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{{#Wiki_filter:.* -*UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555April 16, 1990NRC INFORMATION NOTICE NO. 90-25: LOSS OF VITAL AC POWER WITH SUBSEQUENTREACTOR COOLANT SYSTEM HEAT-UP
{{#Wiki_filter:.* -*UNITED STATES NUCLEAR REGULATORY
 
COMMISSION
 
===OFFICE OF NUCLEAR REACTOR REGULATION===
WASHINGTON, D.C. 20555 April 16, 1990 NRC INFORMATION
 
NOTICE NO. 90-25: LOSS OF VITAL AC POWER WITH SUBSEQUENT
 
REACTOR COOLANT SYSTEM HEAT-UP


==Addressees==
==Addressees==
:All holders of operating licenses or construction permits for nuclear powerreactors.
:
All holders of operating
 
licenses or construction
 
permits for nuclear power reactors.


==Purpose==
==Purpose==
:This information notice is being provided to inform addressees of a significantoperating event which occurred at the Georgia Power Company's Vogtle NuclearPlant on March 20, 1990. The event took place while Unit 1 was in mid-loopin operational mde 6 and demonstrates the need for operating personnel to beprudent in removing equipment from service or establishing atypical equipmentalignments during shutdown. It is expected that recipients will review theinformation for applicability to their facilities and consider actions, asappropriate,.to avoid similar problems. However, suggestions contained inthis information notice do not constitute NRC requirements; therefore, nospecific action or written response is required.
: This information
 
notice is being provided to inform addressees
 
of a significant
 
operating
 
event which occurred at the Georgia Power Company's
 
Vogtle Nuclear Plant on March 20, 1990. The event took place while Unit 1 was in mid-loop in operational
 
mde 6 and demonstrates
 
the need for operating
 
personnel
 
to be prudent in removing equipment
 
from service or establishing
 
atypical equipment alignments
 
during shutdown.
 
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 requirements;  
therefore, no specific action or written response is required.Description
 
of Circumstances:
On March 20, 1990, a loss of vital ac power occurred while Vogtle Unit 2 was operating
 
at 100 percent power and Unit 1 had been in a refueling
 
outage for about 4 weeks. Unit 1 was in mid-loop in operational
 
mode 6 with plant equip-ment conditions
 
as follows: o The Unit 1 B reserve auxiliary
 
transformer (RAT) was tagged out of service for maintenance
 
o The Unit 1 B emergency
 
diesel generator (EDG) was tagged out of service and disassembled
 
for maintenance
 
o The Unit 1 A RAT was supplying
 
offsite power to the crosstied
 
Unit 1 A and B vital buses o The reactor coolant system (RCS) temperature
 
was being maintained
 
at around 90 degrees Fahrenheit (F) via the train A residual heat removal (RHR) pump, the-train
 
B pump was in standby o The vessel head was in place with the bolts not fully tensioned o The pressurizer
 
manway cover was removed_ __ A l e ,
IN 90-25 April 16, 1990 o The manways for steam generators
 
2 and 3 were partially
 
bolted in place and the manways for steam generators
 
1 and 4 were in place with bolts fully tensioned o The inboard charging line check valve and an accumulator
 
isolation valve were open for inspection
 
o The containment
 
equipment
 
hatch and the containment
 
personnel
 
hatch were open At about 9:20 a.m., a truck carrying fuel and lubricants
 
in the plant low voltage switchyard
 
backed into a support column for the feeder line supplying power to the Unit 1 A RAT and the Unit 2 B RAT. The insulator
 
for the C phase of the feeder line fractured
 
and initiated
 
a phase-to-ground
 
electrical
 
fault.The fault resulted in a loss of power to the Unit 1 A RAT and the Unit 2 B RAT.The Unit 2 B EDG started and loaded to the deenergized
 
Unit 2 B vital bus. How-ever, a Unit 2 turbine trip and reactor trip occurred because of an improperly
 
connected (wrong tap) differential
 
current transformer (DCT). The DCT initiated the trip when the current surge associated
 
with the phase-to-ground
 
fault was sensed. The Unit 2 trip was uncomplicated.
 
