[Federal Register Volume 72, Number 99 (Wednesday, May 23, 2007)]
[Notices]
[Pages 29010-29015]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 07-2557]
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NUCLEAR REGULATORY COMMISSION
Proposed Generic Communication; Managing Gas Intrusion in
Emergency Core Cooling, Decay Heat Removal, and Containment Spray
Systems
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of opportunity for public comment.
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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is proposing to
issue a generic letter (GL) to address the issue of gas intrusion into
the emergency core cooling, decay heat removal, and containment spray
systems (hereinafter referred to as the ``subject systems'').
Specifically, the NRC is issuing this GL for the following two
purposes:
(1) to request addressees to submit information demonstrating that
the subject systems are in compliance with the current licensing and
design bases, and applicable regulatory requirements, and that suitable
design, operational, and testing control measures are in place for
maintaining this compliance, and
(2) to collect the requested information to determine if additional
regulatory action is required.
This Federal Register notice is available through the NRC's
Agencywide Documents Access and Management System (ADAMS) under
accession number ML0704001003.
DATES: Comment period expires July 23, 2007. 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: Submit written comments to the Chief, Rulemaking,
Directives, and Editing 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 a.m. and 4:15 p.m. on Federal
workdays.
FOR FURTHER INFORMATION, CONTACT: Warren C. Lyon, NRR, at 301-415-2897
or by e-mail: [email protected] or David P. Beaulieu, NRR, at 301-415-3243 or
by e-mail: [email protected].
SUPPLEMENTARY INFORMATION:
NRC Generic Letter 2007-XX, Managing Gas Intrusion in Emergency
Core Cooling, Decay Heat Removal, and Containment Spray Systems
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
The U.S. Nuclear Regulatory Commission (NRC) is issuing this
generic letter (GL) to address the issue of gas \1\ intrusion into the
emergency core cooling, decay heat removal \2\, and containment spray
systems (hereinafter referred to as the ``subject systems'').
Specifically, the NRC is issuing this GL:
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\1\ Gas as used here includes, air, nitrogen, hydrogen, water
vapor, or any other void that is not filled with liquid water.
\2\ Decay heat removal (DHR), residual heat removal (RHR), and
shutdown cooling (SDC) are common names for systems used to cool the
reactor coolant system (RCS) during some phases of shutdown
operation. The NRC staff generally uses DHR here.
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(1) To request addressees to submit information to demonstrate that
the subject systems are in compliance with the current licensing and
design bases and applicable regulatory requirements, and that suitable
design, operational, and testing control measures are in place for
maintaining this compliance, and
(2) to collect the requested information to determine if additional
regulatory action is required.
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR)
Section 50.54(f), addressees are required to submit a written response
to this GL.
Background
Instances of gas intrusion into the subject systems have occurred
since the beginning of commercial nuclear power plant operation. The
NRC has published 20 information notices (INs), two GLs, and a NUREG
\3\ that are related to this issue and has interacted with the nuclear
industry many times in relation to these publications and in response
to gas intrusion events. The following paragraphs summarize a few
events to illustrate some of the technical and regulatory requirements
issues.
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\3\ GL 88-17, ``Loss of Decay Heat Removal,'' October 17, 1988
(ML031200496); GL 97-04, ``Assurance of Sufficient Net Positive
Suction Head for Emergency Core Cooling and Containment Heat Removal
Pumps,'' October 7, 1997 (ML031110062); and NUREG-0897, Revision 1,
``Containment Emergency Sump Performance--Technical Findings Related
to USI A-43,'' October 1985.
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In May 1997, at Oconee Nuclear Station Unit 3, hydrogen ingestion
during plant cooldown damaged and rendered nonfunctional two high-
pressure injection (HPI) pumps. If the operators had started the
remaining HPI pump, it too would have been damaged. The NRC responded
with an augmented inspection team (IN 97-38, ``Level-Sensing System
Initiates Common-Mode Failure of High-Pressure-Injection Pumps,''
Agencywide Documents Access and Management System (ADAMS) Accession No.
