Information Notice 1991-29, Deficiencies Identifie During Electrical Distribution System Functional Inspections
4AUNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555April 15, 1991NRC INFORMATION NOTICE NO. 91-29: DEFICIENCIES IDENTIFIED DURING ELECTRICALDISTRIBUTION SYSTEM FUNCTIONAL INSPECTIONS
Addressees
- All holders of operating licenses or construction permits for nuclear powerreactors.
Purpose
- This information notice is intended to alert addressees to deficiencies identi-fied during recently performed electrical distribution system functionalinspections (EDSFIs). It is expected that recipients will review the informa-tion for applicability to their facilities and consider actions, as appropri-ate, to avoid similar problems. However, suggestions contained in thisinformation notice do not constitute NRC requirements; therefore, no specificaction or written response is required.
Description of Circumstances
- During multidisciplinary inspections, the U.S. Nuclear Regulatory Commission(NRC) has identified many deficiencies related to tWeelectrical distributionsystem. To address these deficiencies, the NRC has developed an inspection tospecifically evaluate the electrical distribution system. During the lastyear, the NRC completed eight EDSFIs, performing at least one in each of thefive NRC geographical regions. During these inspections, the staff foundseveral common deficiencies in the licensees' programs and in the electricaldistribution systems as designed and configured at each plant. These deficien-cies included inadequate ac voltages at the 480 Vac and 120 Vac distributionlevels, inadequate procedures to test circuit breakers, and inadequate determi-nations and evaluations of setpoints.Discussion:Inadequate VoltageDuring inspections conducted at the San Onofre Nuclear Generating Station(Inspection Reports 50-361/89-200 and 50-362/89-200), the Susquehanna SteamElectric Station (Inspection Reports 50-387/90-200 and 50-388/90-200), and the9104090124
' JIN 91-29April 15, 1991 Waterford Steam Electric Station (Inspection Report 50-382/90-23), the stafffound that, under certain conditions, the voltage available at the safety buseswould be inadequate to Operate safety-related loads and associated equipment.These conditions could occur when the plan~t's electrical distribution systemswere being supplied from an offsite grid that had become degraded but thatcontinued to supply voltages that remained above the setpoints at which thedegraded grid relays would be activated.At San Onofre, the numerous voltage drops throughout the system could cause thevoltage to 120 Vaciontactors to drop below the-voltage range for which thesecontactors were certified as acceptable by their manufacturers. To resolvethis problem the licensee has performed testing that established a loweracceptable voltage range for this equipment.At Susquehanna, the degraded grid relay setpoint'was'set at 84 percent on the4160 Yac buses. Th'i's setpoint could have allowed inadequate voltage to be-delivered to numerous safety-related loads at both the 480 Vac and 120 Vaclevels. The licensee calculated that setpoints'of at least 93 percent would berequired to ensure adequate voTtage to all safety-related equipment. Toresolve this problem, the lice'isee has raised the setpoints of the degradedgrid relays and has initiated a modification to install 120 Vac regulatingtransformers.At the Waterford nuclear plant, the degraded grid relays were set at87.5 percent'as sensed on the'4160 Vac buses. :Although this setting was foundto be marginally adequate-'for-equipment connected to the 4160 Vac buses, thesetting was too low to ensure that adequate v6ltage would'be maintained at the480 Vac and 120 Vac levels. The licensee is 6e4aluating solutions to thisproblem and has instituted a procedure- to manually'separate from the grid ifthe voltage falls to unacceptable levels but remains above the relay setpoints.The function of the degraded grid relays is to en'sure that adequate voltage isavailable tooperate all Class lE loads at all distribution levels. In orderto ensure-that all required' Class E 'loads will remain operable during degradedvoltage conditions, some licensees are currently'reanalyzing the basis for thedegraded grid relay setpoints. The new analyses consider all required Class 1Eloads and include the assumption that the voltage on the buses being sensed bythese relays can remain at a level just above the relay setpoints.Inadequate Circuit Breaker Testing ProceduresDuring recent EDSFIs ahd previously on other NRC inspections, the staff identi-fied repetitive deficiencies in licensees' programs to test circuit breakers.These deficiencies included inadequate procedures, inadequate test acceptancecriteria, inadequate test equipment, and inadequate control of testing. At theSusquehanna plant (Inspection Reports 50-387/90-200 and 50-388/90-200), thestaff found that the licensee was testing dc molded case circuit breakers witha procedure written for testing ac breakers. The licensee had not establishedspecific acceptance criteria for the dc breakers.
