RIS 2011-12, 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: |
| References | |
| RIS-11-012, Rev 1 | |
| Preceding documents: |
|
| Download: ML11357A142 (69) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001 ctober 65,2414L2ýTE]
NRC REGULATORY ISSUE SUMMARY 2011-12, REVISION 1 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM
VOLTAGES
ADDRESSEES
All holders of, or applicants for, a power reactor operating license or construction permit under Title 10 of the Code of FederalRegulations (10 CFR) Part 50, "Domestic Licensing of Production and Utilization Facilities," except those who have permanently ceased operations and 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 licenses under 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 (second level undervoltage protection) setting bases and Transmission Network/Offsite/Station electric power system design bases for meeting the regulatory requirements specified in General Design Criteria (GDC) 17 to 10 CFR Part 50, Appendix A. For nuclear power plants that were licensed before GDC 17 applied, the updated final safety analysis report provides the applicable design criteria. This RIS does not transmit any new requirements or staff positions. No specific action or written response is required.
BACKGROUND
The events at Millstone and Arkansas Nuclear One (ANO) that led to the NRC staff's position regarding degraded voltage protection for nuclear power plant Class 1 E electrical safety buses for sustained degraded transmission network (grid) voltage conditions, and expectations for voltage calculations for the plant offsite/station electric power system design respectively, are discussed below as a reminder of past operating experience.
Millstone Unit 2 Electrical grid events at the Millstone Station, in July of 1976 demonstrated that when the Class
1E buses are supplied by the offsite power system, sustained degraded voltage conditions on ML-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 voltage conditions will not be detected by the Loss-of-Voltage Relays (LVRs) which are designed to detect loss of power to the bus from the offsite circuit(s). The LVR's low voltage dropout setting is 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 voltage protection logic can also cause adverse effects on the Class 1E systems and equipment, such as spurious load shedding of Class 1 E loads from the standby diesel generators and spurious separation of Class 1E systems from offsite power due to normal motor starting transients. For more information regarding this event, see Agencywide Documents Access and Management System (ADAMS) Accession No. ML093521388.
As a result of these Millstone events, the NRC requested that all licensees implement degraded voltage protection as described in a 1977 Generic Action (Multi-plant Action B-23) to ensure automatic protection of safety buses and loads. Multi-plant Action B-23 provides guidance which applies to all operating reactors at that time and plants licensed since, on how to comply with the requirements in 10 CFR Part 50, Appendix A, GDC 17. Since degradation of the offsite power system can lead to or cause the failure of redundant Class 1 E safety-related electrical equipment, the NRC requested that licensees install degraded voltage protection schemes (second level of voltage protection (Degraded Voltage Relays (DVRs)) for the station electric power 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 NRC
letter dated June 2, 1977, ADAMS Accession No. ML1 00610489, sent to the licensee for Peach Bottom Atomic Power Station. In this letter, the NRC requested that these DVR circuits satisfy the following criteria:
a) The selection of voltage and time delay setpoints shall be determined from an analysis of the voltage requirements of the safety-related loads at all station electric power system distribution levels;
Note: Voltage requirements of all safety-related loads should be determined based on manufacturers design and operating requirements. For example, safety injection motors have starting and running voltage requirements. Motor operated valves have minimum operating voltage requirements. Motor Control Center contactors have minimum pickup and operating voltages. All voltage requirements for all safety-related loads need to be preserved by the DVR circuit(s) during all operating and accident conditions.
b) The voltage protection shall include coincidence logic to preclude spurious trips of the offsite 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 maximum time delay that is assumed in the final safety analysis report (FSAR) accident analyses;
RIS 2011-12, Rev. 1 Note: Time delay condition (1) indicates that the DVR circuits should be designed assuming coincident sustained degraded grid voltage and accident events. Upon the onset of the coincident accident and degraded grid event, the time delay for the DVR circuit should allow for separation of the 1E buses from the offsite circuit(s) and connection to the 1E onsite supplies in time to support safety system functions to mitigate the accident in accordance with the FSAR accident analyses.
(2) The time delay shall override the effect of expected short duration grid disturbances, preserving availability of the offsite power source(s); and
(3) The allowable time duration of a degraded voltage condition at all distribution system levels shall not result in failure of safety-related systems or components;
d) The voltage monitors (or DVRs as defined above) shall automatically initiate the disconnection of offsite power source(s) whenever the voltage and time delay limits have been exceeded; and e) The voltage monitors (DVRs) shall be designed to satisfy the requirements of IEEE
Standard 279-1971, "Criteria for Protection Systems for Nuclear Power Generating Stations"; and f) The Technical Specifications shall include limiting conditions for operation, surveillance requirements, trip setpoints with minimum and maximum limits, and allowable values for second-level voltage protection DVRs.
The NRC incorporated the staff positions to meet GDC-17 requirements in Multi-plant Action B-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 the SRP, Revision 3, "Adequacy of Station Electric Distribution System Voltages," dated March
2007 (ADAMS Accession No. ML070710478). In addition, the SRP provides a design approach, consistent with the original Multi-plant Action B-23, with respect to the selection of the time delay for the DVR circuit.
Arkansas Nuclear One Another degraded voltage event, in September of 1978, at ANO station demonstrated that degraded voltage conditions could exist on the Class 1 E buses even with normal transmission network (grid) voltages, due to deficiencies in equipment between the grid and the Class 1E
buses (Offsite/Station electric power system design) or by the starting transients experienced during certain accident events not originally considered in the sizing (design) of these circuits.
Information Notice No. 79-04, "Degradation of Engineered Safety Features," (ADAMS
Accession No. ML031180118) provides additional information regarding this event.
The NRC staff issued Generic Letter 79-36, August 8, 1979, "Adequacy of Station Electric I 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 of their nuclear power plants to determine analytically if, assuming all onsite sources of AC power are not available, the offsite power system and the station electric power system is of sufficient capacity and capability to automatically start as well as run all required safety-related loads.
Recent Inspection Findingqs Despite lessons learned from past events, and the generic communications on degraded voltage protection and adequate station voltages, NRC inspectors have identified incorrect implementation of degraded voltage protection schemes by the licensees at various plants during inspections. Specifically, the existing degraded voltage setpoints at some plants were not adequate to protect the safety-related components during degraded voltage conditions for accident and non-accident conditions. In some cases, the voltage conditions were too low to power the safety-related equipment but high enough to prevent transferring of safety loads to the standby power source. In addition, the time delays provided for the degraded voltage protection 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 other licensees might not have adequately implemented the staff positions and guidance issued previously to address the adequacy of station electrical distribution system voltages. Examples of inspection findings recently identified by the inspectors include the following:
DC Cook Units 1 and 2 I During the safety system design and performance capability, biennial baseline inspection (NRC
Inspection 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 identified that the degraded voltage protection scheme was bypassed whenever the 4160V buses were not being supplied through the reserve auxiliary transformers. This resulted in a lack of automatic degraded voltage protection during normal operation and for the first 30 seconds of an 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 scheme is contrary to the design criteria for degraded voltage protection stated in an NRC letter to the licensee (a version of a letter sent to all licensees) dated June 3, 1977. This issue was reviewed by the NRR technical staff under Task Interface Agreement (TIA) 2004-02, and the staff concluded that the degraded voltage protection design at DC Cook was inadequate and as such 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's degraded voltage protection design in 1980, the staff's 2005 determination that the design was inadequate constituted a change in position and was subject to a backfit analysis. By letter I 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 into compliance with its license, the rules and orders of the Commission, and the licensee's written commitments. The licensee implemented a plant modification to the degraded voltage relaying circuit to make it functional during normal operation (see ADAMS Accession No. ML060530405)
addressing the backfit issue.
RIS 2011-12.,Rev. 1 Fermi Unit 2 In May of 2008, NRC inspectors determined that the time delay settings of the degraded voltage relays 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 timing requirements of the licensee's 10 CFR 50.46 loss-of-coolant accident (LOCA) analysis during a degraded voltage condition. The licensee's degraded voltage protection scheme could result in the voltage being too low to adequately power the ECCS equipment but high enough to prevent the emergency diesel generators from connecting to the safety-related buses in a timely manner. This issue was reviewed by the NRR technical staff under TIA 2007-03 (ADAMS
Accession No. ML080420435). The staff determined that the current degraded voltage protection scheme was inadequate as the time delay relay settings for the degraded voltage relays for both divisions could impact the emergency core cooling system injection timing requirements. 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 to prevent emergency diesel generator start. Because the NRC staff had approved Fermi's degraded voltage protection design in 1981, the staff's 2008 determination that the design was inadequate constituted a change in position and was subject to a backfit analysis. The staff determined that the provisions of 10 CFR 50.109 (a) (4) were applicable, and that a modification was 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) for additional details. The NRC approved the plant modification in License Amendment No. 183 (ADAMS Accession No. ML102770382).
Peach Bottom Atomic Power Station Units 2 and 3 Exelon did not use the safety-related degraded grid relay trip setpoint specified in the Technical Specifications (TS) as a design input in calculations to ensure adequate voltage was available to all safety-related components required to respond to a design basis LOCA. Instead, Exelon used the results from a Voltage Regulation Study to establish the voltage level for system operability. The study credited the use of non-safety-related equipment (load tap changers) to raise the voltage level. This allowed higher voltages to be used in the design calculations for components than would be allowed by the TS setpoint. The NRR technical staff reviewed the issue in TIA 2009-07 (ADAMS Accession No. ML102710178). The staff concluded that the licensee must demonstrate that the existing degraded voltage trip setpoints, including allowable values and time delays shown in the licensees TS Table 3.3.8.1, are adequate to protect and provide the required minimum voltage to all safety-related equipment. Since the load tap changers 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 for design basis calculations. For additional details, see NRC Inspection Report
05000277/2010004 and 05000278/2010004 (ADAMS Accession No. ML103140643). The licensee 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 a result of lower voltages that could exist during a postulated design basis loss-of-coolant event coupled with certain degraded voltage conditions.
RIS 2011-12,_ Rev. Palo Verde Nuclear Generating Station Units 1, 2, and 3 In July of 2009, an NRC inspection team questioned the calculations that demonstrate adequate voltage to safety-related loads during worst case loading conditions and the adequacy of a time delay of 35 seconds for transfer of safety buses to the onsite power supplies should an actual degraded voltage condition occur. The licensee's calculation assumed a voltage above the degraded bus setpoint to demonstrate adequate voltage at the terminals of the safety-related loads rather than the degraded voltage dropout setpoint value. The licensee maintains that a degraded voltage condition concurrent with a design basis accident is not credible. See NRC
Inspection Report 05000528; -529; and -530/2009008, ADAMS Accession No. ML093240524 regarding 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 calculation must demonstrate that the trip setpoint adequately protects the Class 1E equipment powered by the safety-related bus from a potentially damaging degraded voltage condition, and the time delay to transfer from a degraded offsite source to the standby power source to support the emergency core cooling equipment operation must be consistent with accident analysis time assumptions, as recommended by BTP PSB-1 (NUREG 0800).
SUMMARY OF ISSUE
S
Because 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 of calculations for the design of the electric power systems of a nuclear power plant and its interface with the transmission network as defined in GDC 17. The two issues are (1) Degraded Voltage Relaying Design Calculations, and (2) Offsite/Station Electric Power System Design Calculations.
(1) The Degraded Voltage Relaying Design Calculations establish the necessary settings of the DVRs to ensure that all safety-related components are provided adequate voltage based 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 limiting operating configuration(s).
(2) The Offsite/Station Electric Power System Design Calculations specify the voltage operating parameters of the plant electrical distribution system based on the transmission network (grid) operating parameters. This interface calculation establishes operating voltage bands for all plant electrical buses, which ensures that all plant safety-related components and systems have proper voltage for starting and running in all operational configurations (expected operational and accident line-ups and conditions). Therefore, based on normal grid operation (including (grid)
post-contingency), the degraded voltage relays will not operate, maintaining the offsite power supply to the plant electrical distribution system.
(1) Degraded Voltage Relaying Design Calculations Proper design of a degraded voltage relaying scheme is needed to ensure that safety-related systems 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 1977 Generic 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 satisfy the requirements). The DVR design should protect (ensure voltage requirements are met)
Class 1E safety-related buses and components from sustained degraded voltage conditions on the 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 (or immediately if the design philosophy recommended in BTP PSB-1 is followed) if an accident occurs 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 a short interval if sustained degraded voltage conditions are detected. The time delay chosen should be optimized to ensure that permanently connected Class 1E loads are not damaged under sustained degraded voltage conditions (such as a sustained degraded voltage below the DVR voltage setting(s) for the duration of the time delay setting).
DVR Setting Design Calculations Licensee voltage calculations should provide the basis for their DVR settings, ensuring safety-related equipment is supplied with adequate voltage (dependent on equipment manufacturers design requirements), based on bounding conditions for the most limiting safety-related load (in terms of voltage) in the plant.
Note: All voltage requirements for the safety-related equipment must be preserved by the DVR circuit(s). For example, safety injection motors have starting and running voltage requirements. Motor operated valves have minimum operating voltage requirements. Motor Control Center contactors have minimum pickup and operating voltages. All voltage requirements for all safety-related loads need to be preserved during all operating and accident conditions.
These voltage calculations should model offsite circuits and the plant electrical distribution system, including the plant safety-related electrical distribution system, such that the limiting voltage at the bus monitored by the DVR can be calculated in terms of the voltage at the terminals of the most limiting safety-related component in the plant in all required operating conditions (such as starting and running). These models should include all plant equipment (including non-safety-related) that can affect voltage supplied to the safety-related equipment. As a minimum, the model should utilize loads on the plant distribution system consistent with the specific transient or accident being analyzed. These models would allow calculation of voltages at terminals of all safety-related equipment with the voltage at the DVR monitored bus at the DVR dropout setting, providing the necessary design basis for the DVR voltage settings. In this manner, the DVR circuit ensures adequate voltage (starting and running) to all safety-related equipment. Voltage-time settings for DVRs should be selected so as to avoid inadvertent separation of safety buses from the offsite power system during unit startup, normal operation (including motor starting), and shutdown.
These DVRs should disconnect the Class 1 E buses from any power source other than the emergency diesel generators (onsite sources) ifthe degraded voltage condition exists for a time interval that could prevent the Class 1 E safety-related loads from achieving their safety function.
RIS 2011-12,_Rev. 1 Note: Upon the onset of the coincident accident and degraded grid event, the time delay for the DVR circuit must allow for separation of the 1 E buses from the offsite circuit(s) and connection to the 1 E onsite supplies in time to support safety system functions to mitigate the accident in accordance with the FSAR accident analyses.
The DVRs should also prevent prolonged operation of Class 1E safety-related loads at degraded 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 Calculations The offsite power source is the preferred source of power to safely shut down the plant during design basis accidents, abnormal operational occurrence, and reactor trips. The licensee's voltage calculations should provide the basis for proper operation of the plant safety-related electrical distribution system, when supplied from the offsite circuit(s) (from the transmission network). These calculations should demonstrate that the voltage requirements (both starting and running voltages) of all plant safety-related systems and components are satisfied based on operation of the transmission system (including the bounding transmission system single contingency in terms of voltage drop) and the plant onsite electric power system during all operating configurations of transmission network and plant systems. In addition, during accident conditions, the nuclear unit generator trip (transmission system single contingency)
and associated transmission system voltage drop should be factored into the accident case voltage 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 running voltages during all plant conditions and the DVRs will not actuate (separating the transmission network supply). The following are guidelines for voltage drop calculations derived from Generic Letter 79-36, which have been supplemented to add clarifying information. They do not represent new NRC staff positions.
Guidelines for voltage drop calculations a) The plant voltage analysis, while supplied from the transmission network, should be based on the operating voltage range of the transmission network connection. This transmission owner/operator supplied voltage range should address all transmission network and plant system operating configurations and should also include voltage drop due to the bounding worst case transmission system contingency (transmission system contingencies include trip of the nuclear power plant). The unit trip grid contingency voltage drop value should be used in the accident cases in accordance with the plant accident analyses since a unit trip occurs with an accident.
b) Separate analyses should be performed assuming the power source to the safety buses is (1) the unit auxiliary transformer; (2) the startup transformer; and (3) other available connections (e.g., from all available connections) to the offsite network one by one assuming the need for electric power is initiated by (1) an anticipated transient such as a unit trip (e.g., anticipated operational occurrence), or (2) an accident, whichever presents the bounding load demand on the power source.
RIS 2011-12,_Rev. 1 c) For multi-unit stations, a separate analysis should be performed for each unit assuming (1) an accident in the unit being analyzed and simultaneous shutdown and cooldown 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 unit being analyzed (e.g., unit trip) and simultaneous shutdown and cooldown of all other units at that station, whichever presents the largest load situation.
d) All actions that the electric power system is designed to automatically initiate or control should be assumed to occur as designed (e.g., automatic bulk or sequential loading or automatic transfers of bulk loads from one transformer to another, automatic starts of components, operation of automatic voltage controlling equipment such as capacitor bank switching or load tap changers). All non-safety-related plant auxiliary loads should be included, as applicable, in the plant loading studies since their 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 mode of operation of the unit at the time of the event should be assumed in addition to all loads caused by expected automatic actions and manual actions permitted by administrative procedures.
g) The voltage analysis should include documentation for each condition analyzed, of the voltage at the input and output of each transformer and at each intermediate bus between the connection of the offsite circuit(s) and the terminals of each safety-related load.
h) The calculated voltages at the terminals of each safety-related load should be compared with the required voltage range for normal operation and starting of that load calculated in Item a) above. Any identified inadequacies of calculated voltage should require immediate remedial action.
i) For each case evaluated, the calculated voltages on each safety bus should demonstrate adequate voltage at the safety bus and down to the component level.
j) To provide assurance that actions taken to assure adequate voltage levels for safety-related loads do not result in excessive voltages, assuming the maximum expected value of voltage at the connection to the offsite circuit(s), a determination should be made of the maximum voltage expected at the terminals of all safety-related equipment and their starting circuits (if applicable). If this voltage exceeds the maximum voltage rating of any safety-related equipment, immediate remedial action should be taken.
k) Analysis documentation should include a statement of the assumptions for each case analyzed.
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 to Emergency 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 the aforementioned regulations and generic communications, while providing more detailed discussion concerning the necessary voltage calculations supporting DVR settings based only on 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 a modification of the procedures required to operate a facility and may result from the imposition of a regulatory staff position that is either new or different from a previously applicable staff position.
FEDERAL REGISTER NOTIFICATION
Although this RIS is informational and does not represent a departure from the current regulatory requirements, a notice of opportunity for public comment on this RIS was published in the Federal Register (76 FR 2924) on January 18, 2011, for 30 days. On February 23, 2011, a Notice was published in the Federal Register extending the comment period for additional 30
days to March 19, 2011, based on the request from Nuclear Energy Institute (ADAMS
I Accession No. ML1 10330025). There were fourteen organizations/individuals that provided comments, which were considered before issuance of this RIS. Each of the comments were documented 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 in ADAMS at Accession Nos. ML11 16006590.ML1 11600659 and ML1 12371830, which were incorrectly released as final documents when in fact they were drafts. Changes between the draft 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 the requirements of the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.).
Public Protection Notification The NRC may not conduct or sponsor, and a person is not required to respond to, a request for information or an information collection requirement unless the requesting document displays a I currently valid Office of Management and Budget QMB-control number.
RIS 2011-12,_Rev. 1
CONTACT
This RIS requires no specific action or written response. If you have any questions, please contact the technical contact listed below or the appropriate regional office.
A'R by RNeISon fGr Laura A. Dudes, Director Timothy J. McGinty, Director Division of Construction Inspection Division of Policy and Rulemakina and Oierational Proerams Office of Nuclear Reactor Reaulation Office of New Reactor Tioh -1 FtG~Atu D;i,+.,
Dr:Ic0A Of PGoIcvy and IRulemaking .v ,N,-:!:ar ReaJ!3tion R*actcr cf Off!-',,*.*
Offic-e of Nhuclear Reacutor Regula;tionR
Technical Contacts: Roy Mathew, NRR/DE/EEEB
301-415-2965 E-mail: roy.mathew(@nrc.,ov Gurcharan Matharu, NRR/DE/EEEB
301-415-4057 E-mail: .urcharan.matharuanrc.gov Kenn A Miller, RES/DE/MEEB
301-251-7458 E-mail: kenn.milleranrc.qov
RIS 20102011-12,_Rev. 1
CONTACT
This RIS requires no specific action or written response. If you have any questions, please contact the technical contact listed below or the appropriate regional office.
iRA by RNMcsGn ftre Laura A Dude Direactor Timothy J McGintv~ Director flivi~inn nf Pnlirv ~ncI RiiI~m~kinn Division of Construction Inspection Division of Policv and Rulemakinn
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Office of New Reactor Timothy j. I1;GGinty, Dilroao Wiwi IF W MI MUM! Morti! E9 P1'_rGIAucae cJrOn Rezacter Reaulauwi~
Technical Contacts: Roy Mathew, NRR/DE/EEEB
301-415-2965 E-mail: roy.mathew(Dnrc.qov Gurcharan Matharu, NRR/DE/EEEB
301-415-4057 E-mail: qurcharan.matharucnrc..ov Kenn A Miller, RES/DE/MEEB
301-251-7458 E-mail: kenn.millercnrc.qov Note: 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 attached OFFICE NRRIDE/EEEB Tech Editor NRR/DE/EEEB NRR/DE NRR/DORL OE
NAME KMiller * RMathew PHiland JGiitter * NHilton DATE 11/18/10 11/18/10 11/18/10 12/21/10 12/9/10 12/7/10
OFFICE PMDA OIS RES/DE/MEEB NRO/DE/EEB OGC (CRA) OGC (NLO)
NAME LHill * TDonnell TKoshy * RJenkins PHirsch GMizuno DATE 12/3/10 12/8/10 12/16/10 12/14/10 1/7/11 1/6/11 OFFICE OGC (CRA) OGC (NLO) LA:PGCB PM:PGCB BC:PGCB NRR/DPR
NAME GKim BJonesB&eAes CHawes TMensah SRosenberg TMcGinty DATE 8/24/11 4--11/28,3/11 11/28/1140/04/ 11/29/11--1046 12/ /11404&44 W/2614411/16/1 44 144
1_ 11 11 1. 1 1 OFFICE NRO
NAME LDudes DATE 12/13/11
OFFICAL RECORD COPY
RESPONSE TO PUBLIC COMMENTS ON DOCKET ID NRC-2011-0013 PROPOSED GENERIC COMMUNICATIONS: DRAFT NRC REGULATORY ISSUE
SUMMARY 2011-XX: ADEQUACY OF STATION ELECTRIC DISTRIBUTION
SYSTEM VOLTAGE*
On January 18, 2011, a Notice of Opportunity for Public Comment was published in the Federal Register to clarify the NRC staffs technical position on existing regulatory requirements and guidance for Degraded Voltage Relay (second level undervoltage protection) protection setting bases and Transmission Network/Offsite/Onsite station electric power system design bases. On February 23, 2011, a Notice was published in the Federal Register extending the comment period to March 19, 2011, based on the request from NEI (ADAMS Accession No.
