Information Notice 1991-06, Lock-up of Emergency Diesel Generator and Load Sequencer Control Circuits Preventing Restart of Tripped Emergency Diesel Generator

Lock-up of Emergency Diesel Generator and Load Sequencer Control Circuits Preventing Restart of Tripped Emergency Diesel Generator

ML031190689
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:	01/31/1991
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-91-006, NUDOCS 9101280052
Download: ML031190689 (6)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 January 31, 1991 NRC INFORMATION NOTICE NO. 91-06: LOCK-UP OF EMERGENCY DIESEL GENERATOR

AND LOAD SEQUENCER CONTROL CIRCUITS

PREVENTING RESTART OF TRIPPED EMERGENCY

DIESEL GENERATOR

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

The information in this notice is intended to alert addressees of potential

problems involving the restart of a tripped emergency diesel generator (EDG)

because of "lock-up" of EDG or load sequencer control circuits. 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 do not constitute NRC require- ments; therefore, no specific action or written response is required.

Description of Circumstances

On March 20, 1990, operations personnel at the Alvin W. Vogtle Plant, Unit 1, experienced difficulties when attempting to restart the in-service EDG. In

response to a valid bus undervoltage condition, the EDG had automatically started

and energized its associated 4.16 kV ac safety bus per design. The EDG tripped

after approximately one minute of operation. A spurious jacket water high

temperature signal is believed to have caused the trip. The load sequencer had

completed its cycle before the trip. The EDG could not be restarted following

the trip even though the condition that had caused the trip had cleared and a

valid undervoltage condition and automatic start signal existed. The EDG

control circuits had functioned as designed but had locked-up such that sub- sequent restart attempts were prevented. Although the EDG could have been

started in the "emergency' mode by using the emergency start switch at the

local panel, the local and remote control switches used for "normal" EDG start

were ineffective. No equipment failures or malfunctions were involved.

The design of the load sequencer circuits that provide an automatic start

signal upon sensing bus undervoltage and the interface between these circuits

and the interlocks in the EDG air start system are such that the circuits will

lock-up whenever a trip results in an undervoltage condition on the associated

t 8O180052 3

IN 91-06 -

January 31, 1991 safety bus. During the March 1990 event at the Vogtle Plant, the initial attempts

to reset the lock-up were unsuccessful, and the EDG was not restarted for

approximately 18 minutes. Had proper action been taken to reset the locked-up

circuits, the EDG could have been restarted promptly. However, the operations

personnel involved were not trained concerning the lock-up condition, and pro- cedures providing guidance concerning actions required for restart did not exist.

A detailed explanation of the design of the Vogtle Unit 1 load sequencer and EDG

air start system is presented in NUREG 1410, "Loss of Vital AC Power and the

Residual Heat Removal System During Mid-Loop Operations at Vogtle Unit 1 on

March 20, 1990."

On November 14, 199G, the 1A EDC at the Kewaunee Nuclear Power Plant was being

tested following replacement of the governor. Because of an improper governor

setting, the EDG tripped on overspeed before the load sequencer completed its

cycle. This trip caused the sequencer control circuits to lock-up in a condition

that would have prevented loading of the EDG following a valid start. Mainten- ance technicians present during the testing had to lift leads in the sequencer

cabinet to clear the lock-up condition. The first attempt to clear the lock-up

condition was unsuccessful because the leads were only removed momentarily, which resulted in remote indications that led the operators to believe that the

sequencer had been reset. However, the leads were relanded before time delay

relays could time out and reset (approximately 90 seconds is required). Approxi- mately two hours were required for the plant personnel to troubleshoot the load

sequencer and complete successful testing-of the EDG. Apparten-tythe-plant

staff were not adequately trained to recognize and reset the lock-up condition, and plant procedures were not appropriately detailed to allow operators to cope

with a situation where the EDG trips before the load sequencer completes its

cycle. The licensee is considering a modification to the sequencer to install

a conveniently located reset switch to allow reset to be accomplished without

having to lift leads.

Discussion:

These incidents have raised concerns regarding the understanding of EDG and

load sequencer control circuits and their interfaces, and the adequacy of

procedures for restarting EDGs following unexpected trips. EDG and load

sequencer control systems are often complex. As the result of either a valid

or spurious trip signal, an EDG can shut down at any time before, during, or

after cycling of the load sequencer. Successful mitigation of the effects of

accidents or transients and maintenance of the overall reliability of EDGs

depends upon operations personnel having (1) sufficient knowledge of the

associated instrumentation and controls; and (2) the ability to recognize and

reset a lock-up condition.

