RIS 2011-12, Rev. 1 - Adequacy of Station Electric Distribution System Voltages (Track Changes)

Rev. 1 - Adequacy of Station Electric Distribution System Voltages (Track Changes)

ML11357A142
Person / Time
Issue date:	12/29/2011
Revision:	1
From:	Office of New Reactors, Office of Nuclear Reactor Regulation
To:
Mensah, T M, NRR/DPR, 415-3610
Shared Package
ML113050591	List: ML113050583 ML113050588 RIS 2011-12, Response to Public Comments on Docket Id NRC-2011-0013-NRC Regulatory Issue Summary 2011-12, Revision 1, Adequacy of Station Electric Distribution System Voltages RIS 2011-12, Rev. 1 - Adequacy of Station Electric Distribution System Voltages (Track Changes)
References
RIS-11-012, Rev 1
Preceding documents:	ML113050583 (29 December 2011) ML113050588 (29 December 2011) ML11222A135 (6 October 2011)
Download: ML11357A142 (69)

NRC Concerns Associated with NRC Release of RIS 2011-12, Revision 1, Attachment

ML12059A462
Person / Time
Site:
Issue date:	02/28/2012
Revision:	1
From:	Nuclear Energy Institute
To:	Office of Nuclear Reactor Regulation
Shared Package
ML120590853	List: ML12059A461 ML12059A462 RIS 2011-12, Response to Public Comments on Docket Id NRC-2011-0013-NRC Regulatory Issue Summary 2011-12, Revision 1, Adequacy of Station Electric Distribution System Voltages
References
RIS 2011-12, Rev 1
Preceding documents:	ML113050583 (29 December 2011) ML113050588 (29 December 2011) ML11222A135 (6 October 2011)
Download: ML12059A462 (4)

ctober 65, 2414

L2ýTE]NRC REGULATORY ISSUE SUMMARY 2011-12, REVISION 1ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEMVOLTAGES

ADDRESSEES

All holders of, or applicants for, a power reactor operating license or construction permit underTitle 10 of the Code of Federal Regulations (10 CFR) Part 50, "Domestic Licensing ofProduction and Utilization Facilities," except those who have permanently ceased operationsand have certified that fuel has been permanently removed from the reactor vessel.All holders of, and applicants for design Geeter-s certifications and combined epeFating licensesunder 10 CFR Part 52, "Licenses, Certificateions and Approvals for Nuclear Power Plants."

INTENT

The U.S. Nuclear Regulatory Commission (NRC) is issuing this Regulatory Issue Summary(RIS) to clarify the NRC staff's technical position on existing regulatory requirements.Specifically, this RIS clarifies voltage studies necessary for Degraded Voltage Relay (secondlevel undervoltage protection) setting bases and Transmission Network/Offsite/Station electricpower system design bases for meeting the regulatory requirements specified in GeneralDesign Criteria (GDC) 17 to 10 CFR Part 50, Appendix A. For nuclear power plants that werelicensed before GDC 17 applied, the updated final safety analysis report provides the applicabledesign criteria. This RIS does not transmit any new requirements or staff positions. No specificaction or written response is required.

BACKGROUND

The events at Millstone and Arkansas Nuclear One (ANO) that led to the NRC staff's positionregarding degraded voltage protection for nuclear power plant Class 1 E electrical safety busesfor sustained degraded transmission network (grid) voltage conditions, and expectations forvoltage calculations for the plant offsite/station electric power system design respectively, arediscussed below as a reminder of past operating experience.Millstone Unit 2Electrical grid events at the Millstone Station, in July of 1976 demonstrated that when the Class1 E buses are supplied by the offsite power system, sustained degraded voltage conditions onML-I 2222A.1 36ML1 13050583 RIS 2011-12,_Rev. 1 the grid can cause adverse effects on the operation of Class 1 E loads. These degraded voltageconditions will not be detected by the Loss-of-Voltage Relays (LVRs) which are designed todetect loss of power to the bus from the offsite circuit(s). The LVR's low voltage dropout settingis generally in the range of 0.7 per unit voltage or less, with a time delay of less than 2 seconds.As a result of further evaluation of the Millstone events, it was determined that improper voltageprotection logic can also cause adverse effects on the Class 1 E systems and equipment, suchas spurious load shedding of Class 1 E loads from the standby diesel generators and spuriousseparation of Class 1 E systems from offsite power due to normal motor starting transients. Formore information regarding this event, see Agencywide Documents Access and ManagementSystem (ADAMS) Accession No. ML093521388.As a result of these Millstone events, the NRC requested that all licensees implement degradedvoltage protection as described in a 1977 Generic Action (Multi-plant Action B-23) to ensureautomatic protection of safety buses and loads. Multi-plant Action B-23 provides guidancewhich applies to all operating reactors at that time and plants licensed since, on how to complywith the requirements in 10 CFR Part 50, Appendix A, GDC 17. Since degradation of the offsitepower system can lead to or cause the failure of redundant Class 1 E safety-related electricalequipment, the NRC requested that licensees install degraded voltage protection schemes(second level of voltage protection (Degraded Voltage Relays (DVRs)) for the station electricpower system) as described in NRC letters dated June 2 & 3, 1977 (Multi-plant Action B-23),"Statement of Staff Positions Relative to Emergency Power Systems for Operating Reactors,"which were sent to all operating nuclear power plant licensees. As an example, see the NRCletter dated June 2, 1977, ADAMS Accession No. ML1 00610489, sent to the licensee for PeachBottom Atomic Power Station. In this letter, the NRC requested that these DVR circuits satisfythe following criteria:a) The selection of voltage and time delay setpoints shall be determined from ananalysis of the voltage requirements of the safety-related loads at all station electricpower system distribution levels;Note: Voltage requirements of all safety-related loads should be determinedbased on manufacturers design and operating requirements. Forexample, safety injection motors have starting and running voltagerequirements. Motor operated valves have minimum operating voltagerequirements. Motor Control Center contactors have minimum pickupand operating voltages. All voltage requirements for all safety-relatedloads need to be preserved by the DVR circuit(s) during all operating andaccident conditions.b) The voltage protection shall include coincidence logic to preclude spurious trips of theoffsite power source;c) The time delay selected shall be based on the following conditions:(1) The allowable time delay, including margin, shall not exceed the maximumtime delay that is assumed in the final safety analysis report (FSAR) accidentanalyses; RIS 2011-12, Rev. 1 Note: Time delay condition (1) indicates that the DVR circuits should bedesigned assuming coincident sustained degraded grid voltage andaccident events. Upon the onset of the coincident accident anddegraded grid event, the time delay for the DVR circuit should allowfor separation of the 1 E buses from the offsite circuit(s) andconnection to the 1 E onsite supplies in time to support safetysystem functions to mitigate the accident in accordance with theFSAR accident analyses.(2) The time delay shall override the effect of expected short duration griddisturbances, preserving availability of the offsite power source(s); and(3) The allowable time duration of a degraded voltage condition at all distributionsystem levels shall not result in failure of safety-related systems orcomponents;d) The voltage monitors (or DVRs as defined above) shall automatically initiate thedisconnection of offsite power source(s) whenever the voltage and time delay limitshave been exceeded; ande) The voltage monitors (DVRs) shall be designed to satisfy the requirements of IEEEStandard 279-1971, "Criteria for Protection Systems for Nuclear Power GeneratingStations"; andf) The Technical Specifications shall include limiting conditions for operation,surveillance requirements, trip setpoints with minimum and maximum limits, andallowable values for second-level voltage protection DVRs.The NRC incorporated the staff positions to meet GDC-17 requirements in Multi-plant ActionB-23 into Branch Technical Position (BTP) of the Standard Review Plan (SRP/NUREG-0800),PSB-1, Revision 0, "Adequacy of Station Electric Distribution System Voltages," dated July 1981(ADAMS Accession No. ML052350520), which was updated later becoming BTP 8-6 of theSRP, Revision 3, "Adequacy of Station Electric Distribution System Voltages," dated March2007 (ADAMS Accession No. ML070710478). In addition, the SRP provides a designapproach, consistent with the original Multi-plant Action B-23, with respect to the selection of thetime delay for the DVR circuit.Arkansas Nuclear OneAnother degraded voltage event, in September of 1978, at ANO station demonstrated thatdegraded voltage conditions could exist on the Class 1 E buses even with normal transmissionnetwork (grid) voltages, due to deficiencies in equipment between the grid and the Class 1 Ebuses (Offsite/Station electric power system design) or by the starting transients experiencedduring certain accident events not originally considered in the sizing (design) of these circuits.Information Notice No. 79-04, "Degradation of Engineered Safety Features," (ADAMSAccession No. ML031180118) provides additional information regarding this event.The NRC staff issued Generic Letter 79-36, August 8, 1979, "Adequacy of Station ElectricI Distribution Systems Vvoltages" (ADAMS Legacy No. 7908230155), expanding its generic RIS 2011-12,_Rev. 1 review of the adequacy of electric power systems for operating nuclear power plants.Specifically, the NRC requested that all licensees review the electric power systems at each oftheir nuclear power plants to determine analytically if, assuming all onsite sources of AC powerare not available, the offsite power system and the station electric power system is of sufficientcapacity and capability to automatically start as well as run all required safety-related loads.Recent Inspection FindingqsDespite lessons learned from past events, and the generic communications on degradedvoltage protection and adequate station voltages, NRC inspectors have identified incorrectimplementation of degraded voltage protection schemes by the licensees at various plantsduring inspections. Specifically, the existing degraded voltage setpoints at some plants werenot adequate to protect the safety-related components during degraded voltage conditions foraccident and non-accident conditions. In some cases, the voltage conditions were too low topower the safety-related equipment but high enough to prevent transferring of safety loads tothe standby power source. In addition, the time delays provided for the degraded voltageprotection relays were not consistent with the accident analysis assumptions for those plants.Although the licensees analyses were site-specific, the NRC staff is concerned that otherlicensees might not have adequately implemented the staff positions and guidance issuedpreviously to address the adequacy of station electrical distribution system voltages. Examplesof inspection findings recently identified by the inspectors include the following:DC Cook Units 1 and 2I During the safety system design and performance capability, biennial baseline inspection (NRCInspection Report No. 50-315/03-07(DRS); 50-316/03-07(DRS)) (ADAMS Accession No.ML032260201) at the DC Cook Nuclear Power Plant, in July of 2003, NRC inspectors identifiedthat the degraded voltage protection scheme was bypassed whenever the 4160V buses werenot being supplied through the reserve auxiliary transformers. This resulted in a lack ofautomatic degraded voltage protection during normal operation and for the first 30 seconds ofan accident when engineered safety feature loads were being sequenced onto the safety buses.This condition did not meet the staff position described in BTP PSB-1 and the electrical schemeis contrary to the design criteria for degraded voltage protection stated in an NRC letter to thelicensee (a version of a letter sent to all licensees) dated June 3, 1977. This issue wasreviewed by the NRR technical staff under Task Interface Agreement (TIA) 2004-02, and thestaff concluded that the degraded voltage protection design at DC Cook was inadequate and assuch should be modified to include degraded voltage protection during normal operation as well(ADAMS Accession No. ML043480350). Because the NRC staff had approved DC Cook'sdegraded voltage protection design in 1980, the staff's 2005 determination that the design wasinadequate constituted a change in position and was subject to a backfit analysis. By letterI dated November 9, 2005 (ADAMS Accession No. ML050680057), the NRC imposed a facility:-specific compliance backfit on DC Cook Nuclear Plant, Units 1 and 2 to bring the facility intocompliance with its license, the rules and orders of the Commission, and the licensee's writtencommitments. The licensee implemented a plant modification to the degraded voltage relayingcircuit to make it functional during normal operation (see ADAMS Accession No. ML060530405)addressing the backfit issu RIS 2011-12.,Rev. 1 Fermi Unit 2In May of 2008, NRC inspectors determined that the time delay settings of the degraded voltagerelays for both divisions I and II of the Class 1E electrical distribution system were inadequate.The time delays could impact the emergency core cooling system (ECCS) injection timingrequirements of the licensee's 10 CFR 50.46 loss-of-coolant accident (LOCA) analysis during adegraded voltage condition. The licensee's degraded voltage protection scheme could result inthe voltage being too low to adequately power the ECCS equipment but high enough to preventthe emergency diesel generators from connecting to the safety-related buses in a timelymanner. This issue was reviewed by the NRR technical staff under TIA 2007-03 (ADAMSAccession No. ML080420435). The staff determined that the current degraded voltageprotection scheme was inadequate as the time delay relay settings for the degraded voltagerelays for both divisions could impact the emergency core cooling system injection timingrequirements. Additionally, for a short period of time under degraded voltage conditions,voltage could be too low for the proper operation of safety-related motors but high enough toprevent emergency diesel generator start. Because the NRC staff had approved Fermi'sdegraded voltage protection design in 1981, the staff's 2008 determination that the design wasinadequate constituted a change in position and was subject to a backfit analysis. The staffdetermined that the provisions of 10 CFR 50.109 (a) (4) were applicable, and that a modificationwas necessary to bring the facility into compliance with the rules and orders of the Commission.See NRC Inspection Report 05000341/2008008 (ADAMS Accession No. ML081720585) foradditional details. The NRC approved the plant modification in License Amendment No. 183(ADAMS Accession No. ML102770382).Peach Bottom Atomic Power Station Units 2 and 3Exelon did not use the safety-related degraded grid relay trip setpoint specified in the TechnicalSpecifications (TS) as a design input in calculations to ensure adequate voltage was availableto all safety-related components required to respond to a design basis LOCA. Instead, Exelonused the results from a Voltage Regulation Study to establish the voltage level for systemoperability. The study credited the use of non-safety-related equipment (load tap changers) toraise the voltage level. This allowed higher voltages to be used in the design calculations forcomponents than would be allowed by the TS setpoint. The NRR technical staff reviewed theissue in TIA 2009-07 (ADAMS Accession No. ML102710178). The staff concluded that thelicensee must demonstrate that the existing degraded voltage trip setpoints, including allowablevalues and time delays shown in the licensees TS Table 3.3.8.1, are adequate to protect andprovide the required minimum voltage to all safety-related equipment. Since the load tapchangers are not safety-related and are subject to operational limitations and credible failures,they cannot be relied on to establish degraded voltage relay setpoints and time delay input fordesign basis calculations. For additional details, see NRC Inspection Report05000277/2010004 and 05000278/2010004 (ADAMS Accession No. ML103140643). Thelicensee subsequently issued Licensee Event Report 2-10-04 (ADAMS Accession No.ML1 03280505) based on the determination that certain plant equipment could be degraded as aresult of lower voltages that could exist during a postulated design basis loss-of-coolant eventcoupled with certain degraded voltage condition RIS 2011-12,_ Rev. Palo Verde Nuclear Generating Station Units 1, 2, and 3In July of 2009, an NRC inspection team questioned the calculations that demonstrate adequatevoltage to safety-related loads during worst case loading conditions and the adequacy of a timedelay of 35 seconds for transfer of safety buses to the onsite power supplies should an actualdegraded voltage condition occur. The licensee's calculation assumed a voltage above thedegraded bus setpoint to demonstrate adequate voltage at the terminals of the safety-relatedloads rather than the degraded voltage dropout setpoint value. The licensee maintains that adegraded voltage condition concurrent with a design basis accident is not credible. See NRCInspection Report 05000528; -529; and -530/2009008, ADAMS Accession No. ML093240524regarding the inspection finding. The NRR technical staff reviewed the issue in TIA 2010-05(ADAMS Accession No. ML102800340). The staff concluded that the licensee's calculationmust demonstrate that the trip setpoint adequately protects the Class 1 E equipment powered bythe safety-related bus from a potentially damaging degraded voltage condition, and the timedelay to transfer from a degraded offsite source to the standby power source to support theemergency core cooling equipment operation must be consistent with accident analysis timeassumptions, as recommended by BTP PSB-1 (NUREG 0800).

SUMMARY OF ISSUE

SBecause the NRC continues to identify inspection findings associated with degraded voltage,the NRC is providing clarifying information on two issues related to the need for two sets ofcalculations for the design of the electric power systems of a nuclear power plant and itsinterface with the transmission network as defined in GDC 17. The two issues are (1) DegradedVoltage Relaying Design Calculations, and (2) Offsite/Station Electric Power System DesignCalculations.(1) The Degraded Voltage Relaying Design Calculations establish the necessary settings ofthe DVRs to ensure that all safety-related components are provided adequate voltagebased on the design of the plant power distribution system (and the offsite circuits),including the design of the Class 1 E distribution system in the plant and its most limitingoperating configuration(s).(2) The Offsite/Station Electric Power System Design Calculations specify the voltageoperating parameters of the plant electrical distribution system based on thetransmission network (grid) operating parameters. This interface calculation establishesoperating voltage bands for all plant electrical buses, which ensures that all plantsafety-related components and systems have proper voltage for starting and running inall operational configurations (expected operational and accident line-ups andconditions). Therefore, based on normal grid operation (including (grid)post-contingency), the degraded voltage relays will not operate, maintaining the offsitepower supply to the plant electrical distribution system.(1) Degraded Voltage Relaying Design CalculationsProper design of a degraded voltage relaying scheme is needed to ensure that safety-relatedsystems are supplied with adequate voltages. The purpose of the NRC-developed BTP PSB-1(revised later to become BTP 8-6) is to provide additional guidance to supplement the 1977Generic Action (Multi-plant Action B-23) and the SRP and to provide some design details of a RIS 2011-12,_Rev. 1 DVR circuit that satisfies the regulatory requirements (there may be other designs that satisfythe requirements). The DVR design should protect (ensure voltage requirements are met)Class 1 E safety-related buses and components from sustained degraded voltage conditions onthe offsite power system coincident with an accident as well as during non-accident conditions.The Class 1 E buses should separate from the offsite power system within a few seconds (orimmediately if the design philosophy recommended in BTP PSB-1 is followed) if an accidentoccurs coincident with sustained degraded voltage conditions. During normal plant operation,the Class 1 E safety-related buses should automatically separate from the power supply within ashort interval if sustained degraded voltage conditions are detected. The time delay chosenshould be optimized to ensure that permanently connected Class 1 E loads are not damagedunder sustained degraded voltage conditions (such as a sustained degraded voltage below theDVR voltage setting(s) for the duration of the time delay setting).DVR Setting Design CalculationsLicensee voltage calculations should provide the basis for their DVR settings, ensuringsafety-related equipment is supplied with adequate voltage (dependent on equipmentmanufacturers design requirements), based on bounding conditions for the most limitingsafety-related load (in terms of voltage) in the plant.Note: All voltage requirements for the safety-related equipment must bepreserved by the DVR circuit(s). For example, safety injection motors havestarting and running voltage requirements. Motor operated valves have minimumoperating voltage requirements. Motor Control Center contactors have minimumpickup and operating voltages. All voltage requirements for all safety-relatedloads need to be preserved during all operating and accident conditions.These voltage calculations should model offsite circuits and the plant electricaldistribution system, including the plant safety-related electrical distribution system, suchthat the limiting voltage at the bus monitored by the DVR can be calculated in terms ofthe voltage at the terminals of the most limiting safety-related component in the plant inall required operating conditions (such as starting and running). These models shouldinclude all plant equipment (including non-safety-related) that can affect voltage suppliedto the safety-related equipment. As a minimum, the model should utilize loads on theplant distribution system consistent with the specific transient or accident beinganalyzed. These models would allow calculation of voltages at terminals of allsafety-related equipment with the voltage at the DVR monitored bus at the DVR dropoutsetting, providing the necessary design basis for the DVR voltage settings. In thismanner, the DVR circuit ensures adequate voltage (starting and running) to allsafety-related equipment. Voltage-time settings for DVRs should be selected so as toavoid inadvertent separation of safety buses from the offsite power system during unitstartup, normal operation (including motor starting), and shutdown.These DVRs should disconnect the Class 1 E buses from any power source other thanthe emergency diesel generators (onsite sources) if the degraded voltage conditionexists for a time interval that could prevent the Class 1 E safety-related loads fromachieving their safety functio RIS 2011-12,_Rev. 1 Note: Upon the onset of the coincident accident and degraded grid event, thetime delay for the DVR circuit must allow for separation of the 1 E buses from theoffsite circuit(s) and connection to the 1 E onsite supplies in time to support safetysystem functions to mitigate the accident in accordance with the FSAR accidentanalyses.The DVRs should also prevent prolonged operation of Class 1 E safety-related loads atdegraded voltage, which could result in equipment damage.The operation of voltage correcting equipment, external to the 1 E distribution system,should not be assumed for DVR setpoint analyses.(2) Offsite/Station Electric Power System Design CalculationsThe offsite power source is the preferred source of power to safely shut down the plant duringdesign basis accidents, abnormal operational occurrence, and reactor trips. The licensee'svoltage calculations should provide the basis for proper operation of the plant safety-relatedelectrical distribution system, when supplied from the offsite circuit(s) (from the transmissionnetwork). These calculations should demonstrate that the voltage requirements (both startingand running voltages) of all plant safety-related systems and components are satisfied based onoperation of the transmission system (including the bounding transmission system singlecontingency in terms of voltage drop) and the plant onsite electric power system during alloperating configurations of transmission network and plant systems. In addition, duringaccident conditions, the nuclear unit generator trip (transmission system single contingency)and associated transmission system voltage drop should be factored into the accident casevoltage calculations since unit trip occurs as a result of the accident. In this way, all safety-:related systems and components will function as designed with proper starting and runningvoltages during all plant conditions and the DVRs will not actuate (separating the transmissionnetwork supply). The following are guidelines for voltage drop calculations derived fromGeneric Letter 79-36, which have been supplemented to add clarifying information. They do notrepresent new NRC staff positions.Guidelines for voltage drop calculationsa) The plant voltage analysis, while supplied from the transmission network, should bebased on the operating voltage range of the transmission network connection. Thistransmission owner/operator supplied voltage range should address all transmissionnetwork and plant system operating configurations and should also include voltagedrop due to the bounding worst case transmission system contingency (transmissionsystem contingencies include trip of the nuclear power plant). The unit trip gridcontingency voltage drop value should be used in the accident cases in accordancewith the plant accident analyses since a unit trip occurs with an accident.b) Separate analyses should be performed assuming the power source to the safetybuses is (1) the unit auxiliary transformer; (2) the startup transformer; and (3) otheravailable connections (e.g., from all available connections) to the offsite network oneby one assuming the need for electric power is initiated by (1) an anticipated transientsuch as a unit trip (e.g., anticipated operational occurrence), or (2) an accident,whichever presents the bounding load demand on the power sourc RIS 2011-12,_Rev. 1 c) For multi-unit stations, a separate analysis should be performed for each unitassuming (1) an accident in the unit being analyzed and simultaneous shutdown andcooldown of all other units at the station in accordance with the plant's licensing basis;or (2) an anticipated transient (anticipated operational occurrence/GDC 17) in the unitbeing analyzed (e.g., unit trip) and simultaneous shutdown and cooldown of all otherunits at that station, whichever presents the largest load situation.d) All actions that the electric power system is designed to automatically initiate orcontrol should be assumed to occur as designed (e.g., automatic bulk or sequentialloading or automatic transfers of bulk loads from one transformer to another,automatic starts of components, operation of automatic voltage controlling equipmentsuch as capacitor bank switching or load tap changers). All non-safety-related plantauxiliary loads should be included, as applicable, in the plant loading studies sincetheir operation can affect voltage to safety-related equipment.e) Manual load shedding should not be assumed.f) For each event analyzed, the maximum load necessitated by the event and the modeof operation of the unit at the time of the event should be assumed in addition to allloads caused by expected automatic actions and manual actions permitted byadministrative procedures.g) The voltage analysis should include documentation for each condition analyzed, ofthe voltage at the input and output of each transformer and at each intermediate busbetween the connection of the offsite circuit(s) and the terminals of eachsafety-related load.h) The calculated voltages at the terminals of each safety-related load should becompared with the required voltage range for normal operation and starting of thatload calculated in Item a) above. Any identified inadequacies of calculated voltageshould require immediate remedial action.i) For each case evaluated, the calculated voltages on each safety bus shoulddemonstrate adequate voltage at the safety bus and down to the component level.j) To provide assurance that actions taken to assure adequate voltage levels forsafety-related loads do not result in excessive voltages, assuming the maximumexpected value of voltage at the connection to the offsite circuit(s), a determinationshould be made of the maximum voltage expected at the terminals of all safety-relatedequipment and their starting circuits (if applicable). If this voltage exceeds themaximum voltage rating of any safety-related equipment, immediate remedial actionshould be taken.k) Analysis documentation should include a statement of the assumptions for each caseanalyze RIS 2011-12, Rev. 1

BACKFIT DISCUSSION

The NRC has evaluated this RIS against the criteria of 10 CFR SeGtien 50.109, 10 CFR Part 50,Appendix A, GDC 17, NRC Letter dated June 2, 1977, "Statement of Staff Positions Relative toEmergency Power Systems for Operating Reactors," BTP-1 and later BTP 8-6 (both of NUREG_0800) and Generic Letter 79-36, and has determined that it does not represent a backfit.I Specifically, NRC Sstaff technical positions outlined in this RIS are consistent with theaforementioned regulations and generic communications, while providing more detaileddiscussion concerning the necessary voltage calculations supporting DVR settings based onlyon voltage requirements of Class 1 E components and the Class 1 E distribution system design.I Under seetieR10 CFR 50.109, a backfit can be defined as a proposed action that is amodification of the procedures required to operate a facility and may result from the impositionof a regulatory staff position that is either new or different from a previously applicable staffposition.

FEDERAL REGISTER NOTIFICATION

Although this RIS is informational and does not represent a departure from the currentregulatory requirements, a notice of opportunity for public comment on this RIS was published inthe Federal Register (76 FR 2924) on January 18, 2011, for 30 days. On February 23, 2011, aNotice was published in the Federal Register extending the comment period for additional 30days to March 19, 2011, based on the request from Nuclear Energy Institute (ADAMSI Accession No. ML1 10330025). There were fourteen organizations/individuals that providedcomments, which were considered before issuance of this RIS. Each of the comments weredocumented and responded to by NRC staff and are available in ADAMS at Accession No.ML=ML1 130505884442374!8W. This response supersedes the information provided earlier inADAMS at Accession Nos. ML11 16006590.ML1 11600659 and ML1 12371830, which wereincorrectly released as final documents when in fact they were drafts. Changes between thedraft and final public comment resolution documents can be viewed in ADAMS at Accession No.MLxxxxxxxxx.This RIS does not represent a departure from current regulatory requirements.

CONGRESSIONAL REVIEW ACT

This RIS is not a rule as designated by the Congressional Review Act (5 U.S.C. §§ 801-886)and, therefore, is not subject to the Act.

