H. Tel

Structural and thermal investigations on cerium oxalate and derived oxide powders for the preparation of (Th,Ce)O2 pellets

Abstract Ce2(C2O4)3·nH2O powder was prepared by adding oxalic acid to a cerium nitrate solution. Cerium oxalate was identified by chemical and thermal analysis (DTA/TGA). Cerium oxalate powder was calcined to oxides at different temperatures and the powder properties (specific surface area, particle size distribution, mean particle size, bulk and tap densities) of these oxides were determined. X-ray diffraction (XRD) patterns of cerium dioxide powders obtained at different calcination temperatures were evaluated. The crystallite size was calculated both from XRD data using Sherrers equation and from specific surface area data for each temperature. (Th0.95Ce0.05)O2 powder was prepared by mixing the binary oxides. The compacted pellets were calcined in air at 1050 °C. The XRD patterns of these pellets were evaluated to characterise the formed solid solution.

Sorption kinetics of cesium on hydrous titanium dioxide

Summary Two types of hydrous titanium dioxide possessing different surface properties were prepared and characterized to study the sorption kinetics of cesium. The effect of pH on the adsorption capacity were determined in both type sorbents and the maximum adsorption percentage of cesium were observed at pH 12. To elucidate the kinetics of ion-exchange reaction on hydrous titanium dioxide, the isotopic exchange rates of cesium ions between hydrous titanium dioxides and aqueous solutions were measured radiochemically and compared with each other. The diffusion coefficients of Cs+ ion for Type1 and Type2 titanium dioxides at pH 12 were calculated as 2.79×10-11m2s-1 and 1.52×10-11m2s-1, respectively, under particle diffusion controlled conditions.

Preparation of homogeneous (Th0.8U0.2)O2 pellets via coprecipitation of (Th,U)(C2O4)2·nH2O powders

Abstract Thorium and uranium dioxides form a complete series of solid solutions. The formation from the individual oxides can be performed only by extensive co-milling and reaction at high temperatures. In this study, we prepared 80% ThO 2 -20% UO 2 via coprecipitation of the mixed oxalates from nitrate solutions using an excess of oxalic acid. The parameters which may effect the powder properties were investigated, such as oxalic acid and thorium concentrations, temperature and type of agitation. The specific surface of the oxalates and their derived oxides were measured. Among the precipitation parameters, temperature of 10°C and mechanical stirring resulted in the highest surface area. The coprecipitated Th,U(IV) oxalate powders were decomposed at 350°C, calcinated at 900°C each for 24 h in air and were reduced during 2 h at 650°C in H 2 atmosphere. X-ray diffraction resulted in a single-phase mixed oxide solid solution. The green densities of pellets made from these mixed oxides varied between 36 and 38% TD. Pellets were sintered in flowing CO 2 at 1100°C for 30 min and achieved 81% TD.

Investigation of production conditions of ThO2-UO3 microspheres via the sol-gel process for pellet type fuels

Abstract The aim of the present study is the preparation of ThO 2 –UO 3 gel microspheres up to 40% UO 3 , suitable as press feed for producing homogeneous and sinterable ThO 2 and thorium based (Th,U)O 2 pellet type fuels using sol–gel process. Without reducing the uranium oxidation state to (IV) and without using any complexing agent, a simple external gelation process was studied taking full advantage of the gelation features of thorium. The source sols used for the processes were prepared by the ammonia addition method where starting thorium and uranium nitrate solutions were heated and partially neutralized by aqueous ammonia under pH control at different pH set and neutralization mode for each uranium mole ratio. Crackfree microspheres suitable for gelation were obtained using a hexone–(10%) CCl 4 mixture as the drop formation medium and ammonia as the gelling agent. The dimensions, sphericity, bulk densities and specific surface area of microspheres were determined. The microspheres were compacted and then the pellets were sintered in a 75% Ar–25% H 2 atmosphere at 1100°C for 150 min.

Preparation and characterization of uranyl oxalate powders

Abstract Uranyl oxalate powders are prepared by adding 0.5 M oxalic acid solution to the uranyl nitrate (UNH) solutions purified with TBP extraction from dissolution of the Canada originated U3O8 commercial concentrate. Uranyl oxalate powders are identified by chemical analysis, TGA/DTG analysis, IR analysis and by single-crystal X-ray diffraction. The effects of the precipitation conditions on the powder properties are determined. A broad particle size distribution is obtained for all precipitation variants. These powders including very fine particles are difficult to filter and are not free flowing. The reactor and mixing type have a considerable effect on the powder properties of the uranyl oxalate powders. It was possible to ameliorate the filtration and the flowability to a certain degree using a conical air agitated reactor. The flowability of these powders is 0.4 g/s with a specific surface area 6.64 m2/g and an average particle size of 11 μm.

