The Research Institute of Nuclear Reactors (a facility of ROSATOM in Dimitrovgrad) started tests of VVER type fuel rods with uranium-plutonium MOX fuel in the MIR research reactor. Based on the results of irradiation and special experiments, Rosatom scientists are committed to validate efficiency and reliability of MOX fuel operation in VVER reactors units, which make up the core of the nuclear power sector in Russia and are widely applied in other countries at Russian-designed nuclear power plants.
This is a new milestone of the Russian nuclear industry in closing the nuclear fuel cycle. At present, Rosatom produces MOX fuel only for fast-neutron reactors, in particular, the world's most powerful BN-800 fast reactor at the Beloyarsk NPP. For light-water thermal neutron VVER reactors, Rosatom had developed uranium-plutonium REMIX fuel, which successfully passed the full lead-test rods program on a commercial VVER-1000 reactor, and now is undergoing lead-test assemblies operation.
The plutonium content in REMIX fuel is up to 1.5%; it is based on a mixture of regenerated uranium and plutonium bred in the reactor. MOX (mixed oxides fuel), in turn, is a mixture of plutonium oxides and of depleted uranium oxides. The MOX fuel for VVERs is expected to contain approximately 5.5-7.5% of plutonium. This will ensure greater flexibility and efficiency of regenerated nuclear materials involvement in the VVER fuel cycle and optimize the costs of uranium-plutonium fuel fabrication before its full-scale introduction.
"Today, as decades ago, nuclear fuel for VVER is enriched natural uranium, in rare cases - regenerated uranium. However, in the near future, having proven references for uranium-plutonium fuel operation, we will be able to offer the whole range of options for the fuel matrix, depending on NPP requirements and fuel cycle strategy. As light-water thermal reactors make up the core of nuclear power, this will be enable expand their resource base, reprocess irradiated fuel instead of storage, and significantly reduce the volume of nuclear waste," Alexander Ugryumov, Senior Vice President for Research and Development at TVEL JSC, commented.
For irradiation in the MIR reactor, 21 MOX fuel rods (with plutonium content of 5-12%) had been manufactured in cooperation between the enterprises of TVEL Fuel Company of Rosatom – Bochvar Institute, Novosibirsk Chemical Concentrates Plant an and Siberian Chemical Combine. The experimental fuel assembly loaded into the research reactor loop contains twelve fuel rods. Another nine fresh fuel rods will be gradually inserted in the bundle replacing the irradiated ones, which will be partly extracted at each stage for post-irradiation studies (achieving certain levels of the fuel burnup).
For reference:
TVEL Fuel Company of Rosatom (the Fuel division of the State Corporation Rosatom) includes enterprises for the manufacture of nuclear fuel, conversion and enrichment of uranium, production of gas centrifuges, as well as research and design organizations. Being the only exclusive of nuclear fuel for Russian nuclear power plants, TVEL provides fuel to a total of 75 power reactors in 15 countries, research reactors in nine countries of the world, as well as transport reactors of the Russian nuclear fleet. Every sixth power reactor in the world is powered by TVEL fuel. ROSATOM's fuel division is the world's largest producer of enriched uranium, as well as the leader of the global market for stable isotopes. The Fuel Division is actively developing new businesses in the field of chemistry, metallurgy, energy storage technologies, 3D printing, digital products, as well as decommissioning of nuclear facilities. Rosatom's industry integrators for additive technologies and power storage systems have been created in the Fuel Company TVEL circuit. http://www.tvel.ru
The strategy of the Russian nuclear power development is aimed at establishment of the dual-component nuclear power system with both thermal and fast-neutron reactors and wide introduction of the closed nuclear fuel cycle technologies, based on fabrication of fresh uranium-plutonium fuel from spent fuel. As fast-neutron reactors become more widespread, it is expected to achieve the balance in "circulation" of nuclear fuel materials between fast and thermal reactors.

Source: Communications Department of TVEL JSC