Above: A large-scale test programme at Ferguson Structural Engineering Laboratory at the University of Texas at Austin this helped determine the best way to measure and track ASR progression in structures similar to the walls at Seabrook
Action under way The meeting heard that ASR affects 28 structures at Seabrook (depending on the structure definition, as some are made up of smaller structures). Six of these are currently outside the licensing basis, ie the original concrete design code equations that have been revised in accordance with a licence amendment that includes ASR loads. Corrective action has to be taken to bring them back into conformance with the licensing basis. That is likely to involve further analysis for four of the six structures. They are the Service Water Cooling Tower, the Primary Auxiliary Building, the Containment Enclosure Building, and the Residual Heat Removal Vault. An example of the additional analysis required comes from the Service Water Cooling Tower, which has areas with limited access for monitoring the ASR below the water level. That requires a conservative assumption on the ASR expansion level, which increases load demand in the structure. Additional monitoring data to support the underlying assumptions could reduce load demand and bring it back into conformance. Where reanalysis is not an option, physical modification
is required. Two structures – the Control and Diesel Generator Building and the Emergency Feedwater Pumphouse – are planned for physical modification.
The NRC staff members said ASR cannot be ‘remediated’ in the sense that ASR is removed and the expansion stops – that would require total replacement of the area. Instead, it refers to various types of reinforcement, such as through- wall or corner braces, or the addition of thick metal plates to resist vertical expansion in the structure. Monitoring for ASR expansion continues once the remediation is complete. The ACRS meeting also heard from the C-10 Research and
Education Foundation, a group of citizens within a 10-mile (16 km) radius of Seabrook (ie the evacuation pathway emergency planning zone). The group had sought a rulemaking on ASR in 2014, but it
was denied in 2019. The group was concerned that measures were “static and relatively unchangeable because they’re packaged with their licence renewal”. A specialist working with C-10 said the dynamic analysis
relied on obsolete models. He was particularly concerned over an assumption that ASR does not reduce shear strength, noting that shear strength was required to manage seismic load. He also said better understanding was needed of internal microcracking caused by ASR and the effect on air tightness, calling for a stronger inspection regime (which is currently on a 15-year basis). The group also had concerns over violations relative to ASR license amendments and licence conditions. The
Above: Alkali-silica reaction (ASR) is a reaction driven by aggregates containing certain forms of silica Source: University of Ottawa Faculty of Engineering
18 | June 2025 |
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