ML031050514, June 24, 1997). The NRC team reported that there had been
a total lack of HPI capability during power operation, a failure to
meet technical specification (TS) HPI operability requirements, design
deficiencies, inadequate maintenance practices, operators that were
less than attentive to plant parameters, a failure to adequately assess
operating experience, and a violation of 10 CFR part 50, Appendix
[[Page 29011]]
B, Criterion III (``Notice of Violation and Proposed Imposition of
Civil Penalties --$330,000,'' August 27, 1997, http://www.nrc.gov/reading-rm/doc-collections/enforcement/actions/reactors/ea97297.html).
As a result of this Oconee Unit 3 event, the industry initiated an
industry-wide improvement activity to address the gas issue. Based on
the industry actions, the NRC concluded that no generic action was
necessary. However, significant gas events that jeopardized the
operability of the subject systems continued to occur, as illustrated
in the following paragraphs. Dresden Nuclear Power Station Unit 3
experienced a reactor scram on July 5, 2001, that was accompanied by a
water hammer as a result of high pressure coolant injection (HPCI)
system voids due to inadequate pipe venting. The licensee discovered a
damaged pipe support that rendered the HPCI system inoperable on July
19, 2001. On September 28, 2001, NRC inspectors discovered
discrepancies in another HPCI hanger that may have been caused by the
water hammer. The licensee repaired the hangers on September 30, 2001,
and vented the system. An NRC inspector identified a high point that
had not been vented and air was removed when the licensee vented that
location. The HPCI system was inoperable from July 5, 2001, to
September 30, 2001 (NRC Supplemental Inspection Report 50-237, 50-239/
2003-012, ML033530204, December 18, 2003). The NRC found violations of
10 CFR 50.9, a TS, and 10 CFR part 50, Appendix B, Criterion XVI
(``Notice of Violation and Proposed Imposition of Civil Penalty--
$60,000, and Final Significance Determination for a White Finding,''
ML031740755, June 23, 2003).
On August 14, 2003, the Perry Nuclear Power Plant scrammed from 100
percent power due to a loss of offsite power. This caused a momentary
loss of common water leg pumps \4\ and a discharge pressure decrease
from 44 psig to 7 psig allowed accumulated gas to completely void a
water leg pump and the associated feedwater leakage control system
piping. Pump operation was restored by venting the pump casing but a
piping high point that was not included in fill and vent procedures was
not vented. On September 10, 2003, the licensee vented enough gas from
the high point that would have caused the pump to be non-functional if
another loss of offsite power would occur. If the RHR and/or the LPCS
pumps had started while the leakage control system piping was voided,
the resulting water hammer could have caused the system piping to
rupture. The NRC characterized the inspection finding as white; the
finding resulted in a TS violation, escalated enforcement action, and a
supplemental inspection (NRC Inspection Report 50-440/2003-009,
ML032880107, October 10, 2003, and ML040330980, January 30, 2004).
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\4\ These are 40 gpm pumps used to compensate for back-leakage
through check valves in RHR and LPSI piping into the suppression
pool. The purpose is to keep piping full of water where the pipe
elevation is higher than the suppression pool. The system is often
referred to as a ``keep-full'' system.
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On July 28, 2004, the Palo Verde licensee identified that emergency
core cooling system (ECCS) suction piping voids in all three Palo Verde
units could have resulted in a loss of the ECCS during transfer to the
recirculation mode for some loss-of-coolant accident (LOCA) conditions.
The condition had existed since plant startups in 1986, was contrary to
the Palo Verde final safety analysis reports (FSARs), and would not be
identified during testing because water is not drawn from the
containment emergency sumps. The NRC inspectors identified multiple
violations of 10 CFR part 50, Appendix B, Criteria III and V, and
violations of 10 CFR 50.59. The NRC responded with a special
inspection, issued a yellow finding, and imposed a civil penalty of
$50,000 (NRC Special Inspection Report 50-328, 50-329, 50-330/2004-014,
ML050050287, January 5, 2005). The Palo Verde licensee identified the
ECCS piping suction voids after being contacted by engineer from
another plant where an NRC inspector identified the same problem.
