SEDIMENT RADIONUCLIDE PROFILES - IMPLICATIONS FOR MECHANISMS OF SELLAFIELD WASTE DISPERSAL IN THE IRISH SEA

Evaluation of the radiological significance of Sellafield waste radion uclide discharges to the Irish Sea requires characterisation of redist ribution processes affecting contaminated marine sediment, and investi gations of sediment radionuclide concentration profiles are often used in this context. Results are presented here for a study of radionucli de concentrations in saltmarsh sediments in south-west Scotland, which provide a record of Sellafield waste radionuclide deposition since th e 1960s. Comparison of the results with data for the Sellafield discha rge and other sediment studies indicates that the dominant mechanism o f transport of Sellafield waste to the study sites involves redistribu tion of contaminated silt. It is also observed that the sediment profi les preserve a record of the time-integrated Sellafield discharge rath er than of the annual variations. Temporal variations in sediment radi onuclide concentrations are explained in terms of a simple model which includes the effects of dispersion/dilution of this contaminated silt and of radionuclide redissolution. It is concluded that, provided Sel lafield discharges do not increase substantially, continuation of thes e processes will result in a decrease with time of pollutant radionucl ide concentrations in the sediment being deposited, but in an increase in radionuclide inventories in accumulating Irish Sea intertidal and saltmarsh sediments.