Because both of the Unit 1 vital buses were crosstied
 
and being supplied by the Unit 1 A RAT, the loss of the transformer
 
deenergized
 
both vital buses.Deenergizing
 
these buses resulted in the loss of power to the operating
 
RHR pump. Since the Unit 1 B EDG was tagged out of service and disassembled
 
for maintenance, the emergency
 
power supply for the B vital bus was unavailable
 
and the standby B RHR pump could not be started.The available
 
Unit 1 A EDG started on bus undervoltage, but for unknown reasons, it shut down automatically
 
after 1 minute and 20 seconds. At 9:40 a.m., plant operators
 
declared a site area emergency.
 
A loss of all onsite and offsite ac power at Vogtle for more than 15 minutes is classified
 
as a site area emergency.
 
The licensee made their declaration
 
because all vital ac power was lost for greater than 15 minutes. Approximately
 
18 minutes after the first start of the A EDG, the operators
 
locally reset the load sequencer
 
which automatically
 
restarted
 
the A EDG on undervoltage.
 
However, after 1 minute and 10 seconds, the diesel again shut down automatically.
 
At 9:56 a.m., plant operators
 
per-formed an "emergency" manual start of the diesel, which bypassed most of the diesel's protective
 
trips. The diesel started and loaded to the bus, the A RHR pump was restarted, and core cooling was reestablished
 
to Unit 1. With the start of the diesel, the site area emergency
 
was downgraded
 
to an "alert" at 10:15 a.m. Containment
 
integrity
 
was established
 
at 11:03 a.m.Plant personnel
 
returned the Unit 1 B RAT to service after completing
 
formal tagout removal procedures.
 
However, attempts to energize the transformer
 
were delayed for several minutes because of a sticking mechanical
 
interlock
 
in the control circuitry
 
for a motor-operated
 
disconnect
 
switch on the high side of the B RAT. Power was restored to the B vital bus via the B RAT at 11:40 a.m.At 12:38 a.m., core cooling was shifted to the B RHR train to facilitate
 
sub-sequent electrical
 
alignment
 
changes.
 
e. v -%IN 90-25 April 16, 1990 According
 
to control roon indication, RCS temperature
 
increased
 
from 90 to 136 degrees F during the 36 minutes required to reenergize
 
the A bus (1.3 degrees F/min).Throughout
 
the event, non-vital
 
power was continuously
 
provided to Unit 1 from offsite sources, via backfeed through the main generator
 
transformer.
 
Also, the Unit 2 electrical
 
distribution
 
system remained energized (aside from the momentary
 
loss of power before the reactor trip). However, the Vogtle electrical
 
system was not designed to permit easy interconnection
 
of the Unit 1 vital buses to nonvital power or to the Unit 2 electrical
 
buses. Therefore, there were no procedures
 
in place to provide guidance on interconnecting
 
the Unit 1 vital and nonvital buses or for interconnecting
 
the Unit 1 electrical
 
distribution
 
system with the distribution
 
system at Unit 2. (There are no regulatory
 
requirements
 
that direct the licensee to develop Interconnection
 
procedures.)
Discussion:
The NRC has previously
 
identified
 
concerns with the operability
 
of necessary equipment
 
in shutdown modes. In Information
 
Notice (IN) 80-2O, "Loss of Decay Heat Removal Capability
 
at Davis-Besse
 
Unit 1 While in a Refueling
 
Mode" an extended loss of decay heat removal capability
 
was attributed
 
to a number of factors, including
 
inadequate
 
procedures, inadequate
 
administrative
 
controls, and the conduct of extensive
 
maintenance
 
activities.
 
Information
 
Notice 84-42, "Equipment
 
Availability
 
for Conditions
 
During Outages Not Covered by Technical
 
Specifications," describes
 
an event at the Palisades Nuclear Plant involving
 
the total loss of all ac power. The Palisades
 
event was precipitated
 
by personnel
 
performing
 
actions during a refueling
 
outage without an appreciation
 
for the effect of those actions on the plant as it was configured.
 
