[Federal Register Volume 68, Number 93 (Wednesday, May 14, 2003)]
[Notices]
[Pages 25909-25912]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-11960]
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NUCLEAR REGULATORY COMMISSION
Proposed Generic Communication; Requirements for Steam Generator
Tube Inspections
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 (1) advise all holders of operating
licenses for pressurized-water reactors (PWRs), except those who have
permanently ceased operations and have certified that fuel has been
permanently removed from the reactor vessel, that the NRC's
interpretation of technical specification (TS) requirements in
conjunction with Appendix B to part 50 of title 10 of the Code of
Federal Regulations (10 CFR part 50) raises questions as to whether
steam generator (SG) tube inspection practices ensure compliance with
these requirements, (2) request that addressees submit a description of
the tube inspections performed at their plants, including an assessment
of whether these inspections ensure compliance with the requirements
contained in their TS in conjunction with 10 CFR part 50, Appendix B,
(3) request that addressees propose plans for coming into compliance
with these requirements if they conclude they are not in compliance,
and (4) request that addressees submit a safety assessment addressing
any differences from the NRC's position regarding these requirements.
The NRC is seeking comment from interested parties on the clarity and
utility of the proposed GL under the SUPPLEMENTARY INFORMATION heading.
The NRC will consider the comments received in its final evaluation of
the proposed GL.
This Federal Register notice is available through the NRC's
Agencywide Documents Access and Management System (ADAMS) under
accession number ML031270171.
DATES: Comment period expires July 14, 2003. 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, 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 a.m. and 4:15 p.m. on Federal workdays.
FOR FURTHER INFORMATION CONTACT: Paul Klein at (301) 415-4030 or by E-
mail to [email protected].
SUPPLEMENTARY INFORMATION:
NRC Generic Letter 2003-XX: Requirements for Steam Generator Tube
Inspections
Addressees
All holders of operating licenses for pressurized-water reactors
(PWRs), 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 to
(1) Advise addressees that the NRC's interpretation of the
technical specification (TS) requirements in conjunction with 10 CFR
part 50, Appendix B, raises questions whether certain licensee steam
generator (SG) tube inspection practices ensure compliance with these
requirements,
(2) Request that addressees submit a description of the tube
inspections performed at their plants, including an assessment of
whether these inspections ensure compliance with the requirements
contained in their TS in conjunction with 10 CFR part 50, Appendix B,
(3) Request that addressees that conclude they are not in
compliance with the SG tube inspection requirements contained in their
TS in conjunction with 10 CFR part 50, Appendix B, propose plans for
coming into compliance with these requirements, and
(4) Request that addressees submit a safety assessment that
addresses any differences from the NRC's position regarding the
requirements of the TS in conjunction with 10 CFR part 50, Appendix B.
Background
Steam generator tubes function as an integral part of the reactor
coolant pressure boundary (RCPB) and, in addition, serve to isolate
radiological fission products in the primary coolant from the secondary
coolant and the environment. For the purposes of this generic letter,
tube integrity means that the tubes are capable of performing these
functions in accordance with the plant licensing basis, including
applicable regulatory requirements.
Title 10 of the Code of Federal Regulations (10 CFR) establishes
the fundamental regulatory requirements with respect to the integrity
of the SG tubing. Specifically, the general design criteria (GDC) in
Appendix A to 10 CFR part 50 state that the RCPB shall be ``designed,
fabricated, erected, and tested so as to have an extremely low
probability of abnormal leakage * * * and of gross rupture'' (GDC 14),
``designed, fabricated, erected, and tested to the highest quality
standards practical'' (GDC 30), and ``designed to permit periodic
inspection and testing * * * to assess * * * structural and leaktight
integrity'' (GDC 32). (There are similar requirements in the licensing
basis for plants licensed prior to 10 CFR part 50, Appendix A.)
Given the importance of SG tube integrity, all current PWR
licensees have TS governing the surveillance of SG tubes. These TS
typically do not prescribe non-destructive test methods for conducting
tube inspections or specify where a particular methodology should be
used. For example, current TS may employ the following or similar
nonspecific language:
Tube inspection for tubes selected in accordance with Table
[xxxx] means an inspection of the steam generator tube from the
point of entry (hot leg side) completely around the U-bend to the
top support of the cold leg, excluding sleeved areas.
[[Page 25910]]
The surveillance requirements do, however, specify acceptance
limits for SG tubes (often called plugging or repair limits). The
surveillance requirements seek to ensure that enough information is
obtained about imperfections (flaws) in the tubes to determine if TS
plugging limits are being met. Tube imperfections are defined in the TS
and include circumferential and axial cracks.
