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

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
Issue date:	04/16/1990
From:	Rossi C E Office of Nuclear Reactor Regulation
To:
References
IN-90-025, NUDOCS 9004120133
Download: ML031130253 (8)

.* -*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

Addressees

All holders of operating licenses or construction permits for nuclear powerreactors.

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.

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.

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.

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

, 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

tNOW,IN 90-25--April 16, 1990

OFFICIAL RECORD COPYDocument Name: VOGTLEOFC O .DOEA pNAME NFleldsDATE yv"1/90OFC O X -DOEANAME DFISCHERDATE f /11/90