Many pieces of equipment
 
were tagged out of service for maintenance.
 
Personnel
 
intentionally
 
interrupted
 
offsite power. This action caused the loss of the only available
 
service water pump. As a result, cooling water was interrupted
 
to the only available (and operating)
diesel generator.
 
The diesel overheated
 
and was manually tripped. As a result, all station ac power was interrupted, causing the loss of fuel pool cooling. (The reactor had been defueled, and its fuel was being stored in the spent fuel pool).The recent Vogtle event reemphasizes
 
the need for careful planning of equipment outages during shutdown.
 
Licensees, in general, have considerable
 
latitude in removing equipment
 
from service and altering normal system lineups while in shutdown modes if only the minimum technical
 
specification
 
requirements
 
are considered.
 
The desire to return nuclear units to service as quickly as possible can result in maintenance
 
being conducted
 
on redundant, safety-related systems, concurrently.
 
The appropriateness
 
of conducting
 
parallel maintenance
 
activities
 
should be considered
 
in light of the availability
 
of alternate
 
equipment
 
and procedures
 
to mitigate the consequences
 
of potential operational
 
problems.
 
It is important
 
that plant outage plans assure that an adequate complement
 
of equipment
 
capable of responding
 
to potential
 
events remains available
 
throughout
 
the outage. Particular
 
care is needed when the reactor pressure boundary is not intact or the reactor coolant system is at mid-loop.
 
IN 90-25 April 16, 1990 A special investigation
 
of the Vogtle event is being conducted
 
by an NRC Incident Investigation
 
Team (1IT). The information
 
contained
 
in this notice is preliminary
 
and is subject to change, pending the findings made by the IIT.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
 
NRR project manager.~6hfares Eossi, Director Division of Operational
 
===Events Assessment===
Office of Nuclear Reactor Regulation
 
Technical
 
Contacts:
N. Fields, NRR (301) 492-1173 E. Trager, AEOD (301) 492-4496 Attachment:
List of Recently Issued NRC Information
 
Notices
 
, 0 --u Attachment
 
IN 90-25 April 16, 1990 LIST OF RECENTLY ISSUED NRC INFORMATION
 
NOTICES Intormation
 
Date ot Notice No. Subject Issuance Issued to 90-24 90-23 90-22 90-21 90-20 90-19 90-18 90-17 Transportation
 
of Model Spec 2-T Radiographic
 
Exposure Device Improper Installation
 
of Patel Conduit Seals Unanticipated
 
Equipment Actuations
 
Following Restoration
 
of Power to Rosemount
 
Transmitter
 
Trip Units Potential
 
Failure of Motor-Operated Butterfly
 
Valves to Operate Because Valve Seat Friction was Under-estimated Personnel
 
Injuries Resulting from Improper Operation
 
of Radwaste Incinerators
 
Potential
 
===Loss of Effective Volume for Containment===
Recirculation
 
===Spray at PWR Facilities===
Potential
 
Problems with Crosby Safety Relief Valves Used on Diesel Generator Air Start Receiver Tanks Weight and Center of Gravity Discrepancies
 
for Copes-Vulcan
 
Valves 4/10/90 4/4/90 3/23/90 3/22/90 3/22/90 3/14/90 3/9/90 3/8/90 All NRC licensees authorized
 
to use, transport, or operate radiographic
 
exposure devices and source changers.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All NRC licensees who process or incinerate
 
radio-active waste.All holders of OLs or CPs for PWRs.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.OL = Operating
 
License CP = Construction
 
Permit
 
tNOW, IN 90-25--April 16, 1990 A special investigation
 
of the Vogtle event is being conducted
 
by an NRC Incident Investigation
 
Team (IIT). The information
 
contained
 
in this notice is preliminary
 
and is subject to change, pending the findings made by the IIT.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
 
