Conservative behaviour of 125 antimony in marine waters under the influence of discharges from La Hague reprocessing plant

125Sb is one of the soluble radionuclides in the radioactive wastes dumped into the sea by the COGEMA nuclear reprocessing plant of La Hague. Its removal from the liquid waste was started in 1976, first by chemical extraction with titanium hydroxide, and since 1990, by evaporation and vitrification of the residues. Compared to 1975, this results in an improvement in the reprocessing process by a factor of 1,500. The behaviour of 125Sb in sea water is depending on hydrolysis of Sb oxidation state V. Its transfer capacity from sea water to other compartments of the environment is low; transfer factor values are below 50 L kg-1 (wet weight) for seaweeds and animals and between 60 and 900 L kg-1 for sediments (depending on clays fraction). Thus, 125Sb is a reliable tracer of water mass flows which was used to fit hydrodynamic models in the Channel and the North Sea with the real conditions in the environment. Since the setting up of the reprocessing plant in 1966, the highest rate of 125Sb discharge was 150 to 180 TBq y-1 between 1983 and 1987. Then, it has markedly dropped and it is below 0.5 TBq y-1 in 1995 and 1996. (author)