Long-term fate of Ra-226 originating from offshore produced water discharges
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Formation water in oil and gas fields contain elevated concentrations of several radionuclides compared with seawater. It is therefore of interest to track the fate of these radionuclides when they are released into the ocean along with the produced water stream. In this work we have simulated the fate of radionuclides in produced water discharge from all relevant installations on the Norwegian continental shelf for periods up to 20 years. We investigated separately the fate of the radionuclide Ra-226 in solid and in dissolved phase. Our findings show that when Ra-226 spreads as a solid it has the highest potential for reaching the sediments in the areas around the Oseberg and Ekofisk fields. The estimated contribution above background at these sites over a 30 year period was estimated to be from 2 Bq/kg to 10 Bq/kg, depending on the degree of burial, bioturbation and sediment mixing. Our simulations of dissolved Ra-226 showed transport along the Norwegian coast up past Svalbard. We found that the maximal contribution of dissolved Ra-226 to radioactivity in sediments over a 30 year period lies in the range 0.6 - 2 Bq/kg at several locations along the Norwegian coast.