MLI 10330025). Comments were received from 14 organizations/individuals. The staff also conducted a workshop on June 28-29, 2011, to discuss the NRC's existing regulatory requirements and guidance for nuclear power plant electric power system degraded voltage protection and addressed workshop participants' questions
1. (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 NW
ML110540357) ML110540358) (ADAMS Accession No. Washington, DC, 20006 ML110540360) (ADAMS Accession Nos.
ML110660379, ML1 10810619)
5. (49-51) Jerry Nicely 6. (52-58) Larry Nicholson 7. (97-108) PPL 8. (109-124) APS, Palo Self Nextera Susquehanna, LLC Verde Nuclear Generating (ADAMS Accession No. (ADAMS Accession No. (ADAMS Accession No. Station ML110800530) ML110800536) ML110830675) (ADAMS Accession No.
9. (125-131) Nextera 10. (132) TVA 11. (133-137)Progress 12. (138-139) STARS
Energy (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 Wilson Diablo Canyon (ADAMS Accession No.
Email (ADAMS Accession ML1 10960076)
No. ML112010028) 1 The 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 final documents when in fact they were drafts. Changes between the draft and final public comment resolution documents can be viewed in ADAMS at Accession No. MLxxxxxxxxx.
No. Section of RIS Originator Specific Comment NRC Resolution SUMMARY OF Dominion Section DVR Setting Design ISSUES - 1. DVR Resources Setting Design Services, Inc In this manner, the DVR ensures adequate Calculations operational (starting and running) voltage to all safety related equipment, independent of voltage controlling equipment external to the plant safety related electrical distribution system.
The approach could imply that the load(s) should Disagree start from the lowest DVR dropout setting. A
specific example for illustration is as follows: NRC Staff has the following clarification with I If voltage is at the lowest possible value above this position.
I
No. Section of RIS Originator Specific Comment ] NRC Resolution dropout, starting a load will cause DVR dropout, but, since the new steady state voltage will be If the offsite power has adequate capacity lower than the initial value, then DVR reset cannot and capability, any voltage just above the occur. DVR setpoint should not separate the offsite power source from the safety bus when Many utilities use the ABB 27N with harmonic filter starting large motors. The grid voltage is which has a minimum 0.5% reset. Thus, with a expected to recover.
setting of 93.6% +/- 0.9%, dropout could be as low as 92.7%. However, for motors causing more than The key point is that the voltage setting(s)
0.5% voltage dip at initial start, even if the voltage selected should ensure that adequate at the beginning of the event was 93.2% and a load voltage is available at the component was started, then DVR will dropout and never reset terminal(s) to operate the most limiting causing a separation. A clarification that allows component (s) at a plant during the most evaluation of motor starting as well-as other limiting design basis event. The offsite/onsite conditions is: interface calculation should show that, with the grid at the lower limit of the normal If the DVR could possibly not cause separation operating range, voltage at the safety bus is then the required safety functions must be always well above the degraded voltage performed successfully. Thus, depending on the setpoint for all design basis event loading design of the plant, a voltage value for beginning conditions (normal, abnormal and accident the event with all required starts could be conditions including anticipated operational determined by an iterative process. occurrence).
The safety related equipment should be protected from two types of low voltage issues:
1. Loss of voltage event which implies a sudden sharp voltage drop in grid system. Typically a nominal delay is allowed for relay actuation to separate onsite busses from the grid if voltage does not recover to normal operating band.
2. Degraded voltage event that postulates sustained low voltage conditions for several seconds and subsequent recovery to normal operating band. If the offsite power system does not recover to nominal operating conditions, it is preferable to separate from the source.
The ABB relay with harmonic filter should be able to reset if the grid perturbation is limited to a short duration.
4- - 4- + --
2. SUMMARY OF Dominion This section contains elements that are too Disagree ISSUES-- 2. Resources prescriptive. Many analyses will show that the unit Offsite/Onsite Services, Inc loads/sequences assessed for determination of NRC Staff has the following clarification for Design Interface DVR setpoint adequacy for equipment protection this position.
Calculations(page are the same as those for evaluating offsite power.
7) Since evaluating offsite power always involves To meet GDC 17 requirements, the licensee higher voltages, it is clear the equipment will must demonstrate capability to safely shut function and providing terminal voltages for this down the plant for all design basis events equipment is bounded by DVR adequacy analysis. with the grid voltage at the lowest allowable A clarification that helps frame adequate analysis value as afforded by the transmission system is: operator.
Ifthe DVR could initiate separation then offsite The voltage studies done for evaluating power is not operable. Using the example above offsite power/onsite power interface should when evaluating offsite power would require that use minimum expected voltage at the the safety bus recover above 93.6%+0.9%+0.5% plant/grid interface node, demonstrating or 95% before the earliest time delay for the DVR adequate voltage for starting and running of expires. Since a reset also resets the time delay, plant components during normal, abnormal multiple DVR drop outs could occur without and accident conditions. The expected plant separation during load sequencing. Also, since loading at 100% power operation may be
92.7% was evaluated for equipment protection. hiaher than accident loadina. Hence the
2
No. Section of RIS Originator Specific Comment NRC Resolution evaluating 95% (used for offsite power evaluation) voltage drop in the plant auxiliary system will would 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 avoid evaluation. Thus, providing calculation detail to multiple spurious actuations. A separate motor terminals for offsite power evaluation is analysis may be needed for DVR setpoint.
unnecessary in many designs.
The comment implies that DVR setpoint overlaps with system voltage during normal operation.
Calculation details to motor terminals are helpful in gaining margin between DVR
setpoint and normal grid operating voltages.
To avoid spurious DVR actuation during normal plant operation and during load sequencing, the DVR setpoint should be lower than normal operating band for offsite power. This can be achieved by:
1) Specifying equipment for safety related applications to function at voltage levels well below the nominal bus voltage.
2) Reducing the onsite system impedance/voltage drop. This can be achieved by reducing the cable impedance for the limiting safety loads and tripping non-essential loads after unit trip.
SUMMARY OF Dominion Part a states:
ISSUES -- 2. Resources This transmission owner/operator supplied voltage Offsite/Onsite Services, Inc range should address all transmission Design Interface network and plant system operating configurations Calculations(page and should also include voltage drop due to
7) the bounding worst case transmission system contingency (transmission system contingencies include trip of the nuclearpower unit).
Certainly the trip of the nuclear power unit must Disagree always be considered. However, the definition of the worst case transmission system contingency requires clarifying statements. Certainly some analyses are done using "strong grid" for fault analyses or "weak grid" for voltage analyses.
These modeled sources have a number of contingencies built into them. Voltage drop from the The plant electrical distribution system loss of the unit can vary considerably with system should be designed based on the grid conditions. Arguments can be made that the worst voltage range including the bounding worst case contingency (if different than the nuclear case grid contingency (strong or weak grid power unit) should only be considered once it has depending on which one is bounding). In this occurred. However, a key question should be way, the plant's design ensures adequate applied: Is the contingency of interest monitored? If voltage to plant equipment as long as grid is the 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 basis nuclear unit switchyard is known, either by (line outages during peak grid loading instrumentation at the plant or timely notification conditions) that occur during plant operation by the grid operator, then the contingencies need should be evaluated uniquely to assess the only be considered when applicable. When capability of offsite power to provide evaluating voltage drop, most situations which shutdown capability post trip as required by cause meaningful changes are nearby and can be GDC 17.
monitored.
GDC 17 requires that offsite power has sufficient capacity and capability to assure that (1) specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences, and (2) the core is cooled and containment integrity and other vital functions are maintained in the event of
3
No. Section of RIS Originator . Specific Comment NRC Resolution postulated accidents.
4. SUMMARY OF Dominion Part c states:
ISSUES-- 2. Resources Offsite/Onsute Services, Inc For multi-unit stations, a separateanalysis should Design Interface be performed for each unit assuming (1) an Calculations(page accident in the unit being analyzed and
8) simultaneous shutdown of all other units at the station,' or (2) an anticipatedtransient (anticipated operationaloccurrence) in the unit being analyzed (e.g., unit trip) and simultaneous shutdown of all other units at that station, whichever presents the largestload situation.
This requires clarification as an accident or anticipated transient both require unit trip. The Disagree word used for other units at the station is
"shutdown" which is more orderly and takes more time. 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 analyses show the worst voltage drop for the loss of the Multi-unit sites have been licensed in nuclear unit is when all of the nearby units (any accordance with above documents and type of generation) are already off. Changing that should therefore evaluate the plants to tripping all units at the same time increases the according to their licensing basis.
voltage drop because grid compensatory actions are not included. Even a small (minute) time difference between losses of units can be meaningful in the voltage result. However, if the intent of the wording was simultaneous trip, then this is a special case of item 3 above, which is likely a monitored contingency.
5. SUMMARY OF Dominion Part j states:
4
No. Section of RIS Originator Specific Comment NRC Resolution ISSUES-- 2. Resources Offsite/Onsite Services, Inc To provide assurance that actions taken to assure Design Interface adequate voltage levels for safety related loads Calculations(page do not result in excessive voltages, assuming the
8) maximum expected value of voltage at the connection to the offsite circuit,a determination should be made of the maximum voltage expected at the terminals of all safety related equipment and their starting circuits (if applicable).
If this voltage exceeds the maximum voltage rating of any safety related equipment, immediate remedial action should be taken.
The word "immediate" describing remedial action Disagree should be removed from this section. Immediate remedial action could imply control room intervention. The control room has alarm procedures to address high voltage should it occur.
Timeliness of remedial actions depends on how high actual voltage is since minor incursions have only long term implications for most equipment. The wording is consistent with GL 79-36.
Analyses of high grid voltage with light plant load are standard and provide insights as to what grid The Offsite/Onsite design should address all voltage upper limit should be or what compensating grid operating conditions to prevent activities might be required for light load operations overvoltages from occurring.
(refueling). In those cases where unit trip can result in a step increase in grid voltage (most common on The point here is that if a design problem is higher voltage connections like 765kv), anticipated identified such as overvoltage conditions, excursions above desired voltages should be immediate actions should be taken addressed by compensating measures (changing (compensatory and/or permanent design excitation for nearby units, switching in reactor changes) to address the design problem banks, etc.). rather than taking actions after it occurs.
6. SUMMARY OF Dominion States: This interface calculation establishes ISSUES (top of Resources operating voltage bands for all plant electrical page 6) Services, Inc buses, which ensures that all plant components and systems (Class 1E and Non Safety Related)
have propervoltage for starting and runningin all operationalconfigurations(expected operational and accident conditions).
This statement needs clarification in that not all Agree non-safety load voltages need to be evaluated.
Typically, large motors (like reactor coolant pumps)
need to be evaluated for starting impact on the safety bus. However, once a motor is found to be small enough to not impact safety bus operation, further evaluation is unnecessary. The statement in the RIS can easily be interpreted as requiring The reference to 'non-safety related' is being evaluation of all non-safety loads down to the removed. However, non-safety related loads lowest levels of distribution, should be modeled to the extent that their operation can affect safety bus/equipment voltage.
7. SUMMARY OF Dominion States:
ISSUES - 1. DVR Resources Setting Design Services, Inc Licensee voltage calculationsshould provide the Calculations (page basis for theirDVR settings, ensuring safety related
6) equipment is supplied with adequate operating voltage (typically a minimum of 0.9per unit voltage at the terminals of the safety related equipment per equipment manufacturers requirements), based on bounding conditions for the most limiting safety related load (in terms of voltage) in the plant Clarification that voltages other than 90% voltage Agree.
are common based on detailed plant analysis should be added. As an example, motors below 90% was mentioned as an example used for
1 90% voltage continue to have plenty of margin in illustration. The voltage values are plant-
5
No. Section of RIS Originator Specific Comment NRC Resolution torque but may encroach on long time thermal specific. Evaluations like mentioned in this limits. However, unless a motor is fully into its comment could be acceptable as long as service factor (typically 1.15), as well as below 90% there is adequate engineering justification.
voltage, operation will be acceptable. Ensuring that voltages are within nominal limits greatly simplifies the analysis required.
8. General Exelon General Comments:
Generation Company, The RIS uses terms such as "LVR (loss-of-voltage Background - LLC relay) voltage setting," "DVR (degraded Pages 2 and 3 voltage relay) settings" and "DVR dropout setting" Disagree.
without clarifying the intent or highlighting the differences.
IEEE 741-2006, Annex A (Reference 1), has a The terminology used in the RIS is discussion on the tolerances to be considered and consistent with the guidance documents.
recommends following ANSI/ISA 67.04.01 (Reference 2) treating the voltage relays and associated time delays as instruments.
For the DVR, one example might be The setpoint accuracies and methodologies represented as follows: are beyond the scope of this RIS.
Analyticallimit: Minimum voltage that assures actuation of the relay Allowable value, Lower, Higher than analytical limit to allow for drift and test equipment tolerance;
abbreviated AVDO. Tech Spec value.
Dropout setpoint: Lower voltage band of nominal setpoint. Abbreviated SPc DO (Setpoint calculated Drop Out)
Pickup setpoint: Upper voltage band of nominal setpoint. Abbreviated SPc PU (Setpoint calculated Pick Up)
Allowable value, Upper: Higher than SPc PU to allow for drift and test equipment tolerance;
abbreviated AVPU. Tech Spec value.
Maximum Dropout: Highest voltage that relay could actuate. Only importance is for establishing reset voltage.
Maximum Pickup: The voltage required to assure DVR resets.
The RIS states that two sets of calculations are required. It appears that at least three (3) The point of the RIS was to highlight that the distinctly different calculations are required (four if DVR setting and design interface the site has different DVR time delays for accident calculations have different requirements.
and normal conditions). These would be at different bus voltage values. The "degraded voltage relaying The staff agrees that there are other design calculations" would be a load flow calculations required to demonstrate the performed at the DVR analytical limit; the "plant electrical system design basis.
voltage analysis" would be load flows and motor starting performed at the minimum transmission contingency voltage with an acceptance criterion of greater than relay maximum pickup (the voltage where DVR reset is assured) at the bus where the degraded voltage relays are connected (generally the medium voltage bus where the Emergency Diesel Generator is connected); finally, the evaluation of protective device actuation would be performed at the analytical limit of the loss of voltage relay setting comparing the motor running current to the thermal damage curve and protective
6
No. Section of RIS Originator Specific Comment NRC Resolution device characteristic curve, Page 2, criteria b) - Some approved DVR designs sense and trip at an emergency bus level, and take RIS is consistent with the NRC letter dated advantage of inherent redundancy of the June 2, 1977.
emergency buses. It should be an owner's option The coincident logic is to ensure that with respect to coincident logic. Change the "shall" spurious or inadvertent separation of a to "may." reliable offsite power source. The Page 2/3 - The listed 6 criteria are good for setting redundancy of the safety buses alone does the DVR. Eariy correspondence of the issue not address the above concern also included a second function for the DVR in that the design should minimize the effects of Current wording seems adequate to address spuriously disconnecting the offsite sources. the point that spurious trips of offsite power Although criteria b) and c)(2) are intended to add should be precluded by the design.
robustness to the design, a few sentences should be added to the discussion to accentuate the point.
9. SUMMARY OF Exelon Under "Degraded Voltage Relaying Design Disagree.
ISSUES - 1. Generation Calculations," the RIS states in part "During normal Degraded 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 power Calculations (page supply within a short interval (typically less than 60 RIS will be revised to remove the reference
6) seconds) if sustained degraded voltage to auto separate in 60 seconds. The 60
conditions are detected." Branch Technical Position seconds time delay was identified as an PSB-1 clause B.1 .b.2 included provisions example to illustrate that the time delay for operator manual actions to restore bus voltage chosen for the sustained degraded condition on the Class 1 E distribution system. The (DVR settings) should be short to ensure that sixty second time delay would not allow operator permanently connected Class 1 E loads are actions. This appears to be a new NRC not damaged.
position.
However, it should be noted that when voltage alarms occur (alarm setpoint is set higher than the DVR setpoint), the grid voltage at that point may be well below the normal operating values and is approaching the DVR setpoint and operator actions may be taken to improve the voltage conditions to prevent separation from offsite power.
The time delay chosen should ensure that until the relay automatic action is initiated, all Class 1E equipment are protected. The licensee must provide the bases and justification in support of the actual delay chosen.
10. SUMMARY OF Exelon The next to last sentence under item 1 states: 'The Disagree.
ISSUES - 1. Generation staff considers degraded voltage Degraded Voltage Company, conditions coincident with a postulated design The point being made in the RIS is that Relaying Design LLC basis accident to be a credible event. The event setting of the DVR should include Calculations Page is credible in that it has occurred previously consideration of a coincident accident, in that
6 (although nonaccident). It is acknowledged that the time delay chosen for the DVR should safety loads combined with loss of generator support the accident analysis assumptions reactive power support will cause a decrease in consistent with the NRC1 977 letter.
bus voltage. However, if the plant is operated within the bounds of the operating procedures Operating a plant within allowable voltage (which are reflected in the voltage regulation range should minimize the potential for calculations as described under the subsequent degraded voltage conditions on 1E busses.
section), then the Class 1 E equipment should not However, grid perturbations cannot be experience a degraded voltage condition, predicted. Hence the need for automatic The sentence can be removed without diminishing protection.
the need for the DVR, or without changing the 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 plant Degraded Voltage Company, distribution system consistent with the specific The suggested sentence will be added to the Relaying Design LLC transient or accident being analyzed." RIS.
Calculations -
7
No. Section of RIS Originator Specific Comment NRC Resolution Page 6,
12 SUMMARY OF Exelon In addition, Branch Technical Position (BTP) PSB-1 Disagree ISSUES - 1. Generation clause B. 1 .b.2 (Reference 4) included provisions All actions required to protect the Class 1 E
Degraded Voltage Company, for operator manual actions to restore bus voltage equipment from degraded voltage must be Relaying Design LLC on the Class 1 E distribution system. The RIS automatic in accordance with 10 CFR
Calculations - specifically excludes manual load shedding under 50.55a(h)(2).
Page 6, the Offsite/Onsite Design Interface Calculations whereas the BTP allows for manual actions to Manual actions are allowed as stated in avoid separation from offsite power. Please clarify PSB-1, B.l.b.2 for improving the voltage in if manual actions taken to restore voltages now response to the alarm in control room that require prior NRC approval, alerted the operator to the degraded condition. However, to demonstrate the adequacy of onsite/offsite interface design and offsite power capacity and capability, as specified in GL 79-36, manual load shedding should not be assumed.
13 SUMMARY OF Exelon Under "DVR Setting Design Calculations," the RIS Agree ISSUES - 1. Generation states in part "...would allow calculation of Degraded 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 not Page 6, clear what "contacts" are in this context. It is assumed that the concern is motor control center contactors and/or motor starting control circuits.
14 SUMMARY OF Exelon Under discussion of DVR setting calculations, the Disagree ISSUES - 1. Generation RIS states that setting cannot cause any Degraded Voltage Company, degradation of the safety related components, The DVR ensures that voltage requirements Relaying Design LLC including actuation of their protective devices, of the Class 1E loads are always preserved Calculations - The BTP only stated damage to normally operating for operating the equipment under accident Page 6, safety related equipment. The RIS language and non accident conditions including all seems broader then BTP and appears to open up abnormal operational occurrences.
the position that the DVR studies have to consider starting 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 on Degraded 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 grid Calculations - RIS. Under Guidelines for Voltage Drop well below normal. It is understood that grid Page 6, Calculations, the summary states that the plant- operating procedures should prevent voltage analysis, while supplied from the sustained voltages at such low levels but transmission network, should be based on the regardless of what happens on the grid the operating voltage range of the transmission DVRs will preserve the voltage limits for the network connection. Grid operating voltage ranges equipment.
do not allow operation down to levels that would cause sustained operation at LVR levels. Plant operation at LVR setpoint is not Therefore, consideration for operation at the LVR expected and is not within the scope of the setpoint would be inconsistent with this guidance. RIS.
The condition that occurred at Arkansas Nuclear One (ANO) in 1978 would appear to be related to inadequate operating procedures and a lack of a rigorous analysis of the AC power distribution system. It would not be credible for present day operation. In addition, the operator would be alerted by an alarm on degraded voltage conditions (less than the analytical limit) as required by Branch 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 an used) Design LLC for the most part to rotating equipment example and was not meant to cover Calculations - (motors). Motor Control Center (MCC) contactors, everything. RIS will be revised to delete Page 6 battery chargers, Motor Operated Valves references to specific numbers and (MOVs) all have less than a 90% operating voltage emphasize voltage requirements and voltage requirement. This distinction should be requirements are plant-specific.
made and/or clarified.
