The first Russian-made experimental nuclear fuel assemblies based on accident-tolerant fuel (ATF) for light water reactors have been loaded for testing into the water loops of the MIR research reactor at the State Research Institute of Atomic Reactors in Dimitrovgrad.
Announcing the milestone yesterday, TVEL, the nuclear fuel manufacturer subsidiary of Rosatom, said this work is a part of its project to develop Russian ATF resistant to severe beyond-design basis accidents, and bring it to the market.
Two experimental fuel assemblies, manufactured at Novosibirsk Chemical Concentrates Plant, a TVEL subsidiary, consist either of VVER or pressurised water reactor geometry fuel rods with four different combinations of cladding materials and fuel matrix. Fuel pellets are made of one of two materials, either traditional uranium dioxide or uranium-molybdenum alloy with increased density and thermal conductivity. The fuel rods' cladding is either a zirconium alloy with chromium coating or a chromium-nickel alloy.
Each fuel assembly contains 24 fuel rods with different combinations of materials. Fuel assemblies are being tested in the MIR reactor under conditions "as close as possible" to the operational ones, including the parameters of the VVER and PWR coolant. The research reactor design enables parallel studies in separate loops, which is especially important, TVEL said, given simultaneous fuel testing for reactors of Russian and foreign design.
"The fabrication of the first accident tolerant fuel followed the large-scale work of scientists and design engineers of Rosatom’s fuel unit, including in-depth materials research, introduction of new coating technologies and resistance butt-welding, and successful laboratory testing of the samples," Alexander Ugryumov, TVEL's vice president for research and development, said. "Besides the research analysis, the choice of materials was based on the long-standing experience of the Russian nuclear industry, considering that some of the materials have been successfully used for research reactor nuclear fuels or the core of power and propulsion reactors."
The first phase of the reactor tests and post-reactor studies of ATF will be completed this year, TVEL said. Based on the data obtained, it will be necessary to select the optimal combination of cladding materials, calculate and validate the neutron-physical characteristics of light water reactors cores, it said. The next important stage includes loading experimental fuel assemblies with some ATF fuel rods into a commercial power reactor in Russia.
ATF is nuclear fuel resistant to severe beyond-design basis accidents at nuclear power plants with the loss of coolant in the reactor.
"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," TVEL said, adding that ATF is of “critical importance” for further improvement of the integral safety and reliability of nuclear power.
The research, design and testing of the ATF by TVEL is provided and coordinated by the Bochvar High-Technology Scientific Research Institute of Inorganic Materials.
According to the World Nuclear Association, the term accident-tolerant fuel describes new technologies that enhance the safety and performance of nuclear fuel. Such fuels may incorporate the use of new materials and designs for cladding and fuel pellets.