Rosatom’s Research Institute of Atomic Reactors (NIIAR) and the AA Bochvar Research Institute of Inorganic Materials (VNIINM), part of TVEL fuel company, have completed new stages in the development of Russian accident tolerant fuel (ATF) for VVER and pressurised water reactors. New fuel assemblies with experimental fuel rods have completed a second cycle of irradiation tests in NIIAR’s MIR research reactor in Dimitrovgrad. Each of the two experimental fuel assemblies contained 24 fuel elements with four different combinations of cladding materials and fuel composition. Fuel pellets were made from traditional uranium dioxide and uranium-molybdenum alloy with increased density and thermal conductivity. After the first and second cycles of irradiation, several fuel elements from each fuel cassette were removed for post-reactor material science studies, and new non-irradiated samples were inserted instead. After two cycles of irradiation in the MIR reactor, all the fuel elements were still hermetically sealed.
In addition, TVEL has ordered VNIINM to began R&D work on the development of technology for the manufacture of ATF tablets using uranium disilicide (a compound of uranium and silicon - U3Si2). An experimental U3Si2 ingot has already been manufactured for the subsequent development of the technology for the production of powder and tablets.
“The new study on tolerant fuels is driven by the benefits of uranium disilicide. Firstly, it has higher density and uranium content, which makes possible the transition to longer fuel cycles without increasing the enrichment in uranium-235,” said Alexander Ugryumov, Rosatom’s Vice President for Science and Technology Activities and Quality. “Secondly, high thermal conductivity and low heat capacity means less stored heat in the reactor core and a lower temperature of the cladding of the fuel elements. Thirdly, a lower operating temperature can lead to an improvement in the operational characteristics of the fuel.”