18 SUMMARY OF Exelon The Degraded Voltage Relaying Design ISSUES - 1. Generation Calculations section should include a statement to Agree.
8
No. Section of RIS Originator Specific Comment NRC Resolution DVR Setting Company, emphasize that only steady state loading and Design LLC steady state acceptable voltages at the class IE 0.9 per unit voltage was mentioned as an Calculations - equipment are to be considered in determining the example and was not meant to cover Page 6 DVR drop out settings including the allowable everything. RIS will be revised to delete tolerances. The paragraph does mention 0.9 per references to specific numbers and unit voltages at the terminals which is steady state emphasize voltage requirements and voltage but a positive statement about steady state loading requirements are plant-specific.
and steady state acceptable voltages would be helpful. Also, there are alternatives to the 90% The suggested analysis may be acceptable if terminal voltage criterion. The concern is heating, properly developed and supported in the causing a temperature rise, which decreases useful design. The 90% voltage criteria may not be life of the insulation. Inspectors may read too much adequate for certain components such as into the 90% criterion; a motor loaded to less than SOVs, motor control center contactors, etc.
nameplate will draw less than service factor current at a lower terminal voltage. Therefore, a lower voltage would prove adequate as long as adequate torque 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 and Design LLC analysis. GL 89-10 (Reference 3) programs the DVR settings must support adequate Calculations - perform these calculations. A statement in this voltages for all Class 1E equipment including Page 6 section that MOVs loads are not to be considered MOVs.
in this calculation will be helpful if NRC agrees with this interpretation
20 SUMMARY OF Exelon The starting voltage requirement is unclear. Some Disagree.
ISSUES - 1. Generation sites have evaluated the capability of starting each DVR Setting Company, required safety related motor individually at the The intent of the RIS is not to prescribe DVR
Design LLC degraded voltage analytical limit. Other sites use a relay setpoint methodology for every plant.
Calculations - "block start analysis" where multiple motors are Page 6 started simultaneously on the offsite source. There The RIS provides the conditions for which have been violations associated with both plant specific analyses should be performed.
approaches. The RIS should describe an The specific design of the plant dictates the acceptable methodology for determination of motor type of analyses required to demonstrate starting voltage adequacy. adequacy of DVR setting. If the plant design requires load sequencing on the offsite source, then individual motor start is the appropriate methodology. If the plant design requires block starting accident loads, then the DVR setpoint should be based on multiple motor starts.
21 SUMMARY OF Exelon The RIS implies this portion of the calculations Disagree ISSUES - 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 a Calculations - setpoint. However, with voltage just above the DVR subsequent motor start will eventually Page 6 drop out value, any load addition (starting or separate the plant from offsite source as the running) 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 and equipment is taken. Therefore, the purpose of this time setpoints shall be determined from an requirement is not clear. The intent of the starting analysis of the voltage requirements of the voltage evaluation should be clarified, safety related loads". Safety related (Class
1E) equipment, particularly large motors, Some stations have evaluated the performance of have starting and running "voltage protective 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 as suggested that the NRC add a statement for resulting in Class 1E bus voltages down acceptability of the same. close to where DVRs are set based on Class
1E equipment requirements), and the grid does not automatically recover, separation from the grid is appropriate. The DVR is expected to reset after a perturbation of sustainedduration when automatic actions such as clearing the grid 'fault' that resulted in degraded voltage conditions.
The NRC staff will accept standard industry practices to evaluate performance
9
No. Section of RIS Originator Specific Comment NRC Resolution capabilities of DVR. Analyses supported by calculation should clearly and succinctly define plant design basis and compliance with regulation.
22 SUMMARY OF Exelon Under Offsite/Onsite Design Interface Calculations, Agree.
ISSUES - 1. Generation Guidelines for voltage drop calculations item DVR Setting Company, 2, i), the acceptance criteria for demonstrating RIS Section 2 (i) will be modified to state: For Design LLC voltage adequacy would appear to be DVR each case evaluated, the calculatedvoltages Calculations - Maximum Pickup (the voltage required to assure on each safety bus should demonstrate Page 6 relay reset) and not component level voltage adequate voltage at the safety bus and down values, to the component leveL It is based on Class
1E component terminal voltage requirements.
23 SUMMARY OF Exelon Item 2 (Offsite/Onsite Design Interface ISSUES - 2. Generation calculations) appears to be additional requirements Disagree Offsite/Onsite Company, for those sites licensed to the Standard Review Design Interface LLC Plan (NUREG 0800) Chapter 8 Appendix A Branch RIS highlights the guidelines provided in GL
Calculations Technical Position PSB-1, "Adequacy of Station 79-36 and NUREG 0800, Chapter 8 Electric Distribution System Voltages." Appendix A Branch Technical Position PSB-1, "Adequacy of Station Electric Distribution System Voltages.". There are no new requirements
24 SUMMARY OF Exelon Page 7- The phrase "...all operating configurations ISSUES - 2. Generation of transmission network and plant Offsite/Onsite Company, systems..." appears in a few sentences. The station Design Interface LLC interface agreement with the transmission Calculations provider integrates the considerations among the Disagree.
transmission network, the operability of the off site sources, and the voltage regulation (drop) This is addressed in RIS Section 2 a.
calculations. The calculations identify certain controlling parameters for the transmission As discussed in GL2006-02 "Grid Reliability network. These controlling parameters are then and Impact on Plant Risk and the Operability incorporated into the Bases for the operability of of Offsite Power", licensees are required to the offsite source(s). If the plant configuration provide the transmission system operator or transmission network parameters are not (TSO), the operating voltage parameters bounded by the calculations, then the operability of required by the plant during all modes of the offsite sources needs to be examined. In most operation. The analyses discussed in this cases, the plant operator has no control over comment should be the bases for the the "configuration" of the transmission network, but information provided to the TSO.
does have agreements with the transmission system operator that normal operating voltages The DVR protects the safety related and post unit trip contingency voltages are equipment when a perturbation in the grid controlled within established bounds. Add a few system results in degraded voltage sentences detailing that the intent of the conditions and the normal operating phrase "all operating conditions of the transmission parameters cannot be restored immediately network" means that the controlling to protect safety related equipment. The parameters from the transmission network that are DVR setpoint evaluation should be a used in the calculations are consistent with separate analysis.
those utilized in the Bases for operability of the offsite sources.
25 SUMMARY OF Exelon Page 7, item a) - Change the last sentence to read ISSUES - 2. Generation "... include voltage drop due to all Disagree.
Offsite/Onsite Company, transmission system contingencies that are a direct Design Interface LLC result of the transient or accident being A transient grid perturbation may be a result Calculations analyzed (typically this will include tripping of the in a plant trip. The DVR setpoint should be nuclear power unit)." based on bounding voltage resulting from a transient grid condition. The actual reason for the perturbation is not a consideration. A
plant trip may result in limiting conditions for DVR setpoint calculation.
26 SUMMARY OF Exelon Page 7, item a) - Either add to a) or add another ISSUES - 2. Generation section immediately after a). "The transmission Agree.
Offsite/Onsite Company, system controlling parameters are assumed to Design Interface LLC remain unchanged throughout the initial stages of RIS will be revised to state a): The unit trip
10
No. Section of RIS Originator Specific Comment NRC Resolution Calculations the event with the exception of those effects grid contingency voltage drop value should resulting from the event (contingency due to the be used in the accident cases in accordance loss of the unit). For purposes of the calculation, with the plant accident analyses since a unit the Unit trip contingency can be coincident with the trip occurs with an accident.
accident, or at a later time consistent with the assumptions in the plant accident sequence analyses."
27 SUMMARY OF Exelon Page 7, item b) - Delete the tabulation of sources ISSUES - 2. Generation of power to the emergency buses and replace with Disagree.
Offsite/Onsite Company, a simple statement of "all credited sources of offsite Design Interface LLC power to the emergency buses." The recommendation does not change the Calculations intent of the tabulation. To maintain consistency with GL 79-36, it is preferable to maintain the tabulation.
28 SUMMARY OF Exelon Page 8, item c) - Change to read: "(1) an ISSUES - 2. Generation accident in the unit being analyzed and shutdown Disagree.
Offsite/Onsite Company, of all other units at the station consistent with the Design 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 to other units at that station consistent with the be uniquely considered.
licensing basis of the station, whichever represents the largest load situation." Typically, the licensing basis for multi-units site allow for an orderly 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 positive ISSUES - 2. Generation statement for allowing the credit for voltage Disagree.
Offsite/Onsite Company, controlling equipment external to the class IE
Design Interface LLC equipment for this calculation. Licensees perform Use of LTCs is acceptable for regulating Calculations LOCA load sequencing under this section of the voltage during normal plant operation. LTCs calculations and take credit for LTCs (or other do not afford protection during a transient voltage regulating devices) to demonstrate the degraded voltage condition that can affect adequacy 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 in this scenario, even though it appears from the the RIS: Add the following in section 2 RIS that MOVs and other equipment like contactors (general) and d.
are to be evaluated with voltages obtained from the Degraded Voltage Relaying Design Calculations All actions the electric power system is with voltage just above the lowest set point of DGV designed to automaticallyinitiate or control relays. 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 equipment, etc.,)
Yes. All equipment including MOVs, contactors, solenoids, etc., should be evaluated for adequate voltage based on the DVR set point.
30 SUMMARY OF Exelon Under Item a), for units with LTCs, please clarify if ISSUES - 2. Generation the analysis is to be performed with the grid Disagree Offsite/Onsite Company, at minimum expected voltage, maximum expected Design Interface LLC voltage, or at both. See Question 29.
Calculations Analyses for normal operation should evaluate effect of LTC operation at the extreme settings for impact on operating equipment. DVR setpoint should be based on minimum voltage required for operation of accident mitigation loads. For units with LTCs, it is unlikely that voltage correction can be achieved within the short time it takes for contactors to drop out or fuses to blow during a sustained degraded voltage or overvoltage condition.
31 General Exelon In general the clarifications contained in the draft Generation RIS appear to be more restrictive and Disagree.
1I
No. Section of RIS Originator Specific Comment NRC Resolution Company, prescriptive than the cited historical regulatory LLC documentation, and do not support plant unique Unique designs that may have been design and current licensing bases that have been previously 'accepted' should have developed and accepted in previous licensing appropriate justification with NRC approval of activities. Unique design and licensing bases that the licensing documents. Typically, detailed have previously been accepted and calculations have not been reviewed as part approved that may not be strictly aligned with the of Technical Specification changes. The staff darifications in the draft RIS may include use has relied on licensee correspondence of an inverse time under voltage relay set between stating adequacy of DVR setpoint to approve the DVR and LVR relays (such as .875 to license amendment requests. Onsite
0.70 PU for a maximum of 60 seconds). Some inspections are used to verify analytical sites may not provide coincident logic to methods used to meet regulations.
preclude spurious trips: rather, the logic may include alternate design features to conform to the Alternate methods used to demonstrate intent of the requirements of BTP PSB-1. conformance may be acceptable provided they meet the intent of BTP PSB-1 to protect safety related equipment
32 Southern General Nuclear Agree Operating Include a definition of key terms (ex. Normal grid Company operation, sustained degraded voltage) Additional clarifications will be provided in the RIS wherever appropriate.
33 General Southern The RIS does not address completely the specific Nuclear requirements in the PSB-1 (ADAMS Accession No. Disagree Operating ML052350520). Arkansas Nuclear One (ADAMS
Company 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 in the above documents were omitted from the RIS. The reference documents should be reviewed for more details.
Proposedresolution: include missing positions especially those related to determiningminimum The expected offsite system voltages can expected offsite system voltages and testing, vary between G-110 percent. The objective of the LVR and DVR is to afford protection and separation from the grid when plant specific needs cannot be satisfied.
34 General Southern The RIS lacks adequate guidance to perform the Nuclear requested calculation(s) without additional Disagree Operating interpretations by the licensee and auditors as to Company the intent of the provided guidance. The RIS is consistent with GL 79-36. The licensee is responsible for performing Proposed resolution: Provide a guideline with calculations, in accordance with industry examples on how to perform the calculation(s) engineering practices, with properly including expected assumptions,other supported inputs and assumptions that considerations, and criteria to be used for demonstrate compliance in accordance with acceptance. 10 CFR Part 50. Appendix B. Criterion I11.
The RIS addresses certain problem areas identified mainly through NRC inspections and to re-emphasize the existing NRC
requirements and staff positiooiuidance.
35 General Southern The RIS provides some examples of plants that Nuclear have NRC reviewed and approved analyses and Disagree Operating goes on to point out that "backfit rule" was applied Company because the staff believed the sites were not in The licensee must be in compliance with all compliance with regulations even though they had regulations pertaining to onsite and offsite approved the analysis. How is a licensee who has power systems. Unless, licensees are an NRC approved or acceptable analysis supposed exempted from meeting certain regulatory to know that their analysis is no longer acceptable? requirements, changes to the design and The RIS needs more clarification with regard to licensing bases are required to meet the individual plant licensing bases if it is to be useful regulations in accordance with 10 CFR
to licensees. 50.109. The RIS identified some of the recent inspection findings.
Some plants have installed degraded grid alarm systems and, at the staff request, included them in Unit Operating Technical Specifications. Required Operator actions could be used only to
12
No. Section of RIS Originator Specific Comment NRC Resolution operator actions related to degraded grid supplement the automatic DVR scheme by conditions are specified in the bases and providing alarm in the control room when grid procedures. The RIS does not discuss this voltage is below nominal operating range.
approach. Operator actions cannot be substituted for protecting the safety related equipment from There 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 be used 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 basis for DVR requirements and preclude future findings in plant designs. The RIS does not provide new guidelines for issuing violations.
36 Summary of Southern The RIS states "The Class 1 6 buses should Issues", pg. 6, Nuclear separate from the offsite power system within a few Disagree.
Item 1. "Degraded Operating seconds if an accident occurs coincident with Voltage Relaying Company sustained degraded voltage conditions." The RIS correctly states that if an accident Design signal is received during sustained Calculations", GDC 17 describes the requirements for onsite and degraded grid conditions, it may be prudent Line 5. offsite power systems. One of its requirements is to separate from the grid as :
that they each provide sufficient capacity and capability to mitigate postulated events. The events 1. The duration of degraded are described in Chapter 15 "Accident Analysis". conditions on the grid is unknown These analyses assume Loss of Offsite Power 2. It precludes other complications simultaneous with the event. They do not require such as double sequencing.
assuming degraded grid voltage condition prior to an event occurring. In addition because of FERC Chapter 15 "Accident Analyses" assumes and NERC requirements for voltage control, the "Loss of Offsite Power" as a limiting case for likelihood of a chapter 15 accident occurring safe shutdown in view of the limited power concurrent with a serious degraded grid voltage and resources available from the onsite condition is not believed to be credible. power sources. The preferred power source for all operating modes and accident related Proposedresolution: Remove or clarify this safe shutdown is the offsite source. The statement since proper offsite system design and DVR provides assurance that the plant operation renders such simultaneous postulated shutdown capability is not compromised events as incredible. when the offsite source is degraded and a fast transfer can occur to the onsite sources if the offsite source does not recover within the allotted time. This preserves the Chapter
15 accident analyses.
NERC and FERC requirements for voltage control are beneficial to nuclear plant operators as they provide assurance that grid parameters will be maintained within acceptable limits for normal nuclear plant operations. However, the transmission system is always vulnerable to perturbations such as line outages, overload conditions, generation shortages etc. which are beyond the control of the grid operator. The magnitude and duration of these perturbations cannot be predicted. The safety of the nuclear plant must not be compromised during these conditions. The function of the DVR is to protect redundant safety related equipment during these grid perturbations.
The staff considers degraded voltage condition and coincident LOCA can occur.
Until the DVR relay takes automatic action, the offsite power is considered to have adequate capacity and capability. Therefore, the accident analysis assumption for a LOCA
with offsite power available applies.
37 Summary of Southern The RIS states "During normal plant operation, the T
Issues", pg. 6, Nuclear Class 1 E safety related buses should Disagree.
Item 1. "Degraded Operating automatically separate from the power supply I
13
No. Section of RIS Originator Specific Comment NRC Resolution Voltage Relaying Company within a short interval (typically less than 60 See staff's response to Comment No. 9 Design seconds) if sustained degraded voltage conditions Calculations", are detected."
Line 7 Voltages down at the DVR level should be During 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 actions conservative. Therefore automatic separation from when voltages fall below the normal low level the preferred power supply may not be desired. (or post contingency low) well above the DVR value (assuming the plant design is Proposed resolution: Transmission Operators proper given the grid operating voltage should be allowed time to correct the degraded range).
voltage condition while Plant Operators monitor the safey bs or aequte vltaes oltge. The plant electrical distribution system safety bus voltages for adequate voltage, design should be based on the grid voltage range including the bounding worst case grid contingency (strong or weak grid depending on which one is bounding). In this way, the plant's design ensures adequate voltage to plant equipment as long as grid is operating as "expected".
GDC 17 requires that offsite power has sufficient capacity and capability to assure that (1) specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences, and (2) the core is cooled and containment integrity and other vital functions are maintained in the event of postulated accidents.
38 Summary of Southern The discussion on time delays does not provide Issues, Last Nuclear adequate criteria for time delay selections. Disagree paragraph of Operating
"DVR criteria for Company Proposed Resolution: Clarify. The acceptable level of time delay is based time delay on plant specific accident analyses and selections. The RIS states " In this manner, the DVR ensures electrical systems designs.
Setting Design Different time delays may be selected for Calculations", pg. adequate operational (starting and running) voltage different plant designs. BTP PSB-1 suggests
7 to all safety related equipment, independent of voltage controlling equipment external to the plan pat two relays with different settings to accommodate motor starts and sustained safety related electrical distribution system. For the degraded conditions. Typically, chapter 15 purposes of this calculation, no t credit should be assume 10 second time taken for voltage controlling the las 1Edisribtio sysem uchasexternal equipment utoat.to delay for analyses accident onsite power sources to energize the Class 1 E distribution system such as automatic safety busses. DVR time delay of 1Oseconds load tap changers and capacitor banks." or less may be acceptable to demonstrate Proposed Resolution: This statement needs to be that the assumptions in the accident clarified to allow reasonable assumptions for the analyses remain valid.
status of equipment external to the Class 1E External voltage regulating equipment (tap distribution system. For example it is unclear how changers) does not afford timely protection to perform motor starting calculations without for safety related equipment during sudden taking credit for some Non I E voltage controlling grid perturbations and therefore cannot be equipment. Additionally, normal Transmission grid credited for DVR settings including transient switching to prepare for the next contingency to maintain.minimum expected transmission system voltages during motor starts.
voltages should be allowed.
See staffs response to Comment Nos. 76 and 118.
39 Summary of Southern After paragraph (f) the RIS leaves out the guidance Disagree Issues, Guidelines Nuclear in GL 79-36 concerning minimum expected values for voltage drop Operating (item 6 of enclosure 2) was omitted from the RIS Item 6 was addressed in item(a) in the RIS
calculations, item Company guidance.
(f) pg. 8 Proposed resolution: Add item 6 of enclosure 2 in GL 79-36 to the RIS.
40 General NEI 3/2/11 NEI contends that RIS represents new positions
14
No. Section of RIS Originator Specific Comment NRC Resolution Letter Disagree The RIS provides clarifications to avoid the misconception of the existing requirements and NRC staff peititnisuiance, No new requirements are identified in the RIS.
41 NEI 3/2/11 77 Letter and PSB-1 Not consistent. Degraded Letter voltage event and accident coincident vs. Disagree subsequent. Also, starting and running voltage vs. PSB just states how the scheme should just running (term sustained in PSB-1) react to a subsequent degraded voltage.
The 77 letter indicates that the time delay should support the accident analysis which means coincident events.
42 NEI 3/2/11 77 Letter and 79 GL are generic communications Letter Both communications provide guidance on not requirements how to meet regulatory criteria. To that extent, they are related to compliance with regulations, but are not themselves regulatory requirements.
43 NEI 3/2/11 Multi-unit sites, accident and simultaneous Letter shutdown vs. orderly shutdown and cooldown per Disagree GDC 5 This RIS is consistent with GDC 17, GL 79-
36, and IEEE Standard 308-1971, "Class IE
Electrical Systems," Section 8, "Multi-Unit Station Considerations
44 NEI 3/2/11 During normal plant operation, a degraded voltage Letter for 60 seconds resulting in separation doesn't give Disagree the operator enough time (implied by PSB-1) to See NRC response to Comment No. 9.
take actions
45 NEI 3/2/11 Offsite/Onsite design interface calculations doesn't
48 Le- allow for manual actions Disagree sot This means that manual actions for the used)
purposes of analyses of the offsite power
8dso see system voltages should not be assumed.
Nos See GL 79-36 for more details.
86-96 PSB-1 allows manual actions after first alarm forthis at higher voltage.
NE,
Len.,
49 Page 6, DVR Jerry Nicely Section DVR Setting Design Calculations states: Disagree Setting Design At the DVR dropoutsetting. the DVR ensures Calculations adequate operational(startingand running) voltage See Responses to Questions 1 & 2.
to all safety related equipment, independent of voltage controlling equipment external to the plant 'Sustained' in the context that the loss of safety related electrical distribution system. voltage relay was designed for momentary dip in voltage or complete loss of voltage.
BTP PSB-1 states, "sustained", implying a steady Steady state operation is expected at normal state voltage condition and not a transient voltage operating band.
condition that exists during a motor starting event.
