Proposed Generic Communications; Draft NRC Regulatory Issue Summary 2011-XX; Adequacy of Station Electric Distribution System Voltages, 2924-2928 [2011-888]
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[NRC–2011–0013]
Proposed Generic Communications;
Draft NRC Regulatory Issue Summary
2011–XX; Adequacy of Station Electric
Distribution System Voltages
Nuclear Regulatory
Commission.
ACTION: Notice of opportunity for public
comment.
AGENCY:
The U.S. Nuclear Regulatory
Commission (NRC or the Commission)
is issuing this Regulatory Issue
Summary (RIS) to clarify the NRC staff’s
technical position on existing regulatory
requirements and voltage studies
SUMMARY:
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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. No specific action or
written response is required.
Comment period expires 30 days
after publication. Comments submitted
after this date will be considered if it is
practical to do so, but assurance of
consideration cannot be given except for
comments received on or before this
date.
DATES:
You may submit comments
by any one of the following methods.
Please include Docket ID NRC–2011–
0013 in the subject line of your
comments. Comments submitted in
writing or in electronic form will be
posted on the NRC Web site and on the
Federal Rulemaking Web site
Regulations.gov. Because your
comments will not be edited to remove
any identifying or contact information,
the NRC cautions you against including
any information in your submission that
you do not want to be publicly
disclosed.
The NRC requests that any party
soliciting or aggregating comments
received from other persons for
submission to the NRC inform those
persons that the NRC will not edit their
comments to remove any identifying or
contact information, and therefore, they
should not include any information in
their comments that they do not want
publicly disclosed.
Federal rulemaking Web site: Go to
https://www.regulations.gov and search
for documents filed under Docket ID
NRC–2011–0013. Address questions
about NRC dockets to Carol Gallagher,
telephone: 301–492–3668, e-mail:
Carol.Gallagher@nrc.gov.
Mail comments to: Cindy Bladey,
Chief, Rules, Announcements and
Directives Branch (RADB), Division of
Administrative Services, Office of
Administration, Mail Stop: TWB–05–
B01M, U.S. Nuclear Regulatory
Commission, Washington, DC 20555–
0001, or by fax to RADB at 301–492–
3446.
ADDRESSES:
FOR FURTHER INFORMATION CONTACT:
Kenn A. Miller, Office of Nuclear
Reactor Regulation, Division of
Engineer, U.S. Nuclear Regulatory
Commission, Washington, DC 20555–
0001, telephone: 301–415–3152, e-mail:
kenneth.miller2@nrc.gov.
SUPPLEMENTARY INFORMATION:
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Federal Register / Vol. 76, No. 11 / Tuesday, January 18, 2011 / Notices
NRC Regulatory Issue Summary 2011–
XX; 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 of
design centers and combined operating
licenses under 10 CFR Part 52,
‘‘Licenses, Certificate and Approvals for
Nuclear Power Plants.’’
Intent
The U.S. Nuclear Regulatory
Commission (NRC or the Commission)
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
Network/Offsite/Onsite station electric
power system design bases. This RIS
does not transmit any new requirements
or staff positions. No specific action or
written response is required.
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Background
The events at Millstone and Arkansas
Nuclear One (ANO) that led to the NRC
staff’s position requiring degraded
voltage protection for nuclear power
plant Class 1E (or safety related)
electrical safety buses and expectations
for voltage calculations for the plant
offsite/onsite electric power system
interface, are discussed below as a
reminder of past operating experience.
Millstone Unit 2
Electrical grid events at the Millstone
Station, in July of 1976, have shown that
when the Class 1E buses are supplied by
the offsite power system, sustained
degraded voltage conditions on the grid
can cause adverse effects on the
operation of Class 1E 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. 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 about 2 seconds.
As a result of further evaluation of the
Millstone events, it was also determined
that improper voltage protection logic
can also cause adverse effects on the
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Class 1E systems and equipment, such
as spurious load shedding of Class 1E
loads from the standby diesel generators
and spurious separation of Class 1E
systems from offsite power due to
normal motor starting transients. See
ADAMS Accession No. ML093521388
for more information regarding this
event.
