[Federal Register Volume 70, Number 69 (Tuesday, April 12, 2005)]
[Notices]
[Pages 19125-19132]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E5-1674]
-----------------------------------------------------------------------
NUCLEAR REGULATORY COMMISSION
Proposed Generic Communication; Grid Reliability and the Impact
on Plant Risk and the Operability of Offsite Power
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of opportunity for public comment.
-----------------------------------------------------------------------
SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is proposing to
issue a generic letter (GL) to request that addressees submit
information to the NRC concerning the status of their compliance with
GDC 17, 10 CFR 50.63, 10 CFR 50.65, and plant technical specifications
governing electric power in accordance with 10 CFR 50.54(f). This
request is to obtain information from addressees in four areas: (1) Use
of nuclear power plant/transmission system operator protocols and real
time contingency analysis programs to monitor grid conditions to
determine operability of offsite power systems under plant technical
specifications, (2) use of nuclear power plant/transmission system
operator protocols and real time contingency analysis programs to
monitor grid conditions for consideration in maintenance risk
assessments, (3) offsite power restoration procedures in accordance
with Section 2 of Regulatory Guide 1.155, ``Station Blackout,'' and (4)
losses of offsite power caused by grid failures at a frequency of >= 20
Years in accordance with Regulatory Guide 1.155.
This Federal Register notice is available through the NRC's
Agencywide Documents Access and Management System (ADAMS) under
accession number ML050810504.
DATES: Comment period expires June 13, 2005. 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.
ADDRESSEES: Submit written comments to the Chief, Rules and Directives
Branch, Division of Administrative Services, Office of Administration,
U.S. Nuclear Regulatory Commission, Mail Stop T6-D59, Washington, DC
20555-0001, and cite the publication date and page number of this
Federal Register notice. Written comments may also be delivered to NRC
Headquarters, 11545 Rockville Pike (Room T-6D59), Rockville, Maryland,
between 7:30 am and 4:15 pm on Federal workdays.
FOR FURTHER INFORMATION, CONTACT: John G. Lamb at 301-415-1446 or by e-
mail at [email protected] or Jose Calvo at 301-415-2774 or by e-mail at
[email protected].
SUPPLEMENTARY INFORMATION:
NRC Generic Letter 2005-XX: Grid Reliability and the Impact on Plant
Risk and the Operability of Offsite Power
ADDRESSES: All holders of operating licenses for nuclear power reactors
except those who have permanently ceased operations and have certified
that fuel has been permanently removed from the reactor vessel.
Purpose: In order to determine if compliance is being maintained
with U.S. Nuclear Regulatory Commission (NRC) regulatory requirements
governing electric power for your plant, the NRC is issuing this
generic letter to obtain information from its licensees in four areas:
(1) Use of nuclear power plant/transmission system operator
protocols and real time contingency analysis programs to monitor grid
conditions to determine operability of offsite power systems under
plant technical specifications
(2) Use of nuclear power plant/transmission system operator
protocols and real time contingency analysis programs to monitor grid
conditions for consideration in maintenance risk assessments
(3) Offsite power restoration procedures in accordance with Section
2 of Regulatory Guide 1.155, ``Station Blackout''
(4) Losses of offsite power caused by grid failures at a frequency
of >= 20 Years
[[Page 19126]]
in accordance with Regulatory Guide 1.155.
Pursuant to 10 CFR 50.54(f), addressees are required to submit a
written response to this generic letter.
Background
Based on information obtained from inspections and risk insights
developed by an internal NRC expert panel, and further described below,
the staff is concerned with several conditions associated with
assurance of grid reliability such that compliance with applicable
regulations may not be assured. Use of long term periodic grid studies
and informal communication arrangements to monitor real time grid
operability, potential shortcomings in grid reliability evaluations
performed as part of maintenance risk assessments, lack of
preestablished arrangements identifying local grid power sources and
transmission paths, and potential elimination of grid events from
operating experience are some conditions that could potentially impact
compliance. The staff identified these issues as a result of
considering the August 14, 2003 blackout event.
On August 14, 2003, the largest power outage in U.S. history
occurred in the Northeastern United States and parts of Canada. Nine
U.S. nuclear power plants (NPPs) tripped. Eight of these, along with
one NPP that was already shut down, lost offsite power. The length of
time until power was available to the switchyard ranged from
approximately 1 hour to six and one-half hours. Although the onsite
emergency diesel generators (EDGs) functioned to maintain safe shutdown
conditions, this event was significant in terms of the number of plants
affected and the duration of the power outage.
The loss of all alternating current (AC) power to the essential and
nonessential switchgear buses at a NPP involves the simultaneous loss
of offsite power (LOOP), turbine trip, and the loss of the onsite
emergency power supplies (typically EDGs). Such an event is referred to
as a station blackout (SBO). Risk analyses performed for NPPs indicate
that the loss of all AC power can be a significant contributor to the
core damage frequency. Although NPPs are designed to cope with a LOOP
event through the use of onsite power supplies, LOOP events are
considered precursors to SBO. An increase in the frequency or duration
of LOOP events increases the probability of core damage.