In February 2005, an HPI pump at Indian Point Energy Center Unit 2
was found inoperable because the pump casing was filled with gas. The
licensee then found numerous locations in the ECCS piping with gas
accumulation. The licensee did not initially understand the
implications of the gas condition, and the licensee's early assessments
were inadequate, particularly with respect to assessing the operability
of the other two HPI pumps. The NRC conducted a special inspection that
found one HPI pump was not functional and the other two HPI pumps had a
75 percent failure probability. The NRC found several violations of 10
CFR part 50, Appendix B, Criterion XVI, and issued a white finding (NRC
Inspection Report 50-247/2005-006, ML051680119, June 17, 2005).
In March 2005, the NRC reported that Diablo Canyon had a sustained
history of gas voiding in piping that could possibly result in gas
binding or damage to the centrifugal charging pumps or the HPSI pumps
during switchover from cold-leg to hot-leg injection.\5\ The NRC
inspectors concluded that the licensee focused on managing the symptom
of the problem rather than finding and eliminating the cause, which is
contrary to 10 CFR part 50, Appendix B, Criterion XVI (NRC Inspection
Report 50-275, 50-323/2005-006, ML050910120, March 31, 2005).
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\5\ A similar gas accumulation problem under closed valves in
the recirculation piping from the DHR discharge to the HPSI and
charging pump suctions has occurred at several plants. This has the
potential to cause loss of all high pressure RCS makeup capability
when shifting suction to the emergency containment sump from the
refueling water or borated water storage tank following a LOCA.
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In September 2005, operators discovered a void in the HPCI pump
discharge piping at the Duane Arnold Energy Center due to ``turbulent
penetration'' that caused hot water from the feedwater pipe to
penetrate downward into the HPCI discharge pipe. This heated the HPCI
pipe on the low pressure side of a closed valve to greater than the
saturation temperature and caused steam to be generated in the low
pressure pipe as fast as it was vented. The condition had existed since
plant startup (Licensee Event Report 50-331/2005-004, ML053360261,
November 28, 2005). The NRC opened an unresolved item (URI 05000331/
2006002-03) for further NRC review of the licensee's piping analysis
that evaluated HPSI system operability with the voided piping (NRC
Inspection Report 50-331/2006-002, ML061210448, April 27, 2006, and NRC
Inspection Report 50-331/2006-008, ML070640515, March 2, 2007).
In October 2005, an NRC inspection team at the Palo Verde Nuclear
Generating Station identified that, following a postulated accident
when refueling water tank (RWT) level reached the setpoint for
containment sump recirculation, the licensee's design basis credited
containment pressure for preventing the ECCS pumps from continuing to
reduce RWT level and drawing air into the ECCS. However, a recent
licensee analysis showed that the minimum containment pressure would be
less than needed. The licensee declared the ECCS inoperable at all
three units, requiring a shutdown of Units 2 and 3 (Unit 1 was already
shut down). The NRC found multiple violations of 10 CFR part 50,
Appendix B, Criteria III and V (NRC Supplemental Inspection Report 50-
528, 50-529, 50-530/2005-012, ML060300193, January 27, 2006).
These are a few of the more than 60 gas intrusion events reported
during recent years involving the subject
[[Page 29012]]
systems. The number is larger if other similar events at the same plant
are counted. Further, many events do not have to be reported to the
NRC, and many of them have not been addressed during the NRC's
inspections. For example, at least 40 RHR water hammer events have
occurred at the Sequoyah Nuclear Plant, although none of them rendered
the RHR system inoperable. Additionally, if an ECCS pump has been
damaged because of gas but is repaired and tested operable within the
TS completion time (typically, 72 hours), the licensee is not required
to report the occurrence to the NRC. The frequency and the significance
of these events and the likelihood that unidentified gas issues exist
require licensee action to ensure compliance with regulatory
requirements that will maintain operability of the subject systems.
