Information Notice 1991-64, Site Area Emergency Resulting from a Loss of Non-Class 1E Uninterruptible Power Supplies

Site Area Emergency Resulting from a Loss of Non-Class 1E Uninterruptible Power Supplies

ML031190491
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:	10/09/1991
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-91-064, NUDOCS 9110030270
Download: ML031190491 (10)

UNITED STATES

NUCLEAR REGULATORY-COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 October 9, 1991 NRC INFORMATION NOTICE 91-64: SITE AREA EMERGENCY RESULTING FROM A LOSS OF

NON-CLASS 1E UNINTERRUPTIBLE POWER SUPPLIES

Addressees

nuclear power

All holders of operating licenses or construction permits for

reactors.

Purpose

information notice

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

to alert addressees to problems resulting from the common mode

nonsafety-related applications at Unit 2 uninterruptible power supplies used in recipients will

of the Nine Mile Point Nuclear Station. It is expected that

to their facilities and consider

review the information for applicability suggestions

actions, as appropriate, to avoid similar problems. However, therefore, no

contained in this information notice are not NRC requirements;

specific action or written response is required.

Description of Circumstances

On August 13, 1991, Nine Mile Point.Unit 2 was operating caused at full power when a

main transformer which the generator, fault occurred on phase B of the automatically

turbine, and reactor to trip. Station loads were transferred

power from the

from the normal station service transformer, which receives power from the

generator, to the reserve station transformer, which-receives

voltage on the

grid. During the transient which lasted for about 12 cycles, of normal value

station's phase B buses decreased to approximately .50 percent

before returning to normal.

five of eight

The voltage transient resulted in loss of the power output from power supplies

nonsafety-related uninterruptible power supplies. 'Loss of these control rod posi- caused the loss of control room annunciators,.indication of the safety

tions, the core thermal limits computer, the process computer, some instru- parameter display system computer, the feedwater control system, the plant

mentation for balance-of-plant systems, some instrument recorders, Some of the

the plant.

radio and paging systems, and some of the lighting forFor.example, the average

instrument recorders that were lost failed "as is."

tripped.

power range monitors continued to indicate 100% after the reactor average power

Nevertheless, control room operators were able to verify from panels'and from other

range meters and local power range lights mounted on back down...

indications that the reactor actually had tripped and.was shut

2A.

9110030

IN91-64 October 9, 1991 Because of the loss of control room annunciators

resulting from automatic tripping of the generator, and the reactor transient

Niagara Mohawk Power Corporation (the licensee) turbine, and reactor, in conformance with the emergency plan. The declared a site area emergency

accordance with emergency operating procedures. operators shut down the plant in

trip, plant personnel had restored power output Thirty-four minutes after the

uninterruptible power supplies using the alternate from the five nonsafety-related

Thirteen hours after the trip, the reactor maintenance power sources.

was

and an hour later, the licensee ended the site in the cold shutdown condition, area emergency.

As shown in Attachment 1, each uninterruptible

3-phase 600-Vac power from the plant's electrical power supply cabinet receives

system is connected to either the generator distribution system. This

the 600-Vac input power passes through an or the grid. Inside the cabinet, ac-to-dc

mately 140-Vdc power which then passes through converter to obtain approxi-

3-phase 2 08/120-Vac power that is within specified an inverter to generate quality

tude, frequency, and phase. The output from limits for voltage ampli- critical loads, many of which are sensitive the cabinet is distributed to

are sometimes present with normal ac power. to the voltage irregularities that

power to these loads when the normal supply To prevent the interruption of

is connected to the uninterruptible power of power is lost, a 125-Vdc battery

and the dc-to-ac inverter. supply between the ac-to-dc converter

The uninterruptible power supply cabinet also

208/120-Vac maintenance power. This power receives three-phase

regulator and is used to supply critical loadsis provided through a voltage

ruptible power from the inverter is not available. when the supply of uninter- control logic system selects either inverter Within the cabinet, a

tion to the critical loads. or maintenance power for distribu- Prior to and at the time of the event, the

received power from phase B of the maintenancecontrol logic power supply normally

power was not available, the input for the power source. If maintenance

control

cally transferred to the output of the inverter. logic power supply automati- the control logic tripped the uninterruptible However, on August 13, 1991, transient on phase B of the maintenance power power supply in response to the

expected that the control logic power supply source. The licensee had

the inverter and, when inplant electrical would transfer to the output of

distribution system voltages returned

to normal, would transfer back to the maintenance

the uninterruptible power supply would have source. Had this happened, loads. continued'to supply the critical

If the control logic power supply had

from the inverter and backup power frombeen wired to receive its normal power

the maintenance source, the control

logic would have had a continuous source

of power and the loss of power output

from the uninterruptible power supplies would

not have occurred. The control

logic power supplies for the three nonsafety-related

uninterruptible power supplies that were and the two safety-related

receive dc power for control logic through not lost during the event normally

a dc-to-dc converter.

