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#REDIRECT [[RIS 2011-12, Rev. 1 - Adequacy of Station Electric Distribution System Voltages (Track Changes)]]
{{Adams
| number = ML11357A142
| issue date = 12/29/2011
| title = Rev. 1 - Adequacy of Station Electric Distribution System Voltages (Track Changes)
| author name =
| author affiliation = NRC/NRO, NRC/NRR
| addressee name =
| addressee affiliation =
| docket =
| license number =
| contact person = Mensah, T M, NRR/DPR, 415-3610
| document report number = RIS-11-012, Rev 1
| package number = ML113050591
| document type = NRC Regulatory Issue Summary
| page count = 69
}}
See also: [[followed by::RIS 2011-12]]
 
=Text=
{{#Wiki_filter: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 Federal Regulations
(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 1 E buses are supplied by the offsite power system, sustained
degraded voltage conditions
on ML-I 2222A.1 36ML1 13050583
RIS 2011-12,_Rev.
1 Page 2 of 11 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 1 E systems and equipment, such as spurious load shedding of Class 1 E loads from the standby diesel generators
and spurious separation
of Class 1 E 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 Page 3 of 11 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 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.(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 1 E 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 Page 4 of 11 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 Page 5 of 11 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.Page 6 of 11 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 1 E 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 ISSUES 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 Page 7 of 11 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 1 E 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 1 E 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) 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.
RIS 2011-12,_Rev.
1 Page 8 of 11 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 1 E 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 Page 9 of 11 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 Page 10 of 11 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 Page 11 of 11 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.Laura A. Dudes, Director A'R by RNeISon fGr Timothy J. McGinty, Director Division of Policy and Rulemakina
Division of Construction
Inspection
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
cf ,N,-:!:ar ReaJ!3tion
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 Page 11 of 11 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 Timothy J McGintv~ Director Laura A Dude Direactor flivi~inn
nf Pnlirv ~ncI RiiI~m~kinn
Division of Construction
Inspection
Division of Policv and Rulemakinn
~nnr mr-afainrnI
IDrr% rurmr r~ffie-m rf IMeLoa Pnnfn Prma "Intinn e M. %I/ tII4 f4 IISIBS.% IFkAh~~II*~%l.I
I~ i~L ~Office of New Reactor Timothy j. I1;GGinty, Dilroao Wiwi I F W MI MUM! Morti! E 9 cJrOn P1'_rGIAucae
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_ 1 1 11 1. 1 1 OFFICE NAME DATE NRO LDudes 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.ML110820342)
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 lower than the initial value, then DVR reset cannot occur.Many utilities
use the ABB 27N with harmonic filter which has a minimum 0.5% reset. Thus, with a setting of 93.6% +/- 0.9%, dropout could be as low as 92.7%. However, for motors causing more than 0.5% voltage dip at initial start, even if the voltage at the beginning
of the event was 93.2% and a load was started, then DVR will dropout and never reset causing a separation.
A clarification
that allows evaluation
of motor starting as well-as other conditions
is: If the DVR could possibly not cause separation
then the required safety functions
must be performed
successfully.
Thus, depending
on the design of the plant, a voltage value for beginning the event with all required starts could be determined
by an iterative
process.If the offsite power has adequate capacity and capability, any voltage just above the DVR setpoint should not separate the offsite power source from the safety bus when starting large motors. The grid voltage is expected to recover.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).
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 ISSUES-- 2.Offsite/Onsite
Design Interface Calculations(page
7)Dominion Resources Services, Inc This section contains elements that are too prescriptive.
Many analyses will show that the unit loads/sequences
assessed for determination
of DVR setpoint adequacy for equipment
protection
are the same as those for evaluating
offsite power.Since evaluating
offsite power always involves higher voltages, it is clear the equipment
will function and providing
terminal voltages for this equipment
is bounded by DVR adequacy analysis.A clarification
that helps frame adequate analysis is: If the DVR could initiate separation
then offsite power is not operable.
Using the example above when evaluating
offsite power would require that the safety bus recover above 93.6%+0.9%+0.5%
or 95% before the earliest time delay for the DVR expires. Since a reset also resets the time delay, multiple DVR drop outs could occur without separation
during load sequencing.
Also, since 92.7% was evaluated
for equipment
protection.
Disagree NRC Staff has the following
clarification
for this position.To meet GDC 17 requirements, the licensee must demonstrate
capability
to safely shut down the plant for all design basis events with the grid voltage at the lowest allowable value as afforded by the transmission
system operator.The voltage studies done for evaluating
offsite power/onsite
power interface
should use minimum expected voltage at the plant/grid
interface
node, demonstrating
adequate voltage for starting and running of plant components
during normal, abnormal and accident conditions.
The expected plant loading at 100% power operation
may be 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 separate analysis 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 anticipated
transient (anticipated
operational
occurrence)
in the unit being analyzed (e.g., unit trip) and simultaneous
shutdown of all other units at that station, whichever
presents the largest load 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 proper voltage for starting and running in all operational
configurations (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 calculations
should provide the Calculations (page basis for their DVR 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 Generation
Company, LLC Background
-Pages 2 and 3 General Comments: The RIS uses terms such as "LVR (loss-of-voltage
relay) voltage setting," "DVR (degraded voltage relay) settings" and "DVR dropout setting" without clarifying
the intent or highlighting
the differences.
IEEE 741-2006, Annex A (Reference
1), has a discussion
on the tolerances
to be considered
and 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 represented
as follows: Analytical
limit: 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)distinctly
different
calculations
are required (four if the site has different
DVR time delays for accident and normal conditions).
These would be at different bus voltage values. The "degraded
voltage relaying design calculations" would be a load flow performed
at the DVR analytical
limit; the "plant 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
Disagree.The terminology
used in the RIS is consistent
with the guidance documents.
The setpoint accuracies
and methodologies
are beyond the scope of this RIS.The point of the RIS was to highlight
that the DVR setting and design interface calculations
have different
requirements.
The staff agrees that there are other calculations
required to demonstrate
the electrical
system design basis.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 1 E 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 1 E 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 1 E 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 1 E) 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 1 E 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 sustained
duration 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 calculated
voltages 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 1 E 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 automatically
initiate or control relays. 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, 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.Proposed resolution:
