Microwave process for sintering of uranium dioxide (original) (raw)
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IOP Conference Series: Materials Science and Engineering
Sintering process is the final stage of fuel kernel manufacturing prior to the coating process. This stage is very important part of the whole process, because it will determine the feasibility of UO2 kernel to comply with the specifications of HTR reactor fuel. The objective of this research was to obtain UO2 kernel with the density of ≥ 95% TD. The results showed that the highest density reached 92.56% TD or about 10.1441 g / cm3. This condition of sintering was gained at the temperature of 1400 °C with sintering time of 2 hours. The sintering product diameter gained was around 919 μm, the specific surface area 4.4213 m 2 / g, and a total pore volume 4,751 x10-3 cm 3 / g. The density of UO2 kernel produced from this research is the best compared to previous finding because of its density already approaches the HTR fuel specification requirements
The possible usage of ex-ADU uranium dioxide fuel pellets with low-temperature sintering
Journal of Nuclear Materials, 2000
UO 2 fuel pellets are prepared conventionally by high-and low-temperature sintering. Both ex-ammonium uranyl carbonate (AUC) and ex-ammonium diuranate (ADU) UO 2 are used in these techniques. Larger quantities of chemicals (NH 3 and CO 2 ) are required for the AUC process which is a signi®cant complication compared with the ADU process. In this work, it is aimed to search the important parameters such as theoretical density (TD) and grain size of ex-ADU UO 2 pellets which are in an oxidative atmosphere at low temperature. A density of %95% TD is obtained at 1150°C. The grain structure of the pellets sintered in an oxidative atmosphere is monomodal unlike the duplex grain structure of ex-AUC oxide, but it is in accord with ex-ammonium uranate (AU) oxide. The grain structure, distribution and size are compared with the ex-AUC and ex-AU conversion processes. It is shown that the grain structure development depends on both the powder properties and the sintering atmosphere. Ó
Pressureless Rapid Sintering of UO 2 Assisted by High-frequency Induction Heating Process
Journal of the American Ceramic Society, 2008
Heat generation of uranium dioxide (UO 2) powder and its pressureless rapid sintering behaviors have been studied using a highfrequency induction heating apparatus. The porous graphite housing has been used to prevent heat loss and to preheat the uranium oxides, simultaneously. At an elevated temperature, UO 2 powder generated extra heat by itself. The synergism of individual heat generation between the graphite and UO 2 powder could effectively heat the UO 2 to the sintering temperature of 17001C. Using this process, densification behavior of cylindrical and disk-type UO 2 green pellets according to the heating rate and grain structure of sintered UO 2 pellets were investigated. Rapid sintering caused a large crack around the circumference of the sintered pellet. The formation of cracks could be avoided when the heating rate or sample dimension are properly reduced. A dense and crack-free UO 2 pellet with a relative density of up to 96% was produced within 5 min of the process time. The induction heat sintering process can be a potential candidate for the rapid fabrication of ceramics and composites. I.-W. Chen-contributing editor This work has been carried out under the nuclear R&D program supported by the
ADVANCES IN PROCESS MATERIALS FOR PRODUCTION OF UO
… ASSOCIATION OF INDIA
article deal with the development of a nano/meso hybrid microstructure by mechanical alloying of stainless steel and titanium powders followed by hot rolled sintering resulting in improved mechanical properties. This is followed by design, fabrication and performance evaluation of a high energy mill and the preparation of nanocrystalline stainless steel powders from powders of iron and ferrochromium by mechanical alloying. On line density determination of MIM parts inside the sintering furnace using model based supervisory control system is another contribution.
Study on sintering kinetics and activation energy of UO2 pellets using three different methods
Journal of Nuclear Materials, 2006
During early stages of sintering of UO 2 , diffusion of metallic ions plays the vital role as this is the rate controlling step of the sintering at that stage. Sintering kinetics and the activation energy at the early stages of sintering of UO 2 in reducing atmosphere has been studied by several workers using different methods of calculation. The diffusion mechanisms that have been found to operate at this stage are grain boundary diffusion and volume diffusion. The activation energy calculated by different studies also varies widely. In the following study, sintering mechanism and activation energy for sintering of UO 2 in reducing atmosphere has been studied by three different methods, namely, rate controlled sintering, constant heating rate and Dorn's method. The kinetics of sintering and activation energy has been found to change with temperature. Initially grain boundary diffusion operates and in the later stage volume diffusion controls. Calculation of activation energy by the above methods shows that the rate controlled sintering and constant heating rate produces similar results, whereas the results of Dorn's method are not quite matching.
