Information Notice 1992-36, Intersystem LOCA Outside Containment

Intersystem LOCA Outside Containment

ML031200356
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	05/07/1992
From:	Rossi C E Office of Nuclear Reactor Regulation
To:
References
IN-92-036, NUDOCS 9205010045
Download: ML031200356 (10)

UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555May 7, 1992NRC INFORMATION NOTICE 92-36: INTERSYSTEM LOCA OUTSIDE CONTAINMENT

Addressees

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

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information noticeto alert addressees of potential plant vulnerabilities to intersystem loss-of-coolant accidents (ISLOCAs). It is expected that recipients will reviewthe information for applicability to their facilities and consider actions, asappropriate. However, suggestions contained in this information notice are notNRC requirements; therefore, no specific action or written response is required.This information notice provides information gathered during a concerted NRCstaff effort to study plant vulnerabilities to ISLOCAs. The staff gatheredthis information by performing (a) detailed evaluations of operating events,(b) inspections of a limited sample of pressurized water reactors (PWRs), and(c) extensive analyses of the sample PWRs. The information may be of use inrecipients' individual plant examination (IPE) programs.BackgroundThe ISLOCA is a class of accidents in which a break occurs in a system con-nected to the reactor coolant system (RCS), causing a loss of the primarysystem inventory. This type of accident can occur when a low pressure system,such as the residual heat removal (RHR) system, is inadvertently exposed tohigh RCS pressures beyond its capacity. ISLOCAs of most concern are thosethat can discharge the break flow outside the reactor containment building,primarily because they can result in high offsite radiological consequences butalso because the RCS inventory lost cannot be retrieved for long-term corecooling during the recirculation phase.In the "Reactor Safety Study," (WASH-1400), published in 1975, and inNUREG-1150, "Severe Accident Risks: An Assessment for Five U.S. Nuclear PowerPlants," the NRC described the ISLOCA outside containment as an event of lowcore damage frequency, but as one of the main contributors to plant risk. Inthose studies the NRC referred to the ISLOCA as "Event-V." Most probabilisticrisk assessments (PRAs) have also shown that the ISLOCA is very unlikely.However, these PRAs typically have modelled only those Event-V sequences thatinclude only the catastrophic failure of check valves that isolate the RCS from92050_ 45AMA IN 92-36May 7, 1992 low pressure systems. These PRAs included little consideration of human errorsleading to an ISLOCA. Also, most existing PRAs have given little or no creditfor operator actions to terminate an ISLOCA or to mitigate its radiologicalconsequences if core melt were to occur.On January 22, 1992, the Virginia Electric Power Company, licensee for theNorth Anna Power Station, reported that the RHR relief valves would not passthe design-basis flow to relieve an overpressurization of the RHR system whenthe latter is aligned to the RCS. The function of these relief valves isimportant when the RCS is water solid and therefore susceptible to overpressur-ization events, such as from a charging-letdown flow mismatch or a temperaturechange.The licensee made this report after conducting an engineering evaluation torespond to a notification by the nuclear steam supply vendor, the WestinghouseElectric Corporation. In February 1990, Westinghouse reviewed the RHR reliefvalve design basis for the Westinghouse Owners Group and recommended that itscustomers review the following three items:The adequacy of the RHR relief valves for protecting against coldoverpressure eventsDischarge capability of relief valves for probable back pressuresDesign basis commitments for valve specifications, commitments in thefinal safety analysis report, and technical specificationsThe NRC has issued several information notices to discuss certain operationalevents regarding ISLOCAs. In IN 90-05, "Inter-system Discharge of ReactorCoolant," the staff. discussed an event during which about 68,000 gallons ofreactor water was discharged outside the containment. The staff has alsoanalyzed operational experience and documented its findings in augmentedinspection team (AIT) reports. On October 23, 1990, the staff issued AITReport 50-456/90-020 on an event at Braidwood that resulted in primary waterleakage outside the containment and in the contamination of three personnel,one of whom received a second degree burn. Table 3 is a selected list ofinformation notices and AIT reports that the staff has issued on ISLOCAs andrelated events.DiscussionAlthough no ISLOCA has caused core damage, accumulated operational experience,both in the United States and abroad, indicates that ISLOCA-like events haveoccurred at a rate higher than expected. In conducting this study, the staffdefined an ISLOCA-like event, or an ISLOCA precursor, as an event that resultsfrom the failure, degradation, or inadvertent opening of the pressure isolationvalves (PIYs) between the RCS and lower pressure systems. An ISLOCA precursormay become an ISLOCA if it occurs during different plant conditions, or if someof the failures occur together.The NRC staff conducted root cause analyses of ISLOCA precursors, extensiveplant inspections, and detailed analyses of a sample of PWRs. These analyses IN 92-36May 7, 1992 included thermal-hydraulic analyses, fragility analyses to determine the likelysizes and locations of a break, and human reliability analyses. The staff usedthe results of these analyses in PRAs to gain insights about the significantcontributors to ISLOCA risk.The staff directed the studies described in this information notice towardsfinding vulnerabilities of PWR plants to ISLOCAs, since the primary pressurespresent in PWRs are greater than those found in boiling water reactors (BWRs),while the design pressures of low pressure systems are about the same in bothPWRs and BWRs. However, BWR licensees also may find this information to berelevant to their plants.Upon conducting these studies, the staff made the following observations on theISLOCA risk at nuclear power plants:1. The estimated core damage frequency caused by ISLOCAs could be greaterthan was estimated in PRAs for some plants.The ISLOCA risk depends on both the accident initiators and the capabili-ties for recovery. These factors vary from plant to plant. The maincontributors to ISLOCA initiation and/or recovery include (a) human errorsand (b) the effects of the accident-caused harsh environment on plantequipment and recovery activities. Both factors have significant uncer-tainties. Existing PRAs have provided little or no treatment of thesefactors. Plants that are particularly vulnerable to either of these twofactors could have a higher ISLOCA risk than indicated by existing PRAs.2. Most plants lack contingency plans to provide backup water supplies thatcan be transferred readily to provide long-term core cooling after anISLOCA.By examining a plant's emergency procedures, a licensee can findinsights for improving the plant's features to address the concerns forboth ISLOCAs and other accidents.3. The root cause analyses of operational events indicate that ISLOCA precur-sors most likely would be initiated by human errors, notably duringtesting and maintenance or because of procedural deficiencies. This maybe attributed to the general lack of awareness of the possibility orconsequences of an ISLOCA.Licensees may significantly reduce the probability of ISLOCA precursorsby improving the ability of operators and maintenance personnel to recog-nize ISLOCAs, mechanisms that can cause them, actions to prevent them, andmethods to manage them if they occur.4. Most observed ISLOCA precursors have low public risk consequences. However,an ISLOCA precursor can require a shutdown or extension of a shutdown,require radioactivity cleanup operations, and cause personnel injur IN 92-36May 7, 1992 Table 1 presents the staff's observations from root cause analyses and plantinspections. Table 2 presents insights gained from the ISLOCA PRAs.The staff is completing its ISLOCA research program under Generic Issue 105,"Intersystem Loss of Coolant Accidents in Light Water Reactors." Upon complet-ing this research, the staff may issue further generic correspondence tolicensees.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact oneof the technical contacts listed below or the appropriate Office of NuclearReactor Regulation (NRR) project manager.es ERossi, DrectrDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Kazimieras Campe, NRR(301) 504-1092Sammy Diab, RES(301) 492-3914Gary Burdick, RES(301) 492-3812