PAPERWORK REDUCTION ACT STATEMENT

This RIS does not contain any information collections and, therefore, is not subject to therequirements of the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.).Public Protection NotificationThe NRC may not conduct or sponsor, and a person is not required to respond to, a request forinformation or an information collection requirement unless the requesting document displays aI currently valid Office of Management and Budget QMB-control numbe RIS 2011-12,_Rev. 1

CONTACT

This RIS requires no specific action or written response. If you have any questions, pleasecontact the technical contact listed below or the appropriate regional office.Laura A. Dudes, DirectorA'R by RNeISon fGrTimothy J. McGinty, DirectorDivision of Policy and RulemakinaDivision of Construction Inspectionand Oierational ProeramsOffice of Nuclear Reactor ReaulationOffice of New ReactorTioh -1 FtG~Atu D;i,+.,Dr:Ic0A Of PGoIcvy and IRulemaking.vcf ,N,-:!:ar ReaJ!3tionOffic-e of Nhuclear Reacutor Regula;tionRTechnical Contacts:Roy Mathew, NRR/DE/EEEB301-415-2965E-mail: roy.mathew(@nrc.,ovGurcharan Matharu, NRR/DE/EEEB301-415-4057E-mail: .urcharan.matharuanrc.govKenn A Miller, RES/DE/MEEB301-251-7458E-mail: kenn.milleranrc.qov RIS 20102011-12,_Rev. 1

CONTACT

This RIS requires no specific action or written response. If you have any questions, pleasecontact the technical contact listed below or the appropriate regional office.iRA by RNMcsGn ftreTimothy J McGintv~ DirectorLaura A Dude Direactorflivi~inn nf Pnlirv ~ncI RiiI~m~kinnDivision of Construction Inspection Division of Policv and Rulemakinn~nnr mr-afainrnI IDrr% rurmrr~ffie-m rf IMeLoa Pnnfn Prma "Intinne M. %I/ tII4 f4 IISIBS.% IFkAh~~II*~%l.I I~ i~L ~Office of New ReactorTimothy j. I1;GGinty, DilroaoWiwi I F W MI MUM! Morti! E 9cJrOn P1'_rGIAucae Rezacter Reaulauwi~Technical Contacts:Roy Mathew, NRR/DE/EEEB301-415-2965E-mail: roy.mathew(Dnrc.qovGurcharan Matharu, NRR/DE/EEEB301-415-4057E-mail: qurcharan.matharucnrc..ovKenn A Miller, RES/DE/MEEB301-251-7458E-mail: kenn.millercnrc.qovNote: NRC generic communications may be found on the NRC public website,http://www.nrc.Qov, under Electronic Reading Room/Document Collections.DISTRIBUTION:I ADAMS A~inn No.: ML113O5flSR~ML11222A13~* Fmail attachedOFFICE NRRIDE/EEEB Tech Editor NRR/DE/EEEB NRR/DE NRR/DORL OENAME KMiller

• RMathew PHiland JGiitter

• NHiltonDATE 11/18/10 11/18/10 11/18/10 12/21/10 12/9/10 12/7/10OFFICE PMDA OIS RES/DE/MEEB NRO/DE/EEB OGC (CRA) OGC (NLO)NAME LHill