Applicable Regulatory Requirements
10 CFR part 50 Appendix A or similar plant-specific principal
design criteria \6\ provide design requirements, and 10 CFR part 50
Appendix B, TSs, and licensee quality assurance programs provide
operating requirements. Appendix A requirements applicable to gas
management in the subject systems include the following:
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\6\ For facilities with a construction permit issued prior to
May 21, 1972, that are not licensed to Appendix A.
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General Design Criterion (GDC) 1 requires that the subject
systems be designed, fabricated, erected, and tested to quality
standards.
GDC 34 requires an RHR system designed to maintain
specified acceptable fuel design limits and to meet design conditions
that are not exceeded if a single failure occurs and specified
electrical power systems fail.
GDC 35, 36, and 37 require an ECCS design that meets
performance, inspection, and testing requirements. Specified
performance criteria are provided in 10 CFR 50.46.
GDC 38, 39, and 40 require a containment heat removal
system design that meets performance, inspection, and testing
requirements.
Quality assurance criteria provided in Appendix B that apply to gas
management in the subject systems include the following:
Criteria III and V require measures to assure that
applicable regulatory requirements and the design basis, as defined in
10 CFR 50.2, ``Definitions,'' and as specified in the license
application, are correctly translated into controlled specifications,
drawings, procedures, and instructions.
Criterion XI requires a test program to assure that the
subject systems will perform satisfactorily in service. Test results
shall be documented and evaluated to assure that test requirements have
been satisfied.
Criterion XVI requires measures to assure that conditions
adverse to quality, such as failures, malfunctions, deficiencies,
deviations, defective material and equipment, and nonconformances, are
promptly identified, corrected, documented, and reported to management.
Criterion XVII requires maintenance of records of
activities affecting quality.
Further, as part of the licensing basis, licensees have committed
to certain quality assurance provisions that are identified in both
their TSs and quality assurance programs. Licensees have committed to
use the guidance of Regulatory Guide (RG) 1.33, ``Quality Assurance
Requirements (Operation),'' which endorses American National Standards
Institute (ANSI) N18.7-1976/American Nuclear Society 3.2,
``Administrative Controls and Quality Assurance for the Operational
Phase of Nuclear Power Plants,'' or equivalent licensee-specific
guidance. Section 5.3.4.4, ``Process Monitoring Procedures,'' of ANSI
N18.7 that states that procedures for monitoring performance of plant
systems shall be required to assure that engineered safety features and
emergency equipment are in a state of readiness to maintain the plant
in a safe condition if needed. The limits (maximum and minimum) for
significant process parameters shall be identified. Operating
procedures shall address the nature and frequency of this monitoring,
as appropriate.
10 CFR 50.36(c)(3) defines TS surveillance requirements (SRs) as
``relating to test, calibration, or inspection to assure'' maintenance
of quality, operation within safety limits, and operability. Typically,
TS Section 5 or 6 requires that licensees establish, implement, and
maintain written procedures covering the applicable procedures
recommended in Appendix A to RG 1.33, Revision 2 (February 1978).
Appendix A to RG 1.33 identifies instructions for filling and venting
the ECCS and DHR system, as well as for draining and refilling heat
exchangers. Surveillance requirements to verify that at least some of
the subject system piping is filled are provided in standard technical
specifications (STSs) and in most licensee TSs.
Discussion
The events discussed in the BACKGROUND section illustrate that many
of the regulatory requirements identified in the APPLICABLE REGULATORY
REQUIREMENTS section are not being met. The NRC inspectors often find
that the 10 CFR part 50 Appendix B criteria identified above are not
adequately addressed in plant venting procedures. In some cases,
venting procedures were almost nonexistent, there were no records of
gas quantities that were vented and licensees unsuccessfully attempted
to recreate the history by asking operators for their recollections.
