Staff Recommended Actions Stemming from NRC Integrated Program for the Resolution of Unresolved Safety Issues Regarding Steam Generator Tube Integrity (Generic Letter No. 85-02)
UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D.C. 20555
April 17, 1985
TO ALL PWR LICENSEES OF OPERATING REACTORS, APPLICANTS FOR OPERATING
LICENSES, AND HOLDERS OF CONSTRUCTION PERMITS, AND FT. ST. VRAIN
Gentlemen:
SUBJECT: STAFF RECOMMENDED ACTIONS STEMMING FROM NRC INTEGRATED PROGRAM FOR
THE RESOLUTION OF UNRESOLVED SAFETY ISSUES REGARDING STEAM
GENERATOR TUBE INTEGRITY (GENERIC LETTER 85-02)
The Commission has recently approved issuance of this generic letter to all
nuclear power plants utilizing steam generators, to obtain information on
their overall program for steam generator tube integrity and steam generator
tube rupture mitigation. This information will allow the staff to assess the
areas of concern addressed by the staff's recommended actions (see Enclosure
1) which were developed as part of the integrated program for the resolution
of Unresolved Safety Issues A-3, A-4 and A-5 regarding steam generator tube
integrity. The staff's program report, NUREG-0844 (draft report for
comment), is provided as Enclosure 3. NUREG-0844 will be issued in final
form following a 90-day period for public comment.
Steam generator tube integrity was designated an unresolved safety issue
(USI) in 1978 and Task Action Plans (TAP) A-3, A-4 and A-5 were established
to evaluate the safety significance of degradation in Westinghouse,
Combustion Engineering and Babcock & Wilcox steam generators, respectively.
These studies were later combined into one effort due to the similarity of
many problems among the PWR vendors.
Staff concerns relative to steam generator tube degradation stem from the
fact that the steam generator tubes are a part of the reactor coolant system
(RCS) boundary and that tube ruptures allow primary coolant into the
secondary system where its isolation from the environment is not fully
ensured. The leakage of primary coolant into the secondary system has two
potential safety implications which were considered. The first is the direct
release of radioactive fission products to the environment; and the second
is the loss of primary coolant water which is needed to prevent core damage.
An extended, uncontrolled loss of coolant outside of containment could
result in the depletion of the initial RCS water inventory and ECCS water
without the capability to recirculate the water.
An integrated program was initiated by the staff in May 1982 to consider
initial recommendations from the USI effort, and to assess the lessons which
could be learned from the four domestic SGTR events; Point Beach 1 in 1975;
Surry 2 in 1976; Prairie Island 1 in 1979; and Ginna in 1982. A number of
potential requirements for industry were identified and subjected to a value
impact evaluation.
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These analyses indicate that: the probability of core melt from events
involving steam generator tube ruptures is not a major contributor to total
core melt risk; that steam generator tube ruptures are an important
contributor to the probability of significant non-core melt releases; and
that steam generator tube degradation is a major contributor to occupational
radiation exposure at PWR's.
Based upon the results of the staff's integrated program, the staff has
developed recommended actions in the following areas:
1. Prevention and Detection of Loose Parts and Foreign Objects
2. Steam Generator Tube Inservice Inspection
3. Secondary Water Chemistry Program
4. Condenser Inservice Inspection Program
5. Primary to Secondary Leakage Limit
6. Coolant Iodine Activity Limit
7. Safety Injection Signal Reset
The staff's recommended actions have been found to be effective measures on
a plant specific basis for significantly reducing (1) the incidence of tube
degradation, (2) the frequency of tube ruptures and the corresponding
potential for significant non-core melt releases, and (3) occupational
exposures, and are consistent with good operating and engineering practices.
Accordingly, operating reactor licensees and applicants for an operating
license (this letter is for information only for those utilities that have
not applied for an operating license) are requested to furnish to the
Director, Division of Licensing, Office of Nuclear Reactor Regulation, no
later than 60 days from the date of this letter, a description of their
overall programs for assuring steam generator tube integrity and for steam
generator tube rupture mitigation. The description of the plant specific
programs should be sufficiently detailed to allow the staff to compare these
actions with the staff recommended actions as presented in Enclosure 1.
The staff recommended actions above do not address supplemental tube sample
inspections for the case where Category C-2 results are obtained during
initial sample inspections. The staff initially considered a proposed
upgrading of existing Technical Specification requirements in this area (see
Section 2.2.1. of the enclosed draft NUREG-0844), and this proposal was
commented upon extensively by industry. The staff has concluded that the
particular proposal considered was not warranted as a generic staff position
or recommendation. However, as part of the information requested by this
letter, licensees and applicants are requested to describe practices they
employ to ensure adequate inspection samples are taken in the event that
Category C-2 results are obtained during initial sampling. The information
requested is described in additional detail in Enclosure 2.
