Density, phase composition, microstructure and thermal conductivity of the U-10 wt. % Zr alloy manufactured by induction melting with subsequent casting into quartz molds and turning to size have been investigated at JSC “SSC RF - IPPE”. For comparison, the density and thermal conductivity of the U-10 wt. % Zr alloy produced by melting followed by extrusion and turning to size were investigated. To determine the density, a hydrostatic weighing method was used. The average density values of the cast and extruded alloy were respectively 98.8 and 97.5 % of the theoretical density, which was calculated according to the rule of mixtures. The results of studying the microstructure using a scanning electron microscope are presented. It is shown that the cast alloy U-10 % Zr is a metal matrix in which zirconium-enriched particles of arbitrary shape are distributed. In a metal matrix, the bulk of the volume is occupied by the α-U, and there are also precipitates of the δ-phase in the form of thin plates. A lower value of the microhardness of the alloy is noted in comparison with the data published in the known literature. The results of measuring the thermal conductivity at temperatures from 100 to 750 °C for the U-10 wt. % Zr alloy obtained by casting and extrusion are presented. The stationary axial heat flux method (or method of plate) was used to measure the thermal conductivity. Alloy samples made in different ways have almost the same thermal conductivity at 200 °C. With an increase in temperature, the discrepancy in thermal conductivity between the samples of the cast and extruded alloy gradually increases, and the thermal conductivity of the extruded alloy turns out to be lower, which is especially noticeable in the temperature range of 600-750 °C. The data obtained are compared with the results of published works. The measured values of the thermal conductivity of the cast alloy U-10 wt. % Zr up to a temperature of 750 °C do not disagree with the literature data. It was found that at a higher temperature, the alloy softens, which, in turn, leads to deformation of the test specimen and an increase in the measurement error when using the axial heat flux method.

The article provides a review of well-known foreign scientific publications devoted to the study of the properties of metallic nuclear fuel based on U-Zr, in composition close to U 10 wt. % Zr, which is widely used in reactors. Differences in the microstructure of fuel made by different methods: extrusion and casting - are considered. The effect of thermal annealing on the change in the microstructure of the alloy is shown. The photographs obtained using optical and electron microscopes are presented, as well as crystallographic data for two phases: α-U and δ-UZr2. The known literature data indicate that the density of uranium-rich U-Zr alloys corresponds to the rule of mixtures. The theoretical density of the alloy U-10 wt. % Zr (U-22.5 at. % Zr) should be taken as 16.2 g/cm3. The results of thermophysical studies of 10 wt. % Zr fuel using the method of differential scanning calorimetry (DSC) are presented. Data on measurements of thermal expansion of U-Zr alloys, as well as thermal conductivity are presented. Most of the thermal conductivity data are either calculated from the measured density, specific heat and thermal diffusivity, or obtained from simulations.

It is known that the thermal shock resistance of ceramic crucibles is insufficient for melting uranium alloys in them. Typically, crucibles withstand one or more heats and then break down. The possibility of using nanostructured ceramic crucibles based on ZrO2-MgO-CaO to obtain a U-10 % Zr alloy in an induction electric furnace has been substantiated at IPPE. Crucibles were made in JSC “ONPP “Tekhnologiya” named after A.G. Romashin” from a mixture of zirconium dioxide powders, partially stabilized with nanocrystalline CaO and MgO in a ratio of 30 and 70 wt. %, using two-stage sintering. Such crucibles have a sufficiently high resistance to thermal shock in contact with melts of metals and alloys and withstand 1-3 melts without destruction. Crucibles with various densities (from 5.206 to 5.29 g/cm3) and porosity (from 5 to 9 %) were tested under conditions of heating the melt at a rate of 12 to 19 °C/min to a maximum temperature of 1455 to 1560 °C. The tested crucible ZrO2-MgO-CaO was inserted into a graphite crucible to prevent leakage of the melt in the electric furnace in case of destruction of the ceramic crucible. There was no complete destruction of the crucibles; some crucibles with small cracks could be reused. The best result (three melts) was obtained when using such a crucible with a porosity of about 5 % for melting a charge containing uranium and zirconium. In order to determine the degree of interaction of a uranium-zirconium melt with a crucible based on ZrO2-MgO-CaO, the microstructure and microhardness of the crucible surface in contact with the melt were studied at an elevated temperature of 1600 °C. The surface of all tested crucibles is not wetted by liquid uranium-zirconium melt, and there is no chemical interaction. Nanostructured ceramic crucibles based on ZrO2-MgO-CaO are suitable for melting uranium-containing materials in an electric induction furnace.