United States Nuclear Regulatory Commission - Protecting People and the Environment

"NRC Position on Intergranular Stress Corrosion Cracking (IGSCC) in BWR Austenitic Stainless Steel Piping" (Generic Letter 88-01, Supplement 1)


                                        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.


9201300217


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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 200�F 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


                                    - 3 -



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.

                                    - 4 -



(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.

                                    - 5 -



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

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