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Standards Urged for Nuclear Concrete

Friday, September 13, 2013

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Outdated standards, coatings issues, and no concrete repair code for nuclear power plants top a list of red flags cited by experts in a new report on the needs of the aging nuclear industry.

The report, compiled over several years by the Nuclear Energy Standards Coordination Collaborative, aims to identify gaps, overlaps or conflicts in existing codes and standards in hopes of "harmonizing" commonly cited concrete standards.

"Codes and Standards for the Repair of Nuclear Power Plant Concrete Structures: Recommendations for Future Development" was authored by the NESCC's Concrete Repair Task Group and provides an overview of recommendations for improving the repair of concrete in nuclear power plants.

Nuclear Power Plant concrete repair
ANSI

A new report on nuclear power plant concrete structures found that concrete repair standards are non-existent and documents from the Nuclear Regulatory Commission are based on information that is up to 15 years old.

The NESCC is a joint initiative of the American National Standards Institute and the U.S. Department of Commerce's National Institute of Standards and Technology. Created in June 2009, the NESCC "seeks to identify the standards needed for the design, operation, development, licensing, and deployment of nuclear power plants and other nuclear technologies."

Formed in July 2011, the Concrete Repair Task Group has an open membership and tries to include representatives of standards developing organizations, construction industry firms, and those involved in repairing reinforced concrete in the nuclear power plant industry.

Objectives

The 100-page document follows the "logical progression" of the repair process: from initial inspection of the structure to monitoring the repair, including structure evaluation, developing a repair strategy and design, implementing the repair, and monitoring quality control.

The report is intended for use by researchers, standards development organizations and other relevant parties to improve knowledge about concrete repair in the nuclear industry.

The task group's objectives were to:

  • Categorize all concrete repair codes and standards referenced in Nuclear Regulatory Commission documents as "up-to-date," "outdated but appropriate for application," or "reference needs revision";
  • Identify relevant repair concrete codes and standards missing from the NRC regulatory documents;
  • Identify technologies and new research that could translate to new standards and codes for adoption by a standards development organization (e.g., seismic retrofitting, waterproofing, corrosion repair, pre-stressing tendons); and
  • Identify new technology and research needs to fill knowledge gaps in existing repair concrete codes and standards.

While working on the report, the task group also reviewed some international literature about repairing nuclear power plant concrete, and noted that global perspectives could be an "important resource" for future documents developed for the United States.

Call for a Repair Code

According to the report, no concrete repair code currently exists for nuclear power plants—an omission that the task force wants corrected. Creating a code would require an examination of the unique characteristics of concrete in power plants and related safety and design effects, the task group says.

Additionally, the task group recommended developing models to predict the service life of concrete, standard test methods for repair evaluations, and quality control and assurance. According to the report, models to predict service life or repairs for these structures are "non-existent."

The report also expressed concern about the lack of research on the effects of radiation on concrete, especially combined with the effect of long-term temperature exposure.

Nuclear Regulatory Commission
NRC

According to the task group, the nuclear power plant industry could benefit from a database of information on protective coatings for concrete structures.

Further complicating the matter, definitions related to repair differ between organizations, which can confuse specifiers and owners, the report says. The task group developed recommended definitions, suggesting that organizations work together to determine the best definitions and collaborate on future developments.

Obsolete Standards in Use

The report also found that some Nuclear Regulatory Commission documents reference obsolete versions of standards and recommended that the NRC implement a new way to review and adopt new relevant standards. Some documents cited by the NRC are 15 years old, so the materials and techniques referenced might well not be available today, the task group states.

The NRC should start pre-approving new technology and materials, as the Department of Transportation does now, the report says. Currently, each plant approves materials and techniques on a case-by-case basis, which is costly and prevents the use of new technology, it says.

"A combination of research and regulations could unify the various methodologies into a best practice that could be pre-approved by NRC to be used by any of the licensees," the report states.

The NRC could also benefit from adopting bridge technology such as sensors and remote monitoring of concrete degradation. \

Few models exist to predict the remaining service life of concrete in nuclear power plants while also accounting for past and future environments. Without the ability to predict the remaining service life, "it would be hard to ensure that any repair would last 40 years and more, as is needed for the renewal process."

Coatings for Corrosion

While many documents address protective coatings to prevent corrosion in concrete structures, strategies for mitigating the effects of corrosion in nuclear power plants is becoming increasingly important as the structures start to age.

Protective coating systems for nuclear power plants need clear standards, and tests for coatings and products should be established, specifically the acceptability of cathodic protection, the task group says. The report suggested developing a database to track the coating systems, products that have been used and how the products have performed.

When it comes to strengthening concrete, the report suggests turning to fiber-reinforced polymers, as they have shown to be a cost-effective and "widely utilized strengthening strategy in the building and transportation industries."

   

Tagged categories: ANSI; Certifications and standards; Concrete; Concrete defects; Concrete repair; Nuclear Power Plants

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