28-9 Geologic Foundations for Nuclear Waste Storage: Evaluating Host Rock Systems and Long-Term Containment Strategies

Session: Geoscience and Hydrogeology in the AI Era: From Predictive Models to Real-Time Applications (Posters)

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The long-term storage of nuclear waste presents one of the most complex challenges in environmental and geologic engineering. Geologic disposal, which involves isolating radioactive waste deep underground in specially selected rock formations, is widely regarded as the most viable solution for ensuring safety over the tens of thousands of years required for radioactive decay. This work reviews the key geologic principles underpinning nuclear waste storage, including rock stability, hydrologic isolation, geochemical buffering, and tectonic quiescence. Host rock types such as crystalline granites, bedded and domal salt formations, and indurated clays or shales are evaluated for their capacity to limit radionuclide migration through low permeability and favorable geochemical environments.

Geological repositories rely on a multi-barrier system - combining engineered barriers with the natural properties of host rocks - to delay or prevent the movement of radioactive materials into the biosphere. Crystalline rocks offer mechanical strength and a stable tectonic framework, though attention must be given to fracture networks. Salt formations are highly valued due to their ability to self-seal, flow plastically, and exclude water—making them excellent for containment. Clay-rich sediments, such as shales and mudstones, provide low permeability and strong sorptive capacities that retard radionuclide diffusion.

The suitability of a site also depends on regional tectonic stability, minimal seismic activity, hydrologic isolation, and long-term predictability of subsurface processes. Key geotechnical considerations include thermal conductivity and the ability of the host formation to dissipate heat generated by radioactive decay without compromising structural integrity. Groundwater movement is another critical concern, as it can act as a transport medium for radionuclides; therefore, formations with long groundwater residence times are preferred.

Worldwide, countries are pursuing geologic disposal in various settings. Finland’s Onkalo repository, located in crystalline bedrock, is the most advanced. Others, like the Waste Isolation Pilot Plant (WIPP) in the U.S. and proposed sites in Canada, Sweden, and Switzerland, offer diverse geological and engineering approaches to this global issue.

Ultimately, nuclear waste storage is not only a technical problem but also a societal one, requiring transparent risk communication, long-term stewardship, and intergenerational responsibility alongside geologic understanding.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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