include missing positions especially
those related to determining
minimum 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 Issues", pg. 6, Item 1. "Degraded Voltage Relaying Design Calculations", Line 5.Southern Nuclear Operating Company The RIS states "The Class 1 6 buses should separate from the offsite power system within a few seconds if an accident occurs coincident
with sustained
degraded voltage conditions." GDC 17 describes
the requirements
for onsite and 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".
These analyses assume Loss of Offsite Power simultaneous
with the event. They do not require assuming degraded grid voltage condition
prior to 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 not believed to be credible.Proposed resolution:
Remove or clarify this statement
since proper offsite system design and operation
renders such simultaneous
postulated
events as incredible.
Disagree.The RIS correctly
states that if an accident signal is received during sustained degraded grid conditions, it may be prudent to separate from the grid as : 1. The duration of degraded conditions
on the grid is unknown 2. It precludes
other complications
such as double sequencing.
Chapter 15 "Accident
Analyses" assumes"Loss of Offsite Power" as a limiting case for safe shutdown in view of the limited power and resources
available
from the onsite power sources. The preferred
power source for all operating
modes and accident related safe shutdown is the offsite source. The DVR provides assurance
that the plant shutdown capability
is not compromised
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 vltaes or aequte 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 two relays with different
settings to pat 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 taken for voltage controlling
equipment
external to accident analyses assume 10 second time the las 1Edisribtio
sysem uchas utoat. delay for onsite power sources to energize the Class 1 E distribution
system such as automatic
safety busses. DVR time delay of 1 Oseconds 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 1 E 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 Le- 48 allow for manual actions Disagree sot This means that manual actions for the used)purposes of analyses of the offsite power 8dso system voltages should not be assumed.see Nos See GL 79-36 for more details.86-96 PSB-1 allows manual actions after first alarm for this at higher voltage.NE, Len., 49 Page 6, DVR Jerry Nicely Section DVR Setting Design Calculations
states: Disagree Setting Design At the DVR dropout setting .the DVR ensures Calculations
adequate operational (starting
and 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 simultaneous
shutdown 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 1 E) 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 1 E 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 "For multi-unit
stations a separate Nexterra analysis should be performed
for each unit assuming (1) an accident in the unit being analyzed and simultaneous
shutdown of all other units at the station; or (2) an anticipated
transient
in 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
"(anticipated
operational
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 "portions
or 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 1 E 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 1 E 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 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
requirements
and voltage studies necessary
for Degraded Voltage Relay (second level undervoltage
protection)
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 "...assuming
all onsite sources of AC powerare not Nuclear One Letter / 6 available, the offsite power system and the onsite distribution
system is of sufficient
capacity and capability
to automatically
start 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 based on 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...Components
are provided adequate voltage provided adequate voltage based on the based on the design of the Class 1 E distribution
design of the plant power distribution
system 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 operating
parameters
of 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
calculation
establishes
operating paragraph
Letter /9 voltage bands for all plant electrical
buses, which ensures that all plant components
and systems (Class IE and Non Safety Related) have proper voltage for starting and running in all operational
configurations (expected
operational
and 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 1 E 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 related buses 22
No. Section of RIS Originator
Specific Comment NRC Resolution
and components
from sustained
degraded voltage 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 1 E 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 automatically
separate 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, ensuring safety related equipment
is supplied with adequate operating voltage (typically
a 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 plant safety related electrical
distribution
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 1 E) 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 1 E 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 "For the purposes of this calculation, no credit paragraph
Letter /19 should be taken for voltage controlling
equipment external to the Class 1E distribution
system such as automatic
load tap changers and 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 1 E 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 "Guidelines
for 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 "For multi-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 simultaneous
shutdown of all other units at the station; or (2) an anticipated
transient (anticipated
operational
occurrence)
in the unit being analyzed (e.g., unit trip) and simultaneous
shutdown of all other units at that station, whichever
presents the largest load 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 automatically
initiate 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 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." 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 related loads 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 terminals
of all safety related actual 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 a sttaff 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 licensed 6 ize,
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.
Des r ' 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 in dztAil regulations
[GDC 17] and generic ip the appli....
I, i .I ......s sad T-As communications
[1977 letter, Generic if appl 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 1 E NRC sta# a.. rtg that Ithe egulatigns
and distribution
system design.19
staff P0 tionA arti.nz'"azd
A the ROi ars This analysis misses the point. First, GDC 17 (like guidance
and ."erzefte-de-ne4
most GDC) is cast in broad, general terms: .Z.,tit-tz
ne',z OF diffzRat p.. itizric with therefore, the fact that the specific positions
the
l F
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 1 E 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 1 E 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
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 1 E 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 1 E 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 Failure from 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  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 UFSAR.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
scenario, which is a malfunction
of an SSC with a different
result than previously
evaluated
pursuant to 10 CFR 50.59, for PVNGS. It could result in core damage regardless
of the time delay value at which the DVR actuation (delayed LOOP) occurs. This is the reason APS precludes
such an event by establishing
appropriate
initial conditions, with TS LCO 3.8.1, Condition
G, through license amendment
123.Disagree.The point being made in the RIS is that setting of the DVR should include consideration
of a coincident
degraded grid and accident in that the time delay chosen for the DVR should support the accident analysis assumptions
consistent
with the NRC1977 letter.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 1 E 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 1 E 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 "For mulfi-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 anticipated
