[Federal Register Volume 63, Number 152 (Friday, August 7, 1998)]
[Notices]
[Pages 42460-42461]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-21166]



[[Page 42460]]

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NUCLEAR REGULATORY COMMISSION


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.

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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 Internals 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 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.
    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.
    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 
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 September 8, 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-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, NW (Lower Level), Washington, DC.

FOR FURTHER INFORMATION, CONTACT: Gene Carpenter, (301) 415-2169.

SUPPLEMENTARY INFORMATION:

Addresses

    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.

Purpose

    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 Internals 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 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.

Background

    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 submitted the 
Electric Power Research Institute (EPRI) proprietary report TR-105697, 
``BWR Vessel and Internals 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 for 
alternative inspection requirements, and provides a technical basis for 
these recommended requirements. It initially proposed to reduce the 
scope of inspection of the BWR reactor pressure vessel (RPV) welds from 
essentially 100 percent of all RPV shell welds to 50 percent 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 circumferential welds will be inspected under this 
proposal.
    On August 7, 1997, the NRC issued Information Notice (IN) 97-63, 
``Status of NRC Staff's Review of BWRVIP-05,'' regarding licensee 
requests for relief. IN 97-63 stated that the staff 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 
welds during the fall 1997 or spring 1998 outage seasons''. The staff 
issued schedular reliefs for 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 shell 
welds only. Licensees will still need to perform their required 
inspections of ``essentially 100 percent'' of all axial welds.''

Discussion

    The staff has completed its final review of the information 
submitted by the BWRVIP and the staff's safety evaluation (SE) was 
transmitted to Carl Terry, Chairman of the BWRVIP, in a letter 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 
conditions that could lead to cold over-pressure events that could 
challenge vessel integrity. The BWRVIP's estimate of the frequency of

[[Page 42461]]

over-pressurization events that could challenge the RPV is 9.5  x  
10-4/yr for BWR-4 facilities and 9  x  10-4/yr 
for other than BWR-4 facilities. After accounting for actual injections 
which were not included in the BWRVIP analysis, the staff 
conservatively estimates that the total frequency could be as high as 1 
 x  10-3/yr (a point estimate).
    The initial industry review determined that the failure frequency 
of circumferential welds was 2.2  x  10-41/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 over-pressure events, 
determined that the limiting plant-specific conditional probability of 
vessel failure, P(F|E) for circumferential welds at 32 effective full 
power years (EFPY) were 1  x  10-6 from the BWRVIP's re-
analysis and 8.2  x  10-6 from the NRC staff's analysis. 
Combining the frequency of cold over-pressure events with the P(F|E), 
the BWRVIP failure frequency for the limiting circumferential welds was 
9.0  x  10-10/yr [(9  x  10-4/yr event frequency 
for a BWR-3)  x  (1.0 x 10-6 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  10-8/yr [(1  x  10-3/yr event frequency)  x  
(8.2  x  10-5 P(F|E))]. As depicted in NUREG 1560, Vol. I, 
core damage frequencies (CDF) for BWR plants were reported to be 
approximately 10-7/yr to 10-4/yr. In 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 pressurized thermal shock events 
is less than 5  x  10-6/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 below the acceptable core damage 
frequency (CDF) and large early release 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.

Permitted Action

    BWR licensees 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 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 operator 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 welds.
    This generic letter requires no specific action or written 
response. Any action on the part of addressees to request relief from 
the inservice inspection 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,
Jack W. Roe,
Acting Director, Division of Reactor Program Management, Office of 
Nuclear Reactor Regulation.
[FR Doc. 98-21166 Filed 8-6-98; 8:45 am]
BILLING CODE 7590-01-P