Information Notice 1993-71, Fire at Chernobyl Unit 2

Fire at Chernobyl Unit 2

ML031070103
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:	09/13/1993
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-93-071, NUDOCS 9309080104
Download: ML031070103 (13)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 September 13, 1993 NRC INFORMATION NOTICE 93-71: FIRE AT CHERNOBYL UNIT 2

Addressees

power

All holders of operating licenses or construction permits for nuclear

reactors.

Purpose

information

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

notice to alert addressees to the fact that extensive fires

Chernobyl Nuclear

unanticipated challenges such as happened at Unit 2 of the the information for

Power Station. It is expected that recipients will review

appropriate, to

applicability to their facilities and consider actions, as in this information

avoid similar problems. However, suggestions contained action or written

notice are not NRC requirements; therefore, no specific

response is required. ,

Description of Circumstances

Station was

On October 11, 1991, Unit 2 of the Chernobyl Nuclear Power twin, independent

operating at 70-percent power. Each Chernobyl unit has twohall (see

turbogenerators and all four units share a common turbine on

• Attachment 1). In order to perform minor repairs and adjustments

power and isolated

turbogenerator 4 (TG-4), operators reduced Unit 2 reactor off the

the steam supply to TG-4. At 7:46 p.m., the operators switched 2, and 3 in the

generator excitation field and opened disconnect breakers 1,

330 kV switchyard to electrically isolate TG-4.

disconnect breaker 2 At 8:10 p.m., TG-4 had coasted down to about 150 rpm when The generator

spuriously closed and reconnected TG-4 to the electrical grid.

to synchronous

rotor motorized on the reverse-power condition and acceleratedto TG-4 speed (3000 rpm) in under 30 seconds. The influx of current

of the

overheated the conductor elements and caused a rapid degradation A centrifugal

mechanical end joints of the rotor and excitation windings. 14 and the seal

imbalance developed and damaged generator bearings 10 through the generator

oil system allowing hydrogen gas and seal oil to leak from

ignited the leaking hydrogen

enclosure. Electrical arcing and frictional heat and dense smoke

and seal oil creating hydrogen flames 8 meters [27 feet] high

which obstructed the visibility of plant personnel.

caused a

When the burning oil reached the busbar of the generator it the generator

three-phase 120,000 amp short circuit. Within 0.07 seconds, breaker 2, fault protective circuits sensed the short and opened disconnect

9309080104 5"

isPD , _ o- J., r

IN 93-71 September 13, 1993 which spuriously closed again 0.25 seconds later.

reopened the breaker 0.2 seconds after the closure The protection system

spuriously closed. Finally, protection circuits inand again the breaker

the 330 kV electrical grid

disconnected the generator 0.27 seconds after the closure

breaker located in the town of Korosten, about 120 by opening a remote

Unit 2 control room operators shut down the reactor kilometers [72 miles] away.

and initiated

allowable cooldown rate to achieve a safe reactor configuration. the maximum

Fire fighting efforts focused on containing the fire

spreading to adjacent equipment. There was little and preventing it from

concern for the turbine

hall roof catching fire because the asphalt coating

removed after the 1986 accident at Chernobyl Unit 4.on the roof had been

ventilation systems, which were the only method available However, the local

removal, were unable to cope with the smoke and heat for heat and smoke

The fire brigade was concerned for the structural generated by the fire.

integrity

because the roof supports had no heat retardant coating of the roof

systems in the turbine hall were not designed to cool and because sprinkler

The fire brigade attempted to cool the supports by the structural supports.

from below but were unsuccessful because the plant spraying them with water

provide adequate flow to the area sprinkler systems fire pumps could not

fire-fighting efforts at the same time. The metal and the local

structure reached a temperature greater than 9000 C trusses of the roof

[1650'F] and collapsed at

8:35 p.m. I

A 50 meter by 50 meter [165 feet by 165 feet] section

onto the turbine deck and also onto an adjacent pit of the roof collapsed

feedwater pumps, the auxiliary feedwater pumps and that contained the main

cabinets. Damage to the pump systems and a fire in their associated control

disrupted makeup water flow to the reactor cooling one control cabinet

system.