transient
in 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 that station, whichever
presents the largest Calculations", 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
"(anticipated
operational
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 "anticipated
transient
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 1 E 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 (1 st 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 Energy 2 Background:
The use of on-load automatic
load tap 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 nuclear plants to use and take credit for on load automatic
load tap changing transformers
for nuclear plant offsite power supplies to prevent degraded voltage events and improve the voltage transient
ride through capability
of the nuclear plants.Agree Load tap changers help improve voltage regulation
for normal plant operation.
Load tap changers do not help protect safety 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 Energy 3 Comment: Please also consider the italicized
changes below: DVR Setting Design Calculations
Licensee voltage calculations
should provide the basis for their DVR settings, ensuring safety related equipment
is supplied with adequate operating voltage (typically
a 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 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 Agree!fafcizd Ghanges suggested
wer'GORtdOFzd
alOAg With OthOF 8imil!ar.nd dg..fi.d in the RIS wr.... Italicized
changes were not incorporated
in the RIS s...e.... .o..r.. s.w.... o.. .o.. s.. n wan.....since mhe comments were riot consistent
with the staff's existing guidance for DVR settings.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 electrical
distribution
system, the DVR ensures that all safety related equipment
can continue to operate at the degraded voltage relay drop out setting if previously
in service, small loads will not be damaged if successfully
started at the 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 larger loads will not be damaged or trip on overload/protective
relaying 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 degraded voltage source before the overloads
and/or protective
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 degraded voltage from occurring
and thus, by definition, should not be included in a bottom up analysis to determine minimum voltage requirements
for the safety related loads. 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 degraded voltage relay drop out setting if previously
in service, small loads will not be damaged if successfully
started at the degraded voltage without DVR time out, and larger loads will not be damaged or trip on overload/protective
relaying if starting the equipment
results in sustained
degraded voltage for the duration of the DVR time delay resulting
in separation
from offsite power and realignment
to the emergency
onsite power supply. 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 1 E 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."Contacts" was deleted.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 wt;h oher sim -la basis accidents, abnormal operational
occurrence, commaiti rzezizvd fro' other
and reactor trips. The licensee's
voltage And d in the RiS riev!ir.etjalici.._
calculations
should provide the basis for proper changes were not incorporated
in the 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
Femr.-tc from ether qtAktIhclder
network connection.
This transmission
And nlrwfied nR the P.IS
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 and periodically
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 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.3. Licensees
were required to change their operating
license because the staff position.However, this in and of itself, does not change the licensees'
Current Licensing
Basis.4. The "1977" letters apply only to addressees, i.e., plants licensed before 1977."Adequacy
of Station Electric Distribution
System Voltages" 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.Disagree NRC staff does not agree with this position.As a result of these Millstone
events, the NRC requested
that all licensees
implement degraded protection
as described
in the 1977 Letter to ensure automatic
protection
of safety buses and loads. This Letter provides staff posilie uuidance, 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 Design Criteria 17 (GDC 17).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 1 E 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 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 cannot predict future operating
conditions.
Consequently, the DVR can't distinguish
between voltage transients
that are expected to recover and those that are not. Therefore, in the context of the original NRC position (i.e. Point #1), I believe the term spurious was in the context of false signals from within the DVR instrumentation
and not any group of bus voltage transients.
The IEEE 308 requirement
that RIS Page 8, Item (i) is trying to convey is "The preferred
power supply shall be capable of starting and operating
all required loads." accident conditions.
NRC Staff agrees with commenter's
position on use of the term spurious with respect to the design of the DVR scheme to prevent false actuations
due to DVR component failures of miss-operations
NRC Staff agrees with the commenter's
position that the intent of item i) is to specify that the preferred
power supply is able to start and run all required 1E equipment
in accordance
with its voltage requirements
while not separating
Backup power CBrian Wilson, 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)
RESPONSES
TO NEI 3-2-2-11 BACKFITTING
COMMENTS RIS On Adequacy of Station Electric Distribution
Voltages Comment: The RIS represents
an NRC attempt to standardize
varied approaches
to providing
protection
during degraded grid voltage conditions, as currently
memorialized
in the licensing
bases of individual
plants. However, given the complex regulatory
and licensing
history associated
with providing
degraded grid voltage protection
at each plant, a conclusion
that the guidance in the proposed RIS is "consistent
with" 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 As the NRC cUrrcRtl'y
has no
way of easily...Pi.. .,nd reviowingas
it is difficult
for the NRC to efficiently
compile and review the licenses bases of 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.
Formatted:
Font: Italic, Underline Formatted:
Centered Formatted:
Centered The NrC holia-,e n moren irnsi -nro rh iý if the NRr, hns nenpr~iiv
maintninpd
a rnnsiistpnt
nosition for at least-d no c eas a!ition) and has ir f oosition.
and i nitifn In m , t manner, then the NRC may issue mn in connection
with any NRC action which imposes the cuidance on a licensee ý) imposition
4 action may he ;notice of vinltin nr i rthinqs, a NRC determination
of a license amen ice of an order directing
the licensee to comply isinQ history for that plant can be compiled and ackfitting
The NRC-the issuance of a In this manner the specific NRC's r I hv the NR. as nart of the....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 flC..17 -1 .de iraded voltage orotection.
Based upon that review, the voltage Protection
has been consistent
over time.)not constitute
neneric backfittinl.
In addition, the NRC j Formatted:
Font: 9 pt Formatted:
Font: Italic Formatted:
Font color: Auto Formatted:
Font: 9 pt I 5 Dresented
in I has reviewed its records and believes that (with one exceotion
which is being dealt with in a plant-specific
manner, I, it position on a plant-si t and is nrenarinn
the ;,basis. The?y in the process of applyinq!d bv the Backfit Rule Hence s that n oft I I t appropriate.
Gonsistent
P004-4- (o noer, than the N RC fl Gonn1 h ccwi th any--K101, maryi-1D? , I Ca,'Hc
irri 3 .0 Ar- fr t4 An 1 and t Formatted:
Font; (Default)
Arial, 9 pt-that Formatted:
Font: (Default)
Arial, 9 pt, Not Superscript/
Subscript-UV F9r thiS RIS, the NRC rcvIPWAGIc
Mhc Fegulatzr~y
guidanse and NRC practice in this area, and cencluded
that the guiane n te ISis consistent
iAwith the NRG'c regulations
and 6taff guidance.
as well as tho AIRG' approval at Formatted:
Font: (Default)
Anal, 9 pt{ Formatted:
Font: (Default)
Arial, 9 pt, Not If I, ,, ,/ / ý a uper.sc lpL/ Subscript If the NRC prepared a detailed discussion
of a plant's licensing
bases to support the issuance of guidance, then it, Formatted:
Font: (Default)
Anal, 9 pt, 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 52
 
