[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