• TDonnell TKoshy

• RJenkins PHirsch GMizunoDATE 12/3/10 12/8/10 12/16/10 12/14/10 1/7/11 1/6/11OFFICE OGC (CRA) OGC (NLO) LA:PGCB PM:PGCB BC:PGCB NRR/DPRNAME GKim BJonesB&eAes CHawes TMensah SRosenberg TMcGintyDATE 8/24/11 4--11/28,3/11 11/28/1140/04/ 11/29/11--1046 12/ /11404&44W/2614411/16/1 44 1441_ 1 1 11 1. 1 1OFFICENAMEDATENROLDudes12/13/11 OFFICAL RECORD COPY RESPONSE TO PUBLIC COMMENTS ON DOCKET ID NRC-2011-0013PROPOSED GENERIC COMMUNICATIONS: DRAFT NRC REGULATORY ISSUESUMMARY 2011-XX: ADEQUACY OF STATION ELECTRIC DISTRIBUTIONSYSTEM VOLTAGE*On January 18, 2011, a Notice of Opportunity for Public Comment was published in the FederalRegister to clarify the NRC staffs technical position on existing regulatory requirements andguidance for Degraded Voltage Relay (second level undervoltage protection) protection settingbases and Transmission Network/Offsite/Onsite station electric power system design bases. OnFebruary 23, 2011, a Notice was published in the Federal Register extending the commentperiod to March 19, 2011, based on the request from NEI (ADAMS Accession No.MLI 10330025). Comments were received from 14 organizations/individuals. The staff alsoconducted a workshop on June 28-29, 2011, to discuss the NRC's existing regulatoryrequirements and guidance for nuclear power plant electric power system degraded voltageprotection and addressed workshop participants' questions1. (1-7) Dominion 2. (8-31) Exelon 3. (32-39) Southern 4. (40-45, 59-85 & 86-96)Resources, Inc Generation Company, LLC Nuclear Operating NEI(ADAMS Accession No. (ADAMS Accession No. Company 1776 1 Street NWML110540357) ML110540358) (ADAMS Accession No. Washington, DC, 20006ML110540360) (ADAMS Accession Nos.ML110660379,ML1 10810619)5. (49-51) Jerry Nicely 6. (52-58) Larry Nicholson 7. (97-108) PPL 8. (109-124) APS, PaloSelf Nextera Susquehanna, LLC Verde Nuclear Generating(ADAMS Accession No. (ADAMS Accession No. (ADAMS Accession No. StationML110800530) ML110800536) ML110830675) (ADAMS Accession No.ML110820342)9. (125-131) Nextera 10. (132) TVA 11. (133-137)Progress 12. (138-139) STARSEnergy (ADAMS Accession No. Energy (ADAMS Accession No.(ADAMS Accession No. ML110840041) (ADAMS Accession No. ML110870916)ML1 10820119) ML110840040)13. (140) Greg Reimers/ 14. (141) Brian WilsonDiablo Canyon (ADAMS Accession No.Email (ADAMS Accession ML1 10960076)No. ML112010028) 1The NRC staffs review and disposition of the comments are provided in the following Table.*This response supersedes the information provided earlier in ADAMS at Accession Nos.ML1 11600659 and ML1 12371830. These documents were incorrectly released as finaldocuments when in fact they were drafts. Changes between the draft and final public commentresolution documents can be viewed in ADAMS at Accession No. MLxxxxxxxxx.No. Section of RIS Originator Specific Comment NRC ResolutionSUMMARY OF Dominion Section DVR Setting DesignISSUES -1. DVR ResourcesSetting Design Services, Inc In this manner, the DVR ensures adequateCalculations operational (starting and running) voltage to allsafety related equipment, independent of voltagecontrolling equipment external to the plant safetyrelated electrical distribution system.The approach could imply that the load(s) should Disagreestart from the lowest DVR dropout setting. Aspecific example for illustration is as follows: NRC Staff has the following clarification withI If voltage is at the lowest possible value above this positio No. Section of RIS Originator Specific Comment ] NRC Resolutiondropout, starting a load will cause DVR dropout,but, since the new steady state voltage will belower than the initial value, then DVR reset cannotoccur.Many utilities use the ABB 27N with harmonic filterwhich has a minimum 0.5% reset. Thus, with asetting of 93.6% +/- 0.9%, dropout could be as lowas 92.7%. However, for motors causing more than0.5% voltage dip at initial start, even if the voltageat the beginning of the event was 93.2% and a loadwas started, then DVR will dropout and never resetcausing a separation. A clarification that allowsevaluation of motor starting as well-as otherconditions is:If the DVR could possibly not cause separationthen the required safety functions must beperformed successfully. Thus, depending on thedesign of the plant, a voltage value for beginningthe event with all required starts could bedetermined by an iterative process.If the offsite power has adequate capacityand capability, any voltage just above theDVR setpoint should not separate the offsitepower source from the safety bus whenstarting large motors. The grid voltage isexpected to recover.The key point is that the voltage setting(s)selected should ensure that adequatevoltage is available at the componentterminal(s) to operate the most limitingcomponent (s) at a plant during the mostlimiting design basis event. The offsite/onsiteinterface calculation should show that, withthe grid at the lower limit of the normaloperating range, voltage at the safety bus isalways well above the degraded voltagesetpoint for all design basis event loadingconditions (normal, abnormal and accidentconditions including anticipated operationaloccurrence).The safety related equipment should beprotected from two types of low voltageissues:1. Loss of voltage event whichimplies a sudden sharp voltagedrop in grid system. Typically anominal delay is allowed for relayactuation to separate onsitebusses from the grid if voltagedoes not recover to normaloperating band.2. Degraded voltage event thatpostulates sustained low voltageconditions for several seconds andsubsequent recovery to normaloperating band. If the offsite powersystem does not recover tonominal operating conditions, it ispreferable to separate from thesource.The ABB relay with harmonic filter should beable to reset if the grid perturbation is limitedto a short duration.4- -4- + --2.SUMMARY OFISSUES-- 2.Offsite/OnsiteDesign InterfaceCalculations(page7)DominionResourcesServices, IncThis section contains elements that are tooprescriptive. Many analyses will show that the unitloads/sequences assessed for determination ofDVR setpoint adequacy for equipment protectionare the same as those for evaluating offsite power.Since evaluating offsite power always involveshigher voltages, it is clear the equipment willfunction and providing terminal voltages for thisequipment is bounded by DVR adequacy analysis.A clarification that helps frame adequate analysisis:If the DVR could initiate separation then offsitepower is not operable. Using the example abovewhen evaluating offsite power would require thatthe safety bus recover above 93.6%+0.9%+0.5%or 95% before the earliest time delay for the DVRexpires. Since a reset also resets the time delay,multiple DVR drop outs could occur withoutseparation during load sequencing. Also, since92.7% was evaluated for equipment protection.DisagreeNRC Staff has the following clarification forthis position.To meet GDC 17 requirements, the licenseemust demonstrate capability to safely shutdown the plant for all design basis eventswith the grid voltage at the lowest allowablevalue as afforded by the transmission systemoperator.The voltage studies done for evaluatingoffsite power/onsite power interface shoulduse minimum expected voltage at theplant/grid interface node, demonstratingadequate voltage for starting and running ofplant components during normal, abnormaland accident conditions. The expected plantloading at 100% power operation may behiaher than accident loadina. Hence the2 No. Section of RIS Originator Specific Comment NRC Resolutionevaluating 95% (used for offsite power evaluation) voltage drop in the plant auxiliary system willwould require the two sequences be substantially be higher for normal operating conditions.different (2.3%) for the DVR adequacy evaluation The DVR setpoint should be below the(at 92.7%) to not be bounding for equipment normal operating voltage of the plant to avoidevaluation. Thus, providing calculation detail to multiple spurious actuations. A separatemotor terminals for offsite power evaluation is analysis may be needed for DVR setpoint.unnecessary in many designs.The comment implies that DVR setpointoverlaps with system voltage during normaloperation.Calculation details to motor terminals arehelpful in gaining margin between DVRsetpoint and normal grid operating voltages.To avoid spurious DVR actuation duringnormal plant operation and during loadsequencing, the DVR setpoint should belower than normal operating band for offsitepower. This can be achieved by:1) Specifying equipment for safety relatedapplications to function at voltage levelswell below the nominal bus voltage.2) Reducing the onsite systemimpedance/voltage drop. This can beachieved by reducing the cable impedancefor the limiting safety loads and trippingnon-essential loads after unit trip.SUMMARY OF Dominion Part a states:ISSUES -- 2. Resources This transmission owner/operator supplied voltageOffsite/Onsite Services, Inc range should address all transmissionDesign Interface network and plant system operating configurationsCalculations(page and should also include voltage drop due to7) the bounding worst case transmission systemcontingency (transmission system contingenciesinclude trip of the nuclearpower unit).Certainly the trip of the nuclear power unit must Disagreealways be considered. However, the definition ofthe worst case transmission system contingencyrequires clarifying statements. Certainly someanalyses are done using "strong grid" for faultanalyses or "weak grid" for voltage analyses.These modeled sources have a number ofcontingencies built into them. Voltage drop from the The plant electrical distribution systemloss of the unit can vary considerably with system should be designed based on the gridconditions. Arguments can be made that the worst voltage range including the bounding worstcase contingency (if different than the nuclear case grid contingency (strong or weak gridpower unit) should only be considered once it has depending on which one is bounding). In thisoccurred. However, a key question should be way, the plant's design ensures adequateapplied: Is the contingency of interest monitored? If voltage to plant equipment as long as grid isthe status is not monitored, then how would the operating as "expected".nuclear unit know when to apply the contingency?Thus, if the status of a key transmission line to the Contingencies that are beyond design basisnuclear unit switchyard is known, either by (line outages during peak grid loadinginstrumentation at the plant or timely notification conditions) that occur during plant operationby the grid operator, then the contingencies need should be evaluated uniquely to assess theonly be considered when applicable. When capability of offsite power to provideevaluating voltage drop, most situations which shutdown capability post trip as required bycause meaningful changes are nearby and can be GDC 17.monitored.GDC 17 requires that offsite power hassufficient capacity and capability to assurethat (1) specified acceptable fuel designlimits and design conditions of the reactorcoolant pressure boundary are not exceededas a result of anticipated operationaloccurrences, and (2) the core is cooled andcontainment integrity and other vitalfunctions are maintained in the event of3 No. Section of RIS Originator .Specific Comment NRC Resolutionpostulated accidents.4. SUMMARY OF Dominion Part c states:ISSUES-- 2. ResourcesOffsite/Onsute Services, Inc For multi-unit stations, a separate analysis shouldDesign Interface be performed for each unit assuming (1) anCalculations(page accident in the unit being analyzed and8) simultaneous shutdown of all other units at thestation,' or (2) an anticipated transient (anticipatedoperational occurrence) in the unit being analyzed(e.g., unit trip) and simultaneous shutdown of allother units at that station, whichever presents thelargest load situation.This requires clarification as an accident oranticipated transient both require unit trip. The Disagreeword used for other units at the station is"shutdown" which is more orderly and takes moretime. Simultaneous unit trip results in bigger This statement is consistent with GDC 17,voltage drops from VAR support (not loading). This GL 79-36, and IEEE Standard 308-1971,is because VARs are local. System XR is typically "Class IE Electrical Systems," Section 8,-50 so it is 50 times more difficult to move a VAR a "Multi-Unit Station Considerations.hundred miles than a watt. Thus, most analysesshow the worst voltage drop for the loss of the Multi-unit sites have been licensed innuclear unit is when all of the nearby units (any accordance with above documents andtype of generation) are already off. Changing that should therefore evaluate the plantsto tripping all units at the same time increases the according to their licensing basis.voltage drop because grid compensatory actionsare not included. Even a small (minute) timedifference between losses of units can bemeaningful in the voltage result. However, if theintent of the wording was simultaneous trip, thenthis is a special case of item 3 above, which islikely a monitored contingency.5. SUMMARY OF Dominion Part j states:4 No. Section of RIS Originator Specific Comment NRC ResolutionISSUES-- 2. ResourcesOffsite/Onsite Services, Inc To provide assurance that actions taken to assureDesign Interface adequate voltage levels for safety related loadsCalculations(page do not result in excessive voltages, assuming the8) maximum expected value of voltage at theconnection to the offsite circuit, a determinationshould be made of the maximum voltageexpected at the terminals of all safety relatedequipment and their starting circuits (if applicable).If this voltage exceeds the maximum voltage ratingof any safety related equipment, immediateremedial action should be taken.The word "immediate" describing remedial action Disagreeshould be removed from this section. Immediateremedial action could imply control roomintervention. The control room has alarmprocedures to address high voltage should it occur.Timeliness of remedial actions depends on howhigh actual voltage is since minor incursions haveonly long term implications for most equipment. The wording is consistent with GL 79-36.Analyses of high grid voltage with light plant loadare standard and provide insights as to what grid The Offsite/Onsite design should address allvoltage upper limit should be or what compensating grid operating conditions to preventactivities might be required for light load operations overvoltages from occurring.(refueling). In those cases where unit trip can resultin a step increase in grid voltage (most common on The point here is that if a design problem ishigher voltage connections like 765kv), anticipated identified such as overvoltage conditions,excursions above desired voltages should be immediate actions should be takenaddressed by compensating measures (changing (compensatory and/or permanent designexcitation for nearby units, switching in reactor changes) to address the design problembanks, etc.). rather than taking actions after it occurs.6. SUMMARY OF Dominion States: This interface calculation establishesISSUES (top of Resources operating voltage bands for all plant electricalpage 6) Services, Inc buses, which ensures that all plant componentsand systems (Class 1E and Non Safety Related)have proper voltage for starting and running in alloperational configurations (expected operationaland accident conditions).This statement needs clarification in that not all Agreenon-safety load voltages need to be evaluated.Typically, large motors (like reactor coolant pumps)need to be evaluated for starting impact on thesafety bus. However, once a motor is found to besmall enough to not impact safety bus operation,further evaluation is unnecessary. The statement inthe RIS can easily be interpreted as requiring The reference to 'non-safety related' is beingevaluation of all non-safety loads down to the removed. However, non-safety related loadslowest levels of distribution, should be modeled to the extent that theiroperation can affect safety bus/equipmentvoltage.7. SUMMARY OF Dominion States:ISSUES -1. DVR ResourcesSetting Design Services, Inc Licensee voltage calculations should provide theCalculations (page basis for their DVR settings, ensuring safety related6) equipment is supplied with adequate operatingvoltage (typically a minimum of 0.9perunit voltage at the terminals of the safety relatedequipment per equipment manufacturersrequirements), based on bounding conditions forthe most limiting safety related load (in terms ofvoltage) in the plantClarification that voltages other than 90% voltage Agree.are common based on detailed plant analysisshould be added. As an example, motors below 90% was mentioned as an example used for1 90% voltage continue to have plenty of margin in illustration. The voltage values are plant-5 No. Section of RIS Originator Specific Comment NRC Resolutiontorque but may encroach on long time thermal specific. Evaluations like mentioned in thislimits. However, unless a motor is fully into its comment could be acceptable as long asservice factor (typically 1.15), as well as below 90% there is adequate engineering justification.voltage, operation will be acceptable. Ensuring that voltages are within nominallimits greatly simplifies the analysis required.8.GeneralExelonGenerationCompany,LLCBackground -Pages 2 and 3General Comments:The RIS uses terms such as "LVR (loss-of-voltagerelay) voltage setting," "DVR (degradedvoltage relay) settings" and "DVR dropout setting"without clarifying the intent or highlighting thedifferences.IEEE 741-2006, Annex A (Reference 1), has adiscussion on the tolerances to be considered andrecommends following ANSI/ISA 67.04.01(Reference 2) treating the voltage relays andassociated time delays as instruments.For the DVR, one example might berepresented as follows:Analytical limit: Minimum voltage that assuresactuation of the relayAllowable value, Lower, Higher than analytical limitto allow for drift and test equipment tolerance;abbreviated AVDO. Tech Spec value.Dropout setpoint: Lower voltage band of nominalsetpoint. Abbreviated SPc DO (Setpoint calculatedDrop Out)Pickup setpoint: Upper voltage band of nominalsetpoint. Abbreviated SPc PU (Setpoint calculatedPick Up)Allowable value, Upper: Higher than SPc PU toallow for drift and test equipment tolerance;abbreviated AVPU. Tech Spec value.Maximum Dropout: Highest voltage that relay couldactuate. Only importance is for establishing resetvoltage.Maximum Pickup: The voltage required to assureDVR resets.The RIS states that two sets of calculations arerequired. It appears that at least three (3)distinctly different calculations are required (four ifthe site has different DVR time delays for accidentand normal conditions). These would be at differentbus voltage values. The "degraded voltage relayingdesign calculations" would be a load flowperformed at the DVR analytical limit; the "plantvoltage analysis" would be load flows and motorstarting performed at the minimum transmissioncontingency voltage with an acceptance criterion ofgreater than relay maximum pickup (the voltagewhere DVR reset is assured) at the bus where thedegraded voltage relays are connected (generallythe medium voltage bus where the EmergencyDiesel Generator is connected); finally, theevaluation of protective device actuation would beperformed at the analytical limit of the loss ofvoltage relay setting comparing the motor runningcurrent to the thermal damage curve and protectiveDisagree.The terminology used in the RIS isconsistent with the guidance documents.The setpoint accuracies and methodologiesare beyond the scope of this RIS.The point of the RIS was to highlight that theDVR setting and design interfacecalculations have different requirements.The staff agrees that there are othercalculations required to demonstrate theelectrical system design basi No. Section of RIS Originator Specific Comment NRC Resolutiondevice characteristic curve,Page 2, criteria b) -Some approved DVR designssense and trip at an emergency bus level, and take RIS is consistent with the NRC letter datedadvantage of inherent redundancy of the June 2, 1977.emergency buses. It should be an owner's option The coincident logic is to ensure thatwith respect to coincident logic. Change the "shall" spurious or inadvertent separation of ato "may." reliable offsite power source. ThePage 2/3 -The listed 6 criteria are good for setting redundancy of the safety buses alone doesthe DVR. Eariy correspondence of the issue not address the above concernalso included a second function for the DVR in thatthe design should minimize the effects of Current wording seems adequate to addressspuriously disconnecting the offsite sources. the point that spurious trips of offsite powerAlthough criteria b) and c)(2) are intended to add should be precluded by the design.robustness to the design, a few sentences shouldbe added to the discussion to accentuate thepoint.9. SUMMARY OF Exelon Under "Degraded Voltage Relaying Design Disagree.ISSUES -1. Generation Calculations," the RIS states in part "During normalDegraded Voltage Company, plant operation, the Class 1 E safety related buses This is not a new requirement.Relaying Design LLC should automatically separate from the powerCalculations (page supply within a short interval (typically less than 60 RIS will be revised to remove the reference6) seconds) if sustained degraded voltage to auto separate in 60 seconds. The 60conditions are detected." Branch Technical Position seconds time delay was identified as anPSB-1 clause B.1 .b.2 included provisions example to illustrate that the time delayfor operator manual actions to restore bus voltage chosen for the sustained degraded conditionon the Class 1 E distribution system. The (DVR settings) should be short to ensure thatsixty second time delay would not allow operator permanently connected Class 1 E loads areactions. This appears to be a new NRC not damaged.position.However, it should be noted that whenvoltage alarms occur (alarm setpoint is sethigher than the DVR setpoint), the gridvoltage at that point may be well below thenormal operating values and is approachingthe DVR setpoint and operator actions maybe taken to improve the voltage conditions toprevent separation from offsite power.The time delay chosen should ensure thatuntil the relay automatic action is initiated, allClass 1E equipment are protected. Thelicensee must provide the bases andjustification in support of the actual delaychosen.10. SUMMARY OF Exelon The next to last sentence under item 1 states: 'The Disagree.ISSUES -1. Generation staff considers degraded voltageDegraded Voltage Company, conditions coincident with a postulated design The point being made in the RIS is thatRelaying Design LLC basis accident to be a credible event. The event setting of the DVR should includeCalculations Page is credible in that it has occurred previously consideration of a coincident accident, in that6 (although nonaccident). It is acknowledged that the time delay chosen for the DVR shouldsafety loads combined with loss of generator support the accident analysis assumptionsreactive power support will cause a decrease in consistent with the NRC1 977 letter.bus voltage. However, if the plant is operatedwithin the bounds of the operating procedures Operating a plant within allowable voltage(which are reflected in the voltage regulation range should minimize the potential forcalculations as described under the subsequent degraded voltage conditions on 1 E busses.section), then the Class 1 E equipment should not However, grid perturbations cannot beexperience a degraded voltage condition, predicted. Hence the need for automaticThe sentence can be removed without diminishing protection.the need for the DVR, or without changingthe intent of this section.11. SUMMARY OF Exelon DVR Setting Design Calculations -Add a sentence Agree.ISSUES -1. Generation "The model should utilize loads on the plantDegraded Voltage Company, distribution system consistent with the specific The suggested sentence will be added to theRelaying Design LLC transient or accident being analyzed." RIS.Calculations -7 No. Section of RIS Originator Specific Comment NRC ResolutionPage 6,12 SUMMARY OF Exelon In addition, Branch Technical Position (BTP) PSB-1 DisagreeISSUES -1. Generation clause B. 1 .b.2 (Reference 4) included provisions All actions required to protect the Class 1 EDegraded Voltage Company, for operator manual actions to restore bus voltage equipment from degraded voltage must beRelaying Design LLC on the Class 1 E distribution system. The RIS automatic in accordance with 10 CFRCalculations -specifically excludes manual load shedding under 50.55a(h)(2).Page 6, the Offsite/Onsite Design Interface Calculationswhereas the BTP allows for manual actions to Manual actions are allowed as stated inavoid separation from offsite power. Please clarify PSB-1, B.l.b.2 for improving the voltage inif manual actions taken to restore voltages now response to the alarm in control room thatrequire prior NRC approval, alerted the operator to the degradedcondition. However, to demonstrate theadequacy of onsite/offsite interface designand offsite power capacity and capability, asspecified in GL 79-36, manual load sheddingshould not be assumed.13 SUMMARY OF Exelon Under "DVR Setting Design Calculations," the RIS AgreeISSUES -1. Generation states in part "...would allow calculation ofDegraded Voltage Company, voltages at terminals or contacts of all safety RIS will be revised to just state "terminals"Relaying Design LLC related equipment with the voltage at the DVR and not "Contacts".Calculations -monitored bus at the DVR dropout setting:" It is notPage 6, clear what "contacts" are in this context. Itis assumed that the concern is motor control centercontactors and/or motor starting control circuits.14 SUMMARY OF Exelon Under discussion of DVR setting calculations, the DisagreeISSUES -1. Generation RIS states that setting cannot cause anyDegraded Voltage Company, degradation of the safety related components, The DVR ensures that voltage requirementsRelaying Design LLC including actuation of their protective devices, of the Class 1 E loads are always preservedCalculations -The BTP only stated damage to normally operating for operating the equipment under accidentPage 6, safety related equipment. The RIS language and non accident conditions including allseems broader then BTP and appears to open up abnormal operational occurrences.the position that the DVR studies have to considerstarting of loads under non-accident conditions.15 SUMMARY OF Exelon The DVR time delay seems to be considering Disagree.ISSUES -1. Generation operation down to LVR setting for evaluations. The point is that the DVR setting is based onDegraded Voltage Company, However, there is no discussion on LVR setting the voltage requirements of the equipment,Relaying Design LLC considerations in any original requirements or the which should equate to voltages on the gridCalculations -RIS. Under Guidelines for Voltage Drop well below normal. It is understood that gridPage 6, Calculations, the summary states that the plant- operating procedures should preventvoltage analysis, while supplied from the sustained voltages at such low levels buttransmission network, should be based on the regardless of what happens on the grid theoperating voltage range of the transmission DVRs will preserve the voltage limits for thenetwork connection. Grid operating voltage ranges equipment.do not allow operation down to levels that wouldcause sustained operation at LVR levels. Plant operation at LVR setpoint is notTherefore, consideration for operation at the LVR expected and is not within the scope of thesetpoint would be inconsistent with this guidance. RIS.The condition that occurred at Arkansas NuclearOne (ANO) in 1978 would appear to be related toinadequate operating procedures and a lack of arigorous analysis of the AC power distributionsystem. It would not be credible for present dayoperation. In addition, the operator would bealerted by an alarm on degraded voltage conditions(less than the analytical limit) as required byBranch Technical Position PSB- B.I.b.l.16 SUMMARY OF Exelon In Section "DVR Setting Design Calculation" Agree.ISSUES -1. Generation reference is made to 0.9 per unit voltage for(17 not DVR Setting Company, adequate operating voltage. This would only apply 0.9 per unit voltage was mentioned as anused) Design LLC for the most part to rotating equipment example and was not meant to coverCalculations -(motors). Motor Control Center (MCC) contactors, everything. RIS will be revised to deletePage 6 battery chargers, Motor Operated Valves references to specific numbers and(MOVs) all have less than a 90% operating voltage emphasize voltage requirements and voltagerequirement. This distinction should be requirements are plant-specific.made and/or clarified.18 SUMMARY OF Exelon The Degraded Voltage Relaying DesignISSUES -1. Generation Calculations section should include a statement to Agre No. Section of RIS Originator Specific Comment NRC ResolutionDVR Setting Company, emphasize that only steady state loading andDesign LLC steady state acceptable voltages at the class IE 0.9 per unit voltage was mentioned as anCalculations -equipment are to be considered in determining the example and was not meant to coverPage 6 DVR drop out settings including the allowable everything. RIS will be revised to deletetolerances. The paragraph does mention 0.9 per references to specific numbers andunit voltages at the terminals which is steady state emphasize voltage requirements and voltagebut a positive statement about steady state loading requirements are plant-specific.and steady state acceptable voltages would behelpful. Also, there are alternatives to the 90% The suggested analysis may be acceptable ifterminal voltage criterion. The concern is heating, properly developed and supported in thecausing a temperature rise, which decreases useful design. The 90% voltage criteria may not belife of the insulation. Inspectors may read too much adequate for certain components such asinto the 90% criterion; a motor loaded to less than SOVs, motor control center contactors, etc.nameplate will draw less than service factor currentat a lower terminal voltage. Therefore, a lowervoltage would prove adequate as long as adequatetorque is available.19 SUMMARY OF Exelon MOVs are not steady state loads. MOVs have Disagree.ISSUES -1. Generation traditionally been considered transient loads and,DVR Setting Company, therefore, not included in the steady state voltage MOVs should be addressed specifically andDesign LLC analysis. GL 89-10 (Reference 3) programs the DVR settings must support adequateCalculations -perform these calculations. A statement in this voltages for all Class 1 E equipment includingPage 6 section that MOVs loads are not to be considered MOVs.in this calculation will be helpful if NRC agrees withthis interpretation20 SUMMARY OF Exelon The starting voltage requirement is unclear. Some Disagree.ISSUES -1. Generation sites have evaluated the capability of starting eachDVR Setting Company, required safety related motor individually at the The intent of the RIS is not to prescribe DVRDesign LLC degraded voltage analytical limit. Other sites use a relay setpoint methodology for every plant.Calculations -"block start analysis" where multiple motors arePage 6 started simultaneously on the offsite source. There The RIS provides the conditions for whichhave been violations associated with both plant specific analyses should be performed.approaches. The RIS should describe an The specific design of the plant dictates theacceptable methodology for determination of motor type of analyses required to demonstratestarting voltage adequacy. adequacy of DVR setting. If the plant designrequires load sequencing on the offsitesource, then individual motor start is theappropriate methodology. If the plant designrequires block starting accident loads, thenthe DVR setpoint should be based onmultiple motor starts.21 SUMMARY OF Exelon The RIS implies this portion of the calculations DisagreeISSUES -1. Generation require that the licensee demonstrate that all NRC staff disagrees with the interpretation.DVR Setting Company, class IE motors can be started with the voltages The staff agrees that a grid voltage 'freeze'Design LLC just above the analytical limit of the DVR corresponding to the DVR selpoint and aCalculations -setpoint. However, with voltage just above the DVR subsequent motor start will eventuallyPage 6 drop out value, any load addition (starting or separate the plant from offsite source as therunning) will result in separating from the offsite voltage will not recover to reset the DVR.source if no credit for external voltage controlling The 1977 NRC letter states that "voltage andequipment is taken. Therefore, the purpose of this time setpoints shall be determined from anrequirement is not clear. The intent of the starting analysis of the voltage requirements of thevoltage evaluation should be clarified, safety related loads". Safety related (Class1 E) equipment, particularly large motors,Some stations have evaluated the performance of have starting and running "voltageprotective devices during degraded grid conditions requirements".by mechanisms other than calculations (e.g.,technical evaluations or computations). It is When grid voltages are degraded (such assuggested that the NRC add a statement for resulting in Class 1E bus voltages downacceptability of the same. close to where DVRs are set based on Class1 E equipment requirements), and the griddoes not automatically recover, separationfrom the grid is appropriate. The DVR isexpected to reset after a perturbation ofsustained duration when automatic actionssuch as clearing the grid 'fault' that resultedin degraded voltage conditions.The NRC staff will accept standard industrypractices to evaluate performance9 No. Section of RIS Originator Specific Comment NRC Resolutioncapabilities of DVR. Analyses supported bycalculation should clearly and succinctlydefine plant design basis and compliancewith regulation.22 SUMMARY OF Exelon Under Offsite/Onsite Design Interface Calculations, Agree.ISSUES -1. Generation Guidelines for voltage drop calculations itemDVR Setting Company, 2, i), the acceptance criteria for demonstrating RIS Section 2 (i) will be modified to state: ForDesign LLC voltage adequacy would appear to be DVR each case evaluated, the calculated voltagesCalculations -Maximum Pickup (the voltage required to assure on each safety bus should demonstratePage 6 relay reset) and not component level voltage adequate voltage at the safety bus and downvalues, to the component leveL It is based on Class1 E component terminal voltagerequirements.23 SUMMARY OF Exelon Item 2 (Offsite/Onsite Design InterfaceISSUES -2. Generation calculations) appears to be additional requirements DisagreeOffsite/Onsite Company, for those sites licensed to the Standard ReviewDesign Interface LLC Plan (NUREG 0800) Chapter 8 Appendix A Branch RIS highlights the guidelines provided in GLCalculations Technical Position PSB-1, "Adequacy of Station 79-36 and NUREG 0800, Chapter 8Electric Distribution System Voltages." Appendix A BranchTechnical Position PSB-1, "Adequacy ofStation Electric Distribution SystemVoltages.". There are no new requirements24 SUMMARY OF Exelon Page 7- The phrase "...all operating configurationsISSUES -2. Generation of transmission network and plantOffsite/Onsite Company, systems..." appears in a few sentences. The stationDesign Interface LLC interface agreement with the transmissionCalculations provider integrates the considerations among the Disagree.transmission network, the operability of theoff site sources, and the voltage regulation (drop) This is addressed in RIS Section 2 a.calculations. The calculations identify certaincontrolling parameters for the transmission As discussed in GL2006-02 "Grid Reliabilitynetwork. These controlling parameters are then and Impact on Plant Risk and the Operabilityincorporated into the Bases for the operability of of Offsite Power", licensees are required tothe offsite source(s). If the plant configuration provide the transmission system operatoror transmission network parameters are not (TSO), the operating voltage parametersbounded by the calculations, then the operability of required by the plant during all modes ofthe offsite sources needs to be examined. In most operation. The analyses discussed in thiscases, the plant operator has no control over comment should be the bases for thethe "configuration" of the transmission network, but information provided to the TSO.does have agreements with the transmissionsystem operator that normal operating voltages The DVR protects the safety relatedand post unit trip contingency voltages are equipment when a perturbation in the gridcontrolled within established bounds. Add a few system results in degraded voltagesentences detailing that the intent of the conditions and the normal operatingphrase "all operating conditions of the transmission parameters cannot be restored immediatelynetwork" means that the controlling to protect safety related equipment. Theparameters from the transmission network that are DVR setpoint evaluation should be aused in the calculations are consistent with separate analysis.those utilized in the Bases for operability of theoffsite sources.25 SUMMARY OF Exelon Page 7, item a) -Change the last sentence to readISSUES -2. Generation "... include voltage drop due to all Disagree.Offsite/Onsite Company, transmission system contingencies that are a directDesign Interface LLC result of the transient or accident being A transient grid perturbation may be a resultCalculations analyzed (typically this will include tripping of the in a plant trip. The DVR setpoint should benuclear power unit)." based on bounding voltage resulting from atransient grid condition. The actual reasonfor the perturbation is not a consideration. Aplant trip may result in limiting conditions forDVR setpoint calculation.26 SUMMARY OF Exelon Page 7, item a) -Either add to a) or add anotherISSUES -2. Generation section immediately after a). "The transmission Agree.Offsite/Onsite Company, system controlling parameters are assumed toDesign Interface LLC remain unchanged throughout the initial stages of RIS will be revised to state a): The unit trip10 No. Section of RIS Originator Specific Comment NRC ResolutionCalculations the event with the exception of those effects grid contingency voltage drop value shouldresulting from the event (contingency due to the be used in the accident cases in accordanceloss of the unit). For purposes of the calculation, with the plant accident analyses since a unitthe Unit trip contingency can be coincident with the trip occurs with an accident.accident, or at a later time