,.n ,,3rioue ,,ocn,,,i.g
twltr
wnfcn a, oe',,n, o3'a;. w. in J pcmns' apocsic I). Hence, thC NRCccu~ plnt ....fi cv .....o, , cf backfitting
impkoiot~ns
of thiz R~S C. apppepripa.e.
The NRC emphasizes
that this approach to addressing
backfitting
in connection
with the issuance of guidance (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 represent
backfitting.
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 individual
plant's NRC-approved
voltage protection
scheme.(NEI -pp.6-7) (See NRC Comment/Resolution
table item No. 96)NRC Response:
In general, the NRC agrees with the comment that many (but not all) of the GDC are cast in broad, general, performance-based
language.
However, the NRC disagrees
with the comment's
implicit assertion
that 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 separate and independent
basis for that licensee to invoke backfitting
protection
when the NRC proposes to impose that NRC position on that licensee.3 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,'
tWAt is 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 Operatmg C.mpC,.n, the l fth, Hath PlanM (,,L 111903h0)The situation
involving
the imposition
of a new NRC position on an acceptable
way of complying
with GDC-17 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).
53
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 reactor licensees, 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
occurrence
of a safety injection
signal...should
immediately
separate the Class 1 E 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 established
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 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.54
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 grid recovery (Long time Delay.) Causes alarm and Time delay is bypassed on SI signal if a subsequent
SI occurs. Provide adequate time sofor plant or grid operator to take manual actions.fi c a n t ly I l -nDVR (BTP PSB-1) DVR-2 Protection
with short time Sbdmdelay
to rideout the motor starting transients.
qired at equipment
terminal Ensures minimum voltage required for all all safety related equipment
equipment
to prevent control fuse blowing, relay lockout, contactor
opening etc., concurrent
DVR-2 rcondition
I S sianal causes relav to time out if Alarm a iý,n if h 19 '.setpo DVR set pýoltaqe re to operate the voltage doesn't within the time delay and s transfers
to onsite power system.OR 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 1 E equipment.
Large 1 E 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, 55
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.-ti fie 1 terms 4f 1i autolmdat
protcotio
oW the las Eeqipme tn dtion t80 allowg OR for Qoror 4 a ctions(i psil) See DVR1 ad 1 -2 relay aQnd time deays delay hic d 6n Fi 1 -w- is 1 jin accorn w ithot 4T4 PSB-1sotaffpGoRtod
is an Iacc design to W eattgoe Folfos"g ition iOln'; it 4t1o oprtpof hc ...od tW eo.orh seletion of9voltage0
tnd tme elay sitpointi
syhall bhoded bet f''trtiomaly
o fpthog fper t11W voltage po 6y@4044.-
R6166 aRd jW64t4604tor
WRnWx we P-o"'d 'r6 o.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 y levend time delay would not s llb e cperston atonroe This appcaro to bo a row oNR pot 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 1 E 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~ Lo th acua~~la~.~floen .TedrRRL soc~aty xcldesmanua[lo
stO=ied~ding
under the Otsitel~rnsile
Design Interface
Calculations
whereas the BTP PSB-1 allows fQr Manual actmio to avoid Separation
comn offsite ~ower.herefore, there is no conflict between the RIS and BTP PSB-1.Comment: Given the variability
in NRC's generic communications
and guidance, the draft RIS' statement
that 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-approved
protection
scheme (and thereby constitute
backfitting), (NEI -p. 7)NRC Response:
As discussed
above in response to NEI- pp.4-5, while the NRC agrees that there is some.variability" in NRC's communications
and guidance on degraded voltage protection, the NRC does not agree 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.56
}}

