In the processing of spent nuclear fuel using the Purex process, nitrosyl complexes control the chemical behaviour of ruthenium in Solution. These highly stable and unreactive Compounds restrict the efficiency of the purification techniques usually applied to ruthenium-bearing radioactive wastes.The coprecipitation method presented in this study is based on the addition of ferrocyanide ions to the Solution. The reaction mechanism involves the transfer of ruthenium from a nitrosyl complex to a soluble ruthenocyanide structure. The ruthenocyanide ion is subsequently coprecipitated as a copper ruthenoferrocyanide. Optimal Ru precipitation conditions (pH and reagcnt concentrations) are established using '°®Ru as a tracer. The highest yields are obtained with 5 x 10"" M sodium ferrocyanide and 1 X 10"^ M copper-II nitrate; this method allows the removal of up to 98% of the '"^Ru contained in effluent samples from the La Hague reprocessing plant before their controlled release into the sea.

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A sampling cruise carried out in the North Sea in July 1988 has enabled the construction of general maps showing the distribution of salinity and temperature as well as the activities of the radionuclides 125 Sb, 137 Cs and 134 Cs. An inspection of the raw data and the distribution patterns so obtained shows the important role of meteorological fluctuations in the movement of near-surface waters throughout the North Sea.A simple mixing model is used to interpret the North Sea dataset in terms of four contributory watermasses (the Atlantic, Irish Sea, English Channel and Baltic), each of which can be identified by its specific characteristics. Maps are drawn up which indicate the contribution factor in percentage of each of these water masses at all points in the North Sea to a precision better than 15%. Pt is also possible to extract the contribution of direct fallout resulting from the Chernobyl accident; comparison with previously obtained results allows an evaluation of the rate of renewal of surface waters in the North Sea over a period of two years. In all areas, this value appears to be better than 75%.