consistent with theassumptions in the plant accident sequenceanalyses."27 SUMMARY OF Exelon Page 7, item b) -Delete the tabulation of sourcesISSUES -2. Generation of power to the emergency buses and replace with Disagree.Offsite/Onsite Company, a simple statement of "all credited sources of offsiteDesign Interface LLC power to the emergency buses." The recommendation does not change theCalculations intent of the tabulation. To maintainconsistency with GL 79-36, it is preferable tomaintain the tabulation.28 SUMMARY OF Exelon Page 8, item c) -Change to read: "(1) anISSUES -2. Generation accident in the unit being analyzed and shutdown Disagree.Offsite/Onsite Company, of all other units at the station consistent with theDesign Interface LLC licensing basis of the station; ... in the unit The RIS is consistent with GL 79-36.Calculations being analyzed (e.g., unit trip) and shutdown of all The licensing basis of multi-unit sites has toother units at that station consistent with the be uniquely considered.licensing basis of the station, whichever representsthe largest load situation." Typically, thelicensing basis for multi-units site allow for anorderly shutdown of the unit not being analyzed,and do not require a "simultaneous" shutdown.29 SUMMARY OF Exelon It is recommended that the NRC provide a positiveISSUES -2. Generation statement for allowing the credit for voltage Disagree.Offsite/Onsite Company, controlling equipment external to the class IEDesign Interface LLC equipment for this calculation. Licensees perform Use of LTCs is acceptable for regulatingCalculations LOCA load sequencing under this section of the voltage during normal plant operation. LTCscalculations and take credit for LTCs (or other do not afford protection during a transientvoltage regulating devices) to demonstrate the degraded voltage condition that can affectadequacy of the offsite sources. In addition, operation of redundant equipment,please clarify if MOVs are to be modeled during The following changes will be incorporated inthis scenario, even though it appears from the the RIS: Add the following in section 2RIS that MOVs and other equipment like contactors (general) and d.are to be evaluated with voltages obtained from theDegraded Voltage Relaying Design Calculations All actions the electric power system iswith voltage just above the lowest set point of DGV designed to automatically initiate or controlrelays. should be assumed to occur as designed(e.g., automatic bulk or sequential loading orautomatic transfers of bulk loads from onetransformer to another, automatic starts ofcomponents, operation of automatic voltagecontrolling equipment, etc.,)Yes. All equipment including MOVs,contactors, solenoids, etc., should beevaluated for adequate voltage based on theDVR set point.30 SUMMARY OF Exelon Under Item a), for units with LTCs, please clarify ifISSUES -2. Generation the analysis is to be performed with the grid DisagreeOffsite/Onsite Company, at minimum expected voltage, maximum expectedDesign Interface LLC voltage, or at both. See Question 29.Calculations Analyses for normal operation shouldevaluate effect of LTC operation at theextreme settings for impact on operatingequipment. DVR setpoint should be basedon minimum voltage required for operation ofaccident mitigation loads. For units withLTCs, it is unlikely that voltage correctioncan be achieved within the short time it takesfor contactors to drop out or fuses to blowduring a sustained degraded voltage orovervoltage condition.31 General Exelon In general the clarifications contained in the draftGeneration RIS appear to be more restrictive and Disagree.1I No. Section of RIS Originator Specific Comment NRC ResolutionCompany, prescriptive than the cited historical regulatoryLLC documentation, and do not support plant unique Unique designs that may have beendesign and current licensing bases that have been previously 'accepted' should havedeveloped and accepted in previous licensing appropriate justification with NRC approval ofactivities. Unique design and licensing bases that the licensing documents. Typically, detailedhave previously been accepted and calculations have not been reviewed as partapproved that may not be strictly aligned with the of Technical Specification changes. The staffdarifications in the draft RIS may include use has relied on licensee correspondenceof an inverse time under voltage relay set between stating adequacy of DVR setpoint to approvethe DVR and LVR relays (such as .875 to license amendment requests. Onsite0.70 PU for a maximum of 60 seconds). Some inspections are used to verify analyticalsites may not provide coincident logic to methods used to meet regulations.preclude spurious trips: rather, the logic mayinclude alternate design features to conform to the Alternate methods used to demonstrateintent of the requirements of BTP PSB-1. conformance may be acceptable providedthey meet the intent of BTP PSB-1 to protectsafety related equipment32 SouthernGeneral Nuclear AgreeOperating Include a definition of key terms (ex. Normal gridCompany operation, sustained degraded voltage) Additional clarifications will be provided inthe RIS wherever appropriate.33 General Southern The RIS does not address completely the specificNuclear requirements in the PSB-1 (ADAMS Accession No. DisagreeOperating ML052350520). Arkansas Nuclear One (ADAMSCompany Accession No.ML0311801180), and Millstone The RIS covered the key topics intended to(ADAMS Accession No. ML093521388) address inspection findings.documents. In some cases specific positions inthe above documents were omitted from the RIS. The reference documents should bereviewed for more details.Proposed resolution: include missing positionsespecially those related to determining minimum The expected offsite system voltages canexpected offsite system voltages and testing, vary between G-110 percent. The objective ofthe LVR and DVR is to afford protection andseparation from the grid when plant specificneeds cannot be satisfied.34 General Southern The RIS lacks adequate guidance to perform theNuclear requested calculation(s) without additional DisagreeOperating interpretations by the licensee and auditors as toCompany the intent of the provided guidance. The RIS is consistent with GL 79-36. Thelicensee is responsible for performingProposed resolution: Provide a guideline with calculations, in accordance with industryexamples on how to perform the calculation(s) engineering practices, with properlyincluding expected assumptions, other supported inputs and assumptions thatconsiderations, and criteria to be used for demonstrate compliance in accordance withacceptance. 10 CFR Part 50. Appendix B. Criterion I11.The RIS addresses certain problem areasidentified mainly through NRC inspectionsand to re-emphasize the existing NRCrequirements and staff positiooiuidance.35 General Southern The RIS provides some examples of plants thatNuclear have NRC reviewed and approved analyses and DisagreeOperating goes on to point out that "backfit rule" was appliedCompany because the staff believed the sites were not in The licensee must be in compliance with allcompliance with regulations even though they had regulations pertaining to onsite and offsiteapproved the analysis. How is a licensee who has power systems. Unless, licensees arean NRC approved or acceptable analysis supposed exempted from meeting certain regulatoryto know that their analysis is no longer acceptable? requirements, changes to the design andThe RIS needs more clarification with regard to licensing bases are required to meet theindividual plant licensing bases if it is to be useful regulations in accordance with 10 CFRto licensees. 50.109. The RIS identified some of therecent inspection findings.Some plants have installed degraded grid alarmsystems and, at the staff request, included them inUnit Operating Technical Specifications. Required Operator actions could be used only to12 No. Section of RIS Originator Specific Comment NRC Resolutionoperator actions related to degraded grid supplement the automatic DVR scheme byconditions are specified in the bases and providing alarm in the control room when gridprocedures. The RIS does not discuss this voltage is below nominal operating range.approach. Operator actions cannot be substituted forprotecting the safety related equipment fromThere are a number of plants that have URIs degraded voltage. 10 CFR 50.55a(h)(2)related to this issue. Issuance of this RIS could be requires all protective actions to beused by inspectors to close the URIs to violations automatic.without regard to plant specific licensing bases,resulting in regulation by inspection. The intent of the RIS is to highlight the basisfor DVR requirements and preclude futurefindings in plant designs. The RIS does notprovide new guidelines for issuing violations.36Summary ofIssues", pg. 6,Item 1. "DegradedVoltage RelayingDesignCalculations",Line 5.SouthernNuclearOperatingCompanyThe RIS states "The Class 1 6 buses shouldseparate from the offsite power system within a fewseconds if an accident occurs coincident withsustained degraded voltage conditions."GDC 17 describes the requirements for onsite andoffsite power systems. One of its requirements isthat they each provide sufficient capacity andcapability to mitigate postulated events. The eventsare described in Chapter 15 "Accident Analysis".These analyses assume Loss of Offsite Powersimultaneous with the event. They do not requireassuming degraded grid voltage condition prior toan event occurring. In addition because of FERCand NERC requirements for voltage control, thelikelihood of a chapter 15 accident occurringconcurrent with a serious degraded grid voltagecondition is not believed to be credible.Proposed resolution: Remove or clarify thisstatement since proper offsite system design andoperation renders such simultaneous postulatedevents as incredible.Disagree.The RIS correctly states that if an accidentsignal is received during sustaineddegraded grid conditions, it may be prudentto separate from the grid as :1. The duration of degradedconditions on the grid is unknown2. It precludes other complicationssuch as double sequencing.Chapter 15 "Accident Analyses" assumes"Loss of Offsite Power" as a limiting case forsafe shutdown in view of the limited powerand resources available from the onsitepower sources. The preferred power sourcefor all operating modes and accident relatedsafe shutdown is the offsite source. TheDVR provides assurance that the plantshutdown capability is not compromisedwhen the offsite source is degraded and afast transfer can occur to the onsite sourcesif the offsite source does not recover withinthe allotted time. This preserves the Chapter15 accident analyses.NERC and FERC requirements for voltagecontrol are beneficial to nuclear plantoperators as they provide assurance thatgrid parameters will be maintained withinacceptable limits for normal nuclear plantoperations. However, the transmissionsystem is always vulnerable to perturbationssuch as line outages, overload conditions,generation shortages etc. which are beyondthe control of the grid operator. Themagnitude and duration of theseperturbations cannot be predicted. Thesafety of the nuclear plant must not becompromised during these conditions. Thefunction of the DVR is to protect redundantsafety related equipment during these gridperturbations.The staff considers degraded voltagecondition and coincident LOCA can occur.Until the DVR relay takes automatic action,the offsite power is considered to haveadequate capacity and capability. Therefore,the accident analysis assumption for a LOCAwith offsite power available applies.37 Summary of Southern The RIS states "During normal plant operation, the TIssues", pg. 6, Nuclear Class 1 E safety related buses should Disagree.Item 1. "Degraded Operating automatically separate from the power supply I13 No. Section of RIS Originator Specific Comment NRC ResolutionVoltage Relaying Company within a short interval (typically less than 60 See staff's response to Comment No. 9Design seconds) if sustained degraded voltage conditionsCalculations", are detected."Line 7 Voltages down at the DVR level should beDuring normal plant operation (i.e. non LOCA), the well below the normal grid voltage levels.degraded gdd relay settings may be overly Transmission operators will be taking actionsconservative. Therefore automatic separation from when voltages fall below the normal low levelthe preferred power supply may not be desired. (or post contingency low) well above theDVR value (assuming the plant design isProposed resolution: Transmission Operators proper given the grid operating voltageshould be allowed time to correct the degraded range).voltage condition while Plant Operators monitor thesafey bs vltaes or aequte oltge. The plant electrical distribution systemsafety bus voltages for adequate voltage, design should be based on the grid voltagerange including the bounding worst case gridcontingency (strong or weak grid dependingon which one is bounding). In this way, theplant's design ensures adequate voltage toplant equipment as long as grid is operatingas "expected".GDC 17 requires that offsite power hassufficient capacity and capability to assurethat (1) specified acceptable fuel designlimits and design conditions of the reactorcoolant pressure boundary are not exceededas a result of anticipated operationaloccurrences, and (2) the core is cooled andcontainment integrity and other vitalfunctions are maintained in the event ofpostulated accidents.38 Summary of Southern The discussion on time delays does not provideIssues, Last Nuclear adequate criteria for time delay selections. Disagreeparagraph of Operating"DVR criteria for Company Proposed Resolution: Clarify. The acceptable level of time delay is basedtime delay on plant specific accident analyses andselections. The RIS states " In this manner, the DVR ensures electrical systems designs.Setting Design Different time delays may be selected forCalculations", pg. adequate operational (starting and running) voltage different plant designs. BTP PSB-1 suggests7 to all safety related equipment, independent ofvoltage controlling equipment external to the plan two relays with different settings topat accommodate motor starts and sustainedsafety related electrical distribution system. For the degraded conditions. Typically, chapter 15purposes of this calculation, no t credit should betaken for voltage controlling equipment external to accident analyses assume 10 second timethe las 1Edisribtio sysem uchas utoat. delay for onsite power sources to energizethe Class 1 E distribution system such as automatic safety busses. DVR time delay of 1 Osecondsload tap changers and capacitor banks." or less may be acceptable to demonstrateProposed Resolution: This statement needs to be that the assumptions in the accidentclarified to allow reasonable assumptions for the analyses remain valid.status of equipment external to the Class 1 E External voltage regulating equipment (tapdistribution system. For example it is unclear how changers) does not afford timely protectionto perform motor starting calculations without for safety related equipment during suddentaking credit for some Non I E voltage controlling grid perturbations and therefore cannot beequipment. Additionally, normal Transmission grid credited for DVR settings including transientswitching to prepare for the next contingency tomaintain.minimum expected transmission system voltages during motor starts.voltages should be allowed.See staffs response to Comment Nos. 76and 118.39 Summary of Southern After paragraph (f) the RIS leaves out the guidance DisagreeIssues, Guidelines Nuclear in GL 79-36 concerning minimum expected valuesfor voltage drop Operating (item 6 of enclosure 2) was omitted from the RIS Item 6 was addressed in item(a) in the RIScalculations, item Company guidance.(f) pg. 8Proposed resolution: Add item 6 of enclosure 2 inGL 79-36 to the RIS.40 General NEI 3/2/11 NEI contends that RIS represents new positions14 No. Section of RIS Originator Specific Comment NRC ResolutionLetter DisagreeThe RIS provides clarifications to avoid themisconception of the existing requirementsand NRC staff peititnisuiance,No new requirements are identified in theRIS.41 NEI 3/2/11 77 Letter and PSB-1 Not consistent. DegradedLetter voltage event and accident coincident vs. Disagreesubsequent. Also, starting and running voltage vs. PSB just states how the scheme shouldjust running (term sustained in PSB-1) react to a subsequent degraded voltage.The 77 letter indicates that the time delayshould support the accident analysis whichmeans coincident events.42 NEI 3/2/11 77 Letter and 79 GL are generic communicationsLetter Both communications provide guidance onnot requirements how to meet regulatory criteria. To thatextent, they are related to compliance withregulations, but are not themselvesregulatory requirements.43 NEI 3/2/11 Multi-unit sites, accident and simultaneousLetter shutdown vs. orderly shutdown and cooldown per DisagreeGDC 5 This RIS is consistent with GDC 17, GL 79-36, and IEEE Standard 308-1971, "Class IEElectrical Systems," Section 8, "Multi-UnitStation Considerations44 NEI 3/2/11 During normal plant operation, a degraded voltageLetter for 60 seconds resulting in separation doesn't give Disagreethe operator enough time (implied by PSB-1) to See NRC response to Comment No. 9.take actions45 NEI 3/2/11 Offsite/Onsite design interface calculations doesn'tLe- 48 allow for manual actions Disagreesot This means that manual actions for theused)purposes of analyses of the offsite power8dso system voltages should not be assumed.seeNos See GL 79-36 for more details.86-96 PSB-1 allows manual actions after first alarmfor this at higher voltage.NE,Len.,49 Page 6, DVR Jerry Nicely Section DVR Setting Design Calculations states: DisagreeSetting Design At the DVR dropout setting .the DVR ensuresCalculations adequate operational (starting and running) voltage See Responses to Questions 1 & 2.to all safety related equipment, independent ofvoltage controlling equipment external to the plant 'Sustained' in the context that the loss ofsafety related electrical distribution system. voltage relay was designed for momentarydip in voltage or complete loss of voltage.BTP PSB-1 states, "sustained", implying a steady Steady state operation is expected at normalstate voltage condition and not a transient voltage operating band.condition that exists during a motor starting event.The 1977 NRC letter states that "voltage andThe original 1977 NRC Letter, the later PSB-1, or time setpoints shall be determined from anGL 79-36 does not require plants to demonstrate analysis of the voltage requirements of thethe ability to start motors at the DVR settings, safety related loads." Safety relatedequipment, particularly large motors, haveRequiring the ability to start motors at the DVR starting and running "voltage requirements."dropout setting does not accomplish anything or This second level of protection shouldmake sense, since starting a motor at this voltage address these "voltage requirements."will ensure a resultant voltage below the DVR Sustained degraded voltage, as discussed indropout; result in not being able to be reset the the 1977 NRC letter, refers to grid voltagerelay, and as a result causing a spurious below the expected low value given normaldisconnection from offsite power and transferring to grid operation and grid post contingency15 No. Section of RIS Originator Specific Comment NRC Resolutionthe emergency diesel generator. Having a (Single, N-i). Thus, when grid voltages arerequirement to be able to start motors at the DVR degraded beyond the minimum voltagedropout setting will result in the raising the DVR assured by the grid operator(such assettings to a higher value and is more likely to resulting in SR bus voltages down close toresult in spurious separation from the grid which is where DVRs are set based on SR equipmentin direct conflict with PSB-1. requirements), separation from the grid isappropriate. Proper design of the plantelectrical distribution system and setting ofthe DVRs, based on the grid voltage range(described above) should provide propermargin such that spurious separation fromthe grid should not occur.The key point is that the voltage setting(s)selected should ensure that adequatevoltage is available at the componentterminal(s) to operate the most limitingcomponent (s) at a plant during the mostlimiting design basis event. The offsite/onsiteinterface calculation should show that, withthe grid at the lower limit of the normaloperating range, voltage at the safety bus isalways well above the degraded voltagesetpoint for all design basis event loadingconditions (normal, abnormal and accidentconditions including anticipated operationaloccurrence).50 Page 5, Peach Jerry Nicely In the RIS section of recent inspection findings forBottom Peach Bottom, it was stated that since the load tap Agreechangers are not safety-related and are subject tooperational limitations and credible failures, they The finding is correct.cannot be relied on.The safety related equipment should beprotected by Class1 E relays and notdependent on non safety LTCs functioning.The DVR action is independent of LTCaction. Therefore, no credit should be takenfor determining the setpoint of DVR relay.The response time of tap changers isrelatively slow. Redundant safety relatedequipment may be exposed to degradedvoltage conditions that can last for minutesdepending on tap changer response time.51 Page 8, c) Jerry Nicely In the Offsite/Onsite Design Interface Calc section(C) it states: an accident in the unit being analyzed Disagreeand simultaneous shutdown of all other units at thestation. For electrical system, the statement in theRIS is consistent with GDC 17, GL 79-36,RG 1.81 states: The Regulatory staff has and IEEE Standard 308-1971, "Class IEdetermined that, because of the low probability of a Electrical Systems," Section 8, "Multi-Unitmajor reactor accident, a suitable design basis for Station Considerations.multi-unit nuclear power plants is the assumptionthat an accident occurs in only one of the units at atime, with all remaining units proceeding to anorderly shutdown and a maintained cooldowncondition; 10CFR50 App A Criterion 5 states: .. inthe event of an accident in one unit, an orderlyshutdown and cooldown of the remaining units;NUREG 0800 Section 8.2 states: ..... in the eventof an accident in one unit, with a simultaneousorderly shutdown and cooldown of the remainingunits. Based on the above Regulatory positions,the RIS should consider rewording theI__I_"simultaneous shutdown" to "orderly shutdown".52 Page 6, DVR Larry This paragraph could be interpreted to require theSetting Design Nicholson, LOCA sequence to be modeled at the DVR dropout DisagreeCalculations Nexterra setting. LOCA sequencing modeled at the DVR16 No. Section of RIS Originator Specific Comment NRC Resolutiondropout setting would result in separation of the See response to questions 1 &2buses from the Preferred Power Source (off-sitepower) as the voltage would not recover above the The sustained degraded voltage conditionsDVR reset value, are not expected to last the total sequencingprocess. The analyses should demonstrateProposed Resolution: Clarify the intent to show that the largest load (limiting case) forsafety related equipment will function at the accident mitigation can be successfullyselected DVR dropout setting voltage and that it is started under degraded grid conditions andnot expected to start the LOCA sequence from this the loads that are normally operating will notvoltage level, be adversely impacted. It is expected thatthe grid will either recover to nominal voltageClarify that LOCA sequencing is evaluated using and reset the DVR for the rest of theminimum switchyard voltage as the starting point, sequencing process or the DVR will separatethe plant from source that cannot supportsafe shutdown.53 Page 6, DVR Larry Having a sustained degraded voltage just aboveSetting Design Nicholson, the LVR voltage setling (70%) is not practical AgreeCalculations Nexterra without grid collapse and does not exist in BranchTechnical Position #1 (PSB-1). Although undervoltage protection (first level)is not within the scope of the RIS, theProposed Resolution: Clarify degraded voltages to licensees' analysis should ensure that thebe analyzed to a credible level. LVR and DVR settings protect the Class 1Ecomponents from voltage ranges betweenthe DVR and LVR settings due to sustaineddegraded conditions.54 Page 6, DVR Larry The statement that the DVR ensures adequateSetting Design Nicholson, operational (starting and running) is the first time inCalculations Nexterra NRC correspondence that starting equipment at Disagreethe DVR setpoint is expected. The example lettersent to Peach Bottom in June 1977 did not require The NRC 1977 letter states that "voltage andstarting of equipment at the DVR setpoint. This time setpoints shall be determined from anrequirement should be removed from the RIS since analysis of the voltage requirements of theit is not possible to start equipment at the DVR safety related loads". Safety related (Classsetpoint and not subsequently separate from offsite 1 E) equipment, particularly large motors,power. If the equipment starts at the DVR setpoint, have starting and running "voltagethe voltage will dip during the transient and must requirements". This second level ofthen recover above the reset point to avoid undervoltage protection should addressseparation from offsite power. Since the reset point these "voltage requirements"will always beabove the DVR dropout point it willbe impossible to reset the relay.Proposed Resolution: Remove starting equipmentat the DVR setpoint as a requirement.55 Page 7, DVR Larry It is agreed that no credit is to be taken for voltageSetting Design Nicholson, controlling equipment external to the Class 1 E AgreeCalculations Nexterra distribution system for the establishing thedegraded voltage relay (DVR) settings; however, it Grid Interface calculations can take credit forshould be clarified that for credit may be taken for voltage correction equipment. The DVRminimum switchyard voltage/voltage drop setpoint should be set independent ofcalculations (or the Offsite/Onsite Design Interface voltage correction equipment that cannotCalculations). operate'in a timely manner to protect 1Eequipment. RIS will be clarified regardingProposed Resolution: Clarify that credit must be crediting voltage controlling equipmenttaken for automatic load tap changers and/or external to the 1 E system for Offsite/Onsitecapacitor for minimum switchyard voltage/voltage Design Interface.drop calculations (or the Offsite/Onsite DesignInterface Calculations).56 Page 8, c) Larry NRC Generic Letter 79-36, Enclosure 2, Item 2Nicholson, states that "For multi-unit stations a separateNexterra analysis should be performed for each unitassuming (1) an accident in the unit being analyzedand simultaneous shutdown of all other units at thestation; or (2) an anticipated transient in the unitbeing analyzed (e.g., unit trip) and simultaneous17 No. Section of RIS Originator Specific Comment NRC Resolutionshutdown of all other units at that station,whichever presents the largest load situation."Comment:NRC Draft RIS re-states NRC GL 79-36 verbatim, Disagreewith an attempt to clarify "anticipated transient" byadding in parenthesis "(anticipated operational Anticipated Operational Transient is a moreoccurrence)" immediately afterwards. It is not clear general term for operational events per thewhat the added parenthetical statement is meant to design except for design basis accidentsconvey, other than unit trip (which already exists in This is consistent with the term used in GDCGL 79-36). 17.Proposed Resolution: It is recommended that thiseither be removed, or stated "anticipated transientper station licensing basis".57. Page 8, c) Larry NRC should clarify "simultaneous shutdown" withNicholson, consideration to:NexterraMost multi-unit station's Licensing Basis consideran "orderly or controlled safe shutdown" of theother unit(s) not being analyzed.NERC Std TPL-004-0; particularly Category Devents per Table 1, where a "loss of all generatingunits at a station" may result in "portions or all ofthe interconnected systems may or may notachieve a new, stable operating point'.IEEE Std 308-1974, Clause 8, subclause 8.1.1 Disagree"Capacity" describes this as a "concurrent safeshutdown on the remaining units".This statement is consistent with GDC 17,Proposed Resolution: The wording for the GL 79-36, and IEEE Standard 308-1971,proposed RIS, sub clause 2.c should be revised to "Class IE Electrical Systems," Section 8,indicate "orderly or controlled safe shutdown of the "Multi-Unit Station Considerations.remaining units, as per the station's licensingbasis" instead of "simultaneous shutdown".Alternatively, the wording "shutdown consistentwith the station licensing basis" could be usedinstead of "simultaneous shutdown".58 Page 8, e) and f) Larry These guidelines seem contradictory that youNicholson, cannot credit procedurally controlled operator DisagreeNexterra actions to reduce load but you have to assume theactions will be carried out when load is added. Adding loads manually per procedure isconservative in terms of maximum loading,Proposed Resolution: Delete "e) Manual load but not for load reductions. Plant designshedding should not be assumed" or add should not depend on manual load shedding.allowance to credit procedurally controlled operator This is not conservative. That was the pointactions to decrease load. of item e).But General NEI 3/18/11 The RIS should identify that plant compliance withnot59 Letter / 1 the regulation (GDC 17) is by each plant operating Agreewithin its Licensing Basis.Second level undervoltage protection(degraded voltage protection) applies to alloperating plants whether the plant is GDC orpre-GDC plant.60 General NEI 3/18/11 Definitions vary for the same words used withLetter / 2 respect to this topic. AgreeThe RIS should include definitions for key terms, Clarifications will be provided in the RISe.g. normal grid operation, sustained degraded wherever appropriate.voltage, etc.18 No. Section of RIS Originator Specific Comment NRC Resolution61 General NEI 3/18/11 There are various documents that address theLetter 1 3 Adequacy of Station Electric Distribution System DisagreeVoltages. These documents have differences in themethodology, terminology, and level of detail. Such The RIS provides adequate clarifications todifferences challenge the users of these guidance the existing guidance.documents when they conflict.The staff positions described in the NRCAttachment 2 to the NEI supplemental comment 1977 letteris-are guidance for all licenseesletter provides a table that shows the differences as to how to meet GDC 17 or applicablebetween GL 79-36, (BTP) PSB-1, IEEE 741, and plant's principle design criteria. This letterthe draft RIS. focuses on the need for a second levelundervoltage protection scheme to protectThe RIS should identify the guidance document the Class 1 E electrical components from thedifferences, establish the NRC position on each consequences of sustained degradedconflicting topic, and provide the basis for each voltage conditions.change in previously accepted guidance.GL 79-36 emphasizes the electrical designattributes to be considered for the interfaceof onsite and offsite distribution systems toensure adequate voltages to the Class 1 Ebuses and safety related components fornormal, abnormal, and accident conditions tocomply with GDC 17 or applicable plant'sprinciple design criteria requirements.BTP PSB-1 incorporates both-the aboveetat/-peit.ioe guidance to meet GDC 17requirements.IEEE 741 is only referenced in the SRP. TheNRC has not endorsed this industry________________________________________________ uidance.62 Page 1,3' NEI 3/18/11 "The U.S. Nuclear Regulatory Commission (NRC)paragraph Letter / 4 is issuing this Regulatory Issue Summary (RIS) toclarify the NRC staff's technical position on existingregulatory requirements and voltage studiesnecessary for Degraded Voltage Relay (secondlevel undervoltage protection) setting bases andTransmission NetworkWOffsite/Onsite stationelectric power system design bases."No regulatory requirements are referenced exceptfor a generic reference to GDC 17.Reword the paragraph to read: Agree'The U.S. Nuclear Regulatory Commission (NRC)is issuing this Regulatory Issue Summary (RIS) to The RIS will be revised to incorporate thisclarify the NRC staffs technical position on comment.Degraded Voltage Relay (second levelundervoltage protection) setting bases andTransmission NetworkJOffsite/Onsite stationelectric power system design bases appropriate formeeting the regulatory requirements specified inGDC 17.'63 Page 2, NEl 3/18/11 "The selection of voltage and time delay setpointsParagraph a) Letter /5 shae/ be determined from an analysis of theoperating voltage requirements of safety relatedloads at alf onsite system distribution levels"Requirements for DVR settings have never usedthe term "operating voltage". They instead used Disagree in part."sustained voltage" which by definition would besteady state voltage, running voltage, or voltage Voltage requirements -all voltageheld at a constant value requirements of SR equipment(BTP) PSB-1 and BTP 8-6 are silent on The term "operating" voltage is beingoperating/running voltage in the DVR settings removed from the RIS as recommended.section; however, running is implied by using the I19 No. Section of RIS Originator Specific Comment NRC Resolutionterm "sustained" in the Time Delay settings section. The term sustained voltage used in the 1977letter and the BTPs is referring to the voltageTo be consistent with (BTP) PSB-1, NRC letter, condition on the grid, not steady stateand BTP 8.6 remove the word "operating". voltage64 Page 3, Arkansas NEI 3/18/11 "...assuming all onsite sources of AC powerare notNuclear One Letter / 6 available, the offsite power system and the onsitedistribution system is of sufficient capacity andcapability to automatically start as well as operateall required safety related loads."This sentence implies that the NRC use of the term"operate" does not mean the same thing as 'start'. Agreei.e., operate/start/running are not synonymous. NEIsupports this interpretation; however, it conflictswith the words "proper voltage for starting andrunning in all operational configurations" in the 1st The term operating voltage is being removedparagraph of page 6. from RIS.65 Page 6, 1' NEI 3/18/11 "...components are provided adequate voltageParagraph Letter /7 based on the design of the Class 1E distributionsystem in the plant and its most limiting operatingconfiguration."There is a need to better define "most limiting Agree.operating configuration", since experience showsthat a component is most limiting. RIS will be revised to state the following:Reword the RIS to: "... all safety related components arec...Components are provided adequate voltage provided adequate voltage based on thebased on the design of the Class 1 E distribution design of the plant power distribution systemsystem in the plant.' (and the offsite circuits), including the designof the Class 1E distribution system in theplant and its most limiting operatingconfiguration(s)."Operating configurations affect limits as wellas components.66 Page 6, 1` NEI 3/18/11 "The Offsite/Onsite Design Interface Calculationsparagraph Letter 1 8 specify the voltage operating parameters of theplant electrical distribution system based on thetransmission system (Offsite) operatingparameters."This paragraph could be interpreted to require the DisagreeLOCA sequence to be modeled at the DVR dropoutsetting. LOCA sequencing modeled at the DVRdropout setting would result in separation of the This sentence is not referring to calculationsbuses from the referred Power Source (off-site for setting the relays but referring topower) as the voltage would not recover above the Offsite/Onsite Design Interface Calculations.DVR reset value.The RIS should state that the intent is to showsafety related equipment will function at theselected DVR dropout setting voltage and that it isnot expected to start the LOCA sequence from thisvoltage level. The RIS should state that LOCAsequencing is typically evaluated using minimumswitchyard voltage as starting point.67 Page 6 1. NEI 3/18/11 "This interface calculation establishes operatingparagraph Letter /9 voltage bands for all plant electrical buses, whichensures that all plant components and systems(Class IE and Non Safety Related) have propervoltage for starting and running in all operationalconfigurations (expected operational and accidentconditions)."This statement needs clarification in that not all20 No. Section of RIS Originator Specific Comment NRC Resolutionnon-safety load voltages need to be evaluated. DisagreeThe statement that the DVR ensures adequateoperational (starting and running) is the first time in See response to questions 1 &2 forNRC correspondence that starting equipment at clarification.the DVR setpoint is expected.The 1977 NRC letter refers to SR equipmentHaving a sustained degraded voltage just above voltage requirements.the LVR voltage setting (70%) is not practicalwithout grid collapse and does not exist in Branch NSR items are being removed from thisTechnical Position #1 ((BTP) PSB-1). sentence in the RIS. However, non safetyrelated loads should be modeled to theTypically, large motors (like reactor coolant pumps) extent that their operation can affect safetyneed to be evaluated for starting impact on the bus/equipment voltage.safety bus. Once a motor is found to be smallenough to not impact safety bus operation, furtherevaluation is unnecessary. The statement in theRIS can easily be interpreted as requiringevaluation of all non-safety loads down to the DVR setpoints are based on low voltageslowest levels of distribution, that can occur due to sustained gridperturbations and can potentially degradeTechnical compliance with determining the capability of onsite safety related equipment.degraded voltage relay setpoint would not beachievable because the RIS requires the DVRdropout setpoint to be based on the starting voltage The NRC 1977 letter states that "voltage andrequired for motors. Basing the DVR setpoint time setpoints shall be determined from an(dropout setting) on starting voltage requirements analysis of the voltage requirements of the(rather than steady-state operating voltage) safety related loads". Safety relatedappears to be a new NRC requirement/position. It equipment, particularly large motors, haveis technically flawed in that it would not actually starting and running "voltage requirements".provide the required protection for the Classl IE This second level of protection shouldloads. It also appears to disagree