Revision as of 13:57, 26 January 2019

Rev. 1 - Adequacy of Station Electric Distribution System Voltages (Track Changes)
ML11357A142
Person / Time
Issue date: 12/29/2011
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)
v • d • e


See also: RIS 2011-12

Text

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 Federal Regulations

(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 1 E buses are supplied by the offsite power system, sustained

degraded voltage conditions

on ML-I 2222A.1 36ML1 13050583

RIS 2011-12,_Rev.

1 Page 2 of 11 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 1 E systems and equipment, such as spurious load shedding of Class 1 E loads from the standby diesel generators

and spurious separation

of Class 1 E 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 Page 3 of 11 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 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.(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 1 E 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 Page 4 of 11 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 Page 5 of 11 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.Page 6 of 11 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 1 E 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 ISSUES 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 Page 7 of 11 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 1 E 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 1 E 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) 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.

RIS 2011-12,_Rev.

1 Page 8 of 11 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 1 E 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 Page 9 of 11 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 Page 10 of 11 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 Page 11 of 11 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.Laura A. Dudes, Director A'R by RNeISon fGr Timothy J. McGinty, Director Division of Policy and Rulemakina

Division of Construction

Inspection

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

cf ,N,-:!:ar ReaJ!3tion

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 Page 11 of 11 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 Timothy J McGintv~ Director Laura A Dude Direactor flivi~inn

nf Pnlirv ~ncI RiiI~m~kinn

Division of Construction

Inspection

Division of Policv and Rulemakinn

~nnr mr-afainrnI

IDrr% rurmr r~ffie-m rf IMeLoa Pnnfn Prma "Intinn e M. %I/ tII4 f4 IISIBS.% IFkAh~~II*~%l.I

I~ i~L ~Office of New Reactor Timothy j. I1;GGinty, Dilroao Wiwi I F W MI MUM! Morti! E 9 cJrOn P1'_rGIAucae

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_ 1 1 11 1. 1 1 OFFICE NAME DATE NRO LDudes 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.ML110820342)

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 lower than the initial value, then DVR reset cannot occur.Many utilities

use the ABB 27N with harmonic filter which has a minimum 0.5% reset. Thus, with a setting of 93.6% +/- 0.9%, dropout could be as low as 92.7%. However, for motors causing more than 0.5% voltage dip at initial start, even if the voltage at the beginning

of the event was 93.2% and a load was started, then DVR will dropout and never reset causing a separation.

A clarification

that allows evaluation

of motor starting as well-as other conditions

is: If the DVR could possibly not cause separation

then the required safety functions

must be performed

successfully.

Thus, depending

on the design of the plant, a voltage value for beginning the event with all required starts could be determined

by an iterative

process.If the offsite power has adequate capacity and capability, any voltage just above the DVR setpoint should not separate the offsite power source from the safety bus when starting large motors. The grid voltage is expected to recover.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).

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 ISSUES-- 2.Offsite/Onsite

Design Interface Calculations(page

7)Dominion Resources Services, Inc This section contains elements that are too prescriptive.

Many analyses will show that the unit loads/sequences

assessed for determination

of DVR setpoint adequacy for equipment

protection

are the same as those for evaluating

offsite power.Since evaluating

offsite power always involves higher voltages, it is clear the equipment

will function and providing

terminal voltages for this equipment

is bounded by DVR adequacy analysis.A clarification

that helps frame adequate analysis is: If the DVR could initiate separation

then offsite power is not operable.

Using the example above when evaluating

offsite power would require that the safety bus recover above 93.6%+0.9%+0.5%

or 95% before the earliest time delay for the DVR expires. Since a reset also resets the time delay, multiple DVR drop outs could occur without separation

during load sequencing.

Also, since 92.7% was evaluated

for equipment

protection.

Disagree NRC Staff has the following

clarification

for this position.To meet GDC 17 requirements, the licensee must demonstrate

capability

to safely shut down the plant for all design basis events with the grid voltage at the lowest allowable value as afforded by the transmission

system operator.The voltage studies done for evaluating

offsite power/onsite

power interface

should use minimum expected voltage at the plant/grid

interface

node, demonstrating

adequate voltage for starting and running of plant components

during normal, abnormal and accident conditions.

The expected plant loading at 100% power operation

may be 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 separate analysis 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 anticipated

transient (anticipated

operational

occurrence)

in the unit being analyzed (e.g., unit trip) and simultaneous

shutdown of all other units at that station, whichever

presents the largest load 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 proper voltage for starting and running in all operational

configurations (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 calculations

should provide the Calculations (page basis for their DVR 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 Generation

Company, LLC Background

-Pages 2 and 3 General Comments: The RIS uses terms such as "LVR (loss-of-voltage

relay) voltage setting," "DVR (degraded voltage relay) settings" and "DVR dropout setting" without clarifying

the intent or highlighting

the differences.

IEEE 741-2006, Annex A (Reference

1), has a discussion

on the tolerances

to be considered

and 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 represented

as follows: Analytical

limit: 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)distinctly

different

calculations

are required (four if the site has different

DVR time delays for accident and normal conditions).

