This is what the press office of Rosenergoatom, the Russian nuclear power station operations subsidiary of Atomenergoprom, told Construction.RU. BN-800 reactor is required to perfect the technology of nuclear fuel cycle closure.
Peculiarity of fast-breeder reactors is the capacity to produce more nuclear fuel, than the facility can consume, as well as to burn weapon-grade plutonium with high environmental credentials of electricity production.
We should remind you that the Beloyarsk Nuclear Power Plant was the second of the then Soviet Union's NPPs.