Tests are underway using the MIR.M1 research reactor at Russia’s Research Institute of Atomic Reactors (NIIAR – Nauchno Issledovatelskii Institut Atomnikh Reaktorov) in Dimitrovgrad of nuclear fuel for VVER reactors with a burnable erbium neutron absorber and uranium enrichment of about 5%. Currently, most reactors at NPPs use fuel enriched to 3-4.95% of uranium-235.
This is the first step in the project for a phased justification of nuclear fuel with enrichment above 5%. The use of such fuel would incease the economic efficiency of nuclear power and the competitiveness of NPPs compared with other energy sources. According to Rosatom scientists, this will make it possible to increase the reactor’s fuel cycle from the current 12-18 months to 24 months, reducing the number of outages needed for refuelling and so producing more electricity.
Additional economic benefits can also be achieved by reducing the number of fresh nuclear fuel cassettes required for each refuelling, as well as by potentially increasing reactor power. The test programme in the MIR.M1 is designed for four one-year irradiation cycles. For this purpose, an experimental assembly consisting of 12 fuel elements for a VVER-1000 based on uranium-erbium fuel was manufactured at the Machine-Building Plant (MSZ -Mashinostroitelny Zavod in Elektrostal.
VVER fuel with a uranium-erbium composition was loaded into the reactor for the first time. According to scientists, erbium is a better neutron absorber than gadolinium for operating fuel with enrichment above 5% in fuel cycles longer than 18 months, which is currently standard for VVER reactors, A burnable absorber is added to nuclear fuel to compensate for reactivity in the reactor core.
To manufacture the experimental fuel rods, MSZ used its extensive experience in the fabrication of uranium-erbium fuel for RBMK channel reactors. The research results will help create a technology for serial production of uranium-erbium fuel for VVER reactors, as well as justify the operation of such fuel at Russian design NPPs.
“Increasing uranium enrichment to 6%, and in future to 7-8%, is a global trend and a task that key players in the global market are working on, explained Alexander Ugryumov, Vice President for Scientific & Technical Activities at Rosatom’s fuel company TVEL. “Until now, the efficiency of reactors has been increased through the introduction of new designs and modifications of fuel assemblies. Mainly, this was to increase the physical volume of enriched uranium in the fuel rod and ultimately produce more energy from a single fuel cartridge. The nuclear industry has now reached the point where further optimisation of NPP economics may require exceeding the 5% uranium enrichment threshold for high-power thermal reactors. Considering that there are 163 fuel assemblies in the core of modern VVER reactors, each containing more than 500 kg of uranium, the effect of increasing enrichment by just 1% will already be very significant.”
