BN-800 running on 60% MOX

Thursday, 27 January 2022

The BN-800 is unique in the world," said Ilya Filin, the plant's Deputy Chief Operating Engineer. "Six years after the start-up of the unit, we checked the effect of operation on the metal of the pipelines, studied the condition of more than 700 welded joints of the second circuit." About 150 people were involved in the work, which brought in specialists from six branches of the maintenance specialist Atomenergoremont.

​The unit is a sodium-cooled fast reactor which produces about 820 MWe. It started operation in 2016 and in 2020 achieved a capacity factor of 82% despite having an experimental role in proving reactor technologies and fuels. "New equipment and new materials were used in its construction," said Filin.

As well as welding checks, engineers replaced the diverter of the main circulation pump, carried out repairs on one the unit's three steam generators, and performed maintenance on its steam turbine and generator.

The reactor core itself was refuelled and is now using 60% mixed uranium-plutonium oxide fuel, supplied by TVEL and manufactured at its Zheleznogorsk site. The plutonium for this was produced from uranium during the operation of other nuclear power plants and recovered from the used fuel assemblies through reprocessing.

The uranium came from depleted uranium tails left over from the enrichment process that creates fuel for light-water reactors. In this way MOX uses depleted uranium that had no other immediate use and was held in storage with plutonium recycled from previously used fuel.

Using this "fuel of the future," said Rosenergoatom, "increases the resource base of the nuclear power industry ten-fold and makes it virtually waste free."

Beloyarsk 4 is planned to progress to running completely on MOX fuel. At present its blend of uranium-based fuel and MOX is referred to as a 'hybrid core'. It is arranged to produce new uranium and plutonium fuel within the reactor core as it operates.