Information Notice 1990-05, Inter-System Discharge of Reactor Coolant

Inter-System Discharge of Reactor Coolant

ML031130342
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, 05000000, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	01/29/1990
From:	Rossi C E Office of Nuclear Reactor Regulation
To:
References
IN-90-005, NUDOCS 9001230126
Download: ML031130342 (8)

UKUNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555January 29, 1990NRC INFORMATION NOTICE NO. 90-05: INTER-SYSTEM DISCHARGE OF REACTOR COOLANT

Addressees

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

Purpose

This information notice is intended to. alert addressees to a potentiallysignificant problem in identifying and terminating reactor coolant systemleakage in operating modes 4 and 5. It is expected that licensees willreview the information for applicability to their facilities and consideractions, as appropriate, to avoid similar problems. However, suggestionscontained in this information notice do not constitute NRC requirements;therefore, no specific action or written response is required.

Description of Circumstances

On December 1, 1989, Braidwood Unit 1 experienced the unplanned inter-systemdischarge of approximately 68,000 gallons of water. The discharge was causedby the inadvertent opening of a residual heat removal (RHR) system suctionrelief valve. The valve failed to reclose, allowing an open flow path fromthe reactor vessel, through the RHR system, into the unit's two recycle hold-uptanks (HUTs).The unit, which had been in a refueling outage since September 2, 1989, washeating up in operational mode 5, preparing to enter operational mode 4. Theplant was solid and in the process of drawing a bubble in the pressurizer. TheRHR train "A" pump was in operation and, although the "BO pump was not running,the "B" train was unisolated and available. The reactor coolant system (RCS)was at a pressure of 350 psig .and a temperature of 1750F. Charging flow to thevessel was being provided by the "A" charging pump. Pressurizer heaters wereon. The "B" charging pump was Isolated and tagged out of service. (TechnicalSpecifications governing cold overpressure protection require that only onecharging pump be available. The other charging pump and the safety injectionpumps are required to be tagged out of service, with power supplies removed).To protect against a pressure switch failure and the subsequent automaticisolation of the RHR system, the train "A" RHR suction isolation valve wasopen and tagged out of service.90130126 Z #

IN 90-05January 29, 1990 At 1:42 a.m., operators throttled the charging flow and maximized the letdownflow in preparation for drawing a bubble in the pressurizer. The RCS pressurewas 404 psig and the pressurizer level was off scale, high. At 1:44 a.m., arapid reduction in the pressurizer level occurred, with the pressurizer leveloff scale, low, at 1:52 a.m. Approximately 14,000 gallons of water drainedfrom the pressurizer and the pressurizer surge line; however, the reactor vessellevel instrumentation system indicated that the vessel level remained at 100percent. At 1:49 a.m., the charging flow was increased and the charging pumpsuction was switched from the volume control tank to the refueling water storagetank (RWST).About 30 to 50 gallons of water were observed on the floor of the auxiliarybuilding in proximity to the RHR train "AN suction relief valve, leading plantpersonnel to believe that this valve had lifted. At 1:53 a.m., the letdownflow was reduced to minimum and charging was maximized. The RHR trains wereswitched from "A" to EB", the "A" pump was stopped, and the isolation of the"A" train was initiated. At 1:59 a.m., one of the two running reactor coolantpumps (RCPs) was stopped because of low RCS pressure.A second charging pump, NBN, was started following completion of the formal pro-cedure for tagout removal. At 2:35 a.m., the "A RHR suction isolation valvewas returned to service and closed, completing the isolation of the "A" trainof the RHR system. The pressurizer level began to recover and the RCS pressureincreased slightly, giving operators the impression that the discharge had beenisolated. The *B" charging pump was therefore secured at 2:45 a.m. The pres-surizer level, however, did not recover. At 2:54 a.m., the ABN charging pumpwas restarted. At 3:49 a.m., the inter-system discharge was terminated whenthe RHR train WA" pump was started, the "B pump shut down, and the "8' trainwas isolated. The level indication for the HUTs stabilized and the pressurizerlevel began to recover at 3:52 a.m.By 5:06 a.m., the pressurizer level had fully recovered and the unit was sta-bilized at 360 psi and 1750F. Approximately 68,000 gallons of water had beendischarged from the reactor vessel to the HUTs. (The total amount of waterwas composed of 14,000 gallons of initial pressurizer inventory and 54,000gallons of makeup water).Following the event, it was determined that the RHR MB" train suction reliefvalve had lifted at 411 psi. The lift setpoint for the valve should have been450 psi. The valve should have reclosed on reducing pressure but failed to doso. The premature opening of the valve was attributed to the presence of foreignmaterial lodged between the valve spindle and the spindle guide. This foreignmaterial either prohibited the correct adjustment of the valve or affected thevalve's lift setpoint. The valve's failure to reclose was attributed to im-proper nozzle ring adjustment. The reset pressure is strongly influenced bythe dynamic forces created by the nozzle ring. If the ring is located too highon the nozzle, it may result in an inadequate ventilation area just above thenozzle. Undesirable forces will develop which may cause a much lower reseatpressure.The water found near the RHR train "A" suction relief valve had leaked froma weep hole on a relief valve in a radwaste evaporator line connected to the

