Three trial uranium-plutonium MOX fuel assemblies containing americium-241 and neptunium-237 have completed three fuel campaigns in the Beloyarsk BN-800 fast neutron reactor. 

These assemblies, which were loaded into the reactor core in the summer of 2024, are now cooling in a used fuel pool. After the cooling period, they will undergo post-irradiation studies to evaluate the transmutation process. 

This trial is a stage of a research program for minor actinide afterburning that began in 2021 and is scheduled to run until 2035.

Minor actinides, including neptunium, americium, and curium, are transuranic elements produced in nuclear fuel during reactor operation. Although they represent a small percentage of the mass of used fuel, they contribute to its radioactive toxicity and residual heat. 

These isotopes have half-lives lasting hundreds of thousands of years, which determines the conditions for isolating radioactive waste from the environment.

“Minor actinides are characterized by high radioactivity and toxicity, as well as the presence of isotopes with long half-lives, which makes them hazardous components of radioactive waste,” said Rosatom.

Transmuting actinides into isotopes

Rosatom stated that fast neutron reactors can burn minor actinides by transmuting them into isotopes that are either stable or have shorter half-lives.

The goal of this technology is to reduce the volume of radioactive waste that requires deep geological disposal. Rosatom indicated that eliminating minor actinides could allow nuclear waste to reach radiation equivalence with the original uranium feedstock hundreds of times faster than natural decay. 

Alexander Ugryumov, Senior Vice President for Research and Development at TVEL, stated that burning minor actinides in a commercial reactor is a long-term strategy rather than a single experiment. 

“Burning minor actinides in a commercial reactor is not a one-off experiment, but a long-term strategy,” noted Ugryumov. “Before scaling this solution to an industrial level, we are demonstrating the very technological feasibility, that this idea actually works.”

Enhancing fourth-gen nuclear reactor capabilities

The current focus is to demonstrate technological feasibility before scaling to an industrial level. Future stages of the program involve increasing the concentration of minor actinides in trial MOX fuel and adding them to nitride uranium-plutonium fuel.

TVEL also plans to test heterogeneous burning, where minor actinides are placed in separate fuel rods or assemblies within specific zones of the reactor rather than being mixed into the fuel matrix.

Yuri Nosov, Director of the Beloyarsk plant, said that post-irradiation studies will define the role of this technology in the fuel cycle. Fourth-generation power units are intended to improve safety by using used fuel instead of storing it. 

“Over approximately 60 years of operation, such installations will be capable of utilizing about four tons of minor actinides, which is more than several thermal reactors can produce,” concluded Nosov.

The BN-800 is a sodium-cooled fast reactor with an output of 820 MWe. It entered commercial operation in 2016 and transitioned to a full load of MOX fuel in September 2022. MOX fuel is produced by mixing plutonium recovered from used fuel with depleted uranium.