Potential incursion of marine sediment inland during storms: the radiological importance of actinides

An assessment of the possible future incursion of marine sediment inland in Cumbria and Lancashire has been carried out. The assessment indicated that material from the patch of clay and silt offshore from Sellafield would not be readily mobilised and would not be brought ashore during a single-storm event. Several low-lying areas are potentially at risk of flooding as a result of severe storms, but any marine sediment deposited inland would have come from the nearshore zone. The original assessment, published in 1996, was made using measurement data for 1988. The results indicated that, in many cases, external irradiation was the most important contributor to the doses to those involved in clean-up operations and to residents, 137Cs being the radionuclide of importance. The predicted doses were a small fraction of the principal limit recommended by ICRP for members of the public. In this paper, the dose estimates have been refined using newly available data for 1995. Since 1988, activity concentrations of 137Cs have declined markedly because of remobilisation from the sediment, but changes in the values of 241Am and Pu are much less. As a result, the predicted overall doses to the various population groups are lower than those estimated previously, and in many cases actinides have become the radionuclides of importance.