Mohamed Shams, Ph.D., PE
Structural Engineering BC
US NRC, Office of New Reactors
July 23, 2013

• Present NRC staff view, from an engineering perspective
(civil/structural), on construction inspection efforts and license amendment requests.

• AP1000 Rev. 19 certification on December 30, 2011
– Vogtle Units 3 & 4 license issuance February 10, 2012
– Summer Units 2 & 3 license issuance on March 30, 2012
3

License Amendment Requests
Modular
Construction
Nuclear
Island RC
Structures,
Shield
Building &
Basemat
Turbine
Building
Containment
• Stud Spacing
• Structural Module Details
• Nuclear Island Wall Reinforcement
Criteria
• Development Length for Basemat
Reinforcement
• Basemat Shear Reinforcement Design
Details
• Basemat Shear Reinforcement Spacing
• Basemat Concrete and Rebar Details
• Bracing System and UBC vs. IBC
• Battery Room and Electrical Equipment
Changes
• Layout & Floor Elevation Changes
• Additional Electrical Penetrations
• Chemical and Volume Control System
• Primary Sampling System

Shear Reinforcement (T-heads)
• Inspection of basemat rebar identified two issues for the concrete slabs below the elevator and sump pits
– Headed shear reinforcement not demonstrated to comply with ACI 349-01 Appendix B
– Shear reinforcement spacing exceeded d/2
Typical T-head Installation
Source: Headed Reinforcement Corporation (HRC) Website
5

Licensing Basis
– Shear stirrups have Theaded anchors at each end
– T-headed anchors are used where rebar mechanical anchorage is required
– Criteria of ACI 349
Chapter 12 are applied for rebar development
Source: AP1000 DCD, Rev 19
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Objective - Ensure adequate anchorage for ductile rebar behavior
• ACI 349, Section 12.6, Mechanical Anchorage
– Appendix B, Anchorage to Concrete
• ASTM A970
• Staff open to alternative approaches to demonstrate adequate anchorage
– Manufacturer literature
– Research and testing
– Alternative models (Strut-and-tie)
– Other relevant codes (e.g., ACI 318)
7

8

Resolution
– Approved License
Amendment Requests
• ACI 318-11 provisions for headed reinforcement
• Increase elevator and sump pits thickness
– Revise shear design of walls
9

• Basemat Hooked Reinforcement
During a March 2012 inspection, NRC staff identified a deviation in the detailed/installed nuclear island basemat rebar relative to the typical reinforcement depicted from the AP1000 DCD.
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Licensing Basis
• Design and analysis procedures for seismic Category I structures are in accordance with ACI 349.
• Foundation walls act integrally with the basemat to provide stiffness and distribute foundation loads.
• Basemat designed as a two-way slab.
• Basemat considered as a diaphragm, as such is part of the lateral-force resisting system.

Objective - Ensure ductile behavior of connection of perimeter walls to the basemat
• ACI 349-01
– Chapter 13 – Negative moment reinforcement must be developed at support
– Chapter 12 – #14 bar splices are prohibited
– Chapter 21
• Ductile connections
• Cannot invoke excess reinforcement provision (12.5.3.4) for elements in lateral force-resisting system.
12

Resolution
– Re-constitution of reinforcement hooks in basemat design.
– Approved License
Amendment Requests
• Increase in basemat concrete compressive strength to decrease required development length.
13

• Provide quantitative technical justifications for LARs
• Adhere to codes and standards in all areas of the design
• Detailed design must satisfy both the DCD and code commitments
• Perform detailed engineering analysis sufficiently in advance of installation
• Institute consistency checks
• Balance specificity and flexibility in licensing basis