The NRC issued a regulatory issue summary (RIS 2004-5, ``Grid
Operability and the Impact on Plant Risk and the Operability of Offsite
Power,'' dated April 15, 2004) to advise NPP addressees of the
requirements in Section 50.65 of Title 10 of the Code of Federal
Regulations (10 CFR 50.65), ``Requirements for monitoring the
effectiveness of maintenance at nuclear power plants''; 10 CFR 50.63,
``Loss of all alternating current power''; 10 CFR Part 50, Appendix A,
General Design Criterion (GDC) 17, ``Electric power systems''; and
plant technical specifications on operability of offsite power. In
addition, the NRC issued Temporary Instruction (TI) 2515/156, ``Offsite
Power System Operational Readiness,'' dated April 29, 2004, which
instructed the regional offices to perform follow up inspections at
plant sites on the issues identified in the RIS. The NRC needs
additional information from its licensees in the four areas identified
above in order to determine if regulatory compliance is being
maintained.
Applicable Regulatory Requirements
GDC 17 and Plant Technical Specifications (TSs)
For NPPs licensed in accordance with the GDC in Appendix A to 10
CFR Part 50, the design criteria for onsite and offsite electrical
power systems are provided in GDC 17. For NPPs not licensed in
accordance with the GDC in Appendix A, the applicable design criteria
are provided in the updated final safety analysis report. These reports
set forth criteria similar to GDC 17, which requires, among other
things, that an offsite electric power system be provided to permit the
functioning of certain structures, systems, and components (SSCs)
important to safety in the event of anticipated operational occurrences
and postulated accidents.
The transmission network (grid) is the source of power to the
offsite power system. The final paragraph of GDC 17 requires, in part,
provisions to minimize the probability of the loss of power from the
transmission network given a loss of power generated by the nuclear
power unit. The loss of power generated by the nuclear power unit
(trip) is an anticipated operational occurrence. It is therefore
necessary that the offsite power circuits be designed to be available
following a trip of the unit in order to permit the functioning of SSCs
necessary to respond to the event.
The trip of an NPP, however, can affect the grid so as to result in
a LOOP. Foremost among such effects is a reduction in the plant's
switchyard voltage as a result of the loss of the reactive power supply
to the grid from the NPP's generator. If the voltage is low enough, the
plant's degraded voltage protection could actuate and separate the
plant safety buses from offsite power. A less likely event would be
that the trip of a nuclear plant causes grid instability, potential
grid collapse, and subsequent LOOP due to the loss of the real and/or
reactive power support supplied to the grid from the plant's generator.
In general, plant TSs require the offsite power system to be
operable as part of the limiting condition for operation and specify
what actions to be taken when the offsite power system is not operable.
Plant operators should therefore be aware of (1) the capability of the
offsite power system to supply power, as specified by TS, during
operation and (2) situations that can result in a LOOP following a trip
of the plant. If the offsite power system is not capable of providing
the requisite power in either situation, the system should be declared
inoperable and pertinent plant TS provisions followed.
10 CFR 50.65
Section 50.65(a)(4) requires that licensees assess and manage the
increase in risk that may result from proposed maintenance activities
before performing the maintenance activities. These activities include,
but are not limited to, surveillances, post-maintenance testing, and
corrective and preventive maintenance. The scope of the assessment may
be limited to structures, systems, and components (SSCs) that a risk-
informed evaluation process has shown to be significant to public
health and safety.
In NRC Regulatory Guide (RG) 1.182, the NRC endorsed the February
22, 2000, revision to Section 11 of NUMARC 93-01, Revision 2, as
providing methods that are acceptable for meeting 10 CFR 50.65(a)(4).
The revised Section 11 addressed grid stability and offsite power
availability in several areas. Section 11.3.2.8 states:
Emergent conditions may result in the need for action prior to
conduct of the assessment, or could change the conditions of a
previously performed assessment. Examples include plant
configuration or mode changes, additional SSCs out of service due to
failures, or significant changes in external conditions (weather,
offsite power availability) [emphasis added].
Additionally, Section 11.3.4 states, in part, that ``the assessment
for removal from service of a single SSC for the planned amount of time
may be limited to the consideration of unusual external conditions that
are present or imminent (e.g., severe weather, offsite power
instability)'' [emphasis added].
Accordingly, licensees should perform grid reliability evaluations
as
[[Page 19127]]
part of the maintenance risk assessment required by 10 CFR 50.65 before
taking a risk-significant piece of equipment (including but not limited
to an EDG, a battery, a steam-driven pump, an alternate AC power
source, etc.) out of service to do maintenance activities, including
surveillances, post-maintenance testing, and corrective and preventive
maintenance. The likelihood of LOOP and SBO should be considered in the
maintenance risk assessment, whether quantitatively or qualitatively.