NRR project manager.Charles E. Rossi, Director Division of Operational
 
===Events Assessment===
Office of Nuclear Reactor Regulation
 
Technical
 
Contacts: N. Fields, NRR (301) 492-1173 E. Trager, AEOD (301) 492-4496 Attachment:
List of Recently Issued NRC Information
 
Notices*SEE PREVIOUS PAGE FOR CONCURRENCE
 
OFC NAME DATE OFC NAME DATE*OEAB:DOEA
 
NFields 4/11/90*OEAB:DOEA


==Description of Circumstances==
DFISCHER 4/11/90*TECH ED 4/11/90*C:OEAB:DOEA
:On March 20, 1990, a loss of vital ac power occurred while Vogtle Unit 2 wasoperating at 100 percent power and Unit 1 had been in a refueling outage forabout 4 weeks. Unit 1 was in mid-loop in operational mode 6 with plant equip-ment conditions as follows:o The Unit 1 B reserve auxiliary transformer (RAT) was tagged out ofservice for maintenanceo The Unit 1 B emergency diesel generator (EDG) was tagged out ofservice and disassembled for maintenanceo The Unit 1 A RAT was supplying offsite power to the crosstied Unit 1A and B vital buseso The reactor coolant system (RCS) temperature was being maintained ataround 90 degrees Fahrenheit (F) via the train A residual heat removal(RHR) pump, the-train B pump was in standbyo The vessel head was in place with the bolts not fully tensionedo The pressurizer manway cover was removed_ __ A l e ,
IN 90-25April 16, 1990 o The manways for steam generators 2 and 3 were partially bolted in placeand the manways for steam generators 1 and 4 were in place with boltsfully tensionedo The inboard charging line check valve and an accumulator isolationvalve were open for inspectiono The containment equipment hatch and the containment personnel hatchwere openAt about 9:20 a.m., a truck carrying fuel and lubricants in the plant lowvoltage switchyard backed into a support column for the feeder line supplyingpower to the Unit 1 A RAT and the Unit 2 B RAT. The insulator for the C phaseof the feeder line fractured and initiated a phase-to-ground electrical fault.The fault resulted in a loss of power to the Unit 1 A RAT and the Unit 2 B RAT.The Unit 2 B EDG started and loaded to the deenergized Unit 2 B vital bus. How-ever, a Unit 2 turbine trip and reactor trip occurred because of an improperlyconnected (wrong tap) differential current transformer (DCT). The DCT initiatedthe trip when the current surge associated with the phase-to-ground fault wassensed. The Unit 2 trip was uncomplicated.Because both of the Unit 1 vital buses were crosstied and being supplied bythe Unit 1 A RAT, the loss of the transformer deenergized both vital buses.Deenergizing these buses resulted in the loss of power to the operating RHRpump. Since the Unit 1 B EDG was tagged out of service and disassembled formaintenance, the emergency power supply for the B vital bus was unavailableand the standby B RHR pump could not be started.The available Unit 1 A EDG started on bus undervoltage, but for unknown reasons,it shut down automatically after 1 minute and 20 seconds. At 9:40 a.m., plantoperators declared a site area emergency. A loss of all onsite and offsite acpower at Vogtle for more than 15 minutes is classified as a site area emergency.The licensee made their declaration because all vital ac power was lost forgreater than 15 minutes. Approximately 18 minutes after the first start ofthe A EDG, the operators locally reset the load sequencer which automaticallyrestarted the A EDG on undervoltage. However, after 1 minute and 10 seconds,the diesel again shut down automatically. At 9:56 a.m., plant operators per-formed an "emergency" manual start of the diesel, which bypassed most of thediesel's protective trips. The diesel started and loaded to the bus, the ARHR pump was restarted, and core cooling was reestablished to Unit 1. Withthe start of the diesel, the site area emergency was downgraded to an "alert"at 10:15 a.m. Containment integrity was established at 11:03 a.m.Plant personnel returned the Unit 1 B RAT to service after completing formaltagout removal procedures. However, attempts to energize the transformer weredelayed for several minutes because of a sticking mechanical interlock in thecontrol circuitry for a motor-operated disconnect switch on the high side ofthe B RAT. Power was restored to the B vital bus via the B RAT at 11:40 a.m.At 12:38 a.m., core cooling was shifted to the B RHR train to facilitate sub-sequent electrical alignment changes.


