Resolution of Generic Safety Issues: Issue 86: Long Range Plan for Dealing with Stress Corrosion Cracking in BWR Piping (Rev. 1) ( NUREG-0933, Main Report with Supplements 1–34 )
In March 1982, leaks were detected in the heat-affected zones of the safe-end-to-pipe welds in two of the 28 in. diameter recirculation loop safe ends at Nine Mile Point Unit 1. Subsequent UT revealed extensive cracking at many weld joints in the recirculation system. The cause of the cracking was determined to be intergranular stress corrosion cracking (IGSCC).
Although cracking in large diameter piping had been found previously in Germany and Japan, the finding at Nine Mile Point Unit 1 was the first known U.S. occurrence of IGSCC in large piping (pipe diameters > 10 in.). IE Information Notice 82-39608 was issued on September 21, 1982 to alert all BWR licensees to the problem. The staff held meetings with GE, EPRI, and BWR Owners to discuss the relevance of the Nine Mile Point cracking to other BWRs. The near-term inspection of welds in large-diameter recirculation piping was discussed at a meeting of the staff with BWR licensees on September 27, 1982. Following this, IE Bulletin 82-03609 was issued on October 14, 1982 and required the 8 BWRs that were scheduled for outages through January 31, 1983 to perform inspections of a reasonable sample of the recirculation system welds during their respective outages.
After cracking in large-diameter piping was observed in 5 of the first 7 plants inspected in response to IE Bulletin 82-03,609 the staff issued IE Bulletin 83-02610 to extend the inspection requirements to all other BWRs. On August 1, 1983, the EDO established a Piping Review Committee to investigate specific incidents of pipe cracking at all plants with emphasis to be placed on IGSCC that had been reported in the recirculating systems of BWRs. Under the auspices of the NRC Piping Review Committee, a Task Group on Pipe Cracking was convened to develop a long-range plan for dealing with IGSCC.
The status and results of inspections of piping welds for IGSCC conducted at various operating BWRs were reported to the Commission in SECY-83-267,612 SECY-83-267A,613 SECY-83-267B,614 SECY-83-267C,615 SECY-84-9,616 SECY-84-9A,617 and SECY-84-166.618 The short-term reinspection and repair criteria were issued to BWR licensees in Generic Letter 84-11620 on April 19, 1984, and were to be used in inspections subsequent to the issuance of IE Bulletins 82-03609 and 83-02.610 The Task Group report (NUREG-1061,611 Volume 1) was drafted in April 1984 and submitted to the Commission in July 1984 with SECY-84-301,619 the staff's long-range plan for dealing with IGSCC in BWR piping. NUREG-1061,611 Volume 1, which includes value/impact analyses for the four possible solutions discussed below, was published in August 1984.
Pipe cracking resulting from IGSCC can cause a LOCA which, in turn, contributes to core-melt frequency.
The results of the Task Group study indicate that there are four possible solutions for preventing IGSCC in BWRs: (1) piping replacement without hydrogen water chemistry (HWC) - considered to be a long-term fix; (2) induction heating stress improvement and HWC - considered to be a long-term fix; (3) augmented inspection, weld repair, and HWC - considered to be a partial intermediate fix; and (4) augmented inspection and weld repair without HWC - considered to be only a short-term fix.
The staff's long range plan for resolving the problem called for the following actions: (1) issuance of NUREG-1061611; (2) incorporation of the Task Group recommendations into NUREG-0313,750 Revision 2, and issuance of this document; (3) preparation of a generic letter that incorporated NUREG-0313,750 Revision 2, and issuance of this letter to all BWR licensees requesting their proposals for bringing their plants into compliance with 10 CFR 50.55a(g); and (4) pursuance with the appropriate industry Code Committees changes in the areas of NDE personnel qualification and inspection procedures to bring ASME XI14 requirements into conformance with the staff's recommendations.
In January 1988, NUREG-0313,750 Revision 2, was published and Generic Letter 88-011111 was issued outlining the staff positions on IGSCC in BWR austenitic stainless steel piping; MPA B-84 was established by NRR for implementation purposes. Thus, this issue was RESOLVED and requirements were established.