If the grid reliability evaluation indicates that marginally adequate
grid conditions may exist during maintenance activities, the licensee
should consider rescheduling maintenance activities that tend to
increase the LOOP frequency or reduce the capability to cope with a
LOOP or SBO. If there is some overriding need to perform maintenance on
risk-significant equipment under conditions of degraded grid stability,
the licensee should consider alternate equipment protection measures
and compensatory actions to reduce the risk. With regard to conditions
that emerge during a maintenance activity in progress, Section 11.3.2.8
in NUMARC 93-01, Revision 2, states that emergent conditions could
change the conditions of a previously performed risk assessment.
Offsite power availability is one of the examples given of an emergent
condition that could change the conditions of a previously performed
risk assessment. Therefore, licensees should reassess the plant risk in
view of an emergent condition, taking the worsening grid condition into
account. However, this reassessment of the risk should not interfere
with or delay measures to place and maintain the plant in a safe
condition in response to or preparation for those worsening grid
conditions. 10 CFR 50.63
Pursuant to 10 CFR 50.63, ``Loss of all alternating current
power,'' the NRC requires that each NPP licensed to operate be able to
withstand an SBO for a specified duration and recover from the SBO. NRC
Regulatory Guide (RG) 1.155 provides guidance for licensees to use in
developing their approach for complying with 10 CFR 50.63. The RG has a
series of tables that define a set of pertinent plant and plant site
parameters that have been found to affect the likelihood of a plant
experiencing an SBO event of a given duration. Using the tables allows
a licensee to determine a plant's relative vulnerability to SBO events
of a given duration and identify an acceptable minimum SBO coping
duration for the plant. With regard to grid-related losses of offsite
power, Table 4 in RG 1.155 indicates that the following plant sites
should be assigned to Offsite Power Design Characteristic Group P3:
Sites that expect to experience a total loss of offsite power caused
by grid failures at a frequency equal to or greater than once in 20
site-years, unless the site has procedures to recover AC power from
reliable alternative (nonemergency) ac power sources within
approximately one-half hour following a grid failure.
The majority of U.S. NPPs fall into the 4-hour minimum coping
capability category set forth in RG 1.155. Table 2 in RG 1.155,
however, indicates that a typical plant with two redundant EDGs per
nuclear unit should have at least an 8-hour minimum coping duration if
it falls into the P3 group. Therefore, plants that have experienced a
grid-related LOOP since they were evaluated in accordance with the SBO
guidance in RG 1.155 may no longer be consistent with that guidance.
Section 2 of RG 1.155 provides guidance on the procedures necessary
to restore offsite power, including losses following ``grid
undervoltage and collapse.'' Section 2 states: ``Procedures should
include the actions necessary to restore offsite power and use nearby
power sources when offsite power is unavailable.'' These procedures are
a necessary element in minimizing LOOP durations following a LOOP or
SBO event.
Discussion
Use of Nuclear Power Plant/Transmission System Operator Protocols and
Real Time Contingency Analysis Programs To Monitor Grid Conditions To
Determine Operability of Offsite Power Systems Under Plant Technical
Specifications
As discussed above, a licensee's ability to comply with TS
governing offsite power may depend on grid conditions and plant status,
in particular, maintenance being performed on, and inoperability of,
key elements of the plant switchyard and offsite power grid can affect
the operability of the offsite power system, particularly during times
of high grid load and high grid stress. A communication interface with
the plant's transmission system operator (TSO), together with other
local means used to maintain NPP operator awareness of changes in the
plant switchyard and offsite power grid, is important to enable the
licensee to determine the effects of these changes on operability of
the offsite power system. The staff found a good deal of variability in
the TI 2515/156 responses on the use of these NPP/TSO communication
protocols. Some licensees appear to be relying on informal NPP/TSO
communication arrangements and long term grid studies without real time
control of operation to within the limits of the studies to assure
offsite power operability. However, the staff also learned that most
TSOs serving NPP sites now have, or will shortly have, enhanced
computer capability in the form of real time contingency analysis
(RTCAs) programs.
The RTCAs give the TSO the capability to determine the impact of
the loss or unavailability of various transmission system elements
(called contingencies) on the condition of the transmission system. The
transmission systems can generally cope with a number of contingencies
without undue impairment of grid reliability, but it is important for
the NPP operator to know when the transmission system near the NPP can
no longer sustain NPP voltage based on the TSO's analysis of a
reasonable level of contingencies. This knowledge can help the operator
understand the general condition of the NPP offsite power system. In
order to satisfy the maintenance rule, the NPP operator should know the
grid's condition before taking a risk-significant piece of equipment
out of service and monitor it for as long as the equipment remains out
of service.
It is especially important for the NPP operator to know when the
trip of the NPP will result in the loss of offsite power to the plant.
