Preparation Of Uranium Carbide Nuclear Fuel Particles From Uranium Oxide Powder

Because fossil energy reserves are limited and non-renewable,in order to meet the demands of sustainable development of human society for energy,other energy sources,including nuclear energy,are being developed and used to replace fossil fuels.Nuclear energy has the advantage of high capacity density and nuclear energy resources are abundant.However,nuclear reactors produce a lot of spent fuel during operation.If is not properly disposed,the minor actinides(MA)and the long-lived fission products(LLFP)in spent fuel will cause serious radioactive contamination to the environment.People adopt the partition&transmutation(P&T)strategy to process the spent fuel.This method reduces the influence of spent fuel on the environment by separating the MA and LLFP from the spent fuel and transmuting them into medium-lived,short-lived nuclides or stable nuclides.Accelerator Driven Sub-critical System(ADS)has a strong capability of transmuting minor actinides and long life fission products,people has done a lot of research on it.Due to the high thermal conductivity,high density and high burn-up of carbide dispersion nuclear fuel,it becomes one of the alternative fuels for the ADS reactor in China.It is necessary to prepare the carbide nuclear fuel microspheres when preparing the carbide dispersion nuclear fuel.At present,the preparation methods of carbide nuclear fuel microspheres include powder metallurgic method and sol gel method.The oxide powder obtained from the spent fuel cannot directly be used as the raw material for the preparation of carbide nuclear fuel microspheres by sol-gel method and the powder metallurgy method will cause the radioactive dust contamination and the spontaneous combustion of carbide during the preparation of carbide nuclear fuel microspheres.In this paper,a wet preparation process of carbide nuclear fuel microspheres start with oxide powder is designed.As a pilot basic research,in this experiment,uranium carbide(UC)microspheres were prepared by using the triuranium octoxide(U3O8)powder as raw materials and the oxide powder containing MA and LLFP was not doped in the raw material powder.The research contents of this paper are as follows:1.The designed preparation process is as follows.Firstly,prepare the raw material slurry containing U3O8.Secondly,disperse the slurry into droplets by capillary-based microfluidic device.Thirdly,glue the slurry droplets into gel microspheres.Lastly,calcine the gel microspheres at high temperature to prepare UC nuclear fuel microspheres.Microfluidic control technique was used in this experiment.Obtained microspheres are of good sphericity and the size of microspheres is controllable and uniform.2.Two kinds of gel reaction systems were designed to realize the transformation of liquid droplets to gel microspheres.The effects of two gel reaction systems on the sphericity of gel microspheres were studied in detail.The boric acid-polyvinyl alcohol gel reaction system was determined to prepare U3O8/C gel microspheres.The effect of boric acid mass fraction on the sphericity of gel microspheres was investigated and the best mass fraction of boric acid was determined.3.Thermal analysis of gel microspheres was performed in the research.Obtained TG-DTG curve of gel microspheres was used to determine the subsection heating method,thus avoiding the rupture of gel microspheres during calcination.4.SEM analysis,XRD analysis and EDX analysis were carried out for the prepared UC nuclear fuel microspheres.The microstructure and chemical composition of obtained microspheres were studied in detail.5.Influence of some preparation parameters on the properties of prepared microspheres was explored,including influence of soaking time and solid content of raw material slurry on the density of microspheres and the influence of the C/U ratio in raw material slurry on the composition of microspheres.