United States Nuclear Regulatory Commission - Protecting People and the Environment

Special NRC Oversight at Seabrook Nuclear Power Plant: Concrete Degradation

In 2009, NextEra Energy Seabrook, LLC (NextEra) realized that the intrusion of moisture into sections of walls in certain below-grade structures at the Seabrook nuclear power plant, in Seabrook, N.H., could cause the degradation of some of the concrete as evidenced by pattern cracking.

It was confirmed in 2010 that what is occurring at Seabrook is alkali silica reaction, or ASR. The result of the reaction is a gel, which can expand and may cause micro-cracks in the concrete. Graphics detailing the chemical reaction and the expansive gel can be viewed on slide 9 of the May 10, 2012 presentation titled, "Seabrook Station Safety in Light of the Alkali-Silica Reaction Occurring in Plant Structures."

The structures identified to be affected by ASR are considered “operable but degraded”, meaning that NextEra and the NRC have determined the structures can continue to safely perform their function based on: 1.) the extra safety margin that was included when the structures were designed and built; 2.) visual observations by licensee design engineers; 3.) the limited, localized areas where ASR is occurring; and 4.) slow progression of the concrete degradation.  For more information on the event and the status of NRC follow-up and planned activities, see the following topics on this page:

Summary of Event and Plant Conditions

In 2009 during the Seabrook License Renewal process, it was identified that the aggressiveness of the groundwater chemistry on concrete structures in contact with groundwater/soil needed to be determined. Testing was performed and in August 2010, Seabrook confirmed the presence of ASR degradation of concrete in below-grade walls of several Category 1 structures. Seabrook is the first plant in the U.S. nuclear industry to exhibit ASR in concrete structures on site. In response, NRC issued Information Notice (IN) 2011-20, “Concrete Degradation by Alkali Silica Reaction,” on November 18, 2011, to provide the industry with information related to the ASR identified at Seabrook.

The NRC staff’s review of this issue to date has determined that there are no immediate safety concerns due, in part, to existing safety margins, the localized nature of the ASR, and ongoing crack monitoring.

Concrete issues, other than ASR, have also been experienced at other nuclear power plants. Crystal River 3 was shut down due to cracking (e.g., delamination) of the concrete walls in the plant's containment building.  The issue occurred during work on an opening in the containment in preparation for a steam generator replacement project. Duke Energy, the plant's owner, announced on Feb. 5, 2013 that it planned to permanently cease operations at the Florida facility. In 2011, the Davis-Besse nuclear power plant discovered cracking in the Ohio plant's Shield Building wall, a concrete enclosure around containment, while contractors were creating an opening for replacement of the reactor vessel head. Information related to this issue can be found in NRC Inspection Report IR 05000346/2012007. It should be noted that the concrete degradation mechanisms in these plants is different than that identified at Seabrook.

Confirmatory Action Letter

On May 16, 2012, the NRC staff issued a Confirmatory Action Letter (CAL) to the plant’s owner, NextEra, confirming regulatory commitments made by the company to address ASR at the plant as a result of a management meeting with NRC staff on April 23, 2012.

On May 24, 2012, NextEra sent NRC a response to the CAL which included the root cause for the organizational causes associated with the occurrence of ASR at Seabrook and an evaluation entitled, “Impact of ASR on Concrete Structures and Attachments.”

On May 1, 2013, NextEra sent NRC a second submittal addressing the remaining CAL items, which included the details of their large specimen testing program and revised integrated corrective action plan.

The NRC conducted inspections to independently review NextEra’s actions to complete their commitments. NRC documented the results in NRC Inspection Reports (IR) 05000443/2012009 and 05000443/2012010.  Based on our reviews, NRC issued a closure letter on October 9, 2013, which closed CAL 1-2012-002.

Enhanced Oversight

On July 9, 2012, a “Working Group Charter” was developed to ensure that all aspects of the ASR issue were coordinated with the staff.

Further, on Sept. 14, 2012, a “Deviation Memorandum” that allows the agency to continue to devote additional review resources to the Seabrook ASR issues was approved by the NRC's Executive Director for Operations. The NRC's Reactor Oversight Process does not prescribe increased oversight for the plant based on its overall performance. However, the NRC staff determined that additional inspections and assessments were needed to support the review of licensee commitments and planned large-scale concrete specimen testing by the licensee, the development of staff technical guidance, and stakeholder communications and outreach activities.

