Radionuclides in shoreline waters of the Northeast Irish sea

Abstract

The shoreline waters of the Irish Sea along the Cumbrian coast near the British Nuclear Fuels plc works at Sellafield have been sampled at three locations over a 3 1 2 year period from December 1980. The particulate content was analysed for 238Pu, 239+240Pu, 241Am, 137Cs and stable Al. In some cases the radionuclide concentrations in filtered seawater were also determined. The results showed that the suspended particulate loads were high (typically about 100 mg l −1) and variable, and that they contained about 65 mg g −1 of aluminium. The isotopic ratio 238Pu/ 239+240Pu, which can indicate the chronology of the discharge, was about 0.26, which suggested that the Sellafield discharges over at least 5 years contributed to the observed concentrations. The 239+240Pu and 241Am annual average concentrations in the particulate material were in the ranges 3.0–5.1 and 3.3–5.2 Bq g −1, respectively. The individual values were very variable in time, but highly correlated with each other. No significant downward trends in the concentrations could be identified over this period. This is consistent with the behaviour of a reservoir (the northeast Irish Sea) where Pu and Am, which are available for suspension in particulate material, are fed by the Sellafield discharges and are subject to a mean removal time of several years. Thus the effects of the large reduction in the Sellafield discharges which occurred over this period should only be observable over a longer time interval. The concentrations in the dissolved fractions in seawater were negligible compared with the particulate fraction concentrations, in sharp contrast with the situation in offshore seawater. For 137Cs, the annual average concentration in filtered seawater was in the range 7.6–12.0 Bq l −1, which was 87–90% of the total concentration in seawater, proportions rather lower than some results reported in the 1970s, possibly reflecting a residual effect of the higher discharges. In general, the work showed that measurements of shoreline seawater are necessary in order to interpret littoral effects such as the sea-to-land transfer of radionuclides and the uptake of radionuclides by molluscs, in the environment of the Irish Sea.