IN 91-64 October 9, 1991 e 5Page te

3 of 4 rechargeable lead-acid cells

Six battery packs, each consisting of 3 small the control logic and

ith nInterruptible.Rower.kupply, provide power to

&itfi'io t~ir pio vowerrfs2Isaqisl'bW1 *If the.ibattery packs

Wen~fdr

i

n .1 tfb i

1A rtWIt46Glid hWteprbVided sufficient

NeltdJ &fiebei~rsiti df the

td:h&Viepreveivtedilos

e to hfeoltccnSeerfoundithatsthe

uninterruptible power supplies. After thi9Evhtt

electrolyte in the lead-acid cells was dry.

in the vendor's manual does not

Although the prev nt ve zintenahcg:section

address the bdittNe 0 aSotb Pecti bn of the manual states that theypacks

had installed the battery

stiyl be rb la 4 Si* ry r4i rg .2Tbvendor 2 rtie licensee determined that the battery

z03 r

pac k1s9gb6iI2 9 e' e d q because of the environmental condi- tions within the cabinets.

The licensee obtained the unintaiript~ bEt.iber ideas es:ffomEx-de-slettronics

obtained)-a" eieV-- Wn'ual for the

in 1981. In 1985, the licensee which recognized the

uninterruptible power supplies from Exide Electronics power for the

importance of reversing the connectios o$foWatTWndbackupElectronics did have

control logic power supplies. New unitsb~pl-dtk(,Exide did not specifically

the connections reversed. However, Exide Electronics had obtained the

advise the licensee of this change. The licensee  :>-t;mti1A

uninterruptible power supplies as commercial grade products.

Ot'-' miDIG 5 98 xrqqu2 9 , i- i4J .1 f 4Mb p'WdI' zuppliesttOlpravide normal

The licensee has modifi logic power supplies from the output of the inverter

input power to the control The licensee has also

and alternate power from the maintenance source. and has established an annual

logic

replaced the battery packs for the control to evaluate the performance of the

replacement schedule. The licensee intends

to the control logic under

switching circuitry for supplying input power changes to the vendor's manual.

various conditions and to process appropriate

Discussion

turbine, and reactor trips. The

The transformer fault caused the generator, of voltage on the plant's

transformer fault also led to a momentary degradation the common mode failure of the

electrical distribution system and, in turn, of the loss of control rod

five uninterruptible power supplies. Because power supplies, the

position indicators due to loss of the uninterruptibleall control rods had fully inserted

operators could not Immediately verify that difficulty in implementing the

into the reactor core. This resulted in some

was in a safe condition at all

emergency procedures. However, the reactorall safety parameters, except for

times, and operators were able to monitor The two safety-related uninter- control rod positions, throughout the event. a design basis accident occurred in

ruptible power supplies were not lost. Had been available for the instrumen- conjunction with this event, power would have safety systems.

tation and control components in the required

IN 91-64 October 9, 1991 This information notice requires no specific action or writtin response. If

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

of the technical contacts listed below or the appropriate Office-of Nuclear

Reactor Regulation project manager.

ars E. Rossi, 1rector- Division of Operational Eve ts Agssssment

Office of Nuclear.Reactor Regulation

Technical contacts: Jack E. Rosenthal, AEOD

(301) 492-4440

Roger Woodruff, NRR.

(301) 49Z-1152 Attachments:

1. Unlnterruptible Power Supply Before Design Change

2. List of Recently Issued NRC Information Notices

I

=-- 125-VDC

BATTERY

(i, (D 0 AD 0

. o&s v-,.T amO

UN INTERRUPTIBLE POWER SUPPLY BEFORE DESIGN CHANGE

-A

to

o?

Attachment 2 IN 91-64 October 9, 1991 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

91-63 Natural Gas Hazards 10/03/91 All holders of OLs or CPs

at Fort St. Vrain for nuclear power reactors

Nuclear Generating Station

91-62 Diesel Engine Damage 09/30/91 All holders of OLs or CPs

Caused by Hydraulic for nuclear power reactors

Lockup Resulting from

Fluid Leakage Into

Cylinders

91-61 Preliminary Results of 09/30/91 All holders of OLs or CPs

Validation Testing of for nuclear power reactors

Motor-Operated Valve and motor-operated valve

Diagnostic Equipment (MOV) diagnostic equipment

vendors identified herein.