Attachments:

1. Table 1. "Observed Plant Vulnerabilities to ISLOCA Precursors"2. Table 2. "ISLOCA Risk Insights"3. Table 3. "A Selected List of ISLOCA Reports and References"4. List of Recently Issued NRC Information Notices Attachment 1IN 92-36May 7, 1992 Table 1. Observed Plant Vulnerabilities to ISLOCA Precursors(Obtained from root cause analyses of ISLOCA precursors and plant inspections)1. Lack of awareness of the nature or consequences of ISLOCAs2. Inadequate emergency procedures for ISLOCA outside containment, especiallyfor non-power operational modes3. Poor or incorrect valve labels4. Different nomenclature used for the same equipment in the same plant5. Poor coordination between concurrently run tests6. Miscommunications between the control room operators and auxiliary opera-tors ("get the valve" is meant as "crack open then close," but understoodto mean "open")7. Poor shift turn-over communications8. Poor post-maintenance testing or operability checks9. Inadequate application of independent verification10. Tendency not to check diverse instrument indications11. Tendency to commit personnel to extensive overtime work, especially duringshutdown and startup operations, thus increasing the fatigue level and thelikelihood of errors Attachment 2IN 92-36May 7, 1992 Table 2. ISLOCA Risk Insights(Obtained from ISLOCA PRAs)1. The staff's studies suggest that the core damage frequency caused by anISLOCA could be substantially greater than previous PRA estimates for someplants. This is primarily caused by the effects of operator errors andharsh environments caused by the accident. Valve alignment errors duringtransition between operating modes can be particularly important.2. Equipment qualified for a harsh environment is likely to survive theadverse ISLOCA temperature and humidity, but not the possible submersioncaused by flooding.3. Multiple system failures may result from the ISLOCA harsh environment orflooding, depending on the size and location of the break in relation toaffected equipment, the separation of redundant trains, and the effect offire sprays on flooding.4. ISLOCA recovery is limited by harsh environments, which may damage essen-tial equipment thus complicating long-term cooling, and the rate of lossof reactor water outside the containment. If the water is not quicklyreplenished, an ISLOCA may lead to core damage, even after the leak hasbeen isolated.5. Symptom-based procedures may lead the operator to realize that an ISLOCAhas occurred. However, unless the emergency procedures refer to plantprovisions for conserving and replenishing water, the operator may havedifficulty managing the accident.6. Most observed ISLOCA precursors have low risk consequences, primarilybecause of the presence of one or more of the following conditions: smallleak size, redundant means of detecting and isolating a leak, and lowpower or shutdown condition Attachment 3IN 92-36May 7, 1992 Table 3. A Selected List of ISLOCA Reports and ReferencesIdentificationIN 90-64IN 90-05IN 89-73Title or SubjectPotential for Common-Mode Failure ofHPSI Pumps or Release of Reactor CoolantOutside Containment During a LOCAInter-system Discharge of Reactor CoolantPotential Overpressurization of LowPressure SystemsDate10/04/9001/29/9011/01/8910/23/9005/08/89AIT Report50-456/90-20AIT Report50-293/89-80An assessment of the 10/4/90 Braidwoodloss of reactor coolant inventory andpersonnel contamination and injuryAn assessment of the 4/12/89 Pilgrimoverpressurization event, which occurredduring the conduct of the RCIC logic testInspectionReport50-382/90-200InspectionReport50-413,414/90-200InspectionReport50-346/89-201ISLOCA Program InspectionplantISLOCA Program InspectionplantsISLOCA Program InspectionBesse plantof the Waterfordof the Catawbaof the Davis09/14/9006/11/9012/21/89AuditReportDocket No. 50-213NUREG/CR-5745NUREG/CR-5744NUREG/CR-5604NUREG/CR-5124NUREG/CR-5102Haddam Neck ISLOCA Audit Report: July 24 -August 4, 1989, Enclosure to Memorandumfrom Frank J. Congel, NRC, toSteven A. Varga, NRC*Assessment for ISLOCA Risks -Draft Methodology and Application:Combustion Engineering PlantAssessment for ISLOCA Risks -Draft Methodology and Application:Westinghouse Four-Loop Ice Condenser PlantAssessment for ISLOCA Risks -Draft Methodology and Application: Babcockand Wilcox Nuclear Power StationInterfacing Systems LOCA, BoilingWater ReactorsInterfacing Systems LOCA, PressurizedWater Reactors09/20/89June 91Feb 91Feb 91Feb 89Feb 89-A COpy OT this report is available in the NRC Public Document Room,2120 L Street, N.W., Washington, D Attachment 4IN 92-36May 7, 1992 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to92-3592-3492-3392-3292-3192-30Higher Than Predicted Ero-sion/Corrosion in Unisol-able Reactor Coolant Pres-sure Boundary Piping InsideContainment at A BoilingWater ReactorNew Exposure Limits forAirborne Uranium andThoriumIncreased InstrumentResponse Time WhenPressure DampeningDevices are InstalledProblems Identified withEmergency VentilationSystems for Near-Site(Within 10 Miles) Emer-gency Operations Facili-ties and Technical SupportCentersElectrical ConnectionProblem in JohnsonYokogawa CorporationYS-80 Programmable Indi-cating ControllersFalsification of PlantRecordsSpent Fuel Pool Re-activity Calculations05/06/9205/06/9204/30/9204/29/9204/27/9204/23/9204/22/92All holders of OLs or CPsfor nuclear power reactors.All licensees whose opera-tions can cause airborneconcentrations of uraniumand thorium.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactorsand all licensed operatorsand senior operators.All holders of OLs or CPsfor nuclear power reactors.92-21,Supp. 1OL = Operating LicenseCP = Construction Permit IN 92-36May 7, 1992 Table 1 presents the staff's observations from root cause analyses and plantinspections. Table 2 presents insights gained from the ISLOCA PRAs.The staff is completing its ISLOCA research program under Generic Issue 105,"Intersystem Loss of Coolant Accidents in Light Water Reactors." Upon complet-ing this research, the staff may issue further generic correspondence tolicensees.This information notice requiresyou have any questions about theof the technical contacts listedReactor Regulation (NRR) projectno specific action or written response. Ifinformation in this notice, please contact onebelow or the appropriate Office of Nuclearmanager.Original Signed byCharles E ReiCharles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts:Kazimieras Campe, NRR(301) 504-1092Sammy Diab, RES(301) 492-3914Gary Burdick, RES(301) 492-3812

