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 tha t material from the patch of clay and silt offshore from Sellafield would n ot be readily mobilised and would not be brought ashore during a single-sto rm event. Several low-lying areas are potentially at risk of flooding as a result of severs storms, but any marine sediment deposited inland would hav e come from the nearshore zone. The original assessment, published in 1996, was made using measurement data for 1988, The results indicated that, in m any cases, external irradiation was the most important contributor to the d oses to those involved in clean-up operations and to residental Cs-137 bein g the radionuclide of importance. The predicted doses were a small fraction of the principal limit recommended by ICRP for members of the public. In t his paper, the dose estimates have been refined using newly available data for 1995. Since 1988, activity concentrations of Cs-137 have declined marke dly because of remobilisation from the sediment, but changes in the values of Am-241 and Pu are much less. As a result, the predicted overall doses to the various population groups are lower than those estimated previously, a nd in many cases actinides have become the radionuclides of importance. (C) 1999 National Radiological Protection Board. Published by Elsevier Science Ltd. All rights reserved.