with the intended address these "voltage requirements".purpose of the existing regulations (1977 NRC Sustained degraded voltage, as discussed inLetters on degraded voltage protection and (BTP) the 1977 letter, refers to grid voltage belowPSB-1). the expected low value given normal gridoperation and grid post contingency (Single,The letter sent to Peach Bottom in June 1977 did N-i). Thus, when grid voltages are degradednot require starting of equipment at the DVR (such as resulting in SR bus voltages downsetpoint. This new requirement should be removed close to where DVRs are set based on SRfrom the RIS, since it is not possible to start equipment requirements), separation fromequipment at the DVR setpoint and not the grid is appropriate. The design of thesubsequently separate from offsite power. If the plant electrical distribution system andequipment starts at the DVR setpoint, the voltage setting of the DVRs, based on the gridwill dip during the transient and must then recover voltage range (described above) shouldabove the reset point to avoid separation from provide proper margin such that spuriousoffsite power, Since the reset point will always be separation from the grid should not occurabove the DVR dropout point, it will be impossible due to sequencing or block loading of loadsto reset the relay. during a design basis events.Motor starts have been discussed in severalquestions above. An accident signalconcurrent with degraded grid conditions willrequire motor starts. All NRCcommunications discuss the requirement forsafe shutdown of the plant followingpostulated events.68 Page 6, 2n NEI 3/18/11 "The staff considers degraded voltage conditionsparagraph Letter / 10 coincident with a postulated design basis accidentto be a credible event. DVRs should be set toprotect the safety related equipment from sustaineddegraded voltage conditions."GDC 17 should be identified as the regulatoryrequirement. This RIS is creating conditions in Disagreeexcess of GDC 17.The RIS concludes that the staff considers The 1977 NRC letter staff pe Gs-ouidancedegraded voltage conditions coincident with a (implementation second level undervoltage_ _ _postulated design basis accident to be a credible protection scheme) apfy-applies to all21 No. Section of RIS Originator Specific Comment NRC Resolutionevent; however, this is not consistent with GDC 17. operating plants and provides guidance onhow to meet regulatory criteria..The RIS should identify that plant compliance withthe regulation (GDC 17) is by each plant operating The 1977 NRC letter indicates that the DVRwithin its Licensing Basis that was developed from scheme time delays should support accidentavailable NRC and industry guidance. analysis assumptions which ties degradedevent with an accident.Most licensees are committed to a version of IEEE308, Standard Criteria for Class 1E Power Systemsfor Nuclear Power Generating Stations. ThisStandard defines the malfunctions, accidents,environmental events, and operating modes (i.e.,design basis events) that could physically damageClass 1 E power systems or lead to degradation ofsystem performance and for which provisions shallbe incorporated.A degraded voltage condition coincident with apostulated design basis accident is not among theidentified design basis events; however, theStandard does include a requirement for theprotection from common mode failure.69 Page 6, 2" NEI 3/18/11 "The Class 1E buses should separate from theparagraph Letter/ 11 offsite power system within a few seconds if anaccident occurs coincident with a sustaineddegraded voltage conditions."GDC 17 describes the requirements for onsite and Disagreeoffsite power systems. One of its requirements isthat they each provide sufficient capacity andcapability to mitigate postulated events. The eventsare described in Chapter 15 "Accident Analysis". The NRC 1977 letter indicates that the DVRThese analyses assume Loss of offsite Power scheme time delays should support accidentsimultaneous with the event. They do not require analysis assumptions which ties degradedassuming degraded grid voltage condition prior to event with an accident.an event occurring. In addition, because of FERCand NERC requirements for voltage control, thelikelihood of a chapter 15 accident occurringconcurrent with a serious degraded grid voltagecondition is so low that it is believed to be not See NRC response to Comment No. 36credible.Remove or clarify this statement, since properoffsite system design and operation renders suchsimultaneous postulated events as incredible.This position assumes (BTP) PSB-1 (BTP 8-6) ispart of the license and design basis for alllicensees. An equivalent position was not identifiedin the NRC letters issued following the Millstoneevent. Specifically, this requirement is morestringent than the position stated on Page 2, Itemd) and may constitute a backfit to some licensees.Care must be exercised with regards to the scope Section 2 is not about DVR schemes andof this position. It does not apply to Section 2, separation during a degraded voltage"Offsite/Onsite Design Interface Calculations" of the condition. It is about operation of the plantRIS. This is confirmed in the draft RIS on Page 8, during normal, abnormal and accidentParagraph d) which states all electric system action conditions and assuming the normaloccur "as designed". It would be beneficial to clarify operation of the grid (including the boundingthe scope limitations associated with this or any N-1 contingency and the trip of the unit forrevised position, the accident cases).70 Page 6, 2'6 NEI 3/18/11 "... Position (BTP) PSB-l (revised later to become1 paragraph Letter / 12 1TP-6), is to protect Class 1E safety related buses22 No. Section of RIS Originator Specific Comment NRC Resolutionand components from sustained degraded voltageconditions on the offsite power system coincidentwith an accident as well as during non-accidentconditions."A definition of the word "protect" is needed. It is not Disagreeclear what is being protected: the components(MOV, motor, etc.) or the class 1 E function or Protect means guard or defend safetysomething else. related components against theconsequence of sustained degraded voltageThe word "coincident" should read "subsequent to" conditions.or followed by", per (BTP) PSB-1 and BTP 8-6.Coincident is appropriate based on the 1977NRC letter verbiage. The BTPs just provide adesign which would also deal with an eventwhen a SIAS signal would occur subsequentto the degraded voltage condition as well(not conflicting)71 Page 6, 2nr NEI 3/18/11 'The Class 1 E buses should separate from theparagraph Letter / 13 offsite power system within a few seconds if anaccident occurs coincident with a sustaineddegraded voltage condition."Per (BTP) PSB-1, the text should read: Agree.'The Class 1 E buses should separate from theoffsite power system immediately if an accident RIS will be revised to incorporate theoccurs subsequent to a sustained degraded comment.voltage condition.'72 Page 6, 2"n NEI 3118/11 "... Class 1E safety related buses shouldparagraph Letter 14 automatically separate from the power supplywithin a short interval (typically less than 60seconds)..."There is no basis for "typically less than 60 Agreeseconds". In the original context of the time delaysection, it was sufficient time for an operator to RIS will be revised to delete the parenthesisintervene" which is much greater than 60 seconds. section of the sentence as suggested.Remove the parenthesis section of the sentence.With this guidance during normal plant operation, Disagreethe degraded grid relay settings may be overlyconservative; automatic separation from the 10 CFR 50.55a(h(2)) requires all protectivepreferred power supply may occur under conditions actions to be automatic. Operatorwhere this action is inappropriate, intervention is probably not possible whenvoltage gets down to the DVR setpoint (gridThe RIS should allow Transmission Operators time voltage is well below normal).to correct the degraded voltage condition whilePlant Operators monitor the safety bus voltages for Operator action takes minutes. Operation atadequate voltage, degraded voltage conditions can degradeequipment performance capabilities withinseconds.73 Page 6, 3' NEI 3/18/11 DVR Setting Design Calculationsparagraph Letter / 15This section would be a good place to describe thistype of analysis as having a "bottom-up" approach. DisagreeSuch calculations would prevent confusion ofcrediting anything above the DVR voltage sensors' The approach is already described in thisvalues, paragraph.In the context of DVR Setting Design Calculations,using a steady state or sustained voltage analysis23 No. Section of RIS Originator Specific Comment NRC Resolutionis the only way that can result in a voltage 'setting' The term sustained voltage used in the NRCrequirement. 1977 letter and the BTPs is referring to thevoltage condition on the grid, not steadystate voltage74 Page 6, 3 NEI 3/18/11 "... DVR ensures adequate operational (startingparagraph Letter / 16 and running) voltage..."The "operational voltage" cannot define both Agreestarting and running voltages.RIS will be revised to state ". DVR ensuresThe only place "operational voltage" is referenced adequate voltage (start and runin the associated documents is in the tap setting conditions)..."section of (BTP) PSB-1 and BTP 8-6 when a plantis connected to the offsite power supply. The onlyqualifying term used in the protection of theequipment is 'sustained' which is synonymous withsteady state or running. DisagreeReword the RIS to: The term sustained voltage used in the NRCDVR ensures adequate sustained voltage...' 1977 letter and the BTPs is referring to thevoltage condition on the grid, not steadystate voltage75 Page 6, 3" NEI 3/18/11 -Licensee voltage calculations shouldprovide theparagraph Letter /17 basis for their DVR settings, ensuring safety relatedequipment is supplied with adequate operatingvoltage (typically a minimum of 0.9 per unit voltageat the terminals of the safety related equipment perequipment manufacturers requirements), based onbounding conditions for the most limibng safetyrelated load (in terms of voltage) in the plant."Equipment manufacturers do not provide the samevoltage requirement to perform both running and Agreedstarting a motor. The 0.9 per unit in this contextrefers to the typical running voltage requirement of This sentence is being rewordeda motor; whereas, 0.85 per unit is typical for astarting voltage requirement.The RIS should identify that voltages other than Starting requirements for motors have been90% voltage are common based on detailed plant observed over a range of 0.75 to 0.85. Itanalysis. depends on the particular plant and how themotors were procured. Either way, theFor example, motors below 90% voltage continue voltage requirements must be preservedto have plenty of margin in torque but may (starting and running). However, there couldencroach on long time thermal limits. Unless a be other components that are more sensitivemotor is fully into its service factor (typicallyl.1 5) to voltage for operation.and below 90% voltage, operation will be 0.9 per unit voltage was mentioned as anacceptable. example and was not meant to covereverything. RIS will be revised to deletereferences to specific numbers andemphasize voltage requirements and voltagerequirements are plant-specific.The design basis of the plant shoulddetermine the adequacy of voltage. The RISclarifies the regulation.24 No. Section of RIS Originator Specific Comment NRC Resolution76 Page 6, 3' NEI 3/18/11 "In this manner, the DVR ensures adequateparagraph Letter /18 operational (starting and running) voltage to allsafety related equipment, independent of voltagecontrolling equipment external to the plant safetyrelated electrical distribution system."The draft RIS suggests the DVR dropout setpointto be based on the starting voltage required for Disagreemotors.Basing the DVR dropout setpoint on starting The NRC 1977 letter states that "voltage andvoltage requirements rather than steady-state time setpoints shall be determined from anoperating voltage appears to be a new NRC analysis of the voltage requirements of therequirement/position. It also appears to disagree safety related loads". Safety related (Classwith the intended purpose of the existing 1 E) equipment, particularly large motors,requirements and guidance (1977 NRC Letters on have starting and running "voltagedegraded voltage protection and (BTP) PSB-1). requirements". This second level ofundervoltage protection should addressAs suggested, the approach incorrectly implies that these "voltage requirements". Sustainedthe load(s) should start from the lowest DVR degraded voltage, as discussed in the NRCdropout setting. A specific example for illustration is 1977 letter as well, refers to grid voltageas follows: If the initial voltage value is at the lowest below the expected low value given normalpossible value above dropout actuation, starting a grid operation. Thus, when grid voltages areload will cause the DVR dropout. Since the new degraded (such as resulting in Class 1 E bussteady state voltage will be lower than the initial voltages down close to where DVRs are setvalue because of the added loads, the DVR reset based on Class 1E equipmentwill never occur, requirements), and the grid does notautomatically recover, separation from theMany utilities use the ABB 27N with harmonic filter grid is appropriate. Proper design of the plantwhich has a minimum 0.5% reset. Thus, with a electrical distribution system and setting ofsetting of 93.6% +/- 0.9%, the dropout value could the DVRs, based on the grid voltage rangebe as low as 92.7%. For motors causing more than (described above) should provide proper0.5% voltage dip at initial start, even if the voltage margin such that spurious separation fromat the beginning of the event was 93.2% and a load the grid should not occur due to sequencingwas started, the DVR will dropout and never reset, or block loading of loads during a designThis will lead to a grid separation, basis event.Reword the RIS to remove "(starting and running)" Also, see response to questions 1 & 2.77 Page 6, 3' NEI 3/18/11 "For the purposes of this calculation, no creditparagraph Letter /19 should be taken for voltage controlling equipmentexternal to the Class 1E distribution system suchas automatic load tap changers and capacitorbanks."The intent of the position appears to ensure that Disagreethe DVR setpoint(s) protect against the potential This sentence is being re-wordedloss of ESF equipment, regardless of thecomponent mode of operation. It does not implythat the Class 1E bus must remain connected tooffsite power after starting a large motor with an The point being made is that calculations forinitial bus voltage corresponding to the DVR the DVR voltage settings should have casessetpoint and no voltage regulation capability, at voltages just above the DVR voltagesettings (well below what would be based onnormal grid operations and voltageActually, the calculation should be performed with controlling equipment if applicable) tothe DVR monitored bus voltage at the TS limit, not demonstrate that the settings enforce the SRthe DVR setpoint. All that is required is that under equipment voltage requirements.motor starting conditions, separation from offsitepower occurs before starting loads trip on overload. This is covered in Offsite/Onsite DesignThe intent could be conveyed in more detail. Section calculations (not DVR calculationssection)The RIS should allow reasonable assumptions for The offsite source is the preferred source ofthe status of equipment external to the Class 1 E power for plant shutdown. The DVR shoulddistribution system. For example it is unclear how not separate the plant from the grid for motorto perform motor starting calculations without starts. In the event that grid conditionstaking credit for some Non 1E voltage controlling degrade beyond an acceptable point and anequipment. Additionally, normal transmission grid accident signal is actuated, BTP PSB-11 switching should be allowed to prepare for the next recommends separation from the grid.25 No. Section of RIS Originator Specific Comment NRC Resolutiongrid event, so that minimum expected transmissionsystem voltages are maintained. Credit for voltage controlling equipment inthe Offsite/Onsite Design Sectioncalculations is appropriate if corrective actioncan be taken in a timely manner to precludesafety related equipment malfunctions.78 Page 7, 1 NEI 3/18/11 "Voltage-time settings for DVR's should be selectedparagraph Letter /20 so as to avoid spurious separation of the safetybuses from the offsite power system during unitstartup, normal operation and shutdown."This position is new and contrary to the NRC Disagreehistorical position stated on Page 2, Item (c)(3).Either the DVR protection scheme favors ESF- This sentence is being re-wordedequipment-protection or connectivity-to-offsite-power. Otherwise, this position would result in amutually exclusive requirement. The prevention of DVR setting always enforce SR equipmentspurious separation is addressed by coincident voltage requirements. Offsite/Onsite Designlogic channels (Page 2, Item (b)), not the setpoint. should ensure that there is proper marginbetween where voltage is in the plant duringIf no credit is to be taken for voltage controlling normal grid operation as compared toequipment external to the Class 1iE distribution voltages in the plant when the DVRs actuate.system for the establishing the degraded voltagerelay (DVR) settings, then the RIS should state thatcredit may be taken for minimum switchyard Credit for voltage controlling equipment involtage/voltage drop calculations (Offsite/Onsite the Offsite/Onsite Design SectionDesign Interface Calculations). calculations is appropriate. However, it is notappropriate to use it for DVR calculationssince DVR setpoint is derived from theminimum voltage required at the componentterminal at all voltage levels. (Also seeresponse to question #77)79 Page 7, 1 NEI 3/18/11 "These DVRs should disconnect the Class 1Eparagraph Letter / 21 buses from any power source other than theemergency diesel generators (onsite sources) if thedegraded voltage condition exists for a time intervalthat could prevent the Class 1E safety relatedloads from achieving their safety function."This position ensures ESF functionality, should an Disagreeundervoltage condition persist.The BTP PSB-1 offers an option to set a(BTP) PSB-1 was written before the application of higher voltage alarm level to supportvoltage regulating devices within the nuclear power corrective action to restore voltage to normalplant offsite power circuit boundary. The RIS operating band.should clarify that if the calculations necessary tosupport RIS positions in Section 1, "DegradedVoltage Relaying Design Calculations" and Section Since offsite power is the preferred source of2, "Offsite/Onsite Design Interface Calculations" power to mitigate design basis event, it isdemonstrate completion of ESF functions within important that the Offsite/Onsite Designaccident analysis assumptions, then immediate Interface calculations ensure the capacityseparation per (BTP) PSB-1, Section B(1)(b)(i), is and capability of the offsite power isno longer the preferred NRC position, adequate to sequence or block load duringdesign basis events without actuating DVRs(BTP) PSB-1 (BTP 8-6) states: with sufficient margin available at the safety'The subsequent occurrence of a safety injection buses. Separation of the safety buses fromactuation signal (SIAS) [after an undervoltage the grid is only appropriate when the DVRcondition longer than a motor starting transient] relays actuate indicating that SR equipmentshould immediately separate the Class 1E voltage requirements are not being met (notdistribution system from the offsite power system." able to protect or provide adequate voltageto the terminals of the SR limitingThe RIS should state that this (BTP) PSB-1 components at the plant).position is not included in the draft RIS because itprovides no added protection in terms of Analyses to determine such setpoints alwaysestablishing the DVR setpoint(s) or in establishing should have included modeling the plantoperability of the offsite power interface. To the power distribution system such that propercontrary, this (BTP) PSB-1 increases the voltages throughout the plant system can beprobability of separation from offsite power. calculated in all operating and accident26 No. Section of RIS Originator Specific Comment NRC Resolutionconditions.80 Page 7, NEI 3/18/11 "Guidelines for voltage drop calculationsparagraph 2 a) Letter /22a) The plant voltage analysis, whilesupplied from the transmissionnetwork, should be based on theoperating voltage range of thetransmission network connection."It is recommended that the first sentence of DisagreeParagraph 2(a) be deleted. It is covered byParagraph 2(b), as the switchyard is the "power Enclosure 2 of GL 79-36 provides guidelinessource" for the offsite power circuits. for voltage drop calculations.Paragraph 2(a) addresses both plant andtransmission operator analyses. The purpose is toidentify that the switchyard voltage results from thetransmission operator analysis should be used asan input to the power plant analysis. From thenuclear power plant point of view, thedetermination as to whether each offsite power Accident cases consider the unit trip gridcircuit is individually capable of performing its contingency since a trip is assumed to occurdesign function is based on a postulated post-trip coincident with an accident. However, if theswitchyard voltage for the present grid unit trip is not the most limiting gridconfiguration and operating level (i.e. RIS contingency (not the largest grid voltageParagraph 2(b)). drop), the cases which assess normal andabnormal operation (non-accident) need toAs written, it is conceivable that a reader of this assume the bounding grid contingencyparagraph could conclude that the transmission (normal grid operating range)"contingency analysis" is a factor in the nuclearplant analysis regarding "when" the contingency ispostulated to occur relative to the postulated plantevent. The alteration of the present basis to includeconcurrent grid/plant events is a change in positionand would be subject to backfit consideration.81 Page 8, NEI 3/18111 "For multi-unit stations, a separate analysis shouldparagraph 2 c) Letter 123 be performed for each unit assuming (1) anaccident in the unit being analyzed andsimultaneous shutdown of all other units at thestation; or (2) an anticipated transient (anticipatedoperational occurrence) in the unit being analyzed(e.g., unit trip) and simultaneous shutdown of allother units at that station, whichever presents thelargest load situation.The RIS wording should be revised to indicate Disagree"orderly or controlled safe shutdown of theremaining units, as per the station's licensing basis" Wording is the same as provided in GL 79-instead of "simultaneous shutdown". Alternatively, 36the wording 'shutdown consistent with the stationlicensing basis" could be used instead of"simultaneous shutdown'.This statement is consistent with GDC 17,Most multi-unit stations' Licensing Basis consider GL 79-36, and IEEE Standard 308-1971,an "orderly or controlled safe shutdown" of the "Class IE Electrical Systems," Section 8,other unit(s) not being analyzed. "Multi-Unit Station Considerations.NERC Std TPL-004-0; particularly Category Devents per Table 1, where a "loss of all generatingunits at a station" may result in "portions or all ofthe interconnected systems may or may notachieve a new, stable operating point".IEEE Std 308-1974, Clause 8, sub-clause 8.1.1"Capacity" describes this as a "concurrent safeshutdown on the remaining units".27 No. Section of RIS Originator Specific Comment NRC ResolutionThis RIS re-states part of GL 79-36, with anattempt to clarify "anticipated transient" by addingin parenthesis "(anticipated operationaloccurrence)". It is not clear what the addedparenthetical statement is meant to convey, otherthan unit trip (which already exists in GL 79-36).The RIS should remove this parenthetical additionor state '...an anticipated transient per stationlicensing basis...'82 Page 8, NEI 3/18/11 "All actions the electrc power system is designedparagraph 2 d) Letter / 24 to automatically initiate should be assumed tooccur as designed..."This statement is consistent with GDC 17 in that Agree.the presumption is the onsite AC sources are lost.The postulation of concurrent malfunctions in both No change to this sentence.the onsite and offsite sources is not required.The RIS should retain this sentence, since it maynot have been consistently applied during recentCDBI's.83 Page 8, NEI 3/18/11 "a) Manual load shedding should not be assumed.paragraph 2 e) & Letter / 25f) f For each event analyzed, the maximum loadnecessitated by the event and the mode ofoperation of the unit at the time of the event shouldbe assumed in addition to all loads caused byexpected automatic actions and manual actionspermitted by administrative procedures."These guidelines seem contradictory in that e) Disagreestates that there may be no credit for procedurallycontrolled operator actions to reduce load but f)states that the manual action loads must be This guidance is consistent GL 79-36.considered in the maximum load.The RIS should delete "e) Manual load shedding Adding loads manually per procedure isshould not be assumed" or add allowance to credit conservative in terms of maximum loading,procedurally controlled operator actions to but not for load reductions. Plant design fordecrease load. maximum load should not depend on manualload shedding (not conservative). That wasthe point of item e).84 Page 8, NEI 3/18/11 Omissionparagraph 2 f) Letter /26 DisagreeAfter paragraph 2 f), the RIS leaves out theguidance in GL 79-36 concerning minimum It was not omitted. This is covered in item a)expected values (item 6 of enclosure 2).Add item 6 of enclosure 2 in GL 79-36 to the RIS:"6. The voltage at the terminals of each safety loadshould be calculated based on the above listedconsideration and assumptions and based on theassumption that the grid voltage is at the "minimumexpected value". The "minimum expected value"should be selected based on the least of thefollowing:a. The minimum steady-state voltageexperience at the connection to theoffsite circuit.b. The minimum voltage expected at theconnection to the offsite circuit due tocontingency plans which may result inreduced voltage from this grid.c. The minimum predicted voltage from gridstability analysis. (e.g., load flow28 No. Section of RIS Originator Specific Comment NRC Resolutionstudies)."85 Page 8, NEI 3/18/11 "To provide assurance that actions taken to assureparagraph 2 j) Letter /27 adequate voltage levels for safety related loads donot result in excessive voltages, assuming themaximum expected value of voltage at theconnection to the offsite circuit, a determinationshould be made of the maximum voltage expectedat the terminals of all safety related actualequipment and their starting circuits (if applicable).If this voltage exceeds the maximum voltage ratingof any safety related equipment, immediateremedial action should be taken."The RIS should remove the word "immediate" Disagreedescribing remedial action. Immediate remedialaction could imply control room intervention. Thecontrol room has alarm procedures to address highvoltage should it occur. Timeliness of remedial The Offsite/Onsite design should address allactions depends on how high actual voltage grid operating conditions to preventreaches and is addressed by procedures. overvoltages from occurring,Analyses of high grid voltage with light plant load The point here is that if a design problem isare standard and provide insights as to what the identified such as overvoltage conditions,grid voltage upper limit should be or what immediate actions should be takencompensating activities might be required for light (compensatory and/or permanent designload operations (refueling). changes) to address the design problemrather than taking actions after it occurs.The RIS should provide examples of typicalresponses to high grid voltages. For example: in It is not the intent of the RIS to highlightthose cases where unit trip can result in a step reasons for voltage perturbations.increase in grid voltage (most common on highervoltage connections like 765kv), anticipatedexcursions above desired voltages should beaddressed by compensating measures (changingexcitation for nearby units, switching in reactorbanks, etc.).86 General NEI 3/2/11 Page 2, Paragraph 1Letter While NEI supports efforts to obtain greater clarity Disagreewith respect to the staffs technical position in thisimportant area, the draft RIS greatly oversimplifies NRC Staffs position is that the RIS isthe regulatory and licensing aspects of the intended to clarify the requirements anddegraded grid voltage protection issue. As a result associated existing staff pesitions-gidanof this oversimplification, the draft RIS which would apply to all plants.inappropriately combines several genericcommunications and guidance documents that Any inspection findings that questions theaffected the licensing bases of individual plants in plant-specific licensing bases will bedifferent ways, and fails to adequately address the reviewed by the NRR staff in accordancesignificant backfitting concerns that arise when NRC's TIA process.attempting to eliminate licensing basis variabilityvia a RIS (or any other guidance document).87 General NEI 3/2/11 Page 2, Paragraph 2Letter Unless it is revised, the draft RIS will unnecessarily Disagreeincrease the potential for loss of the preferred off-site power source and, consequently, increase Proper design of the plant electricalreliance on emergency diesel generators. NEI distribution system, given the operatingbelieves that the use of emergency diesel range of the grid and the proper selection ofgenerators more frequently than necessary is DVR settings (based on the voltageinconsistent with GDC 17 and results in an requirements of the 1E equipment), shouldunnecessary loss of defense-in-depth, provide more than adequate operatingmargin, preventing unnecessary separationfrom offsite power.88 General NEI 3/2/11 Page 2, Paragraph 3, Comment ILetter The Draft RIS Fails to Adequately Consider Agreein osrt.Licensing Basis Variability in the Area ofDegraded Grid Voltage Protection As a general matter, NRC staff positions areThe only generic obligation or legally binding "ouidance," as are, among other things,29 No. Section of RIS Originator Specific Comment NRC Resolutionrequirement mentioned in the Discussion section of regulatory guides and Interim Staff Guidancethe draft RIS is GDC 17. (ISG). As guidance, NRC staff Positions, likereaulatory auides, are not legally bindingunless the NRC legally imposes them on alicensee or the licensee binds itself tocomplying with them in a document subiectto NRC-mandated controls, In other words,for any particular nuclear oower plant.guidance may be Part of the licensina basisfor that plant because of past NRC orlicensee actions, For instance, guidancemay be legally imposed upon a vlant byvirtue of the issuance of an order or througha license condition that imposes theguidance on that particular plant. As anotherexample, a licensee may have committed tocompliance with the guidance in the plant'sfinal safety analysis report IFSAR) or otherdocument subiect to NRC controls (e.ag. thedescription of the olant's auality assuranceProgram, an emergency Plant. or a securityplan)t The NRC resolutions for all the Publiccomments received on this RIS should beunderstood in liaht of this explanation.89 General NEI 3/2/11 Page 3, Paragraph 2, Comment I (Cont.)Letter The Draft RIS Fails to Adequately Consider Disagree.Licensing Basis Variability in the Area ofDegraded Grid Voltage Protection The 77 Letter is a sttaff 99itin-whhappliesAlthough these letters resulted in changes to the to-aWopating rna~t~rc at that time a:dlicensing bases of the nuclear power plants that licensed 6 ize, received them, they do not function the same way the ......m t. in 10 CFFI Par- f n , .Ge.eralas generally applicable regulatory requirements. Des r ' Criteria 17 (GDC- 7*.The 1977 letterThat is, these generic communications were only as well as other staff guidance. were madereceived by plants that were licensed at the time available or sent to all operating plants atthe communications were issued. Operating that time. In addition, the NRC's regulatorylicenses for the current fleet were issued during a practice-which has been understood by theperiod that ranged from the late 1960s through the industry-is that staff guidance represents the1990s. Thus, not all operating plants received and staff position until subsequently modified orresponded to the generic communications issued in withdrawn. While the staff recognizes that1977 and 1979. there is variability among plants' licensingbases with respect to degraded voltageprotection, the NRC believes (with oneexception identified elsewhwere) that theoverall licensing basis provisions withrespect to degraded voltage protection areconsistent with the staffs position.90 General NEI 3/2/11 Page 3, Paragraph 2, Comment I (Cont.)Letter The Draft RIS Fails to Adequately ConsiderLicensing Basis Variability in the Area of Disagree.Degraded Grid Voltage ProtectionFurther, the Branch Technical Position (BTP) The 1977 Letter is a-ffpdescribed in the draft RIS BTP PSB-1, Rev. 0, which applies to all operating reactors at that"Adequacy of Station Electric Distribution System time and plants licensed since, on how toVoltages"--was issued in 1981. BTP PSB-1 and the comply with the requirements in 10 CFRStandard Review Plan in which it is included were Part 50, General Design Criteria 17 (GDC"prepared for the guidance of the Office of Nuclear 17).Reactor Regulation staff responsible for the reviewof applications to construct and operate nuclearpower plants.... Standard review plans are notsubstitutes for regulatory guides or theCommission's regulations and compliance withthem is not required." Thus, BTP PSB-1 wouldhave been directly relevant to plants licensed afterits issuance, but not before. Further, the specificdetails in the information provided in the 1977letters, Generic Letter 79-36, and BTP PSB-I arenot identical. I30 No. Section of RIS Originator Specific Comment NRC Resolution91 General NEI 3/2/11 Page 3, Paragraph 3, Comment I (Cont.)Letter The Draft RIS Fails to Adequately Consider Disagree.Licensing Basis Variability in the Area ofDegraded Grid Voltage Protection NRC Staff asserts that coincident degradedFor example, the draft RIS makes several grid and accident is specified in the 77 Letterrecommendations that may be inconsistent with the and the BTP approach supports thatapproved licensing bases for operating plants, position.including:The draft RIS proposes "Degraded See also staff response to Comment No. 36.voltage conditions coincident with apostulated design basis accident." BTPPSB-1 says "subsequent occurrence."92 General NEI 3/2/11 Page 4, First Bullet, Comment I (Cont.)Letter The Draft RIS Fails to Adequately Consider Disagree.Licensing Basis Variability in the Area ofDegraded Grid Voltage Protection The staff position is consistent with 1977The draft RIS proposes "DVR Dropout setting letter and BTP PSB-1.based on starting and running voltage." BTP PSB-1says "sustained," implying a steady state voltagecondition and not a transient voltage condition thatI exists during a motor starting event.93 General NEI 3/2/11 Page 4, Second Bullet, Comment I (Cont.)Letter The Draft RIS Fails to Adequately Consider DisagreeLicensing Basis Variability in the Area ofDegraded Grid Voltage Protection This statement is consistent with GDC 17,The draft RIS proposes "separate analysis should GL 79-36, and IEEE Standard 308-1971,be performed for each unit assuming (1) an "Class IE Electrical Systems," Section 8,accident in the unit being analyzed and "Multi-Unit Station Considerations.simultaneous shutdown of all other units at thestation."GDC 5 says:in the event of an accident in one unit, anorderly shutdown and cooldown of the remainingunits."94 General NEI 3/2/11 Page 4, Third Bullet, Comment I (Cont.)Letter The Draft RIS Fails to Adequately ConsiderLicensing Basis Variability in the Area of DisagreeDegraded Grid Voltage ProtectionThe draft RIS proposes "During normal plantoperation, the Class 1E safety related busesshould automatically separate from the powersupply within a short interval (typically less than 60seconds) if sustained degraded voltage conditionsare detected." BTP PSB-1 clause B.1 .b.2 includedprovisions for operator manual actions to restorebus voltage on the Class 1 E distribution system.See staffs response to Comment No. 37.BTP PSB-1 B.1.b.2 says:'The second time delay should be of a limitedduration such that the permanently connectedClass'lE loads will not be damaged. Following thisdelay, if the operator has failed to restore adequatevoltages, the Class 1 E distribution system shouldbe automatically separated from the offsite powersystem. Bases and justification must be provided insupport of the actual delay chosen."Manual actions for the purposes of reducingThe draft RIS specifically excludes manual load load for the design of the plant electricalshedding under the Offsite/Onsite Design Interface distribution system should not be assumed.Calculations whereas the BTP PSB-1 allows for This is not precluding load shedding as partmanual actions to avoid separation from offsite of normal operation when there is sufficientpower. time to do so to support adequate voltage.See GL 79-36 for more details.The sixty second time delay would not allowoperator actions. This appears to be a new NRCposition.31 No. Section of RIS Originator Specific Comment NRC Resolution95 General NEI 3/2/11 Page 5, Paragraph 2, Comment I (Cont.)Letter The Draft RIS Fails to Adequately Consider DisagreeLicensing Basis Variability in the Area ofDegraded Grid Voltage Protection The 77 Letter indicates that the DVR circuitsIn addition to the specific examples provided should be designed assuming coincidentabove, the draft RIS states "[tlhe staff considers sustained degraded grid voltage anddegraded voltage conditions coincident with a accident events. Upon the onset of thepostulated design basis accident to be a credible coincident accident and degraded grid event,event." It is unclear what exactly the staff intended the time delay for the DVR circuit shouldwith this statement, allow for separation of the 1 E buses from theoffsite circuit(s) and connection to the 1Eonsite supplies in time to support safetysystem functions to mitigate the accident inaccordance with the FSAR accidentanalyses.96 General NEI 3/2/11 Page 6-7, Comment i1Letter The

