuitry

Inadequate Testing of Emergency Bus Undervoltage Logic Circuitry
	ML031200294
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, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	05/27/1992
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-92-040, NUDOCS 9205200239
	Download: ML031200294 (8)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C 20555 May 27, 1992 NRC INFORMATION NOTICE 92-40: INADEQUATE TESTING OF EMERGENCY BUS

UNDERVOLTAGE LOGIC CIRCUITRY

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

PurDose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice to alert addressees to a safety problem that could result from the use

of an undervoltage logic test method that fails to verify the de-energization

of the emergency safety busses. It is expected that recipients will review

the information for applicability to their facilities and consider actions, as

appropriate, to avoid similar problems. However, suggestions contained in

this information notice are not NRC requirements; therefore, no specific

action or written response is required.

Description of Circumstances

In November 1991, an NRC electrical distribution functional inspection team at

the LaSalle County Nuclear Station discovered that the surveillance testing

method used for the loss of offsite power test was not testing the capability

of the undervoltage logic circuitry to de-energize the emergency bus. This

deficiency affected all six of the electrical divisions for both nuclear power

units. The undervoltage circuitry automatically opens the emergency bus feed

breakers from the offsite power system to isolate the emergency bus when a

loss of voltage is sensed. This circuitry also initiates load shedding, starts the emergency diesel generator (EDG), re-energizes the emergency bus, and sequences the necessary emergency loads onto the emergency bus.

This test deficiency is significant because the failure of the normally closed

feed breaker to open automatically in response to a loss of offsite power

would prevent the emergency diesel from automatically re-energizing the

emergency bus and also would result in the emergency bus remaining connected

to a degraded offsite power source.

In conducting an internal lessons learned program for the Byron and Braidwood

stations, the Commonwealth Edison Company (the licensee) determined that it

was performing inadequate tests of its undervoltage logic circuitry in a

manner similar to the LaSalle Station tests.

(9205200239 2 mob ZDO

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May 27, 1992 Discussion

The technical specifications for the LaSalle County Nuclear Station require

the licensee to simulate a loss of offsite power and to verify the

de-energization of the emergency busses. The licensee was simulating a loss

of offsite power by manually opening the emergency bus main feed breaker. By

simulating a loss of offsite power in this manner, the licensee did not

demonstrate that the undervoltage logic circuitry would automatically

de-energize the emergency bus in response to an undervoltage condition. Thus, the licensee did not test the capability of two undervoltage relay contacts to

trip the normal bus feed breaker from the main station transformer and the

unit tie breaker. These breakers provide an EDG output breaker closure

permissive. If a feed breaker failed to trip open automatically, it would

prevent the EDG output breaker from closing automatically and also result in

the emergency bus remaining connected to a degraded offsite power source.

After discovering this problem, LaSalle personnel successfully tested all of

the affected undervoltage logic circuits. The licensee simulated the loss of

offsite power by opening the undervoltage relay potential transformer test

switches and verifying that the appropriate breakers had tripped. The

licensee satisfactorily tested the capability of the logic circuits to shed

loads from the emergency busses, the capability of the EDGs to start automati- cally, and the capability to energize the emergency safety loads with the

--emergency busses.

g L_ ___

The Byron and Braidwood staff also revised their testing method and success- fully tested the capability of their undervoltage logic circuitry to auto- matically de-energize the emergency busses.

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager.

-Is E b or

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contact: David S. Butler, RIII

(708) 790-5796 Attachment: List of Recently Issued NRC Information Notices

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Attachment

IN 92-40

May 27, 1992 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

92-39 Unplanned Return to 05/13/92 All holders of OLs or CPs

Criticality during for nuclear power reactors.

Reactor Shutdown

92-38 Implementation Date for 05/12/92 All holders of OLs or CPs

the Revision to the EPA for nuclear power reactors, Manual of Protective non-power reactors and

Action Guides and Pro- materials licensees auth- tective Actions for orized to possess large

Nuclear Incidents quantities of radioactive

material.

92-37 Implementation of the 05/08/92 All Nuclear Regulatory

Deliberate Misconduct Rule Commission Materials

Licensees.

92-16, Loss of Flow from the Re- 05/07/92 All holders of OLs- or CPs

Supp. 1 sidual Heat Removal Pump for nuclear power reactors.

during Refueling Cavity

Draindown

92-36 Intersystem LOCA Outside 05/07/92 All holders of OLs or CPs

Containment for nuclear power reactors.

92-35 Higher Than Predicted Ero- 05/06/92 All holders of OLs or CPs

sion/Corrosion in Unisol- for nuclear power reactors.

able Reactor Coolant Pres- sure Boundary Piping Inside

Containment at A Boiling

Water Reactor

92-34 New Exposure Limits for 05/06/92 All licensees whose opera- Airborne Uranium and tions can cause airborne

Thorium concentrations of uranium

and thorium.

92-33 Increased Instrument 04/30/92 All holders of OLs or CPs

Response Time When for nuclear power reactors.

Pressure Dampening

Devices are Installed

OL = Operating License

CP = Construction Permit

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S IN 92-40