These would be at different bus voltage values. The "degraded

voltage relaying design calculations" would be a load flow performed

at the DVR analytical

limit; the "plant 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

Disagree.The terminology

used in the RIS is consistent

with the guidance documents.

The setpoint accuracies

and methodologies

are beyond the scope of this RIS.The point of the RIS was to highlight

that the DVR setting and design interface calculations

have different

requirements.

The staff agrees that there are other calculations

required to demonstrate

the electrical

system design basis.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 1 E 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 1 E 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 1 E 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 1 E) 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 1 E 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 sustained

duration 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 calculated

voltages 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 1 E 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 automatically

initiate or control relays. 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, 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.Proposed resolution:

include missing positions especially

those related to determining

minimum 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 Issues", pg. 6, Item 1. "Degraded Voltage Relaying Design Calculations", Line 5.Southern Nuclear Operating Company The RIS states "The Class 1 6 buses should separate from the offsite power system within a few seconds if an accident occurs coincident

with sustained

degraded voltage conditions." GDC 17 describes

the requirements

for onsite and 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".

These analyses assume Loss of Offsite Power simultaneous

with the event. They do not require assuming degraded grid voltage condition

prior to 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 not believed to be credible.Proposed resolution:

Remove or clarify this statement

since proper offsite system design and operation

renders such simultaneous

postulated

events as incredible.

Disagree.The RIS correctly

states that if an accident signal is received during sustained degraded grid conditions, it may be prudent to separate from the grid as : 1. The duration of degraded conditions

on the grid is unknown 2. It precludes

other complications

such as double sequencing.

Chapter 15 "Accident

Analyses" assumes"Loss of Offsite Power" as a limiting case for safe shutdown in view of the limited power and resources

available

from the onsite power sources. The preferred

power source for all operating

modes and accident related safe shutdown is the offsite source. The DVR provides assurance

that the plant shutdown capability

is not compromised

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 vltaes or aequte 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 two relays with different

settings to pat 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 taken for voltage controlling

equipment

external to accident analyses assume 10 second time the las 1Edisribtio

sysem uchas utoat. delay for onsite power sources to energize the Class 1 E distribution

system such as automatic

safety busses. DVR time delay of 1 Oseconds 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 1 E 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 Le- 48 allow for manual actions Disagree sot This means that manual actions for the used)purposes of analyses of the offsite power 8dso system voltages should not be assumed.see Nos See GL 79-36 for more details.86-96 PSB-1 allows manual actions after first alarm for this at higher voltage.NE, Len., 49 Page 6, DVR Jerry Nicely Section DVR Setting Design Calculations

states: Disagree Setting Design At the DVR dropout setting .the DVR ensures Calculations

adequate operational (starting

and 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 simultaneous

shutdown 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 1 E) 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 1 E 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 "For multi-unit

stations a separate Nexterra analysis should be performed

for each unit assuming (1) an accident in the unit being analyzed and simultaneous

shutdown of all other units at the station; or (2) an anticipated

transient

in 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

"(anticipated

operational

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 "portions

or 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 1 E 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 1 E 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 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

requirements

and voltage studies necessary

for Degraded Voltage Relay (second level undervoltage

protection)

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 "...assuming

all onsite sources of AC powerare not Nuclear One Letter / 6 available, the offsite power system and the onsite distribution

system is of sufficient

capacity and capability

to automatically

start 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 based on 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...Components

are provided adequate voltage provided adequate voltage based on the based on the design of the Class 1 E distribution

design of the plant power distribution

system 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 operating

parameters

of 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

calculation

establishes

operating paragraph

Letter /9 voltage bands for all plant electrical

buses, which ensures that all plant components

and systems (Class IE and Non Safety Related) have proper voltage for starting and running in all operational

configurations (expected

operational

and 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 1 E 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 related buses 22

No. Section of RIS Originator

Specific Comment NRC Resolution

and components

from sustained

degraded voltage 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 1 E 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 automatically

separate 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, ensuring safety related equipment

is supplied with adequate operating voltage (typically

a 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 plant safety related electrical

distribution

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 1 E) 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 1 E 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 "For the purposes of this calculation, no credit paragraph

Letter /19 should be taken for voltage controlling

equipment external to the Class 1E distribution

system such as automatic

load tap changers and 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 1 E 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 "Guidelines

for 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 "For multi-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 simultaneous

shutdown of all other units at the station; or (2) an anticipated

transient (anticipated

operational

occurrence)

in the unit being analyzed (e.g., unit trip) and simultaneous

shutdown of all other units at that station, whichever

presents the largest load 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 automatically

initiate 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 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." 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 related loads 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 terminals

of all safety related actual 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 a sttaff 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 licensed 6 ize,

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.

Des r ' 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 in dztAil regulations

[GDC 17] and generic ip the appli....

