Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
February 4, 1992
TO: ALL LICENSEES OF OPERATING BOILING WATER REACTORS (BWRs) AND
HOLDERS OF CONSTRUCTION PERMITS FOR BWRs
SUBJECT: "NRC POSITION ON INTERGRANULAR STRESS CORROSION CRACKING
(IGSCC) IN BWR AUSTENITIC STAINLESS STEEL PIPING" (GENERIC
LETTER 88-01, SUPPLEMENT 1)
The supplement provides acceptable alternative staff positions to some of
those delineated in Generic Letter (GL) 88-01, "NRC Position on IGSCC in BWR
Austenitic Stainless Steel Piping," dated January 25, 1988. The
alternatives are with regard to the inspection of reactor water cleanup
(RWCU) system piping outboard of the containment isolation valves and the
leak detection requirements pertaining to the operability of leakage
measurement instruments and the frequency of monitoring leakage rates. The
supplement also provides clarification or guidance on the staff's positions
regarding the sample expansion for Category D welds, the effect of
shrinkages resulting from weld overlay repairs or stress improvement (SI) on
the piping system and its supports and pipe whip restraints and the
technical specification (TS) amendments for incorporating the inservice
inspection statement and leak detection requirements as delineated in GL
88-01.
GL 88-01 addressed IGSCC near weldments in BWR piping that had occurred for
almost 20 years. Early cases of the cracking occurred in relatively small-
diameter piping. In early 1982, cracking was found in large-diameter piping
in a recirculation system of an operating BWR plant in this country. Since
then extensive inspection programs have been implemented for BWR piping
systems. These inspections resulted in the detection of significant numbers
of cracked weldments in almost all operating BWRs.
A number of domestic and foreign BWR owners have replaced or plan to replace
piping systems that experienced IGSCC with more resistant material. Other
owners are implementing countermeasures such as stress improvement or
hydrogen water chemistry to reduce the susceptibility of the piping to
IGSCC. In many cases, cracked weldments were repaired by reinforcing them
with weld overlay.
The BWR Owners' Group has sponsored substantial efforts pertaining to IGSCC
research. The results of these efforts, along with other related work by
vendors and consulting firms and confirmatory research sponsored by the NRC,
were the basis for the development of the Staff Positions delineated in GL
88-01 regarding the IGSCC problem.
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The technical bases for these positions are given in NUREG-0313, Revision 2,
"Technical Report on Material Selection and Processing Guidelines for BWR
Coolant Pressure Boundary Piping." This revision was a major task in the
staff's long-range plan to deal with BWR pipe cracking that was presented to
the Commission in SECY 84-301. The revision includes the relevant
recommendations of the Piping Review Committee Task Group on Pipe Cracking
that were issued as NUREG-1061, Volume 1, "Report of USNRC Piping Review
Committee," and consideration of public comments on that document,
NUREG-0313, Revision 2, describes the technical bases for the staff's
positions on materials, processes and primary coolant chemistry to minimize
and control IGSCC problems. Inspection schedules and inspection sample
sizes are based on the susceptibility of weldments to the initiation and
propagation of IGSCC. Inspection schedules are comparable to those
specified in Section XI of the ASME Boiler and Pressure Vessel Code for
piping material that is IGSCC resistant. Varying amounts of augmented
inspections are specified for piping that has a greater susceptibility to
cracking, for cases where there is less certainty about the effectiveness of
mitigation measures used, or for cases where repairs have been made.
The purpose of GL 88-01 was to seek information regarding the implementation
of the 13 staff positions that cover the above technical areas. The
GL 88-01 supersedes GL 84-11, "Inspection of BWR Stainless Steel Piping."
GL 88-01 applies to all BWR austenitic stainless steel piping that is 4
inches or larger in nominal diameter and that contains reactor coolant at a
temperature above 200øF during power operation regardless of ASME Code
classification. It also applies to reactor vessel attachments and
appurtenances such as jet pump instrumentation penetration assemblies and
head spray and vent components.
GL 88-01 does not apply to carbon steel piping classified as P-1 by the ASME
Code.
The staff's positions in GL 88-01 cover the following topics:
(1) materials
(2) processes
(3) water chemistry
(4) weld overlay reinforcement
(5) partial replacement
(6) stress improvement of cracked weldments
(7) clamping devices
(8) crack characterization and repair criteria
(9) inspection methods and personnel
(10) inspection schedules
(11) sample expansion
(12) leakage detection
(13) reporting requirements
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These staff positions are fully delineated in Attachment A of GL 88-01.
After GL 88-01 was issued, the staff discussed the generic letter with
several BWR operators and owners' group and concluded that the staff
positions on the following would create unnecessary hardship for plant
operators: frequency of reactor coolant system leakage measurement,
operability of leakage measurement instruments and inspection sample size of
RWCU system welds outboard of the containment isolation valves.