As a result of these Millstone events,
the NRC required all licensees to
implement degraded voltage protection
under Generic Action (Multi-plant
Action B–23) to ensure automatic
protection of safety buses and loads.
Since degradation of the offsite power
system can lead to or cause the failure
of redundant Class 1E safety related
electrical equipment, the NRC required
licensees to install degraded voltage
protection schemes (second level of
voltage protection (Degraded Voltage
Relays (DVRs)) for the onsite power
system) 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.
ML100610489, sent to the licensee for
Peach Bottom Atomic Power Station.
These DVRs were to satisfy the
following criteria:
(a) 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;
(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 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 sources 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
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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 outlined the purpose of the
degraded voltage relays to protect Class
1E safety related buses from sustained
degraded voltage conditions on the
offsite power system under accident and
non-accident conditions in 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), and in
the current BTP 8–6 of the SRP,
Revision 3, ‘‘Adequacy of Station
Electric Distribution System Voltages,’’
dated March 2007, (ADAMS Accession
No. ML070710478).
Arkansas Nuclear One
Another degraded voltage event, in
September of 1978, at Arkansas Nuclear
One (ANO) station demonstrated that
degraded voltage conditions could exist
on the Class 1E buses even with normal
grid voltages, due to deficiencies in
equipment between the grid and the
Class 1E buses or by the starting
transients experienced during certain
accident events not originally
considered in the sizing of these
circuits. Information Notice No. 79–04,
‘‘Degradation of Engineered Safety
Features,’’ (ADAMS Accession No.
ML0311801180) provides additional
information regarding this event.
The NRC staff issued Generic Letter
79–36, August 8, 1979, ‘‘Adequacy of
Station Electric Distribution Systems
voltages’’ (ADAMS Legacy No.
7908230155), expanding its generic
review of the adequacy of electric power
systems for operating nuclear power
plants. Specifically, the NRC required
all licensees to 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 onsite
distribution system is of sufficient
capacity and capability to automatically
start as well as operate all required
safety related loads.
Recent Inspection Findings
Despite lessons learned from past
events, and the generic communications
on degraded voltage protection and
adequate station voltages, NRC
inspectors have identified incorrect
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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 nonaccident 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
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 D.C. 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 (RATs). 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 (ESF) 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 (ADAMS Accession No.
ML042460579), and the staff concluded
that the degraded voltage protection
design at D.C. Cook was inadequate and
as such should be modified to include
degraded voltage protection during
normal operation as well. Because the
NRC staff had approved D.C. 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 dated
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November 9, 2005 (ADAMS Accession
No. ML050680057), the NRC imposed a
facility-specific compliance backfit on
D.C. 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.
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 Title 10 of
the Code of Federal Regulations (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 (EDGs)
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, in that, 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).
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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 loss-of-coolant accident
(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 licensee’s 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 (LER) 2–10–04
(ADAMS Accession No. ML103280505)
based on the determination that certain
plant equipment could be degraded as a
result of lower voltages that may exist
during a postulated design basis loss-ofcoolant event coupled with certain
degraded voltage conditions.
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
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with a design basis accident is not
credible. See NRC Inspection Report
05000528; –529; and –530/2009008,
ADAMS Accession No. ML093240524
regarding the inspection finding. The
NRR technical staff reviewed the issue
in TIA 2010–05 (ADAMS Accession No.
ML102800340). The staff concluded that
the licensee’s calculation must
demonstrate that the trip setpoint
adequately protects the Class 1E
equipment powered by the safety
related bus from a potentially damaging
degraded voltage condition, and the
time delay to transfer from a degraded
offsite source to the standby power
source to support the emergency core
cooling equipment operation must be
consistent with accident analysis time
assumptions, as required by BTP PSB–
1 (NUREG 0800).
Discussion
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 10 CFR Part 50,
General Design Criteria 17. The two
issues are (1) Degraded Voltage Relaying
Design Calculations, and (2) Offsite/
Onsite Design Interface Calculations.