I, i .I ......s sad T-As communications

[1977 letter, Generic if appl 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 1 E NRC sta# a.. rtg that Ithe egulatigns

and distribution

system design.19

staff P0 tionA arti.nz'"azd

A the ROi ars This analysis misses the point. First, GDC 17 (like guidance

and ."erzefte-de-ne4

most GDC) is cast in broad, general terms: .Z.,tit-tz

ne',z OF diffzRat p.. itizric with therefore, the fact that the specific positions

the

l F

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 1 E 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 1 E 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

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 1 E 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 1 E 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 Failure from 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 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 UFSAR.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

scenario, which is a malfunction

of an SSC with a different

result than previously

evaluated

pursuant to 10 CFR 50.59, for PVNGS. It could result in core damage regardless

of the time delay value at which the DVR actuation (delayed LOOP) occurs. This is the reason APS precludes

such an event by establishing

appropriate

initial conditions, with TS LCO 3.8.1, Condition

G, through license amendment

123.Disagree.The point being made in the RIS is that setting of the DVR should include consideration

of a coincident

degraded grid and accident in that the time delay chosen for the DVR should support the accident analysis assumptions

consistent

with the NRC1977 letter.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 1 E 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 1 E 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 "For mulfi-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 anticipated

transient

in 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 that station, whichever

presents the largest Calculations", 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

"(anticipated

operational

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 "anticipated

transient

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 1 E 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 (1 st 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 Energy 2 Background:

The use of on-load automatic

load tap 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 nuclear plants to use and take credit for on load automatic

load tap changing transformers

for nuclear plant offsite power supplies to prevent degraded voltage events and improve the voltage transient

ride through capability

of the nuclear plants.Agree Load tap changers help improve voltage regulation

for normal plant operation.

Load tap changers do not help protect safety 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 Energy 3 Comment: Please also consider the italicized

changes below: DVR Setting Design Calculations

Licensee voltage calculations

should provide the basis for their DVR settings, ensuring safety related equipment

is supplied with adequate operating voltage (typically

a 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 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 Agree!fafcizd Ghanges suggested

wer'GORtdOFzd

alOAg With OthOF 8imil!ar.nd dg..fi.d in the RIS wr.... Italicized

changes were not incorporated

in the RIS s...e.... .o..r.. s.w.... o.. .o.. s.. n wan.....since mhe comments were riot consistent

with the staff's existing guidance for DVR settings.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 electrical

distribution

system, the DVR ensures that all safety related equipment

can continue to operate at the degraded voltage relay drop out setting if previously

in service, small loads will not be damaged if successfully

started at the 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 larger loads will not be damaged or trip on overload/protective

relaying 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 degraded voltage source before the overloads

and/or protective

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 degraded voltage from occurring

and thus, by definition, should not be included in a bottom up analysis to determine minimum voltage requirements

for the safety related loads. 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 degraded voltage relay drop out setting if previously

in service, small loads will not be damaged if successfully

started at the degraded voltage without DVR time out, and larger loads will not be damaged or trip on overload/protective

relaying if starting the equipment

results in sustained

degraded voltage for the duration of the DVR time delay resulting

in separation

from offsite power and realignment

to the emergency

onsite power supply. 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 1 E 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."Contacts" was deleted.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 wt;h oher sim -la basis accidents, abnormal operational

occurrence, commaiti rzezizvd fro' other

and reactor trips. The licensee's

voltage And d in the RiS riev!ir.etjalici.._

calculations

should provide the basis for proper changes were not incorporated

in the 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

Femr.-tc from ether qtAktIhclder

network connection.

This transmission

And nlrwfied nR the P.IS

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 and periodically

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 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.3. Licensees

were required to change their operating

license because the staff position.However, this in and of itself, does not change the licensees'

Current Licensing

Basis.4. The "1977" letters apply only to addressees, i.e., plants licensed before 1977."Adequacy

of Station Electric Distribution

System Voltages" 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.Disagree NRC staff does not agree with this position.As a result of these Millstone

events, the NRC requested

that all licensees

implement degraded protection

as described

in the 1977 Letter to ensure automatic

protection

of safety buses and loads. This Letter provides staff posilie uuidance, 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 Design Criteria 17 (GDC 17).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 1 E 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 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 cannot predict future operating

conditions.

Consequently, the DVR can't distinguish

between voltage transients

that are expected to recover and those that are not. Therefore, in the context of the original NRC position (i.e. Point #1), I believe the term spurious was in the context of false signals from within the DVR instrumentation

and not any group of bus voltage transients.

The IEEE 308 requirement

that RIS Page 8, Item (i) is trying to convey is "The preferred

power supply shall be capable of starting and operating

all required loads." accident conditions.

NRC Staff agrees with commenter's

position on use of the term spurious with respect to the design of the DVR scheme to prevent false actuations

due to DVR component failures of miss-operations

NRC Staff agrees with the commenter's

position that the intent of item i) is to specify that the preferred

power supply is able to start and run all required 1E equipment

in accordance

with its voltage requirements

while not separating

Backup power CBrian Wilson, 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)

RESPONSES

TO NEI 3-2-2-11 BACKFITTING

COMMENTS RIS On Adequacy of Station Electric Distribution

Voltages Comment: The RIS represents

an NRC attempt to standardize

varied approaches

to providing

protection

during degraded grid voltage conditions, as currently

memorialized

in the licensing

bases of individual

plants. However, given the complex regulatory

and licensing

history associated

with providing

degraded grid voltage protection

at each plant, a conclusion

that the guidance in the proposed RIS is "consistent

with" 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 As the NRC cUrrcRtl'y

has no

way of easily...Pi.. .,nd reviowingas

it is difficult

for the NRC to efficiently

compile and review the licenses bases of 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.

Formatted:

Font: Italic, Underline Formatted:

Centered Formatted:

Centered The NrC holia-,e n moren irnsi -nro rh iý if the NRr, hns nenpr~iiv

maintninpd

a rnnsiistpnt

nosition for at least-d no c eas a!ition) and has ir f oosition.

and i nitifn In m , t manner, then the NRC may issue mn in connection

with any NRC action which imposes the cuidance on a licensee ý) imposition

4 action may he ;notice of vinltin nr i rthinqs, a NRC determination

of a license amen ice of an order directing

the licensee to comply isinQ history for that plant can be compiled and ackfitting

The NRC-the issuance of a In this manner the specific NRC's r I hv the NR. as nart of the....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 flC..17 -1 .de iraded voltage orotection.

