Information Notice 1995-37, Inadequate Offsite Power System Voltages During Design-Basis Events

Inadequate Offsite Power System Voltages During Design-Basis Events

ML031060285
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:	09/07/1995
From:	Crutchfield D Office of Nuclear Reactor Regulation
To:
References
IN-95-037, NUDOCS 9508310198
Download: ML031060285 (12)

Io

UNITED STATES

I N

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 September 7, 1995 NRC INFORMATION NOTICE 95-37: INADEQUATE OFFSITE POWER SYSTEM VOLTAGES

DURING DESIGN-BASIS EVENTS

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

The Nuclear Regulatory Commission (NRC) is issuing this information notice to

alert addressees to circumstances that could result in inadequate offsite

power system voltages during design-basis events. 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.

DescriDtion of Circumstances

In response to a deficiency identified at Palo Verde Nuclear Generating

Station by an electrical distribution system functional inspection (EDSFI)

team, the licensee undertook an electrical design-basis reconstitution effort

to upgrade and reverify the voltage regulation calculations at the plant.

Subsequently, Licensee Event Report (LER)93-011, dated December 25, 1993, reported on shortcomings in the plant site voltage regulation. Specifically, with the switchyard voltage in the lower two-thirds of its expected operating

range and the startup transformer heavily loaded, the Class 1E loads might

separate from the transformer and load onto the diesel generators; or the

Class 1E bus undervoltage relays may not actuate even though sustained, substandard voltages might occur at the terminals of Class 1E loads. The

heavy loading of the startup transformer would occur following a main

generator or turbine trip with successful fast bus transfer of house loads to

the transformer, or following manual transfer of house loads to the

transformer.

In a recent supplement to LER 93-011, dated February 6, 1995, the Palo Verde

licensee identified a different series of events that could occur as a result

of the same problem. If a loss of coolant accident (LOCA) should occur with

the switchyard voltage in the lower two-thirds of its operating range, the

engineered safety feature (ESF) loads would begin sequencing onto the

preferred offsite power source and the house loads would fast transfer to the

startup transformer following the main generator or turbine trip that would

accompany the LOCA. The resulting voltage drops at the safety buses would

cause the bus degraded voltage relays to drop out during the ESF load

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V s~IN 95-37 September 7, 1995 sequencing and to fail to reset before timing out. Thisload circumstance would

result in the ESF loads separating from offsite power, shedding of the

and resequencing of the

safety buses, closing of the diesel generator breaker, administratively

ESF loads onto the diesel generators. The licensee is

maintaining the switchyard voltage in the upper one-third of its operating

range until a long-term solution to the problem is in place.

On August 8, 1995, the licensee for Diablo Canyon reported the same voltage

vulnerability when one of the offsite power sources are unavailable.

for Arkansas

In LER 91-010, Supplement 1, dated March 27, 1993, thea licensee

500-kV autotransformer

Nuclear One, (AND), Units 1 and 2, reported that had

161-kV system might

been lost during summer peak conditions in the past,thethesafety

voltage to loads of both

not have been able to maintain adequate dispatcher actions were

units unless local hydro generation was available and

load. The 500-kV autotransformer is a

taken to shed some of the 161-kV system Upon a unit

common link between the Unit 1 and Unit 2 startup transformers. to their respective

trip the loads of each unit are automatically transferred

autotransformer that feeds both startup

startup transformer. If the 500-kV units are transferred

transformers is lost or unavailable, the loads of both

system. The long- to a third common startup transformer fed from the 161-kVregulator from the

term resolution of this problem was to install a voltage

161-kV offsite power source.

Discussion

their

In the case of Palo Verde and ANO, the licensees determined through capabilities, analyses, which utilized updated computer-aided computational the course of a year

that offsite power system voltages that could occur over

may not be adequate to support all design-basis events. system,At Palo Verde the

weakness exists in the plant's electrical distribution and at AND, the

system.

problem existed in the offsite power switchyard and transmission

In the case of Palo Verde, the licensee determined that the system normal anticipated

design could

switchyard voltage variance is greater than the electrical system voltage

accommodate and still provide acceptable onsite distribution minimum and

spread characteristics. The licensee has indicated that the respectively greater

maximum loading conditions used in previous analyses were could support, than and less than those that actual plant operating experience not auditable, and a

the configuration control of transformer tap settingsnotwasfully understood and

fast bus transfer undervoltage blocking feature was of weaknesses

documented. This situation occurred and went undetected because

in the original design and previous analyses of the plant's electrical of the

distribution system, and because of a less than full understanding

original design basis.

IN 95-37 September 7, 1995 voltage problem

At ANO, the licensee indicated that the 161-kV inadequate with time. The

occurred because of an increase in the 161-kV grid loading

periodically review

problem went undetected because the ANO staff failed to voltage requirements

the grid network voltage capability relative to the ANO

voltage levels

or to consider how many years the required minimum offsite

could be maintained following the initial analysis.