IN 91-29April 15, 1991 At the Shearon Harris Nuclear Power Plant (Inspection Report 50-400/90-200),the staff identified that the licensee was.testing molded case circuit breakersagainst National Electrical Manufacturers Association (NEMA),acceptance crite-ria, which were less stringent than the manufacturer's time-current curves forthese breakers. In addition, the staff identified that the licensee wastesting 480 V air circuit breakers with test equipment that applied a testsignal (secondary injection) to the solid state trip units in the circuitbreakers. Although this method adequately verified that the trip units func-tioned properly, it did not verify that the breaker's current transformerfunctioned properly or that the wiring and connectors were adequate between thecurrent transformer and the solid state trip units. Other licensees haveperformed testing by primary current injection or by individually checking eachcomponent of the circuit breaker, including the wiring and connectors todemonstrate that the circuit breaker functions properly.Inadequate Determinations and Evaluations of SetpointsMany of the findings identified during recent EDSFIs were related to inadequatesetpoint determinations. Useful guidance for determining setpoints is providedby Instrument Society of America Standard 67.04-1982, "Setpoints for NuclearSafety-Related Instrumentation used in Nuclear Power Plants," which the NRCstaff has endorsed by Regulatory Guide 1.105 Revision 2 -1986, "InstrumentSetpoints for Safety-Related Systems." This guidance applies both to processinstrumentation and, in part, to certain relays that perform a safety function.Some licensees have operated equipment outside of acceptable limits becausethey did not determine proper setpoints and did not evaluate and account forinstrument drift. Operating the equipment under these conditions couldcompromise the safety functions of the equipment. The staff has identifiedthese circumstances primarily for those instruments in which the licensee hasdetermined the setpoints as opposed to those instruments for which thesetpoints were determined by the architect/engineer or the nuclear safetysystem supplier. Those setpoints not contained in the plant technical specifi-cations were also more frequently found to be deficient. During recent EDSFIs,the staff identified deficiencies in setpoints for diesel day tank levelindicators, diesel air start compressor controllers and alarms, inverter lowvoltage shutdown circuitry, degraded grid relays, and diesel overcurrentrelays.In addition to identifying deficiencies in the setpoints themselves, the NRChas determined that not all the licensees are typically verifying that themagnitude of instrument drift that was assumed in the original setpoint calcu-lation coincides with the magnitude of drift observed in the plant. Somelicensees have corrected this deficiency by verifying the magnitude of instru-ment drift by trending, (comparing "as found" calibration data to previous "asleft" data). This is particularly important for the degraded grid relaysetpoints, which often require very tight calibration tolerance bands, and forwhich very low drift values are often assumed.
v-IN 91-29April 15, 1991 This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact thetechnical contact listed below or the appropriate NRR project manager.Charles E. Rossi, eirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR(301) 492-0996Attachment: List of Recently Issued NRC Information Noticesi
Attachment 1IN 91-29April 15, 1991 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to91-2891-2789-90,Supp. 191-2691-2591-2491-23Cracking in FeedwaterSystem PipingIncorrect Rotation ofPositive Displacement PumpPressurizer Safety ValveLift Setpoint ShiftPotential NonconservativeErrors in the Working FormatHansen-Roach Cross-SectionSet Provided with The Kenoand Scale CodesCommercial-Grade StructuralFraming Components SuppliedAs Nuclear Safety-RelatedEquipmentRecent Operating ExperienceInvolving Reactor OperationWithout A Licensed ReactorOperator or Senior ReactorOperator Present in theControl RoomAccidental Radiation Over-exposures to Personnel Due toIndustrial Radiography Acces-sory Equipment Malfunctions04/15/91 All holders of OLs orCPs for pressurizedwater reactors (PWRs).04/10/91 All holders of OLs orCPs for nuclear powerreactors.04/10/91 All holders of OLs orCPs for nuclear powerreactors.04/02/91 All fuel cycle licenseesand other licensees, in-cluding all holders ofoperating licenses fornuclear power reactors,who use physics codes tosupport criticalitysafety in the use offissile material.04/01/91 All holders of OLs orCPs for nuclear powerreactors.03/26/91 All holders of OLs orCPs for nuclear power,test, and research re-actors, and all Part 55licensed operators.03/26/91 All Nuclear RegulatoryCommission (NRC) licens-ees authorized to usesealed sources for indus-trial radiography.OL = Operating LicenseCP = Construction Permit