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The staff will review each response from licensees and applicants, and
evaluate the overall effectiveness of plant-specific programs to prevent and
mitigate the occurrence of steam generator tube ruptures. The staff
recognizes, however, that plants specific programs may differ from the staff
recommended actions, and still be adequately effective. The results of the
staff review will be reported directly to the Commission. The Commission has
specifically requested that the staff include in its report the number and
quality of the responses, noting in particular any utilities delinquent in
providing the requested information and any recommended corrective actions.
The staff will continue to monitor licensees' commitments and programs
relative to steam generator integrity and SGTR mitigation to determine if
they are being effectively implemented. As has been true in the past,
additional actions may become necessary in plant specific instances of
extensive or severe degradation.
This request for information was approved by the Office of Management and
Budget under clearance number 3150-0011 which expires April 30, 1985.
Comments on burden and duplication may be directed to the Office of
Management and Budget, Report Management Room 3208, New Executive Office
Building, Washington, D. C. 20503.
Mr. Emmett Murphy, Operating Reactors Assessment Branch, will be the point
of contact. If you have questions or desire additional information, he can
be reached on (301) 492-7457.
Sincerely,
Hugh Thompson, Jr., Director
Division of Licensing
Office of Nuclear Reactor Regulation
Enclosures:
1. Staff Recommended Actions
Stemming from NRC Integrated
Program for the Resolution
of Unresolved Safety Issues
Regarding Steam Generator
Tube Integrity
2. Request for Information
Concerning Category C-2
Steam Generator Tube
Inspections
3. NUREG-0844 (Draft Report For
Comment), NRC Integrated
Program for the Resolution
of Unresolved Safety
Issues
4. List of Generic Letters
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ENCLOSURE 1
STAFF RECOMMENDED ACTIONS AND REVIEW GUIDELINES
STEMMING FROM NRC INTEGRATED PROGRAM
FOR THE RESOLUTION OF UNRESOLVED SAFETY ISSUES
REGARDING STEAM GENERATOR TUBE INTEGRITY
1.a PREVENTION AND DETECTION OF LOOSE PARTS (INSPECTIONS)
Staff Recommended Action
Visual inspections should be performed on the steam generator secondary
side in the vicinity of the tube sheet, both along the entire periphery
of the tube bundle and along the tube lane, for purposes of identify
loose parts or foreign objects on the tubesheet, and external damage to
peripheral tubes just above the tubesheet. An appropriate optical
device should be used (e.g., mini-TV camera, fiber optics). Loose parts
or foreign objects which are found should be removed from the steam
generators. Tubes observed to have visual damage should be eddy current
inspected and plugged if found to be defective.
These visual inspections should be performed: (1) for all steam gener-
ators at each plant at the next planned outage for eddy current
testing, (2) after any secondary side modifications, or repairs, to
steam generator internals, and (3) when eddy current indications are
found in the free span portion of peripheral tubes, unless it has been
established that the indication did not result from damage by a loose
part or foreign object.
For PWR OL applicants, such inspections should be part of the
preservice inspection.
For steam generator models where certain segments of the peripheral
region can be shown not to be accessible to an appropriate optical
device, licensees and applicants should implement alternative actions
to address these inaccessible areas, as appropriate.
Licensees should take appropriate precautions to minimize the potential
for corrosion while the tube bundle is exposed to air. The presence of
chemical species such as sulfur may aggravate this potential, and may
make exposure to the atmosphere inadvisable until appropriate remedial
measures are taken.
Reference
Section 2.1 of NUREG-0844.
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1.b PREVENTION AND DETECTION OF LOOSE PARTS (QUALITY ASSURANCE)
Staff Recommended Action Quality assurance/quality control procedures
for steam generators should be reviewed and revised as necessary to
ensure that an effective system exists to preclude introduction of
foreign objects into either the primary or secondary side of the steam
generator whenever it is opened (e.g., for maintenance, sludge lancing,
repairs, inspection operations, modifications). As a minimum, such
procedures should include: (1) detailed accountability procedures for
all tools and equipment used during an operation, (2 appropriate
controls on foreign objects such as eye glasses and film badges, (3)
cleanliness requirements, and (4) accountability procedures for
components and parts removed from the internals of major components
(e.g., reassembly of cut and removed components).
Reference
Section 2.1 of NUREG-0844.
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2.a INSERVICE INSPECTION PROGRAM (FULL LENGTH TUBE INSPECTION)
Staff Recommended Action
The Standard Technical Specifications (STS) and Regulator Guide 1.83,
Part C.2.f, currently define a U-tube inspection as meaning an
inspection of the steam generator tube from the point of entry on the
hot-leg side completely around the U-bend to the top support of the
cold-leg side. The staff recommends that tube inspections should
include an inspection of the entire length of the tube (tube end to
tube end) including the hot leg side, U-bend, and cold leg side.
This recommended action does not mean that the hot leg inspection
sample and the cold leg inspection sample should necessarily involve
the same tubes. That is, it does not preclude making separate entries
from the hot and cold leg sides and selecting different tubes on the
hot and cold leg sides to meet the minimum sampling requirements for
inspection.