Power Station

NRC Generic Letters dated June 3, 1977 ('Millstone Nuclear of Station Electric

Degraded Grid Voltage"), and August 8, 1979 ("Adequacy

subsequently replaced by Branch

Distribution Systems Voltages), which were plan, provide the

Technical Position (BTP) PSB-1 in the NRC standard review

the degraded voltage issue.

basis for original analyses and commitments on an anticipated range

As part of this issue, licensees were asked to establish then required to

of normal offsite grid voltages over which they were

be provided to the terminals of all

demonstrate that adequate voltages would identified by the

events. As

safety-related equipment for all design-basis a range of offsite

ANO and Palo Verde licensees, operating the plant outside

voltage to safety equipment, or that

grid voltages that would provide adequate because of operation

would result in separation from the offsite power system to meet plant

of degraded voltage protection relays may constitute a failure

adequate capability and capacity of the

technical specifications relative to

offsite power system circuits.

to periodically update

As demonstrated by the above described-events, failure grid or plant

the original voltage analyses as the result of changing offsite regulatory

conditions could result in unintentional operation outsideidentified a need to

requirements. In addition, many licensees recently have

relays to ensure

increase the setpoints of their undervoltage protection equipment as a result

adequate voltages at the terminals of all safety-related

or design

of NRC EDSFIs or their own in-house electrical inspection inadequate

this measure ensures that

reconstitution efforts. Although for any unacceptable

voltages will not exist at the terminals of the equipment

for

length of time, increasing the setpoints increases the potential over the range

during design-basis events

separation from the offsite system An additional concern

of normally anticipated offsite system grid voltages. voltage protection

in this area is plants with no upper limit on degraded in the upward

relay setpoints. If these setpoints are allowed to drift potential for

direction, this trend could also lead to the same increased events.

separation from the offsite power system during design-basis

process could

An unanticipated voltage drop during emergency load sequencingthat may require remote

lead to sequencer lockup or circuit breaker operation Vogtle Unit 1 and is

manual reset action. This problem was experienced at RHR During Mid-Loop

documented in NUREG 1410, Loss of Vital AC Power and mitigation could be

Operations at Vogtle Unit 1 on March 20, 1990." Accident the sequencer and

delayed if procedures and training do not address restarting

other compensatory actions.

<_JIN 95-37 K.

September 7, 1995 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 (NRR) project manager.

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: James Lazevnick, NRR

(301) 415-2782 Thomas Koshy, NRR

(301) 415-1176 Attachment:

List of Recently Issued NRC Information Notices

X4 4 544 f rcA7

".4achment

IN 95-37 September 7, 1995 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

95-36 Potential Problems with 08/29/95 All holders of OLs or CPs

Post-Fire Emergency for nuclear power reactors.

Lighting

95-35 Degraded Ability of 08/28/95 All holders of OLs or CPs

Steam Generators to for pressurized water

Remove Decay Heat by reactors (PWRs).

Natural Circulation

95-34 Air Actuator and Supply 08/25/95 All holders of OLs or CPs

Air Regulator Problems in for nuclear power reactors.

Copes-Vulcan Pressurizer

Power-Operated Relief Valves

93-83, Potential Loss of Spent 08/24/95 All holders of OLs or CPs

Supp. 1 Fuel Pool Cooling After a for nuclear power reactors.

Loss-of-Coolant Accident

or a Loss of Offsite Power

95-33 Switchgear Fire and 08/23/95 All holders of OLs or CPs

Partial Loss of Offsite for nuclear power reactors.

Power at Waterford

Generating Station, Unit 3

95-10, Potential for Loss of 08/11/95 All holders of OLs or CPs

Supp. 2 Automatic Engineered for nuclear power reactors.

Safety Features Actuation

95-32 Thermo-Lag 330-1 Flame 08/10/95 All holders of OLs or CPs

Spread Test Results for nuclear power reactors.

95-31 Motor-Operated Valve 08/09/95 All holders of OLs or CPs

Failure Caused by Stem for nuclear power reactors.

Protector Pipe Inter- ference

95-30 Susceptibility of Low- 08/03/95 All holders of OLs or CPs

Pressure Coolant Injection for nuclear power reactors.

and Core Spray Injection

Valves to Pressure Locking

OL - Operating License

CP - Construction Permit

'~-V IN 95-37 September 7, 1995 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 (NRR) project manager.

orig /s/'d by DMCrutchfield

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: James Lazevnick, NRR

(301) 415-2782 Thomas Koshy, NRR

(301)415-1176 Attachment:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: 95-37. IN

• See previous concurrence

To eceive a copy of this document, Indicate in the box: 'C" = Copy without attachmentlenclosure 'E' Copy with attachmentlenclosure AN"= No copy

OFFICE JEELB:DE I E ADM: PUB I N PECB:DRPM E SC/PECB:DRPMI N C/EELB:DE FE

NAME JLazevnick* Tech Ed/BCalure TKoshy* EGoodwin* JCalvo*

DATE 107/26/95 07/07/95* 07/24/95 08/14/95 08/14/95 1 OFFICE PECB:DRPM I C/PECB:DRPM D/W , t35 1 NAME RKiessel* AChaffee* DCW field . ._._._. I

