Radionuclide associations in a concrete core extracted from the decommissioned hunterston A spent nuclear fuel pond

• Concrete core from the decommissioned Hunterston A spent nuclear fuel storage pond contaminated with Sr-90, Cs-137, Am-241, and Pu isotopes. • Autoradiography identified areas of increased radioactivity on the painted surface and ingress of radionuclides into bulk concrete. • Strong acids required for the extraction of radionuclides from concrete. • Hydrogels used to decontaminate fission products and actinides from the painted surface. Characterisation of a unique concrete core obtained from beneath the water level of the decommissioned Hunterston A spent nuclear fuel (SNF) storage pond has been conducted to aid understanding of long-term radionuclide contamination in nuclear infrastructure. Radionuclide contamination is primarily isolated to the protective coatings adhering to the concrete walls, with the majority of activity arising from fission products (Sr-90 and Cs-137) and actinides (Am-241 and Pu-241) as determined by gamma spectroscopy and liquid scintillation counting. Analysis of this core in vertical cross-section showed that radionuclides had penetrated through the protective layers and into the underlying, bulk concrete, with Cs-137 detected to a depth of 10 mm. X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and autoradiography suggest that Sr-90 contamination was concentrated within the cement phases, via interaction with calcium silicate hydrate (CSH), while Cs-137 was associated with aggregate materials, including quartz and gabbro. Decontamination experiments using cross-linked polymer hydrogels demonstrate time-dependent decontamination of the painted surface where the hydrogels were effective in removing both fission products and actinides.