91-60 False Alarms of Alarm 09/24/91 All Nuclear Regulatory Comi

Ratemeters Because of mission (NRC) licensees

Radiofrequency Inter- authorized to use sealed

ference sources for industrial

radiography.

91-59 Problems with Access 09/23/91 All holders of OLs or CPs

Authorization Programs for nuclear power reactors.

91-58 Dependency of Offset 09/20/91 All holders of OLs or CPs

Disc Butterfly Valve's for nuclear power reactors.

Operation on Orientation

with Respect to Flow

91-57 Operational Experience 09/19/91 All holders of OLs or CPs

on Bus Transfers for nuclear power reactors.

91-56 Potential Radioactive 09/19/91 All holders of OLs or CPs

Leakage to Tank Vented for nuclear power reactors.

to Atmosphere

OL = Operating License

CP = Construction Permit

IN 91-64 October 9, 1991 This information notice requires no specific action or written response. If

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

of the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: Jack E. Rosenthal, AEOD

(301) 492-4440

Roger Woodruff, NRR

(301) 492-1152 Attachments:

1. Uninterruptible Power Supply Before Design Change

2. List of Recently Issued NRC Information Notices

Document Name: IN 91-64

• SEE PREVIOUS CONCURRENCES:

• OEAB *ADM/RPB *SC:OEAB *BC:OEAB *TL:IIT *PM:PD11 RWWoodruff JOMain RLDennig AEChaffee JERosenthal DSBrinkman

9/12/91 9/12/91 9/17/91 9/17/91 9/24/91 9/25/91

• BC:SICB

SNewberry

• BC:OGCB

CHBerlinger

0I

Ro \W

9/25/91 9/27/91

IN 91-XX

September xx, 1991 condition at all times, and operators were able to monitor all safety

parameters, except for control roa positions, throughout the event. The two

safety-related uninterruptible power supplies were not lost. Had a loss of

coolant accident occurred in conjunction with this event, power would have

been available for the instrumentation and control components in the

emergency core cooling system.

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

you have any questionrabout the information in this notice, please contact Y'

one of the cal conta low or the appropria project manager .

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical ntact5 Jack E. Rosenthal, AEOD

(301) 492-4440

I1 Roger Woodruff, NRR

(301) 492-1152 Attachments:

1. Uninterruptible Power Supply Before Design Change

2. List of Recently Issued Information Notices sy_

K#

CONCURRENCE:

• OEAB *ADM/RPB *SC0OEAB *BC: OEAB

RWWoodruff JDrain RLDennig AE~haffee IT I DSB9rn9

9/12/91 9/12/91 9/17/91 9/17/91 9?IAA791 9/ S791 B: OCEC 4ID: DOEA

CHBerlinger CERossi

9gt51 91-1191 9/ /91

• SEE PREVIOUS CONCURRENCES

IN 91-XX

September xx, 1991 lighting. However, the two safety-related uninterruptible power supplies

were not lost. Had a loss of coolant accident occurred in conjunction with

this event, power would have been available for the instrumentation and

control components in the emergency core cooling system.

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

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

one of the technical contacts listed below or the appropriate project manager

in the Office of Nuclear Reactor Regulation.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Jack E. Rosenthal, AEOD

(301) 492-4440

Roger Woodruff, NRR

(301) 492-1152 Attachments:

1. Uninterruptible Power Supply Before Design Change

2. List of Recently Issued Information Notices

CONCURECE:

• OEAB *ADM/RfB TL: IIT PM:PD11 RWWoodruff JI)Main

9

&6ig

91 AIEChaffee JERosenthal DSBrinkman

9/12/91 9/12/91 /r1/ 9/I1/91 9/ /91 9/ /91 BC:SICB BC:OGCB D:DOEA

SNewberry CHBerlinger CERossi

9/ /91 9/ /91 9/ /91

• SEE PREVIOUS CONCURRENCES

a

IN 91-XX

September xx, 1991 one of the technical contacts listed below or the appropriate project manager

in the Office of Nuclear Reactor Regulation.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Jack E. Rosenthal, AEOD

(301) 492-4440

Roger Woodruff, NRR

(301) 492-1152 Attachment:

1. List of Recently Issued Information Notices

CONCURRECE:

OEAB thWS TECH EDITOR SC: OEAB BC:OEAB TL: IT FM:PD11 RWWoodruff ?fla;i £9A RLDennig AEChaffee JERosenthal DSBrinkman

9/q,/91 9/11/91 9/ /91 9/ /91 9/ /91 9/ /91 BC:OGCB D:DOEA

CHBerlinger CERossi

9/ /91 9/ /91