Backfit Discussion

Provided in the DraftRIS is InadequateGiven the complex regulatory and licensing history Disagreeassociated with providing degraded grid voltageprotection, the backfitting discussion included in thedraft RIS is inadequate. Despite the fact thatfacility-specific backfits were required as a result ofseveral recent inspection findings on degradedvoltage protection,1 8 the entire backfittingdiscussion included in the draft RIS consists ofthree sentences. Of those three sentences, onlyone provides any analysis:Specifically, NRC Staff technicalpositions outlined in this draft RIS are The-etiails of the inzpeGzt9A findings azdconsistent with the aforementioned eforcement atins ;Ie in dztAilregulations [GDC 17] and generic ip the appli.... I, i .I ......s sad T-Ascommunications [1977 letter, Generic if appl refereced in the ,RISLetter 79-36, BTP PSB-1], whileproviding more detailed discussionconcerning the necessary voltagecalculations supporting DVR settingsbased only on voltage requirements ofClass 1 E components and the Class 1 E NRC sta# a.. rtg that Ithe egulatigns anddistribution system design.19 staff P0 tionA arti.nz'"azd A the ROi arsThis analysis misses the point. First, GDC 17 (like guidance and ."erzefte-de-ne4most GDC) is cast in broad, general terms: .Z.,tit-tz ne',z OF diffzRat p.. itizric withtherefore, the fact that the specific positions the l F discussed in the draft RIS are "consistent with" the See the supplemental response attached atdesign criteria does not necessarily mean that they the end of this Comment/Response Table.escape the definition of a backfit. Specifically, thereare any number of staff positions that are"consistent with" a broad design principle, but therelevant inquiry when examining the backfitdefinition is whether the staff position beingarticulated is new or different from a previouslyapplicable staff position. The draft RIS does notaddress this issue. Further, as discussed above,the generic communications and guidancediscussed in the draft RIS are not completelyconsistent with one another and were not equallyrelevant in developing the licensing bases for allreactor licensees. Given the variability in theprotection schemes approved by the NRC, merelyconcluding that the positions provided in the draftRIS are "consistent with" one or more of thesedocuments, does not address the obvious fact that"providing more detailed discussion" on how todemonstrate compliance with GDC 17 could I32 No. Section of RIS Originator Specific Comment NRC Resolutionconstitute a staff position that is new or differentfrom a previously approved protection scheme.97 General PPL Page 1-2, First Bullet DisagreeContrary to the stated intent, PPL believes that theRIS does transmit new requirements and staff The NRC 1977 letter states that "voltage andpositions. Specific comments applicable to time setpoints shall be determined from anSusquehanna Steam Electric Station (SSES) are analysis of the voltage requirements of theas follows: safety related loads". Safety relatedequipment, particularly large motors, haveThe RIS introduces the need to consider starting and running "voltage requirements".both "starting and running" conditions This second level of protection shouldduring all operating configurations while address these "voltage requirements".maintaining the offsite power supply Sustained degraded voltage, as discussed inconnected to the plant electrical the 1977 letter, refers to grid voltage belowdistribution system. The establishment of the expected low value given normal grida degraded voltage relay (DVR) to detect operation and grid post contingency. Thus,a "sustained" degraded voltage condition when grid voltages are degraded (such aschallenges the relay's basis for resulting in SR bus voltages down close to"protection" if its actuation (dropout) where DVRs are set based on SR equipmentsetpoint must accommodate both starting requirements), separation from the grid isand running voltage conditions. The term appropriate. The design of the plant electrical"sustained degraded voltage" implies a distribution system and setting of the DVRs,steady state degraded voltage condition, based on the grid voltage range (describedand excludes starting voltage above) should provide proper margin suchconsideration that spurious separation from the grid shouldnot occur due to sequencing or block loadingof loads during a design basis events.98 Page 6, Section 1 PPL Page 2, Paragraph 2 DisagreeRIS 201 1-XX, Page 6, Section 1. "DegradedVoltage Relaying Design Calculations" contains the NRC Staff asserts that this statement meansstatement "staff considers degraded voltage that while the events are coincident (which iscondition coincident with a postulated design basis important from the standpoint that the timeaccident to be a credible event." This statement delay chosen for the DVR must support theimplies a requirement to demonstrate capability of accident analysis), it does not mean thatconnected loads to start and run at the degraded connected loads must start and run at thevoltage relay dropout setting. For Susquehanna, dropout setting. The dropout setting shouldsequencing of loads from the offsite power source be developed based on the voltagecannot be demonstrated at the relay dropout requirements (starting and running) andsetpoint because operation at this voltage level therefore to develop values which arewould result in separation from the offsite bounding, the studies should be done undertransmission system. Furthermore, the statement worst starting and loading conditions, whichon page 6 of the RIS is not in agreement with other means the required voltage at the 1 E busregulatory position documents such as GSI 171, prior to the start or run case would have to"Engineered Safety Features Failure (ESF) from a be higher than the setpoint. The main point isLoss of Offsite Power (LOOP) subsequent to a that the setpoint should equate to the limitingLoss of Coolant Accident (LOCA)," which voltage at the limiting component during theconcluded a degraded voltage condition coincident bounding starting or running scenario towith a postulated design basis accident is not a protect the 1 E equipment.credible event.99 Page 6, Section 1 PPL Page 2, Paragraph 3Additional clarification is necessary if starting Disagree.transients must be included when determining the Proper design of the plant electricaldegraded voltage relay (DVR) dropout setpoint. distribution system, given the operatingThis condition will increase the probability of range of the grid and the proper selection ofseparating from the offsite transmission system DVR settings (based on the voltageand increase the likelihood of a double sequencing requirements of the 1 E equipment), shouldevent, which is a potential nuclear safety concern, provide more than adequate operatingmargin, preventing unnecessary separationfrom offsite power.100 Page 8, Section c) PPL Page 2, Paragraph 3The RIS requires performance of analyses for an Disagree.accident in the unit being analyzed andsimultaneous shutdown of all other units at the This statement in the RIS is consistent withstation. This is not consistent with the present GDC 17, GL 79-36, and IEEE StandardSusquehanna design and licensing basis, which is 308-1971, "Class IE Electrical Systems,"an accident on one unit followed by the safe Section 8, "Multi-Unit Station Considerations.shutdown of the second (non-accident) unit. Thesafe shutdown of the non-accident unit is33 No. Section of RIS Originator Specific Comment NRC Resolutionconsidered a controlled shutdown, which followsautomatic operation of the safety related loads onthe accident unit. This accident response is alsoconsistent with the NERC requirements for thedesign of the transmission system. The RIS shouldbe revised to be in agreement with the currentNERC requirementsr101 General PPL Page 2-3, First BulletThe draft RIS attempts to clarify the requirements Disagree.for setting the DVRs based on the criteriaestablished in the following three main documents: The 1977 Letter is a staff which applies to all operating reactors at that1) NRC letters to licensees dated June 2 & 3, 1977, time and plants licensed since, on how to2) Branch Technical Position (BTP), PSB-1 comply with the requirements in 10 CFRRevision 0, Part 50, General Design Criteria 17 (GDC3) Generic Letter 79-36, "Adequacy of Station 17). In addition, NRC's staff position is thatElectric Distribution Systems Voltages" while the BTP's go into some more detail,they are consistent with the 77 Letter.The guidance listed in the draft RIS is notconsistent with all the requirements listed in thesethree documents and a new interpretation isprovided in some cases.It should be generally recognized that a nuclearplant operating license may not have been issuedbased on the above documents. For example, the1977 letters discussed above are not applicable toSSES.102 General PPL Page 3, First BulletThe lack of regulatory clarity in the RIS could result Disagree.in revising the degraded voltage setpoint for aplant's DVR thus increasing the possibility of Proper design of the plant electricalpremature separation from the offsite circuit (i.e., distribution system, given the operatingundervoltage relay actuation). This relay operation range of the grid and the proper selection ofcould lead to an increase in the likelihood of a DVR settings (based on the voltagedouble sequencing event, which has the potential requirements of the 1 E equipment), shouldto create a nuclear safety concern, provide more than adequate operatingmargin, preventing unnecessary separationfrom offsite power.103 General PPL Page 3, Second BulletThe RIS introduces the need for two sets of Disagree.calculations, one to establish the DVR relaysetpoint and one for the interface with the offsite The RIS is primarily identifying that differenttransmission system. The RIS should not specify types of calculations are necessary tothe number of calculations that are necessary for a address different requirements. DVR settingplant to meet a regulatory requirement, calculations consider the voltage of the 1 Eequipment while the plant design is moreabout the operating range of the grid and theresulting voltages in the plant system (whichshould be well above the DVR voltages)104 General PPL Page 3, Third BulletThe condition the DVR is required to "protect" Disagree.needs to be specifically defined along with theapplicable relay setting. (i.e., relay minimum The DVR's function is specified in that itdropout, maximum dropout, or reset). If the DVR is ensures that 1E equipment is supplied withinstalled to provide a level of protection then the adequate voltage in accordance with itsanalysis must demonstrate that the safety related design requirements.equipment is capable of performing its requiredsafety function. An example of this would be thecase where the DVR analysis would need todemonstrate acceptable operation at both thestarting and running equipment ratings when at theDVR dropout setting.105 General PPL Page 3, Fourth BulletA clarification of the term "sustained" is needed to Disagree.determine if "sustained" refers to a steady statevoltage condition (i.e., no equipment starting Sustained degraded voltage, as discussed involtage effects) for which the DVR setting is to be the NRC 1977 letter as well, refers to gridestablished. voltage below the expected low value given34 No. Section of RIS Originator Specific Comment NRC Resolutionnormal grid operation.106 General PPL Page 3, Fifth BulletThe guidance in the RIS is too general when Disagree.referring to operating voltages. The specific voltagerequirements need to be specified instead of The term voltage requirements used in theimplied by a general term. The RIS needs to clarify RIS is defined in terms of equipmentthat the impact of the nuclear unit trip on the manufacturer design requirements. NRCtransmission system voltage must be considered in Staff feels that this terminology is sufficientlythe plants voltage analysis. specific. Additional wording has been addedto the RIS to clarify that unit trip voltageimpact should be factored into the accidentanalysis cases.107 General PPL Page 3, Sixth BulletThe time delays suggested are not consistent with Disagree.PSB-I. The PSB established one time delay toallow for operator action. The RIS does not While there may be differences, the BTPsaddress this requirement, are guidance documents and represent anapproach but not necessarily the onlyapproach. In addition, following the guidancedocuments approach will satisfy the GDC 17requirements.108 General PPL Page 4, First BulletThe RIS also lacks any acknowledgement of Disagree.preventative measures the licensees have taken tominimize the potential for a degraded voltage Regardless of improvements made in termscondition. Advancements in plant loadflow of grid operation and understanding of gridanalyses and measures to increase the reliability of operation's impact on plant voltages, thethe offsite transmission system are industry plant design has always had to properlyimprovements that have occurred since the address grid operating parameters and theirdegraded voltage events that occurred 35 years impact on plant voltages in all modes ofago. operation. This point was properlyemphasized in the RIS as was in the originalregulations and guidance.109 General APS Page 2. 1.The draft RIS asserts that there is a simple and Disagree.singular set of design criteria that have beenapplied universally to the industry. Over the years The 77 Letter provides staff positions on thethe degraded voltage performance requirements design criteria in that the voltagehave changed, as a specific issue, and on a requirements for the 1 E equipment has to becomponent basis (e.g., motor operated valves and ensured by the DVR circuits by automaticcontactors), for individual nuclear power plants. As separation from offsite and transfer to thea result, each nuclear power plant has specific onsite sources.licensing bases, and there is no singular set ofrequirements that have been applied universally tothe industry.110 General APS Page 2, 2.The draft RIS asserts that the guidance provided to Disagree.the industry to address the Millstone and otherdegraded voltage events adequately addresses The DVR circuits will automatically separatethis potential common mode failure. The common the 1 E circuits from offsite power whenmode failure potential is that multiple trains of voltage requirements are not met which willsafety equipment could be simultaneously prevent the Millstone type eventnegatively impacted if off-site power is degraded. automatically.The deterministic guidance provided does notappear to effectively address integrated plantresponse nor preclude a Millstone type event. Theuse of degraded voltage relays to address thispotential failure mode is not consistent withoperating experience and lacks adequate technicalbasis as described in the detailed technicalcomments that follow.111 Page 6 APS Page 2, 3.The draft RIS (page 6 of 10) states: Disagree'The staff considers degraded voltage conditions The point being made in the RIS is thatcoincident with a postulated design basis accident setting of the DVR should includeto be a credible event." consideration of a coincident accident signalin that the time delay chosen for the DVR35 No. Section of RIS Originator Specific Comment NRC ResolutionIt is our understanding that the established staff should support the accident analysisinterpretation is that this is not a credible event, as assumptions consistent with the NRC1977discussed and supported by analysis in NUREG- letter.0933, Supplement 33, dated August 2010,Resolution of Generc Safety Issues, Issue 171,ESF Failure from LOOP Subsequent to a LOCA,and Brookhaven National Laboratory NUREG/CR-6538 (BNL-NUREG-52528), Evaluation of LOCAWith Delayed Loop and Loop With Delayed LOCAAccident Scenarios, Technical Findings Related toGSI-1 71, 'ESF Failure from LOOP Subsequent toLOCA' published July 1997. This appears to be anew staff interpretation and no documentedanalysis is provided to support it. Therefore, if thescenario is credible, as the draft RIS asserts, thenGSI-171 is not adequately resolved and should bereevaluated.112 General APS Page 5, 4. DisagreeThe recent licensing actions in the industry whichhave mandated setpoint changes for the degraded Setting the DVRs in accordance with thevoltage relays (DVRs) and loss of voltage relays voltage requirements of the 1E equipment(such as the one cited in the draft RIS for Fermi-2) coupled with a properly designed plantonly serve to increase the probability of the 'ESF electrical distribution system (and based onFailure from LOOP Subsequent to a LOCA' event the grid's allowable voltage range) mustdiscussed in NUREG/CR-6538 without providing provide adequate voltage margin to precludean advantage for any credible scenario. As such, offsite separation.these changes may increase core damagefrequency (CDF).DisagreeIt is APS's understanding that a comprehensivereview of guidance related to degraded grid voltage NRC staff asserts that the regulations andhas not been performed using the cost-benefit and positio 3uidance articulated in the RIS arerisk criteria of 10 CFR 50.109 (backflit rule), nor is it consistent with the existing regulatoryapparent that risk insights have been used to requirements and NRC staff inform this guidance. guidance therefore do not constitute new ordifferent positions with respect to the backfitrule (50.109).113 General APS Page 5, 5.The draft RIS does not address the implication of Disagree.the Branch Technical Position (BTP) PSB-1requirement that "The Class 1 E bus load shedding The design of the plant electrical distributionscheme should automatically prevent shedding- system and the onsite sources shouldduring sequencing of the emergency loads to the provide for adequate voltage to all 1 Ebus." A large variety of voltage conditions could equipment in all normal, abnormal andexist during the sequencing period while the accident conditions.shedding is blocked, and no analytical methods arediscussed that could demonstrate that equipment Typical designs do not block the DVR or thedamage or malfunction would not occur. LOV relay when sequencing loads on theoffsite source. Hence load shedding in theevent of a loss of offsite power should bepart of the design basis. A large variation ofvoltage conditions can occur during variousoperating modes of a nuclear plant. TheDVR setpoint should be based on limitingconditions. If the recommendations of BTPPSB-1 are followed, the probability of eventssuch as double sequencing is minimized.114 Page 7 APS Page 5-7, 6.In light of the summary of the resolution of GSI- Disagree.171, the draft RIS statement (page 7 of 10) that"the time-delays(s) chosen for DVRs during Degraded voltage conditions can beaccident conditions should meet the accident postulated to occur at anytime. The DVRanalysis assumptions..." does not seem setpoint should accommodate the limitingappropriate. The degraded voltage condition could case for equipment protection. If theoccur at various times during the initial energization recommendations of BTP PSB-1 areof the accident mitigation equipment, and the relay followed, then a separation from theI time delay value only affects the additional time degraded grid coupled with accident signal is36 No. Section of RIS Originator Specific Comment NRC Resolutionuntil the subsequent LOOP occurs, the preferred approach to resolve the issueand satisfy accident analyses.115 Page 8 APS Page 7-8. 7.It is not feasible for multi-unit nuclear plants to Disagreesuccessfully demonstrate that voltage from theoffsite circuits would be adequate, as described inthe draft RIS (page 8 of 10), for:This wording in the RIS is the same as was"(1) an accident in the unit being analyzed and used in GL 79-36.simultaneous shutdown of all other units at thestation; or (2) an anticipated transient (anticipatedoperation occurrence) in the unit being analyzed(e.g.. unit trip) and simultaneous shutdown of allother units at that station." TPL-004 requires transmission planning toaddress simultaneous multiple transmissionNorth American Electric Reliability Corporation contingencies.(NERC) Standard TPL-004 recognizes that thedesign and operating constraints of the The requirements of TPL-004 are not withintransmission network are such that the loss of all the scope of RIS.generating units at a station could result in portionsor all of the interconnected system not achieving anew, stable operating point.It is beyond the nuclear plant operator's authority orcapability to ensure otherwise.116 Page 6 APS Page 8, 8.The draft RIS (page 6 of 10) contains the followingstatement:"The Class I E buses should separatefrom the offsite power system within afew seconds if an accident occurscoincident with sustained degradedvoltage conditions."This statement appears to reflect the position ofRevision 3 of BTP 8-6, which states, in part:"The first time delay should be longenough to establish the existence of asustained degraded voltage condition(i.e., something longer than a motor-starting transient). Following this delay,an alarm in the control room should alertthe operator to the degraded condition.The subsequent occurrence of a safetyinjection actuation signal (SIAS) shouldimmediately separate the Class 1 Edistribution system from the offsite powersystem. In addition, the degraded voltagerelay logic should appropriately functionduring the occurrence of an SIASfollowed by a degraded voltagecondition." Disagree.This is not currently a design or licensingrequirement for all existing plants. As such the RIS As a result of these Millstone events, theprocess would not be the appropriate method to NRC requested that all licensees implementcommunicate a new regulatory position. degraded protection as described in the1977 Letter to ensure automatic protection ofsafety buses and loads. This Letter providesstaff post3nguidance, which applies to alloperating reactors at that time and plantslicensed since, on how to comply with therequirements in 10 CFR Part 50, GeneralI Design Criteria 17 (GDC 17).37 No. Section of RIS Originator Specific Comment NRC Resolution117 Page 6 APS Page 8-9, 9.The draft RIS (page 6 of 10) contains the followingstatement:'The time delay chosen should be optimized toensure that permanently connected Class I Eloads are not damaged under sustained degradedvoltage conditions (such as sustained degradedvoltage just above the LVR voltage setting for theduration of the DVR time delay setting)."This deterministic approach, while appearing Disagreeconservative, has the net effect of increasing thefrequency of delayed LOOP events during The voltage studies done for evaluatingtransients, even when the subsequent sustained offsite power/onsite power interface shouldvoltage condition is not degraded (see Comment use minimum expected voltage at the4), with resulting adverse effects as discussed in plant/grid interface node, demonstratingthe resolution of GSI-171. It also neglects adequate voltage for starting and running ofconsideration of the voltage levels that must be plant components during normal, abnormalmaintained in the event of a unit trip and coincident and accident conditions. The voltage studiesaccident to prevent delayed LOOP events. Finally, for the DVR setpoints should requirethe draft RIS is silent on the particulars of the plant/grid interface node voltages well belowvoltage studies that would be acceptable to use to the minimum expected values (including postdetermine the optimum time delay (such as the grid contingency).plant operating conditions and voltage profile).118 Page 6 APS Page 9, 10.The DVR Setting Design Calculations section(page 6 of 10) indicates that:"models would allow calculation of voltages atterminals or contacts of all safety relatedequipment with the voltage of the DVR monitoredbus at the DVR dropout setting, providing thenecessary design basis for the DVR voltagesettings. In this manner, the DVR ensuresadequate operational (starting and running) voltageto all safety related equipment, independent ofvoltage controlling equipment external to the plantsafety related electrical distribution system."This seems to impose a new requirement. Further, Disagreethe described model is of a nondegraded voltagescenario that does not result in DVR actuation. The DVR dropout setting should beTherefore, it does not demonstrate that "required developed based on the voltagesafety related components are provided adequate requirements (starting and running) andvoltage" for accidents with degraded voltage therefore to develop values which arescenarios. That conclusion could only be bounding, the studies should be done underdemonstrated by modeling degraded voltage worst starting and loading conditions whichscenarios that involve DVR actuation. However, in means the required voltage at the 1E busall cases involving degraded voltage coincident prior to the start or run case would have towith postulated accidents, such models would be higher than the setpoint. The main point isresult in delayed LOOP scenarios as discussed in that the setpoint should equate to the limitingGSI-171. voltage at the limiting component during thebounding starting or running scenario toAlso, it reflects a non-conservative voltage profile. protect the 1 E equipment.If the voltage at the DVR monitored bus was at theDVR dropout setting prior to starting a motor, it The RIS does not impose any newwould be lower than that during and after starting requirements. It provides clarification onthe motor, and the voltage at the motor terminals existing requirements.would be correspondingly lower, as well, comparedto the results using the constant bus voltage The DVR setpoint should be optimized formethodology described in the draft RIS. motor starting transient and protection ofI safety related equipment.119 Page 5 APS Page 10, 11.The draft RIS discussion asserts that the NRC DisagreeOffice of Nuclear Reactor Regulation (NRR) Task38 No. Section of RIS Originator Specific Comment NRC ResolutionInterface Agreement (TIA) response (TIA 2010-05) The point being made in the RIS is that"concluded ... the time delay to transfer from a setting of the DVR should includedegraded offsite source to the standby power consideration of a coincident degraded gridsource to support the emergency core cooling and accident in that the time delay chosenequipment operation must be consistent with for the DVR should support the accidentaccident analysis time assumptions, as required by analysis assumptions consistent with theBTP PSB-1 (NUREG 0800)." This statement is not NRC1 977 letter.included in the TIA response. The TIA response(pages 4 and 5) quotes the Palo Verde UFSARdescription for the design requirements of thedegraded voltage relays, and this specific timedelay provision is not included in the PVNGSUFSAR.This specific time delay provision was removed aspart of the PVNGS license amendment 123 Task Interface Agreement 2010-005process and was specifically addressed in the NRC (ADAMS Accession No. ML102800340)and APS correspondence (NRC Letter dated June provides more details regarding Palo Verde14, 1999, and APS letter dated July 16, 1999, degraded voltage inspection finding.Question 13). The subject matter of the TIA did notinclude the time delay element of the design, with Plant specific findings are not in the scope ofregard to the accident analysis time assumptions, the RIS.but rather was focused upon whether licenseamendment 123 bounded the need to performdesign basis electrical calculations for thedegraded voltage relay low setpoint value of 3697volts or below.120 Page 5 APS Page 10-11, 12.The draft RIS asserts that PVNGS erroneouslymaintains that a degraded voltage conditionconcurrent with a design basis accident is notcredible. PVNGS had originally implemented thedesign approach included in the NRC letterQualification Review of the PVNGS Units 1,2 and3, dated December 12, 1977. Based on operatingexperience (LER 50-528/529/530-93-01 1)-and sitespecific license amendment 123, PVNGS tookaction to preclude such an event, by implementingnew TS LCO 3.8.1, Condition G. This approachwas consistent with the resolution of GS1-171,alternative 3, and was approved. Disagree.The prevention strategy was implemented to The point being made in the RIS is thatpreclude a concurrent degraded voltage condition setting of the DVR should includeand design basis accident because the PSB-1 type consideration of a coincident degraded griddesign is not capable of adequately coping with and accident in that the time delay chosensuch an event. All such events would result in for the DVR should support the accidentdelayed LOOP/double sequencing scenarios, as analysis assumptions consistent with thedescribed in GSI-171, for which there is no viable NRC1977 letter.analytical approach.The licensee should ensure that SI actuationat a point just above the DVR set pointshould not cause double sequencing.See staff response to Task InterfaceAgreement 2010-005 (ADAMS AccessionNo. ML102800340) for more detailsregarding Palo Verde degraded voltageinspection finding.121 Page 5 APS Page 11,13.PVNGS originally implemented the second leveldegraded voltage protection design consistent withNRC letter Qualification Review of the PVNGS Disagree39 No. Section of RIS Originator Specific Comment NRC ResolutionUnits 1,2 and 3, dated December 12, 1977. As aresult, reference to PSB-1 in the draft RIS for The licensee's analysis must show thatPVNGS does not reflect the historic licensing basis degraded voltage trip setpoint adequatelyfor PVNGS. protects the equipment powered by the 4.16kV ESF bus from a potentially damagingdegraded voltage condition.The NRC regulatory requirement is Criterion17 of Appendix A to 10 CFR Part 50. TheNRC staff guidance and positions aredescribed in PSB-1.See staff response to Task InterfaceAgreement 2010-005 (ADAMS AccessionNo. ML102800340) for more detailsregarding Palo Verde degraded voltageinspection finding.122Page 5APSPage 11, 14.Inspection Report 2009-008 is described in thedraft RIS. The specific elements of the inspectionreport that require response are next described.The inspection report states:"the time delay of 35 seconds for transfer of safetybuses to the onsite power supplies may be too longto prevent core damage in case of a sustaineddegraded voltage condition concurrent with anaccident. This time delay could result in a delay insupplying water to the core in case of an accidentconcurrent with degraded voltage, due to theinability of electrical equipment to respond asrequired during the timeout period."APS Response: This is a double sequencingscenario, which is a malfunction of an SSC with adifferent result than previously evaluated pursuantto 10 CFR 50.59, for PVNGS. It could result in coredamage regardless of the time delay value at whichthe DVR actuation (delayed LOOP) occurs. This isthe reason APS precludes such an event byestablishing appropriate initial conditions, with TSLCO 3.8.1, Condition G, through licenseamendment 123.Disagree.The point being made in the RIS is thatsetting of the DVR should includeconsideration of a coincident degraded gridand accident in that the time delay chosenfor the DVR should support the accidentanalysis assumptions consistent with theNRC1977 letter.The focus of the RIS is to clarify regulatoryrequirements.See staff response to Task InterfaceAgreement 2010-005 (ADAMS AccessionNo. ML102800340) for more detailsregarding Palo Verde degraded voltageinspection finding.The double sequencing issue is a plant-specific issue. The staff determined that theamendment that addressed the specificdesign issue (double sequencing) at PVNGSdid not change the licensing requirements forthe degraded voltage protection at PVNGS.123 Page 5 APS Page 11-12, 15.The inspection report states:"A shorter time delay will not delay the timerequired to provide water to the core, but willactually improve it."APS Response: APS is not aware of any analysis Disagreein the GSI-171 resolution document to suggest that I40 No. Section of RIS Originator Specific Comment NRC Resolutiona shorter time delay (e.g., delayed LOOP occurring This is a plant specific issue. The issue willsooner) would be of any benefit in preventing the be reviewed through the ROP.failure mechanisms associated with a delayedLOOP or assuring that water would be successfullyprovided to the core. See Technical Comment 6 forfurther discussion on the lack of correlationbetween the DVR time delay setting, accidentanalysis time, and core damage.The PVNGS current licensing basis for the DVRtime delay is > 28.6 seconds. During the reviewthat led to issuance of PVNGS license amendment123, the staff expressed a concern that a minimumallowable time delay be specified to assure thatunnecessary separation from offsite power wouldnot occur. The safety evaluation for licenseamendment 123 states:"APS responded by adding a lower limit (> 28.6seconds) to the time delay allowable valuespecified for the degraded voltage function in itsrevised submittal date6 September 29, 1999. Thischange resolves the staffs concern on this matter."The NRC staff was aware and approved theexisting time delay values for the DVRs and thestaff considered a shorter time delay to be aconcern. The inspection report is inconsistent withthe current safety evaluation.124 Page 5 APS Page 12,16.The inspection report states:'The licensee had offered the proposition thatdegraded voltage concurrent with an accident wasnot credible, but the team could not find evidencethat the NRC had accepted this position, or that thedegraded voltage relays were no longer required toperform a protective function during accidents."APS Response: The PVNGS current licensingbasis is documented in the safety evaluation for Disagree.PVNGS license amendment 123, which states:See staffs response to Comment No. 123'The licensee's proposed revision to TS 3.8.1,Condition G is designed to preclude a degradedvoltage/double sequencing scenario from occurringat the Palo Verde site. The staff finds this approachacceptable.The safety evaluation recognizes that theprevention strategy precludes degraded voltageconditions from occurring. All scenarios involvingdegraded voltage concurrent with an accident aredelayed LOOP/double-sequencing scenarios. Thepurpose for PVNGS license amendment 123 wasto implement a method to prevent this degradedvoltage concurrent with an accident (which wouldalways result in a delayed LOOP and doublesequencing). APS is not aware of an acceptedmethod to ensure that core damage will not result,if such an event were to occur. Design basiscalculations to justify the function of the degradedvoltage relays during accidents are not feasible,because they would be unable to justify thedelayed LOOP/double sequencing effectsdiscussed in GSI-171.125 Page 6 Nextera 1 This paragraph could be interpreted to require theLOCA sequence to be modeled at the DVR dropout Disagreesetting. LOCA sequencing modeled at the DVR41 No. Section of RIS Originator Specific Comment NRC Resolutiondropout setting would result in separation of the The dropout setting should be developedbuses from the Preferred Power Source (off-site based on the voltage requirements (startingpower) as the voltage would not recover above the and running) and therefore to develop valuesDVR reset value, which are bounding, the studies should bedone under worst starting and loadingClarify the intent is to show safety related conditions which means the required voltageequipment will function at the selected DVR at the 1 E bus prior to the start or run casedropout setting voltage and that it is not expected would have to be higher than the setpoint.to start the LOCA sequence from this voltage level. The main point is that the setpoint shouldequate to the limiting voltage at the limitingClarify that LOCA sequencing is evaluated using component during the bounding starting orminimum switchyard voltage as starting point, running scenario to protect the 1 Eequipment.126 Page 6 Nextera 2 Having a sustained degraded voltage just above Agree.the LVR voltage setting (70%) is not practicalwithout grid collapse and does not exist in Branch The DVR setpoints are calculated based onlyTechnical Position #1 (PSB-1). on the voltage requirements of the 1Eequipment, not based on whether the gridClarify degraded voltages to be analyzed to a can sustain voltage at levels that result incredible level, such conditions.127 Page 6 Nextera 3 The statement that the DVR ensures adequateoperational (starting and running) is the first time in DisagreeNRC correspondence that starting equipment atthe DVR setpoint is expected. The example letter The dropout setting should be developedsent to Peach Bottom in June 1977 did not require based on the voltage requirements (startingstarting of equipment at the DVR setpoint. This and running) and therefore to develop valuesrequirement should be removed from the RIS since that are bounding, the studies should beit is not possible to start equipment at the DVR done under worst starting and loadingsetpoint and not subsequently separate from offsite conditions, which means the required voltagepower. If the equipment starts at the DVR setpoint, at the 1 E bus prior to the start or run casethe voltage will dip during the transient and must would have to be higher than the setpoint.then recover above the reset point to avoid The main point is that the setpoint shouldseparation from offsite power. Since the reset point equate to the limiting voltage at the limitingwill always be above the DVR dropout point it will component during the bounding starting orbe impossible to reset the relay. running scenario to protect the 1 Eequipment.Remove starting of equipment at the DVR setpointas a requirement.128 Page 7 Nextera 4 It is agreed that no credit is to be taken for voltagecontrolling equipment external to the Class 1 E Agreedistribution system for the establishing thedegraded voltage relay (DVR) settings; however, it Additional wording has been added to theshould be clarified that for credit may be taken for Offsite/Plant distribution discussion to makeminimum switchyard voltage/voltage drop it more clear that equipment like automaticcalculations (or the Offsite/Onsite Design Interface load tap changers can be credited if theCalculations). response time will support normal operation.Clarify that credit may be taken for automatic loadtap changers and/or capacitor banks for minimumswitchyard voltage/voltage drop calculations (or theOffsite/Onsite Design Interface Calculations).129 Page 8 Nextera 5 NRC Generic Letter 79-36, Enclosure 2, Item 2states that It is recommended that "For mulfi-unitstations a separate analysis should be performedfor each unit assuming (1) an accident in the unitbeing analyzed and simultaneous shutdown of allother units "Offsite/Onsite at the station; or (2) ananticipated transient in the unit being Designanalyzed (e.g., unit trip) and simultaneous42 No. Section of RIS Originator Specific Comment NRC Resolutionshutdown of all Interface other units at that station,whichever presents the largest Calculations", loadsituation."Comment:NRC Draft RIS re-states NRC GL 79-36 verbatim, Disagreewith an attempt to clarify "anticipated transient' byadding in parenthesis "(anticipated operational The reference added is the wording used inoccurrence)" immediately afterwards. It is not clear GDC 17 (for consistency).what the added parenthetical statement is meant toconvey, other than unit trip (which already exists inGL 79-36).It is recommended that this either be removed, orstated "anticipated transient per station licensingbasis".130 Page 8 Nextera 6 NRC should clarify "simultaneous shutdown" withconsideration to:Most multi-unit station's Licensing Basis consideran "orderly or controlled safe shutdown" of the Disagreeother unit(s) not being analyzed.NERC Std TPL-004-0; particularly Category D This wording in the RIS is the same as wasevents per Table 1, where a "loss of all generating used in GL 79-36.units at a station" may result in "portions or all ofthe interconnected systems may or may not TPL-004 requires transmission planning toachieve a new, stable operating point'. address simultaneous multiple transmissioncontingencies.IEEE Std 308-1974, Clause 8, subclause 8.1.1"Capacity' describes this as a "concurrent safe The plant licensing basis provides basis forshutdown on the remaining units", analyses related to multi unit sites.The wording for the proposed RIS, subclause 2.cshould be revised to indicate "orderly or controlledsafe shutdown of the remaining units, as per thestation's licensing basis" instead of "simultaneousshutdown". Alternatively, the wording "shutdownconsistent with the station licensing basis" could beused instead of "simultaneous shutdown".131 Page 8 Nextera 7 These guidelines (e) and f )seem contradictorythat you cannot credit procedurally controlled Disagree.operator actions to reduce load but you have toassume the actions will be carried out when load is These guidelines are not contradictory in thatadded, one is considering load shedding (notconservative) for design of system based onDelete "e) Manual load shedding should not be maximum load, while the other is about loadassumed" or add allowance to credit procedurally additions that occur per procedurecontrolled operator actions to decrease load. (conservative for maximum loading design).132 General TVA Comment: The RIS suggests that demonstratingadequate motor starting voltage is a reasonableobjective or outcome of a setpoint calculation for aDegraded Voltage Relay whose purpose is to Disagreeprotect Class 1 E equipment.TVA's position is that such an objective or outcomeis not technically achievable for the reasonsdiscussed below:1) A Voltage Relay is not a Predictive DeviceThe DVR dropout setting should beVoltage sensing equipment cannot provide a developed based on the voltagepredictive function without crediting the capacity or requirements (starting and running) andcapability of the upstream system, since it cannot therefore to develop values that aredetermine the capacity or capability provided bounding, the studies should be done underduring a transient condition such as a motor start, worst starting and loading conditions, whichSince the existing regulatory framework for means the required voltage at the 1 E bus43 No. Section of RIS Originator Specific Comment NRC Resolutiondegraded voltage protection was based on use of prior to the start or run case would have tovoltage relaying, it is not clear how the existing be higher than the setpoint. The main point isrelaying equipment could be used to demonstrate that the setpoint should equate to the limitingcompliance with an adequate motor starting voltage at the limiting component during thedemonstration requirement. bounding starting or running scenario toprotect the 1 E equipment. In addition, the2) A Degraded Voltage Relay Protection Setpoint time delay would be determined based onBased on Starting Voltage Does Not Provide Motor the limiting starting transient duration onlyProtection (not based on allowing time for operatoraction). In this manner, if the voltage dropsThis method could potentially be calculated but below expected values during startingwould mean that the DVR setpoint would have (based on the 1 E equipment limits) andbeen determined during the starting of the most prolongs the start transient, then the DVRlimiting Class-I E motor. A degraded voltage relay will timeout and separation will occursetpoint based on a motor starting would not (providing low starting voltage protection).protect the motor from damage (required byregulations) or preclude tripping of the motorsover-current device(s) prior to transferring to theonsite power supply (required by regulations). Thisis because the DVR time delays are (by definition)required to be longer than a motor starting transient(1 st time delay) and long enough to allow operatorintervention (2nd time delay). If starting of thelimiting (worst-case) motor was attempted in a truedegraded voltage situation (even slightly below theDVR setpoint), the DVR scheme could not performeither of these protective functions prior to trippingthe normal overcurrent relays. Therefore, thiswould not provide any additional protection for theClass-1 E loads.133 General Progress Background: The draft NRC Regulatory IssueEnergy 1 Summary, 2011 -xx, Adequacy of Station ElectricDistribution System Voltages, describes amethodology of implementation for degradedvoltage relay schemes that would impose"Additional Conservatisms" into the settings andtime delays in an effort to further reduce the risk of Disagree.degraded voltage operation on nuclear plant safetyrelated / accident mitigating electrical equipment. Additional conservatism should not be addedfor the sake of adding conservatism."Additional Conservatisms" from this point of view Conservatism is typically added totends to mean that the degraded voltage relaying compensate for assumptions that cannot bewill actuate earlier in a degraded voltage event time accurately verified or proven (e.g. cableline -meaning it would be set to actuate at a higher impedances when actual pull lengths are notdegraded voltage and/or with a shorter time delay. known).In conflict with the NRC's desire to impose NERC and FERC guidelines are reviewed byadditional conservatisms on degraded voltage NRC staff for applicability to nuclear plantprotection at nuclear power plants, the North operation.American Electric Reliability Corporation (NERC),is developing a national standard for Frequency The DVR and loss of voltage relay settingsand Voltage Excursion Ride- Through Performance should not be in conflict with NERC or FERC(PRC-024) for all generating stations in North recommended guidelines for grid operations.America. The Voltage Excursion Ride-ThroughTime Duration Curves currently proposed by theNERC Standards Drafting Team shows thecompeting desire for nuclear power plants to becapable of riding through a grid induced voltagetransient without tripping.Actuation of the degraded voltage relaying in anuclear power plant during a grid induced voltagetransient results in a temporary loss of power to thesafety related loads powered from the plant busesuntil the loads are realigned to an emergencypower source and reenergized. This temporary lossof power will result in a trip of the nuclear plant inmany cases and a significant challenge to44 No. I Section of RIS Originator I Specifc Comment I NRC Resolutioncontinued operation of the plant in all cases.An analysis of current settings and time delays forseveral nuclear plant loss-of-voltage and degradedvoltage relay schemes against the proposed NERCride through criteria shows that existing settings arealready in conflict with the proposed ride-throughcriteria.Imposition of additional conservatisms into therelay settings and time delays for nuclearplant equipment degraded voltage protection willfurther complicate efforts to coordinateNRC required degraded voltage protectionschemes with NERC voltage transient ridethroughcapability needs.Comment: Please coordinate NRC Staff proposeddegraded voltage relay settingmethodology changes with NERC proposedvoltage transient ride-through capabilitystandard (PRC-024) by engaging with NERC underthe current NRC -NERC Memorandum ofAgreement (MOA).134GeneralProgressEnergy 2Background: The use of on-load automatic load tapchanging transformers for nuclear plant offsitepower supplies would aid in minimizing auxiliarybus under voltage or degraded voltage transientsof concern to the NRC while also improving thevoltage transient ride through capability of thenuclear plants that is of concern to NERC.Comment: Please revise the RIS to allow thenuclear plants to use and take credit for on loadautomatic load tap changing transformers fornuclear plant offsite power supplies to preventdegraded voltage events and improve the voltagetransient ride through capability of the nuclearplants.AgreeLoad tap changers help improve voltageregulation for normal plant operation. Loadtap changers do not help protect safetyrelated equipment during degraded gridconditions.Additional wording has been added to theOffsite/Plant distribution discussion to makeit more clear that equipment like automaticload tap changers can be credited for normalplant operation.135 GeneralProgressEnergy 3Comment: Please also consider the italicizedchanges below:DVR Setting Design CalculationsLicensee voltage calculations should provide thebasis for their DVR settings, ensuring safety relatedequipment is supplied with adequate operatingvoltage (typically a minimum of 0.9 per unit voltageat the terminals of the safety related equipment perequipment manufacturers requirements), based onbounding conditions for the most limiting safetyrelated load (in terms of voltage) in the plant.These voltage calculations should model the plantsafety related electrical distribution system suchthat the limiting voltage at the bus monitored by theDVR can be calculated in terms of the voltage atthe terminals of the most limiting safety relatedcomponent in the plant. These models would allowcalculation of voltages at terminals (delete "orcontacts ") of all safety related equipment with thevoltage at the DVR monitored bus at the DVRdropout setting, providing the necessary designAgree!fafcizd Ghanges suggested wer'GORtdOFzd alOAg With OthOF 8imil!ar.nd dg..fi.d in the RIS wr.... Italicizedchanges were not incorporated in the RISs...e.... .o..r.. s.w.... o.. .o.. s.. n wan.....since mhe comments were riot consistent withthe staff's existing guidance for DVRsettings.45 No. I Section of RIS I Originator Specific Comment NRC Resolutionbasis for the DVR voltage settings.In this manner, independent of voltage controllingequipment external to the plant safety relatedelectrical distribution system, the DVR ensures thatall safety related equipment can continue tooperate at the degraded voltage relay drop outsetting if previously in service, small loads will notbe damaged if successfully started at the degradedvoltage without DVR time out (the DVR either doesnot drop out or resets before time out because thestarted load is small), and larger loads will not bedamaged or trip on overload/protective relaying ifstarting the equipment results in sustaineddegraded voltage for the duration of the D VR timedelay (the DVR drops out and does not resetbecause the load is large but the DVR timer timesout and sheds the load from the degraded voltagesource before the overloads and/or protectiverelaying actuates).For the purposes of this DVR Setting Designcalculation, no credit should be taken for voltagecontrolling equipment external to the Class 1 Edistribution system such as automatic load tapchangers and capacitor banks because thesedevices normally prevent degraded voltage fromoccurring and thus, by definition, should not beincluded in a bottom up analysis to determineminimum voltage requirements for the safetyrelated loads. Voltage time settings for DVRsshould be selected so as to avoid spuriousseparation of safety buses from the offsite powersystem during unit startup, normal operation andshutdown. These DVRs should disconnect theClass 1 E buses from any power source other thanthe emergency diesel generators (onsite sources) ifthe degraded voltage condition exists for a timeinterval that could prevent the Class 1 E safetyrelated loads from achieving their safety function.The DVRs should also protect the Class 1 E safetyrelated loads from prolonged operation belowsustained degraded voltage which could result inequipment damage.The licensees should demonstrate that the existingDVR settings including allowable values and timedelays are adequate so that safety related loadscan continue to operate at the degraded voltagerelay drop out setting if previously in service, smallloads will not be damaged if successfully started atthe degraded voltage without DVR time out, andlarger loads will not be damaged or trip onoverload/protective relaying if starting theequipment results in sustained degraded voltagefor the duration of the DVR time delay resulting inseparation from offsite power and realignment tothe emergency onsite power supply. The time-delay(s) chosen for DVRs during accidentconditions should be short enough to meet theaccident analyses assumptions and allow forproper starting of all Class 1 E safety relatedequipment assuming that the DVR time delay timesout and the accident mitigating loads realign to theonsite emergency power supply. Also, the timedelay chosen for DVRs during non-accidentcondition must be short enough to not cause anydegradation of the safety related components,includina actuation of their orotective devices."Contacts" was deleted.46 No. Section of RIS Originator Specific Comment NRC Resolution136 General Progress Comment: Please also consider the italicizedEnergy 3 changes below: AgreeOffsite/Onsite Design Interface CalculationsThe offsite power source is the preferred source of ltzed Ghz'gc suggested werepower to safely shut down the plant during design ....red wt;h oher sim -labasis accidents, abnormal operational occurrence, commaiti rzezizvd fro' other and reactor trips. The licensee's voltage And d in the RiS riev!ir.etjalici.._calculations should provide the basis for proper changes were not incorporated in the RISoperation of the plant safety related electrical since the comments were not consistent withdistribution system, when supplied from the offsite staffs existina auidance for offsite/onsitecircuit (from the transmission network). These design interface calculations.calculations should demonstrate that the voltagerequirements (both starting and operationalvoltages) of all plant safety related systems andcomponents are satisfied based on operation of thetransmission system and the plant onsite electricpower system during normal, startup, shutdown,accident mitigation, and alternate authorizedoperating configurations of transmission networkand plant systems. In this way, all safety relatedsystems and components will function as designedwith proper starting and running voltages during allplant conditions and the DVRs will not actuate(separating the transmission network supply).Following are guidelines for voltage dropcalculations derived from Generic Letter 79-36,which have been supplemented to add clarifyinginformation. They do not represent new NRC staffpositions.137 General Progress Comment: Please also consider the italicizedEnergy 3 changes below: AgreeGuidelines for voltage drop calculationsa) The plant voltage analysis, while supplied from !tR!acized changei Suggested werethe transmission network, should be based on the GG*deFrzdalong with theFr imFiIAroperating voltage range of the transmission Femr.-tc from ether qtAktIhcldernetwork connection. This transmission And nlrwfied nR the P.IS owner/operator supplied voltage range should changes were not incorporated in the RISaddress normal, startup, shutdown, accident since the comments were not consistent withmitigation, and altermate authorized transmission staffs guidance provided in Generic Letternetwork and plant system operating configurations 79-36.and should also include voltage drop due to thebounding worst case transmission system singlecontingency (transmission system contingenciesinclude trip of the nuclear power unit). Normally in-service and periodically tested non-safety relatedequipment (such as automatic load tap changingtransformers that regulate voltage during changingconditions) are to be included in the analysis.b) Separate analyses should beperformed assuming the powersource to the safety buses is (1) theunit auxiliary transformer; (2) thestartup transformer; and (3) otheravailable connections (e.g., from allavailable connections) to the offsitenetwork one by one assuming theneed for electric power is initiatedby (1) an anticipated transient suchas a unit trip (e.g., anticipatedoperational occurrence), or (2) anaccident, whichever presents thebounding load demand on thepower source.47 No. Section of RIS Originator Specific Comment NRC Resolution138GeneralSTARS"Statement of Staff Positions Relative toEmergency Power Systems for OperatingReactors"RIS 201 1-XX states that "the NRC requiredlicensees to install degraded voltage protectionschemes ,.. as described in NRC Letters datedJune 2 & 3, 1977, 'Statement of Staff PositionsRelative to Emergency Power Systems forOperating Reactors,' which were sent to alllicensees of all operating nuclear power plants. Asan example, see the NRC letter dated June 2,1977, ADAMS Accession No. ML1 00610489, sentto the licensee for Peach Bottom Atomic PowerStation." (Ref. 2) However, the RIS does notrecognize the latitude in response allowed to eachLicensee:'We request that you compare the current designof the emergency power systems at yourfacility(ies) with the Staff Positions stated in theenclosure and:(1) propose plant modifications as necessary tomeet the Staff Positions, or(2) provide a detailed analysis which shows yourfacility design has equivalent capabilities andprotective features.Additionally, we require that certain technicalspecifications be incorporated into all facilityoperating licenses."Observations:1. The NRC letters request some actions andrequire some actions -specifically -a technicalspecification change.2. The response makes allowance for variedresponses that account for "equivalent capabilitiesand protective features." These varied responsesbecome part of the licensees' Current LicensingBasis.3. Licensees were required to change theiroperating license because the staff position.However, this in and of itself, does not change thelicensees' Current Licensing Basis.4. The "1977" letters apply only to addressees, i.e.,plants licensed before 1977."Adequacy of Station Electric Distribution SystemVoltages"The technical content, with some modifications, ofthe "Statement of Staff Positions Relative toEmergency Power Systems for OperatingReactors" was put in the Branch Technical Position(BTP) of the Standard Review Plan (SRP/NUREG-0800), PSB-1, Revision 0, "Adequacy ofStation Electric Distribution System Voltages."dated July 1981, and in the current BTP 8-6 ofthe SRP, Revision 3, "Adequacy of Station ElectricDistribution System Voltages," dated March2007.DisagreeNRC staff does not agree with this position.As a result of these Millstone events, theNRC requested that all licensees implementdegraded protection as described in the1977 Letter to ensure automatic protection ofsafety buses and loads. This Letter providesstaff posilie uuidance, which applies to alloperating reactors at that time and plantslicensed since, on how to comply with therequirements in 10 CFR Part 50. GeneralDesign Criteria 17 (GDC 17).48 No. Section of RIS Originator Specific Comment NRC Resolution1. Branch Technical Positions of NUREG-0800 are not requirements but:"represent guidelines intended to supplement theacceptance criteria established inCommission Regulations, guidelines presented inRegulatory Guides, and recommendationspresented in applicable IEEE standards."2. PSB-1 and BTP 8-6 provide subtle butsignificant changes to each other and tothe original "Statement of Staff PositionsRelative to Emergency Power Systemsfor Operating Reactors" (Note: thesedifferences will be provided in acomment letter from the Nuclear EnergyInstitute). If the original statement of staffpositions is considered a requirement,then it is contradictory to subsequentNRC guidance.3. PSB-1 and BTP 8-6 represent guidance ascommitted to in a licensees' CurrentLicensing Basis -which, with plant specificjustification, may depart from NRCguidelines, but are reviewed and approved by theNRC.139 General STARS By characterizing the new contents of RIS 2011 -XX as clarifications to "the NRC staffs technical Disagreeposition on existing regulatory requirements," theRIS seeks to supersede the NRC reviewed and The purpose of the RIS is to clarify the NRCapproved Current Licensing Basis for many staffs technical position on existinglicensees, regulatory requirements and voltage studiesnecessary for Degraded Voltage Relay(second level undervoltage protection)setting bases and TransmissionNetwork/Offsite/Onsite station electric powersystem design bases. This RIS does nottransmit any new requirements or staffpositions.A RIS is an appropriate document for NRCstaff to provide clarification on existingRegulatory Requirements and existing NRCStaff Positions.140 General Greg The issue I am concerned about is the regulatoryReimers conflict created by requiring the DVR setpoint to(DCCP) preclude spurious actuation of the undervoltage Agreeprotection function.The NRC draft RIS 2011-XXX discusses spuriousseparation at least three times.1. The first occurrence is an accurate NRC Staff agrees with commenter's positionrestatement of the 1977 NRC position on use of the term spurious with respect tothat "The voltage protection shall include the design of the DVR scheme to preventcoincidence logic to preclude spurious false actuations due to DVR componenttrips of the offsite power source" (See failures or miss-operationsRIS Page 2, Item (b)).2. The second occurrence is in the"Degraded Voltage Relay Design The RIS will be revised to remove spuriousCalculations" section. Specifically, the from this section. The NRC Staff position issecond sentence of the first paragraph that the settings are to be selected based onon Page 7 reads 'Voltage-time settings the voltage requirements of the 1 Efor DVRs should be selected so as to equipment such that when compared withavoid spurious separation of safety the minimum expected grid voltages, therebuses from the offsite power system should be sufficient margin ensure thatduring unit startup, normal operation and separation from the grid would not beshutdown." This introduces the DVR expected during normal, abnormal or49 No. Section of RIS I Originator I Specific Comment I NRC Resolutionvoltage and time setpoint interaction withthe offsite power circuits as a factor inthe setpoint determination. I believe aconclusion of the workshop was acommon understanding that thefunctional requirement of theDVRprotection is to prevent common modeequipment failure during a sustaineddegraded voltage condition. Asdiscussed, this can best be achieved viaa "bottom up" analysis withoutconsideration of offsite power capacityand capability.3. The third occurrence is in the"Offsite/Onsite Design InterfaceCalculation" Section. Page 8, Item (i)reads "For each case evaluated, thecalculated voltages on each safety busshould demonstrate adequate voltage atthe component level without separationfrom the offsite circuit due to DVRactuation."Points #2&3 above introduce a contradiction forthose stations whose current license basis isconsistent with the Standard TechnicalSpecifications. Referring to NUREG-1431,Standard Technical Specifications WestinghousePlants (typical TS), the degraded voltage TS basesread "The Allowable Value is considered a limitingvalue such that a [DVR] channel is OPERABLE."Thus, at the Allowable Value lower limit, the Class1E electrical distribution system is capable offulfilling its ESF supporting design function. Theoffsite power LCO reads "Each offsite circuit mustbe capable of maintaining rated frequency andvoltage, and accepting required loads during anaccident, while connected to the ESF buses." Novoltage values are defined for the offsite power TSLCO. Therefore, if the offsite power circuit canmaintain the bus voltage such that the DVR lowerAllowable Limit is satisfied, then the offsite powercircuit would also be operable.The DVR dropout and reset setpoints must begreater than the TS lower Allowable Value due toinstrument tolerances and uncertainty. Given theDVR favors the DGs, does not mean bus voltagesbetween the DVR setpoint and the TS lowerAllowable Value reduce the capability of the offsitepower circuit. Consequently, the DVR setpointcannot completely preclude spurious separation.As discussed in the workshop, a voltage relaycannot predict future operating conditions.Consequently, the DVR can't distinguish betweenvoltage transients that are expected to recover andthose that are not. Therefore, in the context of theoriginal NRC position (i.e. Point #1), I believe theterm spurious was in the context of false signalsfrom within the DVR instrumentation and not anygroup of bus voltage transients. The IEEE 308requirement that RIS Page 8, Item (i) is trying toconvey is "The preferred power supply shall becapable of starting and operating all requiredloads."accident conditions.NRC Staff agrees with commenter's positionon use of the term spurious with respect tothe design of the DVR scheme to preventfalse actuations due to DVR componentfailures of miss-operationsNRC Staff agrees with the commenter'sposition that the intent of item i) is to specifythat the preferred power supply is able tostart and run all required 1E equipment inaccordance with its voltage requirementswhile not separatingBackup power CBrian Wilson, Why are there not back-up power sources located141 optonsCA on the roof of the fuel cell tanks with electric lines Disagree50 No. Section of RIS Originator Specific Comment NRC Resolutionconnected directly to the pumps that cool the fuelrods back-up power sources run on both methane This comment is not related to the RISor propane and Ipg. A remote control panel from a regarding "Adequacy of Station Electricdistant site would provide a safe environment to Distribution System Voltage." Therefore,control a dangerous situation safely. staff did not address the comment.51