Based upon that review, the voltage Protection

has been consistent

over time.)not constitute

neneric backfittinl.

In addition, the NRC j Formatted:

Font: 9 pt Formatted:

Font: Italic Formatted:

Font color: Auto Formatted:

Font: 9 pt I 5 Dresented

in I has reviewed its records and believes that (with one exceotion

which is being dealt with in a plant-specific

manner, I, it position on a plant-si t and is nrenarinn

the ;,basis. The?y in the process of applyinq!d bv the Backfit Rule Hence s that n oft I I t appropriate.

Gonsistent

P004-4- (o noer, than the N RC fl Gonn1 h ccwi th any--K101, maryi-1D? , I Ca,'Hc

irri 3 .0 Ar- fr t4 An 1 and t Formatted:

Font; (Default)

Arial, 9 pt-that Formatted:

Font: (Default)

Arial, 9 pt, Not Superscript/

Subscript-UV F9r thiS RIS, the NRC rcvIPWAGIc

Mhc Fegulatzr~y

guidanse and NRC practice in this area, and cencluded

that the guiane n te ISis consistent

iAwith the NRG'c regulations

and 6taff guidance.

as well as tho AIRG' approval at Formatted:

Font: (Default)

Anal, 9 pt{ Formatted:

Font: (Default)

Arial, 9 pt, Not If I, ,, ,/ / ý a uper.sc lpL/ Subscript If the NRC prepared a detailed discussion

of a plant's licensing

bases to support the issuance of guidance, then it, Formatted:

Font: (Default)

Anal, 9 pt, 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 52

,.n ,,3rioue ,,ocn,,,i.g

twltr

wnfcn a, oe',,n, o3'a;. w. in J pcmns' apocsic I). Hence, thC NRCccu~ plnt ....fi cv .....o, , cf backfitting

impkoiot~ns

of thiz R~S C. apppepripa.e.

The NRC emphasizes

that this approach to addressing

backfitting

in connection

with the issuance of guidance (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 represent

backfitting.

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 individual

plant's NRC-approved

voltage protection

scheme.(NEI -pp.6-7) (See NRC Comment/Resolution

table item No. 96)NRC Response:

In general, the NRC agrees with the comment that many (but not all) of the GDC are cast in broad, general, performance-based

language.

However, the NRC disagrees

with the comment's

implicit assertion

that 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 separate and independent

basis for that licensee to invoke backfitting

protection

when the NRC proposes to impose that NRC position on that licensee.3 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,'

tWAt is 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 Operatmg C.mpC,.n, the l fth, Hath PlanM (,,L 111903h0)The situation

involving

the imposition

of a new NRC position on an acceptable

way of complying

with GDC-17 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).

53

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 reactor licensees, 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

occurrence

of a safety injection

signal...should

immediately

separate the Class 1 E 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 established

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 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.54

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 grid recovery (Long time Delay.) Causes alarm and Time delay is bypassed on SI signal if a subsequent

SI occurs. Provide adequate time sofor plant or grid operator to take manual actions.fi c a n t ly I l -nDVR (BTP PSB-1) DVR-2 Protection

with short time Sbdmdelay

to rideout the motor starting transients.

qired at equipment

terminal Ensures minimum voltage required for all all safety related equipment

equipment

to prevent control fuse blowing, relay lockout, contactor

opening etc., concurrent

DVR-2 rcondition

I S sianal causes relav to time out if Alarm a iý,n if h 19 '.setpo DVR set pýoltaqe re to operate the voltage doesn't within the time delay and s transfers

to onsite power system.OR 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 1 E equipment.

Large 1 E 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, 55

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.-ti fie 1 terms 4f 1i autolmdat

protcotio

oW the las Eeqipme tn dtion t80 allowg OR for Qoror 4 a ctions(i psil) See DVR1 ad 1 -2 relay aQnd time deays delay hic d 6n Fi 1 -w- is 1 jin accorn w ithot 4T4 PSB-1sotaffpGoRtod

is an Iacc design to W eattgoe Folfos"g ition iOln'; it 4t1o oprtpof hc ...od tW eo.orh seletion of9voltage0

tnd tme elay sitpointi

syhall bhoded bet ftrtiomaly

o fpthog fper t11W voltage po 6y@4044.-

R6166 aRd jW64t4604tor

WRnWx we P-o"'d 'r6 o.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 y levend time delay would not s llb e cperston atonroe This appcaro to bo a row oNR pot 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 1 E 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~ Lo th acua~~la~.~floen .TedrRRL soc~aty xcldesmanua[lo

stO=ied~ding

under the Otsitel~rnsile

Design Interface

Calculations

whereas the BTP PSB-1 allows fQr Manual actmio to avoid Separation

comn offsite ~ower.herefore, there is no conflict between the RIS and BTP PSB-1.Comment: Given the variability

in NRC's generic communications

and guidance, the draft RIS' statement

that 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-approved

protection

scheme (and thereby constitute

backfitting), (NEI -p. 7)NRC Response:

As discussed

above in response to NEI- pp.4-5, while the NRC agrees that there is some.variability" in NRC's communications

and guidance on degraded voltage protection, the NRC does not agree 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.56

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