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Slow processes in close-to-equilibrium conditions for radionuclides in water/solid systems of relevance to nuclear waste management

Objective

Solid/liquid chemical equilibrium hypotheses (sorption, solubility, solid-solution formation) are key concepts in the assessment of nuclear waste safety. For radionuclides at trace concentrations this corresponds to constant solution concentrations, or solid/liquid distribution ratios, if environmental conditions remain constant. However, these concepts do not account for irreversible incorporation of radionuclides in the solid phases. Indeed, there is often a gradual and very slow transition from simple adsorption processes to incorporation of trace elements in the surface structure of solid phases. For certain tetravalent actinides apparent solubility equilibrium applies to only the surface without bulk phase equilibrium. This can lead to very large uncertainty in solubility values and derived thermodynamic constants. Equilibrium concepts are characterized by a dynamic state of equal forward and backward reaction rates, under conditions where phase compositions remain constant. Most of the problems arise from a lack of understanding of the dynamics of slow processes close to equilibrium, specifically in the coupling of sorption with other surface equilibrium reactions such as dissolution/precipitation, recrystallisation, isotopic exchange and with the bulk phase equilibrium. The project intends to assess the effect of surface properties on apparent solubility as well as the kinetics of incorporation of radionuclides in the structure of a solid phase, and the associated reaction mechanisms for various solids in a systematic manner, using isotope exchange under close-to-equilibrium conditions.
The project results will impact strongly (1) the use/misuse of solubility data for thermodynamics; (2) the understanding of affinity/rate relations close to equilibrium; (3) the inclusion of irreversibility in models on the long-term mobility of radionuclides; and (4) the coupling of radionuclide chemistry with main element chemistry in the repository environment.
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ASSOCIATION POUR LA RECHERCHE ET LE DEVELOPPEMENT DES METHODES ET PROCESSUS INDUSTRIELS

Address

Boulevard Saint Michel 60
75272 Paris

France

Activity type

Research Organisations

EU Contribution

€ 221 691

Participants (9)

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KARLSRUHER INSTITUT FUER TECHNOLOGIE

Germany

EU Contribution

€ 141 400

FORSCHUNGSZENTRUM JULICH GMBH

Germany

EU Contribution

€ 125 305

SVENSK KARNBRANSLEHANTERING AKTIEBOLAG

Sweden

EU Contribution

€ 27 012

AMPHOS 21 CONSULTING SL

Spain

EU Contribution

€ 147 600

CHALMERS TEKNISKA HOEGSKOLA AB

Sweden

EU Contribution

€ 94 600

STOCKHOLMS UNIVERSITET

Sweden

EU Contribution

€ 123 762

PAUL SCHERRER INSTITUT

Switzerland

EU Contribution

€ 167 250

LOUGHBOROUGH UNIVERSITY

United Kingdom

EU Contribution

€ 122 850

PEKING UNIVERSITY

China

Project information

Grant agreement ID: 269688

Status

Closed project

  • Start date

    1 January 2011

  • End date

    31 December 2013

Funded under:

FP7-EURATOM-FISSION

  • Overall budget:

    € 2 004 728

  • EU contribution

    € 1 171 470

Coordinated by:

ASSOCIATION POUR LA RECHERCHE ET LE DEVELOPPEMENT DES METHODES ET PROCESSUS INDUSTRIELS

France