Phase Diagram Calculation Of Partial Metal Uranium-based Nuclear Fuel And Zirconium-based Cladding Material Under Irradiation

Nuclear energy is a very promising new energy,and it needs to be carried out in the nuclear reactors.Nuclear fuel element(nuclear fuel + cladding)materials are a key part of nuclear reactor materials.However,the nuclear fuel element materials are inevitably subject to irradiation during its application,with the appearance of irradiation effects,resulting in the change of phase stability.Therefore,in order to ensure that nuclear fuel element can operate safely and efficiently,it is necessary to study the phase diagram of nuclear fuel element under irradiation conditions.In this paper,based on the CALPHAD method,the equilibrium phase diagram of the metal nuclear fuel U-X binary alloy and the cladding material Zr-X binary alloy under irradiation conditions are calculated.The main work is presented as follows:(1)Based on the thermodynamic parameters and diffusion data of the binary systems of U-X(X:Mo,Zr)reported in the literature,the effective free energy model is used to calculatethe equilibrium phase diagrams of the nuclear fuel U-X(X:Mo,Zr)binary alloy under different irradiation conditions.The results show that the irradiation can hardly affect the phase relationships at high temperatures.However,under irradiation,in U-Mo and U-Zr binary alloy,the y(U,Mo)and the y(U,Zr)phase are remarkably stabilized at lower temperatures,respectively,leading to the emergence of two invariant reactions.That is,due to the effect of irradiation,the high-temperature stable y phase can also be stable at low temperatures.The results of the present work give a reasonable explain to the experimental results of Bleiberg et al.,and provide guidance to the design of metallic U-based nuclear fuel.(2)Based on the thermodynamic parameters and diffusion data of the binary systems of Zr-X(X:Nb,Mo)reported in the literature,the effective free energy model is used to calculatethe equilibrium phase diagrams of the nuclear fuel Zr-X(X:Nb,Mo)binary alloy under different irradiation conditions.The calculated results show that the equilibrium phase diagram under irradiation and the thermodynamic equilibrium phase diagram are basically the same at high temperatures.Whereas,under irradiation,in Zr-Nb and Zr-Mo binary alloy,the BCC(?Zr,Nb)and the BCC(?Zr,Mo)phase are remarkably stabilized at lower temperatures,respectively,leading to the emergence of two invariant reactions,and the solubility of Nb in(aZr)will increase.The results of the present work are consistent with the calculated results of Turkin et al.,and provide important theoretical guidance for the design of Zr-based cladding materials.