the electrical power to the pump motors and the control The operators cut

them as a potential ignition source. Because of the cabinets to remove

damage, the operators believed that the main feedwatersignificant amount of

pumps could not be readily restored. Therefore, the and auxiliary feedwater

the reactor primary coolant circuit by opening the operators added water to

steam

reduce pressure and aligning a low-pressure nonsafety-grade relief valves to

the auxiliary feedwater system piping. This arrangement condensate pump to

steam separator drum water levels difficult but allowed made controlling the

provide core cooling throughout the event. The fire the operators to

was extinguished by

11:30 p.m.

Discussion

An investigation of the event later determined that

a short circuit in the

control wiring for generator disconnect breaker 2 caused

of the breaker to remain open. This condition was the repeated failures

critical

no redundant on-site isolation breaker for the generator because there was

included in the more recent design of Chernobyl Unit output such as is

3.

IN 93-71 September 13, 1993 A notable safety significant aspect of the Chernobyl fire was the complete

loss of the main feedwater and auxiliary feedwater systems. Because redundant

safety components were not truly independent (i.e., there were no separate and

protected cubicles for the auxiliary feedwater pumps), a single structural

component failure led to the common failure of all feedwater pumps. The

proposed corrective actions include: (1) installation of three additional

emergency feed pumps outside of the turbine hall, (2) installation of an

automatic sprinkler system for the metal structure of the turbine hall and

roof, and (3) a review of the design of the smoke removal system in the

turbine hall and installation of a more effective system.

This event illustrates that extensive fires may place unanticipated loads on

fire protection systems and that structural failures could cause failures of

multiple trains of safety-related systems and challenge the true separation, independence, and redundancy of safety-related components.

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.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact: Eric J. Benner, NRR

(301) 504-1171 Attachments:

1. Chernobyl Turbine Hall Layout

2. List of Recently Issued NRC Information Notices

V -)

Attachment 1 IN 93-71 September 13, 1993

CHERNOBYL TURBINE HALL LAYOU f1

/

I

-TURBOGENERATOR TG-4

-TURBINE HALL

Attachment 2 IN 93-71 September 13, 1993 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

93-70 Degradation of Boraflex 09/10/93 All holders of OLs or CPs

Neutron Absorber Coupons for nuclear power reactors.

93-69 Radiography Events at 09/02/93 All holders of OLs or CPs

Operating Power Reactors for nuclear power reactors

and all radiography

licensees.

93-68 Failure of Pump Shaft 09/01/93 All holders of OLs or CPs

Coupling Caused by for nuclear power reactors.

Temper Embrittlement

during Manufacture

92-16, Loss of Flow from the 08/23/93 All holders of OLs or CPs

Supp. 2 Residual Heat Removal for nuclear power reactors.

Pump during Refueling

Cavity Draindown

93-67 Bursting of High 08/16/93 All holders of OLs or CPs

Pressure Coolant for nuclear power reactors.

Injection Steam Line

Rupture Discs Injures

Plant Personnel

93-66 Switchover to Hot-Leg 08/16/93 All holders of OLs or CPs

Injection Following for pressurized water

A Loss-of-Coolant reactors.

Accident in Pres- surized Water Reactors

93-65 Reactor Trips Caused 08/13/93 All holders of OLs or CPs

by Breaker Testing for nuclear power reactors.

with Fault Protection

Bypassed

93-64 Periodic Testing and 08/12/93 All holders of OLs or CPs

Preventive Maintenance for nuclear power reactors.

of Molded Case Circuit

Breakers

93-63 Improper Use of Soluble 08/11/93 All holders of OLs or CPs

Weld Purge Dam Material for nuclear power reactors.

OL = Operating License

CP =,£Cogstruction Permit

IN 93-71 K<) September 13, 1993 A notable safety significant aspect of the Chernobyl fire was the complete

loss of the main feedwater and auxiliary feedwater systems. Because redundant

safety components were not truly independent (i.e., there were no separate and

protected cubicles for the auxiliary feedwater pumps), a single structural

component failure led to the common failure of all feedwater pumps. The

proposed corrective actions include: (1) installation of three additional

emergency feed pumps outside of the turbine hall, (2) installation of an

automatic sprinkler system for the metal structure of the turbine hall and

roof, and (3) a review of the design of the smoke removal system in the

turbine hall and installation of a more effective system.

