Russian state-owned nuclear fuel company Tvel has completed the first phase of accident-tolerant fuel (ATF) testing in the MIR research reactor at the Research Institute of Atomic Reactors in Dimitrovgrad in southeastern Siberia. Two experimental ATF fuel assemblies were loaded into the reactor in January. Each fuel assembly contained 24 fuel elements with four different combinations of cladding and fuel matrix materials. After the first irradiation cycle, both assemblies were removed from the reactor. Tvel said preliminary examination of the assemblies, performed onsite by a team from the Bochvar Institute for Inorganic Materials, a Moscow-based Tvel research facility, revealed neither changes in the fuel rods’ geometry, nor damage to the cladding.