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. The NRC and NextEra confirmed in 2010 that the degradation at Seabrook is caused by alkali silica reaction, or ASR. The result of this reaction is a gel, which can expand and 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 "Seabrook Station Safety in Light of the Alkali-Silica Reaction Occurring in Plant Structures."

Subsequently, NextEra identified that the cumulative effect of ASR-induced micro-cracking has led to larger macro-cracking (bulk expansion) and the displacement of some concrete walls.

NextEra has determined that the structures affected by ASR can continue to perform their safety functions—the regulatory term for this is that they are "operable but degraded and nonconforming." The basis for continued operability includes 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 exceeds any assumed load or specified load combinations. NRC inspectors have reviewed these analyses, design reviews, and design calculations during on-site inspections and have concluded that NextEra has adequately demonstrated that the concrete structures at Seabrook affected by ASR are currently "operable but degraded and nonconforming." For more information on the issue 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
• Developments Since Confirmatory Action Letter Closure
• Licensing
• Advisory Committee on Reactor Safeguards (ACRS)
• Next Steps
• Publicly Available Documents
• Public Meetings

Summary of Event and Plant Conditions

As previously noted, NextEra confirmed the presence of ASR degradation of concrete in below-grade walls of several Category 1 structures in August 2010. Seabrook is the first plant in the U.S. nuclear fleet to exhibit ASR in concrete structures on site. In response, the 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, the slow-moving nature of ASR, and ongoing monitoring.

Concrete issues other than ASR have also occurred 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. This cracking occurred during work on an opening in the containment in preparation for a steam generator replacement project. In response, Duke Energy, the plant’s owner, announced on February 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 the replacement of the reactor vessel head. Information related to this issue can be found in NRC Inspection Report IR 05000346/2012007. The concrete degradation mechanisms in these plants are different from the ASR identified at Seabrook.

Confirmatory Action Letter

On May 16, 2012, the NRC staff issued a Confirmatory Action Letter (CAL) to NextEra confirming regulatory commitments made by the licensee to address ASR at Seabrook 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-scale testing program and revised integrated corrective action plan.

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

Enhanced Oversight

On July 9, 2012, the NRC issued a "Working Group Charter" to ensure that all aspects of the ASR issue were coordinated among the NRC staff. This charter established the Seabrook ASR Issue Technical Team (SAITT) comprised of staff from the NRC Region I and Headquarters offices. The team coordinates the on-site inspections, in-office technical reviews, and other associated evaluations and assessment activities involving NextEra’s resolution of the ASR issue at Seabrook.

Further, on September 5, 2012, the NRC’s Executive Director for Operations approved a "Deviation Memorandum" that allows the agency to continue to devote additional review resources to the Seabrook ASR issue. Although, the NRC’s Reactor Oversight Process does not prescribe increased oversight for Seabrook based on its overall performance, the NRC staff determined that additional inspections and assessments were appropriate in these circumstances.

Following the completion of the second CAL follow-up inspection report (IR 05000443/2012010) and the mid-cycle performance assessment per IMC 0305, the NRC closed the Deviation Memorandum, as documented in NRC letter, "Mid-Cycle Performance Review," dated September 3, 2013. Since the closure of the deviation memorandum, the NRC has conducted focused inspections with specialist inspectors approximately every six months as part of the Reactor Oversight Process baseline inspection program, the results of which are documented in publicly available inspection reports. The NRC plans to continue these inspections in 2019. The NRC also continues to maintain oversight through the SAITT.

Developments Since Confirmatory Action Letter Closure

Following the 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 staff conducted periodic inspections and audits related to the ASR issue at Seabrook and at the Ferguson Structural Engineering Laboratory (FSEL) at the University of Texas, where a large-scale ASR testing program was being conducted for NextEra.

NextEra's large-scale testing program commenced in late 2013 and was completed in February 2016.  Based on testing program developments, in 2015, NextEra revised its structures-monitoring/ASR-monitoring aging management programs to include through-wall expansion monitoring.  This expansion is monitored by devices installed in over 40 representative locations in Seabrook structures.