Consequently, there was no foundation for establishing that the subject
systems were operable prior to venting. In addition, the venting
processes sometimes did not ensure that all gas was removed from the
venting location and often did not adequately establish the quantity of
vented gas. Further, examination of ultrasonic test (UT) processes at
several licensee sites established that one licensee initially did not
know how to acceptably determine liquid level via UT. Additional issues
include TSs, which often do not require venting of suction piping
despite voids in suction pipes generally being of more concern than in
discharge piping, and do not adequately address operability of the
subject systems prior to surveillance and for the time span until the
next surveillance. This GL and the anticipated NRC followup to this GL
are intended to correct such conditions.
It is important that the subject systems are sufficiently filled
with water to ensure that they can reliably perform their intended
functions under all LOCA and non-LOCA conditions that require makeup to
the RCS. Portions of these systems and some of the associated pumps are
normally in a standby condition while other pumps provide both ECCS and
operational functions. For example, some high-pressure pumps are used
for normal RCS makeup, and some low-pressure pumps provide a normal DHR
capability.
The following safety issues are associated with gas intrusion into
the subject systems:
(1) The introduction of gas into a pump can cause the pump to
become air-bound with little or no flow, rendering the pump inoperable.
Air-binding can render more than one pump inoperable when pumps share
common discharge or suction headers, or when the gas accumulation
process affects more than one train, greatly increasing the risk
significance. Such a common-mode failure would result in the inability
of the ECCS or the DHR system to provide adequate core cooling and the
inability of the containment spray system to maintain the containment
pressure and temperature below design limits. An air-bound pump can
become
[[Page 29013]]
damaged quickly, eliminating the possibility of recovering the pump
during an event by simply subsequently venting the pump and suction
piping.
(2) Gas introduced into a pump can render the pump inoperable, even
if the gas does not air bind the pump, because the gas can reduce the
pump discharge pressure and flow capacity to the point that the pump
cannot perform its design function. For example, an HPI pump that is
pumping air-entrained water may not develop sufficient discharge
pressure to inject under certain small break LOCA scenarios.
(3) Gas accumulation can result in water hammer or a system
pressure transient, particularly in pump discharge piping following a
pump start, which can cause piping and component damage or failure. Gas
accumulation in the DHR system has resulted in pressure transients that
have caused DHR system relief valves to open. In some plants, the
relief valve reseating pressure is less than the existing RCS pressure,
a condition that complicates recovery.
(4) Pump cavitation caused by entrained gas results in additional
stresses that can lead to premature failure of pump components that can
render the pump inoperable.
(5) Gas intrusion can result in pumping noncondensible gas into the
reactor vessel that may affect core cooling flow.
(6) The time needed to fill voided discharge piping can delay
delivery of water beyond the time frame assumed in the accident
analysis.
The scope and number of identified gas intrusion problems at some
facilities raise concerns about whether similar unrecognized design,
configuration, and operability problems exist at other reactor
facilities.
A review of the operating experience has identified the following
concerns, which are the focus of this GL:
(1) TS SRs, as implemented by associated surveillance procedures,
have not reliably precluded gas problems. Operating experience shows
many instances in which substantive gas voiding in the system piping
has not been identified. The surveillance procedures may not reliably
reveal as-found conditions in which the system may be inoperable or
degraded because of gas. Additionally, some plants have no TS SR to
verify that the subject systems' piping is sufficiently full of water.
Still other plants have incomplete TS SRs that cover only portions of
the system. For example, the TS may require verifying that ECCS
discharge piping is full of water but may not include verification of
the suction piping or containment spray piping. Although the TS and
FSAR at many facilities indicate that the subject systems are full of
water, in practice it is not uncommon for licensees to vent some gas
during periodic surveillances. Further, there may be some parts of
these systems where it is not possible or practical to verify them to
be full of water. Hence, the current TS and FSAR may establish a
standard that may not be realistic to establish system operability. A
realistic standard should bound the volume of gas that may impact pump
operability and the volume for which water-hammer-induced stress limits
may be exceeded.
