Chiara Ferraris, NISTChairperson

Concrete Codes and Standards

for Nuclear Power Plants (CTG)

in NESCC

NESCCNuclear Energy Standards Coordination Collaborative

• Joint initiative of ANSI and NIST• Scope: identify and respond to the

current needs of the nuclear industry• Inaugural meeting June 2009• Meets at NIST 2-3 times a year • Next meeting is July 28, 2011

NESCC - Mission/Purpose

The NESCC is formed for the purpose of providing a cross-stakeholder forum to bring together representatives of the nuclear industry, standards developing organizations (SDOs), subject matter experts, academia, and national/international governmental organizations to facilitate and coordinate the timely identification, development and/or revision of standards that support the design, operation, development, licensing, and deployment of new nuclear power plants and other nuclear technologies, including advanced reactor concepts.

NESCC TG• Formed December 2009

– Concrete Codes and Standards for NPP (CTG) – report June 2011

– Standards Database Task Group

• Formed in May 2010:– Structural Design and Performance– Polymeric Piping for NPP

• New TG proposed (July 2011)– Electrical Cable Aging and Condition

Monitoring Codes and Standards for NPP – Repair of concrete of Existing NPP

Concrete Codes and Standards for NPP CTG

• Created December 2009

• Meetings: – Monthly conference

calls– in person (March 23,

2010) at the ACI convention in Chicago

• Final report – in print June 2011: – 6 ballots to finalize

the report

Membership - reviewers• 37 members from : ACI, AISC, Amec,

AmerenUE Callaway Nuclear Plant, AREVA, ASME, ASTM, BASF, Bechtel Power, Carrasquillo Associates, Commision Nacional de Seguridad Nuclear, DOE, Dominion Virginia Power, Duke Energy, EPRI, Exelon, FMC Lithium Division, ICA Fluor, INL, J.D. Stevenson, Los Alamos National Laboratory, NCMA, NIST, Purdue Univ., Sargent & Lundy, Savannah River Remediation, Southern Company, Unistar, University of Kansas, US-NRC, Westinghouse

• 34 reviewers from industry, government and SDOs

Scope

• Establish coordination and consistency of safety and non-safety related concrete requirements

• Identify new design requirements for safety related concrete components, and develop a plan to incorporate these new requirements into codes and standards.

• Identify and review all U.S. Nuclear Regulatory Commission (NRC) Regulatory documents related to concrete for nuclear power plant

Objectives • Objective 1: Review NRC documents

– Documents considered: Mattson report, NRC NUREG CR 5973, and NRC-regulatory documents

– Detailed analysis of the gaps in the concrete standards, specification, and codes for all SDO’s.

• Objective 2: Categorize and Identify– Discussion of codes and standards– A list of issues and recommendations

• Objective 3-4: Identify research needs– List of potential areas where research might

improve or facilitate the construction

Report Table of content

1. Introduction2. Objectives overview3. Discussion of Standards

Developing Organizations (SDO) and relevant documents

4. Issues unrelated to SDOs5. Research Needs6. Summary

Goal 2-3: SDO examined• ACI – Amer. Concrete Institute

• ASTM • AISC – Amer. Inst. of Steel Construction

• ASME – Amer. Soc. of Mechanical Engineers

• ANSI – Amer. National Standards Institute

• ASCE - American Society of Civil Engineers

• EPRI - Electric Power Research Institute• NEI - Nuclear Energy Institute

• NFPA - National Fire Protection Association• Foreign standards and code – exploration

SDOs Related issues• Recommendation to revise not recently

(more than 10 yrs) updated documents• List of items that should be addressed

in otherwise updated documents. – Each recommendation was structured:

• Title• a) Status today• b) What needs to be changed for application to

a nuclear power plant?• c) Why does it need to be changed? Provide a

reference or example

Main issues uncovered• ACI:

– Specific recommendations for 318, 349 & 359– Update some related ACI documents, i.e.,

related to Heavyweight concrete– Nuclear inspector certification program

• AISC/ACI: modular construction• Coordination of ACI/ASME

ASTM

• ASTM standards were not examined in detail, because NRC does not reference them directly in their documents.

• Their usage is implemented by referencing other SDO’s standards (codes, specifications, criteria, and guidelines)

Coordination DOE, NRC, SDOs

• NRC and DOE need to review any new version of SDOs documents before they are accepted for use in NPP

• Expedite NRC and DOE review of the most used codes and standards

• Resolve construction requirements in conflict with NRC current technical requirements.

• Better procedure for NRC to adopt SDOs documents

Goal 2-3:Issues unrelated to SDOs

4.1 Materials4.2. Implement new, mature

technologies4.3. Foreign standards and Codes

Materials• Material selection for concrete

mixture designs needs: – to ensure conformity to current standards

and codes – sufficient material supply is locally

available– commercially available concrete batch

mix materials, with adequate records – enable assured concrete service life for

over 60 – 75 years.

Issues to be considered

• Supplementary cementitious material (SCM) usage should be encouraged

• Aggregate sources need to be tested, e.g. ASR or enhanced mitigation procedures

• High density aggregates characterization

• Cement characterization, i.e. SCM interaction

Implement mature technologies

• Self consolidating concrete (SCC). There are no references to SCC in any of the NRC documents.