e. v -%IN 90-25April 16, 1990 According to control roon indication, RCS temperature increased from 90 to136 degrees F during the 36 minutes required to reenergize the A bus (1.3degrees F/min).Throughout the event, non-vital power was continuously provided to Unit 1 fromoffsite sources, via backfeed through the main generator transformer. Also,the Unit 2 electrical distribution system remained energized (aside from themomentary loss of power before the reactor trip). However, the Vogtle electricalsystem was not designed to permit easy interconnection of the Unit 1 vital busesto nonvital power or to the Unit 2 electrical buses. Therefore, there were noprocedures in place to provide guidance on interconnecting the Unit 1 vital andnonvital buses or for interconnecting the Unit 1 electrical distribution systemwith the distribution system at Unit 2. (There are no regulatory requirementsthat direct the licensee to develop Interconnection procedures.)Discussion:The NRC has previously identified concerns with the operability of necessaryequipment in shutdown modes. In Information Notice (IN) 80-2O, "Loss of DecayHeat Removal Capability at Davis-Besse Unit 1 While in a Refueling Mode" anextended loss of decay heat removal capability was attributed to a number offactors, including inadequate procedures, inadequate administrative controls,and the conduct of extensive maintenance activities.Information Notice 84-42, "Equipment Availability for Conditions During OutagesNot Covered by Technical Specifications," describes an event at the PalisadesNuclear Plant involving the total loss of all ac power. The Palisades eventwas precipitated by personnel performing actions during a refueling outagewithout an appreciation for the effect of those actions on the plant as itwas configured. Many pieces of equipment were tagged out of service formaintenance. Personnel intentionally interrupted offsite power. This actioncaused the loss of the only available service water pump. As a result, coolingwater was interrupted to the only available (and operating) diesel generator.The diesel overheated and was manually tripped. As a result, all station acpower was interrupted, causing the loss of fuel pool cooling. (The reactorhad been defueled, and its fuel was being stored in the spent fuel pool).The recent Vogtle event reemphasizes the need for careful planning of equipmentoutages during shutdown. Licensees, in general, have considerable latitude inremoving equipment from service and altering normal system lineups while inshutdown modes if only the minimum technical specification requirements areconsidered. The desire to return nuclear units to service as quickly aspossible can result in maintenance being conducted on redundant, safety-related systems, concurrently. The appropriateness of conducting parallelmaintenance activities should be considered in light of the availability ofalternate equipment and procedures to mitigate the consequences of potentialoperational problems. It is important that plant outage plans assure thatan adequate complement of equipment capable of responding to potential eventsremains available throughout the outage. Particular care is needed when thereactor pressure boundary is not intact or the reactor coolant system is atmid-loop.
PSwetland 4/11/90*REGION I (IIT)WLazarus 4/11/90*C:GCB:DOEA


IN 90-25April 16, 1990 A special investigation of the Vogtle event is being conducted by an NRCIncident Investigation Team (1IT). The information contained in this noticeis preliminary and is subject to change, pending the findings made by the IIT.This Information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate NRR projectmanager.~6hfares Eossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: N. Fields, NRR(301) 492-1173E. Trager, AEOD(301) 492-4496Attachment: List ofRecently Issued NRC Information Notices
CBERLINGER


