Publication Abstract

Prediction of radionuclide behaviour and dose from Sellafield discharges using a compartmental model

K.S. Leonard, D. McCubbin, P.A. Gurbutt and G.D. Round

A multi compartmental box model ofthe Irish Sea (MIRMAID) has begin used to predict radionuclide distributions arising from the authorised discharge of lowlevel liquid effluent from the nuclear reprocessing plant at Sellafield. Dose rates to the Eritical group have been determined from predicted radionuclide concentrations and habit survey data using a dosimetric model (IRISHDOSE). Since the legacy of past disposals has resulted in the accumulation of a significant proportion ofthe total quantity discharged in finegrained sediments close to Sellafield, model calculations have been carried out to distinguish between radionuclide behaviour and the implications ofdose arising from both historic and current discharges.

Over the period 1953-1993, on an integrated year by year basis, the relative contribution of historic and current discharges on dissolved and surface sediment concentrations of 137Cs and 239+240Pu have been predicted in box compartments ofthe Irish Sea. During this time, the predicted concentrations ofdissolved radionuclides from historic discharges have not been significant. The largest historical contributions have occurred shortly after significant decreases in discharge. In contrast, the radionuclide concentrations on surface sediments are predicted to originate almost entirely from historical discharges. Model result have been validated using Pu isotope ratios from environmental data. Year on year, the historical dose contribution from seafood consumption was not significant, although a distinct maximum is predicted for 137Cs in 1986. Mostrecently, the contribution from historical discharges was predicted to be 3% of the total dose.

Reference:

K.S. Leonard, D. McCubbin, P.A. Gurbutt and G.D. Round, 1998. Prediction of radionuclide behaviour and dose from Sellafield discharges using a compartmental model. Radiation Protection Dosimetry, 75(1-4): 85-90.