• Procedure for introduction of new technology in the nuclear construction.

• Performance based design of concrete

• Foreign codes and standards adoption

Goal 4: Research needs

5.1. High Strength reinforcing steel5.2. Concrete Radiation Shielding5.3. Durability of concrete5.4. Performance based design5.5 Ultra-high Performance Concrete (UHPC)5.6 Use of lapped Splices in regions of low

biaxial tension5.7 Temperature loading concrete

High Strength reinforcing steel

• Advantages– Reduce cross-sectional area– Save cost of material, shipping, placement– Reduce reinforcement congestion (fewer rebars)

facilitates concrete placement and consolidation

• Disadvantages– Higher steel stress at service load conditions

potential wider cracks and larger deflections (objectionable for aesthetics and permeability)

– Less deformation capacity– Better used with High strength concrete

Concrete Reinforcing Steel Institute (CRSI) – draft report

• Research plan in nuclear construction.– Feasibility Study for Containment/Safety-

Related Structure Designs– Database of Properties– Stress-Strain Characteristics and Ductility– Development Length and Tension Lap Splices– Compression Lap Splices– Standard Hooks– Mechanical Splices– Bending and Straightening– Headed Bars

– Seismic Design Requirements

Concrete Radiation Shield

• Neutrons and gamma photons incident on a concrete radiation shield can cause thermal gradients that can lead to stresses that cause cracking.

• Not addressed in standards:– Radiation and the thermal cycling of such shields – the dehydration of concrete shields caused by

long term exposure to temperatures above about 90 °C

– degradation in concrete's ability to shield against neutrons.

Durability of concrete

• Nuclear power plants would be more economical if their service life can be reliably designed for ages longer than 60 years.

• Models and standards should be available or developed that can quantitatively, with known uncertainty, predict the service life of the concrete materials used for their construction. Research to fill in knowledge gaps needs to be performed.

Performance based design

• The performance-based design of concrete is not yet fully implemented in non-nuclear construction but still should be considered for NPP.

• The obstacle to full implementation is the lack of test methods to measure desirable properties and the lack of models to predict performance after 50 or 100 years of service.

Ultra-high Performance Concrete (UHPC)

• Relatively new cementitious based materials with low permeability and incorporating fibers to obtain a very ductile and durable material.

• Standards and codes need to be developed to allow a wider use of this material that possibly could reduce the rebar congestion in some components of the plant.

Temperature loading concrete

• Lack of data on concrete subjected to temperature differential up to 100 °F (38°C)

• Better use of slag or FA to reduce heat generation for high strength concrete

Summary

• Main issues– Improve process for NRC, DOE to adopt

new technology and standards– Long list of research need: how can they

be addressed?

Next NESCC meeting• July 28, 2011 at NIST• Open to all• Need to register (free) to gain access

to NIST campus – ANSI website: www.ANSI.org (Standards Activities – Standard panels and forum – NESCC)

• Agenda: – AM Keynote speakers– PM TG presentations

New TG on Repair• Will be proposed that July 2011 meeting• Open for members: NPP owners, SDOs• Scope:

– Establish coordination and consistency for safety and non-safety concrete repairs in existing NPP: evaluate the concrete structure, assess the repair strategy, design and implement the repair and monitor the repair.

– Identify repair requirements .., and develop a plan to incorporate these new requirements into codes and standards.

– Identify U.S. Nuclear Regulatory Commission (NRC) Regulatory documents related to concrete repair for existing nuclear power plants and identify any needs.

Questions for you

• How to help NRC streamline the adoption of revised/new standards and codes?

• How can international standards be adopted by SDOs or NRC?

• How to address research needs? Who and funding?

• What other areas are critical for NPP?

Use of lapped Splices in regions of low biaxial

tension• The use of welded or mechanical splices of

reinforcement in regions of biaxial tension where tensile stresses perpendicular to the reinforcement are well below expected tensile crack stress in the concrete is both time consuming and expensive.

• It may be possible to show by comprehensive testing of this condition that lapped splices will reach the ultimate tensile capacity of the reinforcement being spliced. The testing would have to be very comprehensive.

• This is an area in which there is no data.

HS- reinforced steel – cont’d

Research needs for Grade 80 and higher:

1. splice and development length design of straight bars:• adequate information is available to make

decisions on how to proceed

2. anchorage of hook bars• no information exists

HS- reinforced steel – cont’d

3. use of high-strength bars for seismic loading, three areas require attention:• (a) the spacing of stirrups and ties needed

to limit buckling of Grade 80 bars in compression when they become plastic,

• (b) the inelastic cyclic performance of flexural members, and

• (c) bond slip through beam-column joints under cyclic loading.

HS- reinforced steel – cont’d

4. Use of headed reinforcing bars to develop high strength reinforcing steel:• ACI 318 currently limits fy to 60 ksi for the

design of headed bars. This limitation is based on a total lack of data for headed bars of higher strength, and, as a result, heads cannot be used to anchor Grade 75 or 80 headed bars.

• The formulation of design criteria for high-strength headed bars will require tests that develop bars to at least 80 ksi.

HS- reinforced steel – cont’d

5. use of mechanical splices or couplers with high strength reinforcing steel• data exists on the mechanical splice

performance for high-strength bars. The main task will be to consolidate that information.