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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."

More recently, NextEra has identified that some of the ASR-affected structures at Seabrook have evidence of ASR bulk expansion (macro-cracking and some reinforced concrete wall displacements) due to the aggregate effect of ASR-induced micro-cracking.

The structures identified to be affected by ASR remain "operable but degraded," meaning that NextEra has determined the structures can continue to perform their safety functions.  The basis for continued operability include confirmatory engineering design reviews using computer-based finite element analysis and detailed reviews of structural design calculations that demonstrate that sufficient safety margins remain based upon field measurements and/or bounding (worst-case) ASR degradation values.  Reinforced concrete structural design margins for Seabrook were established in accordance with American Concrete Institute (ACI) Code 318-1971 and ensure that the as-built (design) structural capacity exceed any assumed load or specified load combinations.  NRC inspectors have reviewed these analyses, design reviews and design calculations during onsite inspections and have concluded that NextEra has adequately demonstrated that the concrete structures as Seabrook affected by ASR remain "operable but degraded" while the NRC staff conducts ongoing licensing reviews.  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 are 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 continues 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 maintains 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. On September 6, 2017, the SAITT Charter Revision 2 was issued to reflect the completion of NextEra's large-scale concrete testing program and to update the ongoing NRC objectives.

Developments Since Confirmatory Action Letter Closure

Following closure of the Confirmatory Action Letter on Oct. 9, 2013, the NRC held a public meeting in Hampton, N.H., to discuss the ASR issue in detail, as well as the agency's monitoring efforts going forward. In 2014 and 2015, the NRC conducted periodic inspections and audits at the Seabrook facility and at the University of Texas focused solely on the ASR issue.

NextEra's testing of large-scale ASR-affected test specimens at the Ferguson Structural Engineering Laboratory (FSEL) at the University of Texas – Austin commenced in late 2013 and was completed under NextEra's direction in February 2016. Based on testing program developments in 2015, NextEra revised its structures-monitoring/ASR-monitoring aging-management program to include through-wall expansion monitoring. This expansion will be monitored by devices installed in the first half of 2016 in over 40 representative locations.

In 2014, the NRC documented findings involving discrete, horizontal cracking in an internal wall of the Residual Heat Removal (RHR) vault and displacements and cracking associated with the Fuel Storage Building. In 2015, the NRC documented findings that identified global bulk expansion of the containment enclosure building. The staff concluded these findings were of very low safety significance because the safety function of these structures was not affected. Additionally, as part of the license renewal process, the NRC requested additional information from NextEra to assess whether the effects of aging involving building deformation and discrete cracks will be adequately managed so that intended functions are maintained consistent with the current licensing basis during the period of extended operation. NextEra's response was received by the NRC on Aug. 9, 2016, and is currently under review.

In 2016, the NRC documented an unresolved item when it was identified that further inspection was warranted to review an issue of concern regarding implementation of the Seabrook Structures Monitoring Program and structural evaluations of the CEB and RHR/CS Vault. The inspection that reviewed this unresolved item identified a violation for two examples where NextEra did not perform initial and prompt operability determinations for ASR-affected structures until prompted by NRC inspectors. NextEra responded to this violation in early June 2016, indicating that while the violation occurred, the affected structures in question remained operable. An inspection in the fall of 2016 (IR 2016-004) found that NextEra had taken a number of corrective actions to prevent recurrence and closed this issue. Also in 2016, NextEra has had three meetings with NRC staff, on March 29, April 28 and June 15 to discuss ASR-related issues at Seabrook. As described further in the Licensing section, in August 2016, NextEra submitted License Amendment Request (LAR) 16-03 to revise the Seabrook Updated Final Safety Analysis Report (UFSAR) to include methods for analyzing seismic Category I structures with concrete affected by ASR. The NRC staff plans to perform a regulatory audit of this application. This technical audit will be performed consistent with NRC Office of Nuclear Reactor Regulation, Office Instruction LIC-111, "Regulatory Audits," dated Dec. 29, 2008 (ADAMS Accession No. ML082900195). The date of this audit has not yet been established. The NRC staff performed a regulatory audit of this application. This technical audit was performed March 19 – 23, 2018 consistent with NRC Office of Nuclear Reactor Regulation, Office Instruction LIC-111, "Regulatory Audits," dated Dec. 29, 2008 (ADAMS Accession No. ML082900195).

Licensing

The NRC has two licensing actions under review that are directly associated with ASR: a license renewal application (LRA) and a license amendment request (LAR) to update the current licensing basis to recognize the effects of ASR.

