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Content archived on 2024-04-15

STUDY OF PHYSICO-CHEMICAL PROPERTIES OF THE TRANSURANIAN ELEMENTS NECESSARY TO THE UNDERSTANDING OF THE DELAYING PROCESSES OF THE MIGRATION IN CLOSE FIELD IN THE GEOSPHERE

Objective

THE MODELLING OF THE TRANSFER OF THE TRANSURANIAN ELEMENT THROUGH THE DIFFERENT BARRIERS TO THE GEOSPHERE IMPLIES THE KNOWLEDGE OF :
- THE EXACT NATURE OF THE SPECIES WHICH ARE ABLE TO MIGRATE UNDER THE INFLUENCE OF THE GROUNDWATER ; IONS, MOLECULES, COLLOIDS.
- THE EQUILIBRIUM RELATIONSHIP BETWEEN THESE SPECIES AND THE SURROUNDING DOMINANT OTHER SPECIES EITHER IN A MINERAL OR AN ORGANIC FORM.

FROM THIS POINT OF VIEW IT IS ADMITTED THAT CARBONATE (E.G. THE DIFFERENT SPECIES CO, HCO, CO) DUE TO HIS RELATIVELY HIGH ABUNDANCE IN THE GEOSPHERE PLAY A MAJOR ROLE IN THIS SENSE THAT IT FORMS COMPLEXES WHITH ALMOST ALL THE TRANSURANIAN ELEMENTS.

THEREFORE THE PRESENT WORK IS DEVOTED TOWARD THE IDENTIFICATION OF THE DIFFERENT CARBONATED COMPLEXES OF THE TRANSURANIAN ELEMENTS. THE DETERMINATION OF THEIR STABILITY CONSTANT, THEIR COMPORTMENT IN THE GEOLOGICAL MEDIUM IN THE VICINITY OF THE SOURCE TERM AND IN THE MAN MADE BARRIERS AND FINALLY THE ELABORATION OF A MODEL WHICH WILL DESCRIBE THE MIGRATION OF THESE RADIOELEMENTS.
The properties of transuranium elements, mainly plutonium, neptunium, and americium, have been investigated in terms of complexation by hydroxyl and carbonate ligands in aqueous solution. The aim of the research was to identify the species which are formed in given physicochemical conditions (ionic strength, concentration, etc) and to produce a set of thermodynamical data relevant to the system under investigation.

The transfer of tritiated water, caesium and strontium through highly compacted clay has also been studied, and values of diffusion coefficients are given. The diffusion of strontium is linked to some extent with precipitation processes.

Finally, CONDIMENT, a code for the computation of ion migration and diffusion in areas close to radioactive waste storage facilities, has been set up and developed. It can be coupled with other codes such as METIS, which models the transfer of radionuclides into the biosphere. Different cases have been considered and the results are satisfactory. However, the effects of organic compounds (eg, humic substances), for which at present no reliable thermodynamic formation constants exist, need to be assessed.
B1 - BASIC CHEMISTRY:
MEASUREMENT OF SOLUBILITY AND STABILITY CONSTANT OF THE TRANSURANIAN ELEMENTS WITH THE LIGAND CARBONATE. IDENTIFICATION OF THE DIFFERENT SPECIES E. PH DIAGRAMMS.

B2 - MIGRATION:
EXPERIMENT OF TRANSFERT THROUGH ARGILEOUS MATERIAL. PRELIMINARY ASSAYS OF DIFFUSION CELLS WHITH CS AND SR APPLICATION TO THE MIGRATION OF AMERICIUM (III).

B3 - MODELLING:
A MODEL WICH TAKE IN ACCOUNT THE CHEMICAL PROPERTIES OF THE ELEMENTS ISSUED FROM THE SOURCE TERM WITH BE ELABORATED AND TESTED.

Topic(s)

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Call for proposal

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Coordinator

Commissariat à l'Energie Atomique (CEA)
EU contribution
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Address
Centre d'Études de Fontenay-aux-Roses
92265 Fontenay-aux-Roses
France

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