Anion-exchange separation and determination of thorium and uranium in Eskişehir-Beylikahir ore in Turkey

Eskişehir-Beylikahir ore contains rare earth elements (REE) and thorium as bastnaesite mixed with barite, calcite and fluorite and small amounts of uranium. The mineralogical composition and Th, U, REE contents of the ore samples taken from different sectors of the same region show important variations. For the spectrophotometric determination of Th and U in the ore, successive anion-exchange and solvent extraction procedures are carried out to separate U and Th from each other and from accompanying interfering elements. The accuracy and precision of the method is demonstrated by intercomparison of the thorium standard reference samples S-14, S-15 and S-16 of IAEA. In all cases very good agreement was obtained.

Investigation of production conditions and powder properties of AUC

Ammonium uranyl carbonate (AUC) powders are prepared by adding 25% ammonium carbonate solution into the uranyl nitrate (UNH) solutions purified with TBP extraction from dissolution of the Canada originated U3O8 commercial concentrate. AUC powders are identified by chemical analysis, TGA/DTG analysis, IR analysis and by single crystal X-ray diffraction. The effects of the precipitation conditions on the powder properties are determined. The particle size of AUC increases with the C/U ratio and temperature while it decreases with the increasing uranium concentration. The mixing rate and the addition rate of ammonium carbonate does not have a considerable effect on the particle size. The reactor and the mixing type have great effects on the flowability of the AUC powders. The most flowable powders are obtained in a conical and air agitated reactor. The flowability of these powders is 2.5 g/s with a specific surface area of 5.59 m2/g and particle size of 4 μm. UO2 converted via AUC is also very flowable (3 g/s) with a specific surface area of 5.1 m2/g.

Preparation of homogeneous (Th0.8U0.2)O2 powders by mechanical blending of Th(C2O4)2·6H2O and U(C2O4)2·6H2O powders

Abstract Thorium oxalate and uranium (IV) oxalate powders were prepared and characterized by chemical, TGA/DTG, IR and X-ray diffraction analysis. Th(C2O4)2·6H2O and U(C2O4)2·6H2O powders (80% Th and 20% U) were mechanically mixed in a diagonal rotating drum for 3 h. Mechanically mixed oxalates were decomposed at 623 K, calcined at 1173 K for 24 h in air and reduced for 2 h at 923 K in hydrogen atmosphere. The powders were compacted into pellets and sintered in flowing CO2 at 1373 K for 1 h. The XRD pattern of (Th0.8U0.2)O2 obtained showed that a complete solid solution was formed.

Sorption kinetics of cesium on ZrO2 and ZrO2-SiO2-TiO2 microspheres

Abstract ZrO2 and ZrO2-SiO2-TiO2 (with 1:1:1 mol ratio) microspheres have been prepared by the sol-gel method and characterized to study the sorption kinetics of cesium. The effect of pH on the adsorption capacity was determined for both type sorbents and the maximum adsorption percentage of cesium was observed at pH 10. To elucidate the kinetics of the ion-exchange reaction on pure and ternary oxide microspheres, the isotopic exchange rates of cesium ions between both types of sorbent microspheres and aqueous solution were measured radiochemically and compared with each other. The diffusion coefficients of Cs+ ion for ZrO2 and ZrO2-SiO2-TiO2 sorbent microspheres at pH 10 were calculated as 3.648×10−8 m2 s−1 and 6.383×10−8 m2 s−1, respectively, under particle diffusion controlled conditions.

Preparation and characterization of sol-gel derived (ThxCe1−x)O2 microspheres

Abstract (ThxCe1−x)O2 microspheres (x=0.50, 0.75 and 0.95) with high homogeneity were prepared via sol-gel technique, starting from the initial chemical materials Th(NO3)4·5H2O and (NH4)2[Ce(NO3)6]. The sols were prepared by addition of ammonia under pH and temperature control. Sols were gelated to spherical form in a gelation system consisting of peristaltic pump, flow regulator, nozzle and a glass column. To obtain crack-free spheres suitable for gelation, source sols neutralization conditions, drop formation and pre-hardening medium were investigated and the optimum conditions were determined. After aging, washing and drying steps, gel microspheres were characterized. For this purpose, thermal behaviors of spheres were investigated with TG/DTA analysis. Dried microspheres at 80°C were calcined at three different temperatures, namely 450°C, 800°C and 1150°C, and crystal parameters were calculated from XRD data. BET specific surface area and BJH porosity analyses were also carried out.