DATE 08/29 /95 08/29/95 09/ 1 /95 _

OFFICIAL RECORD COPY

IN 95-XX

August xx, 1995 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 (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: James Lazevnick, NRR

(301) 415-2782 Thomas Koshy, NRR

(301)415-1176 Attachment:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: S:\OFFCAPNT.IN

• See previous concurrence

To teiwve a opy of IN. document, hIdcata hIthe box: C - Copy wthout attachmenVenclosure E - Copy with attachmntlenclosur - No copy

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DATE 07/26/95 07/07/95* 07/24/95 08/14/95 08/14/95 OFFICE PECB:DRPM I C/PECB:DRPM I D/DRPM a - I

NAME RKiessel AChaffee DCrutchfield-A _I

DATE / 95 /195 95 I_

OFFICIAL RECORD COPY

IN 95-XX

August xx, 1995 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 (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: James Lazevnick, NRR

(301) 415-2782 Thomas Koshy, NRR

(301)415-1176 Attachment:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\IN\OFFCAPNT.IN

• See previous concurrence

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NAME JLazevnick* Tech Ed/BCalure lTKoshy* EGoodwin* JCalvo*

DATE 07/26/95 07/07/95* 107/24/95 08/14/95 08/14/95 OFFICE PECB:DRPM 4,O C/PECB:DRP l D/DRPM

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v1 IN 95-XX

May xx, 1995 This information notice requires no specific action or written response. If

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

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

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts: James Lazevnick, NRR

(301) 415-2782 Thomas Koshy, NRR

(301)415-1176 Attachment:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\IN\OFFCAPNT.IN

To receive a copy of this document, Indicate In the box: AC. = Copy without attachmentiencloesure 'E' - Copy with attachmentlenclosure ONE - No copy

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NAME JLazevnick Tech Ed/BCalure TKoshy ,& EGoodwin CBerlinger l

DATE / /95 07/07/95* 7/It /95 I /95 / /95 ]

OFFICE OECB:DOPS I C/OECB:DOPS IZD/DOPS Z I IIII ]

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OFFICIAL RECORD COPY

IN 95-XX

August xx, 1995 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 (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: James Lazevnick, NRR

(301) 415-2782 Thomas Koshy, NRR

(301)415-1176 Attachment:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\IN\OFFCAPNT.IN

To mcelve a copy of tiWe document. Indicate In the box: 'C - Copy without attachmentlenclosurm 'E - Copy with attachmentlencloumxe N - No copy

OFFICE EELB:DE E ADM:PUB PECB:DRPM I E SC/PECB:DRPM C/EELB:DE i

NAME JLazevnick* Tech Ed/BCalure TKoshy* EGoodwin JCalvo

DATE 07/26/95 07/07/95* 07/24/95 j 1/4L/95 08/14/95 OFFICE PECB:DRPM I C/PECB:DRPM I D/DRPM I IIlIlIl

NAME RKiessel AChaffee DCrutchfield

DATE I /95 / /95 I/ /95 OFFICIAL RECORD COPY

IN 95-XX

August xx, 1995 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 (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: James Lazevnick, NRR

(301) 415-2782 Thomas Koshy, NRR

(301)415-1176 Attachment:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\IN\OFFCAPNT.IN

* ji... with attachmentlenclosure 'N' No copy

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To iacelve a copy 0t

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Ibls document, snaicaje In the UUA;

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OFFICE EELB:DE E ADM:PUB I PECB:DRPM lE SC/PECB:DRPM C/EELB:DE L

NAME JLazevnick* Tech Ed/BCalure TKoshy* - EGoodwin JCalvo* l

DATE 07/26/95 07/07/95* 07/24/95 / /95 07/27/95]

OFFICE PECB:DRPM I C/PECB:DRPM I D/DRPM lI I

NAME RKiessel AChaffee DCrutchfield

DATE I /9 / /9 / /95 OFFICIAL RECORD COPY

S

IN 95-XX

May xx, 1995 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 (NRR) project manager.

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts: James Lazevnick, NRR

(301) 415-2782 Thomas Koshy, NRR

(301)415-1176 Attachment:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\IN\OFFCAPNT.IN

To recehe a copy of this

docunmnt, Indicate I the box: C - Copy without attachmentlenclose 'E - Copy with attachment/enclocure N - No copy

jOFFICE EELB:DE oj [EADM:PUB [ljOECBDOPS IJk SC/OECB:DOPS I C/EELB: DE 4&d- NAME JLazevnic Tech Ed/BCalure TK o EGoodwin JCalvo f I

DATE 1 /A6/95 - 07/07/95* 71 /95 /95 7/7/95 '/2i/,*

OFFICE OECB:DOPS l C/OECB:DOPS l D/DOP1 lIIIEI

NAME RKiessel AChaffee BGrimes Ij__I--

DATE / 95 /IJ/95

/ _

OFFICIAL RECORD COPY