ML20237B649
| ML20237B649 | |
| Person / Time | |
|---|---|
| Issue date: | 07/31/1998 |
| From: | Roe J NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20237B637 | List: |
| References | |
| TAC-MA1689, NUDOCS 9808190125 | |
| Download: ML20237B649 (8) | |
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~ 7590-01 (P)
NUCLEAR REGULATORY COMMISSION i
Proposed Generic Communication BOILING WATER REACTOR LICENSEES USE OF THE BWRVIP-05 REPORT TO REQUEST RELIEF FROM AUGMENTED EXAMINATION REQUIREMENTS ON REACTOR PRESSURE VESSEL CIRCUMFERENTIAL SHELL WELDS (MA1689)
AGENCY: Nuclear Regulatory Commission ACTION: Notice of opportunity for public comment
SUMMARY
- The Nuclear Regulatory Commission (NRC) is proposing to issue a generic letter to all holders of operating licenses for boiling-water reactors (BWRs), except those who have permanently ceased operations, and have certified that fuel has been permanently removed from the reactor vessel, to inform addressees that the NRC staff has completed its review of the "BWR Vessel and Intemals Project [BWRVIP), BWR Reactor PrcJsure Vessel Shell Weld Inspection Recommendations (BWRVIP-05)," and that licensees of BWRs may request permanent (i.e., for the remaining term of operation under the existing, initial license) relief from the inservice inspection requirements of 10 CFR 50.55a(g) for the volumetric examination of i
circumferential reactor pressure vessel (RPV) welds. No specific action or written response is required.
The NRC is seeking comment from interested parties on both the technical and regulatory aspects of the proposed generic letter presented under the Supplementary Information heading.
I 9808190125 980731 PDR TOPRP EXIEPRI l
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' The proposed generic letter has been endorsed by the Committee to Review Generic Requirements (CRGR). Relevant infonnation that was sent to the CRGR will be placed in the NRC Public Document Room. 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 [30 days after FRN is published). Comments submitted after this dete 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-D69, 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: Gene Carpenter, (301) 415-2169 l
SUPPLEMENTARY INFORMATION:
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UNITED STATES l
NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555-0001 J
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NRC GENERIC LETTER 98-XX, BOILING-WATER REACTOR LICENSEES USE OF THE BWRVIP-05 REPORT TO REQUEST RELIEF FROM AUGMENTED EXAMINATION REQUIREMENTS ON REACTOR PRESSURE VESSEL CIRCUMFERENTIAL SHELL WELDS Addressees l
All holders of operating licenses for boiling-water reactors (BWRs), except those who have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel.
Puroose I
The U.S. Nuclear Regulatory Commission (NRC) is issuing this generic letter to inform addressees that the NRC staff has completed its review of the "BWR Vessel and Intemals Project (BWRVIP), BWR Reactor Pressure Vessel Shell Weld Inspection Recommendations (BWRVIP-05)," and that licensees of BWRs may request permanent (i.e., for the remaining term l
of operation under the existing, initial, license) relief from the inservice inspection requirements of 10 CFR 50.55a(g) for the volumetric examination of circumferential reactor pressure vessel (RPV) welds. No specific action or written response is required.
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By letter dated September 28,1995, as supplemented by letters dated June 24 and October 29, 1996, May 16, June 4, June 13, and December 18,1997, and January 13,1998, the BWRVIP L
submitted the Electric Power Research Institute (EPRI) proprietary report TR-105697, "BWR Vessel and Intemals Project [BWRVIP), BWR Reactor Pressure Vessel Shell Weld inspection Recommendations (BWRVIP-05)." The BWRVIP-05 report evaluates the current inspection requirements for the reactor pressure vessel shell welds in BWRs, formulates recommendations l
l for attemative inspection re Juirements, and provides a technical basis for these recommended
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l requirements. It initially propsed to reduce the scope of inspection of the BWR reactor i
pressure vessel (RPV) welds frorn essentially 100 percent of all RPV shell welds to 50 percent i
of the axial welds and zero percent of the circumferential welds; however, as modified, it proposes to perform inservice inspections (ISI) on essentially 100 percent of the RPV axial shell welds, and essentially zero percent of the circumferential RPV shell welds, except for the intersections of the axial and circumferential welds. Approximately 2 - 3 percent of the l
circumferential welds will be inspected under this proposal.
1 On August 7,1997, the NRC issued information Notice (lN) 97-63, " Status of NRC Staff's
- Review of BWRVIP-05," regarding licensee requests for relief. IN 97-63 stated that the staff I
would "... consider technically-justified requests for reliefs from the augmented examination in accordance with 10 CFR 50.55a(a)(3)(i),10 CFR 50.55a(a)(3)(ii), and 50.55a(g)(6)(ii)A(5) from BWR licensees who are scheduled to perform inspections of the BWR RPV circumferential shell
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welds during the fall 1997 or spring 1998 outage seasons". The staffissued schedular reliefs for
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inspections of the BWR RPV circumferential shell welds due during the fall 1997 outage season for four units who submitted technically-justified requests, and has issued schedular reliefs for two units during the spring 1998 outage season.
