Russia’s National University of Science and Technology MISIS (NITU MISIS), announced on 5 March that its materials science specialists had developed a unique three-layer steel-vanadium-steel material that can withstand temperatures of up to 700 degrees Celsius for prolonged periods, as well as high radiation levels, mechanical stress and aggressive chemicals.
The material can be used in fuel assemblies for fast reactors. Assemblies need to withstand temperatures of 550-700 degrees Celsius inside new-generation reactors. And liquid sodium coolant impacts their external surfaces. New structural materials are required in order to make possible a closed-loop fuel cycle inside fast reactors. These materials should allow the fuel to burn much faster than it does currently. They should withstand damaging radiation levels of up to 180-200 dislocations per atom, compared with 100-130 dislocations per atom for current materials.
"Our team has developed the sandwich-type three-layer steel-vanadium alloy-steel material whose ferritic stainless steel ensures substantial corrosion resistance. And the material's vanadium alloy (V-4Ti-4Cr) guarantees heat and radiation resistance, to offset the impact of a nuclear reactor's super-aggressive environment," said project co-author and postgraduate student Alexandra Baranova from the NITU MISIS Faculty of Materials Science and Physics of High-Strength Materials.
This production process allowed steel and the vanadium alloy to penetrate each other, scientists said. Members of the research team managed to develop a prototype assembly which is a monolithic three-layer tube. Laboratory tests proved the new alloy's high durability at working temperatures of up to 700 degrees Celsius. Developers are preparing to launch a long-term project to assess the new material's radiation-resistance levels.
Meanwhile, scientists of the Mining and Chemical Combine (part of state nuclear corporation Rosatom) have developed and patented a new technology for manufacturing a mixture of uranium and plutonium dioxides (master mixture), which can significantly improve the environment, economic efficiency and quality of finished products in the fabrication of nuclear fuel. The new technology was developed for the production of mixed oxide (mox) and Remix-fuel, which are made from used nuclear fuel. The new method differs significantly from current methods in that it results in a master mix suitable for the further manufacture of fuel pellets at the stage of used fuel reprocessing. In this case, the mixture is obtained in the form of a solid solution, which ensures the maximum possible parameters of homogenisation.
The new method multiplies the amount of reversed liquids by recycling the mother liquor, significantly reduces labour and energy costs, and also eliminating the use of hydrogen and ammonia in the process chain. Also, the technology has a high level of compliance with the non-proliferation regime. The technology makes it possible to obtain stoichiometric uranium dioxide or a mixture of uranium and plutonium dioxides in any safe ratios as requested by the customer. Fuel pellets have already been manufactured at a pilot industrial level that meet all current requirements for mox-fuel.