[Federal Register Volume 71, Number 226 (Friday, November 24, 2006)]
[Notices]
[Pages 67923-67925]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E6-19838]
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NUCLEAR REGULATORY COMMISSION
Notice of Availability of the Final License Renewal Interim Staff
Guidance--LR-ISG-2006-01: Plant-Specific Aging Management Program for
Inaccessible Areas of Boiling Water Reactor (BWR) Mark I Steel
Containment Drywell Shell
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of availability.
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SUMMARY: The NRC is issuing its Final License Renewal Interim Staff
Guidance LR-ISG-2006-01. This LR-ISG provides interim guidance to
applicants for license renewal for a plant with a BWR Mark I steel
containment to provide a plant-specific aging management program that
addresses the potential loss of material due to corrosion in the
inaccessible areas of their Mark I steel containment drywell shell for
the period of extended operation.
The NRC staff issues LR-ISGs to facilitate timely implementation of
the license renewal rule and to review activities associated with a
license renewal application. The NRC staff will also incorporate the
approved LR-ISG into the next revision of the license renewal guidance
documents.
ADDRESSES: The NRC maintains an Agencywide Documents Access and
Management System (ADAMS), which provides text and image files of NRC's
public documents. These documents may be accessed through the NRC's
Public Electronic Reading Room on the Internet at http://www.nrc.gov/reading-rm/adams.html. Persons who do not have access to ADAMS or who
encounter problems in accessing the documents located in ADAMS should
contact the NRC Public Document Room (PDR) reference staff at 1-800-
397-4209, 301-415-4737, or by e-mail at [email protected].
FOR FURTHER INFORMATION CONTACT: Ms. Linh Tran, License Renewal Project
Manager, Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory
Commission, Washington, DC, 20555-0001, telephone 301-415-4103 or by e-
mail at [email protected].
SUPPLEMENTARY INFORMATION: Attachment 1 to this Federal Register
notice, entitled Staff Position and Rationale for the Final License
Renewal Interim Staff Guidance--LR-ISG-2006-01: Plant-specific Aging
Management Program for Inaccessible Areas of Boiling Water Reactor Mark
I Steel Containment Drywell Shell contains the NRC staff's rationale
for publishing the Final LR-ISG-2006-01. Attachment 2, entitled Final
License Renewal Interim Staff Guidance--LR-ISG-2006-01: Plant-specific
Aging Management Program for Inaccessible Areas of BWR Mark I Steel
Containment Drywell Shell, contains the guidance for developing the
plant-specific aging management program. The NRC staff approves this
LR-ISG for NRC and industry use. The NRC staff will also incorporate
the approved LR-ISG into the next revision of the license renewal
guidance documents.
For the Nuclear Regulatory Commission.
Dated at Rockville, Maryland, this 16th day of November 2006.
Frank P. Gillespie,
Director, Division of License Renewal, Office of Nuclear Reactor
Regulation.
Attachment 1--Staff Position and Rationale for the Final License
Renewal Interim Staff Guidance--LR-ISG-2006-01: Plant-Specific Aging
Management Program for Inaccessible Areas of BWR Mark I Steel
Containment Drywell Shell
Staff Position
The NRC staff determined that a plant-specific aging management
program (AMP) is needed to address the potential loss of material due
to corrosion in the inaccessible areas of the Mark I steel containment
drywell shell for the period of extended operation.
Rationale
The current license renewal guidance documents (LRGDs) do not
provide sufficient guidance to address
[[Page 67924]]
inaccessible areas of the Mark I steel containment drywell shell.
Specifically, the inaccessible areas where the drywell shell is
surrounded by a concrete structure with a narrow distance between the
steel shell and the surrounding concrete inhibit visual inspection.
Past operating experience in Mark I steel containments indicates that
when water is discovered in the bottom outside areas of the drywell
(for example in the sand-bed area), the most likely cause would be the
water seeping through the space between the drywell shell and the
shield concrete.