This event illustrates that extensive fires may place unanticipated loads on

fire protection systems and that structural failures could cause failures of

multiple trains of safety-related systems and challenge the true separation, independence, and redundancy of safety-related components.

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.

orig /s/'d by BKGrimes

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact: Eric J. Benner, NRR

(301) 504-1171 Attachments:

1. Chernobyl Turbine Hall Layout

2. List of Recently Issued NRC Information Notices

L

• See previous concurrences

OFC

NAME

OEAB:DORS

EBenner*

SC/OEAB:DORS

EGoodwin*

PUB:ADM

Tech Ed*

SPLB:DSSA

CM for West*

1 XDATE05/13/93 05/19/93 J05/13/93 08/25/93 OFC C/SPLB:DSSA CEP:OIP C/OEAB:DORS OGCB:DORS

NAME CMcCracken* JERamsey* AChaffee* JBirmingham*

DATE 08/25/93 08/26/93 08/27/93 09/02/93 OFC C/OGCB:DORS

NAME GMarcus*

DATE 09/02/93 09/ /93

[OFFICIAL RECORD COPY]

DOCUMENT NAME: 93-71.IN

IN 93-XX

September xx, 1993 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.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact: Eric J. Benner, NRR

(301) 504-1171 Attachments:

1. Chernobyl Turbine Hall Layout

2. List of Recently Issued NRC Information Notices

• See previous concurrences

OFC OEAB:DORS SC/OEAB:DORS PUB:ADM SPLB:DSSA

NAME EBenner* EGoodwin* Tech Ed* CM for West*

j

E

DATE 05/13/93 I05/19/93 I05/13/93 08/25/93 OFC C/SPLB:DSSA CEP:OIP C/OEAB:DORS OGCB:DORS

NAME lCMcCracken* JERamsey* l AChaffee* JBirmingham*

p DATE , 08/25/93 l08/26/93 108/27/93 l 09/02/93 OFC C/OGCB:DORS D/DORS

NAME GMarcus* BGrimes

DATE , 09/02/93 1 / /93

[OFFICIAL RECORD COPY]

DOCUMENT NAME: S:\DORS\CHERNOBL.JLB

al

IN 93-XX

September xx, 1993 Page x of x

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.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact: Eric J. Benner, NRR

(301) 504-1171 Attachments:

1. Chernobyl Turbine Hall Layout

2. List of Recently Issued NRC Information Notices

• See previous concurrences

OFC lOEAB:DORS SC/OEAB:DORS PUB:ADM SPLB:DSSA

NAME EBenner* EGoodwin* Tech Ed* CM for West*

DATE j05/13/93 105/19/93 105/13/93 I08/25/93 OFC C/SPLB:DSSA CEP:OIP C/OEAB:DORS OGCB:DORS

NAME CMcCracken* JERamsey* AChaffee* JLBirmingham

DATE j08/25/93 08/26/93 J 08/27/93 J09/ /93 OFC

NAME

C/OGCB:DORS

GM arcus (, t ID/DORS

BGrimes

DATE I 9/ Z /93 / /93

[OFFICIAL RECORD COPY]

DOCUMENT NAME: S:\DORS\CHERNOBL.JLB

IN 93-XX

August xx, 1993 structural component failures may cause failures of multiple trains of safety

related systems and may call into question the true separation, independence, and redundancy of safety-related components.

