Federal Register: November 24, 2006 (Volume 71, Number 226)
DOCID: FR Doc E6-19838
NUCLEAR REGULATORY COMMISSION
Nuclear Regulatory Commission
NOTICE: NOTICES
ACTION: Reports and guidance documents; availability, etc.:
DOCUMENT ACTION: Notice of availability.
SUBJECT CATEGORY:
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
DOCUMENT SUMMARY:
The NRC is issuing its Final License Renewal Interim Staff Guidance LRISG200601. This LRISG provides interim guidance to applicants for license renewal for a plant with a BWR Mark I steel containment to provide a plantspecific 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 LRISGs 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 LRISG into the next revision of the license renewal guidance documents.
SUMMARY:
Plant-specific Aging Management Program for inaccessible areas of boiling water reactor Mark I steel containment drywell shell; license renewal,
SUPPLEMENTAL INFORMATION
Attachment 1 to this Federal Register
notice, entitled Staff Position and Rationale for the Final License
Renewal Interim Staff GuidanceLRISG200601: Plantspecific 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 LRISG200601. Attachment 2, entitled Final
License Renewal Interim Staff GuidanceLRISG200601: Plantspecific
Aging Management Program for Inaccessible Areas of BWR Mark I Steel
Containment Drywell Shell, contains the guidance for developing the
plantspecific aging management program. The NRC staff approves this
LRISG for NRC and industry use. The NRC staff will also incorporate
the approved LRISG 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 1Staff Position and Rationale for the Final License
Renewal Interim Staff GuidanceLRISG200601: PlantSpecific Aging
Management Program for Inaccessible Areas of BWR Mark I Steel Containment Drywell Shell
Staff Position
The NRC staff determined that a plantspecific 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
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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 sandbed 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 LRISG 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 plantspecific 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, longlived 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 2Final License Renewal Interim Staff GuidanceLRISG 200601: PlantSpecific Aging Management Program for Inaccessible Areas of Boiling Water Reactor Mark I Steel Containment Drywell Shell Introduction
Line Item II.B1.12 of NUREG1801, 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 freestanding 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 freestanding steel structure with no concrete backing, whereas the steel liner of a drywell is a leaktight membrane in direct contact with the concrete containment.
Historical Background
Information Notice (IN) 8699, ``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 8699, 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 sandbed region of the shell. Discussion
Generic Letter (GL) 8705, ``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 sandbed 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 8705 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 19871988 time frame fall approximately near the midpoint of the current 40year operating license period for most plants with Mark I steel containments.
The drywell shell is a passive, longlived 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 plantspecific 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.B1.12 of NUREG1801, 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 plantspecific 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
8705 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
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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:
\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.
(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 IWE1240 as identified in Table IWE25001, Examination Category EC.
(c) Use examination methods, that are in accordance with ASME Section XI IWE2500, which specifies:
(i) surface areas accessible from both sides shall be visually examined using a VT1 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 agerelated
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. E619838 Filed 112206; 8:45 am]
BILLING CODE 759001P
FOR FURTHER INFORMATION CONTACT
Ms. Linh Tran, License Renewal Project Manager, Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory Commission, Washington, DC, 205550001, telephone 3014154103 or by e mail at lnt@nrc.gov.