, 0 --uAttachmentIN 90-25April 16, 1990 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESIntormation Date otNotice No. Subject Issuance Issued to90-2490-2390-2290-2190-2090-1990-1890-17Transportation of ModelSpec 2-T RadiographicExposure DeviceImproper Installation ofPatel Conduit SealsUnanticipated EquipmentActuations FollowingRestoration of Powerto Rosemount TransmitterTrip UnitsPotential Failure of Motor-Operated Butterfly Valvesto Operate Because ValveSeat Friction was Under-estimatedPersonnel Injuries Resultingfrom Improper Operation ofRadwaste IncineratorsPotential Loss of EffectiveVolume for ContainmentRecirculation Spray atPWR FacilitiesPotential Problems withCrosby Safety Relief ValvesUsed on Diesel GeneratorAir Start Receiver TanksWeight and Center ofGravity Discrepanciesfor Copes-Vulcan Valves4/10/904/4/903/23/903/22/903/22/903/14/903/9/903/8/90All NRC licenseesauthorized to use,transport, or operateradiographic exposuredevices and sourcechangers.All holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors.All NRC licenseeswho process orincinerate radio-active waste.All holders of OLsor CPs for PWRs.All holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors.OL = Operating LicenseCP = Construction Permit
4/11/90*PD23 TReed 4/11/90 4/1 3/90 OFFICIAL RECORD COPY


tNOW,IN 90-25--April 16, 1990 
OFFICIAL RECORD COPY Document Name: VOGTLE OFC O .DOEA p NAME NFlelds DATE yv"1/90 OFC O X -DOEA NAME DFISCHER DATE f /11/90}}
OFFICIAL RECORD COPYDocument Name: VOGTLEOFC O .DOEA pNAME NFleldsDATE yv"1/90OFC O X -DOEANAME DFISCHERDATE f /11/90  
}}


{{Information notice-Nav}}
{{Information notice-Nav}}

Revision as of 13:46, 31 August 2018

Loss of Vital AC Power with Subsequent Reactor Coolant System Heat-Up
ML031130253
Person / Time
Site: Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, 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  Entergy icon.png
Issue date: 04/16/1990
From: Rossi C E
Office of Nuclear Reactor Regulation
To:
References
IN-90-025, NUDOCS 9004120133
Download: ML031130253 (8)
v • d • e


.* -*UNITED STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 April 16, 1990 NRC INFORMATION

NOTICE NO. 90-25: LOSS OF VITAL AC POWER WITH SUBSEQUENT

REACTOR COOLANT SYSTEM HEAT-UP

Addressees

All holders of operating

licenses or construction

permits for nuclear power reactors.

Purpose

This information

notice is being provided to inform addressees

of a significant

operating

event which occurred at the Georgia Power Company's

Vogtle Nuclear Plant on March 20, 1990. The event took place while Unit 1 was in mid-loop in operational

mde 6 and demonstrates

the need for operating

personnel

to be prudent in removing equipment

from service or establishing

atypical equipment alignments

during shutdown.

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 requirements;

therefore, no specific action or written response is required.Description

of Circumstances:

On March 20, 1990, a loss of vital ac power occurred while Vogtle Unit 2 was operating

at 100 percent power and Unit 1 had been in a refueling

outage for about 4 weeks. Unit 1 was in mid-loop in operational

mode 6 with plant equip-ment conditions

as follows: o The Unit 1 B reserve auxiliary

transformer (RAT) was tagged out of service for maintenance

o The Unit 1 B emergency

diesel generator (EDG) was tagged out of service and disassembled

for maintenance

o The Unit 1 A RAT was supplying

offsite power to the crosstied

Unit 1 A and B vital buses o The reactor coolant system (RCS) temperature

was being maintained

at around 90 degrees Fahrenheit (F) via the train A residual heat removal (RHR) pump, the-train

B pump was in standby o The vessel head was in place with the bolts not fully tensioned o The pressurizer

manway cover was removed_ __ A l e ,

IN 90-25 April 16, 1990 o The manways for steam generators

2 and 3 were partially

bolted in place and the manways for steam generators

1 and 4 were in place with bolts fully tensioned o The inboard charging line check valve and an accumulator

isolation valve were open for inspection

o The containment

equipment

hatch and the containment

personnel

hatch were open At about 9:20 a.m., a truck carrying fuel and lubricants

in the plant low voltage switchyard

backed into a support column for the feeder line supplying power to the Unit 1 A RAT and the Unit 2 B RAT. The insulator

for the C phase of the feeder line fractured

and initiated

a phase-to-ground

electrical

fault.The fault resulted in a loss of power to the Unit 1 A RAT and the Unit 2 B RAT.The Unit 2 B EDG started and loaded to the deenergized

Unit 2 B vital bus. How-ever, a Unit 2 turbine trip and reactor trip occurred because of an improperly

connected (wrong tap) differential

current transformer (DCT). The DCT initiated the trip when the current surge associated

with the phase-to-ground

fault was sensed. The Unit 2 trip was uncomplicated.

