Within the frame of a research programme of the Commission of the European Communities investigations into the influence of the synthetic organic complexing agents dibutylphosphate (DBP), tributylphosphate (TBP), ethylenediaminetetraacetic acid (EDTA), citrate and oxalate on the solubilities and sorption behaviour of Agl, CsN0 3 , Na 2 U 2 0 7 , NpOjOH, Pu(OH) 4 and Am(OH) 3 or Eu(OH) 3 were carried out in systems representing the near field of a repository of radioactive waste located in a salt dome. The results obtained show the strong influence of the ligands EDTA, citrate and oxalate on the chemical behaviour of the actinide elements under these simulated practical conditions. They must definitely be taken into consideration for modelling safety aspects of waste repositories.
Experiments have been carried out into the leaching of ILW conditioned in cement and bitumen in concentrated salt solutions. Although difficult to observe with real waste leachates, investigations into the leaching of a simulated waste in cement have indicated leached transuranic levels of ca. 10−9 M ; the amount of activity leached by a quinary salt solution being 102 - 103 times higher . This has been interpreted in terms of a pH effect. For the real waste, spectroscopy has indicated a significantly larger release of Cs from cement than from bitumen. For all waste samples a notable absence of colloidal material was observed ; an observation which can be explained in terms of the high solution ionic strengths and the corresponding influence upon radionuclide solvation.Transuranic mobility studies through salt and sand from a salt dome in Northern Germany have shown the presence of at least two types of species of wildly differing mobility ; one migrating with approximately the same velocity as that of the solvent front and the other strongly retarded. Actinide recoveries (i.e. that passing through the columns) could be strongly influenced by either changing the system pH or by the addition of a competitor such as Ce ; the latter effect pointing to a competitive sorption.
Results are presented from investigations into the solubilities, sorption and migration behaviour of Agi. CsNO3, Na2U2O7. NpO2hOH and Pu(OH)4 in the near-field environment of an ILW repository located in a salt dome. Emphasis is placed on the synthetic complexing organics DBP, TBP, EDTA, citrate and oxalate, which influence the leaching and retardation of the above elements. Leachate data from real ILW forms, obtained from saturated salt solutions, have been compared with the results of the synthetic systems described.
The results from the experiments on the solubilities of the elements iodine, cesium, uranium and plutonium in electrolyte systems are described, which are of high importance for the hypothetical intrusion of saturated salt solutions into a waste repository located in a salt dome. Batch experiments and investigations into the migration of these elements were performed with the saturated solutions equilibrated with corrosion products of the cement and bitumen matrices the ILW was solidified in. The major difficulties for the α-counting of the traces contained in the leachates of the real ILW resulted from the higher β-and inactivities of the fission products being also present. A procedure developed for the separation of the elements uranium, neptunium, plutonium and americium, contained in leachates of real ILW is given and also results obtained by use of this method.
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