Studies of environmental radioactivity in Cumbria, Part 12

A mathematical model is described which represents the sea-to-land transfer of actinides discharged into the Irish Sea from the Sellafield reprocessing plant. The model successfully reproduces the marine distribution of plutonium and americium in the Irish Sea between Cumbria and the Isle of Man and evaluates the magnitude of the transfer process to land. The radiological consequences of this transfer are calculated for the years 1954 to 2000 taking into account actual and future predicted discharges. The contribution from nuclear weapon tests and from Sellafield's atmospheric discharges are also evaluated and compared. The calculated annual dose from sea-to-land transfer to the average person living in Seascale reached a maximum of 24 microSieverts in 1973 and declined subsequently to 4 microSieverts by 1985 compared with the recommended ICRP principal limit for the general public of 1000 microSieverts. Corresponding figures for a hypothetical critical group are 35 microSieverts in 1973 and 20 microSieverts in 1985. The dose has decreased less steeply since 1973 than the corresponding decrease in discharges from Sellafield over the same period reflecting recycling of actinides accumulated in sea-bed deposits. Dose calculations for use of the beach at Seascale are also included. (author)