The 1977 NRC letter states that "voltage and The original 1977 NRC Letter, the later PSB-1, or time setpoints shall be determined from an GL 79-36 does not require plants to demonstrate analysis of the voltage requirements of the the ability to start motors at the DVR settings, safety related loads." Safety related equipment, particularly large motors, have Requiring 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 should make 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 in dropout; result in not being able to be reset the the 1977 NRC letter, refers to grid voltage relay, and as a result causing a spurious below the expected low value given normal disconnection from offsite power and transferring to grid operation and grid post contingency
15
No. Section of RIS Originator Specific Comment NRC Resolution the emergency diesel generator. Having a (Single, N-i). Thus, when grid voltages are requirement to be able to start motors at the DVR degraded beyond the minimum voltage dropout setting will result in the raising the DVR assured by the grid operator(such as settings to a higher value and is more likely to resulting in SR bus voltages down close to result in spurious separation from the grid which is where DVRs are set based on SR equipment in direct conflict with PSB-1. requirements), separation from the grid is appropriate. Proper design of the plant electrical distribution system and setting of the DVRs, based on the grid voltage range (described above) should provide proper margin such that spurious separation from the grid should not occur.
The key point is that the voltage setting(s)
selected should ensure that adequate voltage is available at the component terminal(s) to operate the most limiting component (s) at a plant during the most limiting design basis event. The offsite/onsite interface calculation should show that, with the grid at the lower limit of the normal operating range, voltage at the safety bus is always well above the degraded voltage setpoint for all design basis event loading conditions (normal, abnormal and accident conditions including anticipated operational occurrence).
50 Page 5, Peach Jerry Nicely In the RIS section of recent inspection findings for Bottom Peach Bottom, it was stated that since the load tap Agree changers are not safety-related and are subject to operational limitations and credible failures, they The finding is correct.
cannot be relied on.
The safety related equipment should be protected by Class1 E relays and not dependent on non safety LTCs functioning.
The DVR action is independent of LTC
action. Therefore, no credit should be taken for determining the setpoint of DVR relay.
The response time of tap changers is relatively slow. Redundant safety related equipment may be exposed to degraded voltage conditions that can last for minutes depending 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 Disagree and simultaneousshutdown of all other units at the station. For electrical system, the statement in the RIS is consistent with GDC 17, GL 79-36, RG 1.81 states: The Regulatory staff has and IEEE Standard 308-1971, "Class IE
determined that, because of the low probability of a Electrical Systems," Section 8, "Multi-Unit major reactor accident, a suitable design basis for Station Considerations.
multi-unit nuclear power plants is the assumption that an accident occurs in only one of the units at a time, with all remaining units proceeding to an orderly shutdown and a maintained cooldown condition; 10CFR50 App A Criterion 5 states: .. in the event of an accident in one unit, an orderly shutdown and cooldown of the remaining units;
NUREG 0800 Section 8.2 states: ..... in the event of an accident in one unit, with a simultaneous orderly shutdown and cooldown of the remaining units. Based on the above Regulatory positions, the RIS should consider rewording the I__I_"simultaneous shutdown" to "orderly shutdown".
52 Page 6, DVR Larry This paragraph could be interpreted to require the Setting Design Nicholson, LOCA sequence to be modeled at the DVR dropout Disagree Calculations Nexterra setting. LOCA sequencing modeled at the DVR
16
No. Section of RIS Originator Specific Comment NRC Resolution dropout setting would result in separation of the See response to questions 1 &2 buses from the Preferred Power Source (off-site power) as the voltage would not recover above the The sustained degraded voltage conditions DVR reset value, are not expected to last the total sequencing process. The analyses should demonstrate Proposed Resolution: Clarify the intent to show that the largest load (limiting case) for safety related equipment will function at the accident mitigation can be successfully selected DVR dropout setting voltage and that it is started under degraded grid conditions and not expected to start the LOCA sequence from this the loads that are normally operating will not voltage level, be adversely impacted. It is expected that the grid will either recover to nominal voltage Clarify that LOCA sequencing is evaluated using and reset the DVR for the rest of the minimum switchyard voltage as the starting point, sequencing process or the DVR will separate the plant from source that cannot support safe shutdown.
53 Page 6, DVR Larry Having a sustained degraded voltage just above Setting Design Nicholson, the LVR voltage setling (70%) is not practical Agree Calculations Nexterra without grid collapse and does not exist in Branch Technical Position #1 (PSB-1). Although undervoltage protection (first level)
is not within the scope of the RIS, the Proposed Resolution: Clarify degraded voltages to licensees' analysis should ensure that the be analyzed to a credible level. LVR and DVR settings protect the Class 1E
components from voltage ranges between the DVR and LVR settings due to sustained degraded conditions.
54 Page 6, DVR Larry The statement that the DVR ensures adequate Setting Design Nicholson, operational (starting and running) is the first time in Calculations Nexterra NRC correspondence that starting equipment at Disagree the DVR setpoint is expected. The example letter sent to Peach Bottom in June 1977 did not require The NRC 1977 letter states that "voltage and starting of equipment at the DVR setpoint. This time setpoints shall be determined from an requirement should be removed from the RIS since analysis of the voltage requirements of the it is not possible to start equipment at the DVR safety related loads". Safety related (Class setpoint and not subsequently separate from offsite 1E) equipment, particularly large motors, power. If the equipment starts at the DVR setpoint, have starting and running "voltage the voltage will dip during the transient and must requirements". This second level of then recover above the reset point to avoid undervoltage protection should address separation from offsite power. Since the reset point these "voltage requirements"
will always beabove the DVR dropout point it will be impossible to reset the relay.
Proposed Resolution: Remove starting equipment at the DVR setpoint as a requirement.
55 Page 7, DVR Larry It is agreed that no credit is to be taken for voltage Setting Design Nicholson, controlling equipment external to the Class 1 E Agree Calculations Nexterra distribution system for the establishing the degraded voltage relay (DVR) settings; however, it Grid Interface calculations can take credit for should be clarified that for credit may be taken for voltage correction equipment. The DVR
minimum switchyard voltage/voltage drop setpoint should be set independent of calculations (or the Offsite/Onsite Design Interface voltage correction equipment that cannot Calculations). operate'in a timely manner to protect 1E
equipment. RIS will be clarified regarding Proposed Resolution: Clarify that credit must be crediting voltage controlling equipment taken for automatic load tap changers and/or external to the 1E system for Offsite/Onsite capacitor for minimum switchyard voltage/voltage Design Interface.
drop calculations (or the Offsite/Onsite Design Interface Calculations).
56 Page 8, c) Larry NRC Generic Letter 79-36, Enclosure 2, Item 2 Nicholson, states that "Formulti-unit stations a separate Nexterra analysis should be performed for each unit assuming (1) an accident in the unitbeing analyzed and simultaneousshutdown of all other units at the station; or (2) an anticipated transientin the unit being analyzed (e.g., unit trip) and simultaneous
17
No. Section of RIS Originator Specific Comment NRC Resolution shutdown of all other units at that station, whichever presents the largest load situation."
Comment:
NRC Draft RIS re-states NRC GL 79-36 verbatim, Disagree with an attempt to clarify "anticipated transient"by adding in parenthesis "(anticipatedoperational Anticipated Operational Transient is a more occurrence)" immediately afterwards. It is not clear general term for operational events per the what the added parenthetical statement is meant to design except for design basis accidents convey, other than unit trip (which already exists in This is consistent with the term used in GDC
GL 79-36). 17.
Proposed Resolution: It is recommended that this either be removed, or stated "anticipated transient per station licensing basis".
57. Page 8, c) Larry NRC should clarify "simultaneous shutdown" with Nicholson, consideration to:
Nexterra Most multi-unit station's Licensing Basis consider an "orderly or controlled safe shutdown" of the other unit(s) not being analyzed.
NERC Std TPL-004-0; particularly Category D
events per Table 1, where a "loss of all generating units at a station" may result in "portionsor all of the interconnected systems may or may not achieve a new, stable operating point'.
IEEE Std 308-1974, Clause 8, subclause 8.1.1 Disagree
"Capacity" describes this as a "concurrent safe shutdown 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 licensing basis" instead of "simultaneous shutdown".
Alternatively, the wording "shutdown consistent with the station licensing basis" could be used instead of "simultaneous shutdown".
58 Page 8, e) and f) Larry These guidelines seem contradictory that you Nicholson, cannot credit procedurally controlled operator Disagree Nexterra actions to reduce load but you have to assume the actions will be carried out when load is added. Adding loads manually per procedure is conservative in terms of maximum loading, Proposed Resolution: Delete "e) Manual load but not for load reductions. Plant design shedding 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 point actions to decrease load. of item e).
But General NEI 3/18/11 The RIS should identify that plant compliance with not59 Letter / 1 the regulation (GDC 17) is by each plant operating Agree within its Licensing Basis.
Second level undervoltage protection (degraded voltage protection) applies to all operating plants whether the plant is GDC or pre-GDC plant.
60 General NEI 3/18/11 Definitions vary for the same words used with Letter / 2 respect to this topic. Agree The RIS should include definitions for key terms, Clarifications will be provided in the RIS
e.g. normal grid operation, sustained degraded wherever appropriate.
voltage, etc.
18
No. Section of RIS Originator Specific Comment NRC Resolution
61 General NEI 3/18/11 There are various documents that address the Letter 1 3 Adequacy of Station Electric Distribution System Disagree Voltages. These documents have differences in the methodology, terminology, and level of detail. Such The RIS provides adequate clarifications to differences challenge the users of these guidance the existing guidance.
documents when they conflict.
The staff positions described in the NRC
Attachment 2 to the NEI supplemental comment 1977 letteris-are guidance for all licensees letter provides a table that shows the differences as to how to meet GDC 17 or applicable between GL 79-36, (BTP) PSB-1, IEEE 741, and plant's principle design criteria. This letter the draft RIS. focuses on the need for a second level undervoltage protection scheme to protect The RIS should identify the guidance document the Class 1E electrical components from the differences, establish the NRC position on each consequences of sustained degraded conflicting topic, and provide the basis for each voltage conditions.
change in previously accepted guidance.
GL 79-36 emphasizes the electrical design attributes to be considered for the interface of onsite and offsite distribution systems to ensure adequate voltages to the Class 1E
buses and safety related components for normal, abnormal, and accident conditions to comply with GDC 17 or applicable plant's principle design criteria requirements.
BTP PSB-1 incorporates both-the above etat/-peit.ioe *and guidance to meet GDC 17 requirements.
IEEE 741 is only referenced in the SRP. The NRC 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) to clarify the NRC staff's technical position on existing regulatory requirementsand voltage studies necessary for Degraded Voltage Relay (second level undervoltageprotection) setting bases and Transmission NetworkWOffsite/Onsite station electric power system design bases."
No regulatory requirements are referenced except for 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 this clarify the NRC staffs technical position on comment.
Degraded Voltage Relay (second level undervoltage protection) setting bases and Transmission NetworkJOffsite/Onsite station electric power system design bases appropriate for meeting the regulatory requirements specified in GDC 17.'
63 Page 2, NEl 3/18/11 "The selection of voltage and time delay setpoints Paragraph a) Letter /5 shae/ be determined from an analysis of the operating voltage requirements of safety related loads at alf onsite system distribution levels"
Requirements for DVR settings have never used the term "operating voltage". They instead used Disagree in part.
"sustained voltage" which by definition would be steady state voltage, running voltage, or voltage Voltage requirements - all voltage held at a constant value requirements of SR equipment (BTP) PSB-1 and BTP 8-6 are silent on The term "operating" voltage is being operating/running voltage in the DVR settings removed from the RIS as recommended.
section; however, running is implied by using the I
19
No. Section of RIS Originator Specific Comment NRC Resolution term "sustained" in the Time Delay settings section. The term sustained voltage used in the 1977 letter and the BTPs is referring to the voltage To be consistent with (BTP) PSB-1, NRC letter, condition on the grid, not steady state and BTP 8.6 remove the word "operating". voltage
64 Page 3, Arkansas NEI 3/18/11 "...assumingall onsite sources of AC powerare not Nuclear One Letter / 6 available, the offsite power system and the onsite distributionsystem is of sufficient capacity and capabilityto automaticallystart as well as operate all required safety related loads."
This sentence implies that the NRC use of the term
"operate" does not mean the same thing as 'start'. Agree i.e., operate/start/running are not synonymous. NEI
supports this interpretation; however, it conflicts with the words "proper voltage for starting and running in all operational configurations" in the 1st The term operating voltage is being removed paragraph of page 6. from RIS.
65 Page 6, 1' NEI 3/18/11 "...components are provided adequate voltage Paragraph Letter /7 basedon the design of the Class 1E distribution system in the plant and its most limiting operating configuration."
There is a need to better define "most limiting Agree.
operating configuration", since experience shows that a component is most limiting. RIS will be revised to state the following:
Reword the RIS to: "... all safety related components are c...Componentsare provided adequate voltage providedadequate voltage based on the based on the design of the Class 1 E distribution design of the plantpower distributionsystem system in the plant.' (and the offsite circuits), including the design of the Class 1E distribution system in the plant and its most limiting operating configuration(s)."
Operating configurations affect limits as well as components.
66 Page 6, 1` NEI 3/18/11 "The Offsite/Onsite Design Interface Calculations paragraph Letter 1 8 specify the voltage operatingparametersof the plant electrical distribution system based on the transmission system (Offsite) operating parameters."
This paragraph could be interpreted to require the Disagree LOCA sequence to be modeled at the DVR dropout setting. LOCA sequencing modeled at the DVR
dropout setting would result in separation of the This sentence is not referring to calculations buses from the referred Power Source (off-site for setting the relays but referring to power) 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 show safety related equipment will function at the selected DVR dropout setting voltage and that it is not expected to start the LOCA sequence from this voltage level. The RIS should state that LOCA
sequencing is typically evaluated using minimum switchyard voltage as starting point.
67 Page 6 1. NEI 3/18/11 "This interface calculationestablishesoperating paragraph Letter /9 voltage bands for allplant electricalbuses, which ensures that all plant components and systems (Class IE and Non Safety Related) have proper voltage for startingand running in all operational configurations (expected operationaland accident conditions)."
This statement needs clarification in that not all
20
No. Section of RIS Originator Specific Comment NRC Resolution non-safety load voltages need to be evaluated. Disagree The statement that the DVR ensures adequate operational (starting and running) is the first time in See response to questions 1&2 for NRC correspondence that starting equipment at clarification.
the DVR setpoint is expected.
The 1977 NRC letter refers to SR equipment Having a sustained degraded voltage just above voltage requirements.
the LVR voltage setting (70%) is not practical without grid collapse and does not exist in Branch NSR items are being removed from this Technical Position #1 ((BTP) PSB-1). sentence in the RIS. However, non safety related loads should be modeled to the Typically, large motors (like reactor coolant pumps) extent that their operation can affect safety need to be evaluated for starting impact on the bus/equipment voltage.
safety bus. Once a motor is found to be small enough to not impact safety bus operation, further evaluation is unnecessary. The statement in the RIS can easily be interpreted as requiring evaluation of all non-safety loads down to the DVR setpoints are based on low voltages lowest levels of distribution, that can occur due to sustained grid perturbations and can potentially degrade Technical compliance with determining the capability of onsite safety related equipment.
degraded voltage relay setpoint would not be achievable because the RIS requires the DVR
dropout setpoint to be based on the starting voltage The NRC 1977 letter states that "voltage and required 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 related appears to be a new NRC requirement/position. It equipment, particularly large motors, have is 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 should loads. It also appears to disagree with the intended address these "voltage requirements".
purpose of the existing regulations (1977 NRC Sustained degraded voltage, as discussed in Letters on degraded voltage protection and (BTP) the 1977 letter, refers to grid voltage below PSB-1). the expected low value given normal grid operation and grid post contingency (Single, The letter sent to Peach Bottom in June 1977 did N-i). Thus, when grid voltages are degraded not require starting of equipment at the DVR (such as resulting in SR bus voltages down setpoint. This new requirement should be removed close to where DVRs are set based on SR
from the RIS, since it is not possible to start equipment requirements), separation from equipment at the DVR setpoint and not the grid is appropriate. The design of the subsequently separate from offsite power. If the plant electrical distribution system and equipment starts at the DVR setpoint, the voltage setting of the DVRs, based on the grid will dip during the transient and must then recover voltage range (described above) should above the reset point to avoid separation from provide proper margin such that spurious offsite power, Since the reset point will always be separation from the grid should not occur above the DVR dropout point, it will be impossible due to sequencing or block loading of loads to reset the relay. during a design basis events.
Motor starts have been discussed in several questions above. An accident signal concurrent with degraded grid conditions will require motor starts. All NRC
communications discuss the requirement for safe shutdown of the plant following postulated events.
68 Page 6, 2n NEI 3/18/11 "The staff considers degraded voltage conditions paragraph Letter / 10 coincident with a postulated design basis accident to be a credible event. DVRs should be set to protect the safety related equipment from sustained degraded voltage conditions."
GDC 17 should be identified as the regulatory requirement. This RIS is creating conditions in Disagree excess of GDC 17.
The RIS concludes that the staff considers The 1977 NRC letter staff pe Gs-ouidance degraded voltage conditions coincident with a (implementation second level undervoltage
_ _ _postulated design basis accident to be a credible protection scheme) apfy-applies to all
21
No. Section of RIS Originator Specific Comment NRC Resolution event; however, this is not consistent with GDC 17. operating plants and provides guidance on how to meet regulatory criteria..
The RIS should identify that plant compliance with the regulation (GDC 17) is by each plant operating The 1977 NRC letter indicates that the DVR
within its Licensing Basis that was developed from scheme time delays should support accident available NRC and industry guidance. analysis assumptions which ties degraded event with an accident.
Most licensees are committed to a version of IEEE
308, Standard Criteria for Class 1E Power Systems for Nuclear Power Generating Stations. This Standard defines the malfunctions, accidents, environmental events, and operating modes (i.e.,
design basis events) that could physically damage Class 1E power systems or lead to degradation of system performance and for which provisions shall be incorporated.
A degraded voltage condition coincident with a postulated design basis accident is not among the identified design basis events; however, the Standard does include a requirement for the protection from common mode failure.
69 Page 6, 2" NEI 3/18/11 "The Class 1E buses should separate from the paragraph Letter/ 11 offsite power system within a few seconds if an accident occurs coincident with a sustained degraded voltage conditions."
GDC 17 describes the requirements for onsite and Disagree offsite power systems. One of its requirements is that they each provide sufficient capacity and capability to mitigate postulated events. The events are described in Chapter 15 "Accident Analysis". The NRC 1977 letter indicates that the DVR
These analyses assume Loss of offsite Power scheme time delays should support accident simultaneous with the event. They do not require analysis assumptions which ties degraded assuming degraded grid voltage condition prior to event with an accident.
an event occurring. In addition, because of FERC
and NERC requirements for voltage control, the likelihood of a chapter 15 accident occurring concurrent with a serious degraded grid voltage condition is so low that it is believed to be not See NRC response to Comment No. 36 credible.
Remove or clarify this statement, since proper offsite system design and operation renders such simultaneous postulated events as incredible.
This position assumes (BTP) PSB-1 (BTP 8-6) is part of the license and design basis for all licensees. An equivalent position was not identified in the NRC letters issued following the Millstone event. Specifically, this requirement is more stringent than the position stated on Page 2, Item d) and may constitute a backfit to some licensees.
Care must be exercised with regards to the scope Section 2 is not about DVR schemes and of 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 plant RIS. This is confirmed in the draft RIS on Page 8, during normal, abnormal and accident Paragraph d) which states all electric system action conditions and assuming the normal occur "as designed". It would be beneficial to clarify operation of the grid (including the bounding the scope limitations associated with this or any N-1 contingency and the trip of the unit for revised position, the accident cases).
70 Page 6, 2'6 NEI 3/18/11 "... Position (BTP) PSB-l (revised later to become
1 paragraph Letter / 12 1TP-6), is to protect Class 1E safety relatedbuses
22
No. Section of RIS Originator Specific Comment NRC Resolution and components from sustained degradedvoltage conditions on the offsite power system coincident with an accident as well as during non-accident conditions."
A definition of the word "protect" is needed. It is not Disagree clear what is being protected: the components (MOV, motor, etc.) or the class 1E function or Protect means guard or defend safety something else. related components against the consequence of sustained degraded voltage The word "coincident" should read "subsequent to" conditions.
or followed by", per (BTP) PSB-1 and BTP 8-6.
Coincident is appropriate based on the 1977 NRC letter verbiage. The BTPs just provide a design which would also deal with an event when a SIAS signal would occur subsequent to the degraded voltage condition as well (not conflicting)
71 Page 6, 2nr NEI 3/18/11 'The Class 1 E buses should separate from the paragraph Letter / 13 offsite power system within a few seconds if an accident occurs coincident with a sustained degraded voltage condition."
Per (BTP) PSB-1, the text should read: Agree.
'The Class 1 E buses should separate from the offsite power system immediately if an accident RIS will be revised to incorporate the occurs subsequent to a sustained degraded comment.
voltage condition.'
72 Page 6, 2"n NEI 3118/11 "...Class 1E safety related buses should paragraph Letter 14 automaticallyseparate from the power supply within a short interval (typically less than 60
seconds)..."
There is no basis for "typically less than 60 Agree seconds". In the original context of the time delay section, it was sufficient time for an operator to RIS will be revised to delete the parenthesis intervene" 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, Disagree the degraded grid relay settings may be overly conservative; automatic separation from the 10 CFR 50.55a(h(2)) requires all protective preferred power supply may occur under conditions actions to be automatic. Operator where this action is inappropriate, intervention is probably not possible when voltage gets down to the DVR setpoint (grid The RIS should allow Transmission Operators time voltage is well below normal).
to correct the degraded voltage condition while Plant Operators monitor the safety bus voltages for Operator action takes minutes. Operation at adequate voltage, degraded voltage conditions can degrade equipment performance capabilities within seconds.