The Degraded Voltage Relaying Design
Calculations establish the necessary
settings of the DVRs to ensure that
required safety related components are
provided adequate voltage based on the
design of the Class 1E distribution
system in the plant and its most limiting
operating configuration. The Offsite/
Onsite Design Interface Calculations
specify the voltage operating parameters
of the plant electrical distribution
system based on the transmission
system (Offsite) operating parameters.
This interface calculation establishes
operating voltage bands for all plant
electrical 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).
Therefore, based on normal grid
operation, 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
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NRC developed Branch Technical
Position (BTP) PSB–1 (revised later to
become BTP 8–6), is to protect Class 1E
safety related buses and components
from sustained degraded voltage
conditions on the offsite power system
coincident with an accident as well as
during non-accident conditions. The
Class 1E buses should separate from the
offsite power system within a few
seconds if an accident occurs coincident
with sustained degraded voltage
conditions. 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. The time delay chosen
should be optimized to ensure that
permanently connected Class 1E loads
are not damaged under sustained
degraded voltage conditions (such as
sustained degraded voltage just above
the LVR voltage setting for the duration
of the DVR time delay setting). The staff
considers degraded voltage conditions
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.
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 or contacts 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 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. For the
purposes of this calculation, no credit
should be taken for voltage controlling
equipment external to the Class 1E
distribution system such as automatic
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load tap changers and capacitor banks.
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 1E 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. The
DVRs should also protect the Class 1E
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 to protect and provide the
required minimum voltage to all safety
related equipment. The time-delay(s)
chosen for DVRs during accident
conditions should meet the accident
analyses assumptions and allow for
proper starting of all Class 1E safety
related equipment. Also, the time delay
chosen for DVRs during non-accident
condition must not cause any
degradation of the safety related
components, including actuation of
their protective devices.
2. Offsite/Onsite Design Interface
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 (from the
transmission network). These
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 all
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
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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 unit).
(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.
(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 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.
(d) All actions the electric power
system is designed to automatically
initiate 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 and automatic
starts of components). All non safety
related plant auxiliary loads should be
included, as applicable, in the plant
loading studies.
(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
VerDate Mar<15>2010
16:24 Jan 14, 2011
Jkt 223001
and at each intermediate bus between
the connection of the offsite circuit 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 component level without separation
from the offsite circuit due to DVR
actuation.
(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, 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.
Backfit Discussion
The NRC has evaluated this RIS
against the criteria of Title 10 of the
Code of Federal Regulations (10 CFR)
Section 50.109, 10 CFR Part 50
Appendix A General Design Criteria 17,
NRC Letter dated June 2, 1977
‘‘Statement of Staff Positions Relative to
Emergency Power Systems for Operating
Reactors,’’ Branch Technical Position
BTP–1 and later BTP 8–6 (both of
NUREG 0800) and Generic Letter 79–36
and determined that it does not
represent a backfit. Specifically, NRC
Staff 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 1E
components and the Class 1E
distribution system design. Under
section 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.
PO 00000
Frm 00051
Fmt 4703
Sfmt 4703
Federal Register Notification
To be done after the public comment
period.
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.).
Contact
Kenn A. Miller, Office of Nuclear
Reactor Regulation, Division of
Engineering, U.S. Nuclear Regulatory
Commission, Washington, DC 20555–
0001, telephone: 301–415–3152, e-mail:
kenneth.miller2@nrc.gov.
End of Draft Regulatory Issue Summary
Documents may be examined, and/or
copied for a fee, at the NRC’s Public
Document Room at One White Flint
North, 11555 Rockville Pike (first floor),
Rockville, Maryland. Publicly available
records will be accessible electronically
from the Agencywide Documents
Access and Management System
(ADAMS) Public Electronic Reading
Room on the Internet at the NRC Web
site, https://www.nrc.gov/NRC/ADAMS/
index.html. If you do not have access to
ADAMS or if you have problems in
accessing the documents in ADAMS,
contact the NRC Public Document Room
(PDR) reference staff at 1–800–397–4209
or 301–415–4737 or by e-mail to
pdr@nrc.gov.
Dated at Rockville, Maryland this 11th day
of January 2011.
For the Nuclear Regulatory Commission.