Attachments:

1. Table 1. "Observed Plant Vulnerabilities to ISLOCA Precursors'2. Table 2. "ISLOCA Risk Insights"3. Table 3. "A Selected List of ISLOCA Reports and References"4. List of Recently Issued NRC Information NoticesDocument Name: IN 92-36*See previous concurrence.C/OGCB:DOEA:NRR D/DOEA:NRR*CHBerlinger04/24/92RPB:ADM*TechEd04/09/92D/DSIR:RES*WMinners04/15/92C/RPSIB:DSIR:RES*KKniel04/14/92RPSIB:DSIR:RES*GBurdick04/13/92C/EIB:DSIR:RES*RLBaer04/13/92OGCB:DOEA:NRR*CVHodge04/08/92SC/RAB:DREP:NRR*KCampe04/09/92C/RAB:DREP:NRR*WBeckner04/09/92D/DREP:NRR*FCongel04/09/92EIB:DSIR:RES*SDiab04/13/92 IN 92-XXApril xx, 1992 Table 1 presents the staff's observations from root cause analyses and plantinspections. Table 2 presents insights gained from the ISLOCA PRAs.The staff is completing its ISLOCA research program under Generic Issue 105,"Intersystem Loss of Coolant Accidents in Light Water Reactors." Upon complet-ing this research, the staff may issue further generic correspondence tolicensees.This information notice requires no speciyou have any questions about the informatof the technical contacts listed below orReactor Regulation (NRR) project manager.fic action or written response. Ifion in this notice, please contact onethe appropriate Office of NuclearCharles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts:Kazimieras Campe, NRR(301) 504-1092Sammy Diab, RES(301) 492-3914Gary Burdick, RES(301) 492-3812

Attachments:

1. Table 1. "Observed Plant Vulnerabilities to ISLOCA Precursors"2. Table 2. "ISLOCA Risk Insights"3. Table 3. "A Partial List of ISLOCA Reports and References"4. List of Recently Issued NRC Information NoticesDocument Name:C/OGCB:DOEA:NRR D/D1CHBerling~* fj, CER04/21/92gq"' 04/RPB:ADM D/DTechEd J7Hh9q W"04/ q/92 04/OGCB:DOEA: RR SC/ICVHodge US9 KCai04/od/92 04/ISLOCA REV 2DOEA: NRRtossi lg kS15~/ 92RAB: REP:NRRimpI9/9C L SI R:RES04/A//92C/RAB:DREP:IERWBeckner Xyt04/A /92R Q DSIR:RESGB k04//3/92D/DREP:NFCongel04/9 /92C/EIB:D IRRESRLBaerXiF'04//3/92EIB:DSIR L>SDiab04/,3/92/