.upolementnl Resoonse to NEI Comment No. 96 in CommentlResolution Table (corregted)RESPONSES TO NEI 3-2-2-11 BACKFITTING COMMENTSRIS On Adequacy of Station Electric Distribution VoltagesComment: The RIS represents an NRC attempt to standardize varied approaches to providing protection duringdegraded grid voltage conditions, as currently memorialized in the licensing bases of individual plants. However,given the complex regulatory and licensing history associated with providing degraded grid voltage protection at eachplant, a conclusion that the guidance in the proposed RIS is "consistent with" prior NRC guidance is insufficient tomeet the requirements of the Backfit Rule. (NEI -pp.2-7)NRC Response: The NRC interprets the comment as stating a general principle: if the NRC proposes to issuegeneric guidance applicable to several plants -each of which has a complex regulatory and licensing history, then theNRC complies with the Backfit Rule only if its backfitting discussion for the proposed generic guidance considers andaddresses the licensing basis for each affected plant.The NRC disagrees with the comment, and does not believe that the NRC should, as a matter of policy, adopt such aprinciple to guide the agency's implementation of the Backfit Rule. Application of such a principle would oftentimesimpose substantial resource burdens on the NRC, namuch As the NRC cUrrcRtl'y has no way of easily...Pi.. .,nd reviowingas it is difficult for the NRC to efficiently compile and review the licenses bases of selectedplants on a comparative basis. The more complex the regulatory licensing history for each licensee's plant, the moreresource intensive it would be for the NRC to prepare a "generic" backfitting discussion that essentially constitutes acollection of plant-specific licensing basis reviews. Upon completing the licensing basis review for each plant to whichthe generic guidance is applicable, the NRC (and licensee) may well conclude that imposition of the guidance wouldnot represent backfitting In that situation, the review would constitute an arguably unnecessary expenditure of NRC(and licensee') resources.Formatted: Font: Italic, UnderlineFormatted: CenteredFormatted: CenteredThe NrC holia-,e n moren irnsi -nro rh iý if the NRr, hns nenpr~iiv maintninpd a rnnsiistpnt nosition for at least-d no ceas a!ition) and has irf oosition. and initifn In m ,t manner, then the NRC may issuemn in connection with any NRCaction which imposes the cuidance on a licensee ý) imposition 4action may he ;notice of vinltin nr irthinqs, a NRC determination of a license amenice of an order directing the licensee to complyisinQ history for that plant can be compiled andackfitting The NRC-the issuance of aIn this manner thespecificNRC's rI hv the NR. as nart of the....q ICnnsistent with this neneral nrinninie the NRC has (as nart of the hackfittinn consideration of this RISI reviewed itsr-cnrd, with r-n-rMf toe on GDC017flC..17 -1 .deiraded voltage orotection. Based upon that review, thevoltage Protection has been consistent over time.)not constitute neneric backfittinl. In addition, the NRCj Formatted: Font: 9 ptFormatted: Font: ItalicFormatted: Font color: AutoFormatted: Font: 9 ptI5 Dresented in Ihas reviewed its records and believes that (with one exceotion which is being dealt with in a plant-specific manner, I,it position on a plant-sit and is nrenarinn the ;,basis. The?y in the process of applyinq!d bv the Backfit Rule Hences thatn oftI It appropriate.Gonsistent P004-4- (onoer, than the N RCfl Gonn1 h ccwi th any--K101,maryi-1D? ,I Ca,'Hcirri 3 .0Ar- frt4 An1 andt Formatted: Font; (Default) Arial, 9 pt-that Formatted: Font: (Default) Arial, 9 pt, NotSuperscript/ Subscript-UVF9r thiS RIS, the NRC rcvIPWAGIc Mhc Fegulatzr~y guidanse and NRC practice in this area, and cencluded that theguiane n te ISis consistent iAwith the NRG'c regulations and 6taff guidance. as well as tho AIRG' approval atFormatted: Font: (Default) Anal, 9 pt{ Formatted: Font: (Default) Arial, 9 pt, NotIf I, ,, ,/ / ý a uper.sc lpL/ SubscriptIf the NRC prepared a detailed discussion of a plant's licensing bases to support the issuance of guidance, then it, Formatted: Font: (Default) Anal, 9 pt, Fontwould be likely that the licensee would be required to verify the NRC's discussion. A -'- color: Auto, Not Superscript/ Subscript2This involves the Edwin C. Hatch (Hatch) Plant, for which the NRC staff has prepared a documented evaluation FormAtted:supporting the invocation of the corpliance exception (included irnNRC- Inspetion Report 05000321 and Formatted: Font: (Default) Arial, 9 pt, Not366/2011009, .ML1114507930) .he NRC's reliance on the compliance exception is the subject of a backfit appeal by Superscript/ SubscriptSouthern Nuclear Operating Company, the licensee of the Hatch Plant (MLi 11680360). Zhe NRC h a denied the Formatted: Font: (Default) Anal, 9 pt, Fontbackfit appeal (ML112730194). L color: Auto, Not Superscript/ Subscript52

