Measuring the availability to sediments and biota of radionuclides in wastes discharged to the sea

Radionuclides in waste discharged to the sea are taken up by marine sediments and organisms. The concentrations observed in these materials are determined by a complex process depending upon present and past discharges, and the rates of decay, dispersion, uptake and elimination. A simple, semi-empirical model is derived to predict current concentrations from historical discharges. An important parameter in this model is the mean availability time, the average time for which the radionuclide is effectively available to the material. Maximum likelihood estimates of the modelʹs parameters are derived. The theory is applied to data collected in the marine environment near British Nuclear Fuels plc, Sellafield.