CONCRETE CANCER | COVER STORY
Above: NextEra’s Seabrook nuclear power plant won a renewal of its licence to 2050 Seabrook is the only US nuclear plant where this issue
has arisen so far and a review by the NRC staff determined that there were no immediate safety concerns. It justified this conclusion because there remained (and still remains) a margin of safety, the ASR is localised and is growing slowly, and there is ongoing monitoring. In Seabrook’s ASR timeline:
● 2009 – 2010: Testing confirmed the presence of ASR ● 2013 – 2016: A large-scale test programme was carried out ● 2014 – 2015: NRC identified bulk structural deformation in Seismic Category 1 structures
● March 2019: NRC approved and issued both the license amendment request (LAR) and renewed licence
● Nov 2020: The LAR was challenged by a local advocacy group, but the licensing action was upheld (with modifications) by the Atomic Safety Licensing Board
● Locally-based engineering inspectors now continuously perform ASR-related inspections at Seabrook.
Recently, in September 2024, the independent Advisory Committee on Reactor Safeguards (ACRS) met with the NRC staff for an update on the status of ASR at Seabrook. This followed a previous meeting two years earlier. The meeting discussed recent activities to ensure that the issue remained of ‘no immediate safety concern’.
Inspection and assurance Cracking was found at the plant in 2009, in preparation for NextEra’s submission of its licence renewal application. ASTM standard screening tests at the time have been
determined to have limited ability to screen very slow- reactive aggregates for ASR. Because of this, NextEra mistakenly assumed that the original cement and aggregate selection would preclude ASR development, and therefore did not initially consider that the observed cracking could be caused from ASR. It initially characterised it as shrinkage cracking. New test standards have since been developed. NextEra identified several causes for the ASR issue and
several reasons for why it was not identified until the renewal review. One cause was that concrete mix for initial construction unknowingly utilized an ASR-susceptible aggregate and the aggressiveness of the groundwater chemistry on Seabrook concrete structures was also identified later. NextEra concluded that the affected structures were
operable, but degraded and non-conforming with licence conditions, because ASR was not initially taken into account in the current licensing basis.
In 2012, the NRC increased oversight to ensure structures
remained functional while NextEra developed corrective actions. The company carried out a large-scale test programme at Ferguson Structural Engineering Laboratory at the University of Texas at Austin, using concrete test specimens designed to replicate the reinforced concrete walls at Seabrook. Among other things, this helped determine the best way to measure and track ASR progression in a structure similar to the walls at Seabrook. The test results were used to develop what were referred
to in the ACRS meeting as ‘guard rails’, which included both expansion limits and monitoring techniques, and were incorporated into Seabrook’s current licensing basis via a licence amendment. This means that as long as Seabrook stays within the identified expansion limits, it can continue to use the original design equations and material properties to determine the capacity of the affected concrete. If it should go outside these limits that does not necessarily mean the structure fails, but it is outside the boundaries of the test programme and Seabrook has to re-examine the structures and demonstrate operability. This varies between structures but there is said to be substantial margin for the expansion rates established for the Texas test programme. A member of the panel commented, “you’re not inspecting up to a design-basis limit. You’re inspecting so that you can raise a flag and start a process.” The ACRS meeting heard that on-site NRC staff use the monitoring data to see current expansion levels, along with research and direct inspection that has meant inspectors totalled five weeks of on-site visits between 2022 and 2024. Depending on humidity and temperature, crack sizes open and close slightly. The test programme showed no reduction in capacity up to the limits tested, so the structure can withstand more margin and expansion. The inspectors have to distinguish between ASR and other types of cracking – such as freeze-thaw cracking – and consider whether more than one effect applies. NRC resident inspectors perform daily on-site oversight of the plant status, reviewing corrective action reports and conducting walk-downs through all the accessible areas of the plant, looking at building deformation and less-obvious signs of ASR. Since the NRC staff members’ previous meeting with ACRS
in 2022, it has conducted five weeks of on-site inspections with a team of NRC inspectors, and were “looking at this stuff on a daily basis”.
www.neimagazine.com | June 2025 | 17
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