Dissolution and diffusion of niobium in uranium melt

U-Nb alloy is an important structural and functional material in nuclear engineering for its excellent comprehensive mechanical properties and corrosion resistance. Nb and U differ greatly in melting point and density. The melting point is 2470 ℃ and 1135 ℃ respectively, and the density is 8.57 and 19.1 g/cm³ respectively. The great difference of melting point and density brings great difficulty to the alloying process of uranium niobium alloy. The melting point of niobium is much higher than the cyanosis of most vacuum induction melting materials and the temperature of coating materials. It is difficult to fully alloying uranium-niobium alloy under vacuum induction melting conditions. The alloys with high niobium content were mostly prepared by arc smelting, and vacuum induction smelting was used as remelting. The conventional preparation process of uranium-niobium alloy, especially the uranium-niobium alloy with high niobium content, is to make the uranium-niobium composite electrode first, make the saw element evenly distributed in the uranium melt through vacuum arc smelting, and then use vacuum induction smelting for refining. The conventional preparation process of uranium-niobium alloy is complex, with long preparation period and high manufacturing cost. Therefore, it is of great significance to develop the direct vacuum induction melting technology for high quality uranium-niobium alloy production.

At present, the main problem of direct vacuum induction melting of uranium-niobium alloy is insufficient alloying, which is related to the material characteristics of uranium-niobium alloy and the process characteristics of vacuum induction melting. Based on the capacity of vacuum induction melting equipment and for safety reasons, the melting temperature of silver cannot be reached. The solid niobium is gradually dissolved in liquid uranium. U-Nb phase diagram is a binary homogenizing phase diagram, so the melting point of the mutual diffusion zone in the eutectic system will not decrease, which is conducive to dissolution. In the case of uranium melt at low overheating temperature, the solid niobium cannot be dissolved rapidly. Considering the thermodynamics and kinetics of dissolution and diffusion, the full dissolution of niobium solid is expected by increasing the temperature and melting time of the uranium melt. However, such a method will result in the decline of the resistance of the coating materials and the possible contamination of the uranium-niobium alloy melts, and the quality of the uranium-niobium alloy materials cannot be guaranteed.

The key to solve the problem of direct vacuum induction melting of uranium-niobium alloy is to precisely control the melting temperature and melting time so that niobium can dissolve and diffuse in uranium melt without great influence on crucible and coating. However, the current research on the dissolution and diffusion of niobium in uranium melt has not been carried out, and the correlation data between the dissolution rate of niobium in uranium melt and the melting temperature have not been reported, and the vacuum induction melting process optimization of uranium-niobium alloy lacks data support. In addition, the application of melt mixing technology to improve the melt convection in the induction melting process of uranium-niobium alloy is also a direction to solve the current problem. Based on the high chemical activity of uranium melt, electromagnetic stirring has a high application potential in the direct vacuum induction melting of uranium-niobium alloy. In order to improve the understanding of the dissolution and diffusion of solid saw in uranium melt, the dissolution and diffusion behavior of solid energy in uranium melt was studied. Through the dissolution and diffusion experiment to obtain the saw in uranium melt dissolution rate, nu; nu melt temperature T exists nu; nu; nu; nu; e =0.3651exp(-21150/T);The dissolution and diffusion interfaces of UNb were characterized. The results show that in the process of dissolving in uranium melt, the U/Nb dissolution diffusion interface forms a sheet structure with orientation relation to solid Nb. By comparing the dissolution behavior of niobium in uranium melt with or without electromagnetic stirring and the interface structure of UNb, it is shown that the electromagnetic stirring increases the dissolution rate of niobium in uranium melt and changes it Sheet structure of U/Nb interface.