Information Notice 1990-25, Loss of Vital AC Power with Subsequent Reactor Coolant System Heat-Up: Difference between revisions

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| issue date = 04/16/1990
| issue date = 04/16/1990
| title = Loss of Vital AC Power with Subsequent Reactor Coolant System Heat-Up
| title = Loss of Vital AC Power with Subsequent Reactor Coolant System Heat-Up
| author name = Rossi C E
| author name = Rossi C
| author affiliation = NRC/NRR
| author affiliation = NRC/NRR
| addressee name =  
| addressee name =  
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| page count = 8
| page count = 8
}}
}}
{{#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==
==Description of Circumstances==
: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.
        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
 
_  __                                                                       Al 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


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.
Nuclear Plant involving the total loss of all ac power. The Palisades event


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
was precipitated by personnel performing actions during a refueling outage


, 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
without an appreciation for the effect of those actions on the plant as it


tNOW,IN 90-25--April 16, 1990
was configured. Many pieces of equipment were tagged out of service for
OFFICIAL RECORD COPYDocument Name: VOGTLEOFC O .DOEA pNAME NFleldsDATE yv"1/90OFC O X -DOEANAME DFISCHERDATE f /11/90  
 
}}
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          Transportation of Model        4/10/90  All NRC licensees
 
Spec 2-T Radiographic                  authorized to use, Exposure Device                        transport, or operate
 
radiographic exposure
 
devices and source
 
changers.
 
90-23          Improper Installation of      4/4/90  All holders of OLs
 
Patel Conduit Seals                    or CPs for nuclear
 
power reactors.
 
90-22          Unanticipated Equipment        3/23/90  All holders of OLs
 
Actuations Following                    or CPs for nuclear
 
Restoration of Power                    power reactors.
 
to Rosemount Transmitter
 
Trip Units
 
90-21          Potential Failure of Motor-    3/22/90  All holders of OLs
 
Operated Butterfly Valves              or CPs for nuclear
 
to Operate Because Valve                power reactors.
 
Seat Friction was Under- estimated
 
90-20          Personnel Injuries Resulting  3/22/90  All NRC licensees
 
from Improper Operation of              who process or
 
Radwaste Incinerators                  incinerate radio- active waste.
 
90-19          Potential Loss of Effective    3/14/90  All holders of OLs
 
Volume for Containment                  or CPs for PWRs.
 
Recirculation Spray at
 
PWR Facilities
 
90-18          Potential Problems with        3/9/90  All holders of OLs
 
Crosby Safety Relief Valves            or CPs for nuclear
 
Used on Diesel Generator                power reactors.
 
Air Start Receiver Tanks
 
90-17          Weight and Center of          3/8/90  All holders of OLs
 
Gravity Discrepancies                  or CPs for nuclear
 
for Copes-Vulcan Valves                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      *OEAB:DOEA          *TECH ED        *REGION I (IIT)    *PD23 NAME      NFields                              WLazarus          TReed
 
DATE      4/11/90              4/11/90          4/11/90            4/11/90
  OFC      *OEAB:DOEA          *C:OEAB:DOEA    *C:GCB:DOEA
 
NAME      DFISCHER            PSwetland        CBERLINGER
 
DATE      4/11/90              4/11/90          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}}


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

Latest revision as of 04:03, 24 November 2019

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
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

_ __ Al 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 Transportation of Model 4/10/90 All NRC licensees

Spec 2-T Radiographic authorized to use, Exposure Device transport, or operate

radiographic exposure

devices and source

changers.

90-23 Improper Installation of 4/4/90 All holders of OLs

Patel Conduit Seals or CPs for nuclear

power reactors.

90-22 Unanticipated Equipment 3/23/90 All holders of OLs

Actuations Following or CPs for nuclear

Restoration of Power power reactors.

to Rosemount Transmitter

Trip Units

90-21 Potential Failure of Motor- 3/22/90 All holders of OLs

Operated Butterfly Valves or CPs for nuclear

to Operate Because Valve power reactors.

Seat Friction was Under- estimated

90-20 Personnel Injuries Resulting 3/22/90 All NRC licensees

from Improper Operation of who process or

Radwaste Incinerators incinerate radio- active waste.

90-19 Potential Loss of Effective 3/14/90 All holders of OLs

Volume for Containment or CPs for PWRs.

Recirculation Spray at

PWR Facilities

90-18 Potential Problems with 3/9/90 All holders of OLs

Crosby Safety Relief Valves or CPs for nuclear

Used on Diesel Generator power reactors.

Air Start Receiver Tanks

90-17 Weight and Center of 3/8/90 All holders of OLs

Gravity Discrepancies or CPs for nuclear

for Copes-Vulcan Valves 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 *OEAB:DOEA *TECH ED *REGION I (IIT) *PD23 NAME NFields WLazarus TReed

DATE 4/11/90 4/11/90 4/11/90 4/11/90

OFC *OEAB:DOEA *C:OEAB:DOEA *C:GCB:DOEA

NAME DFISCHER PSwetland CBERLINGER

DATE 4/11/90 4/11/90 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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