IN 91-06O

January 31, 1991 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 NRR project manager.

har es .ossi, Directo

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

E. Nick Fields

(301) 492-1173 Attachment: List of Recently Issued NRC Information Notices Attachment 1 IN 91-06 January 31. 1991 LIST OF RECENTLY ISSUED

IRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance -Issued to

91-05 Intergranular Stress Corrosion 1/30/91 All holders of OLs or

Cracking in Pressurized Water CPs for pressurized

Reactor Safety Injection water reactors PWRs).

Accumulator Nozzles

91-04 Reactor Scram Following Control 01/28/91 All holders of OLs or

Rod Withdrawal Associated with CPs for nuclear power

Low Power Turbine Testing reactors.

91-03 Management of Wastes Contaminated 01/07/91 All medical licensees.

with Radioactive Materials ('Red

Bag* Waste and Ordinary Trash)

91-02 Brachytherapy Source Management 01/07/91 All Nuclear Regulatory

Conmission (NRC) medi- cal licensees author- ized to use byproduct

material for medical

purposes.

91-01 Supplier of Misrepresented 01/04/91 All holders of OLs or

Resistors CPs for nuclear power

reactors.

90-82 Requirements for Use of 12/31/90 All registered users

Nuclear Regulatory Coum- of NRC-approved

ission-(KRC-)Approved packages.

Transport Packages for

Shipment of Type A Quanti- ties of Radioactive Materials.

904l1 Fitness for Duty 12/24/90 All U.S. Nuclear

Regulatory Commission

(NRC)material and

non-power reactor

licensees.

90-80 Sand Intrusion Resulting 12/21/90 All holders of OLs or

in Two Diesel Generators CPs for nuclear power

Becoming Inoperable reactors.

OL

• Operating License

CP = Construction Permit

-

IN 91-06 January 31, 1991 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 NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

E. Nick Fields

(301) 492-1173 Attachment: List of Recently Issued NRC Information Notices

• See previous concurrence

OFC :DOEA:EAB: :SC:DOEA:EAB :C:DST:SELB :C:DOEA:EAB :C:DOEA:OGCB :D:DOEA :TechEd

NAME :ENFields* :DCFischer* :FRosa* :AEChaffee* :CHBerlinger* z:JMan*

DATE :12/19/90 :12/24/90 :1/3/91 :1/9/91 :1/17/91 :01/.;$91 :01/22/91 OFFICIAL RECORD COPY

Document Name: KENDALL IN/TECHED

IN 91-XX

January XX, 1991 Successful mitigation of the effects of accidents or transients and maintenance

of the overall reliability of emergency diesel generators depends upon operations

personnel having (1) sufficient knowledge of the associated instrumentation and

controls; and (2) the ability to quickly recognize and reset a lock-up condition, especially in cases where the cause for the trip is known and easily corrected.

When functioning as designed, the emergency diesel generator and load sequencer

control systems should only present situations to operations personnel for

which the best recovery method is understood and for which the method for

recovery is uncomplicated.

The information in this notice requires no specific action or written response.

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

the technical contact listed below or the appropriate NRR project manager.

Charles E. Rossi

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

E. Nick Fields

(301) 492-1173 Attachment: List of Recently Issued NRC Information Notices.A-1

• See previous concurrence

CA141 ----

OF DE: EAB:

NAME :ENFields*

SC:DOEA:EABY_-Ci~DSTiSEL.B

DCFischer* :FRosa*

-:C:DOEA:EAB :C:DOEA:OGCB :D:DOEA

AEChaffee*

--- :TechEd

CHEerlinger :CERossif- :JMain

DATE :12/19/90 :12/24/90 :1/3/91 :1/9/91  : I//7/91q / /  : /Zt/91 OFFICIAL RECORD COPY

Document Name: KENDALL IN

-

IN 90-XX

December XX, 1990

Page 2 of

The information in this notice requires no specific action or written

response. If you have any questions regarding the information in this notice, please contact the technical contact listed below or the appropriate NRR

project manager.

Charles E. Rossi

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Rick Kendall, NRR

(301) 492-1176 E. Nick Fields

(301) 492-1173 Attachment: List of Recently Issued NRC Information Notices.

OFC :DOEA EAB: :S D0 A: EAB :C:DST:SELB :C-_EQ :C:DOEA:OGCB :D:DOEA

Eb------sI-- --- )~ --

___ iO-: ZWWf----:------------:------------ :-------

NAME :ENFields :DCFischer :FRost qV :AEChaffee :CHBerlinger :CERossi

____________ _____ _____ ____________ _ _ __ :-----------

_ _ _ _

DATE :1/-l/t/) :IL /?fIf/l  ://3/  : L1 /r/  : / /  : / /:

OFFICIAL RECORD COPY

Document Name: KENDALL IN