Because both of the Unit 1 vital buses were crosstied

and being supplied by the Unit 1 A RAT, the loss of the transformer

deenergized

both vital buses.Deenergizing

these buses resulted in the loss of power to the operating

RHR pump. Since the Unit 1 B EDG was tagged out of service and disassembled

for maintenance, the emergency

power supply for the B vital bus was unavailable

and the standby B RHR pump could not be started.The available

Unit 1 A EDG started on bus undervoltage, but for unknown reasons, it shut down automatically

after 1 minute and 20 seconds. At 9:40 a.m., plant operators

declared a site area emergency.

A loss of all onsite and offsite ac power at Vogtle for more than 15 minutes is classified

as a site area emergency.

The licensee made their declaration

because all vital ac power was lost for greater than 15 minutes. Approximately

18 minutes after the first start of the A EDG, the operators

locally reset the load sequencer

which automatically

restarted

the A EDG on undervoltage.

However, after 1 minute and 10 seconds, the diesel again shut down automatically.

At 9:56 a.m., plant operators

per-formed an "emergency" manual start of the diesel, which bypassed most of the diesel's protective

trips. The diesel started and loaded to the bus, the A RHR pump was restarted, and core cooling was reestablished

to Unit 1. With the start of the diesel, the site area emergency

was downgraded

to an "alert" at 10:15 a.m. Containment

integrity

was established

at 11:03 a.m.Plant personnel

returned the Unit 1 B RAT to service after completing

formal tagout removal procedures.

However, attempts to energize the transformer

were delayed for several minutes because of a sticking mechanical

interlock

in the control circuitry

for a motor-operated

disconnect

switch on the high side of the B RAT. Power was restored to the B vital bus via the B RAT at 11:40 a.m.At 12:38 a.m., core cooling was shifted to the B RHR train to facilitate

sub-sequent electrical

alignment

changes.

e. v -%IN 90-25 April 16, 1990 According

to control roon indication, RCS temperature

increased

from 90 to 136 degrees F during the 36 minutes required to reenergize

the A bus (1.3 degrees F/min).Throughout

the event, non-vital

power was continuously

provided to Unit 1 from offsite sources, via backfeed through the main generator

transformer.

Also, the Unit 2 electrical

distribution

system remained energized (aside from the momentary

loss of power before the reactor trip). However, the Vogtle electrical

system was not designed to permit easy interconnection

of the Unit 1 vital buses to nonvital power or to the Unit 2 electrical

buses. Therefore, there were no procedures

in place to provide guidance on interconnecting

the Unit 1 vital and nonvital buses or for interconnecting

the Unit 1 electrical

distribution

system with the distribution

system at Unit 2. (There are no regulatory

requirements

that direct the licensee to develop Interconnection

procedures.)

Discussion:

The NRC has previously

identified

concerns with the operability

of necessary equipment

in shutdown modes. In Information

Notice (IN) 80-2O, "Loss of Decay Heat Removal Capability

at Davis-Besse

Unit 1 While in a Refueling

Mode" an extended loss of decay heat removal capability

was attributed

to a number of factors, including

inadequate

procedures, inadequate

administrative

controls, and the conduct of extensive

maintenance

activities.

Information

Notice 84-42, "Equipment

Availability

for Conditions

During Outages Not Covered by Technical

Specifications," describes

an event at the Palisades Nuclear Plant involving

the total loss of all ac power. The Palisades

event was precipitated

by personnel

performing

actions during a refueling

outage without an appreciation

for the effect of those actions on the plant as it was configured.

Many pieces of equipment

were tagged out of service for maintenance.