IN 91-29April 15, 1991 This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact thetechnical contact listed below or the appropriate NRR project manager.O6ginal agen& byCharles E. Ross!Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR(301) 492-0996Attachment:List of Recently Issued NRC Information Notices*SEE PREVIOUS04/ fI9OGC :DOEA: RRPCWen04/ /91CONCURRENCES*C/OGCB:DOEA:NRR*RPB:ADM *C/SICB:DST:NRRCHBerlinger TechEd SNewberry04/08/91 03/20/91 03/18/91*RSIB:DRIS:NRR *SC/RSIB:DRIS:NRR*C/RSIB:DRIS:NRRJBJacobson:bt EVImbro WDLanning02/08/91 02/08/91 02/19/91*C/SELB:DST:NRRFRosa03/18/91*D/DRIS:NRRBKGrimes02/27/91
- - I IN 91-XXApril xx, 1991 This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact thetechnical contact listed below or the appropriate NRR project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR(301) 492-0996List of Recently Issued NRC Information NoticesAttachment:*SEE PREVIOUS CONCURRENCES *C/SICB:DST:NRRD/DOEA:NRR C/OGCB:DO T*RPB:Ad SNewBerryCERossi Y- CHBerling rjw TechEd04/ /91 04/8/91 03/20/91 03/18/91,c CB:DOEA:NRR *RSIB:DRIS:NRR *SC/RSIB:DRIS:NRR*C/RSIB:DRISNRR4CvPvWen JBJacobson:bt EVImbro WMLanning04/cl/91 02/08/91 02/08/91 02/19/91*C/SELB:DST:NRRFRosa03/18/91*D/DRIS:NRRBKGrimes02/27/91 IN 91-XXMarch xx, 1991 Inadequate Determinations and Evaluations of SetpointsMany of the findings identified during recent EDSFIs related to inadequatesetpoint determinations. Useful guidance for determining setpoints is providedby Instrument Society of America Standard 67.04-1982, "Setpoints for NuclearSafety-Related Instrumentation used in Nuclear Power Plants," which the NRCstaff has endorsed by Regulatory Guide 1.105 Revision 2 -1986, "InstrumentSetpoints for Safety-Related Systems." This guidance applies both to processinstrumentation and, in part, to certain relays that perform a safety function.Licensees have operated equipment outside of acceptable limits because they didnot determine proper setpoints and did not evaluate and account for instrumentdrifts. Operating the equipment under these conditions could compromise thesafety functions of the equipment. The staff has identified these circum-stances primarily for those instruments in which the licensee has determinedthe setpoints as opposed to those instruments for which the setpoints weredetermined by the architect/engineer or the nuclear safety system supplier.Those setpoints not contained in the plant technical specifications were alsomore frequently found to be deficient. During recent EDSFIs, the staffidentified deficiencies in setpoints for diesel day tank level indicators,diesel air start compressor controllers and alarms, inverter low voltageshutdown circuitry, degraded grid relays, and diesel overcurrent relays.In addition to identifying deficiencies in the setpoints themselves, the NRChas determined that licensees are not typically verifying that the magnitudeof instrument drift that was assumed in the original setpoint calculationcoincides with the magnitude of drift observed in the plant. Licensee canverify the magnitude of instrument drift by trending, (comparing 'as found"calibration data to previous 'as left" data). This is particularly importantfor the degraded grid relay setpoints, which often require very tight calibra-tion tolerance bands, and for which very low drift values are often assumed.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact thetechnical contact listed below or the appropriate NRR project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR(301) 492-0996Attachment:RPB:ADMTechEd* imJa03/20/91 PRSIB:DRISJBdacobson*:t02/08/91List of Recently Issued NRC Information NoticesC:OGCB:UOEA D:DOEA *See previous cCHBerlinger CERossi1 03/l/91 03/ /91oncurrencebtSC:RSIB:DRISEVImbro*02/08/91C:RSIB:DRISWDLanning*02/19/91D:DRISBKGrimes*02/27/91C:SELB:DSTFRosa*03/18/91C:SICB:DSTSNewberry*03/18/91
