[Federal Register Volume 63, Number 60 (Monday, March 30, 1998)]
[Notices]
[Pages 15233-15235]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-8189]
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NUCLEAR REGULATORY COMMISSION
Proposed Generic Communication; Augmented Inspection of
Pressurized-Water Reactor Class 1 High Pressure Safety Injection Piping
(M99226)
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of opportunity for public comment.
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SUMMARY: The Nuclear Regulatory Commission (NRC) is proposing to issue
a generic letter to all holders of operating licenses for pressurized-
water reactors, except those who have permanently ceased operations and
have certified that fuel has been permanently removed from the reactor
vessel, to (1) identify a discrepancy in the American Society of
Mechanical Engineers (ASME) Code inspection requirements regarding the
inservice inspection of those portions of the high-pressure safety
injection system piping designated as ASME Code Class 1 with
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nominal pipe sizes between 4 inches and 1\1/2\ inches, inclusive, (2)
emphasize the need for addressees to maintain the integrity of this
reactor coolant pressure boundary piping in accordance with the
provisions of their current facility licensing bases, and (3) request
that addressees report to the NRC their previous actions for verifying
the integrity of the subject piping and their plans regarding future
inspections.
The proposed generic letter has been endorsed by the Committee to
Review Generic Requirements (CRGR). Relevant information that was sent
to the CRGR will be placed in the NRC Public Document Room.
The NRC is seeking comment from interested parties regarding both
the technical and regulatory aspects of the proposed generic letter
presented under the Supplementary Information heading. The NRC will
consider comments received from interested parties in the final
evaluation of the proposed generic letter. The NRC's final evaluation
will include a review of the technical position and, as appropriate, an
analysis of the value/impact on licensees. Should this generic letter
be issued by the NRC, it will become available for public inspection in
the NRC Public Document Room.
DATES: Comment period expires April 29, 1998. 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 Chief, Rules and Directives
Branch, Division of Administrative Services, U.S. Nuclear Regulatory
Commission, Mail Stop T6-D59, Washington, DC 20555-0001. Written
comments may also be delivered to 11545 Rockville Pike, Rockville,
Maryland, between 7:45 am to 4:15 pm, Federal workdays. Copies of
written comments received may be examined at the NRC Public Document
Room, 2120 L Street, N.W. (Lower Level), Washington, D.C.
FOR FURTHER INFORMATION CONTACT: Matthew Mitchell, (301) 415-3303.
SUPPLEMENTARY INFORMATION:
NRC Generic Letter 98-XX: Augmented Inspection of Pressurized-Water
Reactor Class 1 High-Pressure Safety Injection Piping
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) identify a discrepancy in the American Society of Mechanical
Engineers (ASME) Code inspection requirements regarding the inservice
inspection (ISI) of those portions of the high-pressure safety
injection (HPSI) system piping designated as ASME Code Class 1 with
nominal pipe sizes (NPS) between 4 inches and 1\1/2\ inches, inclusive.
Current ASME Code Section XI requirements only mandate a surface
examination for the subject piping while similarly sized sections in
the Class 2 portion of the HPSI system are required to have both
surface and volumetric examinations.
(2) emphasize the need for addressees to maintain the integrity of
this reactor coolant pressure boundary piping in accordance with the
provisions of their current licensing basis, particularly given known
thermal fatigue degradation mechanisms, and
(3) request addressees report to the NRC their previous actions for
verifying the integrity of the subject piping and their plans regarding
future inspections.
Background
This generic letter addresses concerns which have arisen based on
recent domestic and foreign reactor experience with thermal fatigue
degradation in reactor coolant system piping. On April 22, 1997, an
event occurred at Oconee 2, a Babcock and Wilcox-designed PWR, which
involved the unit being shut down due to cracking and leakage from a
weld location in the 2\1/2\-inch (NPS 2\1/2\), Class 1 portion of a
combination makeup and high-pressure injection line (equivalent to a
portion of the HPSI system as designated in the ASME Code). Upon
metallurgical examination of the weld, the licensee determined that the
crack consisted of a 360 deg. inside surface flaw with minimum depth of
30 percent through-wall, with the cracking having penetrated completely
through-wall over an arc length of 77 deg.. The licensee attributed the
cracking to thermal cycling and flow-induced vibration. Also, recent
experience at the Dampierre 1 facility in France has indicated that
thermal fatigue degradation (in a safety injection line) may, under
certain conditions, initiate and propagate through-wall in a time
period less than one ASME Code inspection interval. Additional details
on these events are found in NRC Information Notice 97-46.