SG tube inspections are also subject to the quality assurance
requirements of 10 CFR part 50, Appendix B. Specifically, SG tube
inspections must be performed in accordance with Criterion IX of 10 CFR
part 50, Appendix B, which requires that ``measures shall be
established to assure that special processes, including welding, heat
treating, and nondestructive testing, are controlled and accomplished
by qualified personnel using qualified procedures in accordance with
applicable codes, standards, specifications, criteria, and other
special requirements.''
Licensees currently employ an eddy current test bobbin probe, at
least, to inspect the entire length of tubing required by the TS. The
bobbin probe is a high-speed probe which the industry has demonstrated
to be qualified for and capable of detecting volumetric flaws and
axially oriented cracks in the absence of significant masking signals.
Masking signals may be produced by tube geometry variations or
irregularities along the tube axis (such as small-radius U-bends, dents
and dings, and expansion transitions) or by tube surface
irregularities. Masking signals can also be produced by deposits on the
tube surface, adjacent support structures (such as the tubesheet),
probe wobble, cold working, permeability variations, or electrical
noise.
While the bobbin probe generally provides an effective means of SG
tube inspection over much of the tube length, experience has shown that
the bobbin probe may not be effective at locations where significant
masking signals are present. In addition, the bobbin probe generally
cannot detect circumferential cracks. Circumferential cracks can occur
at locations of high axial stress (e.g., small-radius U-bends and the
tubesheet expansion region).
Plant TS for virtually all PWRs require inspection of the entire
length of hot leg tubing within the tubesheet. With some exceptions
where specified in the plant TS, the acceptance limits (plugging
limits) for these inspections apply to all imperfections along the full
length of the tube in the tubesheet on the hot leg side, including
axial and circumferential cracks. Criterion IX, ``Control of Special
Processes,'' of 10 CFR part 50, Appendix B, requires in part that
nondestructive testing is to be accomplished by qualified personnel
using qualified procedures in accordance with applicable criteria. The
bobbin probe has not been qualified for and is not capable of reliably
detecting axial or circumferential cracks in the expanded region of
tubing inside the tubesheet; however, specialized probes are available
which have been qualified for this application.
As a result of these limitations, the industry practice is to
supplement the bobbin probe inspection with inspections by specialized
probes, such as the rotating pancake coil or plus point probe, that are
qualified for and capable of detecting degradation that is not
detectable with the bobbin probe. However, inspecting tubes with these
specialized probes is slower than with the bobbin probe. Therefore,
these slow-speed probes are typically not applied over the entire
length of a tube that is subject to inspection, but only at tube
locations where degradation which cannot be detected with the bobbin
probe (e.g., circumferential cracks, axial cracks in U-bends and
expansion transitions) is known to be present or considered to have a
potential to occur. This practice involves a degree of engineering
judgment to determine the locations in which potential degradation
mechanisms may exist that could lead to degradation that is not
detectable using a bobbin probe. The EPRI Steam Generator Examination
Guidelines provide guidance on assessing the potential for degradation
to occur at various locations.
In 2002, the staff learned of several instances in which licensees
were not fully implementing inspection methods capable of detecting
circumferentially oriented cracks at all locations where the potential
for such cracks exists and where, based on available evidence, there is
reason to believe such cracks may be present. These licensees were
conducting full-length bobbin probe inspections of the tubes, and were
performing additional inspections using specialized probes to inspect
for axial and circumferential cracks at certain locations, including
the tube expansion transitions near the top of the tubesheet. The
licensees conducted the specialized probe inspections at the tube
expansion transitions in an area that extended from 2 inches above the
top of the tubesheet to about 5 inches below the top of the tubesheet.
At several facilities, circumferential cracks were identified at tube
expansion transitions, as well as below the transitions near the bottom
of the zone being inspected. These results indicate a potential for
circumferential cracks to exist in the tubing below the zone inspected
with the specialized probe. However, each licensee also performed an
analysis indicating that circumferential cracks below the zone being
inspected would not be detrimental to tube structural and leakage
integrity. These licensees concluded, therefore, that inspections for
circumferential cracks with the specialized probe were unnecessary
below the zone already inspected with the probe. These analyses had not
been provided to the NRC staff.
The staff became aware of these activities during the licensees' SG
inspections conducted during refueling outages and asked the licensees
to submit TS amendment requests or safety analyses to obtain NRC
approval of their inspection approaches. The staff reviewed the
resulting submittals on a one-cycle basis before the plants restarted.
Subsequent to these plant-specific actions, the staff evaluated the
appropriate method to interact with licensees on this issue. Given the
potentially generic nature of the issue, the staff decided to
communicate this issue to addressees through issuance of this generic
letter.