Criterion XI of Appendix B to 10 CFR part 50 requires licensees to
perform testing using written test procedures, which include but are
not limited to procedures for TS SRs, that incorporate the requirements
and acceptance limits contained in applicable design documents. TSs
often require surveillance of discharge piping but do not mention
suction piping. Consequently, suction piping surveillances may not be
performed. However, since the subject systems may be rendered
inoperable or degraded because of gas in suction piping, the
regulations require that presence of gas in all piping be assessed to
establish operability.
(2) Typically the FSAR describes that the subject systems are
filled with water. The wording of TS SRs further confirms that the
design-basis configuration calls for the specified piping to be filled
with water. Operating experience provides many examples of licensees
treating the accumulation of gas as an expected condition (rather than
a nonconforming condition) that was not documented even when it
involved a substantial volume of gas that clearly constituted a
significant condition adverse to quality. In such cases, Criterion XVI
of Appendix B to 10 CFR part 50 requires that the cause of the
condition be determined and corrective action taken to preclude
repetition. Based on the as-found volume and location of gas,
corrective actions beyond simply refilling a system may be necessary to
provide reasonable assurance that the affected system will remain
operable until the next surveillance.
(3) Although the subject systems are often susceptible to gas
intrusion, not all plants have vent valves at one or more system high
points. Some licensees have installed additional vent valves at system
high points after operational events. For example, one licensee
installed an additional 21 high-point vent valves. Another licensee,
who installed an additional 17 vent valves, determined that the primary
cause of the gas voiding problem was that the original design
specification did not call for a sufficient number of vent valves. No
specific NRC requirement mandates the installation of vent valves on
the subject systems. However, failure to translate the design basis of
assuring the system is maintained sufficiently full of water to
maintain operability into drawings, specifications, procedures, and
instructions is a violation of Criterion III in Appendix B of 10 CFR
part 50.
Further, Criterion V requires documented instructions, procedures,
or drawings that include appropriate quantitative or qualitative
acceptance criteria for determining that important activities have been
satisfactorily accomplished. This means that each addressee must have
suitable documentation and records, including acceptance criteria, to
establish that the subject systems have been and are maintained
sufficiently full of water to ensure system operability. Vent valves
and their use are often a key ingredient for satisfying these
requirements.
The NRC staff is initiating a Technical Specifications Task Force
(TSTF) activity to address the recognized TS weaknesses associated with
gas intrusion concerns. In the interim, until new TSs are developed,
the NRC staff will treat a SR that the piping be full of water as
satisfied if the piping and pumps of the subject systems are maintained
sufficiently full of water to ensure system operability when
operability is required. This condition must be shown to be satisfied
during the time between surveillances, and either venting or UT
surveillances are acceptable means of obtaining void data. Further, the
NRC staff will consider justification for not conducting a periodic
surveillance or for extending the time between surveillances of certain
sections of piping if an addressee considers surveillance to be
unnecessary. For example, some three loop plants designed by
Westinghouse maintain HPSI discharge lines at a pressure greater than
the RCS operating pressure. This eliminates the potential for leakage
from the accumulators or the RCS as a possible means to introduce gas
into the discharge lines. An assessment for such plants that (1)
acceptably eliminates other means of introducing gas, (2) establishes
acceptable verification that the lines are essentially full following a
condition that reduces the discharge line pressure, and (3) establishes
an operating history confirming that gas has not accumulated will be
adequate justification for not conducting surveillances inside
[[Page 29014]]
containment or at locations that constitute a hazard to personnel
performing the assessment. The NRC memorandum, ``Technical
Considerations for Reasonably Assuring Emergency Core Cooling, Decay
Heat Removal, and Containment Spray Systems Operability,'' ML071030382,
April 17, 2007, provides some operating experience insights. The NRC
staff plans to use this information during inspection activities that
are planned as a followup to this GL and for guidance in the TSTF
program to develop improved TSs.
