Measurements of α-emitting plutonium and americium in the intertidal sands of West Cumbria, UK

Abstract

Samples of surface sand and sand cores were collected from intertidal regions of west Cumbria-between Silloth and Walney Island (including the Duddon Estuary) between 1982 and 1984 and analysed for 238Pu, 239+240Pu and 241Am. Generally, more than 95% of the α-emitting transuranic nuclides were associated with the sand and less than 5% with entrained silt. The greatest concentrations of both plutonium and americium were found at Braystones. Concentrations declined with distance from the Sellafield Works. The largest actinide deposits occurred at Drigg (320 and 720 kBq m −2 of 239+240Pu and 241Am respectively). The integrated deposits in intertidal sand between Silloth and Walney Island were about 4·2 and 7·0 TBq respectively, which represent about 1% of the total α-emitting activity discharged to sea from Sellafield Works up to 1982. The corresponding value for the Duddon Estuary is about 0·3%. Only on beaches close to Sellafield did levels of man-made α-emitters exceed those of natural α-emitting nuclides. The radiological consequences of the intertidal inventory of plutonium and americium are shown to be very small and much less than from the seafood pathway.