In 2014, the NRC staff documented findings involving discrete, horizontal cracking in an internal wall of the Seabrook Residual Heat Removal (RHR) vault and displacements and cracking associated with the Seabrook Fuel Storage Building.  Subsequently, NextEra identified that the cumulative effect of ASR-induced micro-cracking has led to larger macro-cracking (bulk expansion) and the displacement of some concrete walls.  In 2015, the staff documented findings that identified global bulk expansion of the Seabrook Containment Enclosure Building.  The staff concluded that 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 staff 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. 

In 2016, the NRC staff documented an unresolved item after staff had identified that further inspection was warranted to review an ongoing issue of concern regarding NextEra’s implementation of the Seabrook Structures Monitoring Program, which monitors on-site structures for any signs of degradation, and NextEra’s structural evaluations of the Seabrook Containment Enclosure Building and the Residual Heat Removal vault.  In the inspection for this unresolved item, the NRC staff identified a violation based on two instances in which NextEra did not perform initial and prompt operability determinations for ASR-affected structures until pressed by NRC inspectors.  NextEra responded to this violation in early June 2016; NextEra averred 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.

NextEra had three meetings with NRC staff, on March 29, April 28, and June 15, 2016, to discuss ASR-related issues at Seabrook.  Moreover, the NRC staff performed a regulatory audit of NextEra’s license amendment 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 December 29, 2008.

In 2018, the NRC staff completed a second on-site team inspection in accordance with Inspection Procedure 71002, “License Renewal Inspection,” to review NextEra’s actions to address the effects of ASR in Seabrook reinforced concrete structures.  The inspection results support the conclusion that there is reasonable assurance that the effects of aging due to ASR in the Seabrook systems, structures, and components will be managed through implementation of these programs as described in the application for a renewed license.

Licensing

The NRC has completed two licensing actions that are directly associated with ASR at Seabrook: a license renewal application (LRA) to allow operation for an additional 20 years and a license amendment request (LAR) to change the current licensing basis to account for the effects of ASR.

In May 2010, NextEra submitted an LRA to renew the Seabrook facility operating license for an additional 20 years. The Seabrook license renewal Safety Evaluation Report (SER) contained one Open Item related to NRC staff concerns that NextEra had not enhanced the Structures Monitoring Program to manage the effects of ASR. The SER explained that for the NRC staff to complete its LRA review and close this Open Item, NextEra would need to update the LRA to include a sufficient aging management program for concrete structures impacted by ASR to ensure safe operation through the period of extended operation (2030–2050). On August 9, 2016, the NRC received NextEra's updated LRA submittal. As a result of the staff’s review of the updated LRA submittal, the staff performed license renewal audits and issued requests for additional information (RAIs). NextEra provided application supplements to address issues identified during the audits and in the RAIs. In May 2018, the staff received NextEra’s revised Structures Monitoring Aging Management Program for Seabrook, which is based on the methodology for analyzing seismic category I structures with concrete affected by ASR that was provided in the LAR, discussed below. The NRC staff completed its review of the LRA and documented the results of the review in the Safety Evaluation Report, dated September 28, 2018. The license renewal Open Item regarding ASR was discussed during an Advisory Committee on Reactor Safeguards (ACRS) Subcommittee meeting on October 31, 2018. Additional information on the ACRS reviews is detailed below. For additional information on the license renewal process and schedule, see: License Renewal Review Schedule.

On June 15, 2016, the NRC staff held a public meeting with NextEra to discuss NextEra's plan to submit a license amendment request to revise the licensing basis to account for ASR at Seabrook. In August 2016, NextEra submitted the LAR, which would revise the Seabrook Updated Final Safety Analysis Report (UFSAR) to include methods for analyzing seismic Category I structures with concrete affected by ASR. 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. In addition, the NRC staff held a public meeting with NextEra on November 17, 2017, to discuss the path to resolve the staff's requests for additional information (RAIs) related to the LAR. In 2018, the NRC staff performed a second regulatory audit of this application from March 19 – 23, 2018. The NRC staff documented its review of the LAR in a Draft Safety Evaluation and submitted this document to the ACRS on September 28, 2018. The LAR directly supports the staff's review of the LRA, which was evaluated in a separate process, as discussed above.