On the basis of discussions with BWR operators, industry consultants and the
BWR Owners' Group and a review of licensee's responses to GL 88-01, the
staff determined that the following acceptable alternative staff positions
and clarifications would facilitate the implementation of GL 88-01:
(1) The staff found that monitoring reactor coolant system (RCS) leakage
every 4 hours creates an unnecessary administrative hardship for plant
operators. Thus, RCS leakage measurements should be taken at least
once per shift, not to exceed 12 hours.
(2) The staff found that the radiation level associated with the RWCU
system piping outboard of the containment isolation valves is very
high; and this portion of piping is designed to be isolable and is
generally classified as nonsafety piping. Affected licensees requested
that they be exempt from GL 88-01 with regard to the inspection of this
piping. However, the service-sensitive stainless steel RWCU system
piping is subject to the most aggressive environment with regard to
IGSCC; therefore, until the actions associated with GL 89-10 on
motor-operated valves (MOVs) are completed by licensees, the staff
determined that an inspection of the subject piping on a sampling basis
of at least 10 percent of the weld population should be performed
during each refueling outage to ensure the structural integrity of the
piping.
(3) The staff's position on leak detection in GL 88-01 requires that for
BWR plants operating with any IGSCC Category D, E, F, or G welds, at
least one of the leakage measurement instruments associated with each
sump be operable and the outage time for inoperable instruments be
limited to 24 hours. If the outage time is longer than 24 hours, the
licensee should immediately initiate an orderly shutdown. The intent
of this requirement is to ensure that the capability to quantitatively
measure leakage is not lost for more than 24 hours because this
capability is essential for safe plant operation. After discussing
this position with the BWR operators, the staff found that leakage can
also be quantitatively measured by manually pumping the sump or
measuring the differences in sump level. Therefore, the staff finds
that manual leak rate measurements can be acceptable alternatives
during the period (30 days) when the drain sump monitoring system is
being restored, provided the licensee demonstrates their suitability
with regard to accuracy and inspectability.
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(4) GL 88-01 requested Category D welds to be 100% inspected every two
refueling cycles. There is no need for sample expansion if all
Category D welds are examined during each inspection. However, sample
expansion is required if Category D welds are examined on a sampling
basis during each inspection and cracking is identified during
examination. With adequate justification the sample expansion for
Category D welds may be limited to the piping system where cracking was
found.
(5) Consistent with Code requirements and the licensee's written
commitments, when weld overlay repairs or stress improvement (SI) is
applied, the licensee should assess the effect of shrinkages on the
piping system and its supports and pipe whip restraints. In addition,
the licensee should also assess the effect of the increase in
dead-weight and stiffness resulting from weld overlay repairs on the
piping systems.
(6) GL 88-01 requested that a plant's technical specifications be amended
to include a statement in the section on inservice inspection (ISI)
that the ISI program for piping covered by GL 88-01 will conform to the
staff's positions in the generic letter on schedules, methods,
personnel, and sample expansion. It also stated that if the ISI
section is removed from the TS as a result of the TS improvement
program this statement will remain in the ISI section. However, in
preparing the improved BWR Standard Technical Specifications, the staff
determined that the ISI section including the ISI statement will remain
in the TS and should not be incorporated in an administrative document.
(7) GL 88-01 requested that the staff's position on leakage detection be
incorporated into the TS of all affected licensees. The staff
subsequently determined that incorporation of the leakage detection
requirements in an administrative document is not acceptable.
Actions Requested
No specific action is requested beyond that contained in GL 88-01.
Reporting Requirements
No written response is required beyond that contained in GL 88-01.
Backfit Discussion
The backfit considerations of this supplement are unchanged from those
provided with the original generic letter, in that conformance with the
staff position is necessary to assure compliance with the stated regulations
and general design criteria (10 CFR Part 50, Appendix B; GDCs 4, 14, 30, 31
and 32) as well as the plant Technical Specification. The clarifications
and alternative staff positions presented in this supplement also assure
such compliance.
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This request is covered by Office of Management and Budget Clearance Number
3150-0011, which expires on May 31, 1994. The estimated average burden
hours is 160 man-hours per licensee response to GL 88-01, including
assessing of the new recommendations, searching data sources, gathering and
analyzing the data, and preparing the required letters. These estimated
average burden hours pertain only to these identified response-related
matters and do not include the time for actual implementation of the
requested actions. Comments on the accuracy of this estimate and
suggestions to reduce the burden may be directed to Ronald Minsk, Office of
Information and Regulatory Affairs (3150-0011), NEOB-3019, Office of
Management and Budget, Washington, DC 20503, and to the U.S. Nuclear
Regulatory Commission, Information and Records Management Branch, Division
of Information Support Services, Office of Information and Resources
Management, Washington, DC 20555.
If you have any questions about this matter, please contact the technical
contacts listed below or your NRR Project Manager.
James G. Partlow
Associate Director for Projects
Office of Nuclear Reactor Regulation
Enclosure:
List of Recently Issued Generic Letters
Technical Contacts: William H. Koo
(301) 504-2706
Marilee J. Banic
(301) 504-2771