On May 7,1998, the staff issued IN 97-63, Supplement 1, which informed BWR licensees that the staff was extending the period in which it would ... consider technically justified requests for relief from the augmented examination in accordance with 10 CFR 50.55a(a)(3)(i),
50.55a(a)(3)(ii), and 50.55a(g)(6)(ii)(A)(5) from BWR licensees who are scheduled to perform inspections of the BWR RPV circumferential shell welds during the fall 1998 or spring 1999 outage seasons. Acceptably justified relief would be considered for inspection delays of up to two operating cycles for BWR RPV circumferential thell welds only. Licensees will still need to perform their required inspections of ' essentially 100 percent' of all axial welds."
l Discussion The staff has completed its final review of the information submitted by the BWRVIP and the i
staff's safety evaluation (SE) was transmitted to Carl Terry, Chairman of the BWRVIP, in a letter j
dated July 28,1998.
The staff previously concluded that beyond design-basis events occurring during plant shutdown could lead to cold over-pressure events that could challenge vessel integrity. The industry's response concluded that condensate and control rod drive pumps could cause
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conditions that could lead to cold over-pressure events that could challenge vesselintegrity.
The BWRVIP's estimate of the frequency of over-pressurization events that could challenge the RPV is 9.5 x 104/yr for BWR-4 facilities and 9 x 10d/yr for other than BWR-4 facilities. After accounting for actualinjections which were not included in the BWRVIP analysis, the staff conservatively estimates that the total frequency could be as high as 1 x 104/yr (a point l
estimate).
The initial industry review determined that the failure frequency of circumferential welds was 2.2 x 10d'/yr. This frequency was determined using importance sampling, generic weld variables and design basis events. Subsequent analyses using " Monte Carlo" calculation methods, plant-specific weld variables and pressures and temperatures associated with cold
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over-pressure events, determined that the limiting plant-specific conditional probability of vessel failure, P(FjE) for circumferential welds at 32 effective full power years (EFPY) were 1 x 104 from the BWRVIP's re-analysis and 8.2 x 104 from the NRC staffs analysis Combining the frequency of cold over-pressure events with the P(FjE), the BWRVIP failure frequency for the limiting circumferential welds was 9.0 x 104 /yr [(9 x 10d /yr event frequency for a BWR 3) x (1.0 x 104 conditional probability of failure)). The limiting plant-specific failure frequency for circumferential welds at 32 EFPY was determined by the staff to be 8.2 x 104/yr [(1 x 104/yr event frequency) x (8.2 x 104 P(FjE))). As depicted in NUREG 1560, Vol. I, core damage frequencies (CDF) for BWR plants were reported to be approximately 10#/yr to 10 /yr. In d
i addition, Regulatory Guide (RG) 1.154 indicates that PWR plants are acceptable for operation if the plant-specific analyses predict the mean frequency of through-wall crack penetration for l
4 pressurized thermal shock events is less than 5 x 104/yr. The failure frequencies of circumferential welds in BWR vessels are significantly below the criteria specified in RG 1.154.
RG 1.174 provides guidelines as to how defense-in-depth and safety margins are maintained, and states that a risk assessment should be used to address the principle that proposed increases in risk, and their cumulative effect, are small and do not cause the NRC Safety Goals to be exceeded. The estimated failure frequency of the BWR RPV circumferential welds is well be!ow the acceptable core damage frequency (CDF) and large early release l
frequency (LERF) criteria discussed in RG 1.174. Although the frequency of RPV weld failure can not be directly compared to the frequencies of core damage or large early release, the staff believes that the estimated frequency of RPV circumferential weld failure bounds the corresponding CDF and LERF that may result from a vessel weld failure. On the above bases, the staff has concluded that the BWRVIP-05 proposal, as modified, to eliminate BWR vessel circumferential weld examinations, is acceptable.
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Permitted Action BWR licensees may request permanent (i.e., for the remaining term of operation under the l
existing, initial, license) relief from the inservice inspection requirements of 10 CFR 50.55a(g) for the volumetric exarrination of circumferential reactor pressure vessel welds (ASME Code Section XI, Table IWB-2500-1, Examination Category B-A,' Item 1.11, Circumferential Shell Welds) by demonstrating that: (1) at the expiration of their license, the circumferential welds will continue to satisfy the limiting conditional failure probability for circumferential welds in the staff's
~ July 28,1998, safety evaluation, and (2) licensees have implemented opert. tor training and established procedures that limit the frequency of cold over-pressure events to the amount specified in the staff's July 28,1998, safety evaluation. Licensees will still need.to perform their required inspections of " essentially 100 percent" of all axial we:ds.
This generic letter requires no specific action or written response. Any action on the part of addressees to request relief from the inservice ir.spection requirements of 10 CFR 50.55a(g) for the volumetric examination of the circumferential reactor pressure vessel welds, in accordance with the guidance of this generic letter, is strictly voluntary.
Dated at Rockville, Maryland, this 31st day of July 1998.
FOR THE NUCLEAR REGULATORY COMMISSION h
J tW. Roe, Acting Director Civision of Reactor Program Management Office of Nuclear Reactor Regulation l
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