Requested Actions
Each addressee is requested to evaluate their ECCS, DHR system, and
containment spray system designs, operation, and test procedures to
assure that gas intrusion is minimized and monitored in order to
maintain system operability and compliance with the requirements of
Appendix B to 10 CFR part 50.
Requested Information
Each addressee is requested to provide a summary description of how
the REQUESTED ACTIONS have been addressed within 6 months of the date
of this GL. This summary description should specifically address the
quality assurance criteria in 10 CFR part 50, Appendix B, Sections III,
V, XI, XVI, and XVII and the TSs that apply to the subject systems.
This summary should include a general description of: (1) The design,
(2) the operating procedures, and (3) the test procedures to assure
that gas intrusion does not affect the ability of the subject systems
to perform their intended functions.
If an addressee determines that system or procedure modifications
are necessary based on the review of the requested actions and these
changes cannot be accomplished within 6 months of the date of this GL,
then the addressee should also provide a plan and schedule for
completion of these actions.
Required Response
In accordance with 10 CFR 50.54(f), in order to determine whether a
facility license should be modified, suspended, or revoked, or whether
other action should be taken, an addressee is required to respond as
described below. Within 6 months of the date of this generic letter, an
addressee is required to submit a written response if they are unable
to provide the information or they cannot meet the requested completion
date. The addressee must address in its response any alternative course
of action that it proposes to take, including the basis for the
acceptability of the proposed alternative course of action.
The required written response should be addressed to the U.S.
Nuclear Regulatory Commission, ATTN: Document Control Desk, 11555
Rockville Pike, Rockville, MD 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, submit a copy of the
response to the appropriate regional administrator.
Reasons for Information Request
The NRC is requesting this information because a review of
operating experience shows numerous instances of gas intrusion events
involving the subject systems that have rendered or potentially
rendered these risk-significant systems inoperable.
Related Generic Communications
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ADAMS
Document No. Document name accession No.
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GL 88-17....................... Loss of Decay Heat ML031200496
Removal.
GL 97-04....................... Assurance of ML031110062
Sufficient Net
Positive Suction Head
for Emergency Core
Cooling and
Containment Heat
Removal Pumps.
IN 86-63....................... Loss of Safety ML031250058
Injection Capability.
IN 86-80....................... Unit Startup with ML031250214
Degraded High
Pressure Safety
Injection System.
IN 87-63....................... Inadequate Net ML031180034
Positive Suction Head
in Low Pressure
Safety Systems.
IN 88-23....................... Potential for Gas ML031150208
Binding of High-
Pressure Safety.
IN 88-23, Supp. 1.............. Injection Pumps During ML881230018
a Loss-of-Coolant
Accident.
IN 88-23, Supp. 2.............. ...................... ML900125002
IN 88-23, Supp. 3.............. ...................... ML901204023
IN 88-23, Supp. 4.............. ...................... ML921215001
IN 88-74....................... Potentially Inadequate ML031150118
Performance of ECCS
in PWRs during
Recirculation
Operation Following a
LOCA.
IN 89-67....................... Loss of Residual Heat ML031180745
Removal Caused by
Accumulator Nitrogen
Injection.
IN 89-80....................... Potential for Water ML031190089
Hammer, Thermal
Stratification, and
Steam Binding in High-
Pressure Coolant
Injection Piping.
IN 90-64....................... Potential for Common- ML031103251
Mode Failure of High
Pressure Safety
Injection Pumps or
Release of Reactor
Coolant Outside
Containment During a
Loss-of-Coolant
Accident.
IN 91-50....................... A Review of Water ML031190397
Hammer Events after
1985.
IN 94-36....................... Undetected ML031060539
Accumulation of Gas
in Reactor System.
IN 94-76....................... Recent Failures of ML031060430
Charging/Safety
Injection Pump Shafts.
