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IRSN, Institut de radioprotection et de sûreté nucléaire

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Enhancing Nuclear Safety


Research

Theses in progress

Dynamic modelling of the (bio)availability of chemical elements in the soil: comparative model-experimental approach applied to the transfer of strontium and caesium in ZNS


Host laboratory: Biogeochemistry, Bioavailability and Radionuclide Transfer Laboratory (L2BT)

Beginning of the thesis: October 2013

Student name: Mohamed Amine Cherif

 

 

Subject description

 

This PhD project is focused on the improvement of modeling tools for predicting the distribution and fluxes of radionuclides within and between different compartments of terrestrial ecosystems and their evolution over time.


It aims in particular to compare different mechanistic and phenomenological approaches to describe the processes and key factors governing the transfer of ions between the soil, the soil solution and root system of plants. The objective is to determine, for different time scales, the validity domain and limitations that are associated with these different levels of modeling.


The major purposes of the work are: 1) the development of a mechanistic modeling (surface complexation and chemical speciation) of the availability and bioavailability of the chemical elements in soil and rhizosphere at different time scales; 2) a comparison of this approach with the phenomenological or empirical modeling approaches (box model (Kd) and kinetic equilibrium model); 3) the implementation of a predictive tool, both mechanistic and operational, of the (bio) availability of chemical elements in the soil / solution / plant system.


These different modeling approaches are applied to Cs, Sr and their chemical analogue, K and Ca respectively. A particular focus will be set on the modeling of dynamic processes of desorption of these elements (physicochemical availability) that controls the recharge of soil solution from a contaminated soil.


To achieve these objectives it is necessary: i) to take into account the effects of root activity and chemical composition of the soil solution (pH, concentrations of other elements: K, Ca); ii) to consider explicitly the different soil components (minerals, organic matter and Iron/ Aluminum (hydr)oxide) through the use of surface complexation models; iii) to examine if an equilibrium approach (adsorption / desorption) is sufficient, or if the association of a kinetic componentis needed.


In support of these developments, a set of experimental data, obtained in controlled environments and simple laboratory systems, will be compared to the numerical simulations to describe the soil / solution / plant continuum.



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