Following the completion of the second CAL follow-up inspection report (NRC IR 05000443/2012010) and mid-cycle performance assessment per IMC 0305, NRC closed the Deviation Memorandum as documented in NRC letter, “Mid-Cycle Performance Review,” dated September 3, 2013.  The NRC will continue to conduct inspections approximately every six months as part of the Reactor Oversight Process baseline inspection program and document the results in publically available inspection reports.  The NRC also plans to continue oversight by the Seabrook ASR Issue Technical Team (SAITT).  Accordingly, a revision to the SAITT Charter was issued on February 19, 2014 to reflect completion of activities associated with the CAL and to update the NRC ongoing review objectives.

Next Steps

The NRC will continue evaluation of ASR at Seabrook through:

  • Continued review of NextEra's structures monitoring program implementation and results, which will be documented in subsequent inspection reports approximately every six months.
  • Inspections of NextEra's ASR testing program at the University of Texas

Publicly Available Documents

The following table lists the publicly available documents that the NRC has issued in connection with the special oversight of Seabrook.

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Date Title/Description
02/19/2014 Revision to NRC Seabrook Alkali-Silica Reaction Issue Technical Team Charter
01/15/2014 Request for Additional Information for the Review of the Seabrook License Renewal Application – Set 20
12/23/2013 Aging Management Program Audit Report Regarding Seabrook Station License Renewal Application
12/06/2013 NRC response to UCS letter regarding ASR concrete degradation
11/04/2013 Union of Concerned Scientists (UCS) letter regarding ASR concrete degradation at Seabrook Station, dated 11/4/2013
10/09/2013 Seabrook Station, Unit No. 1 – Closure of Confirmatory Action Letter 1-2012-002
09/13/2013 Supplemental license renewal application information submitted to the NRC on September 13, 2013 regarding the Seabrook ASR monitoring program
08/09/2013 Seabrook Station, Unit No. 1 - Confirmatory Action Letter Follow-Up Inspection - NRC Inspection Report 05000443/2012010
05/01/2013 NextEra response to Confirmatory Action Letter Items 2, 4, 8, dated May 1, 2013
02/28/2013 NextEra response to Confirmatory Action Letter Item 11, dated February 28, 2013
01/14/2013 Revision to Confirmatory Action Letter, Seabrook Station, Unit 1 - Information Related to Concrete Degradation Issues
12/13/2012 NextEra response to Confirmatory Action Letter, dated December 13, 2012
12/03/2012 Seabrook Station, Unit No. 1 - Confirmatory Action Letter Follow-Up Inspection - NRC Inspection Report 05000443/2012009
09/05/2012 NRC staff request for deviation from Reactor Oversight Process to provide increased oversight of ASR issues at Seabrook
07/09/2012 Charter for NRC technical team assigned to look at ASR issues at Seabrook
06/28/2012 NexrEra response to CAL:  Large scale testing
06/21/2012 NexrEra response to CAL: Large scale testing (enclosure)
06/08/2012 NexrEra response to CAL:  Corrective Action Plan
05/24/2012 NextEra response to NRC CAL on Seabrook ASR
05/16/2012 Supplemental license renewal application information submitted to the NRC on May 16, 2012 regarding ASR monitoring at Seabrook
05/16/2012 NRC Confirmatory Action Letter (CAL) issued to NextEra on May 16, 2012 regarding information required on ASR issues at Seabrook
05/10/2012 NextEra Supplement to Actions for Resolution of ASR issues
05/03/2012 NextEra Actions for Resolution of ASR Issues
03/26/2012 NRC Inspection Report, issued March 26, 2012 on ASR at Seabrook

Public Meetings

The following table lists the public meetings in connection with the special oversight of Seabrook.

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Date Title/Description

The NRC conducted an open house and a public meeting with NextEra to discuss NextEra's testing program regarding concrete degradation caused by the Alkali-Silica Reaction (ASR) at Seabrook Station.


The NRC conducted a public meeting with NextEra to discuss aging effects and management associated with alkali-silica reaction regarding the license renewal application for Seabrook Station.


The NRC conducted an open house and public meeting to discuss the safety implications and status of its review of NextEra's commitment actions related to the ASR conditions in safety-related structures at Seabrook Station.


The NRC conducted a public meeting with representatives from NextEra to discuss NextEra’s plans and schedule regarding concrete degradation caused by ASR at Seabrook as referenced in the NRC inspection report.

Page Last Reviewed/Updated Thursday, March 20, 2014