Nanostructured actinide materials have gained the attention of the nuclear community after the discovery of enhanced properties in fuels that undergo high burn up. On these conditions, the UO 2 grains experimented recrystallization and formed a new rim of UO 2 nanoparticles, called high burn up structures (HBS). The pellets with HBS showed closed porosity with better fission gas retention and radiation tolerance, ameliorated mechanical properties, and less detriment of the thermal conductivity upon use. In this chapter, we will review different ways to obtain uranium nanoparticles, with emphasis on their synthesis and characterization. On the one hand, we will comment on radiation chemical syntheses, organic precursor-assisted syntheses, denitration processes, and biologically mediated syntheses. On the other hand, we will include for each of them a reference to the appropriate tools of the materials science that are used to fully characterize physical and chemical properties of these actinide nanoparticles.
SiO 2 -Al 2 O 3 -Y 2 O 3 glasses exhibit high glass transition temperatures, water corrosion resistance and good mechanical properties. These properties suggest that yttrium aluminosilicate glasses could potentially replace the borosilicate glasses usually used for immobilization of nuclear wastes. At the same time, yttrium can be used to simulate actinides.During waste immobilization, crystallization of the glassy matrix must be avoided or at least controlled, thus, the understanding of glass crystallization kinetics is essential.We found by XRD that the crystalline phases present on heat treatments are yttrium disilicate and sillimanite/mullite. By optical microscopy on polished cross-sections we could only identify highly yttrium enriched crystals which we associate with yttrium disilicate crystals.In this paper we measure the surface density of nucleation sites Ns in as obtained splat cooled pieces obtaining values of about 1.5 · 10 11 nucleus · m -2 . Crystal growth rate U in the temperature range 1000-1040 o C varies in the range 8-13 m · h -1 . These data are useful for designing sintering or melting thermal paths of YAS glasses in order to control their microstructure. We show the effect of glass particle size on DTA results: crystallization peaks moves towards lower temperatures for smaller particle size, which confirms that mainly surface nucleation is taking place on heating.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.