CONTEMPORARY FLUX OF RADIONUCLIDES TO CONTAMINATED SALT-MARSHES IN THE ESK ESTUARY, CUMBRIA

The Esk estuary is approximately 10 km from the marine outfall from Br itish Nuclear Fuels pie (BNFL) Sellafield Site and saltmarshes here ha ve received significant quantities of radionuclides as reported in man y studies since 1975. These studies have concentrated on the inventory of radionuclides in the estuary, but they have not addressed the cont inual reworking of radionuclides from these deposits. A detailed inves tigation of both the concentration of Cs-137 in the surface 10 cm and gamma air-kerma dose rates has been made where 120 determinations were made in a grid over 14600 m(2) of saltmarsh. The surface microtopogra phy is shown to be important for the continuing deposition of contamin ated sediments to the saltmarsh surface. This study has concentrated o n the development and the possible application of sediment traps made from Astroturf (an artificial grass). They were deployed at three site s which were representative of the major saltmarsh units in the estuar y. The traps were used to investigate the mobile sediments during a si ngle tide, for a week, and for a month. The Astroturf provided a reaso nable analogue for the saltmarsh surface and was arranged such that th e radionuclide concentration of the trapped sediment was measured dire ctly by gamma spectrometry.Sediment deposition rates of between 30 and 240 g m(-2) d(-1) were determined for the study sites, and these were consistent with earlier studies. Measurement of the radionuclide conc entration of the deposited sediment showed the addition of between 90 and 750 Bq Cs-137 m(-2) d(-1) and 200 and 1400 Bq Am-241 m(-2) d(-1). At the depositional sites over the saltmarsh this would represent an a nnual addition of about 90 kBq m(-2) of Cs-137 and 180 kBq m(-2) of Am -241.