Design And Fabrication Of Dispersion Nuclear Fuel For Transmuting Minor Actinides

The development of human civilization is inseparable from the demand for energy.Nuclear energy is an efficient and green energy,and should be one of the key points of energy development.However,the development of nuclear energy also faces some challenges.Among them,the treatment of spent fuel,especially the minor actinides,is particularly important.The accelerator driven subcritical reactor system is an efficient transmutation system of minor actinides.Dispersion nuclear fuel is an ideal form of nuclear fuel for this system.The structure of dispersion nuclear fuel is to disperse nuclear fuel microspheres containing minor actinides in a metal or ceramic matrix.This fuel structure can not only improve the thermal conductivity of the pellet through the high thermal conductivity of the metal or ceramic matrix material,but also limit the range of radiation damage.In addition,nuclear energy is also faced with the challenge of safety issues.Accident tolerant fuel is a new fuel concept that has been widely mentioned after the Fukushima accident and has been researched by various countries.Its purpose is to not only maintain or improve fuel performance under normal operation,but also withstand severe accidents for a long time.As an important form of accident tolerant fuel for accidents,the metal matrix material in dispersion nuclear fuel may react with water vapor under accident conditions,reducing the safety of fuel pellets.Based on the sustainable development of nuclear energy and the significance of accelerator driven subcritical reactor system and accident tolerant nuclear fuel,this paper has conducted a systematic study on the design and preparation of dispersion nuclear fuel pellets,the main work contents and achievements include the following aspects:A capillary based microfluidic device was constructed,combined with the sol-gel process to make the preparation process of nuclear fuel microspheres dust-free.The formation mechanism of droplet was analyzed and the influence factors on the size of microspheres were discussed.Nuclear fuel microspheres with controllable particle size,good monodispersity and good sphericity were successfully prepared by microfluidic technology.In addition,by constructing a capillary based fluid focusing micro fluidic device,the preparation of microspheres with small particle diameters was achieved.The optimized preparation of porous nuclear fuel microspheres based on heat treatment technology was achieved.Adjusting the heating mode basically avoided the breakage of microspheres.Many analysis methods were used to study the effect of heat treatment parameters on the physical and mechanical properties of microspheres.The invention not only ensures the mechanical strength of the fuel microspheres but also improves the adsorption capacity of the microspheres.The infiltration effect of porous nuclear fuel microspheres was characterized.Two physical methods were designed and explored to modify the surface of nuclear fuel microspheres to improve the interfacial compatibility between microspheres and matrix.One method is based on diffusion control to realize the formation of MgO uniform Ce/Mg oxide layer on the surface of the microsphere.The other method is based on electrostatic attraction to realize the formation of a thick MgO coverage on the surface of the microsphere.And the interface improvement situation and difference between the two modification methods are discussed experimentally.The problems of MgO based dispersion nuclear fuel pellet during the compression molding process were analyzed by finite element method,the displacement and stress of the materials during the compression were investigated,and the causes of defects in the fuel pellet in the pressing process were analyzed.According to the analysis results,the forming quality of pellet billet can be improved by adjusting the pressing pressure.The MgO based dispersion nuclear fuel pellet with good integrity was obtained by introducing an open-lobe mold.The dispersion nuclear fuel pellets with core shell structure were designed and prepared for the first time by in-situ fabrication using the particle separation phenomenon between different materials in the mixing process.The core-shell structure can prevent the reaction between metal matrix and water vapor,improve the safety of pellet.Besides,it provides a perspective on integrated manufacture of pellets and claddings by one-step preparation.The influence of mixed parameters on shell thickness is experimentally analyzed and an empirical formula with guiding significance for shell thickness control was established.