In May 2010, NextEra, submitted an LRA to renew the Seabrook facility operating license for up to an additional 20 years. An item was left open in the Seabrook license renewal Safety Evaluation Report (SER) due to NRC staff concerns that NextEra had not enhanced the Structures Monitoring Program to manage the effects of ASR. For the NRC staff to complete its LRA review and close this SER open item, NextEra needs to update the licensing renewal application to include a sufficient aging management program for concrete structures impacted by ASR to ensure safe operation for extended operation (2030–2050). The project schedule and application information can be found on the NRC webpage devoted to the Seabrook Station, Unit 1 – License Renewal Application. On Aug. 9, 2016, the NRC received NextEra's updated LRA submittal and it is currently under NRC staff review. In October 2016, a license renewal audit was conducted and the results were issued in December 2016. Also in December 2016, the staff requested additional information for review of the LRA and later that month NextEra responded.

On June 15, 2016, a public meeting was held with NextEra to provide an opportunity to present to the NRC staff its plan for an LAR regarding revising the licensing basis to account for the Alkali-Silica Reaction at the Seabrook facility. On August 1, 2016, NextEra submitted the LAR to revise the licensing basis of the current operating license. NextEra has requested approval of a methodology to analyze seismic Category I concrete structures affected by ASR. This application is currently under NRC staff review. In October 2016, the staff accepted the LAR for review.  The NRC staff performed a regulatory audit of this application the week of June 5, 2017 (ML 17199T383).  This technical audit was performed consistent with the NRC Office of Nuclear Reactor Regulation, Office Instruction LIC-111, "Regulatory Audits," dated December 29, 2008.  In addition, a public meeting was held between NextEra and the NRC on November 17, 2017, to discuss the path to resolution for requests for additional information (RAIs) related to the structural analysis methods under the NRC staff's review of the ASR license amendment request (ML17340A186).

Earlier in 2017, a request for hearing was submitted by the C-10 Research & Educational Foundation regarding the LAR.  On October 6, 2017, the Atomic Safety and Licensing Board granted C-10's hearing request, determining that C-10 had standing and admitting a single reformulated contention for hearing.  On November 29, 2017, an Initial Scheduling Order was issued by the Board to govern this proceeding.  More information on the NRC's adjudicatory process, as well as documents related to the Seabrook ASLB case (LBP-17-07). In particular, the October 6, 2017, ASLB decision can be found on this webpage.

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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.
  • Review licensing documents and evaluations submitted to the NRC in support of NextEra's request to revise the current licensing basis in LAR 16-03.
  • Review licensing documents and evaluations submitted to the NRC in support of aging management of concrete structures impacted by ASR.

