ML12200A240

Presentation Slides on Davis-Besse Shield Building Crack

ML12200A240
Person / Time
Site:	Davis Besse
Issue date:	02/23/2012
From:	Bryce Lehman, Erickson A NRC/NRR/DLR/RAPB
To:
References
FOIA/PA-2012-0121
Download: ML12200A240 (6)

Text

2/23/2112 DAVIS-BESSE SHIELD BUILDING CRACK BRYCE LEHMAN ALICE ERICKSON I

Agenda oi Initial Condition c Condition Assessment o Licensee's Position o NRC's Position o Impact on License Renewal 1Wýq1 1

2/23/2012 Initial Condition

" Laminar crack identified in architectural flute shoulder area during hydro-demolition for

.replacement of reactor vessel closure head (October 1 0th)

" Crack found on the vertical side of the opening (left side, looking from the outside), generally along main reinforcing steel, and extends -6'across the top and -4' across the bottom 2

2/23/2012 Flute/Shoulder Geometry ILAMINAR CRACKS Condition Assessment o "Chipping back" along cracked " IRtesting performed on 15 of 1 6 areas revealed crack extended flute shoulders beyond construction opening

• Impulse Response (IR) o Core bores taken on 1 2 shoulders methodology employed to to confirm crack boundaries investigate extent of crack

" Core bores inspected using o IR testing indicated crack boroscope to identify crack depths extended -38' above construction opening and widths

• (4) core bores taken to validate IR a Very tight, less than 0.01" results 13 Indicated crack existed near outer reinforcement mat 3

2/23/2012 Condition Assessment wr -----

" IR testing performed on 4 of 8 "n IRtesting performed in 7 of 8 flute areas areas between flute shoulders "n Two small regions adjacent to

" Core Bores taken from 6 of 8 Main Steam Line penetration flute areas blackouts are cracked o IR testing and core bores a Extent of cracking unique to penetrations confirmed laminar cracking not o Cracking regions exist at top 20' present in flute areas of Shield Building wall outside 13 One flute did have a vertical shoulder area crack, but determined to be "n Spring line area appears to have isolated condition little or no cracking (top 5')

Condition Assessment Summary o Cracking is generic to all flute shoulder regions

" Cracks are confined to flute shoulder regions with exception of top 20' of Shield Building wall and two small regions near MSL penetrations

" Cracking exists at top 20' of Shield Building wall outside shoulder region (investigation ongoing) o Cracks are very tight, <0.01 ", and located near the outer reinforcing mat 4

2/23/2012 Licensee's Position o Believe sampling method of IR testing and core bores has characterized the extent of cracking in the structure

" Primary concern is ability of outside rebar to perform its intended function. Observations of construction opening and testing indicate concrete is firmly attached to rebar mat

" Based on structural evaluation, cracking does not impact ability of structure to perform its intended safety function o Root cause is underway NRC's Position

" NRC informed licensee they could restart (12/2) 13 Licensee developed a model with reasonable assumptions which demonstrated adequate margin for operability 13 Staff continues to evaluate whether the shield building conforms to the design code requirements in the CLB

" NRC issued CAL which included commitments to:

13 Determine root cause and develop a long-term monitoring program (due 2/28/12) 13 Select multiple un-cracked areas to investigate to verify the cracking is not spreading (due 90 days) 13 Analyze known cracked areas to verify the cracks are not growing 5

a 2/23/2012 License Renewal Impact

" The degraded shield building is a Part 50 issue affecting license renewal o DLR needs to understand if the degradation is age-related, and if so how it will be managed

" DLR has prepared a draft RAI asking the applicant to explain how the unique OE will be addressed by its AMPs 13 Currently finalizing RAI based on last week's developments and will be prepared to issue shortly a This will be tracked as an Open Item in the SER 6