Russian developments in fast reactor fuels

According to Rosatom, the use of a liquid metal sublayer will improve the characteristics of fuel elements with nitride fuel for fourth-generation fast neutron reactors. It is expected that the temperature of such fuel will be lower while maintaining the coolant parameters, and the uranium-plutonium pellet will expand less, avoiding pressure on the fuel element cladding, which could cause possible depressurisation. This will improve both the economic efficiency and operational reliability of the fuel, it said.

The OS-5 irradiation assembly was manufactured at the Siberian Chemical Plant in Seversk, Tomsk Region in cooperation with colleagues from the Fuel, Scientific and Machine-Building Divisions of Rosatom. After approval by Rostekhnadzor, the innovative fuel will undergo pilot industrial operation in the BN-600 reactor at the Beloyarsk nuclear power plant in the Sverdlovsk Region.

The manufacture of the OS-5 fuel assembly is part of a large-scale programme of work to improve the efficiency of mixed nitride uranium-plutonium (SNUPP) nuclear fuel for the BREST-OD-300 fast neutron reactor. Since 2014, Rosatom scientists and engineers have been conducting pilot industrial operation of SNUPP fuel in the BN-600 reactor and post-reactor studies of irradiated fuel elements.

"The first generation of SNUPP fuel for the BREST-OD-300 starting load was substantiated with a burnup of 6% of heavy atoms. Our goal is to gradually increase the burnup depth to an average value of 12%," said Mikhail Skupov, deputy director general of the Bochvar Institute. "In order to test SNUPP fuel to its maximum limit parameters in the BN-600 reactor, our scientists have already applied a number of non-standard innovative solutions, for example, special removable containers in irradiation assemblies. Fuel elements with a liquid metal sublayer OS-5 are a revolutionary technological solution and another important step in the development of nitride fuel for fast reactors. It is with this assembly that we expect to achieve the design target indicators of fuel for fast reactors of the future."

The BREST-OD-300 fast reactor is part of Rosatom's Proryv, or Breakthrough, project to enable a closed nuclear fuel cycle. The 300 MWe unit will be the main facility of the Pilot Demonstration Energy Complex at the Siberian Chemical Combine site. The complex will demonstrate an on-site closed nuclear fuel cycle with a facility for the fabrication/re-fabrication of mixed uranium-plutonium nitride nuclear fuel, as well as a used fuel reprocessing facility.

Initial operation of the demonstration unit will be focused on performance and after 10 years or so it will be commercially oriented. The plan has been that if it is successful as a 300 MWe (700 MWt) unit, a 1200 MWe (2800 MWt) version will follow - the BN-1200, now known as the BN-1200M.

Fuel for BN-1200

Meanwhile, Rosatom announced that the Mining and Chemical Combine (MCC) in Zheleznogorsk in Krasnoyarsk Krai has been identified as a priority site for the industrial production of uranium-plutonium mixed-oxide (MOX) fuel for the BN-1200M fast neutron reactor.

It said the choice of the MCC is "due to the company's successful experience in ensuring rhythmic deliveries of MOX fuel for the operating BN-800 fast neutron reactor of the Beloyarsk NPP."

Preparations for the construction of the BN-1200M have already begun at the Beloyarsk plant. It is planned that the development of design documentation for the construction of a new site for the production of MOX fuel for the plant will begin this year. In 2026, it is planned to begin licensing the facility. At the same time, the first delivery of fuel assemblies with MOX fuel in the volume of the starting reactor load is expected in 2033 to ensure the physical start-up of the reactor.

The sodium-cooled BN-series fast reactor plans are part of Rosatom's project to develop fast reactors with a closed fuel cycle whose MOX fuel will be reprocessed and recycled. In addition to the BN-600 reactor at Beloyarsk unit 3, which began operation in 1980, the 789 MWe BN-800 fast at Beloyarsk unit 4 entered commercial operation in October 2016. This is essentially a demonstration unit for fuel and design features for the larger BN-1200M, which will be unit 5 at Beloyarsk.