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
02/28/2018 Supplement 60 – Response to Final Requests for Additional Information for the Safety Review of the Seabrook Station License Renewal Application – ASME Section XI, Subsection IWL Program
02/12/2018 Seabrook Station Integrated Inspection Report 05000443/2017004, documenting a semi-annual review of ASR monitoring
12/11/2017 Seabrook Station – Response to Request for Additional Information Regarding License Amendment Request Related to Alkali-Silica Reaction (CAC No. MF8260; EPID L-2016-LLA-0007)
11/03/2017 Supplement 58 – Revised Alkali-Silica Reaction Aging Management Program
10/11/2017 Seabrook Station, Unit No. 1 - Request For Additional Information Regarding License Amendment Request Related To Alkali-Silica Reaction (CAC NO. MF8260; EPID L-2016-LLA-0007)
10/03/2017 Seabrook Station – Response to Request for Additional Information Regarding License Amendment Request 16-03 Related to Alkali-Silica Reaction (CAC No. MF8260)
09/11/2017 Request For Additional Information (RAI) Regarding License Amendment Request (LAR) 16-03 To Revise Current Licensing Basis To Adopt A Methodology For The Analysis Of Seismic Category I Structures With Concrete Affected By Alkali-Silica Reaction, NextEra Energy Seabrook, LLC, Seabrook Station Docket No. 50-443
08/04/2017 Seabrook Station, Unit No. 1 - Request for Additional Information Regarding License Amendment Request Related To Alkali-Silica Reaction (CAC No. MF8260)
07/26/2017 Seabrook Station, Unit No. 1 - Site Visit Report Regarding Regulatory Audit for Alkali Silica Reaction License Amendment Request (CAC No. MF8260)
07/20/2017 Revision to License Renewal ASME Section XL, Subsection IWL, Program Operating Experience
06/27/2017 Response Date Change Related to Request for Additional Information for the Review of the Seabrook Station License Renewal Application - Building Deformation Analyses Related To Concrete Alkali-Silica Reaction
06/16/2017 Seabrook Station - Update to Reply to a Notice of Violation; EA-16-101 Corrective Action Plan
05/05/2017 DRAFT - Request for Additional Information Regarding ASR Amendment Request RAIs (MF8260)
03/29/2017 Request For Additional Information For The Review Of The Seabrook Station License Renewal Application (CAC No. ME4028)
03/01/2017 Summary Of Teleconference Held On December 1, 2016, Between The U.S. Nuclear Regulatory Commission And NextEra Energy Seabrook Concerning Requests For Additional Information Pertaining To The Seabrook Station, License Renewal Application (CAC No. ME4028)
02/27/2017 Request For Withholding Information From Public Disclosure (CAC No. ME4028)
02/08/2017 Alkali-Silica Reaction Monitoring and Closure of NOV for Failure to Complete Operability Determinations for ASR-affected Structures – NRC Inspection Report 05000443/2016004, Sections 4OA2 and 4OA5
01/13/2017 NRR Audit Plan for Seabrook Alkali-Silica Reaction (ASR) LAR Review
12/23/2016 Seabrook Station, License Renewal Application Relating to the Alkali-Silica Reaction (ASR) Monitoring Program
12/21/2016 Alkali Silica Reaction Monitoring Aging Management Program Audit Report Regarding The Seabrook Station, Unit 1, License Renewal (CAC No. ME4028)
12/12/2016 Requests For Additional Information For The Review Of The Seabrook Station License Renewal Application (CAC No. ME4028)
10/13/2016 Regulatory Audit Plan – Alkali Silica Reaction Aging Management Program, Regarding Seabrook Station, Unit 1, License Renewal Application Review (CAC No. ME4028)
10/12/2016 Seabrook Station, Unit No. 1 -Acceptance of Requested Licensing Amendment Action Re: Alkali-Silica Reaction
09/30/2016 Supplement to License Amendment Request 16-03 Revise Current Licensing Basis to Adopt a Methodology for the Analysis of Seismic Category I Structures with Concrete Affected by Alkali-Silica Reaction.
09/19/2016 Seabrook Station, Unit No. 1 -Supplemental Information Needed For Acceptance Of Requested Licensing Action Re: Alkali-Silica Reaction
08/09/2016 Seabrook Station, License Renewal Application (LRA) Relating to the Alkali-Silica Reaction Monitoring Program
08/05/2016 ASR Operability Determinations and Functionality Assessments Sample – NRC Inspection Report 05000443/2016002, Section 1R15
08/01/2016 License Amendment Request (LAR) 16-03, "Revise Current Licensing Basis to Adopt a Methodology for the Analysis of Seismic Category I Structures with Concrete Affected by Alkali-Silica Reaction"
06/29/2016 Seabrook Station, Unit No. 1 – Acknowledgement of Reply to Notice of Violation – NRC Inspection Report 0500443/2016008
06/06/2016 Seabrook Station - Reply to a Notice of Violation EA-16-101 - Seabrook Station, Inspection Report 05000443/2016008 Related to Alkali-Silica Reaction Effects on Safety-Related Concrete Structures and Notice of Violation
05/06/2016 NRC Inspection Report 05000443/2016008  - Alkali-Silica Reaction (ASR) Effects on Safety-Related Concrete Structures and Notice of Violation (NOV)
03/29/2016 NextEra Drop-In with Division of License Renewal (DLR), Division of Operating Reactor Licensing (DORL), and Division of Engineering (DE)
02/12/2016 ASR Problem Identification and Resolution Sample – NRC Inspection Report 05000443/2015004, Section 4OA2
12/23/2015 Summary of Telephone Conference Call Held on December 22, 2015, Between the NRC and NextEra Concerning a RAI Pertaining To Seabrook Station Operability Determinations for ASR-Affected Structures
12/17/2015 ASR Monitoring Aging Management Program Audit Report Regarding the Seabrook Station
12/03/2015 NextEra response to RAI for the Review of the Seabrook License Renewal Application– Set 25
11/19/2015 Schedule Revision and Change of Project Manager for the Review of the Seabrook Station License Renewal Application
10/02/2015 RAI for the Review of the Seabrook License Renewal Application – Set 25
08/05/2015 ASR Problem Identification and Resolution Sample – NRC Inspection Report 05000443/2015002, Section 4OA2
06/30/2015 MPR-4153, Approach for Determining Through-Thickness Expansion from ASR (Enclosure 3 to the letter titled "NextEra second response to RAI – Set 23")
06/30/2015 NextEra second response to RAI for the Review of the Seabrook License Renewal Application – Set 23
05/04/2015 Schedule Revision for the Safety and Environmental Reviews of the Seabrook Station License Renewal Application
02/23/2015 NextEra response to RAI for the Review of the Seabrook License Renewal Application – Set 23
02/06/2015 ASR Problem Identification and Resolution Sample – NRC Inspection Report 05000443/2014005, Section 4OA2
11/25/2014 RAI for the review of the Seabrook License Renewal Application – Set 23
11/21/2014 NextEra Revised response to RAI for the review of the Seabrook License Renewal Application – Set 20
08/05/2014 ASR Maintenance Effectiveness Sample – NRC Inspection Report 05000443/2014003, Section 1R12
05/15/2014 NextEra response to RAI for the Review of the Seabrook License Renewal Application – Set 20
05/06/2014 ASR Problem Identification and Resolution Sample – NRC Inspection Report 05000443/2014002, Section 4OA2
02/19/2014 Revision to NRC Seabrook Alkali-Silica Reaction Issue Technical Team Charter
01/30/2014 ASR Problem Identification and Resolution Sample – NRC Inspection Report 05000443/2013005, Section 4OA2
01/15/2014 Request for Additional Information (RAI) 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 CAL:  Impact of ASR on Concrete Structures and Attachments (Foreign Print 100716)
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 Letter Committing to Supplemental to Actions for Resolution of ASR issues
05/03/2012 NextEra Letter Committing to Actions for Resolution of ASR Issues
03/26/2012 NRC Inspection Report 05000443/2011010, issued March 26, 2012 on ASR at Seabrook
08/12/2011 ASR – 1R15 Operability Samples – NRC Inspection Report  05000443/2011003
05/23/2011 NextEra Energy Seabrook - NRC License Renewal Inspection Report 05000443/2011007
05/12/2011 ASR – 1R12 Maintenance Effectiveness Sample – NRC Inspection Report  05000443/2011002