As indicated in RIS 2004-05, a reduction in NPP switchyard voltage due
to a trip is the main cause of a LOOP event. It is important to
understand that the transmission systems can generally tolerate
voltages lower than those required for NPP SSC operability. As a
result, the TSO will not necessarily keep the transmission system
voltage above the level needed for the NPP unless the TSO has been
informed of the needed voltage level, and agreements have been
formalized to maintain the voltage level. It was not always clear from
the data collected in accordance with TI 2515/156 whether the TSO would
notify the NPP of inadequate transmission system contingency voltages
or inadequate voltages required for the NPP SSC operability.
Inadequate NPP contingency post-trip switchyard voltages will
result in TS inoperability of the NPP offsite power system due to
actuation of NPP degraded voltage protection circuits during certain
events that result in an NPP trip. Occasionally NPPs of certain designs
have experienced other inoperabilities under these
[[Page 19128]]
circumstances (e.g., overloaded EDGs or loss of certain safety features
due to interaction with circuit breaker logic). Safety-related motors
may also be started more than once under these circumstances, which
could result in operation outside the motors' specifications and
actuation of overload protection. Unavailability of plant controlled
equipment such as voltage regulators, transformer auto tap changers,
and generator automatic voltage regulation can contribute to the more
frequent occurrence of inadequate NPP post-trip voltages.
The RTCA programs in use by the TSOs, together with properly
implemented NPP/TSO communication protocols, can keep NPP operators
better informed about conditions affecting the NPP offsite power
system. However, the RTCA programs are not always available to the TSO.
This was the case during the period leading up to the August 14, 2003,
blackout; and events have demonstrated the data used in the programs
sometimes do not represent actual conditions and capabilities. These
shortcomings have been offset to some degree by notification of RTCA
unavailability to NPP operators and their subsequent performance of
operability determinations and by verification of the actual post-trip
switchyard voltages following inadvertent NPP trips.
Use of Nuclear Power Plant/Transmission System Operator Protocols To
Monitor Grid Conditions for Consideration in Maintenance Risk
Assessments
As set forth above, grid reliability evaluations should be
performed as part of the maintenance risk assessment required by 10 CFR
50.65 before taking a risk-significant piece of equipment (including
but not limited to an EDG, a battery, a steam-driven pump, an alternate
AC power source, etc.) out of service to do maintenance activities,
including surveillances, post-maintenance testing, and corrective and
preventive maintenance. Further, worsening grid conditions that emerge
during a maintenance activity in progress could affect offsite power
availability, thereby changing the conditions of a previously performed
assessment. A licensee should therefore reassess the plant risk under
such circumstances, taking the worsening grid condition into account.
An internal NRC expert panel convened to obtain short-term grid-related
risk insights found that it is important to have effective NPP
configuration risk management, as required by the Maintenance Rule,
during periods when the grid is degraded. In particular, a potentially
significant increase in NPP risk may occur if equipment required to
prevent and mitigate station blackout is unavailable when the grid is
degraded.
Recent NRC studies have found that, since 1997, LOOP events have
occurred more frequently during the summer (May-October), than before
1997, the probability of a LOOP event due to a reactor trip has also
increased during the summer months, and the durations of LOOP events
have generally increased. The staff is concerned about extended
maintenance activities scheduled for equipment required to prevent and
mitigate station blackout during these months, especially in areas of
the country that experience a high level of grid stress.
The staff found a good deal of variability in the data collected in
accordance with TI 2515/156 regarding grid reliability evaluations
performed before taking risk-significant equipment out of service. Some
NPPs communicate routinely with their TSOs once per shift to determine
grid conditions, while others rely solely upon the TSOs to inform them
of deteriorating grid conditions and do not inquire about grid
conditions prior to taking risk-significant equipment out of service.
Some do not consider the NPP post-trip switchyard voltages in their
evaluations, and some do not coordinate risk-significant equipment
maintenance with their TSOs.
The NPP/TSO communication protocol is a useful tool to obtain the
information necessary for the grid reliability evaluations performed as
part of the maintenance risk assessment required by 10 CFR 50.65 before
a risk-significant piece of equipment is removed from service. Such a
protocol is also useful in conforming to the guidance in NUMARC 9301,
Rev. 2 for reassessing plant risk in light of emergent conditions. As
discussed under the previous topic, the RTCAs available to most TSOs
give them the capability to determine the impact of various
transmission system contingencies on the condition of the transmission
system. It is important that the NPP operator know when the
transmission system near the NPP cannot sustain a reasonable level of
contingencies. The NPP operator should know the general condition of
the NPP offsite power system before removing an SSC from service under
the maintenance rule and for as long as the equipment remains out of
service.
Offsite Power Restoration Procedures in Accordance With Section 2 of
Regulatory Guide 1.155
LOOP events can also have numerous unpredictable initiators, such
as natural events, potential adversaries, human error, or design
problems. Pursuant to 10 CFR 50.63, ``Loss of all alternating current
power,'' the NRC requires that each NPP licensed to operate be able to
withstand a station blackout (SBO) for a specified duration and recover
from the SBO. NRC Regulatory Guide (RG) 1.155 provides NRC guidance for
licensees to use in developing their approaches for complying with 10
CFR 50.63. Section 2 of RG 1.155 provides guidance on the procedures
necessary to restore offsite power, including losses following ``grid
undervoltage and collapse.'' Section 2 states: ``Procedures should
include the actions necessary to restore offsite power and use nearby
power sources when offsite power is unavailable.''
