Engineering Perspectives on First Year of New Reactor Construction Mohamed Shams, Ph.D., PE...
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Transcript of Engineering Perspectives on First Year of New Reactor Construction Mohamed Shams, Ph.D., PE...
Engineering Perspectives on First Year of New Reactor Construction
Mohamed Shams, Ph.D., PE
Structural Engineering BC
US NRC, Office of New Reactors
July 23, 2013
Purpose
• Present NRC staff view, from an engineering perspective (civil/structural), on construction inspection efforts and license amendment requests.
Background
• 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
• Stud Spacing• Structural Module Details
Nuclear Island RC
Structures, Shield
Building & Basemat
• Nuclear Island Wall Reinforcement Criteria
• Development Length for Basemat Reinforcement
• Basemat Shear Reinforcement Design Details
• Basemat Shear Reinforcement Spacing• Basemat Concrete and Rebar Details
Turbine Building
• Bracing System and UBC vs. IBC• Battery Room and Electrical Equipment
Changes• Layout & Floor Elevation Changes
Containment• Additional Electrical Penetrations• Chemical and Volume Control System• Primary Sampling System
Issued 17 License Amendments
Basemat Technical IssuesShear Reinforcement (T-heads)
5
• 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
Source: Headed Reinforcement Corporation (HRC) Website
Typical T-head Installation
Headed Reinforcement
Licensing Basis– Shear stirrups have T-
headed 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
6
Source: AP1000 DCD, Rev 19
Commitments / Guidance
• 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)
Objective - Ensure adequate anchorage for ductile rebar behavior
7
Headed Reinforcement
Resolution– Approved License
Amendment Requests• ACI 318-11 provisions
for headed reinforcement
• Increase elevator and sump pits thickness
– Revise shear design of walls
9
10
Basemat Technical Issues• 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.
Hooked Reinforcement
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.
Commitments / Guidance
• 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.
Objective - Ensure ductile behavior of connection of perimeter walls to the basemat
12
Basemat technical Issues
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
Lessons Learned• 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