Consistent with the current STS requirement, supplemental sample
inspections (after the initial 3% sample) under this staff recommended
action may be limited to a partial length inspection provided the
inspection includes those portions of the tube length where degradation
was found during initial sampling.
Reference
Section 2.2.2 of NUREG-0844.
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2.b INSERVICE INSPECTION PROGRAM (INSPECTION INTERVAL)
Staff Recommended Action
The maximum allowable time between eddy current inspections of an
individual steam generator should be limited in a manner consistent
with Section 4.4.5.3 of the Standard Technical Specifications, and in
addition should not extend beyond 72 months.
Reference
Section 2.2.4 of NUREG-0844.
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3.a SECONDARY WATER CHEMISTRY PROGRAM
Staff Recommended Action
Licensees and applicants should have a secondary water chemistry
program (SWCP) to minimize steam generator tube degradation.
The specific plant program should incorporate the secondary water
chemistry guidelines in SGOG Special Report EPRI-NP-2704, "PWR
Secondary Water Chemistry Guidelines," October 1982, and should address
measures taken to minimize steam generator corrosion, including
materials selection, chemistry limits, and control methods. In
addition, the specific plant procedures should include progressively
more stringent corrective actions for out-of-specification water
chemistry conditions. These corrective actions should include power
reductions and shutdowns, as appropriate, when excessively corrosive
conditions exist. Specific functional individuals should be identified
as having the responsibility/authority to interpret plant water
chemistry information and initiate appropriate plant actions to adjust
chemistry as necessary.
The referenced SGOG guidelines above were prepared by the Steam
Generator Owners Group Water Chemistry Guidelines Committee and
represent and consensus opinion of a significant portion of the
industry for state-of-the-art secondary water chemistry control.
Reference
Section 2.5 of NUREG-0844.
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3.b CONDENSER INSERVICE INSPECTION PROGRAM
Staff Recommended Action
Licensees should implement a condenser inservice inspection program.
The program should be defined in plant specific safety-related
procedures and include:
1. Procedures to implement a condenser inservice inspection program
that will be initiated if condenser leakage is of such a magnitude
that a power reduction corrective action is required more than
once per three month period; and
2. Identification and location of leakage source(s), either water or
air;
3. Methods of repair of leakage;
4. Methodology for determining the cause(s) of leakage;
5. A preventive maintenance program.
Reference
Section 2.6 of NUREG-0844.
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4. PRIMARY TO SECONDARY LEAKAGE LIMIT
Staff Recommended Action
All PWRs that have Technical Specifications limits for primary to
secondary leakage rates which are less restrictive than the Standard
Technical Specifications (STS) limits should implement the STS limits.
Reference
Section 2.8 of NUREG-0844.
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5. COOLANT IODINE ACTIVITY LIMIT
Staff Recommended Action
PWRs that have Technical Specifications limits and surveillance for
coolant iodine activity that are less restrictive than the Standard
Technical Specification (STS) should implement the STS limits. Those
plants identified above that also have low head high pressure safety
injection pumps should either: (1) implement iodine limits which are
20% of the STS values, or (2) implement reactor coolant pump trip
criteria which will ensure that if offsite power is retained, no loss
of forced reactor coolant system flow will occur for steam generator
tube rupture events up to and including the design basis double-ended
break of a single steam generator tube, and implement iodine limits
consistent with the STS.
Reference
Section 2.9 of NUREG-0844.
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6. SAFETY INJECTION SIGNAL RESET
Staff Recommended Action
The control logic associated with the safety injection pump suction
flow path should be reviewed and modified as necessary, by licensees,
to minimize the loss of safety function associated with safety
injection reset during an SGTR event. Automatic switchover of safety
injection pump suction from the boric acid storage tanks (BAST) to the
refueling water storage tanks should be evaluated with respect to
whether the switchover should be made on the basis of low BAST level
alone without consideration of the condition of the SI signal.
Reference
Section 2.11 of NUREG-0844.
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ENCLOSURE 2
REQUEST FOR INFORMATION CONCERNING CATEGORY C-2
STEAM GENERATOR TUBE INSPECTIONS
Information Requested
The enclosed draft NUREG-0844 Section 2.2.1.2 describes certain limitations
which the staff believes to be inherent in the present Technical
Specification steam generator ISI requirements pertaining to Category C-2
inspection results. Licensees and applicants are requested to provide a
description of their current policy and actions relative to this issue and
any recommendations they have concerning how existing Technical
Specification steam generator ISI requirements pertaining to Category C-2
inspection results could be improved to better ensure that adequate
inspections will be performed. This description should include a response to
the following questions:
1. What factors do, or would, the licensee or applicant consider in
determining (a) whether additional tubes should be inspected
beyond what is required by the Technical Specifications, (b)
whether all steam generators should be included in the inspection
program, and (c) when the steam generators should be reinspected.
2. To what extent do these factors include consideration of the
degradation mechanism itself and its potential for causing a tube
to be vulnerable to rupture during severe transients or postulated
accident before rupture or leakage of that tube occurs during
normal operation.
Reference
Section 2.2 of NUREG-0844.
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