methodology of expertise of uranium base powder to improve the manufacturing process
Abstract
Powders and divided solids are widely used in industry as raw, intermediate or finished products in many fields foods, cosmetics, construction, pharmaceuticals, transport, electronics and nuclear energy. The improvement of the manufacturing processes requires control of processing steps based on an understanding of the phenomena involved (sintering, chemical reactivity, purity, etc.). Modelling and understanding these phenomena require data and characteristics that may be difficult to obtain. The present work mentions examples illustrating different physicochemical characterisation techniques suitable for analysis of uranium based powder samples (oxide, carbide, fluoride and metallic) in the raw state or after preparation (i.e. ion polishing) used in nuclear cycle. The first section discusses dimensional characterisation (particle size, morphology, porosity) by means of image analysis and preparation techniques SEM, TEM, FIB, electron and X ray tomography with possible 2D and 3D image analysis. Morphological data in the form of the powder size and shape can be obtained with new developments in 2D analysis of processed SEM images. Different raw grain of NIST powder, oxalate UNd, and Cu powder has been measured and compared with laser granulometer. A volumetric shape factor was determined for needle particle UNd.Closed porous squeletum of powder could be determined by SEM/FIB cutting and tomography calculation. An example of work in powder UO2 was showed (Fig 1).The second part of this work describes elemental chemical characterisation. Low-voltage EDS spectroscopy on polished powder cross sections is used to map the distribution of phases and to detect possible impurities in the solid grains and agglomerates. The contribution of this type characterisation to understanding the reaction mechanisms of phase transformations (especially solid-gas reactions) is illustrated for the hydro-fluorination of uranium dioxide. Sample preparation by mounting followed by ion polishing, optimisation of the EDS analysis parameters, and the contribution to solid-gas reaction models are discussed in this study. Complementary surface analyses as Auger spectrometry allows powder surface oxidation. An example was used on UAl powder and the detection of UO2 thin film (50 nm) by this ionic abrasive technique. The third section describes the characterisation of the chemical reactivity of powders and property mechanics. Chemical reactivity are performed by high-temperature in situ treatment in an environmental SEM, and allow observation of the powder morphology transformation. UC powder has been treat by high-temperature and we could see a growth of grain size. Property mechanics are performed by in situ treatment in an SEM FEG with plate of compressive force. In case of fundamental study in compressive nuclear fuel, simulant CeO2 powder has been tested in compressive test force with 15 mN. The result has been compared with DEM simulation (Fig. 2).This new analytical capacities allows strong supports to understand the reactivity mechanism of materials used in nuclear fuel fabrication processes.