NESCC 13-073 - NRC Presentation on Engineering

Report
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
Basemat Technical Issues
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
Headed Reinforcement
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
6
Commitments / Guidance
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
ACI 349 Model
8
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
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.
10
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
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
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

similar documents