73 Page 6, 3' NEI 3/18/11 DVR Setting Design Calculations paragraph Letter / 15 This section would be a good place to describe this type of analysis as having a "bottom-up" approach. Disagree Such calculations would prevent confusion of crediting anything above the DVR voltage sensors' The approach is already described in this values, paragraph.
In the context of DVR Setting Design Calculations, using a steady state or sustained voltage analysis
23
No. Section of RIS Originator Specific Comment NRC Resolution is the only way that can result in a voltage 'setting' The term sustained voltage used in the NRC
requirement. 1977 letter and the BTPs is referring to the voltage condition on the grid, not steady state voltage
74 Page 6, 3 NEI 3/18/11 "... DVR ensures adequate operational (starting paragraph Letter / 16 and running) voltage..."
The "operational voltage" cannot define both Agree starting and running voltages.
RIS will be revised to state ". DVR ensures The only place "operational voltage" is referenced adequate voltage (start and run in the associated documents is in the tap setting conditions)..."
section of (BTP) PSB-1 and BTP 8-6 when a plant is connected to the offsite power supply. The only qualifying term used in the protection of the equipment is 'sustained' which is synonymous with steady state or running. Disagree Reword the RIS to: The term sustained voltage used in the NRC
DVR ensures adequate sustained voltage...' 1977 letter and the BTPs is referring to the voltage condition on the grid, not steady state voltage
75 Page 6, 3" NEI 3/18/11 -Licensee voltage calculations shouldprovide the paragraph Letter /17 basis for their DVR settings, ensuringsafety related equipment is supplied with adequate operating voltage (typicallya minimum of 0.9 per unit voltage at the terminals of the safety related equipment per equipment manufacturers requirements), based on bounding conditions for the most limibng safety related load (in terms of voltage) in the plant."
Equipment manufacturers do not provide the same voltage requirement to perform both running and Agreed starting a motor. The 0.9 per unit in this context refers to the typical running voltage requirement of This sentence is being reworded a motor; whereas, 0.85 per unit is typical for a starting voltage requirement.
The RIS should identify that voltages other than Starting requirements for motors have been
90% voltage are common based on detailed plant observed over a range of 0.75 to 0.85. It analysis. depends on the particular plant and how the motors were procured. Either way, the For example, motors below 90% voltage continue voltage requirements must be preserved to have plenty of margin in torque but may (starting and running). However, there could encroach on long time thermal limits. Unless a be other components that are more sensitive motor 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 an acceptable. example and was not meant to cover everything. RIS will be revised to delete references to specific numbers and emphasize voltage requirements and voltage requirements are plant-specific.
The design basis of the plant should determine the adequacy of voltage. The RIS
clarifies the regulation.
24
No. Section of RIS Originator Specific Comment NRC Resolution
76 Page 6, 3' NEI 3/18/11 "In this manner, the DVR ensures adequate paragraph Letter /18 operational(starting and running) voltage to all safety related equipment,independent of voltage controlling equipment external to the plantsafety related electricaldistribution system."
The draft RIS suggests the DVR dropout setpoint to be based on the starting voltage required for Disagree motors.
Basing the DVR dropout setpoint on starting The NRC 1977 letter states that "voltage and voltage requirements rather than steady-state time setpoints shall be determined from an operating voltage appears to be a new NRC analysis of the voltage requirements of the requirement/position. It also appears to disagree safety related loads". Safety related (Class with the intended purpose of the existing 1E) equipment, particularly large motors, requirements and guidance (1977 NRC Letters on have starting and running "voltage degraded voltage protection and (BTP) PSB-1). requirements". This second level of undervoltage protection should address As suggested, the approach incorrectly implies that these "voltage requirements". Sustained the load(s) should start from the lowest DVR degraded voltage, as discussed in the NRC
dropout setting. A specific example for illustration is 1977 letter as well, refers to grid voltage as follows: If the initial voltage value is at the lowest below the expected low value given normal possible value above dropout actuation, starting a grid operation. Thus, when grid voltages are load will cause the DVR dropout. Since the new degraded (such as resulting in Class 1E bus steady state voltage will be lower than the initial voltages down close to where DVRs are set value because of the added loads, the DVR reset based on Class 1E equipment will never occur, requirements), and the grid does not automatically recover, separation from the Many utilities use the ABB 27N with harmonic filter grid is appropriate. Proper design of the plant which has a minimum 0.5% reset. Thus, with a electrical distribution system and setting of setting of 93.6% +/- 0.9%, the dropout value could the DVRs, based on the grid voltage range be as low as 92.7%. For motors causing more than (described above) should provide proper
0.5% voltage dip at initial start, even if the voltage margin such that spurious separation from at the beginning of the event was 93.2% and a load the grid should not occur due to sequencing was started, the DVR will dropout and never reset, or block loading of loads during a design This 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 "Forthe purposes of this calculation, no credit paragraph Letter /19 should be taken for voltage controlling equipment external to the Class 1E distributionsystem such as automatic load tap changersand capacitor banks."
The intent of the position appears to ensure that Disagree the DVR setpoint(s) protect against the potential This sentence is being re-worded loss of ESF equipment, regardless of the component mode of operation. It does not imply that the Class 1E bus must remain connected to offsite power after starting a large motor with an The point being made is that calculations for initial bus voltage corresponding to the DVR the DVR voltage settings should have cases setpoint and no voltage regulation capability, at voltages just above the DVR voltage settings (well below what would be based on normal grid operations and voltage Actually, the calculation should be performed with controlling equipment if applicable) to the DVR monitored bus voltage at the TS limit, not demonstrate that the settings enforce the SR
the DVR setpoint. All that is required is that under equipment voltage requirements.
motor starting conditions, separation from offsite power occurs before starting loads trip on overload. This is covered in Offsite/Onsite Design The intent could be conveyed in more detail. Section calculations (not DVR calculations section)
The RIS should allow reasonable assumptions for The offsite source is the preferred source of the status of equipment external to the Class 1E power for plant shutdown. The DVR should distribution system. For example it is unclear how not separate the plant from the grid for motor to perform motor starting calculations without starts. In the event that grid conditions taking credit for some Non 1E voltage controlling degrade beyond an acceptable point and an equipment. Additionally, normal transmission grid accident signal is actuated, BTP PSB-1
1 switching should be allowed to prepare for the next recommends separation from the grid.
25
No. Section of RIS Originator Specific Comment NRC Resolution grid event, so that minimum expected transmission system voltages are maintained. Credit for voltage controlling equipment in the Offsite/Onsite Design Section calculations is appropriate if corrective action can be taken in a timely manner to preclude safety related equipment malfunctions.
78 Page 7, 1 NEI 3/18/11 "Voltage-time settings for DVR's should be selected paragraph Letter /20 so as to avoid spurious separation of the safety buses from the offsite power system during unit startup,normal operation and shutdown."
This position is new and contrary to the NRC Disagree historical position stated on Page 2, Item (c)(3).
Either the DVR protection scheme favors ESF- This sentence is being re-worded equipment-protection or connectivity-to-offsite- power. Otherwise, this position would result in a mutually exclusive requirement. The prevention of DVR setting always enforce SR equipment spurious separation is addressed by coincident voltage requirements. Offsite/Onsite Design logic channels (Page 2, Item (b)), not the setpoint. should ensure that there is proper margin between where voltage is in the plant during If no credit is to be taken for voltage controlling normal grid operation as compared to equipment external to the Class 1iE distribution voltages in the plant when the DVRs actuate.
system for the establishing the degraded voltage relay (DVR) settings, then the RIS should state that credit may be taken for minimum switchyard Credit for voltage controlling equipment in voltage/voltage drop calculations (Offsite/Onsite the Offsite/Onsite Design Section Design Interface Calculations). calculations is appropriate. However, it is not appropriate to use it for DVR calculations since DVR setpoint is derived from the minimum voltage required at the component terminal at all voltage levels. (Also see response to question #77)
79 Page 7, 1 NEI 3/18/11 "These DVRs should disconnect the Class 1E
paragraph Letter / 21 buses from any power source other than the emergency diesel generators (onsite sources) if the degraded voltage condition exists for a time interval that could prevent the Class 1E safety related loads from achieving their safety function."
This position ensures ESF functionality, should an Disagree undervoltage 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 support voltage regulating devices within the nuclear power corrective action to restore voltage to normal plant offsite power circuit boundary. The RIS operating band.
should clarify that if the calculations necessary to support RIS positions in Section 1, "Degraded Voltage Relaying Design Calculations" and Section Since offsite power is the preferred source of
2, "Offsite/Onsite Design Interface Calculations" power to mitigate design basis event, it is demonstrate completion of ESF functions within important that the Offsite/Onsite Design accident analysis assumptions, then immediate Interface calculations ensure the capacity separation per (BTP) PSB-1, Section B(1)(b)(i), is and capability of the offsite power is no longer the preferred NRC position, adequate to sequence or block load during design 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 from actuation signal (SIAS) [after an undervoltage the grid is only appropriate when the DVR
condition longer than a motor starting transient] relays actuate indicating that SR equipment should immediately separate the Class 1E voltage requirements are not being met (not distribution system from the offsite power system." able to protect or provide adequate voltage to the terminals of the SR limiting The RIS should state that this (BTP) PSB-1 components at the plant).
position is not included in the draft RIS because it provides no added protection in terms of Analyses to determine such setpoints always establishing the DVR setpoint(s) or in establishing should have included modeling the plant operability of the offsite power interface. To the power distribution system such that proper contrary, this (BTP) PSB-1 increases the voltages throughout the plant system can be probability of separation from offsite power. calculated in all operating and accident
26
No. Section of RIS Originator Specific Comment NRC Resolution conditions.
80 Page 7, NEI 3/18/11 "Guidelinesfor voltage drop calculations paragraph 2 a) Letter /22 a) The plant voltage analysis,while supplied from the transmission network, should be based on the operating voltage range of the transmission network connection."
It is recommended that the first sentence of Disagree Paragraph 2(a) be deleted. It is covered by Paragraph 2(b), as the switchyard is the "power Enclosure 2 of GL 79-36 provides guidelines source" for the offsite power circuits. for voltage drop calculations.
Paragraph 2(a) addresses both plant and transmission operator analyses. The purpose is to identify that the switchyard voltage results from the transmission operator analysis should be used as an input to the power plant analysis. From the nuclear power plant point of view, the determination as to whether each offsite power Accident cases consider the unit trip grid circuit is individually capable of performing its contingency since a trip is assumed to occur design function is based on a postulated post-trip coincident with an accident. However, if the switchyard voltage for the present grid unit trip is not the most limiting grid configuration and operating level (i.e. RIS contingency (not the largest grid voltage Paragraph 2(b)). drop), the cases which assess normal and abnormal operation (non-accident) need to As written, it is conceivable that a reader of this assume the bounding grid contingency paragraph could conclude that the transmission (normal grid operating range)
"contingency analysis" is a factor in the nuclear plant analysis regarding "when" the contingency is postulated to occur relative to the postulated plant event. The alteration of the present basis to include concurrent grid/plant events is a change in position and would be subject to backfit consideration.
81 Page 8, NEI 3/18111 "Formulti-unit stations, a separate analysis should paragraph 2 c) Letter 123 be performed for each unit assuming (1) an accident in the unit being analyzed and simultaneousshutdown of all other units at the station; or (2) an anticipatedtransient (anticipated operationaloccurrence)in the unit being analyzed (e.g., unit trip) and simultaneous shutdown of all other units at that station, whichever presents the largestload situation.
The RIS wording should be revised to indicate Disagree
"orderly or controlled safe shutdown of the remaining units, as per the station's licensing basis" Wording is the same as provided in GL 79- instead of "simultaneous shutdown". Alternatively, 36 the wording 'shutdown consistent with the station licensing 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 D
events per Table 1, where a "loss of all generating units at a station" may result in "portions or all of the interconnected systems may or may not achieve a new, stable operating point".
IEEE Std 308-1974, Clause 8, sub-clause 8.1.1
"Capacity" describes this as a "concurrent safe shutdown on the remaining units".
27
No. Section of RIS Originator Specific Comment NRC Resolution This RIS re-states part of GL 79-36, with an attempt to clarify "anticipated transient" by adding in parenthesis "(anticipated operational occurrence)". It is not clear what the added parenthetical statement is meant to convey, other than unit trip (which already exists in GL 79-36).
The RIS should remove this parenthetical addition or state '...an anticipated transient per station licensing basis...'
82 Page 8, NEI 3/18/11 "All actions the electrc power system is designed paragraph 2 d) Letter / 24 to automaticallyinitiate should be assumed to occur 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 may not have been consistently applied during recent CDBI's.
83 Page 8, NEI 3/18/11 "a) Manual load shedding should not be assumed.
paragraph 2 e) & Letter / 25 f) f Foreach event analyzed, the maximum load necessitatedby the event and the mode of operationof the unit at the time of the event should be assumed in addition to all loads causedby expected automatic actions and manual actions permitted by administrativeprocedures."
These guidelines seem contradictory in that e) Disagree states that there may be no credit for procedurally controlled 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 is should 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 for decrease load. maximum load should not depend on manual load shedding (not conservative). That was the point of item e).
84 Page 8, NEI 3/18/11 Omission paragraph 2 f) Letter /26 Disagree After paragraph 2 f), the RIS leaves out the guidance 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 load should be calculated based on the above listed consideration and assumptions and based on the assumption that the grid voltage is at the "minimum expected value". The "minimum expected value"
should be selected based on the least of the following:
a. The minimum steady-state voltage experience at the connection to the offsite circuit.
b. The minimum voltage expected at the connection to the offsite circuit due to contingency plans which may result in reduced voltage from this grid.
c. The minimum predicted voltage from grid stability analysis. (e.g., load flow
28
No. Section of RIS Originator Specific Comment NRC Resolution studies)."
85 Page 8, NEI 3/18/11 "To provide assurance that actions taken to assure paragraph 2 j) Letter /27 adequate voltage levels for safety relatedloads do not result in excessive voltages, assuming the maximum expected value of voltage at the connection to the offsite circuit,a determination should be made of the maximum voltage expected at the terminalsof all safety relatedactual equipment and their starting circuits (if applicable).
If this voltage exceeds the maximum voltage rating of any safety related equipment, immediate remedial action should be taken."
The RIS should remove the word "immediate" Disagree describing remedial action. Immediate remedial action could imply control room intervention. The control room has alarm procedures to address high voltage should it occur. Timeliness of remedial The Offsite/Onsite design should address all actions depends on how high actual voltage grid operating conditions to prevent reaches 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 is are 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 taken compensating activities might be required for light (compensatory and/or permanent design load operations (refueling). changes) to address the design problem rather than taking actions after it occurs.
The RIS should provide examples of typical responses to high grid voltages. For example: in It is not the intent of the RIS to highlight those cases where unit trip can result in a step reasons for voltage perturbations.
increase in grid voltage (most common on higher voltage connections like 765kv), anticipated excursions above desired voltages should be addressed by compensating measures (changing excitation for nearby units, switching in reactor banks, etc.).
86 General NEI 3/2/11 Page 2, Paragraph 1 Letter While NEI supports efforts to obtain greater clarity Disagree with respect to the staffs technical position in this important area, the draft RIS greatly oversimplifies NRC Staffs position is that the RIS is the regulatory and licensing aspects of the intended to clarify the requirements and degraded grid voltage protection issue. As a result associated existing staff pesitions-gidan of this oversimplification, the draft RIS which would apply to all plants.
inappropriately combines several generic communications and guidance documents that Any inspection findings that questions the affected the licensing bases of individual plants in plant-specific licensing bases will be different ways, and fails to adequately address the reviewed by the NRR staff in accordance significant backfitting concerns that arise when NRC's TIA process.
attempting to eliminate licensing basis variability via a RIS (or any other guidance document).
87 General NEI 3/2/11 Page 2, Paragraph 2 Letter Unless it is revised, the draft RIS will unnecessarily Disagree increase the potential for loss of the preferred off- site power source and, consequently, increase Proper design of the plant electrical reliance on emergency diesel generators. NEI distribution system, given the operating believes that the use of emergency diesel range of the grid and the proper selection of generators more frequently than necessary is DVR settings (based on the voltage inconsistent with GDC 17 and results in an requirements of the 1E equipment), should unnecessary loss of defense-in-depth, provide more than adequate operating margin, preventing unnecessary separation from offsite power.
88 General NEI 3/2/11 Page 2, Paragraph 3, Comment I
Letter The Draft RIS Fails to Adequately Consider Agreein osrt.
Licensing Basis Variability in the Area of Degraded Grid Voltage Protection As a general matter, NRC staff positions are The only generic obligation or legally binding "ouidance," as are, among other things,
29
No. Section of RIS Originator Specific Comment NRC Resolution requirement mentioned in the Discussion section of regulatory guides and Interim Staff Guidance the draft RIS is GDC 17. (ISG). As guidance, NRC staff Positions, like reaulatory auides, are not legally binding unless the NRC legally imposes them on a licensee or the licensee binds itself to complying with them in a document subiect to NRC-mandated controls, In other words, for any particular nuclear oower plant.
guidance may be Part of the licensina basis for that plant because of past NRC or licensee actions, For instance, guidance may be legally imposed upon a vlant by virtue of the issuance of an order or through a license condition that imposes the guidance on that particular plant. As another example, a licensee may have committed to compliance with the guidance in the plant's final safety analysis report IFSAR) or other document subiect to NRC controls (e.ag. the description of the olant's auality assurance Program, an emergency Plant. or a security plan)t The NRC resolutions for all the Public comments received on this RIS should be understood 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 of Degraded Grid Voltage Protection The 77 Letter is asttaff 99itin-whhapplies Although these letters resulted in changes to the to-aWopating rna~t~rc at that time a:d licensing bases of the nuclear power plants that pla*t* licensed 6 ize, zro4w-G9n-*erply-wilth received them, they do not function the same way the...... m t. in 10 CFFI Par-f n , .Ge.eral as generally applicable regulatory requirements. r Des ' Criteria 17 (GDC- 7*.The 1977 letter That is, these generic communications were only as well as other staff guidance. were made received by plants that were licensed at the time available or sent to all operating plants at the communications were issued. Operating that time. In addition, the NRC's regulatory licenses for the current fleet were issued during a practice-which has been understood by the period that ranged from the late 1960s through the industry-is that staff guidance represents the
1990s. Thus, not all operating plants received and staff position until subsequently modified or responded to the generic communications issued in withdrawn. While the staff recognizes that
1977 and 1979. there is variability among plants' licensing bases with respect to degraded voltage protection, the NRC believes (with one exception identified elsewhwere) that the overall licensing basis provisions with respect to degraded voltage protection are consistent with the staffs position.
90 General NEI 3/2/11 Page 3, Paragraph 2, Comment I (Cont.)
Letter The Draft RIS Fails to Adequately Consider Licensing Basis Variability in the Area of Disagree.
Degraded Grid Voltage Protection Further, the Branch Technical Position (BTP) The 1977 Letter is a-ffp described 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 to Voltages"--was issued in 1981. BTP PSB-1 and the comply with the requirements in 10 CFR
Standard 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 review of applications to construct and operate nuclear power plants.... Standard review plans are not substitutes for regulatory guides or the Commission's regulations and compliance with them is not required." Thus, BTP PSB-1 would have been directly relevant to plants licensed after its issuance, but not before. Further, the specific details in the information provided in the 1977 letters, Generic Letter 79-36, and BTP PSB-I are not identical. I
30
No. Section of RIS Originator Specific Comment NRC Resolution
91 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 of Degraded Grid Voltage Protection NRC Staff asserts that coincident degraded For example, the draft RIS makes several grid and accident is specified in the 77 Letter recommendations that may be inconsistent with the and the BTP approach supports that approved licensing bases for operating plants, position.
including:
The draft RIS proposes "Degraded See also staff response to Comment No. 36.
voltage conditions coincident with a postulated design basis accident." BTP
PSB-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 of Degraded Grid Voltage Protection The staff position is consistent with 1977 The draft RIS proposes "DVR Dropout setting letter and BTP PSB-1.
based on starting and running voltage." BTP PSB-1 says "sustained," implying a steady state voltage condition and not a transient voltage condition that I 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 Disagree Licensing Basis Variability in the Area of Degraded 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 the station."
GDC 5 says:
in the event of an accident in one unit, an orderly shutdown and cooldown of the remaining units."
94 General NEI 3/2/11 Page 4, Third Bullet, Comment I (Cont.)
Letter The Draft RIS Fails to Adequately Consider Licensing Basis Variability in the Area of Disagree Degraded Grid Voltage Protection The draft RIS proposes "During normal plant operation, the Class 1E safety related buses should automatically separate from the power supply within a short interval (typically less than 60
seconds) if sustained degraded voltage conditions are detected." BTP PSB-1 clause B.1 .b.2 included provisions for operator manual actions to restore bus 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 limited duration such that the permanently connected Class'lE loads will not be damaged. Following this delay, if the operator has failed to restore adequate voltages, the Class 1 E distribution system should be automatically separated from the offsite power system. Bases and justification must be provided in support of the actual delay chosen."
Manual actions for the purposes of reducing The draft RIS specifically excludes manual load load for the design of the plant electrical shedding 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 part manual actions to avoid separation from offsite of normal operation when there is sufficient power. time to do so to support adequate voltage.
See GL 79-36 for more details.
The sixty second time delay would not allow operator actions. This appears to be a new NRC
position.
31
No. Section of RIS Originator Specific Comment NRC Resolution
95 General NEI 3/2/11 Page 5, Paragraph 2, Comment I (Cont.)
Letter The Draft RIS Fails to Adequately Consider Disagree Licensing Basis Variability in the Area of Degraded Grid Voltage Protection The 77 Letter indicates that the DVR circuits In addition to the specific examples provided should be designed assuming coincident above, the draft RIS states "[tlhe staff considers sustained degraded grid voltage and degraded voltage conditions coincident with a accident events. Upon the onset of the postulated 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 should with this statement, allow for separation of the 1 E buses from the offsite circuit(s) and connection to the 1E
onsite supplies in time to support safety system functions to mitigate the accident in accordance with the FSAR accident analyses.