Preestablished agreements with NPP TSOs that identify local power
sources and transmission paths that could be made available to resupply
NPPs following a LOOP event help to minimize the durations of LOOP
events, especially unpredictable LOOP events. Discussions with NPP
licensees indicate that some licensees do not have such agreements in
place, but instead attempt restoration of their EDGs following a
potential SBO. RIS 2004-05 states that NPPs should have procedures
available consistent with the guidance in Section 2 of RG 1.155 for
restoration of offsite power following a LOOP or SBO event.
Losses of Offsite Power Caused by Grid Failures at a Frequency of >= 20
Years in Accordance With Regulatory Guide 1.155
The data collected in accordance with TI2515/156 indicate that some
nuclear power plants have experienced grid-related LOOP events since
the nuclear power plants were initially analyzed in accordance with the
criteria in RG 1.155. The staff is concerned that these nuclear power
plants have not been reanalyzed to determine whether their SBO coping
durations remain consistent with the guidance in RG 1.155 subsequent to
these LOOP events. The staff is also concerned that some plants may be
inappropriately eliminating some of these grid events from their
operating experience data base.
In view of the above, power reactor licensees may depend on
information obtained from their TSOs in order to make operability
determinations for TS compliance; to perform risk assessments under the
maintenance rule; and to assure compliance with the SBO rule.
[[Page 19129]]
Accordingly, the NRC staff is requesting information on such matters
from addresses. The NRC staff has not, however, identified any
corrective actions that might be warranted.
Requested Information
In accordance with 10 CFR 50.54(f), addressees are required to
submit written responses to this generic letter within 60 days of its
date.
In their responses, addressees are requested to answer the
following questions and provide the information to the NRC with respect
to each of their NPPs:
Use of Nuclear Power Plant/transmission System Operator Protocols and
Real Time Contingency Analysis Programs To Monitor Grid Conditions in
Accordance With GDC 17 and To Determine Operability of Offsite Power
Systems Under Plant Technical Specifications
1. General Design Criterion (GDC) 17, ``Electric power systems,''
of Appendix A, ``General Design Criteria for Nuclear Power Plants,'' to
Title 10, Part 50, of the Code of Federal Regulations (CFR) requires,
in part, that licensees minimize the probability of the loss of power
from the transmission network given a loss of power generated by the
nuclear power unit. In order to determine if you have taken the
necessary steps to minimize the probability of loss of offsite power
(LOOP) following a reactor trip in accordance with GDC 17, describe
what formal agreements you have for your transmission system operator
(TSO) to promptly notify you when conditions of the surrounding grid
are such that degraded voltage (i.e., below TS requirements) or LOOP
could occur following a trip of the reactor unit. Would the low
switchyard voltage initiate operation of plant degraded voltage
protection?
Specifically, what is the time period required for the
notification? Do you have procedures to periodically check with the TSO
to determine the grid condition and ascertain any conditions that would
require a notification? Describe the grid conditions that would trigger
a notification.
If you do not have a formal agreement with your TSO, please
describe why you believe you comply with the provisions of GDC 17 as
stated above, or describe what actions you intend to take to establish
the necessary formal agreement with your TSO.
2. GDC 17 requires, in part, that licensees minimize the
probability of the loss of power from the transmission network given a
loss of power generated by the nuclear power unit. In order to
determine if you have taken the necessary steps to minimize the
probability of LOOP following a reactor trip in accordance with GDC 17,
describe how you ensure that the offsite power system will remain
operable following a trip of your NPP.
We are particularly interested in information regarding whether
your NPP's TSO uses a real-time contingency analysis (RTCA) program to
determine grid conditions that would make the NPP offsite power system
inoperable in the event of various contingencies? The type of
information we are interested in includes the following: Does your
NPP's TSO use the RTCA program as the basis for notifying the NPP when
such a condition is identified? Would the RTCA program utilized by your
TSO identify the condition where a trip of the NPP results in
switchyard voltages (immediately and/or long-term) below the minimum TS
requirements and operation of plant degraded voltage protection? How
frequently does the RTCA program update? Provide details of RTCA-
identified contingency conditions that would trigger an NPP
notification from the TSO. Is the NPP notified of periods when the RTCA
program is unavailable to the TSO, and does the NPP conduct an offsite
power system operability determination when such a notification is
received? Subsequent to an unscheduled inadvertent trip of the NPP, are
the resultant switchyard voltages verified by procedure to be bounded
by the voltages predicted by the RTCA?
