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Aquatic chemistry and thermodynamics of actinides and fission products relevant to nuclear waste disposal

Objective

The project aims to improve the scientific basis for the assessment of performance and safety in waste management. It will provide fundamental knowledge about the behaviour of actinides and fission products in natural aquatic systems.
The project focuses on key areas where further research is essential, including:
i) understanding of the mechanisms that govern the interaction of actinides and fission products in natural aquatic systems;
ii) closing existing gaps in the available thermodynamic database; and
iii) reducing uncertainities in currently used constants. Investigations focus on the thermodynamics of aquatic actinide ions, particularly in the tetravalent oxidation state, on the interaction of actinides and fission products at the solid/aqueous solution interface and on the thermodynamics of secondary solid phases. A link will established to theoretical methods for prediction of chemical behaviour in actinide systems.
A notable breakthrough has been achieved filling serious gaps in the database for tetravalent actinides, necessary e.g. to predict the geochemical of plutonium. The understanding of actinide complexation with small organic ligands, which may serve as model compound for natural organic matter, has been substantially increased using various spectroscopic methods and theoretical approaches. Computational methods (molecular modelling) have been applied for the first time to chemical problems related to nuclear waste disposal.

An improved understanding of actinides interaction at the mineral/groundwater interface and sound sorption data have been provided. Mechanistic insight into the sorption of U(VI) on iron oxides including surface enhanced redox reactions has been achieved as well as the elucidation of the speciation of trivalent actinides sorbed onto alumina and clay minerals. Sorption reaction at single crystals have been studied by grazing incidence X-ray absorption spectroscopy and laser fluorescence spectroscopy. For the prediction of the U(VI) sorption onto rock minerals, a 'composite' model has been parameterised successfully using sorption data derived for the mineralogical rock constituents.

The combination of wet chemical methods, surface analysis and spectroscopic techniques available in the different laboratories of the project partners helped in improve the basic understanding of solid solution formation of actinides in calcite, cement degradation secondary phases and phosphates. Such mineralisation processes are believed to be of cardinal importance for the actinide reactions in the near and the far field of a nuclear waste repository. The results gained in the ACTAF project indicate that inclusion in secondary phases can lead to a strong actinide retention in the repository or the surrounding geosphere.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

FORSCHUNGSZENTRUM KARLSRUHE GMBH - TECHNIK UND UMWELT
Address
Herrmann-von-helmholtz-platz 1
76344 Eggenstein-leopoldshafen
Germany

Participants (7)

CENTRO DE INVESTIGACIONES ENERGETICAS, MEDIAMBIENTALES Y TECNOLOGICAS
Spain
Address
22,Avenida Complutense 22
28040 Madrid
ENTERPRIS LIMITED
United Kingdom
Address
Pris, University Of Reading, Whiteknights
RG6 6AB Reading / Silchester
PAUL SCHERRER INSTITUT
Switzerland
Address

5232 Villigen
RESEARCH CENTER ROSSENDORF
Germany
Address
Bautzener Strasse 128
01314 Weissig - Dresden
ROYAL INSTITUTE OF TECHNOLOGY
Sweden
Address
Teknikringen 30
100 44 Stockholm
UNIVERSITAT POLITECNICA DE CATALUNYA
Spain
Address
P.i. Els Dolors - Palau Firal
08240 Manresa
UNIVERSITY OF COPENHAGEN
Denmark
Address
Oester Voldgade 10
1350 Koebenhavn K/copenhaegen