96 General NEI 3/2/11 Page 6-7, Comment i1 Letter The
Backfit Discussion
Provided in the Draft RIS is Inadequate Given the complex regulatory and licensing history Disagree associated with providing degraded grid voltage protection, the backfitting discussion included in the draft RIS is inadequate. Despite the fact that facility-specific backfits were required as a result of several recent inspection findings on degraded voltage protection,1 8 the entire backfitting discussion included in the draft RIS consists of three sentences. Of those three sentences, only one provides any analysis:
Specifically, NRC Staff technical positions outlined in this draft RIS are The-etiails of the inzpeGzt9A findings azd consistent with the aforementioned eforcement atins ;Ie diUs,*ed in dztAil regulations [GDC 17] and generic ip the appli....I, .I i...... s sad T-As communications [1977 letter, Generic if appl c*ble refereced in the ,RIS
Letter 79-36, BTP PSB-1], while providing more detailed discussion concerning the necessary voltage calculations supporting DVR settings based only on voltage requirements of Class 1 E components and the Class 1E NRC sta# a.. rtg that Ithe egulatigns and distribution system design.19 staff P0 tionA arti.nz'"azd Athe ROi ars This analysis misses the point. First, GDC 17 (like guidance dzzument* and ."erzefte-de-ne4 most GDC) is cast in broad, general terms: .Z.,tit-tz ne',z OFdiffzRat p.. itizric with therefore, the fact that the specific positions the baekfitu*
F l (50.*10*1)
discussed in the draft RIS are "consistent with" the See the supplemental response attached at design criteria does not necessarily mean that they the end of this Comment/Response Table.
escape the definition of a backfit. Specifically, there are any number of staff positions that are
"consistent with" a broad design principle, but the relevant inquiry when examining the backfit definition is whether the staff position being articulated is new or different from a previously applicable staff position. The draft RIS does not address this issue. Further, as discussed above, the generic communications and guidance discussed in the draft RIS are not completely consistent with one another and were not equally relevant in developing the licensing bases for all reactor licensees. Given the variability in the protection schemes approved by the NRC, merely concluding that the positions provided in the draft RIS are "consistent with" one or more of these documents, does not address the obvious fact that
"providing more detailed discussion" on how to demonstrate compliance with GDC 17 could I
32
No. Section of RIS Originator Specific Comment NRC Resolution constitute a staff position that is new or different from a previously approved protection scheme.
97 General PPL Page 1-2, First Bullet Disagree Contrary to the stated intent, PPL believes that the RIS does transmit new requirements and staff The NRC 1977 letter states that "voltage and positions. Specific comments applicable to time setpoints shall be determined from an Susquehanna Steam Electric Station (SSES) are analysis of the voltage requirements of the as follows: safety related loads". Safety related equipment, particularly large motors, have The RIS introduces the need to consider starting and running "voltage requirements".
both "starting and running" conditions This second level of protection should during all operating configurations while address these "voltage requirements".
maintaining the offsite power supply Sustained degraded voltage, as discussed in connected to the plant electrical the 1977 letter, refers to grid voltage below distribution system. The establishment of the expected low value given normal grid a degraded voltage relay (DVR) to detect operation and grid post contingency. Thus, a "sustained" degraded voltage condition when grid voltages are degraded (such as challenges 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 equipment setpoint must accommodate both starting requirements), separation from the grid is and 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 (described and excludes starting voltage above) should provide proper margin such consideration that spurious separation from the grid should not occur due to sequencing or block loading of loads during a design basis events.
98 Page 6, Section 1 PPL Page 2, Paragraph 2 Disagree RIS 201 1-XX, Page 6, Section 1. "Degraded Voltage Relaying Design Calculations" contains the NRC Staff asserts that this statement means statement "staff considers degraded voltage that while the events are coincident (which is condition coincident with a postulated design basis important from the standpoint that the time accident to be a credible event." This statement delay chosen for the DVR must support the implies a requirement to demonstrate capability of accident analysis), it does not mean that connected loads to start and run at the degraded connected loads must start and run at the voltage relay dropout setting. For Susquehanna, dropout setting. The dropout setting should sequencing of loads from the offsite power source be developed based on the voltage cannot be demonstrated at the relay dropout requirements (starting and running) and setpoint because operation at this voltage level therefore to develop values which are would result in separation from the offsite bounding, the studies should be done under transmission system. Furthermore, the statement worst starting and loading conditions, which on page 6 of the RIS is not in agreement with other means the required voltage at the 1E bus regulatory 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 is Loss of Offsite Power (LOOP) subsequent to a that the setpoint should equate to the limiting Loss of Coolant Accident (LOCA)," which voltage at the limiting component during the concluded a degraded voltage condition coincident bounding starting or running scenario to with a postulated design basis accident is not a protect the 1E equipment.
credible event.
99 Page 6, Section 1 PPL Page 2, Paragraph 3 Additional clarification is necessary if starting Disagree.
transients must be included when determining the Proper design of the plant electrical degraded voltage relay (DVR) dropout setpoint. distribution system, given the operating This condition will increase the probability of range of the grid and the proper selection of separating from the offsite transmission system DVR settings (based on the voltage and increase the likelihood of a double sequencing requirements of the 1 E equipment), should event, which is a potential nuclear safety concern, provide more than adequate operating margin, preventing unnecessary separation from offsite power.
100 Page 8, Section c) PPL Page 2, Paragraph 3 The RIS requires performance of analyses for an Disagree.
accident in the unit being analyzed and simultaneous shutdown of all other units at the This statement in the RIS is consistent with station. This is not consistent with the present GDC 17, GL 79-36, and IEEE Standard Susquehanna 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. The safe shutdown of the non-accident unit is
33
No. Section of RIS Originator Specific Comment NRC Resolution considered a controlled shutdown, which follows automatic operation of the safety related loads on the accident unit. This accident response is also consistent with the NERC requirements for the design of the transmission system. The RIS should be revised to be in agreement with the current NERC requirementsr
101 General PPL Page 2-3, First Bullet The draft RIS attempts to clarify the requirements Disagree.
for setting the DVRs based on the criteria established in the following three main documents: The 1977 Letter is a staff potifit*od.
which applies to all operating reactors at that
1) NRC letters to licensees dated June 2 & 3, 1977, time and plants licensed since, on how to
2) Branch Technical Position (BTP), PSB-1 comply with the requirements in 10 CFR
Revision 0, Part 50, General Design Criteria 17 (GDC
3) Generic Letter 79-36, "Adequacy of Station 17). In addition, NRC's staff position is that Electric 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 not consistent with all the requirements listed in these three documents and a new interpretation is provided in some cases.
It should be generally recognized that a nuclear plant operating license may not have been issued based on the above documents. For example, the
1977 letters discussed above are not applicable to SSES.
102 General PPL Page 3, First Bullet The lack of regulatory clarity in the RIS could result Disagree.
in revising the degraded voltage setpoint for a plant's DVR thus increasing the possibility of Proper design of the plant electrical premature separation from the offsite circuit (i.e., distribution system, given the operating undervoltage relay actuation). This relay operation range of the grid and the proper selection of could lead to an increase in the likelihood of a DVR settings (based on the voltage double sequencing event, which has the potential requirements of the 1E equipment), should to create a nuclear safety concern, provide more than adequate operating margin, preventing unnecessary separation from offsite power.
103 General PPL Page 3, Second Bullet The RIS introduces the need for two sets of Disagree.
calculations, one to establish the DVR relay setpoint and one for the interface with the offsite The RIS is primarily identifying that different transmission system. The RIS should not specify types of calculations are necessary to the number of calculations that are necessary for a address different requirements. DVR setting plant to meet a regulatory requirement, calculations consider the voltage of the 1E
equipment while the plant design is more about the operating range of the grid and the resulting voltages in the plant system (which should be well above the DVR voltages)
104 General PPL Page 3, Third Bullet The condition the DVR is required to "protect" Disagree.
needs to be specifically defined along with the applicable relay setting. (i.e., relay minimum The DVR's function is specified in that it dropout, maximum dropout, or reset). If the DVR is ensures that 1E equipment is supplied with installed to provide a level of protection then the adequate voltage in accordance with its analysis must demonstrate that the safety related design requirements.
equipment is capable of performing its required safety function. An example of this would be the case where the DVR analysis would need to demonstrate acceptable operation at both the starting and running equipment ratings when at the DVR dropout setting.
105 General PPL Page 3, Fourth Bullet A clarification of the term "sustained" is needed to Disagree.
determine if "sustained" refers to a steady state voltage condition (i.e., no equipment starting Sustained degraded voltage, as discussed in voltage effects) for which the DVR setting is to be the NRC 1977 letter as well, refers to grid established. voltage below the expected low value given
34
No. Section of RIS Originator Specific Comment NRC Resolution normal grid operation.
106 General PPL Page 3, Fifth Bullet The guidance in the RIS is too general when Disagree.
referring to operating voltages. The specific voltage requirements need to be specified instead of The term voltage requirements used in the implied by a general term. The RIS needs to clarify RIS is defined in terms of equipment that the impact of the nuclear unit trip on the manufacturer design requirements. NRC
transmission system voltage must be considered in Staff feels that this terminology is sufficiently the plants voltage analysis. specific. Additional wording has been added to the RIS to clarify that unit trip voltage impact should be factored into the accident analysis cases.
107 General PPL Page 3, Sixth Bullet The time delays suggested are not consistent with Disagree.
PSB-I. The PSB established one time delay to allow for operator action. The RIS does not While there may be differences, the BTPs address this requirement, are guidance documents and represent an approach but not necessarily the only approach. In addition, following the guidance documents approach will satisfy the GDC 17 requirements.
108 General PPL Page 4, First Bullet The RIS also lacks any acknowledgement of Disagree.
preventative measures the licensees have taken to minimize the potential for a degraded voltage Regardless of improvements made in terms condition. Advancements in plant loadflow of grid operation and understanding of grid analyses and measures to increase the reliability of operation's impact on plant voltages, the the offsite transmission system are industry plant design has always had to properly improvements that have occurred since the address grid operating parameters and their degraded voltage events that occurred 35 years impact on plant voltages in all modes of ago. operation. This point was properly emphasized in the RIS as was in the original regulations 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 been applied universally to the industry. Over the years The 77 Letter provides staff positions on the the degraded voltage performance requirements design criteria in that the voltage have changed, as a specific issue, and on a requirements for the 1 E equipment has to be component basis (e.g., motor operated valves and ensured by the DVR circuits by automatic contactors), for individual nuclear power plants. As separation from offsite and transfer to the a result, each nuclear power plant has specific onsite sources.
licensing bases, and there is no singular set of requirements that have been applied universally to the industry.
110 General APS Page 2, 2.
The draft RIS asserts that the guidance provided to Disagree.
the industry to address the Millstone and other degraded voltage events adequately addresses The DVR circuits will automatically separate this potential common mode failure. The common the 1 E circuits from offsite power when mode failure potential is that multiple trains of voltage requirements are not met which will safety equipment could be simultaneously prevent the Millstone type event negatively impacted if off-site power is degraded. automatically.
The deterministic guidance provided does not appear to effectively address integrated plant response nor preclude a Millstone type event. The use of degraded voltage relays to address this potential failure mode is not consistent with operating experience and lacks adequate technical basis as described in the detailed technical comments 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 that coincident with a postulated design basis accident setting of the DVR should include to be a credible event." consideration of a coincident accident signal in that the time delay chosen for the DVR
35
No. Section of RIS Originator Specific Comment NRC Resolution It is our understanding that the established staff should support the accident analysis interpretation is that this is not a credible event, as assumptions consistent with the NRC1977 discussed 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 LOCA
With Delayed Loop and Loop With Delayed LOCA
Accident Scenarios, Technical Findings Related to GSI-1 71, 'ESF Failurefrom LOOP Subsequent to LOCA' published July 1997. This appears to be a new staff interpretation and no documented analysis is provided to support it. Therefore, if the scenario is credible, as the draft RIS asserts, then GSI-171 is not adequately resolved and should be reevaluated.
112 General APS Page 5, 4. Disagree The recent licensing actions in the industry which have mandated setpoint changes for the degraded Setting the DVRs in accordance with the voltage 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 plant only serve to increase the probability of the 'ESF electrical distribution system (and based on Failure from LOOP Subsequent to a LOCA' event the grid's allowable voltage range) must discussed in NUREG/CR-6538 without providing provide adequate voltage margin to preclude an advantage for any credible scenario. As such, offsite separation.
these changes may increase core damage frequency (CDF).
Disagree It is APS's understanding that a comprehensive review of guidance related to degraded grid voltage NRC staff asserts that the regulations and has not been performed using the cost-benefit and positio 3uidance articulated in the RIS are risk criteria of 10 CFR 50.109 (backflit rule), nor is it consistent with the existing regulatory apparent that risk insights have been used to requirements and NRC staff pee*ietn inform this guidance. guidance therefore do not constitute new or different positions with respect to the backfit rule (50.109).
113 General APS Page 5, 5.
The draft RIS does not address the implication of Disagree.
the Branch Technical Position (BTP) PSB-1 requirement that "The Class 1 E bus load shedding The design of the plant electrical distribution scheme should automatically prevent shedding- system and the onsite sources should during sequencing of the emergency loads to the provide for adequate voltage to all 1 E
bus." A large variety of voltage conditions could equipment in all normal, abnormal and exist during the sequencing period while the accident conditions.
shedding is blocked, and no analytical methods are discussed that could demonstrate that equipment Typical designs do not block the DVR or the damage or malfunction would not occur. LOV relay when sequencing loads on the offsite source. Hence load shedding in the event of a loss of offsite power should be part of the design basis. A large variation of voltage conditions can occur during various operating modes of a nuclear plant. The DVR setpoint should be based on limiting conditions. If the recommendations of BTP
PSB-1 are followed, the probability of events such 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 be accident conditions should meet the accident postulated to occur at anytime. The DVR
analysis assumptions..." does not seem setpoint should accommodate the limiting appropriate. The degraded voltage condition could case for equipment protection. If the occur at various times during the initial energization recommendations of BTP PSB-1 are of the accident mitigation equipment, and the relay followed, then a separation from the I time delay value only affects the additional time degraded grid coupled with accident signal is
36
No. Section of RIS Originator Specific Comment NRC Resolution until the subsequent LOOP occurs, the preferred approach to resolve the issue and satisfy accident analyses.
115 Page 8 APS Page 7-8. 7.
It is not feasible for multi-unit nuclear plants to Disagree successfully demonstrate that voltage from the offsite circuits would be adequate, as described in the 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 the station; or (2) an anticipated transient (anticipated operation occurrence) in the unit being analyzed (e.g.. unit trip) and simultaneous shutdown of all other units at that station." TPL-004 requires transmission planning to address simultaneous multiple transmission North American Electric Reliability Corporation contingencies.
(NERC) Standard TPL-004 recognizes that the design and operating constraints of the The requirements of TPL-004 are not within transmission network are such that the loss of all the scope of RIS.
generating units at a station could result in portions or all of the interconnected system not achieving a new, stable operating point.
It is beyond the nuclear plant operator's authority or capability to ensure otherwise.
116 Page 6 APS Page 8, 8.
The draft RIS (page 6 of 10) contains the following statement:
"The Class I E buses should separate from the offsite power system within a few seconds if an accident occurs coincident with sustained degraded voltage conditions."
This statement appears to reflect the position of Revision 3 of BTP 8-6, which states, in part:
"The first time delay should be long enough to establish the existence of a sustained degraded voltage condition (i.e., something longer than a motor- starting transient). Following this delay, an alarm in the control room should alert the operator to the degraded condition.
The subsequent occurrence of a safety injection actuation signal (SIAS) should immediately separate the Class 1 E
distribution system from the offsite power system. In addition, the degraded voltage relay logic should appropriately function during the occurrence of an SIAS
followed by a degraded voltage condition." Disagree.
This is not currently a design or licensing requirement for all existing plants. As such the RIS As a result of these Millstone events, the process would not be the appropriate method to NRC requested that all licensees implement communicate a new regulatory position. degraded protection as described in the
1977 Letter to ensure automatic protection of safety buses and loads. This Letter provides staff post3nguidance, which applies to all operating reactors at that time and plants licensed since, on how to comply with the requirements in 10 CFR Part 50, General I Design Criteria 17 (GDC 17).
37
No. Section of RIS Originator Specific Comment NRC Resolution
117 Page 6 APS Page 8-9, 9.
The draft RIS (page 6 of 10) contains the following statement:
'The time delay chosen should be optimized to ensure that permanently connected Class I E
loads are not damaged under sustained degraded voltage conditions (such as sustained degraded voltage just above the LVR voltage setting for the duration of the DVR time delay setting)."
This deterministic approach, while appearing Disagree conservative, has the net effect of increasing the frequency of delayed LOOP events during The voltage studies done for evaluating transients, even when the subsequent sustained offsite power/onsite power interface should voltage condition is not degraded (see Comment use minimum expected voltage at the
4), with resulting adverse effects as discussed in plant/grid interface node, demonstrating the resolution of GSI-171. It also neglects adequate voltage for starting and running of consideration of the voltage levels that must be plant components during normal, abnormal maintained in the event of a unit trip and coincident and accident conditions. The voltage studies accident to prevent delayed LOOP events. Finally, for the DVR setpoints should require the draft RIS is silent on the particulars of the plant/grid interface node voltages well below voltage studies that would be acceptable to use to the minimum expected values (including post determine 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 at terminals or contacts of all safety related equipment with the voltage of the DVR monitored bus at the DVR dropout setting, providing the necessary design basis for the DVR voltage settings. In this manner, the DVR ensures adequate operational (starting and running) voltage to all safety related equipment, independent of voltage controlling equipment external to the plant safety related electrical distribution system."
This seems to impose a new requirement. Further, Disagree the described model is of a nondegraded voltage scenario that does not result in DVR actuation. The DVR dropout setting should be Therefore, it does not demonstrate that "required developed based on the voltage safety related components are provided adequate requirements (starting and running) and voltage" for accidents with degraded voltage therefore to develop values which are scenarios. That conclusion could only be bounding, the studies should be done under demonstrated by modeling degraded voltage worst starting and loading conditions which scenarios that involve DVR actuation. However, in means the required voltage at the 1E bus all cases involving degraded voltage coincident prior to the start or run case would have to with postulated accidents, such models would be higher than the setpoint. The main point is result in delayed LOOP scenarios as discussed in that the setpoint should equate to the limiting GSI-171. voltage at the limiting component during the bounding starting or running scenario to Also, it reflects a non-conservative voltage profile. protect the 1 E equipment.
If the voltage at the DVR monitored bus was at the DVR dropout setting prior to starting a motor, it The RIS does not impose any new would be lower than that during and after starting requirements. It provides clarification on the motor, and the voltage at the motor terminals existing requirements.
would be correspondingly lower, as well, compared to the results using the constant bus voltage The DVR setpoint should be optimized for methodology described in the draft RIS. motor starting transient and protection of I safety related equipment.
119 Page 5 APS Page 10, 11.
The draft RIS discussion asserts that the NRC Disagree Office of Nuclear Reactor Regulation (NRR) Task
38
No. Section of RIS Originator Specific Comment NRC Resolution Interface 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 include degraded offsite source to the standby power consideration of a coincident degraded grid source to support the emergency core cooling and accident in that the time delay chosen equipment operation must be consistent with for the DVR should support the accident accident analysis time assumptions, as required by analysis assumptions consistent with the BTP 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 UFSAR
description for the design requirements of the degraded voltage relays, and this specific time delay provision is not included in the PVNGS
This specific time delay provision was removed as part of the PVNGS license amendment 123 Task Interface Agreement 2010-005 process and was specifically addressed in the NRC (ADAMS Accession No. ML102800340)
and APS correspondence (NRC Letter dated June provides more details regarding Palo Verde
14, 1999, and APS letter dated July 16, 1999, degraded voltage inspection finding.
Question 13). The subject matter of the TIA did not include the time delay element of the design, with Plant specific findings are not in the scope of regard to the accident analysis time assumptions, the RIS.
but rather was focused upon whether license amendment 123 bounded the need to perform design basis electrical calculations for the degraded voltage relay low setpoint value of 3697 volts or below.
120 Page 5 APS Page 10-11, 12.
The draft RIS asserts that PVNGS erroneously maintains that a degraded voltage condition concurrent with a design basis accident is not credible. PVNGS had originally implemented the design approach included in the NRC letter Qualification Review of the PVNGS Units 1,2 and
3, dated December 12, 1977. Based on operating experience (LER 50-528/529/530-93-01 1)-and site specific license amendment 123, PVNGS took action to preclude such an event, by implementing new TS LCO 3.8.1, Condition G. This approach was 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 that preclude a concurrent degraded voltage condition setting of the DVR should include and design basis accident because the PSB-1 type consideration of a coincident degraded grid design is not capable of adequately coping with and accident in that the time delay chosen such an event. All such events would result in for the DVR should support the accident delayed LOOP/double sequencing scenarios, as analysis assumptions consistent with the described in GSI-171, for which there is no viable NRC1977 letter.
analytical approach.
The licensee should ensure that SI actuation at a point just above the DVR set point should not cause double sequencing.
See staff response to Task Interface Agreement 2010-005 (ADAMS Accession No. ML102800340) for more details regarding Palo Verde degraded voltage inspection finding.