Roy Mathew,
Acting Chief, Division of Engineering, Office
of Nuclear Reactor Regulation.
[FR Doc. 2011–888 Filed 1–14–11; 8:45 am]
BILLING CODE 7590–01–P
NUCLEAR REGULATORY
COMMISSION
[NRC–2011–0006]
Sunshine Act Notice
Nuclear
Regulatory Commission.
DATE: Weeks of January 17, 24, 31;
February 7, 14, 21, 2011.
PLACE: Commissioners’ Conference
Room, 11555 Rockville Pike, Rockville,
Maryland.
AGENCY HOLDING THE MEETINGS:
E:\FR\FM\18JAN1.SGM
18JAN1
]]>Agencies
[Federal Register Volume 76, Number 11 (Tuesday, January 18, 2011)]
[Notices]
[Pages 2924-2928]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-888]
=======================================================================
-----------------------------------------------------------------------
NUCLEAR REGULATORY COMMISSION
[NRC-2011-0013]
Proposed Generic Communications; Draft NRC Regulatory Issue
Summary 2011-XX; Adequacy of Station Electric Distribution System
Voltages
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of opportunity for public comment.
-----------------------------------------------------------------------
SUMMARY: The U.S. Nuclear Regulatory Commission (NRC or the Commission)
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 Network/
Offsite/Onsite station electric power system design bases. This RIS
does not transmit any new requirements or staff positions. No specific
action or written response is required.
DATES: Comment period expires 30 days after publication. Comments
submitted after this date will be considered if it is practical to do
so, but assurance of consideration cannot be given except for comments
received on or before this date.
ADDRESSES: You may submit comments by any one of the following methods.
Please include Docket ID NRC-2011-0013 in the subject line of your
comments. Comments submitted in writing or in electronic form will be
posted on the NRC Web site and on the Federal Rulemaking Web site
Regulations.gov. Because your comments will not be edited to remove any
identifying or contact information, the NRC cautions you against
including any information in your submission that you do not want to be
publicly disclosed.
The NRC requests that any party soliciting or aggregating comments
received from other persons for submission to the NRC inform those
persons that the NRC will not edit their comments to remove any
identifying or contact information, and therefore, they should not
include any information in their comments that they do not want
publicly disclosed.
Federal rulemaking Web site: Go to https://www.regulations.gov and
search for documents filed under Docket ID NRC-2011-0013. Address
questions about NRC dockets to Carol Gallagher, telephone: 301-492-
3668, e-mail: Carol.Gallagher@nrc.gov.
Mail comments to: Cindy Bladey, Chief, Rules, Announcements and
Directives Branch (RADB), Division of Administrative Services, Office
of Administration, Mail Stop: TWB-05-B01M, U.S. Nuclear Regulatory
Commission, Washington, DC 20555-0001, or by fax to RADB at 301-492-
3446.
FOR FURTHER INFORMATION CONTACT: Kenn A. Miller, Office of Nuclear
Reactor Regulation, Division of Engineer, U.S. Nuclear Regulatory
Commission, Washington, DC 20555-0001, telephone: 301-415-3152, e-mail:
kenneth.miller2@nrc.gov.
SUPPLEMENTARY INFORMATION:
[[Page 2925]]
NRC Regulatory Issue Summary 2011-XX; 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 of design centers and combined
operating licenses under 10 CFR Part 52, ``Licenses, Certificate and
Approvals for Nuclear Power Plants.''
Intent
The U.S. Nuclear Regulatory Commission (NRC or the Commission) 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 Network/Offsite/Onsite
station electric power system design bases. 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 requiring degraded voltage protection for
nuclear power plant Class 1E (or safety related) electrical safety
buses and expectations for voltage calculations for the plant offsite/
onsite electric power system interface, are discussed below as a
reminder of past operating experience.
Millstone Unit 2
Electrical grid events at the Millstone Station, in July of 1976,
have shown that when the Class 1E buses are supplied by the offsite
power system, sustained degraded voltage conditions on the grid can
cause adverse effects on the operation of Class 1E 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. 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 about 2 seconds.
