COVER STORY | CONCRETE CANCER
watching brief Keeping a So-called ‘concrete cancer’ was found at Seabrook more than 15 years ago.
NRC documents show how the safety authority works with the plant operators to ensure that structures continue to meet licence requirements.
SINCE 2010, OPERATORS AND REGULATORS have kept a close eye on the effects of the alkali-silica reaction (informally known as ‘concrete cancer’) at NextEra’s Seabrook nuclear power plant. Five years ago the plant won a renewal of its licence to 2050 and recently the NRC’s independent Advisory Committee on Reactor Safeguards (ACRS) checked in on how the site and NRC are monitoring this slow-moving reaction in some parts of the plant’s concrete. Alkali-silica reaction (ASR) is a reaction driven by
aggregates containing certain forms of silica. In an alkaline environment, the silica reacts with hydroxyl ions and a type of gel forms at the interface between the aggregate particles and the cement mortar. The gel expands dramatically as it absorbs water from the surrounding environment. The gel expansion starts off as micro cracking and can later be observed as macro-cracking on the surface. The visual appearance is typically in the form of so-called pattern cracking, with gel staining around the cracks. The reaction process may take years, but once it is
under way, the forces from the expansion cause cracking to appear on the surface. The expansion and cracking of concrete from ASR can potentially impact both the load carrying capacity of the structure, and the load put on that structure.
The American Ceramic Society notes that the concrete used in nuclear power plants is more susceptible to ASR than fine-grained concrete, because it uses high-density aggregates with coarser grains to shield effectively against radiation. The US has a lot of experience with ASR in other industries, such as transportation infrastructure (eg concrete bridges) and dams, so there is extensive expertise in other bodies such as the Department of Transportation and the Federal Highway and Transportation Authority. However, extensive monitoring and remediation of ASR where it has appeared in other sectors has limited the data points on how it fails, because structures are either remediated or taken out of service prior to failure. What is more, those failures that have been seen are largely in unreinforced concrete. NextEra confirmed the presence of ASR degradation
of concrete in below-grade walls of several Category 1 structures at Seabrook in August 2010. Seabrook had unknowingly used a slow-reactive aggregate in the concrete and as the Nuclear Regulatory Commission (NRC) noted recently, there were ineffective American Society for Testing and Materials (ASTM) Standards at the time of construction. Furthermore, ASR was not expected, so inspections were not looking for it.
Above: Seabrook is a single unit nuclear plant in New Hampshire Source: ANS 16 | June 2025 |
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