Origin of artificial radionuclides in soil and sediment from North Wales

During the operations at the Sellafield nuclear fuel reprocessing complex, artificial radionuclides are discharged to the Irish Sea under authorisation, where they are dispersed. In this study, the southern distribution and transport of Sellafield derived radionuclides have been investigated. Both natural and artificial radionuclides have been studied in a soil core from the riverbank of the Afon Goch in Anglesey, North Wales. Particulate input is dominant for all artificial radionuclides (including the more soluble ¹³⁷Cs and ²³⁶U) with an estimated lag time of about a decade. The preferential northward seawater movement in the NE Irish Sea limits solution input of ¹³⁷Cs and ²³⁶U to the areas south of Sellafield. The relatively long lag time reflects both the water circulation pattern and distance between the study site in north Wales and the source point in Cumbria. Two redox active zones are observed in the top and the bottom of this core, although there is no evidence for any redistribution of Pu and natural uranium by these redox processes. However, ²³⁶U, derived from irradiated uranium, showed variable distribution in the core. This could be a potential response to the geochemical conditions, showing that ²³⁶U may be a promising tracer for the environmental processes and a signature of the Sellafield historical discharges of irradiated uranium.