IN 95-03....................... Loss of Reactor ML031060404
Coolant Inventory and
Potential Loss of
Emergency Mitigation
Functions While in a
Shutdown Condition.
IN 96-55....................... Inadequate Net ML031050598
Positive Suction Head
of Emergency Core
Cooling and
Containment Heat
Removal Pumps under
Design Basis Accident
Conditions.
IN 96-65....................... Undetected ML031050500
Accumulation of Gas
in Reactor Coolant
System and Inaccurate
Reactor Water Level
Indication During
Shutdown.
IN 97-38....................... Level-Sensing System ML031050514
Initiates Common-Mode
Failure of High
Pressure Injection
Pumps.
IN 97-40....................... Potential Nitrogen ML031050497
Accumulation
Resulting from Back-
Leakage from Safety
Injection Tanks.
IN 98-40....................... Design Deficiencies ML031040547
Can Lead to Reduced
ECCS Pump Net
Positive Suction Head
During Design-Basis
Accidents.
IN 02-15....................... Potential Hydrogen ML020980466
Combustion Events in
BWR Piping.
IN 02-15, Supp. 1.............. ...................... ML031210054
IN 02-18....................... Effect of Adding Gas ML021570158
Into Water Storage
Tanks on the Net
Positive Suction Head
for Pumps.
[[Page 29015]]
IN 06-21....................... Operating Experience ML062570468
Regarding Entrainment
of Air Into Emergency
Core Cooling and
Containment Spray
Systems.
------------------------------------------------------------------------
Backfit Discussion
Under the provisions of Section 182a of the Atomic Energy Act of
1954, as amended, this GL requests a review and appropriate resulting
actions for the purpose of assuring compliance with applicable existing
requirements. No backfit is either intended or approved by the issuance
of this GL. Therefore, the NRC staff has not performed a backfit
analysis.
Federal Register Notification
To be done after the public comment period.
Congressional Review Act
In accordance with the Congressional Review Act, the NRC has
determined that this GL is not a major rule and the Office of
Information and Regulatory Affairs of the Office of Management and
Budget has confirmed this determination.
Paperwork Reduction Act Statement
This GL contains an information collection that is subject to the
Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.). The Office of
Management and Budget approved this information collection under
clearance number 3150-0011.
The burden to the public for this mandatory information collection
is estimated to average 300 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. The NRC is seeking public comment on the
potential impact of the information collection contained in the GL and
on the following issues:
1. Is the proposed information collection necessary for the proper
performance of the functions of the NRC, including whether the
information will have practical utility?
2. Is the estimate of burden accurate?
3. Is there a way to enhance the quality, utility, and clarity of
the information collected?
4. How can the burden of the information collection be minimized,
including the use of automated collection techniques?
Send comments on any aspect of this information collection,
including suggestions for reducing the burden, to the Records and FOIA/
Privacy Services Branch (T5-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, an information collection
unless the requesting document displays a currently valid OMB control
number.
Contact: Please direct any questions about this matter to the
technical contact or the Lead Project Manager listed below, or to the
appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
Michael J. Case, Director, Division of Policy and Rulemaking,
Office of Nuclear Reactor Regulation.
Technical Contact: Warren C. Lyon, NRR, 301-415-2897, e-mail:
[email protected].
Lead Project Manager: David P. Beaulieu, NRR, 301-415-3243, e-mail:
[email protected].
Note: NRC generic communications may be found on the NRC public
Web site, http://www.nrc.gov, under Electronic Reading Room/Document
Collections.
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 (PDR)
reference staff at 1-800-397-4209 or 301-415-4737 or by e-mail to
[email protected].
Dated at Rockville, Maryland, this 16th day of May 2007.
For the Nuclear Regulatory Commission.
Jennifer Golder, Acting Director, Division of Policy and Rulemaking,
Office of Nuclear Reactor Regulation.
[FR Doc. 07-2557 Filed 5-22-07; 8:45 am]
BILLING CODE 7590-01-P