Fouling and scaling of equipment in the nuclear industry, generally in the form of inorganic precipitates and biofilms, is a significant and challenging problem that effects multiple areas across the nuclear fuel cycle. Consequences such as the blockage of flows, accumulation of radionuclides, reduction of heat-transfer energy and enhancement of corrosion, can have detrimental effects on safety and performance as well as incurring substantial damage and maintenance costs.<br/>Radioactively contaminated scale accumulation within the discharge pipelines of nuclear decommissioning sites has been identified by the UK Nuclear Decommissioning Authority as a problem requiring urgent attention. The nuclear decommissioning site at Winfrith contains more than 25 km of contaminated pipeline. For this project a sampling campaign was organised to obtain unique samples of the contaminated pipe scale for comprehensive characterisation, to attempt to understand the nature and long-stability of the novel samples and thus help to underpin future pipeline decommissioning operations and minimise costs.<br/><br/>Gamma spectroscopy of the samples determined the main gamma emitting contaminants to be Cs-137, Co-60 and Am-241. Parallel non-active pipe scale samples from the site were analysed by XRD which identified multiple solid phases, predominantly iron oxides, but also clays, quartz, barite and calcite. The presence and spatial distribution of these minerals was confirmed with SEM imaging and EDS mapping. Sequential chemical extractions were performed on the active samples, coupled with gamma spectroscopy and ICP-MS analyses, to provide insight into how the radionuclides are distributed between the different phases, as well as the speciation (chemical form) of the radionuclides within these samples e.g. bound to the surface or incorporated. Prokaryotic and eukaryotic DNA has also been identified in both the active and non-active scale samples, highlighting the possibility for a role for biofilms in scale formation and microbially induced corrosion which is being further explored alongside more detailed electron microscopy and spectroscopic analyses.

Nuclear contamination, what’s in the pipeline; a multi-disciplinary approach to characterising discharge pipe-scale accumulation at a nuclear decommissioning site

ACS Spring 2022

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