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.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Eric J. Benner, NRR

(301) 504-1171 Attachments:

1. Chernobyl Turbine Hall Layout

2. List of Recently Issued NRC Information Notices

• See previous concurrences

OFC OEAB:DORS SC/OEAB:DORS PUB:ADM SPLB:DSSA

NAME EBenner* EGoodwin* Tech Ed* CM for West*

DATE 05/13/93 05/19/93 05/13/93 08/25/93 j

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NAME

C/SPLB:DSSA

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NAME GMarcus BGrimes

DATE / /93 / /93 jJ

[OFFICIAL RECORD COPY]

DOCUMENT NAME: G:\EJB1 \CHERNOBY.IN

IN 93-XX

June xx, 1993 structural component failures may cause failures of multiple trains of safety

related systems and may call into question the true separation, independence, and redundancy of safety-related components.

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.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Eric J. Benner, NRR

(301) 504-1171 XXXXXXXXXXXXXX, NRR

(301) 504-XXXX

Attachments:

1. Chernobyl Turbine Hall Layout

2. List of Recently Issued NRC Information Notices

• See previous concurrences

EOFC

NAME

DATE

OEAB:DORS

EBenner*

05/13/93 SC/OEAB:DORS

EGoodwin*

05/19/93 PUB:ADM

Tech Ed*

05/13/93 lS}

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DSSA

/2/93 OFC C/SPDSSA AD/CEP:OIP C/OEAB:DORS C/OGCB:DORS

NAME CMcCracken AKenneke AChaffee GMarcus

DATE At2*793 I /93 / /93 / /93 OFC D/DORS

NAME BGrimes

DATEl / /93

[OFFICIAL RECORD COPY]

DOCUMENT NAME: G:\EJB1\CHERNOBY.IN

IN 93-XX

June xx, 1993 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.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Eric J. Benner, NRR

(301) 504-1171 xxxxxxxxxxxxxx, NRR

(301) 504-XXXX

Attachments:

1. Chernobyl Turbine Hall Layout

2. List of Recently Issued NRC Information Notices

• See previous concurrences

OFC OEAB:DORS SC/OEAB:DORS PUB:ADM SPLB:DSSA

NAME EBenner* EGoodwin - Tech Ed*

DATE 05/13/93 16-//C/93 05/13/93 I / /93 OFC C/SPLB:DSSA C/OEAB:DORS C/OGCB:DORS D/DORS

NAME CMcCracken AChaffee GMarcus BGrimes

DATE , / /93 1 / /93 1 / /93 / /93

[OFFICIAL RECORD COPY]

DOCUMENT NAME: G:\EJB1\CHERNOBY.IN

K>

IN 93-XX

June xx, 1993 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.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Eric J. Benner, NRR

(301) 504-1171 XXXXXXXXXXXXXX, NRR

(301) 504-XXXX

Attachments:

1. Chernobyl Turbine Hall Layout

2. List of Recently Issued NRC Information Notices

[OFC OEAB:DORS SC/OEAB:DORS PUB:ADM SPLB:DSSA

NAME EBenner fyl EGoodwin Tech Ed

[ DATE [§/13/93 / /93 cK/ O/93 / /93 OFC C/SPLB:DSSA C/OEAB:DORS C/OGCB:DORS lD/DORS

NAME CMcCracken AChaffee GMarcus BGrimes

DATE / /93 1 / /93 1 / /93 1 /93

[OFFICIAL RECORD COPY]

DOCUMENT NAME: G:\EJB1\CHERNOBY.IN

IN 93-XX

September xx, 1993 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.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact: Eric J. Benner, NRR

(301) 504-1171 Attachments:

1. Chernobyl Turbine Hall Layout

2. List of Recently Issued NRC Information Notices

• See previous concurrences

lOFC OEAB:DORS SC/OEAB:DORS PUB:ADM SPLB:DSSA

NAME EBenner* EGoodwin* Tech Ed* CM for West*

[DATE 05/13/93 05/19/93 05/13/93 J 08/25/93 OFC C/SPLB:DSSA CEP:OIP C/OEAB:DORS OGCB:DORS

NAME CMcCracken* JERamsey* AChaffee* JBirmingham*

DATE j08/25/93 108/26/93 108/27/93 I 09/02/93 OFC C/OGCB:DORS D/DORS

A GMarcus BGrimes

lDATE , / /93 1 / /93--J

[OFFICIAL RECORD COPY]

DOCUMENT NAME: S:\DORS\CHERNOBL.JLB