In addition, numerous requests for additional information (RAIs)
were necessary on previous and current license renewal applications
(LRAs) to obtain the information needed by the staff to perform its
review. The purpose of this LR-ISG is to provide guidance on the
information that should be provided in the LRA to reduce the number of
RAIs issued to the applicants. Specifically, the staff has determined
that a plant-specific aging management program (AMP) is needed to
address the potential loss of material due to corrosion in the
inaccessible areas of the Mark I steel containment drywell shell for
the period of extended operation.
The drywell shell is a passive, long-lived structure subject to
aging degradation. Pursuant to 10 CFR 54.21, the applicant must
demonstrate that the effects of aging will be adequately managed so
that the intended function will be consistent with the current
licensing basis (CLB) for the period of extended operation.
Attachment 2--Final License Renewal Interim Staff Guidance--LR-ISG-
2006-01: Plant-Specific Aging Management Program for Inaccessible Areas
of Boiling Water Reactor Mark I Steel Containment Drywell Shell
Introduction
Line Item II.B1.1-2 of NUREG-1801, Volume 2, Revision 1, includes a
provision for aging management of the Mark I steel containment drywell
shells. However, the line item requires additional detail to address
the inaccessible areas of the Mark I steel containment drywell shells.
Specifically, the line item does not provide guidance when the distance
between the steel drywell shell and the surrounding concrete structure
is too small for the successful performance of visual examination.
All Mark I containment drywells are free-standing steel
construction, except for Brunswick, Units 1 and 2. The Brunswick Mark I
containment consists of a reinforced concrete drywell and a reinforced
concrete torus with a steel liner. A drywell shell is a free-standing
steel structure with no concrete backing, whereas the steel liner of a
drywell is a leak-tight membrane in direct contact with the concrete
containment.
Historical Background
Information Notice (IN) 86-99, ``Degradation of Steel
Containments,'' dated December 8, 1986, described an event related to
the degradation of the drywell shell at Oyster Creek Nuclear Generating
Station. IN 86-99, Supplement 1, dated February 14, 1991, explained
that the most likely cause of corrosion of the drywell shell in sand-
pocket areas (near the bottom of the drywell) and in the spherical
portion of the drywell at higher elevations, was the water in the gap
between the drywell and the concrete shield. The source of water was
noted as leakage through the seal between the drywell and the refueling
cavity. The IN supplement noted that the stainless steel liners in the
refueling cavity and equipment pool developed cracks along the
perimeter of the liner plates where they were welded to embedded
channels. The IN supplement also noted that ultrasonic testing (UT)
discovered minor corrosion in the cylindrical portion of the drywell,
and significant corrosion in the sand-bed region of the shell.
Discussion
Generic Letter (GL) 87-05, ``Request for Additional Information-
Assessment of Licensee Measures to Mitigate And/Or Identify Potential
Degradation of Mark I Drywells,'' requested additional information
regarding licensee actions to mitigate and/or identify potential
degradation of boiling water reactor Mark I drywells. As a result, a
number of licensees performed UT of their carbon steel drywell shells
adjacent to the sand-bed region. In addition, many licensees
established leakage monitoring programs for drain lines to identify
leakage that may have resulted from refueling or spillage of water into
the gap between the drywell and the surrounding concrete. UT performed
as a result of GL 87-05 provided a set of data points to determine the
drywell shell thickness that could be compared to the nominal
fabrication thickness and the minimum thickness required to withstand
the postulated loads. These UT measurements taken during the 1987-1988
time frame fall approximately near the mid-point of the current 40-year
operating license period for most plants with Mark I steel
containments.
The drywell shell is a passive, long-lived structure within the
scope of license renewal that is subject to aging degradation. Pursuant
to 10 CFR 54.21, the applicant must demonstrate that the effects of
aging will be adequately managed so that the intended function will be
maintained consistent with the current licensing basis for the period
of extended operation. On the basis of license renewal application
reviews and industry operating experience, the NRC staff determined
that a plant-specific aging management program (AMP) is needed to
address the potential loss of material due to corrosion in the
inaccessible areas of the Mark I steel containment drywell shell for
the period of extended operation.