- -IN 91-XXJanuary xx, 1991 Inadequate Setpoint Determinations and EvaluationsMany of the findings identified during recent EDSFIs were related to inadequatesetpoint determinations. In order to properly determine an appropriateinstrument setpoint, all associated inaccuracies and tolerances must beaccounted for. Useful guidance for determining setpoints is provided by ISA67.04-1982, "Setpoints for Nuclear Safety-Related Instrumentation used inNuclear Power Plants' which has been endorsed by Regulatory Guide 1.105Revision 2 -1986, "Instrument Setpoints for Safety Related Systems". Thisguidance is applicable not Just for instrumentation but is also applicable forcertain relays and other control oriented pieces of equipment.The setpoint problem has been identified primarily with those instruments inwhich the licensee has determined the setpoints as opposed to those setpointsdetermined by the NSSS vendor. Those setpoints not contained in the planttechnical specifications are also likely to be suspect. During recent EDSFIs,deficiencies in setpoints related to diesel day tank level indicators, dieselair start compressor controllers and alarms, invertor low voltage shutdowncircuitry, degraded grid relays, and diesel overcurrent relays have beenidentified.In addition to the deficiencies identified in the setpoints themselves, the NRChas determined that licensees are not typically verifying that the magnitude ofsetpoint drift that was assumed in the original setpoint calculation is indeedcorrect. This verification can be performed by trending, i.e., by comparing"as found" calibration data to previous "as left" data. This is particularlyimportant for the degraded grid setpoints where very tight calibrationtolerance bands are often required and where very low drift values are oftenassumed. Failure to evaluate and account for instrument drifts has led to theoperation of equipment outside of acceptable limits which could compromise thesafety functions of the equipment.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact thetechnical contact listed below or the appropriate NRR project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR(301) 492-0996Attachment: List of Recently Issued NRC Information Notices*See previous concurrenceRPB:ADM C:OGCB:DOEA D:DOEATechEd CHBerlinger CERossi02/ /91 02/ /91 02/ /91 Xrt"RSIB:DRIS SC:RSIB:DRIS C: S C:S C:SIJBJacobson*:bt EVImbro* WD ng mes FRoV-rW SNe rry02/08/91 02/08/91 024 7/91 02/t7/91 "- / 91O/91 IN 91-XXJanuary xx, 1991 Inadequate Setpoint Determinations and EvaluationsMany of the findings identified during recent EDSFIs were related to inadequatesetpoint determinations. In order to properly determine an appropriateinstrument setpoint, all associated inaccuracies and tolerances must beaccounted for. Guidance for setpoint determinations is given in ANSI StandardS67.04-1988, 'Setpoints for Nuclear Safety-Related Instrumentation." Thisguidance is applicable not Just for instrumentation but is also applicable forcertain relays and other control oriented pieces of equipment.The setpoint problem is most prevalent for those instruments in which thelicensee has determined the setpoints as opposed to those setpoints determinedby the NSSS vendor. Those setpoints not contained in the plant technicalspecifications are also likely to be suspect. During recent EDSFIs, defi-ciencies in setpoints related to diesel day tank level indicators, diesel airstart compressor controllers and alarms, invertor low voltage shutdowncircuitry, degraded grid relays, and diesel overcurrent relays have beenidentified.In addition to the deficiencies identified in the setpoints themselves, the NRChas determined that licensees are not typically verifying that the magnitude ofsetpoint drift that was assumed in the original setpoint calculation is indeedcorrect. This verification can be performed by trending, i.e., by comparing"as found" calibration data to previous "as left" data. This is particularlyimportant for the degraded grid rely setpoints where very tight calibrationtolerance bands are often required and where very low drift values are oftenassumed. Failure to evaluate and account for instrument drifts has led to theoperation of equipment outside of acceptable limits which could compromise thesafety functions of the equipment.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact thetechnical contact listed below or the appropriate NRR project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR(301) 492-0996Attachment: List of Recently Issued NRC Information NoticesRPB:ADM C:OGCB:DOEA D:DOEATechEd CHBerlinger CERossi02/ /91 02/ /91 02/ /91RSIB: SC:RX RIS C:RSIB:DRIS D:DRIS C:SELB:DST C:SICB:DSTJBJac 6n:bt EVIm 'J>' WDLanning BKGrimes FRosa SNewberry020 A' 02/djz1 02/ /91 02/ /91 02/ /91 02/ /91