Rosatom’s Mining & Chemical Combine (MCC) in Zheleznogorsk, Krasnoyarsk region, has manufactured the first three fuel assemblies with uranium-plutonium mixed oxide (MOX) fuel, which also contain other transuranic elements including americium-241 and neptunium-237. The assemblies, which have completed acceptance tests, will be loaded into the BN-800 fast neutron reactor at unit 4 of the Beloyarsk NPP in 2024. The fuel will undergo pilot operation (lead-test assemblies programme) during three micro-campaigns of approximately one and a half years.
Minor actinides are formed in irradiated nuclear fuel as the result of reactions during operation in a reactor core. Like plutonium, these elements do not occur in nature, but arise only from transmutation of uranium. Neptunium, americium and curium isotopes are particularly important to radiochemists because of their significance in used fuel reprocessing and radioactive waste management. They are highly radioactive and toxic, generate a great deal of heat and have long half-lives, making them the most hazardous components of nuclear waste.
The Russian solution is fast neutron reactors, which can be fuelled not only by enriched natural uranium, but also secondary products of the nuclear fuel cycle, such as depleted uranium and plutonium. In addition, the research has shown that minor actinides from used fuel under the flux of fast neutrons will fission into fragments representing a fairly wide range of radioactive and stable isotopes, which are potentially much less hazardous than the original minor actinides. The transmutation process of minor actinides in a reactor is known as “afterburning”.
“Rosatom is step by step making use of the unique advantages that powerful fast neutron reactors provide to our industry,” said Alexander Ugryumov, Senior Vice President for Research & Development at TVEL fuel company. The introduction of MOX fuel makes possible a multiple expansion to the resource base for nuclear power by using depleted uranium and plutonium, and also to reprocess used fuel instead of storing it. Afterburning of minor actinides is the next step in closing the nuclear fuel cycle. This should not only reduce the amount of nuclear waste for final isolation, but also significantly reduce its radioactivity. In the long term, it would make it possible to avoid the complicated and expensive deep burial of waste.”
The technology of MOX fuel fabrication (including fuel with minor actinides) was developed by the AA Bochvar Research Institute of Inorganic Materials (VNIINM - part of TVEL) in Moscow. The lead-test assemblies of MOX fuel with americium-241 and neptunium-237 were manufactured using standard equipment MCC.
Fabrication of fuel assemblies with minor actinides and their pilot operation in the BN-800 is a key stage in the comprehensive TVEL research programme for minor actinide afterburning. It started in 2021 and is scheduled to run until 2035. The programme includes projects for minor actinide separation into different fractions, their intermediate storage, incorporation in fast reactor fuel, the operation of such fuel, post-irradiation studies, etc. Another important issue is optimisation of reactor facilities for burning the maximum volume of minor actinides.
Image: The assemblies will be loaded into the BN-800 fast neutron reactor at unit 4 of the Beloyarsk nuclear power plant in 2024 (courtesy of Rosatom)