The Ribble Estuary in the UK is contaminated by radionuclides derived from BNFL Sellafield and Springfield. Following the temporary shutdown of the Springfields plant, beta dose and gamma air kerma rates were measured at a range of sites in the estuary. Sediment surface samples were analysed for Cs-137, Pa-234m, Th-234 and Am-241 activity concentrations by gamma spectrometry, Th-230 and Pu isotopes by alpha spectrometry and sediment grain size (percentage <63 mu m) by wet sieving. Temporal variations in Springfields-derived radionuclides are explained by variations in discharges by radionuclides and the distribution of fine grained sediments in the estuary which is controlled mainly by the spring-neap tidal cycle and river runoff. Radionuclide dynamics, modelling variations in the Th-234/Cs-137 activity concentration ratio and calculating environmental beta dose rate and Th-234 half-lives allow the estuary to be split into three areas: (a) upper estuary where fine grained sediments tend to be deposited during periods of low and average river flow; (b) middle reaches of the estuary which encompass most of the main channel sites where fine grained sediments are probably deposited and removed on most tides; (c) outer estuary including large areas of salt marshes which tend to accumulate fine grained sediment. This is confirmed by similar results derived from the Th-234/(239,240) Pu ratio. (C) 1997 Elsevier Science Limited.
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Womens Christian Coll, Dept Phys, Nagercoil 629001, IndiaWomens Christian Coll, Dept Phys, Nagercoil 629001, India
Shanthi, G.
Kumaran, J. Thampi Thanka
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NM Christian Coll, Dept Phys, Marthandam 629165, India
NM Christian Coll, Res Ctr, Marthandam 629165, IndiaWomens Christian Coll, Dept Phys, Nagercoil 629001, India
Kumaran, J. Thampi Thanka
Raj, G. Allen Gnana
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Scott Christian Coll, Dept Chem, Nagercoil 629003, India
Scott Christian Coll, Res Ctr, Nagercoil 629003, IndiaWomens Christian Coll, Dept Phys, Nagercoil 629001, India
Raj, G. Allen Gnana
Maniyan, C. G.
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Indian Rare Earths, Hlth Phys Unit, Manavalakurichi 629252, IndiaWomens Christian Coll, Dept Phys, Nagercoil 629001, India