These neutrons create additional reactions in a "blanket" of material, normally natural or depleted uranium or thorium, where new plutonium- or 233U, respectively, atoms are formed.

For the breeding reaction to produce more fuel than it uses, neutrons released from the core must retain significant energy.

These requirements led to the use of a liquid sodium coolant, as this is an excellent conductor of heat, and is largely transparent to neutrons.

Sodium is highly reactive, and careful design is needed to build a primary cooling loop that can operate safely.

However, these designs deliberately operate at low energy levels for safety reasons, and are not economic for power generation.

This reactor suffered an almost continual series of fires in its sodium coolant, but its safety features contained them.

A slump in uranium prices added to the concerns, making the breeder concept economically infeasible.

The BN-1200 concept is essentially a further developed BN-800 design with the twin goals of economical operation, while also meeting Generation IV reactor safety limits.

Safety enhancements include the elimination of outer primary circuit sodium pipelines and passive emergency heat removal.

[5] OKBM initially expected to commission the first unit with MOX fuel in 2020, growing to eight (11 GWe total output) by 2030.

In early 2012, Rosatom's Science and Technology Council approved the construction of a BN-1200 reactor at the Beloyarsk Nuclear Power Station.