Within the framework of an EC project, work is conducted aiming at determining the influence of humic substances on the long-term safety of high level radioactive waste disposal. Eleven project partners present their results of the first year of the project. Furthermore, an executive summary outlines the objectives and structure of the project and gives a summary of results. The overall objective is to produce generic information for application at a given real site. Statements for specified scenarios on selected real sites is encompassed at a later stage of the project.

Results presented reflect the overall approach of the project, namely (i) sampling and thorough characterization of natural and designed material for experimental investigations; (ii) identification and investigation of relevant basic reactions; (iii) combination of basic reactions for testing of applicability on complex systems under controlled laboratory conditions; and (iv) verification of applicability by comparison with observations in natural aquatic systems (geochemical analogues). Modeling is an integral part of all project activities.

Radionuclides studied are actinides and technetium. Due to their long half-life and high radiotoxicity they are of major concern for the long-term safety of radioactive waste disposal. Their migration behavior in aquatic systems will be influenced by humic substances by (i) generation of humic colloids in the aquatic phase; (ii) influence on the redox state of concerned metal ions; and (iii) coating of sediment surfaces leading to amendment of their radionuclide sorption properties. Consequently, the following individual processes are studied under controlled and near-natural conditions: (i) the actinide interaction with natural humic colloids and purified humic substances in the aquatic phase; (ii) the interaction of radionuclides with humic acid coated mineral surfaces, including humic acid covalently bound to mineral surfaces; (iii) the interaction of humic substances with mineral surfaces and the resulting modification of mineral surface sorption behavior; and (iv) the influence of humic substances on the redox state of relevant actinide ions and technetium. Combined processes are studied on natural groundwater sediment systems by batch and column experiments under near-natural conditions.

A major achievement presented is the successful development and application of a kinetic approach to the actinide migration behavior in natural groundwater sediment systems under near-natural laboratory conditions. Contrary to previous attempts, the present approach results in a consistent description of both the time-dependency of actinide sorption in batch experiments and the actinide elution behavior in column experiments. The developed kinetic approach is also supported by preliminary investigations on the sorption/desorption of actinide ions and desorption of chemical homologues from natural humic colloids. A fraction of natural chemical homologue elements show a kinetic behavior beyond time-scales practicable for laboratory experiments. This indicates the possibility for unretarded humic colloid mediated actinide transport over long time periods.