Establishment of a hydric balance at the scale of a semi-natural sub-catchment area by in situ measures and 2D/3D modelling – Application to the Cadarache CEA site

In order to assess the impact of the operation of its facilities, CEA needs to have methods and tools available to measure, monitor and predict the dispersion of pollutants in soils and aquifers, or controlling the risk of flooding in the event of extreme rainfall. The proposed subject is in this general frame. This subject is in continuation of a precedent thesis which focused on the characterization of the hydrodynamic properties of the unsaturated zone (UZ), the complex interface between surface and groundwater, and more specifically on the quantification of the recharge. Two types of approaches were developed during this thesis: (i) 1D-approach at the scale of a soil pit equipped with water content sensors and tensiometers at different depths, through determination of water retention curves and Van Genuchten-Mualem parameters, and modelling of flows and recharge with HYDRUS, and (ii) a 2D-approach at the scale of Cadarache’s site, through soils’ samplings and analyses for prediction of hydraulic properties of UZ by use of pedotransfer functions (FPT), surface hydraulic conductivities measures, and research of spatialization’s criterias for infiltration (geology, vegetation, …).
The principal objective of the thesis is to spatialize the hydric balance, including both infiltration and surface runoff. The spatial scale is a sub-catchment of Ravin de la Bête, a temporary stream crossing the Cadarache’s site and collecting the runoff waters before flowing into the Durance River. Different in situ measures are considered (water content, hydraulic conductivities on surface and under the root zone, flows, …), along with complementary soils sampling and analyses. An experimental parcel with rain simulation and runoff measure will also be dimensioned and installed during the thesis. Finally, modelling with the coupled Parflow/CLM software is considered, in 1D at the pit soil’s scale (hydric balance with determination of recharge, runoff being neglected), and in 2D/3D at the sub-catchment scale (hydric balance including both runoff and recharge).
This thesis will be conducted in collaboration with the Institute of Geosciences in Environment (IGE) of the Grenoble Alpes University (UGA). It will take place on the CEA Cadarache site, in the Laboratory of Transfer Modelling in the Environment (LMTE), with possible occasional stays in IGE.

Alteration mechanisms study of MOX spent fuel in the presence of cimentious bentonitic material (MREA). Experimental and modeling approaches

In France, the reference way remains the reprocessing of spent fuel and the recovery of certain materials such as uranium and plutonium through the elaboration of MOX fuels and its recycling. However, the direct storage of fuels (UOX and MOX) in deep geological repository is also being studied in order to ensure that French storage concepts (Cigéo) are suitable for spent fuels as requested and included in the National Plan for the Management of Radioactive Materials and Waste (PNGMDR). Therefore, it is essential to study the alteration mechanisms of the spent fuel matrices in the presence of environmental materials that are similar, on a laboratory scale, to the current storage concept of radioactive waste in deep geological disposal: HA cells dug in the Callovo-Oxfordian (COx) clay whose low-alloy steel liner is isolated from the clay by a cimentious bentonitic grout called MREA. There is various objectives : on the one hand, to determine the impact of the environment on the alteration mechanisms of the fuel matrix as well as on the radionuclides release, and on the other hand, to develop a geochemical model to account for the main physicochemical processes involved. These studies are carried out at the ATALANTE facility (DHA) of the CEA Marcoule, where leaching experiments and characterizations of MOX fuels are achievable. This work is performed as part of the COSTO project and is supported by Andra and EDF.