RESUMEN
In order to study the feasibility of coating very dense powders by alumina using Fluidized Bed Metal Organic Chemical Vapour Deposition (FB-MOCVD), experiments were performed on a commercial tungsten powder, 75 microm in median volume diameter and 19,300 kg/m3 in grain density. The first part of the work was dedicated to the experimental study of the tungsten powder fluidization using argon as carrier gas at room temperature and at 400 degrees C. Due to the very high density of the tungsten powder, leading to low initial fixed bed heights and low bed expansions, different weights of powder were tested in order to reach satisfactory temperature profiles along the fluidized bed. Then, using argon as a fluidized bed former and aluminium acetylacetonate Al(C5O2H7)3 as a single source precursor, alumina thin films were deposited on tungsten particles at a low temperature range (e.g., 370-420 degrees C) by FB-MOCVD. The influence of the weight of powder, bed temperature and run duration was studied. Characterizations of the obtained samples were performed by various techniques including scanning electron microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS) analyses, Field Emission Gun SEM (FEG-SEM) and Fourier Transform InfraRed (FT-IR) spectroscopy. The different analyses indicated that tungsten particles were uniformly coated by a continuous alumina thin film. The thickness of the film ranged between 25 and 80 nm, depending on the coating conditions. The alumina thin films were amorphous and contained carbon contamination. This latter may correspond to the adsorption of species resulting from incomplete decomposition of the precursor at so low deposition temperature.
RESUMEN
The work deals with the removal by slow pyrolysis of epoxy resin from samples of spent nuclear fuel embedded in this polymer. Beyond the nuclear field, epoxy resin removal by pyrolysis is a typical issue for the recovery of metals in electronic waste. The main objective is to find the optimal conditions to remove hydrogen in the residual solid waste, in order to avoid hydrogen production by radiolysis during storage and so to prevent any risk of overpressure and explosion. The condensable pyrolysis products (tar-water mixture) and the char were characterised and quantified by elemental analyses, while the permanent gases were quantified by gas chromatography. A data reconciliation method was applied to adjust the values of raw measurements in order to complete the mass balances for both C, H, O and N elements and pyrolysis products. After studying the impact of temperature on the pyrolysis balance, experiments on a pilot furnace were conducted at 450 °C, in the frame of a parametric study of the heating rate, argon gas flow rate, resin mass and plateau time. At fixed temperature, we show that the plateau time is the only significant parameter for minimizing the residual hydrogen content in the char.