Discussion
In the aforementioned instances, tube inspections with a
specialized probe near the top of the tubesheet clearly indicated the
potential for circumferential cracks to occur deeper into the tubesheet
beyond the region inspected with the specialized probes. In each
instance the licensee was aware of the potential for such cracks to
exist deeper into the tubesheet, but the licensee did not employ
techniques qualified for detecting such cracks based on the licensee's
analysis that such cracks did not have safety implications.
The staff acknowledges that there may be circumstances under which
certain flaws at certain locations may not pose a safety concern.
However, it is the staff's position that pending the submission of a
license amendment request clarifying the acceptability of a more
limited inspection approach, licensees are required under existing
requirements (TS in conjunction with 10 CFR part 50, Appendix B) to
employ inspection techniques capable of detecting all flaw types which
may potentially be present at locations which are required to be
inspected pursuant to the TS. The staff is concerned that in instances
similar to those cited above, failure to expand the scope of the
specialized probe inspection deeper into the tubesheet to detect cracks
likely to be present poses a potential compliance issue with
[[Page 25911]]
respect to the plant TS in conjunction with 10 CFR part 50, Appendix B.
In addition, the staff notes that not inspecting for cracks with
qualified procedures in the lower regions of the tubesheet would allow
any such cracks to remain in place. However, most plant TS state that
only tubes with imperfections less than 40 percent of the nominal tube
wall thickness are acceptable for continued service (there are
exceptions specified in some plant TS). While it is not known whether
any such cracks actually exist, the staff notes that the acceptance or
plugging limit for SG tube inspections is a specific technical
specification limit that can only be changed through the license
amendment process.
Also, for the instances cited above, the safety basis developed by
the licensees for not expanding the scope of the specialized probe
inspection beyond a specific distance (x-inches) into the tubesheet was
that any cracks below that distance were not detrimental to tube
integrity. This was based on analyses indicating that tubes only needed
a minimum embedment of x-inches into the tubesheet to exhibit
acceptable structural and accident leakage integrity. These analyses
have been performed to demonstrate that cracks below this embedment
distance do not impair SG tube integrity, even if these cracks cause
complete severance of the tube. According to plant final safety
analysis reports (FSARs), the SGs were designed in accordance with
section III of the American Society of Mechanical Engineers (ASME)
Code. In accordance with section III of the Code, the original design
basis pressure boundary for the tube-to-tubesheet joint included the
tube and tubesheet extending down to and including the tube-to-
tubesheet weld. The criteria of section III of the ASME Code constitute
the ``method of evaluation'' for the design basis. In the event
licensees are using a different ``method of evaluation'' for assessing
the steam generator pressure boundary, an evaluation under 10 CFR 50.59
would determine whether a license amendment is required in these cases.
In summary, for the cases discussed above, the TS required a tube
inspection for the full length of the tube within the tubesheet
(scope), and the findings from this inspection were required to be
evaluated against a repair (plugging) criteria. Neither the scope nor
the repair criteria in the TS contained provisions for limiting the
inspections through a licensee controlled analysis.
Based on these instances, the NRC cannot conclude that addressees
that are using such an approach remain in compliance with their TS in
conjunction with Criterion IX of 10 CFR part 50, Appendix B with regard
to the inspections they are performing. This concern stems, in part,
from the experience with some addressees relying on licensee controlled
analyses to limit the scope and therefore the repair or plugging of
defective SG tubes contrary to the requirements in the TS in
conjunction with Criterion IX of 10 CFR part 50, Appendix B, which
contains no provisions for limiting the inspections in this manner. It
is the staff's position that pending a license amendment clarifying the
inspection approach to be followed, licensees are required to employ
inspection methods capable of detecting all flaw types which may
potentially be present at locations which are required to be inspected
pursuant to the TS, as set forth above.
Based on these staff concerns, the NRC is issuing this generic
letter, consistent with the requirements in 10 CFR 50.54(f) to obtain
information necessary for the staff to determine if addressees are in
compliance with the technical specifications in conjunction with 10 CFR
part 50, Appendix B. In addition, licensees who have not been
implementing inspections consistent with the staff's position should
submit a safety assessment that demonstrates their ability to ensure
continued safe operation and addresses any differences relative to the
staff's position.
For licensees that cannot demonstrate continued compliance with the
TS in conjunction with 10 CFR part 50, Appendix B, owners group
involvement in the development of standard or generic approaches to
this issue, including TS and associated Bases wording, could be helpful
from the standpoint of minimizing resource impacts for both licensees
and the staff.
