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Thorium based fuels offer several benefits compared to uranium based fuels thus they might be an attractive alternative to conventional fuel types. This study is devoted to the synthesis and the characterization of small thorium dioxide microspheres (O

In the Sol–Gel Laboratory at the Institute of Nuclear Chemistry and Technology (INCT), studies of synthesis of various advanced ceramic materials by the sol–gel method have been carried out for 50 years. The ceramics products, such as metal oxides, homogeneous mixtures of metal oxides, cermetals and metals, were obtained in various shapes, as irregular powders, monoliths, coatings, fibers or spherical particles with various diameters. A new method using a water-in-oil technique – the ICHTJ Process (INCT in English) was elaborated to synthesize spherical particles of metal oxide or mixture of metal oxides, with diameters below 100 µm. Through years, the method has been evaluated and optimized. Prepared sol solutions of metal cations are emulsified in 2-ethylhexanol-1 containing 1 volume % of the surfactant sorbitol monooleate. Drops of emulsion are gelled by extracting their water with this organic solvent. The main parameters e.g. flow rate; gelation time, syringe, sol solution etc. that have a strong influence on the optimization of the synthesis method and features of the spherical particles are described in this article through an example of synthesis of uranium oxycarbide – mixture of uranium dioxide with uranium carbide.

Synroc (Synthetic Rocks) materials have been regarded as the second generation of high level waste forms in the world. It allows incorporating into their crystal structures almost all of the elements present in high-level radioactive waste. One of the components of Synroc-C is perovskite (CaTiO 3) which immobilize mainly fission products, but also allow immobilizing in his structure long-lived actinides such as plutonium (Pu). Perovskite phase has been fabricated by a sol-gel route. In the present work complex sol-gel process (CSGP Polish Patent PL 172618, 1997) and method of synthesis Me-titanates (Polish Patent PL 198039, 2001) were adapted to prepare of perovskite. Additions of 10 % molar Sr, Co, Cs and Nd into Ti-Ca-nitrate sols were carried out by CSGP. Gels obtained by evaporation of sols under reduced pressure were thermal treated according thermogravimetric (TG, DTA) analysis. Transformation of ascorbat-nitrate gels into doped orthorhombic perovskite phases was definitely lower (about 650 C) than those pure nitrate gels (approx. 700 C). All structures were confirmed by X-ray diffraction analyses. Surrogates were homogeneously distributed into crystalline structure of perovskite. It means that elaborated process can be applied for synthesis Synroc materials and it might be competitive to vitrification process. © 2013 Akadémiai Kiadó, Budapest, Hungary.

For synthesis of silica glasses designed to contain high-level nuclear wastes，a patented complex sol-gel process has been used. Surrogates of the nuclear waste elements Cs, Sr, Co, and Nd (generically denoted Me) were used. Gels in the forms of powders and sintered compacts were prepared by hydrolysis and polycondensation of tetraethoxide/Me nitrate solutions, which contained ascorbic acid as a catalyst. Transformation to final products was studied by thermogravimetric analysis, infrared spectroscopy, and X-ray diffraction. Preliminary testing of Me leaching was also completed in water. Most of the final products were porous; only a single dense form was resistant to leaching.

A complex Sol-Gel process has been used for synthesis of silica glasses designed to contain high-level nuclear wastes. Cs, Sr, Co, and Nd (generically denoted Me) were used, the last as surrogate for actinides. Gels in the form of powders and sintered compacts were prepared by hydrolysis and polycondensation of tetraethoxide/Me nitrate solutions, which contained ascorbic acid as a catalyst. Thermal treatment studies were conducted on the resulting gels. Transformation to final products was studied by thermogravimetric analysis, infrared spectroscopy, and X-ray diffraction. Preliminary testing of Me leaching was also completed in quiescent water. Only a single dense form was resistant to leaching

Medium sized spherical particles of Li2TiO3 (with diameters below 100 μm) can be prepared from peroxy lithium titanate solution (stabilized with citric acid) by a modified INCT (Institute of Nuclear Chemistry and Technology) variant of the sol–gel process. The process consists of the following main steps: (I) formation of aqueous phase emulsion in 2-ethylhexanol-1; (II) gelation of emulsion drops by extraction of water with partially dehydrated EH; (III) filtration and washing with carbon tetrachloride or acetone; (IV) non-destructive thermal treatment. The medium size particles can be used for increasing pebble bed density by infiltration them into bed larger spheres (1 mm diameter). The tritium release from sol–gel process preparation of Li2TiO3 microspheres was found very close to that observed for other traditional material however, the new process is more efficient than other processes because of the morphology of the sintered specimens.

A modified complex sol-gel process was developed to synthesize LiMn2O4 and LiNixCo1-xO2 powders. Sols were prepared from 1.5 M of Mn2+ or 1 M of xNi2+ and (1-x)Co2+ acetates plus ascorbic acid aqueous solutions by alkalizing them with LiOH and NH4OH. Ascorbic acid was added to prevent precipitation in the precursor solutions. When the sols were concentrated to one-third of their initial volume under reduced pressure and then gelled by drying for 10 days, heat treatment to ≥700 °C was accompanied by foaming, violent self-ignition, and formation of carbonates in the Ni-containing species. Significant improvements to the process and resulting powders were gained by modifying the gelation step. When gelation and drying were carried out under reduced total pressure, subsequent heating produced self-ignition, but no foaming, for all heating rates. The resulting products were determined to be nearly phase pure and carbonate free by thermogravimetric, differential thermal, X-ray, and infrared spectroscopy methods.