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Lab Aims to Test Nuclear-Plant Concrete

Tuesday, April 18, 2017

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Researchers at Oak Ridge National Laboratory are working on a better way to sense whether concrete at nuclear power facilities is experiencing a chemical reaction that can degrade it, putting the structures at risk.

ORNL engineer Dwight Clayton is working with a team from the University of Tennessee to use ultrasonic linear arrays to assess the state of the kind of thick concrete walls that exist at nuclear plants.

ultrasonic testing
Images: Dwight Clayton/ORNL

A team from Oak Ridge National Laboratory is adapting the use of ultrasonic arrays to detect evidence of the alkali-silica reaction in concrete at nuclear facilities.

The alkali-silica reaction (ASR) is a phenomenon that takes place in concrete made with some aggregates that contain silica materials; as the Portland Cement Association explains, alkali hydroxides in the concrete can react with the silica in the presence of water, This causes the formation of a gel, which then leads to cracking and spalling.

ASR at Nuclear Plants

The ASR has notably led to issues at Seabrook Station, a nuclear power plant in Seabrook, New Hampshire, where nuclear regulators cited operator NextEra Energy last year for failing to properly respond to ASR cracking of concrete.

According to ORNL engineer Dwight Clayton, who spoke to the laboratory’s publication ORNL News, the ASR is one factor the Nuclear Regulatory Commission is taking into consideration as it looks at the long-term viability of nuclear plants that were built in the mid- to late 20th century. Many were granted a 40-year license at the time of their construction, and while Clayton says extensions of 20 years are prudent for most, the NRC is now investigating whether further extensions—to a lifespan of 80 to 100 years—will be in the cards.

“That's where our group comes in,” Clayton said. “Our area of expertise is signal processing and instruments, so we looked at various technologies for evaluating concrete structures and settled on ultrasonic linear arrays. These devices use sound waves to examine the internal condition of concrete structures.”

Powering Up

Such arrays are already at work testing thinner slabs of concrete, but much of the work the ORNL team has done has involved using software to increase the instruments’ power to read concrete.

Concrete wall test

Part of the group's work involves building a concrete wall that will develop ASR in short order, so that they can test their detection method.

The arrays can be used to detect any kind of structural issue with the concrete. The team is looking specifically at using the equipment to detect the ASR, and last year it issued a paper indicating that methods already established to detect freeze-thaw cracking could also be applied in order to detect the ASR.

Part of the group's work involves building a concrete wall that will develop ASR in short order.

"By applying elevated temperature and 100 percent humidity to the test wall, we’ll be able to accelerate the process," Clayton said. "We have a two-year project with UT, but these two years of testing will simulate a much longer time in the life of a normal concrete wall.”

The two-year project involving ORNL and the University of Tennessee aims to develop a viable testing method that the NRC can put to work evaluating thick concrete walls by 2020.

   

Tagged categories: alkali-silica reaction (ASR); Colleges and Universities; concrete; Concrete defects; Nuclear Power Plants; Nuclear Regulatory Commission (NRC); Oak Ridge National Laboratory; Research

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