Personnel

intentionally

interrupted

offsite power. This action caused the loss of the only available

service water pump. As a result, cooling water was interrupted

to the only available (and operating)

diesel generator.

The diesel overheated

and was manually tripped. As a result, all station ac power was interrupted, causing the loss of fuel pool cooling. (The reactor had been defueled, and its fuel was being stored in the spent fuel pool).The recent Vogtle event reemphasizes

the need for careful planning of equipment outages during shutdown.

Licensees, in general, have considerable

latitude in removing equipment

from service and altering normal system lineups while in shutdown modes if only the minimum technical

specification

requirements

are considered.

The desire to return nuclear units to service as quickly as possible can result in maintenance

being conducted

on redundant, safety-related systems, concurrently.

The appropriateness

of conducting

parallel maintenance

activities

should be considered

in light of the availability

of alternate

equipment

and procedures

to mitigate the consequences

of potential operational

problems.

It is important

that plant outage plans assure that an adequate complement

of equipment

capable of responding

to potential

events remains available

throughout

the outage. Particular

care is needed when the reactor pressure boundary is not intact or the reactor coolant system is at mid-loop.

IN 90-25 April 16, 1990 A special investigation

of the Vogtle event is being conducted

by an NRC Incident Investigation

Team (1IT). The information

contained

in this notice is preliminary

and is subject to change, pending the findings made by the IIT.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

NRR project manager.~6hfares Eossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

Contacts:

N. Fields, NRR (301) 492-1173 E. Trager, AEOD (301) 492-4496 Attachment:

List of Recently Issued NRC Information

Notices

, 0 --u Attachment

IN 90-25 April 16, 1990 LIST OF RECENTLY ISSUED NRC INFORMATION

NOTICES Intormation

Date ot Notice No. Subject Issuance Issued to 90-24 90-23 90-22 90-21 90-20 90-19 90-18 90-17 Transportation

of Model Spec 2-T Radiographic

Exposure Device Improper Installation

of Patel Conduit Seals Unanticipated

Equipment Actuations

Following Restoration

of Power to Rosemount

Transmitter

Trip Units Potential

Failure of Motor-Operated Butterfly

Valves to Operate Because Valve Seat Friction was Under-estimated Personnel

Injuries Resulting from Improper Operation

of Radwaste Incinerators

Potential

Loss of Effective Volume for Containment

Recirculation

Spray at PWR Facilities

Potential

Problems with Crosby Safety Relief Valves Used on Diesel Generator Air Start Receiver Tanks Weight and Center of Gravity Discrepancies

for Copes-Vulcan

Valves 4/10/90 4/4/90 3/23/90 3/22/90 3/22/90 3/14/90 3/9/90 3/8/90 All NRC licensees authorized

to use, transport, or operate radiographic

exposure devices and source changers.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All NRC licensees who process or incinerate

radio-active waste.All holders of OLs or CPs for PWRs.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.OL = Operating

License CP = Construction

Permit

tNOW, IN 90-25--April 16, 1990 A special investigation

of the Vogtle event is being conducted

by an NRC Incident Investigation

Team (IIT). The information

contained

in this notice is preliminary

and is subject to change, pending the findings made by the IIT.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

NRR project manager.Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

Contacts: N. Fields, NRR (301) 492-1173 E. Trager, AEOD (301) 492-4496 Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS PAGE FOR CONCURRENCE

OFC NAME DATE OFC NAME DATE*OEAB:DOEA

NFields 4/11/90*OEAB:DOEA

DFISCHER 4/11/90*TECH ED 4/11/90*C:OEAB:DOEA

PSwetland 4/11/90*REGION I (IIT)WLazarus 4/11/90*C:GCB:DOEA

CBERLINGER

4/11/90*PD23 TReed 4/11/90 4/1 3/90 OFFICIAL RECORD COPY

OFFICIAL RECORD COPY Document Name: VOGTLE OFC O .DOEA p NAME NFlelds DATE yv"1/90 OFC O X -DOEA NAME DFISCHER DATE f /11/90


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