,.n ,,3rioue ,,ocn,,,i.g twltr wnfcn a, oe',,n, o3'a;. w. in J pcmns' apocsicI). Hence, thC NRCccu~ plnt ....fi cv .....o, , cf backfitting impkoiot~ns of thiz R~S C. apppepripa.e.The NRC emphasizes that this approach to addressing backfitting in connection with the issuance of guidance (suchas this RIS) would not be appropriate if the NRC does not have reasonable certainty that it has articulated (or at leastexpressed no contrary position) and implemented a consistent position over time. However, as stated above, such isnot the case with the guidance on degraded grid voltage protection contained in this RIS. Thus, the degraded voltageRIS does not constitute generic backfitting because it does not constitute a new or different generic NRC staffposition. If there is plant-specific backfit when applying the guidance to a specific plant, then the staff will addressbackfitting in the context of that staff action (and prepare the necessary documentation to support the staff'sbackfitting action). Accordingly, the NRC declines, as a matter of discretion, to prepare a plant-specific backfittingdiscussions for each of the plants that may be affected by the RIS. No change was made to the RIS as a result of thiscomment.Comment: The NRC should not rely upon GDC-17 to conclude that the proposed RIS does not represent backfitting.GDCs are cast in broad, general terms and are non-specific nature. Thus, the relevant backfitting inquiry should bewhether the proposed RIS's guidance differs from any individual plant's NRC-approved voltage protection scheme.(NEI -pp.6-7) (See NRC Comment/Resolution table item No. 96)NRC Response: In general, the NRC agrees with the comment that many (but not all) of the GDC are cast in broad,general, performance-based language. However, the NRC disagrees with the comment's implicit assertion that anyGDC which is expressed in broad, general terms or is "non-specific in nature," or is expressed in performance-basedlanguage, may not be relied upon when the NRC invokes the compliance exception under § 50.109(a)(4)(i). Nothingin the history of the Backfit Rule suggests that the Commission intended to adopt such an interpretation of the BackfitRule.Furthermore, if the NRC were to adopt the position that NRC issuance of changed or new guidance for performance-based regulations must always be accompanied by plant-specific licensing basis analyses for all potentially-affectedplants, this would likely inhibit the adoption of performance-based rules. If the NRC must take into account the plant-specific licensing basis considerations whenever it proposes to take generic regulatory action through the issuance ofrules and regulations, then this effectively converts the administrative process of rulemaking under the AdministrativeProcedures Act (APA) to the administrative process of issuance of orders under the APA. The NRC does not see whyit must limit itself, in light of the several and broadly-worded rulemaking authorities accorded the NRC under variousprovisions of the Atomic Energy Act of 1954, as amended. These rulemaking provisions include, among others,Sections 103.a, 103.b, 161.i, 161.p, 182.a, and 183.Moreover, the GDCs are just one NRC position for which a licensee is protected from backfitting. If there is a morespecific requirement in a plant's licensing basis representing the NRC position on an acceptable way of compliancewith the performance-based requirement (e.g., a GDC), then that position is a separate and independent basis forthat licensee to invoke backfitting protection when the NRC proposes to impose that NRC position on that licensee.3More importantly, the NRC disagrees with the comment's implicit assertion that GDC-17 is a broad, general, andnonspecific GDC. A brief review of GDC-17 shows that its rogulater,' tWAt is ameng the most length; 0f the GDCS,cnsistting of three parographG. The requirements are stated in relatively specific terms using performance-basedregulatory language, but also setting forth very specific conceptual requirements, e.g., the need for electric powerfrom the "transmission network" to the "onsite electrical distribution system" to be supplied by "two physicallyindependent circuits (not necessarily on separate rights of way)...."For these reasons, the NRC disagrees that the relevant inquiry for GDC-1 7 is whether the proposed RIS differs fromany individual plant's licensing and regulatory bases. No change was made to the RIS as a result of this comment.b'-krt appeal by Scuthern Operatmg C.mpC,.n, the l fth, Hath PlanM (,,L 111903h0)The situation involving the imposition of a new NRC position on an acceptable way of complying with GDC-17 isan example where the NRC acknowledges that the NRC approval of the licensee's specific undervoltage protectionscheme) in a license amendment constitutes an applicable staff position for purposes of the Backfit Rule, Thus, theNRC has acknowledged that the proposed new staff position on the Hatch Plant's undervoltage protection schemeconstitutes backfitting. Thus, the issue which is the subject of the licensee's backfit appeal, is whether the NRC mayrely upon the "compliance exception" under 10 CFR 50.109(a)(4)(i).53 Comment: The NRC's generic communications and guidance identified in the draft RIS are not completely consistentwith one another and were not equally relevant in developing the licensing bases for all reactor licensees, citing tovarious statements in the BTP PSB-1. (NEI -pp. 4-5) (See NRC Comment/Resolution table item No. 96)NRC Response: The NRC agrees that there is some "variability" between the scope of depth of information presentedin the NRC's generic communications and guidance on the subject of degraded voltage protection. However, theNRC disagrees with the comment's implicit assertion that there is no consistent NRC staff position. As discussed inresponse to the prior comment, there is some "variability" among the NRC generic communications and guidancedocuments in terms of the scope of issues relating to electrical system design, as well as the detail provided. Thecomment provided four bulleted examples purporting to describe inconsistent or contradictory NRC guidance.However, none of the identified examples set forth statements which are clearly contradictory or implicitly inconsistentwith one another.The first example identifies an apparent conflict between a draft RIS statement that "degraded voltage conditions[must be] coincident with a postulated design basis accident," and a statement for Branch Technical Position (BTP)PSB-1 which states that "The subsequent occurrence of a safety injection signal...should immediately separate theClass 1 E distribution system from the offsite power system" (emphasis added). There is no conflict or inconsistencybetween these two statements, when the BTP (which precedes the RIS) is read in full context. The full text of therelevant portion of the BTP is:Two separate time delays shall be selected for the second level of undervoltageprotection based upon the following conditions:1) The first time delay should be of a duration that established theexistence of a sustained degraded voltage condition (i.e.,something longer than a motor starting transient). Following thisdelay, an alarm in the control room should alert the operator to thedegraded condition. The subsequent occurrence of a safetyinjection actuation signal (SIAS) should immediately separate theClass 1 E distribution system from the offsite system (emphasisadded)."Coincident" means, "happening at the same time," and "coinciding." The Random House College Dictionary,Revised Edition (1980). "Coincide" means, among other things, "to come to occupy the same ... period in time(emphasis added)." Id. "Subsequent" means either "occurring or coming later or after...," or, "following in order ofsuccession, succeeding." Id. Coincidence simply requires that the two events or conditions happen at the same time,or "come to" occupy the same period in time. It is clear that this is what the RIS was addressing -that the postulateddesign basis accident must be assumed to occur at the same time as the degraded voltage (undervoltage) condition.By contrast, the BTP addresses the order or sequence of occurrence of the two events or conditions which must,despite the order or sequence, must also "happen at the same time. The BTP states that the staff will accept a designin which the undervoltage condition occurs first, and then (while the undervoltage condition is still present), the designbasis event occurs (and thereby draws a load on the electrical system). In either case, the result is the same in thatseparation from the grid occurs and the 1E systems are powered from the onsite sources during design basis eventmitigation. The only difference is that in the case of the subsequent design basis event, the actual start of the 1 Eequipment will be later than when the two events occur coincidently. Either way the design basis event assumptionsare satisfied.Figure 1 illustrates the difference. There is no conflict or inconsistency between the RIS and the BTP.54 Degraded Voltage Set Points(BTP PSB-1) DVR -1 Protection -Existence of a sustained degradedvoltage condition100% To account for ECCS motor starting, running of all 1E loads and time forgrid recovery (Long time Delay.) Causes alarm and Time delay isbypassed on SI signal if a subsequent SI occurs. Provide adequate timesofor plant or grid operator to take manual actions.fi c a n t ly I l -nDVR (BTP PSB-1) DVR-2 Protection with short timeSbdmdelay to rideout the motor starting transients.qired at equipment terminal Ensures minimum voltage required for allall safety related equipment equipment to prevent control fuse blowing, relaylockout, contactor opening etc., concurrent DVR-2 rcondition I S sianal causes relav to time out ifAlarma iý,n ifh 19 '.setpoDVR set pýoltaqe reto operatethe voltage doesn't within the time delay ands transfers to onsite power system.ORFolio 1977 letter staff positionThe selection of voltage and timedelay setp ts shall be determined from ananalysis of th operating voltage requirements ofthe safety relat loads at all onsite systemdistribution levels;Figure 1The second example identifies an apparent conflict between the RIS and BTP PSB-1. The draft RIS proposes "DVRDropout setting based on starting and running voltage." BTP PSB-1 says "sustained degraded voltage condition,"during the discussion concerning selection of time delays for the DVR, implying a degraded voltage condition lastingmore than a few seconds and not a transient voltage condition that exists during a motor starting event or during amomentary grid perturbation such a lightning strike that may be cleared by automatic actions of protection schemesand automatic breaker open/reclosure cycle. Specifically, BTP PSB-1 states: 'Two separate time delays shall beselected for the second level of undervoltage protection based on the following conditions: 1) The first time delayshould be of a duration that established the existence of a sustained degraded voltage condition (i.e., somethinglonger than a motor starting transient)."it is clear in the context of the 1977 Letter that the phrase "sustained degraded voltage" is referring to the grid eventand not voltage scenarios in plant electrical system operation (see fig 1). In addition, when selecting an appropriatetime delay for the DVR (which is what the RIS is referring to), one must consider the voltage drop due to large motorstarts in the plant since they can depress voltage momentarily by design and such voltage drops should therefore beoverridden by the time delay since they would mask detection of the sustained degraded grid voltage event. Also, it isI also clear that the 1977 Letter language refers to the DVR voltage setting(s) being based on the voltage requirementsof the 1 E equipment. Large 1 E motors, for example, have starting and running voltage requirements by design whichmust be met to ensure proper operation during accident conditions. Thus, the statement that the BTP implies onlyrunning voltage requirements are required be enforced is not correct. No change was made to the RIS as a result ofthis comment. There is no conflict between the RIS and BTP PSB-1.The third example juxtaposes: (i) the proposed RIS guidance indicating that each unit must have analysis thatassumes "an accident in the unit being analyzed and simultaneous shutdown for all other units (emphasis inoriginal)... ," with language in GDC 5 which states, "...in the event of an accident in one unit, an orderly shutdown andcooldown of the remaining units." The language of GDC 5 concerns sharing of SSCs rather than electrical systems,55 and the language quoted in the comment represents a criterion for allowing sharing of important to safety SSCsamong nuclear power units. This is not the same subject as the determination of how to analyze whether GDC-17'srequirements are being met. Moreover, there is no direct contradiction between "simultaneous shutdown" in theproposed RIS, and "orderly shutdown and cooldown" in GDC 5: an "orderly shutdown" under GDC-5 could also be"simultaneous" for purposes of GDC-17.The fourth example identifies an apparent conflict between the RIS and BTP PSB-1. The draft RIS proposes "Duringnormal plant operation, the Class 1 E safety related buses should automatically separate from the power supply withina short interval (typically less than 60 seconds) if sustained degraded voltage conditions are detected." (emphasisadded). The comment suggests that a sixty second time delay would not allow operator actions, and appears to be anew NRC position.-ti fie 1 terms 4f 1i autolmdat protcotio oW the las Eeqipme tn dtion t80 allowg OR for Qoror 4a ctions(i psil) See DVR1 ad 1 -2 relay aQnd time deays delay hic d 6n Fi 1 -w- is 1 jin accorn w ithot 4T4PSB-1sotaffpGoRtod is an Iacc design to W eattgoe Folfos"g ition iOln'; it 4t1o oprtpof hc ...od tW eo.orhseletion of9voltage0 tnd tme elay sitpointi syhall bhoded bet ftrtiomaly o fpthog fper t11W voltage po6y@4044.- R6166 aRd jW64t4604tor WRnWx we P-o"'d 'r6 o.214r 6WOf5 tho cOwo dIOWy 0006014 "Tho cl-ott Rig 6P0-kaf'llyalrei frmens ofhaf related loads a t al onsitesyst"m pdwis The iuti y levend time delay would not s llb ecperston atonroe This appcaro to bo a row oNR pot CntIOThe reference to 60 seconds has been removed in the revised RIS, however, the time delay chosen still has to bejustified in terms of providing automatic protection of the Class 1 E equipment in addition to allowing time for operatoractions (if possible). See DVR1 and DVR2 relay and time delays depicted in Figure 1 .This is in accordance with BTPPSB-1 staff position and is an acceptable design to meet the staff position in the 1977 letter_-6tatt-pes4ieR-i.e., theselection of voltage and time delay setpoints shall be determined from an analysis of the operating voltagerequirements of the safety related loads at all onsite system distribution levels. frp PSma1 aciause .I b.2 incladeovgisions for operator manual actions to -restore hus Yoite on the Class I E~distruti~jLSysE..TPP.SB- IR I hsay~lhsecnd en lasshold e o amite~cd uratiotisuch tha-ttfie permanentl~y connectetiLClass lE loads wflld~tnuonyte.shud.d.~i~~atcltspaaedfomte-afsitegoe ste aaanelfciomust he~r~p~ Lo th acua~~la~.~floen .TedrRRL soc~aty xcldesmanua[lo stO=ied~ding under theOtsitel~rnsile Design Interface Calculations whereas the BTP PSB-1 allows fQr Manual actmio to avoid Separationcomn offsite ~ower.herefore, there is no conflict between the RIS and BTP PSB-1.Comment: Given the variability in NRC's generic communications and guidance, the draft RIS' statement that thepositions in the RIS are "consistent with" the RIS-identified NRC documents, does not address the possibility that theRIS is new or different from a previously-approved protection scheme (and thereby constitute backfitting), (NEI -p. 7)NRC Response: As discussed above in response to NEI- pp.4-5, while the NRC agrees that there is some.variability" in NRC's communications and guidance on degraded voltage protection, the NRC does not agree thatthis "variability" is of any significance from a backfitting standpoint because there is no contradiction or materialinconsistency between the various NRC communications and guidance documents. Thus, such "variability" does notprovide a sufficient basis for the NRC to perform plant-specific determination on whether imposition of the RISconstitutes backfitting. No change was made to the RIS as a result of this comment.56

NEI Letter "Concerns associated with NRC release of RIS 2011-12, Rev 1", February 2012 INDUSTRY REVIEW OF NRC PROPOSED DEGRADED VOLTAGE RELAY

METHODOLOGY

NEI Task Force on Degraded Voltage Analysis PURPOSE The IEEE Nuclear Power Engineering Committee (NPEC) Working Group 4.71 and the Nuclear Energy Institute (NEI) have been working with the NRC staff to understand their current technical position related to degraded voltage relay (DVR) protection requirements for motor starting voltage as described in Regulatory Issue Summary 2011-12, "Adequacy of Station Electrical Distribution System Voltages". Specifically, there is an industry concern that the guidance in RIS 2011-12 is not being evaluated consistently at all Nuclear Power Generating Stations (NPGS) which could elevate the potential of a nuclear safety event such as a delayed loss of offsite power (LOOP) with double load sequencing effects as discussed in NRC GSI-171 The purpose of this technical paper is to evaluate the technical merits of analytical methodologies proposed by the NRC regarding the starting voltage requirements of safety related equipment at the DVR setpoint. Scope The scope of this evaluation is to determine the potential impact of two NRC proposed methodologies on current NPGS DVR setpoints: Method 1: Referred to as the "independent system method," determines the minimum voltage at the NPGS safety buses (i.e., "safety division") required to support both safety related equipment starting and running voltage limit Safety related buses are not connected to the transmission system and do not credit the effects of the non-Class 1E system: such as upstream impedance, voltage control, load changes, etc. This results in a fixed voltage (i.e., infinite source bus) at the DVR-monitored buses during motor startin Method 2: Referred to as the "dependent system method," determines the minimum voltage that would be required at the NPGS safety buses prior to motor starting to support both safety related equipment starting and running voltage limits; thus accounting for the effects of the non-Class 1E system while connected to the transmission network. This results in a 1 Responsible for IEEE Std 741, "IEEE Standard Criteria for the Protection of Class 1E Power Systems and Equipment in Nuclear Power Generating Stations" 2 NRC Generic Safety Issue 171, "Engineered Safety Features Failure from Loss-of-Offsite-Power subsequent to a Loss-of-Coolant Accident" voltage at the DVR-monitored buses that dips during motor starting; however, for NPGS that utilize load sequencing, the pre-start bus voltage is readjusted between each load step to the original leve In this evaluation, each of these methodologies is applied in actual power system analysis using the AC Auxiliary Power System model of several existing NPGS designs that are typical of the US nuclear industr The impact on the DVR setpoints, as predicted by both these methodologies, is compared to existing setpoint It should be noted that neither method is capable of demonstrating voltage recovery above DVR reset in order to prevent transfer to the emergency onsite power sourc In fact, voltage recovery must be shown to occur once loads have started and/or the transmission system has recovered using further analysis using the methodology presented in the "Offsite/Station Electrical Power System Design Calculation" section of RIS 2011-12 and IEEE Std 741-2007, Annex It is not the intent of this paper to infer that degraded voltage protection is actually achieved during motor starting when the DVR minimum dropout voltage is set to correspond to the analytical value established by one or the other of these methodologie In actuality, the very premise of using a voltage relay to protect a power system's capability (capacity) to start motors is technically inadequat Since a voltage relay only measures voltage (and not power system capacity), any proposed analytical technique must assume some level of power system capacity, thereby violating the stated purpose of the protective functio Background The guidance for DVR protection has been developed through three primary NRC documents (1) NRC issued "Statement of Staff Positions Relative to Emergency Power Systems for Operating Reactors" - June 1977, (2) NUREG 0800 (Standard Review Plan) Appendix A, BTP PSB-1 Revision 0, "Adequacy of Station Electric Distribution System Voltages," dated July 1981, and (3) Generic Letter 79-36, August 8, 1979, "Adequacy of Station Electric Distribution Systems Voltages." NPGS have implemented specific designs and technical specifications to meet the intent of these NRC document In general, the NPGS licensing commitments are specific to the plant distribution system design and time frame in which the technical specifications were approved, based upon one or more of the three NRC documents listed abov NEI Letter "Concerns associated with NRC release of RIS 2011-12, Rev 1", February 2012 The recent Component Design Basis Inspections (CDBI) have resulted in NRC inspection findings that are requiring plants to perform DVR analyses that are not consistent with the plants licensing basis. The evaluations result in scenarios that may potentially lead to double sequencing of the NPGS engineering safety system load NPGS have implemented the NRC DVR requirements based on the steady state equipment ratings and not on the starting voltage requirements of equipmen The current NRC staff position that degraded voltage protection includes motor starting at the DVR analytical minimum dropout is inconsistent with current industry practice in two respects: First, many NPGS have addressed the transient period of motor starting by demonstrating that the DVR time delay is long enough to prevent spurious tripping during the voltage transient Second, NPGS that account for starting voltage transients typically use the DVR relay maximum reset voltage value as an analytical ending condition and establish an initial condition that will ensure that this criterion will be me This initial condition is often the subject of positive administrative controls, alarms, and Technical Specification LCO action statement The reset value is used because any transient that causes a voltage dip below the dropout setpoint must recover to the reset value in order for the electrical distribution system to stay connected to the gri All transients that start below the reset value initiate the DVR, and if they exceed the relay time delay, will result in separation from the offsite source of powe Hence, analyses below the reset value are moot unless they also address the delayed LOOP and double sequencing effects as discussed in NRC GSI-171. Approach As previously identified, there are two NRC proposed methods that will be evaluated to determine the effect on the NPGS DVR setpoin These methodologies are being considered to determine the impact to the current NPGS DVR setpoints when considering starting voltage adequacy, not to suggest changes to DVR protectio The following items were applicable for both methods: 1. Determined an analytical limit for DVR setpoint (dropout) at the safety division measurement poin . Utilized the existing electrical model (i.e., ETAP model) used in current DVR analysis at each NPG . Determined the most limiting motor (defined as the one which received the lowest required percent of starting voltage, down to the NPGS 480V MCC) for the worst case design basis event (e.g., LOCA, Safety Injection, Containment Isolation, Load Rejection).

Other components, such as static loads and MCC contactors, were assumed to be bounded by the current calculation of recor Method 1, independent system, determines the DVR setpoint minimum voltage (analytical limit) without crediting the effects of the non-Class 1E system: upstream impedance of the non-Class1E plant or offsite electrical network, voltage control, load changes, et The intent of the independent system method is to bound any postulated transient condition and assure required starting voltage To accomplish this, voltage is fixed at the safety division measurement point prior to the start of any motor start sequence (sequenced loading or block loading). This represents the voltage seen at the safety division at the moment of a motor start sequence, regardless of the upstream voltage respons Utilizing the existing methodology and loading for each NPGS, the constant voltage source was adjusted and a motor starting analysis was performed until the most limiting component received sufficient starting voltage (terminal voltage). This method provides the base minimum voltage required at the DVR to support starting equipment limit This method cannot predict the required voltage at the DVR prior to the motor start sequence, it can only determine voltage adequacy during the sequenc Key assumptions of Method 1 include: 1. The non-Class 1E system will maintain the voltage throughout the sequence (i.e., infinite source capacity). 2. Nominal load sequencing times are used, as applicabl Method 2, dependent system, determines the DVR setpoint minimum voltage by accounting for the effects of the non-Class 1E system (e.g. non-Class 1E distribution elements, offsite power grid, etc.) and non-Class 1E load change (addition or removal). The intent of the dependent system method is to present the least conservative transient condition (using operable grid capacity) which would assure required motor starting voltages, given that this method is dependent on upstream condition Other upstream conditions (e.g., degraded grid capacity, negative operation of system voltage compensating equipment, spurious operation of any non-Class 1E component) would produce an even higher analytical limi Utilizing the existing methodology and loading for each NPGS, the Transmission voltage source was adjusted and a motor starting analysis was performed until the most limiting component received sufficient starting voltage (terminal voltage). To accomplish this, the transmission system voltage was adjusted until the voltage at the DVR (prior to the motor starting sequence) was at the analytical limi This method 3 NEI Letter "Concerns associated with NRC release of RIS 2011-12, Rev 1", February 2012 attempts to predict the minimum required voltage prior to the design basis even Key assumptions of Method 2 include: 1. Automatic On-Load Tap Changers did not actuate during the event (i.e. were locked in place). 2. The non-Class 1E systems were modeled per NPGS current analytical basi Examples may include: the non-class 1E load shed schemes, bus transfers, load application, and all balance of plant automatic functions (including unit trip delay). 3. Typical transmission system impedance was not degraded below the operable impedance for the offsite transmission syste (Note: This is a non-conservative assumption with respect to capacity, since operable transmission system impedance doesn't represent a degraded grid.) Utilizing the existing methodology and loading of each NPGS, the transmission system voltage source was adjusted and a motor starting analysis was performed until the most limiting component, down to the 480V MCC, received sufficient starting voltage (terminal voltage). Once sufficient starting voltage was achieved, the corresponding pre-event switchyard voltage was recorde Once the analytical limits were established for each method, the required DVR settings were determined using tolerances and minimum ranges (between dropout and reset) applicable to the existing hardware for each NPG The resulting DVR dropout and reset settings for each NPGS are included in the results section for comparison to existing DVR settings. Results Impact on DVR Setpoints Method 1 (Independent System) Plant NPGS 1 NPGS 2 NPGS 3 NPGS 4 NPGS 5 NPGS 6 ECCS Loading Type Load Sequence Block Start Block Start Block Start w/ Bus Xfer Load Sequence Load Sequence w/ Bus Xfer DVR Dropout 1 (minimum) 91.4% 92.8% 91.9% 91.7% 88.7% 91.0% DVR Reset 2 (maximum) 94.7% 95.0% 96.6% 94.2% 91.5% 93.6% DVR Dropout 1 (minimum) 92.4% 93.8% 92.3% 91.7% 89.7% 91.7% DVR Reset 2 (maximum) 95.7% 96.0% 97.0% 94.2% 92.5% 94.2% DVR Setpoint 3 Change (+/-) +1.0% +1.0% +0.4% 0.0% +1.0% +0.7% Notes: 1) The DVR setpoint analytical limit that produces required voltage to all required load Actual DVR setpoint (dropout) will be slightly higher to account for tolerances. 2) The maximum DVR reset value, including tolerances. 3) The change in existing DVR dropout setpoint required to satisfy these criteri The independent system method shows an increase of the existing DVR setpoint from, 0.4% to 1.0% for five of the units while one plant showed no increase. Some of these NPGS may be successful in demonstrating reset of the relay, required for GDC-17 conformance (as historically interpreted); however, others may not have margin in the "Offsite/Station Electrical Power System Design Calculations" as discussed in the RIS. As a minimum, five of the NPGS would require licensing amendments to change the Technical Specifications, unless a more refined analysis can demonstrate lower motor starting voltag Impact on DVR Setpoints Method 2 (Dependent System) Plant NPGS 1 NPGS 2 NPGS 3 NPGS 4 NPGS 5 NPGS 6 ECCS Loading Type Load Sequence Block Start Block Start Block Start w/ Bus Xfer Load Sequence Load Sequence w/ Bus Xfer DVR Dropout 1 (minimum) 91.4% 92.8% 91.9% 91.7% 88.7% 91.0% DVR Reset 2 (maximum) 94.7% 95.0% 96.6% 94.2% 91.5% 93.6% DVR Dropout 1 (minimum) 98.7% 101.3% 102.5% 96.7% 92.7% 99.8% DVR Reset 2 (maximum) 101.8% 103.9% 107.8% 101.4 95.5% 102.4% DVR Setpoint 3 Change (+/-) +7.3% +8.5% +10.6% +5.0% +4.0% +8.8% Switchyard 4 Voltage 104.0% 108.9% 104.9% 103.9% 104.8% 112.2%

Notes: 1) The DVR setpoint analytical limit that produces required voltage to all required load Actual DVR setpoint (dropout) will be slightly higher to account for tolerances. 2) The maximum DVR reset value, including tolerances. 3) The change in existing DVR dropout setpoint required to satisfy these criteria. 4) The switchyard voltage required to produce new DVR Reset (maximum).

All six NPGS show significant setpoint impact under the dependent system method (4 to 10.6% increases). All would require a minimum switchyard voltage greater than currently predicted by the transmission system provider and, in two cases, greater than the maximum voltage typically allowed by a transmission system (105%). The "Offsite/Station Electrical Power System Design Calculations" would not show acceptable results. Setpoints raised to these values would 4 NEI Letter "Concerns associated with NRC release of RIS 2011-12, Rev 1", February 2012 require operating the plant distribution at higher voltage than presently allowed by operating procedures. As an example under light loading conditions, there would be a significant concern of overvoltage conditions. This could result in overexcitation in motors and transformers in addition to other potential concerns such as circuit breaker interrupting ratings as well as bus withstand (close and latch). Conclusion A review of the results demonstrates that setting the DVR on the basis of providing motor starting protection will likely result in increased DVR setpoint Either method is shown to potentially raise the DVR analytical limit, forcing an increase in the dropout setting and therefore the reset settin This will reduce if not eliminate the margin between required switchyard operating voltage and anticipated post-accident voltage, increasing the probability of a LOOP from DVR timeou In the case of Method 2, the results demonstrate a significantly higher DVR setting will be required along with potential elimination of switchyard operating voltage margi Operating in such a manner would be unreliable and would not reflect actual system conditions expected during a response to a design basis even The resulting minimum switchyard voltages required for DVR reset are unrealistic if not unattainable and would be counter to Transmission Operator criteri Although each evaluated methodology is purported to demonstrate that DVRs would provide protection against all eventualities regarding the voltage response of the non-Class 1E electrical system, it fails to do so. To the contrary, each method makes many assumptions about the non-Class 1E system voltage response in an attempt to quantify the magnitude of voltage dip on the Class 1E system during motor startin Making these assumptions violates the intended purpose of the DVR to provide a Class 1E protective function against all condition Resetting DVRs in an attempt to provide perceived motor starting protection has no practical benefit and would have significant negative consequences for the following reasons: Increased DVR settings would significantly increase the probability of spurious LOOP and delayed LOOP with double sequencing effects as discussed in NRC GSI-17 Increased DVR settings would reduce or eliminate switchyard voltage operating bands for NPG If based on Method 2, this may result in a minimum switchyard voltage so high that it would result in overvoltages to plant equipment during light loading condition Since the DVRs provide no protective function while they are timing out, their voltage setting is not a factor in the voltages to which the plant equipment may be exposed during that period and increasing their voltage setpoint would have no benefit during this perio Each evaluated methodology analyzes a scenario that would be incredible at most plants (significant voltage degradation at the same instant as an accident signal) and fails to consider the credible scenario of a voltage change later into the event when the main generator trip NRC GSI-171 concluded that a LOCA with delayed LOOP was an improbable even Raising the DVR setpoint will negate this conclusion, leading to greater possibility of a delayed LOOP with double sequencing effect A more realistic scenario is to set the DVR to protect accident mitigating equipment from damage during steady state conditions (not motor starting), which is the current licensing basis for most plant NPGS typically use the DVR maximum reset voltage value or "minimum anticipated voltage" as described in IEEE Std 741, as an ending condition following automatic load sequencing or block loading of safety related loads and establish an initial switchyard voltage to avoid DVR actuatio This ensures the grid provides sufficient capacity for starting required loads and for resetting the DVR; thus, ensuring continuity of a qualified offsite power sourc Setting the DVR dropout to protect accident mitigating equipment from damage during steady state conditions will avoid the risk of early offsite power separation associated with higher DVR settings based solely upon motor starting voltage demands.