As a result of further evaluation of the Millstone events, it was
also determined that improper voltage protection logic can also cause
adverse effects on the Class 1E systems and equipment, such as spurious
load shedding of Class 1E loads from the standby diesel generators and
spurious separation of Class 1E systems from offsite power due to
normal motor starting transients. See ADAMS Accession No. ML093521388
for more information regarding this event.
As a result of these Millstone events, the NRC required all
licensees to implement degraded voltage protection under Generic Action
(Multi-plant Action B-23) to ensure automatic protection of safety
buses and loads. Since degradation of the offsite power system can lead
to or cause the failure of redundant Class 1E safety related electrical
equipment, the NRC required licensees to install degraded voltage
protection schemes (second level of voltage protection (Degraded
Voltage Relays (DVRs)) for the onsite power system) 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. ML100610489,
sent to the licensee for Peach Bottom Atomic Power Station. These DVRs
were to satisfy the following criteria:
(a) 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;
(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 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 sources
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 outlined the purpose of the degraded voltage relays to
protect Class 1E safety related buses from sustained degraded voltage
conditions on the offsite power system under accident and non-accident
conditions in 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), and in the current BTP 8-6 of the SRP,
Revision 3, ``Adequacy of Station Electric Distribution System
Voltages,'' dated March 2007, (ADAMS Accession No. ML070710478).
Arkansas Nuclear One
Another degraded voltage event, in September of 1978, at Arkansas
Nuclear One (ANO) station demonstrated that degraded voltage conditions
could exist on the Class 1E buses even with normal grid voltages, due
to deficiencies in equipment between the grid and the Class 1E buses or
by the starting transients experienced during certain accident events
not originally considered in the sizing of these circuits. Information
Notice No. 79-04, ``Degradation of Engineered Safety Features,'' (ADAMS
Accession No. ML0311801180) provides additional information regarding
this event.
The NRC staff issued Generic Letter 79-36, August 8, 1979,
``Adequacy of Station Electric Distribution Systems voltages'' (ADAMS
Legacy No. 7908230155), expanding its generic review of the adequacy of
electric power systems for operating nuclear power plants.
Specifically, the NRC required all licensees to 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 onsite distribution system
is of sufficient capacity and capability to automatically start as well
as operate all required safety related loads.
Recent Inspection Findings
Despite lessons learned from past events, and the generic
communications on degraded voltage protection and adequate station
voltages, NRC inspectors have identified incorrect
[[Page 2926]]
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
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 D.C. 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 (RATs). 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 (ESF) 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 (ADAMS Accession No.
ML042460579), and the staff concluded that the degraded voltage
protection design at D.C. Cook was inadequate and as such should be
modified to include degraded voltage protection during normal operation
as well. Because the NRC staff had approved D.C. 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 dated November 9, 2005 (ADAMS
Accession No. ML050680057), the NRC imposed a facility-specific
compliance backfit on D.C. 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.
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 Title 10 of the Code of Federal
Regulations (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 (EDGs) 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, in that, 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 loss-
of-coolant accident (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 licensee's 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
(LER) 2-10-04 (ADAMS Accession No. ML103280505) based on the
determination that certain plant equipment could be degraded as a
result of lower voltages that may exist during a postulated design
basis loss-of-coolant event coupled with certain degraded voltage
conditions.
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
[[Page 2927]]
with a design basis accident is not credible. See NRC Inspection Report
05000528; -529; and -530/2009008, ADAMS Accession No. ML093240524
regarding the inspection finding. The NRR technical staff reviewed the
issue in TIA 2010-05 (ADAMS Accession No. ML102800340). The staff
concluded that the licensee's calculation must demonstrate that the
trip setpoint adequately protects the Class 1E equipment powered by the
safety related bus from a potentially damaging degraded voltage
condition, and the time delay to transfer from a degraded offsite
source to the standby power source to support the emergency core
cooling equipment operation must be consistent with accident analysis
time assumptions, as required by BTP PSB-1 (NUREG 0800).
