Manufacturing Methods Of U-Zr Metallic Fuel

Human beings are facing the energy shortage and environmental pressure brought about by the use of fossil fuel.Because of high energy density and no greenhouse gases,nuclear energy is an important way to solve the energy problem.The fu-sion-fission hybrid reactors,fast neutron reactors and ADS energy systems intend to use metal-based nuclear fuels.Constituent redistribution and swelling in metallic fuels,and interaction of metallic fuel with cladding materials cause long-term stability problems in metallic fuel.So the research of element diffusion,interface reaction and radiation stability in this system is necessary.In this paper,uranium-zirconium alloys are selected as the research objects,and the major research contents and results are as follows:Fabrication technology of uranium-zirconium alloys by induction-melting,and mi-crostructure of U-Zr alloys.U-4wt.%Zr,U-6wt.%Zr,U-8wt.%Zr,U-10wt.%Zr,U-12wt.U-2wt.%Zr and U-15wt.%Zr are prepared in a vacuum-induction melting furnace.The deviation content of the prepared U-10wt.%Zr（name content）alloy is less than 0.5%and total impurity is less than 1000 μg/g.The results show that U-Zr alloys are constitute of supersaturated solid solution a-U phase and δ-UZr₂ phase,even if the Zr content is very low.During cooling of casting U-Zr alloys,firstly,γphase decompose to γ1 phase and γ2 phase.And then γ1→α-U phase transition oc-curred,γ2 phase transforms to ω phase through the crystal surface collapse,which then orders to δ-UZr2 phase.TEM studies show that α-U phase and δ-UZr₂ phase are coherent,and the orientation relationship is（010）[001]_α ‖（0110）[（?）110]_δ.Preparation technology of porous U-10wt.%Zr alloy by powder metallurgy.The pores in U-10wt.%Zr alloy can contain fission products during neutron irradiation.U-10wt.%Zr alloy powders were prepared by hydrogenation-dehydrogenation method.The pressed compacts were prepared by cold isostatic pressing,and then vacuum sin-tering.Hydrogenation-dehydrogenation can be used to obtain U-10wt.%Zr alloy powder which is not oxidized and has a controlled particle-size.The density of the pressed compacts of U-10wt.%Zr alloy powder is not related to the subsequent densi-ty after sintering.With controlling the time and temperature of sintering,a porous uranium-zirconium alloy with a relative density of 70 to 91%can be obtained.The effect of porosity to the thermal conductivity of U-10wt.%Zr alloy is in accordance with the Loeb relationship.Bonded technology of U-10wt.%Zr alloy.The results show that in order to obtain a good interface between U-10wt.%Zr alloy and Zr-4 alloy,the hot pressing tempera-ture and time should be precisely controlled to avoid excessive reaction at the inter-face,δ-UZr2 layers formed at the interface.Uranium is rich in UZr2 layer adjacent to Zr-4 alloy,and the UZr2 layer is coherent with Zr-4 alloy and α-U phase in U-10wt.%Zr alloy,respectively.The results of hot isostatic pressing（HIP）show that the diffusion of alloying elements is inhibited by pressure in HIP,the activation ener-gy increases and the diffusion rate decreases,and the grain boundary diffusion of Zr-4 alloy is less affected.UZr₂ intermetallic compound layer formed at the interface of U-10wt.%Zr/Zr-4 alloy,and a pure zirconium layer was found between U-10wt.%Zr alloy and UZr₂ layer.Compatibilities and interfacial diffusions between U-10wt.%Zr and Zr-4 alloy.The diffusion behavior of U-10wt.%Zr alloy and Zr-4 alloy is controlled by the diffusion rate.The diffusion rate of U element to Zr-4 alloy is relatively fast,and the relation-ship between the growth thickness and the time of diffusion layer is in accordance with the parabolic law.The interdiffusion coefficient of U-10wt.%Zr/Zr-4 alloy sys-tem in the temperature range of 800 ℃～1100 ℃ is 1 × 10^-15～1×10^-13 m²/s.it be-comes relatively smaller when the content of zirconium is less than 40 at.%.In the temperature range of 380 ℃～1100 ℃,the interface diffusion behaviors of U-10wt.%Zr/Zr-4 alloy are divided into three intervals,which are controlled by dif-ferent diffusion growth mechanism of diffusion layers.In the first temperature range of 380 ℃～600℃,the growth rate constant of the element in the δ-UZr2 phase is 9.85 × 104 m²/s and the activation energy is 340.93 kJ/mol.At the temperature of 650 ℃～800 ℃,the U atom is diffused in the α-Zr with substitute mechanism.The growth of the diffusion layer is controlled by this mechanism.The growth rate con-stant of the interdiffusion layer is 4.10 × 10^-4 m²/s and the activation energy is 206.33 kJ/mol.While the growth rate constant is 3.43 × 10^-6 m²/s in the γ（U,Zr）solid solu-tion at the temperature of 900 ℃～1100 ℃,and the activation energy is 158.50 kJ/mol.The experimental results show that the compatibility between U-10wt.%Zr alloy and Zr-4 alloy is good at temperatures below 500 ℃.