Public Meetings

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

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Date Title/Description
11/17/2017

The purpose of the meeting is to discuss with NextEra Energy Seabrook, LLC (NextEra) the path to resolution for stage 3 requests for additional information related to the review of the alkali-silica reaction license amendment request.

08/24/2017

The purpose of this meeting is to discuss with NextEra Energy Seabrook, LLC (NextEra), the NRC staff's review of the Seabrook Station, Unit No. 1, Alkali-Silica Reaction License Amendment Request.

06/07/2017

The NRC will host an open house with the public to discuss the NRC's assessment of safety performance at Seabrook for 2015. Following the open house, the NRC will then give an update and respond to questions regarding the NRC's evaluation of the effect of the ASR in concrete structures at Seabrook

06/05/2017

Summary Of Meeting Held On May 9, 2017, Between The U.S. Nuclear Regulatory Commission Staff And NextEra Energy Seabrook, LLC, Representatives To Discuss The Seabrook Station, License Renewal Application (CAC NO. ME4028)

06/21/2016

The NRC will host an open house with the public to discuss the NRC's assessment of safety performance at Seabrook for 2015. Following the open house, the NRC will then give an update and respond to questions regarding the NRC's evaluation of the effect of the ASR in concrete structures at Seabrook

06/15/2016

The purpose of this meeting is for NextEra Energy to present to the NRC staff its plan for a license amendment request regarding revising the licensing basis for Alkali-Silica Reaction at the Seabrook Station, Unit No. 1.

06/06/2016

The purpose of this public meeting is for C-10 to address the NRC PRB regarding the 2.206 Petition submitted by C-10 on December 22, 2015, regarding Seabrook.

Related Documents

04/28/2016

The purpose of this public meeting is for NextEra Energy Seabrook, LLC (NextEra) to discuss with U.S. Nuclear Regulatory Commission (NRC) staff about (a) the staff request for information (RAI) and (b) NextEra's plan for response to the RAI and the completion of the licensing action for Seabrook Station (Seabrook) license renewal.

06/18/2015

The NRC will host a 1-hour Open House before the meeting, as well as a question and answer session, to discuss NextEra’s performance at Seabrook during 2014.

06/24/2014

The NRC will host a one-hour open house, as well as a question and answer session, to discuss NextEra’s performance at Seabrook during calendar year 2013.

12/18/2013

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.

02/21/2013

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.

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.

Page Last Reviewed/Updated Tuesday, May 01, 2018