[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

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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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