Effect of sediment and groundwater flow heterogeneity on accurately modelling radionuclide transport at UK nuclear sites

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The UK Nuclear Decommissioning Authority is mandated to oversee the removal of buildings and radioactive wastes present at ~20 UK nuclear sites. Its purpose is to deliver the decommissioning and clean-up of the UK's civil nuclear legacy in a safe and cost-effective manner, and where possible to accelerate programmes of work that reduce hazard. The NDA does not directly manage the UK's nuclear sites. It oversees the work through contracts with specially designed companies known as Site Licence Companies. The NDA determines the overall strategy and priorities for managing decommissioning. Its annual budget is £3.2 billion. The vast majority of the NDA budget is spent through contracts with Site Licence Companies, who also sub contract to other companies which provide special services. The Sellafield site is a large nuclear fuel reprocessing, nuclear waste storage, nuclear decommissioning and former nuclear power generating site on the coast of Cumbria, England. The site covers an area of two square miles and comprises more than 200 nuclear facilities and more than 1,000 buildings. It is Europe's largest nuclear site and has the most diverse range of nuclear facilities in the world situated on a single site. It is due to be fully decommissioned by 2120 at a cost of £121bn. Many UK nuclear sites, including Sellafield, are located on coastal plains and are underlain by thick fluvial-glacial alluvium deposits. These sediments are highly heterogeneous in nature and consist of layers ranging from clay size right up to cobble sized materials. There is also often considerable lateral variability in sediment texture reflecting changing depositional environments present during their formation. Historically there has been several events where unauthorised releases of radionuclide and/ or hydrocarbon containing fluids have occurred. These have contained radionuclides such as Tc-99 and H-3 that are highly mobile in groundwater, others such as Sr-90, C-137 and U which display sorption controlled transport. Other chemical contaminants, such as hydrocarbons as Non-Aqueous Phase Liquids and their resulting dissolution products, have also been accidentally released into groundwater. At Sellafield, over 200 groundwater monitoring boreholes exist, where aquifer materials and groundwater data has been recorded. This has provided evidence for the existence of extensive radioactive and chemical contamination plumes in a very complex unconsolidated aquifer structure relating to different releases from specific waste types and processes over time. Historically there has been several events where unauthorised releases of radionuclide and/ or hydrocarbon containing fluids have occurred. These have contained radionuclides such as Tc-99 and H-3 that are highly mobile in groundwater, others such as Sr-90, C-137 and U which display sorption controlled transport. Other chemical contaminants, such as hydrocarbons as Non-Aqueous Phase Liquids and their resulting dissolution products, have also been accidentally released into groundwater. At Sellafield, over 200 groundwater monitoring boreholes exist, where aquifer materials and groundwater data has been recorded. This has provided evidence for the existence of extensive radioactive and chemical contamination plumes in a very complex unconsolidated aquifer structure relating to different releases from specific waste types and processes over time. This project fits within UK research council areas of research within the EPSRC - Nuclear Fission research area. This research area includes waste management, site decommissioning, environmental regulation, and the public acceptability of existing operations at UK nuclear sites. The strategic focus of this research area aims to address the decommissioning challenges faced by current nuclear programmes by facilitating the development of approaches for implementing safe, cost-effective clean-up and waste disposal at existing nuclear sites.