NextEra and NRC to continue monitoring ASR degradation at Seabrook Station Nuclear Power Plant

Degrading concrete at a New Hampshire nuclear plant has prompted the Nuclear Regulatory Commission to alert all of its facilities and applicants to the same risk elsewhere.

The Seacost Online reported on a meeting this week between NextEra Energy, operators of the Seabrook nuclear plant, and the U.S. Nuclear Regulatory Commission on Monday in Bethesda, Md., in which the utility reported that the cause of concrete degradation at Seabrook Station is more pervasive than originally stated, has already brought some of the structures below licensing standards and could further delay the nuclear plant’s effort to extend its operating license to 2050.

The alkali-silica reaction (ASR, caused by the interaction of water and concrete) that has been identified as the reason for the degradation is “outside current licensing requirements, and was first noted at the plant in 2010,” according to Michael Collisions, design engineer manager for NextEra Energy.

Alkali-Silica Reaction-induced (ASR) concrete degradation, a slow chemical degradation process that occurs when alkalis—usually from cement—react with certain types of silica in the aggregate when moisture is present.

The reaction produces an alkali-silica gel that can absorb water and expand to cause micro-cracking of the concrete. Excessive expansion of the gel can lead to significant cracking.

ASR was first noted at in work done in preparation for the submission of a request from the plant to extend its operating license for 20 years, and has already pushed the license extension process back approximately 11 months.

The licensee believes that the waterproof membrane was damaged during original installation or backfill activities causing water intrusion that resulted in the ASR problems.

The meeting this week was focused on areas surrounding how the concrete has already been affected by the reaction, what effect the reaction has had on the rebar that supports the concrete, and the rate of degradation.

The strength of the concrete had been reduced by 22 percent compared to samples taken at the time the concrete was poured during construction in 1979.

NextEra officials also tried to quell NRC concerns by indicating that the cracking of the concrete caused by ASR is more pronounced in the external layers than in portions where rebar supports the structure, implying that even though the structures may look to the naked eye to be degrading, that internally the structure still meets its regulatory function.

“Cracking is contained in the reinforced concrete structure,” said Richard Noble, NextEra’s director of engineering.

NextEra indicated that more in-depth testing of core samples taken last year by staff at the University of Texas will not be completed until 2014, and that a long-range plan for mitigating the effects of ASR will still need be developed at the conclusion of the testing, which may potentially push the licensing extension back even further.

NextEra will submit more information on its proposed Aging Management Program in late May, the company representatives told NRC officials.

The plant’s current license runs until 2030, 40 years from its start-up date in 1990. The extension, if granted, would allow the plant to operate until 2050.

 

At Seabrook, NRC inspectors noted the deterioration in their 2011 report.

“The walk-down inspections discovered the following plant material conditions (at Seabrook Station); (a) large amount of groundwater infiltration, (b) large amount of calcium carbonate deposits, (c) corroded steel supports, base plates and piping, (d) corroded anchor bolts, (e) pooling of water and (f) cracking and spalling of concrete,” the report states.

“The inspection further noted that the below-grade, exterior walls in the Control Building B Electrical Tunnel … have random cracking and for several years have been saturated by groundwater infiltration.

“The severity of the cracking and groundwater infiltration varies from location to location,” the report continues. “A comparison of the 2010 concrete compression test results to the 1979 concrete compression test results indicated a 21.7 percent reduction in the compressive strength of the concrete.”

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