If a RTCA program is not available to the NPP's TSO, are there any
plans for the TSO to obtain one? If so, on what schedule? If an RTCA
program is not available, does your TSO perform periodic studies to
verify that adequate offsite power capability, including adequate NPP
post-trip switchyard voltages (immediate and/or long-term), will be
available to the NPP over the projected time frame of the study? Are
the key assumptions and parameters of these periodic studies translated
into TSO guidance to ensure that the transmission system is operated
within the bounds of the analyses? If the bounds of the analyses are
exceeded, does this condition trigger the notification provisions
discussed in question 1 above?
If your TSO does not use, or you do not have access to the results
of a RTCA program, or that your TSO does not perform and make available
to you periodic studies that determine the adequacy of offsite power
capability; please describe why you believe you comply with the
provisions of GDC 17 as stated above, or describe what actions you
intend to take to ensure that the offsite power system will be
sufficiently reliable and remain operable with high probability
following a trip of your NPP.
3. GDC 17 requires, in part, that licensees minimize the
probability of the loss of power from the transmission network given a
loss of power generated by the nuclear power unit. NPP TS requirements
also require that the plant's offsite power system be operable as part
of the plant's limiting conditions of operation. In order to determine
if you have taken the necessary steps to minimize the probability of
LOOP following a reactor trip in accordance with GDC 17 and your plant
TS, describe how you ensure that the NPP's offsite power system and
safety-related components will remain operable when degraded switchyard
voltages are present.
Specifically, when the TSO notifies the NPP operator a trip of the
NPP would result in switchyard voltages (immediately and/or long term)
below TS minimum requirements and would result in operation of plant
degraded voltage protection, is the NPP offsite power system declared
inoperable under the plant TSs? If not, why not? If onsite safety-
related equipment (e.g., emergency diesel generators or safety-related
motors) are lost and incapable of performing their required safety
functions as a result of responding to an emergency actuation signal
during this condition, are they declared inoperable as well? If not,
why not? Do you evaluate onsite safety-related equipment to determine
whether it will operate as designed during this condition? When the NPP
is notified by the TSO of other grid conditions that may impair the
capability or availability of offsite power, are any plant TS action
statements entered? If so, please identify them. If you believe your
plant TS does not require you to declare your offsite power system or
safety-related equipment inoperable in any of the aforementioned
scenarios, describe why you believe you comply with the provisions of
GDC 17 and your plant TS as stated above, or describe what actions you
intend to take to ensure that the offsite power system and safety-
related components will remain operable when degraded switchyard
voltages are present.
4. GDC 17 requires, in part, that licensees minimize the
probability of the loss of power from the transmission network given a
loss of power generated by the nuclear power unit. NPP TS requirements
also require that the plant's offsite power system be operable as part
of the plant's limiting conditions
[[Page 19130]]
of operation. In order to determine if you have taken the necessary
steps to minimize the probability of LOOP following a reactor trip in
accordance with GDC 17 and your plant TS, describe how you ensure that
the offsite power system will remain operable following a trip of your
NPP.
Specifically, do the NPP operators have any guidance in plant TS
Bases sections, the Final Safety Analysis Report, or plant procedures
regarding situations where the condition of plant-controlled or -
monitored equipment (e.g., voltage regulators, auto tap changing
transformers, capacitors, static VAR compensators, main generator
voltage regulators, etc.) can adversely affect the operability of the
NPP offsite power system? If your TS Bases sections, the Final Safety
Analysis Report, or plant procedures do not provide guidance regarding
situations where the condition of plant-controlled or -monitored
equipment can adversely affect the operability of the NPP offsite power
system, describe why you believe you comply with the provisions of GDC
17 and the plant TS as stated above, or describe what actions you
intend to take to ensure that guidance exists to address situations
where the condition of plant-controlled or -monitored equipment can
adversely affect the operability of the NPP offsite power system.
Use of Nuclear Power Plant/Transmission System Operator Protocols To
Monitor Grid Conditions for Consideration in Maintenance Risk
Assessments Required by 10 CFR 50.65
5. 10 CFR 50.65(a)(4) requires that licensees assess and manage the
increase in risk that may result from proposed maintenance activities
before performing the maintenance activities. As set forth above, grid
reliability evaluations should be performed as part of the maintenance
risk assessment required by 10 CFR 50.65 before taking a risk-
significant piece of equipment (including but not limited to an EDG, a
battery, a steam-driven pump, an alternate AC power source, etc.) out
of service to do maintenance activities, including surveillances, post-
maintenance testing, and corrective and preventive maintenance. In
order to determine if you have taken the necessary steps to assess and
manage the increase in risk that may result from proposed maintenance
activities before performing the maintenance activities, please
describe how you perform the grid reliability evaluations as part of
the maintenance risk assessment required by 10 CFR 50.65.
Specifically, is a grid reliability evaluation performed at your
NPP as part of the maintenance risk assessment required by 10 CFR
50.65, before taking a risk-significant piece of equipment (including
an EDG, a battery, a steam-driven pump, an alternate AC power source,
etc.) out of service to do maintenance activities, including
surveillances, post-maintenance testing, and corrective and preventive
maintenance? Are seasonal variations in the probability of a LOOP at
your plant site considered in the evaluation? Is the summer (May-
October) a period of peak stress on the grid surrounding your NPP site?
