A sediment history of Sellafield discharges

A suite of artificial radionuclides, discharged from the BNFL Sellafield works into the Irish Sea, has been measured in sediment cores taken from a nearby disused and undisturbed dock basin (Senhouse Dock, Maryport). This has provided a comprehensive record of Sellafield discharges from the early 1960s, including radionuclides for which discharge data are incomplete. A chronology was established by comparing a variety of radionuclide concentrations and isotope ratios in the core with the available information on decay-corrected discharges. This allowed an estimate to be made of the quantity of 238Pu discharged in the period 1959-1977 (94 ± 8 TBq) for which no discharge data exist. The transit time from discharge to incorporation in the surface sediment was in the order of 1-1.5 y. Attempts to verify the sediment chronology with conventional 210Pbexcess dating met with difficulties because of uncertainties in the flux of 210Pb, linked to a local, anthropogenic source of 210Pb/226Ra. (author)