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."
While the extent of the problem is still being evaluated, structures identified to be affected by ASR are considered “operable but degraded”, meaning the NRC has 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 qualified NRC inspectors; 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
- Confirmatory Action Letter
- Enhanced Oversight
- Next Steps
- Publicly Available Documents
- Public Meetings
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. More information can be found on the NRC webpage “Crystal River Concrete Containment Separation.” 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.”
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.
Next Steps
NRC will continue its evaluations of ASR at Seabrook. A final decision on the plant’s license renewal application will be postponed pending the resolution of the issues.
The ongoing NRC actions are detailed below:
- Inspect the open Confirmatory Action Letter commitments and observations from NRC Inspection Report 2012-009.
- Continue evaluation of ASR at Seabrook and document results in a follow-up inspection report.
- Inspect NextEra’s ASR test 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.
This page includes links to files in non-HTML format. See Plugins, Viewers, and Other Tools for more information.
| Date | Title/Description |
|---|---|
| 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 |
| 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
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| 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.
This page includes links to files in non-HTML format. See Plugins, Viewers, and Other Tools for more information.
| Date | Title/Description |
|---|---|
| 12/11/2012 | 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. |
| 04/23/2012 | 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.
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