Recommended Action
In addressing Line Item II.B1.1-2 of NUREG-1801, Volume 2, Revision
1, applicants for license renewal for plants with a Mark I steel
containment should perform an aging management review of the
inaccessible areas of its containment drywell shell and provide a
plant-specific aging management program that addresses the potential
loss of material due to corrosion for the period of extended operation.
In conducting the aging management review and developing the plant-
specific aging management program for the drywell shell, the applicant
should consider the following recommended actions based upon plant
design and operating experience:
(1) Develop a corrosion rate that can be reasonably inferred from
past UT examinations or establish a corrosion rate using representative
samples in similar operating conditions, materials, and environments.
If degradation has occurred, provide a technical basis using the
developed or established corrosion rate to demonstrate that the drywell
shell will have sufficient wall thickness to perform its intended
function through the period of extended operation.
(2) Demonstrate that UT measurements performed in response to GL
87-05 did not show degradation inconsistent with the developed or
established corrosion rate.
(3) Where degradation has been identified in the accessible areas
of the drywell, provide an evaluation that addresses the condition of
the inaccessible areas for similar conditions, that is, the applicant
should evaluate the acceptability of inaccessible areas when conditions
exist in the adjacent accessible areas that could indicate the presence
of or could result in degradation to such inaccessible areas.
(4) To assure that there are no circumstances that would result in
degradation of the drywell, demonstrate
[[Page 67925]]
that moisture levels associated with accelerated corrosion rates do not
exist in the exterior portion of the drywell shell, for example: (1)
The sand pocket area drains and/or the refueling seal drains are
monitored periodically; (2) the top of the sand pocket area is sealed
to exclude water accumulation in the sand pocket area; and/or alarms
are used to monitor regions for moisture/leakage.
(5) If moisture has been detected or suspected \1\ in the
inaccessible area on the exterior of the drywell shell or the source of
moisture cannot be determined subsequent to root cause analyses:
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\1\ The term ``suspected'' refers to surface areas likely to
experience accelerated degradation and aging as described in IWE-
1241(a) of Section XI of the ASME Code. Specifically, typical
locations are those areas exposed to standing water, repeated
wetting and drying, persistent leakage, and those with geometries
that permit water accumulation, condensation, and microbiological
attack.
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(a) Include in the scope of license renewal any components that are
identified as a source of moisture, if applicable, such as the
refueling seal or cracks in the stainless steel liners of the refueling
cavity pool walls, and perform an aging management review.
(b) Identify surface areas requiring examination by implementing
augmented inspections for the period of extended operation in
accordance with the American Society of Mechanical Engineers (ASME)
Section XI IWE-1240 as identified in Table IWE-2500-1, Examination
Category E-C.
(c) Use examination methods, that are in accordance with ASME
Section XI IWE-2500, which specifies:
(i) surface areas accessible from both sides shall be visually
examined using a VT-1 visual examination method,
(ii) surface areas accessible from one side only shall be examined
for wall thinning using an ultrasonic thickness measurement method,
(iii) when ultrasonic thickness measurements are performed, one
foot square grids shall be used, unless justified otherwise, and
(iv) ultrasonic measurements shall be used to determine the minimum
wall thickness within each grid. The location of the minimum wall
thickness shall be marked such that periodic reexamination of that
location can be performed.
(d) Demonstrate through use of augmented inspections performed in
accordance with ASME Section XI IWE that corrosion is not occurring, or
that corrosion is progressing so slowly that the age-related
degradation will not jeopardize the intended function of the drywell
shell through the period of extended operation.
(6) If the intended function of the drywell shell cannot be
demonstrated for the period of extended operation (i.e., wall thickness
is less than the minimum required thickness), identify actions that
will be taken as part of the aging management program to ensure that
the integrity of the drywell shell will be maintained through the
period of extended operation.
[FR Doc. E6-19838 Filed 11-22-06; 8:45 am]
BILLING CODE 7590-01-P