CONTEMPORARY FLUX OF RADIONUCLIDES TO CONTAMINATED SALTMARSHES IN THE ESK ESTUARY, CUMBRIA

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Abstract

The Esk estuary is approximately 10 km from the marine outfall from British Nuclear Fuels plc (BNFL) Sellafield Site and saltmarshes here have received significant quantities of radionuclides as reported in many studies since 1975. These studies have concentrated on the inventory of radionuclides in the estuary, but they have not addressed the continual reworking of radionuclides from these deposits. A detailed investigation of both the concentration of 137Cs in the surface 10 cm and gamma air-kerma dose rates has been made where 120 determinations were made in a grid over 14600 m2 of saltmarsh. The surface microtopography is shown to be important for the continuing deposition of contaminated sediments to the saltmarsh surface.

This study has concentrated on the development and the possible application of sediment traps made from Astroturf (an artificial grass). They were deployed at three sites which were representative of the major saltmarsh units in the estuary. The traps were used to investigate the mobile sediments during a single tide, for a week, and for a month. The Astroturf provided a reasonable analogue for the saltmarsh surface and was arranged such that the radionuclide concentration of the trapped sediment was measured directly 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 concentration of the deposited sediment showed the addition of between 90 and 750 Bq 137Cs m−2 d−1 and 200 and 1400 Bq 241Am m−2 d−1. At the depositional sites over the saltmarsh this would represent an annual addition of about 90 kBq m−2 of 137Cs and 180 kBq m−2 of 241Am.

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