Do you contact the TSO to determine current and anticipated grid
conditions as part of the grid reliability evaluation performed prior
to taking risk-significant equipment out of service? Do you use a
formal agreement or use formal procedures with your TSO, or do you
contact the TSO periodically over the course of the out-of-service
condition to check for a worsening grid condition that could emerge
during a maintenance activity in progress? Is the TSO expected to
notify the NPP of such a condition?
If a grid reliability evaluation that includes consideration of
seasonal variations in LOOP probability is not performed as part of the
maintenance risk assessment required by 10 CFR 50.65, and a formal
agreement with the TSO or formal procedures to aid in the communication
between the NPP and TSO are nonexistent (i.e., not part of the
maintenance risk assessment required by 10 CFR 50.65), describe why you
believe you comply with the provisions of 10 CFR 50.65(a)(4) as stated
above; or describe what actions you intend to take to ensure that the
increase in risk that may result from proposed maintenance activities
is assessed and managed in accordance with 10 CFR 50.65(a)(4).
6. 10 CFR 50.65(a)(4) requires that licensees assess and manage the
increase in risk that may result from proposed maintenance activities
before performing the maintenance activities. As set forth above, grid
reliability evaluations should be performed as part of the maintenance
risk assessment required by 10 CFR 50.65 before taking a risk-
significant piece of equipment out of service to do maintenance
activities, including surveillances, post-maintenance testing, and
corrective and preventive maintenance. In order to determine if you
have taken the necessary steps to assess and manage the increase in
risk that may result from proposed maintenance activities before
performing the maintenance activities, please describe how you perform
the grid reliability evaluations as part of the maintenance risk
assessment required by 10 CFR 50.65.
Specifically, does the TSO coordinate transmission system
maintenance activities that can have an impact on the NPP operation
with the NPP operator? Does the NPP operator coordinate NPP maintenance
activities that can have an impact on the transmission system with the
TSO? How are these matters accomplished?
If there is no coordination between the NPP operator and the TSO
regarding transmission system maintenance or NPP maintenance
activities, describe why you believe you comply with the provisions of
10 CFR 50.65(a)(4) as stated above, or describe what actions you intend
to take to ensure that the increase in risk that may result from
proposed maintenance activities is assessed and managed in accordance
with 10 CFR 50.65(a)(4).
Offsite Power Restoration Procedures in Accordance With 10 CFR 50.63 as
Developed in Section 2 of Regulatory Guide 1.155
7. Pursuant to 10 CFR 50.63, the NRC requires that each NPP
licensed to operate be able to withstand a SBO for a specified duration
and recover from the SBO. NRC Regulatory Guide (RG) 1.155 provides
guidance for licensees to use in developing their approach for
complying with 10 CFR 50.63. In order to determine if your current
practices are consistent with the SBO requirements of 10 CFR 50.63 as
developed in RG 1.155 please address the following:
Consistent with the recommendations in Section 2 of RG 1.155, it is
expected that you have established an agreement with your plant's TSO
that identify local power sources and transmission paths that could be
made available to resupply your plant following a LOOP event. Briefly
describe any agreement made with the TSO.
If you have not established an agreement with your plant's TSO that
identifies local power sources and transmission paths that could be
made available to resupply your plant following a LOOP event, describe
why you believe you comply with the provisions of 10 CFR 50.63 as
developed in RG 1.155, or describe what actions you intend to take to
establish such an agreement with your plant's TSO.
Losses of Offsite Power Caused by Grid Failures at a Frequency of >=20
Years in Accordance With 10 CFR 50.63 as Developed in Table 4 of
Regulatory Guide 1.155
8. Pursuant to 10 CFR 50.63, the NRC requires that each NPP
licensed to operate be able to withstand a SBO for a specified duration
and recover from
[[Page 19131]]
the SBO. NRC Regulatory Guide (RG) 1.155 provides guidance for
licensees to use in developing their approach for complying with 10 CFR
50.63. In order to determine if your current practices are consistent
with the SBO requirements of 10 CFR 50.63, describe how your NPP
maintains its SBO coping capabilities in accordance with 10 CFR 50.63.
Specifically, has your NPP site experienced a grid-related total
loss of offsite power since its coping duration under 10 CFR 50.63 was
initially determined? If so, has the NPP been reevaluated using the
guidance in Table 4 of RG 1.155 to determine if it should be assigned
to the P3 offsite power design characteristic group? What were the
results of this reevaluation, and was the initially determined coping
duration for the NPP adjusted?
