[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