121 Page 5 APS Page 11,13.
PVNGS originally implemented the second level degraded voltage protection design consistent with NRC letter Qualification Review of the PVNGS Disagree
39
No. Section of RIS Originator Specific Comment NRC Resolution Units 1,2 and 3, dated December 12, 1977. As a result, reference to PSB-1 in the draft RIS for The licensee's analysis must show that PVNGS does not reflect the historic licensing basis degraded voltage trip setpoint adequately for PVNGS. protects the equipment powered by the 4.16 kV ESF bus from a potentially damaging degraded voltage condition.
The NRC regulatory requirement is Criterion
17 of Appendix A to 10 CFR Part 50. The NRC staff guidance and positions are described in PSB-1.
See staff response to Task Interface Agreement 2010-005 (ADAMS Accession No. ML102800340) for more details regarding Palo Verde degraded voltage inspection finding.
122 Page 5 APS Page 11, 14.
Inspection Report 2009-008 is described in the draft RIS. The specific elements of the inspection report that require response are next described.
The inspection report states:
"the time delay of 35 seconds for transfer of safety buses to the onsite power supplies may be too long to prevent core damage in case of a sustained degraded voltage condition concurrent with an accident. This time delay could result in a delay in supplying water to the core in case of an accident concurrent with degraded voltage, due to the inability of electrical equipment to respond as required during the timeout period."
APS Response: This is a double sequencing Disagree.
scenario, which is a malfunction of an SSC with a different result than previously evaluated pursuant The point being made in the RIS is that to 10 CFR 50.59, for PVNGS. It could result in core setting of the DVR should include damage regardless of the time delay value at which consideration of a coincident degraded grid the DVR actuation (delayed LOOP) occurs. This is and accident in that the time delay chosen the reason APS precludes such an event by for the DVR should support the accident establishing appropriate initial conditions, with TS analysis assumptions consistent with the LCO 3.8.1, Condition G, through license NRC1977 letter.
amendment 123.
The focus of the RIS is to clarify regulatory requirements.
See staff response to Task Interface Agreement 2010-005 (ADAMS Accession No. ML102800340) for more details regarding Palo Verde degraded voltage inspection finding.
The double sequencing issue is a plant- specific issue. The staff determined that the amendment that addressed the specific design issue (double sequencing) at PVNGS
did not change the licensing requirements for the 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 time required to provide water to the core, but will actually improve it."
APS Response: APS is not aware of any analysis Disagree in the GSI-171 resolution document to suggest that I
40
No. Section of RIS Originator Specific Comment NRC Resolution a shorter time delay (e.g., delayed LOOP occurring This is a plant specific issue. The issue will sooner) would be of any benefit in preventing the be reviewed through the ROP.
failure mechanisms associated with a delayed LOOP or assuring that water would be successfully provided to the core. See Technical Comment 6 for further discussion on the lack of correlation between the DVR time delay setting, accident analysis time, and core damage.
The PVNGS current licensing basis for the DVR
time delay is > 28.6 seconds. During the review that led to issuance of PVNGS license amendment
123, the staff expressed a concern that a minimum allowable time delay be specified to assure that unnecessary separation from offsite power would not occur. The safety evaluation for license amendment 123 states:
"APS responded by adding a lower limit (> 28.6 seconds) to the time delay allowable value specified for the degraded voltage function in its revised submittal date6 September 29, 1999. This change resolves the staffs concern on this matter."
The NRC staff was aware and approved the existing time delay values for the DVRs and the staff considered a shorter time delay to be a concern. The inspection report is inconsistent with the current safety evaluation.
124 Page 5 APS Page 12,16.
The inspection report states:
'The licensee had offered the proposition that degraded voltage concurrent with an accident was not credible, but the team could not find evidence that the NRC had accepted this position, or that the degraded voltage relays were no longer required to perform a protective function during accidents."
APS Response: The PVNGS current licensing basis 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 degraded voltage/double sequencing scenario from occurring at the Palo Verde site. The staff finds this approach acceptable.
The safety evaluation recognizes that the prevention strategy precludes degraded voltage conditions from occurring. All scenarios involving degraded voltage concurrent with an accident are delayed LOOP/double-sequencing scenarios. The purpose for PVNGS license amendment 123 was to implement a method to prevent this degraded voltage concurrent with an accident (which would always result in a delayed LOOP and double sequencing). APS is not aware of an accepted method to ensure that core damage will not result, if such an event were to occur. Design basis calculations to justify the function of the degraded voltage relays during accidents are not feasible, because they would be unable to justify the delayed LOOP/double sequencing effects discussed in GSI-171.
125 Page 6 Nextera 1 This paragraph could be interpreted to require the LOCA sequence to be modeled at the DVR dropout Disagree setting. LOCA sequencing modeled at the DVR
41
No. Section of RIS Originator Specific Comment NRC Resolution dropout setting would result in separation of the The dropout setting should be developed buses from the Preferred Power Source (off-site based on the voltage requirements (starting power) as the voltage would not recover above the and running) and therefore to develop values DVR reset value, which are bounding, the studies should be done under worst starting and loading Clarify the intent is to show safety related conditions which means the required voltage equipment will function at the selected DVR at the 1 E bus prior to the start or run case dropout 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 should equate to the limiting voltage at the limiting Clarify that LOCA sequencing is evaluated using component during the bounding starting or minimum switchyard voltage as starting point, running scenario to protect the 1E
equipment.
126 Page 6 Nextera 2 Having a sustained degraded voltage just above Agree.
the LVR voltage setting (70%) is not practical without grid collapse and does not exist in Branch The DVR setpoints are calculated based only Technical Position #1 (PSB-1). on the voltage requirements of the 1E
equipment, not based on whether the grid Clarify degraded voltages to be analyzed to a can sustain voltage at levels that result in credible level, such conditions.
127 Page 6 Nextera 3 The statement that the DVR ensures adequate operational (starting and running) is the first time in Disagree NRC correspondence that starting equipment at the DVR setpoint is expected. The example letter The dropout setting should be developed sent to Peach Bottom in June 1977 did not require based on the voltage requirements (starting starting of equipment at the DVR setpoint. This and running) and therefore to develop values requirement should be removed from the RIS since that are bounding, the studies should be it is not possible to start equipment at the DVR done under worst starting and loading setpoint and not subsequently separate from offsite conditions, which means the required voltage power. If the equipment starts at the DVR setpoint, at the 1E bus prior to the start or run case the 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 should separation from offsite power. Since the reset point equate to the limiting voltage at the limiting will always be above the DVR dropout point it will component during the bounding starting or be impossible to reset the relay. running scenario to protect the 1 E
equipment.
Remove starting of equipment at the DVR setpoint as a requirement.
128 Page 7 Nextera 4 It is agreed that no credit is to be taken for voltage controlling equipment external to the Class 1 E Agree distribution system for the establishing the degraded voltage relay (DVR) settings; however, it Additional wording has been added to the should be clarified that for credit may be taken for Offsite/Plant distribution discussion to make minimum switchyard voltage/voltage drop it more clear that equipment like automatic calculations (or the Offsite/Onsite Design Interface load tap changers can be credited if the Calculations). response time will support normal operation.
Clarify that credit may be taken for automatic load tap changers and/or capacitor banks for minimum switchyard voltage/voltage drop calculations (or the Offsite/Onsite Design Interface Calculations).
129 Page 8 Nextera 5 NRC Generic Letter 79-36, Enclosure 2, Item 2 states that It is recommended that "Formulfi-unit stations a separate analysis should be performed for each unit assuming (1) an accident in the unit being analyzed and simultaneous shutdown of all other units "Offsite/Onsite at the station;or (2) an anticipatedtransientin the unit being Design analyzed (e.g., unit trip) and simultaneous
42
No. Section of RIS Originator Specific Comment NRC Resolution shutdown of all Interface other units at thatstation, whichever presents the largest Calculations", load situation."
Comment:
NRC Draft RIS re-states NRC GL 79-36 verbatim, Disagree with an attempt to clarify "anticipatedtransient'by adding in parenthesis "(anticipatedoperational The reference added is the wording used in occurrence)" immediately afterwards. It is not clear GDC 17 (for consistency).
what the added parenthetical statement is meant to convey, other than unit trip (which already exists in GL 79-36).
It is recommended that this either be removed, or stated "anticipatedtransient per station licensing basis".
130 Page 8 Nextera 6 NRC should clarify "simultaneous shutdown" with consideration to:
Most multi-unit station's Licensing Basis consider an "orderly or controlled safe shutdown" of the Disagree other unit(s) not being analyzed.
NERC Std TPL-004-0; particularly Category D This wording in the RIS is the same as was events per Table 1, where a "loss of all generating used in GL 79-36.
units at a station"may result in "portions or all of the interconnected systems may or may not TPL-004 requires transmission planning to achieve a new, stable operating point'. address simultaneous multiple transmission contingencies.
IEEE Std 308-1974, Clause 8, subclause 8.1.1
"Capacity' describes this as a "concurrent safe The plant licensing basis provides basis for shutdown on the remaining units", analyses related to multi unit sites.
The wording for the proposed RIS, subclause 2.c should be revised to indicate "orderly or controlled safe shutdown of the remaining units, as per the station's licensing basis" instead of "simultaneous shutdown". Alternatively, the wording "shutdown consistent with the station licensing basis" could be used instead of "simultaneous shutdown".
131 Page 8 Nextera 7 These guidelines (e) and f )seem contradictory that you cannot credit procedurally controlled Disagree.
operator actions to reduce load but you have to assume the actions will be carried out when load is These guidelines are not contradictory in that added, one is considering load shedding (not conservative) for design of system based on Delete "e) Manual load shedding should not be maximum load, while the other is about load assumed" or add allowance to credit procedurally additions that occur per procedure controlled operator actions to decrease load. (conservative for maximum loading design).
132 General TVA Comment: The RIS suggests that demonstrating adequate motor starting voltage is a reasonable objective or outcome of a setpoint calculation for a Degraded Voltage Relay whose purpose is to Disagree protect Class 1 E equipment.
TVA's position is that such an objective or outcome is not technically achievable for the reasons discussed below:
1) A Voltage Relay is not a Predictive Device The DVR dropout setting should be Voltage sensing equipment cannot provide a developed based on the voltage predictive function without crediting the capacity or requirements (starting and running) and capability of the upstream system, since it cannot therefore to develop values that are determine the capacity or capability provided bounding, the studies should be done under during a transient condition such as a motor start, worst starting and loading conditions, which Since the existing regulatory framework for means the required voltage at the 1 E bus
43
No. Section of RIS Originator Specific Comment NRC Resolution degraded voltage protection was based on use of prior to the start or run case would have to voltage relaying, it is not clear how the existing be higher than the setpoint. The main point is relaying equipment could be used to demonstrate that the setpoint should equate to the limiting compliance with an adequate motor starting voltage at the limiting component during the demonstration requirement. bounding starting or running scenario to protect the 1 E equipment. In addition, the
2) A Degraded Voltage Relay Protection Setpoint time delay would be determined based on Based on Starting Voltage Does Not Provide Motor the limiting starting transient duration only Protection (not based on allowing time for operator action). In this manner, if the voltage drops This method could potentially be calculated but below expected values during starting would mean that the DVR setpoint would have (based on the 1E equipment limits) and been determined during the starting of the most prolongs the start transient, then the DVR
limiting Class-I E motor. A degraded voltage relay will timeout and separation will occur setpoint based on a motor starting would not (providing low starting voltage protection).
protect the motor from damage (required by regulations) or preclude tripping of the motors over-current device(s) prior to transferring to the onsite power supply (required by regulations). This is because the DVR time delays are (by definition)
required to be longer than a motor starting transient
(1st time delay) and long enough to allow operator intervention (2 nd time delay). If starting of the limiting (worst-case) motor was attempted in a true degraded voltage situation (even slightly below the DVR setpoint), the DVR scheme could not perform either of these protective functions prior to tripping the normal overcurrent relays. Therefore, this would not provide any additional protection for the Class-1 E loads.
133 General Progress Background: The draft NRC Regulatory Issue Energy 1 Summary, 2011 -xx, Adequacy of Station Electric Distribution System Voltages, describes a methodology of implementation for degraded voltage relay schemes that would impose
"Additional Conservatisms" into the settings and time delays in an effort to further reduce the risk of Disagree.
degraded voltage operation on nuclear plant safety related / accident mitigating electrical equipment. Additional conservatism should not be added for the sake of adding conservatism.
"Additional Conservatisms" from this point of view Conservatism is typically added to tends to mean that the degraded voltage relaying compensate for assumptions that cannot be will actuate earlier in a degraded voltage event time accurately verified or proven (e.g. cable line - meaning it would be set to actuate at a higher impedances when actual pull lengths are not degraded voltage and/or with a shorter time delay. known).
In conflict with the NRC's desire to impose NERC and FERC guidelines are reviewed by additional conservatisms on degraded voltage NRC staff for applicability to nuclear plant protection 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 settings and 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-Through Time Duration Curves currently proposed by the NERC Standards Drafting Team shows the competing desire for nuclear power plants to be capable of riding through a grid induced voltage transient without tripping.
Actuation of the degraded voltage relaying in a nuclear power plant during a grid induced voltage transient results in a temporary loss of power to the safety related loads powered from the plant buses until the loads are realigned to an emergency power source and reenergized. This temporary loss of power will result in a trip of the nuclear plant in many cases and a significant challenge to
44
No. I Section of RIS Originator I Specifc Comment I NRC Resolution continued operation of the plant in all cases.
An analysis of current settings and time delays for several nuclear plant loss-of-voltage and degraded voltage relay schemes against the proposed NERC
ride through criteria shows that existing settings are already in conflict with the proposed ride-through criteria.
Imposition of additional conservatisms into the relay settings and time delays for nuclear plant equipment degraded voltage protection will further complicate efforts to coordinate NRC required degraded voltage protection schemes with NERC voltage transient ridethrough capability needs.
Comment: Please coordinate NRC Staff proposed degraded voltage relay setting methodology changes with NERC proposed voltage transient ride-through capability standard (PRC-024) by engaging with NERC under the current NRC - NERC Memorandum of Agreement (MOA).
134 General Progress Background: The use of on-load automatic load tap Energy 2 changing transformers for nuclear plant offsite power supplies would aid in minimizing auxiliary bus under voltage or degraded voltage transients of concern to the NRC while also improving the voltage transient ride through capability of the nuclear plants that is of concern to NERC.
Comment: Please revise the RIS to allow the Agree nuclear plants to use and take credit for on load automatic load tap changing transformers for nuclear plant offsite power supplies to prevent Load tap changers help improve voltage degraded voltage events and improve the voltage regulation for normal plant operation. Load transient ride through capability of the nuclear tap changers do not help protect safety plants. related equipment during degraded grid conditions.
Additional wording has been added to the Offsite/Plant distribution discussion to make it more clear that equipment like automatic load tap changers can be credited for normal plant operation.
135 General Progress Comment: Please also consider the italicized Energy 3 changes below: Agree DVR Setting Design Calculations !fafcizd Ghanges suggested wer'
GORtdOFzd alOAg With OthOF8imil!ar Licensee voltage calculations should provide the basis for their DVR settings, ensuring safety related .nd dg..fi.d in the RIS wr.... Italicized equipment is supplied with adequate operating changes were not incorporated in the RIS
voltage (typically a minimum of 0.9 per unit voltage s...e.... .o..r.. s.w.... . o.. o.. s.. n wan.....
since mhecomments were riot consistent with at the terminals of the safety related equipment per the staff's existing guidance for DVR
equipment manufacturers requirements), based on settings.
bounding conditions for the most limiting safety related load (in terms of voltage) in the plant.
These voltage calculations should model the plant safety related electrical distribution system such that the limiting voltage at the bus monitored by the DVR can be calculated in terms of the voltage at the terminals of the most limiting safety related component in the plant. These models would allow calculation of voltages at terminals (delete "or contacts ") of all safety related equipment with the voltage at the DVR monitored bus at the DVR
dropout setting, providing the necessary design
45
No. I Section of RIS I Originator Specific Comment NRC Resolution basis for the DVR voltage settings.
In this manner, independent of voltage controlling equipment external to the plant safety related electricaldistributionsystem, the DVR ensures that all safety related equipment can continue to operate at the degraded voltage relay drop out "Contacts" was deleted.
setting if previously in service, small loads will not be damaged if successfully started atthe degraded voltage without DVR time out (the DVR either does not drop out or resets before time out because the started load is small), and largerloads will not be damagedor trip on overload/protectiverelaying if starting the equipment results in sustained degraded voltage for the duration of the D VR time delay (the DVR drops out and does not reset because the load is large but the DVR timer times out and sheds the load from the degradedvoltage source before the overloadsand/orprotective relaying actuates).
For the purposes of this DVR Setting Design calculation, no credit should be taken for voltage controlling equipment external to the Class 1 E
distribution system such as automatic load tap changers and capacitor banks because these devices normally prevent degradedvoltage from occurringand thus, by definition, should not be includedin a bottom up analysis to determine minimum voltage requirements for the safety relatedloads. Voltage time settings for DVRs should be selected so as to avoid spurious separation of safety buses from the offsite power system during unit startup, normal operation and shutdown. These DVRs should disconnect the Class 1 E buses from any power source other than the emergency diesel generators (onsite sources) if the degraded voltage condition exists for a time interval that could prevent the Class 1 E safety related loads from achieving their safety function.
The DVRs should also protect the Class 1 E safety related loads from prolonged operation below sustained degraded voltage which could result in equipment damage.
The licensees should demonstrate that the existing DVR settings including allowable values and time delays are adequate so that safety related loads can continue to operate at the degradedvoltage relay drop out setting if previously in service, small loads will not be damagedif successfully started at the degradedvoltage without DVR time out, and largerloads will not be damaged or trip on overload/protectiverelaying if starting the equipmentresults in sustaineddegraded voltage for the duration of the DVR time delay resulting in separationfrom offsite power and realignmentto the emergency onsite powersupply. The time- delay(s) chosen for DVRs during accident conditions should be short enough to meet the accident analyses assumptions and allow for proper starting of all Class 1E safety related equipment assuming that the DVR time delay times out and the accident mitigating loads realign to the onsite emergency power supply. Also, the time delay chosen for DVRs during non-accident condition must be short enough to not cause any degradation of the safety related components, includina actuation of their orotective devices.
46
No. Section of RIS Originator Specific Comment NRC Resolution
136 General Progress Comment: Please also consider the italicized Energy 3 changes below: Agree Offsite/Onsite Design Interface Calculations The offsite power source is the preferred source of ltzed Ghz'gc suggested were power to safely shut down the plant during design .... red alon* wt;h oher - simla basis accidents, abnormal operational occurrence, commaiti rzezizvd fro' other s*tzDlezh*-rc and reactor trips. The licensee's voltage And Glrili* d in the RiS riev!ir.etjalici.._
calculations should provide the basis for proper changes were not incorporated in the RIS
operation of the plant safety related electrical since the comments were not consistent with distribution system, when supplied from the offsite staffs existina auidance for offsite/onsite circuit (from the transmission network). These design interface calculations.
calculations should demonstrate that the voltage requirements (both starting and operational voltages) of all plant safety related systems and components are satisfied based on operation of the transmission system and the plant onsite electric power system during normal, startup, shutdown, accident mitigation, and alternate authorized operating configurations of transmission network and plant systems. In this way, all safety related systems and components will function as designed with proper starting and running voltages during all plant conditions and the DVRs will not actuate (separating the transmission network supply).
Following are guidelines for voltage drop calculations derived from Generic Letter 79-36, which have been supplemented to add clarifying information. They do not represent new NRC staff positions.
137 General Progress Comment: Please also consider the italicized Energy 3 changes below: Agree Guidelines for voltage drop calculations a) The plant voltage analysis, while supplied from !tR!acized changei Suggested were the transmission network, should be based on the *
GG*deFrzdalong with theFr imFiIAr operating voltage range of the transmission r*zcivod from ether qtAktIhclder Femr.-tc network connection. This transmission And nlrwfied nRthe P.IS r*vicgi..Italicized owner/operator supplied voltage range should changes were not incorporated in the RIS
address normal, startup,shutdown, accident since the comments were not consistent with mitigation, and altermate authorized transmission staffs guidance provided in Generic Letter network and plant system operating configurations 79-36.
and should also include voltage drop due to the bounding worst case transmission system single contingency (transmission system contingencies include trip of the nuclear power unit). Normally in- service andperiodically tested non-safety related equipment (such as automatic load tap changing transformers that regulate voltage during changing conditions) are to be included in the analysis.
b) Separate analyses should be performed assuming the power source to the safety buses is (1) the unit auxiliary transformer; (2) the startup transformer; and (3) other available connections (e.g., from all available connections) to the offsite network one by one assuming the need for electric power is initiated by (1) an anticipated transient such as a unit trip (e.g., anticipated operational occurrence), or (2) an accident, whichever presents the bounding load demand on the power source.
47
No. Section of RIS Originator Specific Comment NRC Resolution
138 General STARS "Statement of Staff Positions Relative to Emergency Power Systems for Operating Reactors"
RIS 201 1-XX states that "the NRC required licensees to install degraded voltage protection schemes ,.. as described in NRC Letters dated June 2 & 3, 1977, 'Statement of Staff Positions Relative to Emergency Power Systems for Operating Reactors,' which were sent to all licensees of all operating nuclear power plants. As an example, see the NRC letter dated June 2,
1977, ADAMS Accession No. ML1 00610489, sent to the licensee for Peach Bottom Atomic Power Station." (Ref. 2) However, the RIS does not Disagree recognize the latitude in response allowed to each Licensee:
'We request that you compare the current design of the emergency power systems at your facility(ies) with the Staff Positions stated in the enclosure and:
(1) propose plant modifications as necessary to meet the Staff Positions, or
(2) provide a detailed analysis which shows your facility design has equivalent capabilities and protective features.
Additionally, we require that certain technical specifications be incorporated into all facility operating licenses."
Observations:
1. The NRC letters request some actions and require some actions - specifically - a technical specification change.
2. The response makes allowance for varied responses that account for "equivalent capabilities and protective features." These varied responses become part of the licensees' Current Licensing Basis.