If your NPP site experienced a grid-related total LOOP since the
coping duration under 10 CFR 50.63 was initially determined and has not
been reevaluated using the guidance in Table 4 of RG 1.155, describe
why you believe you comply with the provisions of 10 CFR 50.63 as
stated above, or describe what actions you intend to take to ensure
that the NPP maintains its SBO coping capabilities in accordance with
10 CFR 50.63.
Actions To Ensure Compliance
9. If you determine that any action is warranted to bring your NPP
into compliance with NRC regulatory requirements, including TS, GDC 17,
10 CFR 50.65(a)(4), or 10 CFR 50.53, describe the schedule for
implementing it.
The required written response should be addressed to the U.S.
Nuclear Regulatory Commission, ATTN: Document Control Desk, 11555
Rockville Pike, Rockville, Maryland 20852, under oath or affirmation
under the provisions of Section 182a of the Atomic Energy Act of 1954,
as amended, and 10 CFR 50.54(f). In addition, a copy of the response
should be sent to the appropriate regional administrator.
Addressees may request extension of the time in which a response to
this generic letter is required in writing within 30 days of the date
of this generic letter. The NRC will not grant such an extension except
for good cause shown.
An addressee should consult SECY-04-0191, ``Withholding Sensitive
Unclassified Information Concerning Nuclear Power Reactors From Public
Disclosure,'' dated October 19, 2004, to determine if its response
contains sensitive unclassified (nonsafeguards) information and should
be withheld from public disclosure. SECY-04-0191 is available on the
NRC public Web site.
Reasons for Information Request
This generic letter requests addressees to submit information. The
requested information will enable the NRC staff to determine whether
applicable requirements (plant TSs in conjunction with 10 CFR Part 50,
Appendix A, General Design Criteria 17; 10 CFR 50.65(a)(4); and 10 CFR
50.63) are being met in regard to the grid topics addressed.
Related Generic Communications
NRC Regulatory Issue Summary 2004-05, ``Grid Reliability and the
Impact on Plant Risk and the Operability of Offsite Power,'' dated
April 15, 2004 (ADAMS Accession No. ML040990550).
Backfit Discussion
Under the provisions of Section 182a of the Atomic Energy Act of
1954, as amended, and 10 CFR 50.54(f), this generic letter transmits an
information request for the purpose of verifying compliance with
applicable existing requirements. Specifically, the requested
information will enable the NRC staff to determine whether applicable
requirements (plant TSs in conjunction with 10 CFR Part 50, Appendix A,
General Design Criteria 17; 10 CFR 50.65(a)(4); and 10 CFR 50.63) are
being met in regard to the grid topics addressed. No backfit is either
intended or approved in the context of issuance of this generic letter.
Therefore, the staff has not performed a backfit analysis.
Federal Register Notification
A notice of opportunity for public comment on this generic letter
was published in the Federal Register (xx FR xxxxx) on {date{time} .
[Comments were received from {indicate the number of commentors by
type{time} . The staff considered all comments that were received. The
staff's evaluation of the comments is publicly available through the
NRC's Agencywide Documents Access and Management System (ADAMS) under
Accession No. ML05xxxxxxx.]
Small Business Regulatory Enforcement Fairness Act
The NRC has determined that this action is not subject to the Small
Business Regulatory Enforcement Fairness Act of 1996.
Paperwork Reduction Act Statement
This generic letter contains information collection requirements
that are subject to the Paperwork Reduction Act of 1995 (44 U.S.C. 3501
et seq.). These information collections were approved by the Office of
Management and Budget, approval number 3150-0011, which expires on
February 28, 2007.
The burden to the public for these mandatory information
collections is estimated to average 60 hours per response, including
the time for reviewing instructions, searching existing data sources,
gathering and maintaining the data needed, and completing and reviewing
the information collection. Send comments regarding this burden
estimate or any other aspect of these information collections,
including suggestions for reducing the burden, to the Records and FOIA/
Privacy Services Branch (T-5 F52), U.S. Nuclear Regulatory Commission,
Washington, DC 20555-0001, or by Internet electronic mail to
[email protected]; and to the Desk Officer, Office of Information
and Regulatory Affairs, NEOB-10202, (3150-0011), Office of Management
and Budget, Washington, DC 20503.
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 currently valid
OMB control number.
Contact
Please direct any questions about this matter to the technical
contact(s) or the Lead Project Manager listed below, or to the
appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
Bruce A. Boger, Director, Division of Inspection Program Management,
Office of Nuclear Reactor Regulation.
Technical Contact: James Lazevnick, NRR, 301-415-2782.
Lead Project Manager: John Lamb, NRR, 301-415-1446.
End of Draft Generic Letter
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, http://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
[[Page 19132]]
(PDR) reference staff at 1-800-397-4209 or 301-415-4737 or by e-mail to
[email protected].
Dated at Rockville, Maryland, this 6th day of April 2005.
For the Nuclear Regulatory Commission.
Patrick H. Hiland,
Chief, Reactor Operations Branch, Division of Inspection Program
Management, Office of Nuclear Reactor Regulation.
[FR Doc. E5-1674 Filed 4-11-05; 8:45 am]
BILLING CODE 7590-01-P