Requested Information
Within 30 days of the date of this generic letter, addressees are
requested to provide to the NRC the following information:
1. Addressees should provide a description of the SG tube
inspections performed at their plant during the last inspection. In
addition, addressees should provide an assessment of how the tube
inspections performed at their plant meet the requirements of the TS in
conjunction with Criterion IX of 10 CFR part 50, Appendix B, if they
are not using SG tube inspection methods with capabilities consistent
with the NRC's position. This assessment should also address whether
the tube inspection practices ensured that the tube plugging or repair
limits were implemented for the entire length of tubing required to be
inspected per the TS (i.e., discuss whether the techniques employed
during the tube inspections ensured flaws could be detected such that
the plugging or repair limits could be implemented).
2. If addresses conclude that full compliance with the TS in
conjunction with Criterion IX of 10 CFR part 50, Appendix B, requires
corrective actions to be taken, they should discuss their proposed
corrective actions (e.g., changing inspection practices consistent with
the NRC's position, or submitting a TS amendment request with the
associated safety basis for limiting the inspections). If addressees
choose to change their TS, the staff has included in Attachment 1
suggested changes to the TS definitions for a tube inspection and for
plugging limits to show what may be acceptable to the staff in cases
where the extent of the inspection in the tubesheet region is limited.
3. For plants where SG tube inspections have not been or are not
being performed consistent with the NRC's position on the requirements
contained in the TS in conjunction with Criterion IX of 10 CFR part 50,
Appendix B, the licensee should submit a safety assessment that
addresses any differences relative to the NRC's position (i.e., submit
the safety basis for not employing inspection methods capable of
detecting specific flaw types at specific locations where these flaw
types may potentially occur and where a tube inspection is required by
the TS), and include an evaluation of whether this safety assessment
constitutes a change to the ``method of evaluation'' (as defined in 10
CFR 50.59) for establishing the structural and leakage integrity of the
joint. Licensees should also determine whether a license amendment is
necessary pursuant to 10 CFR 50.59.
Required Response
In accordance with 10 CFR 50.54(f), addressees are required to
submit written responses to this generic letter. Two options are
available:
(a) Addressees may choose to submit written responses providing the
information requested above within the requested time period.
(b) Addressees who cannot meet the requested completion date are
required to notify the NRC in writing as soon as possible but no later
than 30 days from the date of this generic letter. The responses must
address any alternative course of action proposed, including the basis
for the acceptability of the proposed alternative course of action, the
basis for finding that the SGs remain
[[Page 25912]]
operable, and the schedule when the requested information will be
submitted.
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, submit a copy of the
response to the appropriate regional administrator.
Reasons for Requested Information
This generic letter requests that addressees submit information.
The requested information will enable the NRC staff to make a
determination as to whether licensees are implementing SG tube
inspections in accordance with applicable requirements. In cases where
licensees are not implementing inspections in such a manner, the
requested information will allow the staff to make a determination as
to the adequacy of the licensee's inspection program and compliance of
the licensee's program relative to existing requirements (the plant TS
in conjunction with 10 CFR part 50, Appendix B).
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 TS in conjunction with 10 CFR part 50, Appendix B)
are being met. 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
To be done after the public comment period.
Paperwork Reduction Act Statement
This generic letter contains information collections 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 (OMB), control number 3150-0011, which expires on
January 31, 2004.
The burden to the public for these 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
collection of information. The U.S. Nuclear Regulatory Commission is
seeking public comment on the potential impact of the collection of
information contained in the generic letter and on the following
issues:
(1) Is the proposed collection of information necessary for the
proper performance of the functions of the NRC, and will the
information 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 to be collected?
(4) How can the burden of the collection of information be
minimized? Can automated collection techniques be used?
Send comments regarding this burden estimate or on any other aspect
of these information collections, including suggestions for reducing
the burden, to the Information and Records Management Branch (T-6 E6),
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 collection of information unless it displays a currently
valid OMB control number.
If you have any questions about this matter, please contact one of
the persons listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Attachments: 1. Sample Changes to the TS for Plants Limiting
Inspections in the Tubesheet Region
Attachment 1
Sample Changes to the TS for Plants Limiting Inspections in the
Tubesheet Region
Plugging Limit means the imperfection depth at or beyond which
the tube shall be removed from service and is equal to 40% of the
nominal tube wall thickness. All tubes with degradation in the
portion of the tube from x-inches below the bottom of the expansion
transition or the top of the tubesheet to the bottom of the
expansion transition or the top of the tubesheet, whichever is
lower, shall be removed from service.
Tube Inspection means an inspection of the steam generator tube
from x-inches below the hot-leg expansion transition or the top of
tubesheet, whichever is lower, completely around the U-bend to the
top support of the cold leg.
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 in Rockville, Maryland, this 8th day of May, 2003.
For the Nuclear Regulatory Commission.
William D. Beckner,
Program Director, Operating Reactor Improvements, Division of
Regulatory Improvement Programs, Office of Nuclear Reactor Regulation.
[FR Doc. 03-11960 Filed 5-13-03; 8:45 am]
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