NRC staff does not agree with this position.
3. Licensees were required to change their As a result of these Millstone events, the operating license because the staff position. NRC requested that all licensees implement However, this in and of itself, does not change the degraded protection as described in the licensees' Current Licensing Basis. 1977 Letter to ensure automatic protection of safety buses and loads. This Letter provides
4. The "1977" letters apply only to addressees, i.e., staff posilie uuidance, which applies to all plants licensed before 1977. operating reactors at that time and plants licensed since, on how to comply with the
"Adequacy of Station Electric Distribution System requirements in 10 CFR Part 50. General Voltages" Design Criteria 17 (GDC 17).
The technical content, with some modifications, of the "Statement of Staff Positions Relative to Emergency Power Systems for Operating Reactors" was put in the 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, and in the current BTP 8-6 of the SRP, Revision 3, "Adequacy of Station Electric Distribution System Voltages," dated March
2007.
48
No. Section of RIS Originator Specific Comment NRC Resolution
1. Branch Technical Positions of NUREG-
0800 are not requirements but:
"represent guidelines intended to supplement the acceptance criteria established in Commission Regulations, guidelines presented in Regulatory Guides, and recommendations presented in applicable IEEE standards."
2. PSB-1 and BTP 8-6 provide subtle but significant changes to each other and to the original "Statement of Staff Positions Relative to Emergency Power Systems for Operating Reactors" (Note: these differences will be provided in a comment letter from the Nuclear Energy Institute). If the original statement of staff positions is considered a requirement, then it is contradictory to subsequent NRC guidance.
3. PSB-1 and BTP 8-6 represent guidance as committed to in a licensees' Current Licensing Basis - which, with plant specific justification, may depart from NRC
guidelines, but are reviewed and approved by the NRC.
139 General STARS By characterizing the new contents of RIS 2011 -
XX as clarifications to "the NRC staffs technical Disagree position on existing regulatory requirements," the RIS seeks to supersede the NRC reviewed and The purpose of the RIS is to clarify the NRC
approved Current Licensing Basis for many staffs technical position on existing licensees, regulatory requirements and voltage studies necessary for Degraded Voltage Relay (second level undervoltage protection)
setting bases and Transmission Network/Offsite/Onsite station electric power system design bases. This RIS does not transmit any new requirements or staff positions.
A RIS is an appropriate document for NRC
staff to provide clarification on existing Regulatory Requirements and existing NRC
Staff Positions.
140 General Greg The issue I am concerned about is the regulatory Reimers conflict created by requiring the DVR setpoint to (DCCP) preclude spurious actuation of the undervoltage Agree protection function.
The NRC draft RIS 2011-XXX discusses spurious separation at least three times.
1. The first occurrence is an accurate NRC Staff agrees with commenter's position restatement of the 1977 NRC position on use of the term spurious with respect to that "The voltage protection shall include the design of the DVR scheme to prevent coincidence logic to preclude spurious false actuations due to DVR component trips of the offsite power source" (See failures or miss-operations RIS Page 2, Item (b)).
2. The second occurrence is in the
"Degraded Voltage Relay Design The RIS will be revised to remove spurious Calculations" section. Specifically, the from this section. The NRC Staff position is second sentence of the first paragraph that the settings are to be selected based on on Page 7 reads 'Voltage-time settings the voltage requirements of the 1E
for DVRs should be selected so as to equipment such that when compared with avoid spurious separation of safety the minimum expected grid voltages, there buses from the offsite power system should be sufficient margin ensure that during unit startup, normal operation and separation from the grid would not be shutdown." This introduces the DVR expected during normal, abnormal or
49
No. Section of RIS I Originator I Specific Comment I NRC Resolution voltage and time setpoint interaction with accident conditions.
the offsite power circuits as a factor in the setpoint determination. I believe a conclusion of the workshop was a common understanding that the functional requirement of theDVR
protection is to prevent common mode equipment failure during a sustained degraded voltage condition. As discussed, this can best be achieved via a "bottom up" analysis without consideration of offsite power capacity and capability.
3. The third occurrence is in the
"Offsite/Onsite Design Interface Calculation" Section. Page 8, Item (i)
reads "For each case evaluated, the calculated voltages on each safety bus should demonstrate adequate voltage at the component level without separation from the offsite circuit due to DVR
actuation."
Points #2&3 above introduce a contradiction for those stations whose current license basis is consistent with the Standard Technical Specifications. Referring to NUREG-1431, Standard Technical Specifications Westinghouse Plants (typical TS), the degraded voltage TS bases read "The Allowable Value is considered a limiting value such that a [DVR] channel is OPERABLE."
Thus, at the Allowable Value lower limit, the Class
1E electrical distribution system is capable of fulfilling its ESF supporting design function. The offsite power LCO reads "Each offsite circuit must be capable of maintaining rated frequency and voltage, and accepting required loads during an accident, while connected to the ESF buses." No voltage values are defined for the offsite power TS
LCO. Therefore, if the offsite power circuit can maintain the bus voltage such that the DVR lower Allowable Limit is satisfied, then the offsite power circuit would also be operable.
The DVR dropout and reset setpoints must be greater than the TS lower Allowable Value due to instrument tolerances and uncertainty. Given the DVR favors the DGs, does not mean bus voltages between the DVR setpoint and the TS lower Allowable Value reduce the capability of the offsite power circuit. Consequently, the DVR setpoint cannot completely preclude spurious separation.
As discussed in the workshop, a voltage relay NRC Staff agrees with commenter's position cannot predict future operating conditions. on use of the term spurious with respect to Consequently, the DVR can't distinguish between the design of the DVR scheme to prevent voltage transients that are expected to recover and false actuations due to DVR component those that are not. Therefore, in the context of the failures of miss-operations original NRC position (i.e. Point #1), I believe the term spurious was in the context of false signals NRC Staff agrees with the commenter's from within the DVR instrumentation and not any position that the intent of item i) is to specify group of bus voltage transients. The IEEE 308 that the preferred power supply is able to requirement that RIS Page 8, Item (i) is trying to start and run all required 1E equipment in convey is "The preferred power supply shall be accordance with its voltage requirements capable of starting and operating all required while not separating loads."
Backup power CBrianWilson, Why are there not back-up power sources located
141 optonsCA on the roof of the fuel cell tanks with electric lines Disagree
50
No. Section of RIS Originator Specific Comment NRC Resolution connected directly to the pumps that cool the fuel rods back-up power sources run on both methane This comment is not related to the RIS
or propane and Ipg. A remote control panel from a regarding "Adequacy of Station Electric distant 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) Formatted: Font: Italic, Underline RESPONSES TO NEI 3-2-2-11 BACKFITTING COMMENTS Formatted: Centered RIS On Adequacy of Station Electric Distribution Voltages Formatted: Centered Comment: The RIS represents an NRC attempt to standardizevaried approachesto providingprotection during degradedgrid voltage conditions, as currently memorialized in the licensing bases of individual plants. However, given the complex regulatoryand licensing history associatedwith providing degradedgrid voltage protection at each plant, a conclusion that the guidance in the proposed RIS is "consistentwith" prior NRC guidance is insufficient to meet 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 issue generic guidance applicable to several plants - each of which has a complex regulatory and licensing history, then the NRC complies with the Backfit Rule only if its backfitting discussion for the proposed generic guidance considers and addresses 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 a principle to guide the agency's implementation of the Backfit Rule. Application of such a principle would oftentimes impose substantial resource burdens on the NRC, namuch Asthe NRC cUrrcRtl'y has no c*.fcient way of easily
.... Pi..,nd reviowingas it is difficult for the NRC to efficiently compile and review the licenses bases of selected plants on a comparative basis. The more complex the regulatory licensing history for each licensee's plant, the more resource intensive it would be for the NRC to prepare a "generic" backfitting discussion that essentially constitutes a collection of plant-specific licensing basis reviews. Upon completing the licensing basis review for each plant to which the generic guidance is applicable, the NRC (and licensee) may well conclude that imposition of the guidance would not represent backfitting In that situation, the review would constitute an arguably unnecessary expenditure of NRC
(and licensee') resources.
The NrC holia-,e n moren irnsi -nro rh iý if the NRr, hns nenpr~iiv maintninpd a rnnsiistpnt nosition for at least j Formatted: Font: 9 pt
-d no c ition) and has ir nitifn In m , t manner, then the NRC may issue eas a! f oosition. and i mnin connection with any NRC
action which imposes the cuidance on a licensee ý ) imposition 4 ackfitting The NRC
action may he ; rthinqs, a NRC determination of a license amen - the issuance of a notice of vinltin nr i ice of an order directing the licensee to comply In this manner the specific isinQ history for that plant can be compiled and I hv
- T
the
....
NR. as nart of the NRC's r q I
Cnnsistent with this neneral nrinninie the NRC has (as nart of the hackfittinn consideration of this RISI reviewed its r-cnrd, with r-n-rMf to e on GDC017 iraded voltage orotection. Based upon that review, the flC..17 -1 .de voltage Protection has been consistent over time.
I 5 Dresented in I )not constitute neneric backfittinl. In addition, the NRC Formatted: Font: Italic has reviewed its records and believes that (with one exceotion which is being dealt with in a plant-specific manner, I, Formatted: Font color: Auto it position on a plant-si ,basis. The? y in the process of applyinq t and is nrenarinn the ; !d bv the Backfit Rule Hence s that n oft I I t appropriate. Formatted: Font: 9 pt Gonsistent P004-4- (o I Ca,' Hc noer,than the NRC
maryi fl Gonn1 ccwi h th any
-1D? , - -K101, irri inn*.!.P'; .*.cIt* 3 .0
Ar- fr -that t Formatted: Font; (Default) Arial, 9 pt t4 An Formatted: Font: (Default) Arial, 9 pt, Not
1 and -UV Superscript/ Subscript F9r thiS RIS, the NRC rcvIPWAGIc MhcFegulatzr~y guidanse and NRC practice in this area, and cencluded that the Formatted: Font: (Default) Anal, 9 pt guiane n te ISis consistent iAwith the NRG'c regulations and 6taff guidance. as well as tho AIRG' approval at { Formatted: Font: (Default) Arial, 9 pt, Not If I, ,, ,// ý a uper.sc lpL/ Subscript Ifthe 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, Font would be likely that the licensee would be required to verify the NRC's discussion. A -'- color: Auto, Not Superscript/ Subscript
2This 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, Not
366/2011009, .ML1114507930) .he NRC's reliance on the compliance exception is the subject of a backfit appeal by Superscript/ Subscript Southern Nuclear Operating Company, the licensee of the Hatch Plant (MLi 11680360). Zhe NRC h a denied the Formatted: Font: (Default) Anal, 9 pt, Font backfit appeal (ML112730194). L color: Auto, Not Superscript/ Subscript
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- esoren*cthC
- c~trlc.JI' I).Hence, ,.n ,,3rioue NRCccu~,,ocn,,,i.g th,*.*1csJone2twltr t*plnt .... on* *xcepsicno fi .....
cv , o,wnfcn a,backfitting cf the*, oe',,n, o3'a;.impkoiot~ns w. in J pcmns' apocsic of thiz R~S C.n*
apppepripa.e.
The NRC emphasizes that this approach to addressing backfitting in connection with the issuance of guidance (such as this RIS) would not be appropriate if the NRC does not have reasonable certainty that it has articulated (or at least expressed no contrary position) and implemented a consistent position over time. However, as stated above, such is not the case with the guidance on degraded grid voltage protection contained in this RIS. Thus, the degraded voltage RIS does not constitute generic backfitting because it does not constitute a new or different generic NRC staff position. If there is plant-specific backfit when applying the guidance to a specific plant, then the staff will address backfitting in the context of that staff action (and prepare the necessary documentation to support the staff's backfitting action). Accordingly, the NRC declines, as a matter of discretion, to prepare a plant-specific backfitting discussions for each of the plants that may be affected by the RIS. No change was made to the RIS as a result of this comment.
Comment: The NRC should not rely upon GDC-17 to conclude that the proposed RIS does not representbackfitting.
GDCs are cast in broad,general terms and are non-specific nature. Thus, the relevant backfitting inquiry should be whether the proposed RIS's guidance differs from any individualplant'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 any GDC which is expressed in broad, general terms or is "non-specific in nature," or is expressed in performance-based language, may not be relied upon when the NRC invokes the compliance exception under § 50.109(a)(4)(i). Nothing in the history of the Backfit Rule suggests that the Commission intended to adopt such an interpretation of the Backfit Rule.
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-affected plants, 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 of rules and regulations, then this effectively converts the administrative process of rulemaking under the Administrative Procedures Act (APA) to the administrative process of issuance of orders under the APA. The NRC does not see why it must limit itself, in light of the several and broadly-worded rulemaking authorities accorded the NRC under various provisions 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 more specific requirement in a plant's licensing basis representing the NRC position on an acceptable way of compliance with the performance-based requirement (e.g., a GDC), then that position is a separateand independent basis for 3 that licensee to invoke backfitting protection when the NRC proposes to impose that NRC position on that licensee.
More importantly, the NRC disagrees with the comment's implicit assertion that GDC-17 is a broad, general, and nonspecific GDC. A brief review of GDC-17 shows that its rogulater,' tWAtis ameng the most length; 0f the GDCS,
cnsistting of three parographG. The requirements are stated in relatively specific terms using performance-based regulatory language, but also setting forth very specific conceptual requirements, e.g., the need for electric power from the "transmission network" to the "onsite electrical distribution system" to be supplied by "two physically independent 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 from any 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 Nuel;*f Operatmg C.mpC,.n, the l w*. fth, Hath PlanM (,,L 111903h0)
The situation involving the imposition of a new NRC position on an acceptable way of complying with GDC-17 is an example where the NRC acknowledges that the NRC approval of the licensee's specific undervoltage protection scheme) in a license amendment constitutes an applicable staff position for purposes of the Backfit Rule, Thus, the NRC has acknowledged that the proposed new staff position on the Hatch Plant's undervoltage protection scheme constitutes backfitting. Thus, the issue which is the subject of the licensee's backfit appeal, is whether the NRC may rely upon the "compliance exception" under 10 CFR 50.109(a)(4)(i).
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Comment: The NRC's generic communications and guidance identified in the draft RIS are not completely consistent with one another and were not equally relevant in developing the licensing bases for all reactorlicensees, citing to various 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 presented in the NRC's generic communications and guidance on the subject of degraded voltage protection. However, the NRC disagrees with the comment's implicit assertion that there is no consistent NRC staff position. As discussed in response to the prior comment, there is some "variability" among the NRC generic communications and guidance documents in terms of the scope of issues relating to electrical system design, as well as the detail provided. The comment 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 inconsistent with 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 occurrenceof a safety injection signal...should immediately separate the Class 1E distribution system from the offsite power system" (emphasis added). There is no conflict or inconsistency between these two statements, when the BTP (which precedes the RIS) is read in full context. The full text of the relevant portion of the BTP is:
Two separate time delays shall be selected for the second level of undervoltage protection based upon the following conditions:
1) The first time delay should be of a duration that establishedthe existence of a sustained degraded voltage condition (i.e.,
something longer than a motor starting transient). Following this delay, an alarm in the control room should alert the operator to the degraded condition. The subsequent occurrence of a safety injection actuation signal (SIAS) should immediately separate the Class 1 E distribution system from the offsite system (emphasis added).
"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 of succession, 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 postulated design 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 design in which the undervoltage condition occurs first, and then (while the undervoltage condition is still present), the design basis event occurs (and thereby draws a load on the electrical system). In either case, the result is the same in that separation from the grid occurs and the 1E systems are powered from the onsite sources during design basis event mitigation. The only difference is that in the case of the subsequent design basis event, the actual start of the 1 E
equipment will be later than when the two events occur coincidently. Either way the design basis event assumptions are satisfied.
Figure 1 illustrates the difference. There is no conflict or inconsistency between the RIS and the BTP.
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Degraded Voltage Set Points (BTP PSB-1) DVR -1 Protection - Existence of a sustained degraded voltage condition
100% To account for ECCS motor starting, running of all 1E loads and time for gridrecovery (Long time Delay.) Causes alarm and Time delay is bypassed on SI signal if a subsequent SI occurs. Provide adequatetime sofor plant or grid operatorto take manual actions.
Alarm fica n t ly I l -
a iý,nif h 19'.
setpo nDVR (BTP PSB-1) DVR-2 Protection with short time Sbdmdelay to rideout the motor starting transients.
DVR set p
ýoltaqe re qired at equipment terminal Ensures minimum voltage required for all to operate all safety related equipment equipment to prevent control fuse blowing, relay lockout, contactor opening etc., concurrent DVR-
2 rcondition S I sianal causes relav to time out if the voltage doesn't within the time delay and s transfers to onsite power system.
Folio 1977 letter staff position The selection of voltage and time delay setp ts shall be determined from an analysis of th operating voltage requirements of the safety relat loads at all onsite system distribution levels;
Figure 1 The second example identifies an apparent conflict between the RIS and BTP PSB-1. The draft RIS proposes "DVR
Dropout 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 lasting more than a few seconds and not a transient voltage condition that exists during a motor starting event or during a momentary grid perturbation such a lightning strike that may be cleared by automatic actions of protection schemes and automatic breaker open/reclosure cycle. Specifically, BTP PSB-1 states: 'Two separate time delays shall be selected for the second level of undervoltage protection based on the following conditions: 1) The first time delay should be of a duration that established the existence of a sustained degraded voltage condition (i.e., something longer 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 event and not voltage scenarios in plant electrical system operation (see fig 1). In addition, when selecting an appropriate time delay for the DVR (which is what the RIS is referring to), one must consider the voltage drop due to large motor starts in the plant since they can depress voltage momentarily by design and such voltage drops should therefore be overridden by the time delay since they would mask detection of the sustained degraded grid voltage event. Also, it is I also clear that the 1977 Letter language refers to the DVR voltage setting(s) being based on the voltage requirements of the 1E equipment. Large 1E motors, for example, have starting and running voltage requirements by design which must be met to ensure proper operation during accident conditions. Thus, the statement that the BTP implies only running voltage requirements are required be enforced is not correct. No change was made to the RIS as a result of this 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 that assumes "an accident in the unit being analyzed and simultaneous shutdown for all other units (emphasis in original)... ," with language in GDC 5 which states, "...in the event of an accident in one unit, an orderly shutdown and cooldown of the remaining units." The language of GDC 5 concerns sharing of SSCs rather than electrical systems,
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and the language quoted in the comment represents a criterion for allowing sharing of important to safety SSCs among nuclear power units. This is not the same subject as the determination of how to analyze whether GDC-17's requirements are being met. Moreover, there is no direct contradiction between "simultaneous shutdown" in the proposed 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 "During normal plant operation, the Class 1 E safety related buses should automatically separate from the power supply within a short interval (typically less than 60 seconds) if sustained degraded voltage conditions are detected." (emphasis added). The comment suggests that a sixty second time delay would not allow operator actions, and appears to be a new NRC position.
-tifie 1terms 1i
4f autolmdat protcotio oWthe las Eeqipme tn dtion t80allowg OR Qoror 4 for a ctions(i psil) See DVR1
- ad 1 2 relay aQnd time deays delay hic d 6nFi 1 -w- is jinaccorn 1 w ithot
4T4 PSB-1sotaffpGoRtod is an Iacc designW to eattgoe Folfos"gition iOln'; it4t1ooprtpof hc... od tW eo.orh seletion of9voltage0tnd tme elay sitpointi syhall bhoded bet ftrtiomaly o fpthogfper t11W voltage po
6y@4044.- R6166 aRd jW64t4604tor WRnWx we P-o"'d 'r6o.214r
6WOf5 tho cOwo dIOWy 0006014 "Tho cl-ott Rig 6P0-kaf'lly alrei frmens ofhaf related loads a t al onsitesyst"m pdwis The iuti levend y time delay would s not llb e cperston atonroeThis appcaro to bo a row pot oNR CntIO
The reference to 60 seconds has been removed in the revised RIS, however, the time delay chosen still has to be justified in terms of providing automatic protection of the Class 1E equipment in addition to allowing time for operator actions (if possible). See DVR1 and DVR2 relay and time delays depicted in Figure 1. This is in accordance with BTP
PSB-1 staff position and is an acceptable design to meet the staff position in the 1977 letter_-6tatt-pes4ieR-i.e., the selection of voltage and time delay setpoints shall be determined from an analysis of the operating voltage requirements of the safety related loads at all onsite system distribution levels. frp PSma1 aciause .I b.2 inclade ovgisions for operator manual actions to -restore hus Yoite on the Class I E~distruti~jLSysE..TPP.SB- IR I h say~lhsecnd en lasshold e o amite~cd uratiotisuch tha-ttfie permanentl~y connectetiLClass lE loads wfll d~tnuonyte.shud.d.~i~~atcltspaaedfomte-afsitegoe ste aaanelfciomust he
~r~p~
th acua~~la~.~floen Lo .TedrRRL soc~aty xcldesmanua[lo stO=ied~ding under the Otsitel~rnsile Design Interface Calculations whereas the BTP PSB-1 allows fQrManual actmio to avoid Separation comnoffsite ~ower.herefore, there is no conflict between the RIS and BTP PSB-1.
Comment: Given the variabilityin NRC's generic communications and guidance, the draft RIS' statement that the positions in the RIS are "consistent with" the RIS-identified NRC documents, does not address the possibility that the RIS is new or different from a previously-approvedprotection scheme (andthereby 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 that this "variability" is of any significance from a backfitting standpoint because there is no contradiction or material inconsistency between the various NRC communications and guidance documents. Thus, such "variability" does not provide a sufficient basis for the NRC to perform plant-specific determination on whether imposition of the RIS
constitutes backfitting. No change was made to the RIS as a result of this comment.
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