Similar piping failures have also been recorded at other facilities
in the United States (Crystal River 3, Farley 2) and detailed
information on these events is available in the references to this GL.
The cracking observed at Crystal River 3 (a Babcock and Wilcox-designed
PWR) also occurred in a 2\1/2\-inch, Class 1 makeup/HPSI line and was
attributed to thermal fatigue, much like the Oconee event. The piping
failure at Farley 2 (a Westinghouse-designed PWR) also occurred in a
small-diameter high-pressure injection line, but was attributed to
thermal fatigue caused by relatively cold water leaking through a
closed globe valve in a boron injection tank bypass line. Additional
foreign experience has also found active degradation in small-diameter
Class 1 lines.
As a result of the Oconee 2 event and license renewal issues, the
staff reexamined the requirements given in Section XI of the ASME Code
for ISI of HPSI piping, using the 1989 Edition and the 1995 Edition for
reference. The staff examined the requirements given in both Subsection
IWB (for Class 1 piping) and Subsection IWC (for Class 2 piping). The
requirements for the Class 2 portions of the HPSI system are delineated
in Table IWC-2500-1, Examination Category C-F-1, ``Pressure Retaining
Welds in Austenitic Stainless Steel or High Alloy Piping,'' as amended
by the exemption criteria of IWC-1221. In combination, these provisions
require that Class 2 HPSI piping down to NPS 1\1/2\ receive both a
volumetric and a surface examination as part of a facility ISI program.
The requirements for the Class 1 portions of the HPSI system are
delineated in Table IWB-2500-1, Examination Category B-J, ``Pressure
Retaining Welds in Piping,'' as amended by the exemption criteria of
IWB-1220. Table-IWB-2500-1 requires only that a surface examination be
performed for Class 1 piping less than NPS 4, with the one exemption
provision applicable to the subject of this generic letter excluding
piping of NPS 1 and smaller from examination.
Therefore, for the HPSI system, the inspection criteria for Class 2
piping between NPS 4 and NPS 1\1/2\, inclusive, are more comprehensive
than those for Class 1 piping of the same size range.
As a result of these findings, the staff published in the Federal
Register a proposed rule with the intent of amending the requirements
of 10 CFR 50.55a (see 62 FR 63892). In proposed 10 CFR
50.55a(b)(2)(xv), the staff reconciled the differences between Class 1
and Class 2 inspection requirements noted above by requiring volumetric
examination of the Class 1 HPSI piping welds. The Rule change would
require
[[Page 15235]]
licensees to implement these volumetric examinations on a schedule
consistent with their current ISI program requirements.
Discussion
The NRC is issuing this generic letter to alert addressees to the
discrepancy noted above between Class 1 and Class 2 HPSI ISI
requirements and to request that addressees report to the NRC their
previous actions for verifying the integrity of the subject piping and
their plans regarding future inspection activities. Requirements to
ensure the integrity of the reactor coolant pressure boundary are
broadly incorporated in the current licensing basis of each reactor
facility and General Design Criterion 14 of Appendix A to 10 CFR Part
50, which explicitly states that the reactor coolant pressure boundary
must be ``designed, fabricated, erected, and tested to have an
extremely low probability of abnormal leakage, of rapidly propagating
failure, and of gross rupture.'' Effective inservice inspection
activities to monitor known degradation mechanisms and to identify
potential new sources of degradation are an integral element in
maintaining an extremely low probability of failure.
The staff's concern regarding the implementation of an effective
ISI program stems from the nature of the degradation previously
observed in some sections of small-diameter, Class 1 HPSI system
piping. The initiation and propagation of cracking due to thermal
fatigue is directly related to the magnitude of the cyclic thermal
stress range. Since thermal stress cycling in these lines is due to
changes in the temperature of the fluid in contact with the pipe wall,
the magnitude of the thermal stress cycles may be largest at the inside
diameter (ID) of the pipe. Therefore an effective ISI program should
include a volumetric (ultrasonic) evaluation to be able to detect
cracking at the ID before the cracking propagates through-wall. This
indicates that the current ASME Code ISI requirements (surface
examination only) for the Class 1 portion of this piping are
insufficient. In addition, after considering the experience at
Dampierre 1 in France (see Information Notice 97-46), requiring
volumetric inspections (consistent with the quality standards of
Appendix VIII to Section XI) to be conducted on a frequency consistent
with the facility's normal ASME Code Section XI ISI program may not be
sufficient to ensure reactor coolant pressure boundary integrity,
especially if no effective volumetric examination has been conducted
within the last ten years.