Both the LAR and the license renewal Open Item regarding ASR were discussed during an ACRS subcommittee meeting on October 31, 2018, as noted below. The NRC issued Amendment No. 159 approving the LAR on March 11, 2019, and subsequently issued the renewed facility operating license approving the LRA on March 12, 2019.

A request for a hearing on the LAR was filed by the C-10 Research and Education Foundation, Inc. (C-10). On October 6, 2017, the Atomic Safety and Licensing Board (ASLB) granted the hearing request, determining that C-10 had standing and admitting a single reformulated contention for hearing. The ASLB held the evidentiary hearing from September 24-27, 2019. The ASLB found the following four conditions necessary for the license amendment to satisfy regulatory requirements: NextEra will check extensometers every 6 months, monitor rebar to ensure it will not yield from ASR-induced stress, perform engineering evaluations for areas of high ASR-related expansion, and core samples will be checked for internal microcracking and delamination. Subject to these conditions, the ASLB resolved the reformulated contention in favor of NextEra. With the addition of the four conditions to License Amendment No. 159, the ASLB concurred with the Staff that NextEra’s proposed method to evaluate seismic Category I structures affected by ASR is acceptable and provides reasonable assurance that the Seabrook structures will continue to meet the relevant requirements of federal regulations.

More information on the NRC's adjudicatory process can be found on this webpage.

Advisory Committee on Reactor Safeguards (ACRS)

The ACRS is independent of the NRC staff and reports directly to the Commission. It is composed of outside experts in various technical fields. One of the ACRS's purposes is to review and report on safety studies and reactor facility license and license renewal applications.

Due to the first-of-a-kind nature of ASR in the U.S. nuclear industry, the ACRS held a subcommittee meeting on October 31, 2018, to specifically review the technical aspects of ASR at Seabrook. In support of this meeting, the staff provided the subcommittee with both the safety evaluation report for license renewal and the draft safety evaluation for the ASR-related license amendment request. On November 15, 2018, the ACRS subcommittee held a meeting on the remaining issues related to the Seabrook license renewal application. On December 6, 2018, the full Committee held a meeting on the Seabrook license renewal application. On December 14, 2018, the ACRS issued a letter to the Commission stating that the staff's evaluations of ASR at Seabrook provide thorough assessments and findings and that the ACRS agrees with the staff’s conclusions that NextEra's programs related to ASR are acceptable. On December 19, 2018, the ACRS issued a letter to the Commission stating that the Seabrook license renewal application should be approved.

On April 27, 2022, the Fuel Materials and Structures and the Plant Operations Radiation Protection and Fire Protection ACRS Subcommittees met on the Seabrook ASR issue. NRC Region I and Headquarters staff briefed the joint subcommittee on inspection findings related to the inadequacy of NextEra’s structural monitoring program to account for future ASR-related degradation.

On September 4, 2024, a session of a full ACRS meeting was held specific to ASR. The Committee heard from NRR and Region I staff about the status of the progression of ASR at Seabrook and NRC oversight. NRR provided input on ASR-related inspection results, corrective actions, and the licensee’s future plans to address ASR. The committee also received a presentation from C-10, a public interest group. During the planning and procedures session of this meeting, additional topics were proposed for the Seabrook ASR issue. The Committee agreed that the staff would target the next meeting in about 6 – 9 months with the proposed focus to be on the status of NextEra’s evaluation of the progression of ASR and proposed corrective actions.

The ACRS webpage includes meeting schedules, meeting transcripts, and letter reports.

Next Steps

The NRC will continue its evaluation of ASR at Seabrook through inspecting NextEra's monitoring of ASR-affected structures and implementation of the enhanced structures monitoring program.  These activities have been documented in inspection reports approximately every six months beginning in 2019.  Using the normal reactor oversight process, the NRC staff has determined the need for inspections to continue for the remainder of the plant’s operation. Documentation of these inspections can be found in integrated inspection reports for Seabrook listed in Publicly Available Documents below.

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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Public Meetings

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

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