Discussion
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 10 CFR Part 50, General Design Criteria 17. The two issues are (1)
Degraded Voltage Relaying Design Calculations, and (2) Offsite/Onsite
Design Interface Calculations. The Degraded Voltage Relaying Design
Calculations establish the necessary settings of the DVRs to ensure
that required safety related components are provided adequate voltage
based on the design of the Class 1E distribution system in the plant
and its most limiting operating configuration. The Offsite/Onsite
Design Interface Calculations specify the voltage operating parameters
of the plant electrical distribution system based on the transmission
system (Offsite) operating parameters. This interface calculation
establishes operating voltage bands for all plant electrical 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). Therefore, based on normal grid operation, 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 Branch Technical Position (BTP) PSB-1
(revised later to become BTP 8-6), is to protect Class 1E safety
related buses and components from sustained degraded voltage conditions
on the offsite power system coincident with an accident as well as
during non-accident conditions. The Class 1E buses should separate from
the offsite power system within a few seconds if an accident occurs
coincident with sustained degraded voltage conditions. 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.
The time delay chosen should be optimized to ensure that permanently
connected Class 1E loads are not damaged under sustained degraded
voltage conditions (such as sustained degraded voltage just above the
LVR voltage setting for the duration of the DVR time delay setting).
The staff considers degraded voltage conditions 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.
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 or contacts 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 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. For the purposes
of this calculation, no credit should be taken for voltage controlling
equipment external to the Class 1E distribution system such as
automatic load tap changers and capacitor banks. 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 1E 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. The DVRs should also protect the Class
1E 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 to protect and
provide the required minimum voltage to all safety related equipment.
The time-delay(s) chosen for DVRs during accident conditions should
meet the accident analyses assumptions and allow for proper starting of
all Class 1E safety related equipment. Also, the time delay chosen for
DVRs during non-accident condition must not cause any degradation of
the safety related components, including actuation of their protective
devices.
2. Offsite/Onsite Design Interface 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 (from the transmission network). These 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 all 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
[[Page 2928]]
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
unit).
(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.
(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 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.
(d) All actions the electric power system is designed to
automatically initiate 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 and automatic starts of
components). All non safety related plant auxiliary loads should be
included, as applicable, in the plant loading studies.
(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 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 component level without
separation from the offsite circuit due to DVR actuation.
(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, 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.
Backfit Discussion
The NRC has evaluated this RIS against the criteria of Title 10 of
the Code of Federal Regulations (10 CFR) Section 50.109, 10 CFR Part 50
Appendix A General Design Criteria 17, NRC Letter dated June 2, 1977
``Statement of Staff Positions Relative to Emergency Power Systems for
Operating Reactors,'' Branch Technical Position BTP-1 and later BTP 8-6
(both of NUREG 0800) and Generic Letter 79-36 and determined that it
does not represent a backfit. Specifically, NRC Staff 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 1E components and
the Class 1E distribution system design. Under section 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
To be done after the public comment period.
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.).
Contact
Kenn A. Miller, Office of Nuclear Reactor Regulation, Division of
Engineering, U.S. Nuclear Regulatory Commission, Washington, DC 20555-
0001, telephone: 301-415-3152, e-mail: kenneth.miller2@nrc.gov.
End of Draft Regulatory Issue Summary
Documents may be examined, and/or copied for a fee, at the NRC's
Public Document Room at One White Flint North, 11555 Rockville Pike
(first floor), Rockville, Maryland. Publicly available records will be
accessible electronically from the Agencywide Documents Access and
Management System (ADAMS) Public Electronic Reading Room on the
Internet at the NRC Web site, https://www.nrc.gov/NRC/ADAMS/.
If you do not have access to ADAMS or if you have problems in accessing
the documents in ADAMS, contact the NRC Public Document Room (PDR)
reference staff at 1-800-397-4209 or 301-415-4737 or by e-mail to
pdr@nrc.gov.
Dated at Rockville, Maryland this 11th day of January 2011.
For the Nuclear Regulatory Commission.
Roy Mathew,
Acting Chief, Division of Engineering, Office of Nuclear Reactor
Regulation.
[FR Doc. 2011-888 Filed 1-14-11; 8:45 am]
BILLING CODE 7590-01-P
