Simulation of the effective properties of granular media such as thermal conductivity is of a great interest for many applications. Under accident conditions the nuclear fuel may crack and relocate inside its cladding. In this case, the relocation leads to a degraded conductivity of the fuel. Thermal conductivity evaluation is interesting to evaluate the temperature in the fuel rod.
We developped a chained method involving Discrete Element Method (DEM) and Fast Fourier Transform (FFT) : We first compute the packing microstructure,
according to the grains kinetic, with DEM. The microstructure is voxelised and finally the FFT method is employed to compute the effective thermal conductivity of the granular media. This method allows us to compute accurately the effective thermal conductivity of a granular media taking its real microstructure into account.
We also performed a sensitivity analysis over the discretisation parameters, the size of the seed as well as the definition of interfacial voxels having both solid and gas phases (called fuzzy voxels). Thus we propose to define several bounds and estimates of the effective thermal conductivity depending on the definition of the fuzzy voxels. Finally, we compare the results of the DEM/FFT method to experimental measurements available in the litterature[3, 4] and show a good agreement between our simulations and the measurements.
 Frédéric Dubois, Michel Jean, Mathieu Renouf, Rémy Mozul, Alexandre Martin,
and Marine Bagnéris. LMGC90. In 10e colloque national en calcul des structures,
Giens, France, May 2011.
 J.C. Michel, H. Moulinec, and P. Suquet. E?ective properties of composite materials
with periodic microstructure : a computational approach. Computer Methods in
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 JS Boegli and RG Deissler. Measured effective thermal conductivity of uranium
oxide powder in various gases and gas mixtures. 1955.
 R.O.A. Hall and D.G. Martin. The thermal conductivity of powder beds. a model,
some measurements on uo2 vibro-compacted microspheres, and their correlation.
Journal of Nuclear Materials, 101(1) :172 - 183, 1981.