Synthesis and Sintering of UN-UO2 Fuel Composites
Journal of Nuclear Materials, 2015
The design and development of an economical, accident tolerant fuel (ATF) for use in the current light water reactor (LWR) fleet is highly desirable for the future of nuclear power. Uranium mononitride has been identified as an alternative fuel with higher uranium density and thermal conductivity when compared to the benchmark, UO 2 , which could also provide significant economic benefits. However, UN by itself reacts with water at reactor operating temperatures. In order to reduce its reactivity, the addition of UO 2 to UN has been suggested. In order to avoid carbon impurities, UN was synthesized from elemental uranium using a hydride-dehydridenitride thermal synthesis route prior to mixing with up to 10 wt% UO 2 in a planetary ball mill.
Sintering behavior of UO2Er2O3 mixed fuel
Journal of Nuclear Materials, 2018
The incorporation of burnable neutron absorbers into nuclear fuel pellets is important regarding reactivity compensation, which enables longer fuel cycles. The dry mechanical blending route is the most attractive process to accomplish absorbers incorporation because of its simplicity. By using this route, the present work has investigated the sintering behavior of UO 2-Er 2 O 3 mixed fuel. A comparison with UO 2-Gd 2 O 3 sintering behavior was presented. The behavior of UO 2-Er 2 O 3 fuel sintering was similar to that reported for UO 2-Gd 2 O 3 fuel, e.g. two-stage sintering with two peaks in the shrinkage rate curves. The effect showed to be less pronounced for Er 2 O 3. This was attributed to the characteristics of the Er 2 O 3 powder particles used as raw-material, whose agglomerates can be more easily broken and thus better homogenized during the blending with UO 2 powder. These results confirmed that sinterability depends directly on the quality of the homogenization of the powders, as seen previously. A second phase was experimentally detected in the UO 2-Er 2 O 3 system, but its impact on the sintering behavior of this mixed fuel has not yet been clarified.
Preparation, sintering and leaching of optimized uranium thorium dioxides
Journal of Nuclear Materials, 2009
Mixed actinide dioxides are currently studied as potential fuels for several concepts associated to the fourth generation of nuclear reactors. These solids are generally obtained through dry chemistry processes from powder mixtures but could present some heterogeneity in the distribution of the cations in the solid. In this context, wet chemistry methods were set up for the preparation of U 1Àx Th x O 2 solid solutions as model compounds for advanced dioxide fuels. Two chemical routes of preparation, involving the precipitation of crystallized precursor, were investigated: on the one hand, a mixture of acidic solutions containing cations and oxalic acid was introduced in an open vessel, leading to a poorly-crystallized precipitate. On the other hand, the starting mixture was placed in an acid digestion bomb then set in an oven in order to reach hydrothermal conditions. By this way, small single-crystals were obtained then characterized by several techniques including XRD and SEM. The great differences in terms of morphology and crystallization state of the samples were correlated to an important variation of the specific surface area of the oxides prepared after heating, then the microstructure of the sintered pellets prepared at high temperature. Preliminary leaching tests were finally undertaken in dynamic conditions (i.e. with high renewal of the leachate) in order to evaluate the influence of the sample morphology on the chemical durability of the final cohesive materials.
Coarsening-densification transition temperature in sintering of uranium dioxide
Journal of Nuclear Materials, 2001
The concept of coarsening–densification transition temperature (CDTT) has been proposed to explain the experimental observations of the study of sintering undoped uranium dioxide and niobia-doped uranium dioxide powder compacts in argon atmosphere in a laboratory tubular furnace. The general method for deducing CDTT for a given material under the prevailing conditions of sintering and the likely variables that influence the CDTT are described. Though the present work is specific in nature for uranium dioxide sintering in argon atmosphere, the concept of CDTT is fairly general and must be applicable to sintering of any material and has immense potential to offer advantages in designing and/or optimizing the profile of a sintering furnace, in the diagnosis of the fault in the process conditions of sintering, and so on. The problems of viewing the effect of heating rate only in terms of densification are brought out in the light of observing the undesirable phenomena of coring and bloating and causes were identified and remedial measures suggested.
Three different fuels UO2-only, UO2-Gd2O3(5%), and UO2-Gd2O3(10%) were produced by sol-gel technique. Their powder characteristics such as flowability, BET surface area, average pore diameter, and cumulative pore volume were determined. The pore size distributions of powders, green pellets, and sintered fuels were determined by using a mercury porosimeter. The theoretical densities of sintered fuels were found to be 98.01, 95.3, and 95.9%, respectively. Their ruggedness fractal dimensions were 1.111, 1.044, and 1.042, while the fractal dimensions associated with the size distribution of grains were 1.44, 1.58, and 1.60, respectively.