The staff notes that allowing for the potential failure of the
Class 1 portion of a HPSI line, while within a facility's design basis,
would unnecessarily challenge the facility's ability to mitigate such
an accident. Failure of an unisolable portion of the Class 1 HPSI line
could result in a small-break loss-of-coolant accident (SBLOCA) while
directly affecting the HPSI system, which is designed to mitigate a
SBLOCA. For these reasons, it is the staff's conclusion that volumetric
examination of the Class 1 portions of PWR HPSI systems should be
performed, at a minimum, consistent with the ASME Code's ISI
requirements for components of equivalent significance to reactor
safety.
The staff has also formally identified the issue of this
discrepancy between Class 1 and Class 2 ISI requirements to the ASME
Code via a letter to the Chairman of the ASME Section XI Subcommittee,
dated July 18, 1997.
Regulatory Analysis
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 the
applicable existing regulatory requirements. Specifically, the
requested information will enable the staff to determine whether or not
the Class 1 sections of PWR HPSI systems are being maintained in
accordance with 10 CFR Part 50, Appendix A, Criterion 14, or similar
requirements in the licensing bases for these facilities.
Required Information
Within 90 days of the date of this generic letter, each addressee
is required to provide a written report that includes the following
information for its facility:
(1) A discussion of the program, if any, in place at the facility
to perform effective volumetric examinations on those Class 1 portions
of the HPSI system which would be subject to the inspection scope of
ASME Code Section XI. This discussion should include information on the
qualification of the inspection procedure, the frequency of inspection,
the date of the last inspection, and the scope of the locations
inspected. In addition, the same information should be provided for any
inspection that has been (or will be) performed on the subject piping
but not as part of a defined inspection program.
(2) If the addressee currently has no program in place to
volumetrically inspect these portions of the HPSI system, given the
potential for the existence of an active degradation mechanism, a
discussion of any plans for establishing such a program.
Addressees shall submit the required written reports, pursuant to
10 CFR 50.4, to the U.S. Nuclear Regulatory Commission, ATTN: Document
Control Desk, Washington, D.C. 20555-0001, signed 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, addressees
should submit a copy of their respective report to the appropriate
regional administrator.
Backfit Discussion
This generic letter has been promulgated only as a request for
information. No backfit is either intended or approved in the context
of issuance of the generic letter. Therefore, the staff has not
performed a backfit analysis.
Related Generic Communications
NRC Information Notice 82-09, ``Cracking in Piping of Makeup
Coolant Lines at B&W Plants,'' dated March 31, 1982.
NRC Generic Letter 85-20, ``Resolution of Generic Issue 69: High
Pressure Injection/Makeup Nozzle Cracking in Babcock and Wilcox
Plants,'' dated November 11, 1985.
NRC Bulletin No. 88-08, ``Thermal Stresses in Piping Connected to
Reactor Coolant Systems,'' dated June 22, 1988.
NRC Bulletin No. 88-08, Supplement 1, ``Thermal Stresses in Piping
Connected to Reactor Coolant Systems,'' dated June 24, 1988.
NRC Bulletin No. 88-08, Supplement 2, ``Thermal Stresses in Piping
Connected to Reactor Coolant Systems,'' dated August 4, 1988.
NRC Bulletin No. 88-08, Supplement 3, ``Thermal Stresses in Piping
Connected to Reactor Coolant Systems,'' dated April 11, 1989.
NRC Information Notice 97-46, ``Unisolable Crack in High-Pressure
Injection Piping,'' dated July 9, 1997.
Dated at Rockville, Maryland, this 25th day of March 1998.
For the Nuclear Regulatory Commission.
Jack W. Roe,
Acting Director, Division of Reactor Program Management, Office of
Nuclear Reactor Regulation
[FR Doc. 98-8189 Filed 3-27-98; 8:45 am]
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