Russian designed ATF has been loaded into MIR (Credit: Tvel)The first experimental assemblies of Russia’s accident tolerant fuel (ATF) were loaded into the water loops of the MIR research reactor at the Research Institute of Atomic Reactors (NIIAR) in Dimitrovgrad on 29 January.

The two experimental fuel assemblies, manufactured at the Novosibirsk Chemical Concentrates Plant (part of state nuclear corporation Rosatom’s Fuel Company Tvel), consist of fuel rods for VVERs and pressurised water reactors (PWR) with four different combinations of shell materials and a fuel matrix. The fuel pellets are made of both traditional uranium dioxide and uranium-molybdenum alloy with increased density and thermal conductivity. The cladding materials are either zirconium alloy with chrome plating or chromium-nickel alloy.

Each fuel assembly contains 24 fuel elements with different combinations of materials. In the MIR reactor, conditions will be created which are as close as possible to the operating conditions and parameters of the coolants of VVER and PWR  reactors. The design of a research reactor allows simultaneous studies in separate loop installations, which is especially important given the simultaneous testing of fuel for reactors of Russian and foreign design.

The Vice-President for Scientific and Technical Activities at Tvel, Alexander Ugryumov, said: “The production of experimental tolerant fuel was preceded by extensive work undertaken by scientists and designers of the fuel division of Rosatom. Intensive materials science research was carried out, new technologies for applying coatings and butt welding were tested, and laboratory tests of samples were successfully completed. The choice of specific materials is due not only to research, but also to many years of experience in the Russian nuclear industry, since some of them are successfully used in the construction of fuel for research reactors, as well as in the active zones of power and transport reactors.”

The first phase of the reactor tests and post-reactor studies of tolerant fuel will be completed in 2019, he added. “Based on the data obtained, the optimal combination of shell materials will be determined, and calculations and substantiations will be made of the neutron-physical characteristics of the active water-cooled reactor zones. The next important step will be the loading of experimental fuel assemblies with individual accident tolerant fuel rods into a power reactor at one of Russia’s NPPs.” The AA Bochvar Research Institute of Inorganic Materials (VNIINM) work closely with Tvel on ATF development.

"ATF is of critical importance for further improving the integral safety and reliability of nuclear power," Tvel said in a statement. "Even in case of heat removal failure in the core, ATF is supposed to keep its integrity for a long enough time without a zirconium-steam reaction inducing hydrogen release."

Photo: Russian designed ATF has been loaded into MIR (Credit: Tvel)