IN 90-05January 29, 1990 common discharge header of the train "A" and "B" suction relief valves. Con-trary to original assumptions, there was no evidence that the OA" train suctionrelief valve had lifted. The root cause of the problem with the relief valveon the evaporation line is under investigation but is thought to be unrelatedto the failure of the 'BM suction relief valve.Hampering operators' efforts throughout this event was the lack of an appro-priate emergency operating procedure (EOP) to detect coolant leaks while inoperating modes 4 and 5. However, the operators were able to combine tworelated abnormal operating procedures for guidance during this event. Oneof the procedures is designed to locate system leaks while in modes 3 and 4.The other provides guidance for the restoration of the RHR system followingits loss during conditions in which the reactor vessel inventory is at areduced level.Discussion:The event at Braidwood 1 is significant because it underscores the need tohave EOPs available for use in other than 'at power" operating modes. Thefact that over 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> were required to locate the stuck-open valve, toterminate the discharge, and to begin refilling the pressurizer highlightsthe need to provide personnel with adequate tools to perform their tasks.Relying on ad hoc procedures during significant events places an unnecessaryburden on operating personnel. The lack of adequate EOPs could handicap themost competent operators in their efforts to address significant operationalproblems.Also illustrated by this event Is the need for procedures to assure thatadequate RCS makeup capability and cooling options are available in a timelyfashion during shutdown. The discharge through the stuck-open relief valveexceeded the capability of a single charging pump. Starting a second chargingpump required that formal procedures for tag removal be conducted. This effortnecessitated a considerable amount of time, which may not be available should asimilar event occur while the RCS is at a higher temperature.The severity of this event could have been increased if greater decay heat werepresent in the reactor vessel or if a gross failure of the relief valve dischargeheader had occurred. Greater decay heat would have increased the potential forvoiding in the core. Also, because the header discharges to the HUTs which arelocated outside containment, a piping failure could have resulted in all or aportion of the RCS water being discharged to the building floor. This eventwould have necessitated a major cleanup effort and increased the potential forpersonnel contamination.If this event had occurred at one of the nuclear plants that has a singlesuction line from the RCS to the RHR system, all shutdown cooling wouldhave been lost as a result of isolating the failed suction relief valve.An alternate heat sink would likely have been required; however, in mode 5,an alternate heat sink may not be readily available.

IN 90-05January 29, 1990 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 project manager.arl E. ss, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: Nick Fields, NRR(301) 492-1173Julian Hinds, RIII(315) 388-5575Attachment: List of Recently Issued NRC Information Notices

AttachmentIN 90-05January 29, 1990 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice-No.. Subject -Issuance Issued to-el 90-04Cracking of the Upper Shell-to-Transition Cone GirthWelds in Steam Generators1/26/90All holders of OLsor CPs for Westinghouse-designed and CombustionEngineering-designednuclear power reactors.90-0390-0290-0189-9089-8989-8889-8789-45,Supp. 289-86Malfunction of Borg-WarnerBolted Bonnet Check ValvesCaused by Failure of theSwing ArmPotential Degradation ofSecondary ContainmentImportance of ProperResponse to Self-IdentifiedViolations by LicenseesPressurizer Safety ValveLift Setpoint ShiftEvent NotificationWorksheetsRecent NRC-SponsoredTesting of Motor-OperatedValvesDisabling of EmergencyDiesel Generators. byTheir Neutral Ground-FaultProtection CircuitryMetalclad, Low-VoltagePower Circuit BreakersRefurbished withSubstandard PartsType HK Circuit BreakersMissing Close Latch Anti-Shock Springs.1/23/901/22/901/12/9012/28/8912/26/8912/26/8912/19/8912/15/8912/15/89All holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for BWRs.All holders of NRCmaterials licenses.All holders of OLsor CPs for PWRs.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 holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors.OL = Operating LicenseCP = Construction Permit

IN 90-05January 29, 1990 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 project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:Nick Fields, NRR(301) 492-1173Julian Hinds, RIII(315) 388-5575Attachment:List of Recently Issued NRC Information Notices*SEE PREVIOUS PAGE FOR CONCURRENCE*EAB:NRRNFields:db1/12/90*TECH:EDITOR *EAB:NRRDCFischer1/14/90 1/16/90*C:EAB:NRRCJHaughney1/18/90*C:OGCB:NRRCHBerlinger1/22 /90Ross11/.AY9O

.-;IN 90-January , 1990 No specific action or written response is required by this informationnotice. If you have any questions about this matter, please contact one ofthe technical contacts listed below or the Regional Administrator of theappropriate regional office.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:Nick Fields, NRR(301) 492-1173Julian Hinds,RIII(315) 388-5575Attachment:List of Recently Issued Information NoticesJJV I'Insmofi wEAB:NRR TECH:EDITOR EAB:NRRNFields:db DCFischer/ /,1-90 1 /*t/90 1/ i190C: EB:NRRCJHaughneyI As/90coYC:OGCB:NRRCHBerlingerI/.090D:DOEA:NRRCERossi/ /90